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  • 1.
    Andreu-Cabedo, Yasmina
    et al.
    University of Central Lancashire, England.
    Castellano, Pedro
    University of Central Lancashire, England.
    Colantonio, Sara
    National Research Council Italy, Italy.
    Coppini, Giuseppe
    National Research Council Italy, Italy.
    Favilla, Riccardo
    National Research Council Italy, Italy.
    Germanese, Danila
    National Research Council Italy, Italy.
    Giannakakis, Giorgos
    Fdn Research and Technology, Greece.
    Giorgi, Daniela
    National Research Council Italy, Italy.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, Faculty of Science & Engineering.
    Marraccini, Paolo
    National Research Council Italy, Italy.
    Martinelli, Massimo
    National Research Council Italy, Italy.
    Matuszewski, Bogdan
    University of Central Lancashire, England.
    Milanic, Matijia
    Norvegian University of Science and Technology, Norway.
    Pascali, Mariantonietta
    National Research Council Italy, Italy.
    Pediaditis, Mattew
    Fdn Research and Technology, Greece.
    Raccichini, Giovanni
    National Research Council Italy, Italy.
    Randeberg, Lise
    Norvegian University of Science and Technology, Norway.
    Salvetti, Ovidio
    National Research Council Italy, Italy.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, Faculty of Science & Engineering.
    MIRROR MIRROR ON THE WALL... AN INTELLIGENT MULTISENSORY MIRROR FOR WELL-BEING SELF-ASSESSMENT2015In: 2015 IEEE INTERNATIONAL CONFERENCE ON MULTIMEDIA and EXPO (ICME), IEEE , 2015Conference paper (Refereed)
    Abstract [en]

    The face reveals the healthy status of an individual, through a combination of physical signs and facial expressions. The project SEMEOTICONS is translating the semeiotic code of the human face into computational descriptors and measures, automatically extracted from videos, images, and 3D scans of the face. SEMEOTICONS is developing a multisensory platform, in the form of a smart mirror, looking for signs related to cardio-metabolic risk. The goal is to enable users to self-monitor their well-being status over time and improve their life-style via tailored user guidance. Building the multisensory mirror requires addressing significant scientific and technological challenges, from touch-less data acquisition, to real-time processing and integration of multimodal data.

  • 2.
    Bergstrand, Sara
    et al.
    Linköping University, Department of Medical and Health Sciences, Division of Nursing Science. Linköping University, Faculty of Medicine and Health Sciences.
    Morales, Maria-Aurora
    CNR Inst Clin Physiol, Italy.
    Coppini, Giuseppe
    CNR Inst Clin Physiol, Italy.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Division of Biomedical Engineering. Linköping University, Faculty of Science & Engineering.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Division of Biomedical Engineering. Linköping University, Faculty of Science & Engineering.
    The relationship between forearm skin speed-resolved perfusion and oxygen saturation, and finger arterial pulsation amplitudes, as indirect measures of endothelial function2018In: Microcirculation, ISSN 1073-9688, E-ISSN 1549-8719, Vol. 25, no 2, article id e12422Article in journal (Refereed)
    Abstract [en]

    Objective: Endothelial function is important for regulating peripheral blood flow to meet varying metabolic demands and can be measured indirectly during vascular provocations. In this study, we compared the PAT finger response (EndoPAT) after a 5-minutes arterial occlusion to that from forearm skin comprehensive microcirculation analysis (EPOS). Methods: Measurements in 16 subjects with varying cardiovascular risk factors were carried out concurrently with both methods during arterial occlusion, while forearm skin was also evaluated during local heating. Results: Peak values for EPOS skin Perf(conv) and speed-resolved total perfusion after the release of the occlusion were significantly correlated to the EndoPAT RHI (rho =.68, P = .007 and rho =.60, P = .025, respectively), mainly due to high-speed blood flow. During local heating, EPOS skin oxygen saturation, SO2, was significantly correlated to RHI (rho = .62, P =.043). This indicates that SO2 may have diagnostic value regarding endothelial function. Conclusions: We have demonstrated for the first time a significant relationship between forearm skin microcirculatory perfusion and oxygen saturation and finger PAT. Both local heating and reactive hyperemia are useful skin provocations. Further studies are needed to understand the precise regulation mechanisms of blood flow and oxygenation during these tests.

  • 3.
    Briers, David
    et al.
    University of Kingston, England .
    Duncan, Donald D.
    Portland State University, OR USA .
    Hirst, Evan
    Callaghan Innovat, New Zealand .
    Kirkpatrick, Sean J.
    Michigan Technology University, MI USA .
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Steenbergen, Wiendelt
    University of Twente, Netherlands .
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Thompson, Oliver B.
    Callaghan Innovat, New Zealand .
    Laser speckle contrast imaging: theoretical and practical limitations2013In: Journal of Biomedical Optics, ISSN 1083-3668, E-ISSN 1560-2281, Vol. 18, no 6Article in journal (Refereed)
    Abstract [en]

    When laser light illuminates a diffuse object, it produces a random interference effect known as a speckle pattern. If there is movement in the object, the speckles fluctuate in intensity. These fluctuations can provide information about the movement. A simple way of accessing this information is to image the speckle pattern with an exposure time longer than the shortest speckle fluctuation time scale-the fluctuations cause a blurring of the speckle, leading to a reduction in the local speckle contrast. Thus, velocity distributions are coded as speckle contrast variations. The same information can be obtained by using the Doppler effect, but producing a two-dimensional Doppler map requires either scanning of the laser beam or imaging with a high-speed camera: laser speckle contrast imaging (LSCI) avoids the need to scan and can be performed with a normal CCD- or CMOS-camera. LSCI is used primarily to map flow systems, especially blood flow. The development of LSCI is reviewed and its limitations and problems are investigated. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

  • 4.
    Colantonio, Sara
    et al.
    CNR, Italy.
    Germanese, Danila
    CNR, Italy.
    Moroni, Davide
    CNR, Italy.
    Giorgi, Daniela
    CNR, Italy.
    Pascali, Mariantonietta
    CNR, Italy.
    Righi, Marco
    CNR, Italy.
    Coppini, Giuseppe
    CNR, Italy.
    Aurora Morales, Maria
    CNR, Italy.
    Chiarugi, Franco
    FORTH, Greece.
    Pediaditis, Mattew
    FORTH, Greece.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, Faculty of Science & Engineering.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, Faculty of Science & Engineering.
    Henriquez, Pedro
    University of Central Lancashire, England.
    Matuszewski, Bogdan
    University of Central Lancashire, England.
    Milanic, Matijia
    Norwegian University of Science and Technology, Norway.
    Randeberg, Lise
    Norwegian University of Science and Technology, Norway.
    SEMEOTICONS - READING THE FACE CODE OF CARDIO-METABOLIC RISK2015In: 2015 INTERNATIONAL WORKSHOP ON COMPUTATIONAL INTELLIGENCE FOR MULTIMEDIA UNDERSTANDING (IWCIM), IEEE , 2015Conference paper (Refereed)
    Abstract [en]

    What if you could discover your health status by looking at yourself in the mirror? Since November 2013, the EU FP7 Project SEMEOTICONS is working to make this possible. The Project is building a multi-sensory device, having the form of a conventional mirror, able to read the semeiotic code of the face and detect possible evidence of the onset of cardio-metabolic diseases. The device, called Wize Mirror, integrates unobtrusive imaging sensors used to capture videos, images and 3D scans of the face. These are processed to assess the risk of a cardio-metabolic disease and thereby suggest possible strategies to prevent its onset.

  • 5.
    Danielis, Alessandro
    et al.
    CNR, Italy.
    Giorgi, Daniela
    CNR, Italy.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, Faculty of Science & Engineering.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, Faculty of Science & Engineering.
    Colantonio, Sara
    CNR, Italy.
    Salvetti, Ovidio
    CNR, Italy.
    Lip segmentation based on Lambertian shadings and morphological operators for hyper-spectral images2017In: Pattern Recognition, ISSN 0031-3203, E-ISSN 1873-5142, Vol. 63, p. 355-370Article in journal (Refereed)
    Abstract [en]

    Lip segmentation is a non-trivial task because the colour difference between the lip and the skin regions maybe not so noticeable sometimes. We propose an automatic lip segmentation technique for hyper-spectral images from an imaging prototype with medical applications. Contrarily to many other existing lip segmentation methods, we do not use colour space transformations to localise the lip area. As input image, we use for the first time a parametric blood concentration map computed by using narrow spectral bands. Our method mainly consists of three phases: (i) for each subject generate a subset of face images enhanced by different simulated Lambertian illuminations, then (ii) perform lip segmentation on each enhanced image by using constrained morphological operations, and finally (iii) extract features from Fourier-based modeled lip boundaries for selecting the lip candidate. Experiments for testing our approach are performed under controlled conditions on volunteers and on a public hyper-spectral dataset. Results show the effectiveness of the algorithm against low spectral range, moustache, and noise.

  • 6.
    Draijer, Matthijs J
    et al.
    University of Twente.
    Hondebrink, Erwin
    University of Twente.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    G van Leeuwen, Ton
    University of Twente.
    Steenbergen, Wiendelt
    University of Twente.
    Relation between the contrast in time integrated dynamic speckle patterns and the power spectral density of their temporal intensity fluctuations2010In: OPTICS EXPRESS, ISSN 1094-4087, Vol. 18, no 21, p. 21883-21891Article in journal (Refereed)
    Abstract [en]

    Scattering fluid flux can be quantified with coherent light, either from the contrast of speckle patterns, or from the moments of the power spectrum of intensity fluctuations. We present a theory connecting these approaches for the general case of mixed static-dynamic patterns of boiling speckles without prior assumptions regarding the particle dynamics. An expression is derived and tested relating the speckle contrast to the intensity power spectrum. Our theory demonstrates that in speckle contrast the concentration of moving particles dominates over the contribution of speed to the particle flux. Our theory provides a basis for comparison of both approaches when used for studying tissue perfusion.

  • 7.
    Ewerlöf, Maria
    et al.
    Linköping University, Department of Biomedical Engineering, Division of Biomedical Engineering. Linköping University, Faculty of Science & Engineering.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Division of Biomedical Engineering. Linköping University, Faculty of Science & Engineering.
    Salerud, Göran
    Linköping University, Department of Biomedical Engineering, Division of Biomedical Engineering. Linköping University, Faculty of Science & Engineering.
    Spatial and temporal skin blood volume and saturation estimation using a multispectral snapshot imaging camera2017In: IMAGING, MANIPULATION, AND ANALYSIS OF BIOMOLECULES, CELLS, AND TISSUES XV, SPIE-INT SOC OPTICAL ENGINEERING , 2017, Vol. 10068, article id UNSP 1006814Conference paper (Refereed)
    Abstract [en]

    Hyperspectral imaging (HSI) can estimate the spatial distribution of skin blood oxygenation, using visible to near-infrared light. HSI oximeters often use a liquid-crystal tunable filter, an acousto-optic tunable filter or mechanically adjustable filter wheels, which has too long response/switching times to monitor tissue hemodynamics. This work aims to evaluate a multispectral snapshot imaging system to estimate skin blood volume and oxygen saturation with high temporal and spatial resolution. We use a snapshot imager, the xiSpec camera (MQ022HG-IM-SM4X4-VIS, XIMEA (R)), having 16 wavelength-specific Fabry-Perot filters overlaid on the custom CMOS-chip. The spectral distribution of the bands is however substantially overlapping, which needs to be taken into account for an accurate analysis. An inverse Monte Carlo analysis is performed using a two-layered skin tissue model, defined by epidermal thickness, haemoglobin concentration and oxygen saturation, melanin concentration and spectrally dependent reduced-scattering coefficient, all parameters relevant for human skin. The analysis takes into account the spectral detector response of the xiSpec camera. At each spatial location in the field-of-view, we compare the simulated output to the detected diffusively backscattered spectra to find the best fit. The imager is evaluated for spatial and temporal variations during arterial and venous occlusion protocols applied to the forearm. Estimated blood volume changes and oxygenation maps at 512x272 pixels show values that are comparable to reference measurements performed in contact with the skin tissue. We conclude that the snapshot xiSpec camera, paired with an inverse Monte Carlo algorithm, permits us to use this sensor for spatial and temporal measurement of varying physiological parameters, such as skin tissue blood volume and oxygenation.

  • 8.
    Ewerlöf, Maria
    et al.
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Salerud, E. Göran
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Estimating skin blood saturation by selecting a subset of hyperspectral imaging data2015In: Imaging, Manipulation, and Analysis of Biomolecules, Cells, and Tissues XIII / [ed] Daniel L. Farkas; Dan V. Nicolau; Robert C. Leif, SPIE, 2015, Vol. 9328Conference paper (Refereed)
    Abstract [en]

    Skin blood haemoglobin saturation (𝑠b) can be estimated with hyperspectral imaging using the wavelength (λ) range of 450-700 nm where haemoglobin absorption displays distinct spectral characteristics. Depending on the image size and photon transport algorithm, computations may be demanding. Therefore, this work aims to evaluate subsets with a reduced number of wavelengths for 𝑠b estimation. White Monte Carlo simulations are performed using a two-layered tissue model with discrete values for epidermal thickness (𝑇epi) and the reduced scattering coefficient (μ's ), mimicking an imaging setup. A detected intensity look-up table is calculated for a range of model parameter values relevant to human skin, adding absorption effects in the post-processing. Skin model parameters, including absorbers, are; μ's (λ), 𝑇epi, haemoglobin saturation (𝑠b), tissue fraction blood (𝑐b) and tissue fraction melanin (𝑐mel). The skin model paired with the look-up table allow spectra to be calculated swiftly. Three inverse models with varying number of free parameters are evaluated: A(𝑠b, 𝑐b), B(𝑠b, 𝑐b, 𝑐mel) and C(all parameters free). Fourteen wavelength candidates are selected by analysing the maximal spectral sensitivity to 𝑠b and minimizing the sensitivity to 𝑐b. All possible combinations of these candidates with three, four and 14 wavelengths, as well as the full spectral range, are evaluated for estimating 𝑠b for 1000 randomly generated evaluation spectra. The results show that the simplified models A and B estimated 𝑠b accurately using four wavelengths (mean error 2.2% for model B). If the number of wavelengths increased, the model complexity needed to be increased to avoid poor estimations.

  • 9.
    Fredriksson, Ingemar
    et al.
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology. Perimed AB, Järfälla, Sweden.
    Burdakov, Oleg
    Linköping University, Department of Mathematics, Optimization . Linköping University, The Institute of Technology.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Inverse Monte Carlo in a multilayered tissue model: merging diffuse reflectance spectroscopy and laser Doppler flowmetry2013In: Journal of Biomedical Optics, ISSN 1083-3668, E-ISSN 1560-2281, Vol. 18, no 12, p. 127004-1-127004-14Article in journal (Refereed)
    Abstract [en]

    The tissue fraction of red blood cells (RBCs) and their oxygenation and speed-resolved perfusion areestimated in absolute units by combining diffuse reflectance spectroscopy (DRS) and laser Doppler flowmetry(LDF). The DRS spectra (450 to 850 nm) are assessed at two source–detector separations (0.4 and 1.2 mm), allowingfor a relative calibration routine, whereas LDF spectra are assessed at 1.2mmin the same fiber-optic probe. Data areanalyzed using nonlinear optimization in an inverse Monte Carlo technique by applying an adaptive multilayeredtissue model based on geometrical, scattering, and absorbing properties, as well as RBC flow-speed information.Simulations of 250 tissue-like models including up to 2000 individual blood vessels were used to evaluatethe method. The absolute root mean square (RMS) deviation between estimated and true oxygenation was 4.1percentage units, whereas the relative RMS deviations for the RBC tissue fraction and perfusion were 19% and23%, respectively. Examples of in vivo measurements on forearm and foot during common provocations arepresented. The method offers several advantages such as simultaneous quantification of RBC tissue fractionand oxygenation and perfusion from the same, predictable, sampling volume. The perfusion estimate is speedresolved, absolute (% RBC × mm∕s), and more accurate due to the combination with DRS.

  • 10.
    Fredriksson, Ingemar
    et al.
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, Faculty of Science & Engineering.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, Faculty of Science & Engineering.
    On the equivalence and differencesbetween laser Doppler flowmetry andlaser speckle contrast analysis2016In: Journal of Biomedical Optics, ISSN 1083-3668, E-ISSN 1560-2281, Vol. 21, no 12, article id 126018Article in journal (Refereed)
    Abstract [en]

    Laser Doppler flowmetry (LDF) and laser speckle contrast analysis (LASCA) both utilize the spatiotemporalproperties of laser speckle patterns to assess microcirculatory blood flow in tissue. Although the techniquesanalyze the speckle pattern differently, there is a close relationship between them. We present atheoretical overview describing how the LDF power spectrum and the LASCA contrast can be calculatedfrom each other, and how both these can be calculated from an optical Doppler spectrum containing variousdegrees of Doppler shifted light. The theoretical relationships are further demonstrated using time-resolvedspeckle simulations. A wide range of Monte Carlo simulated tissue models is then used to show how perfusionestimates for LDF and LASCA are affected by changes in blood concentration and speed distribution, as well asby geometrical and optical properties. We conclude that perfusion estimates from conventional single exposuretime LASCA are in general more sensitive to changes in optical and geometrical properties and are less accuratein the prediction of real perfusion changes, especially speed changes. Since there is a theoretical one-to-onerelationship between Doppler power spectrum and contrast, one can conclude that those drawbacks with theLASCA technique can be overcome using a multiple exposure time setup.

  • 11.
    Fredriksson, Ingemar
    et al.
    Linköping University, Department of Biomedical Engineering, Division of Biomedical Engineering. Linköping University, Faculty of Science & Engineering. Perimed AB, Sweden.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Division of Biomedical Engineering. Linköping University, Faculty of Science & Engineering.
    Vessel packaging effect in laser speckle contrast imaging and laser Doppler imaging2017In: Journal of Biomedical Optics, ISSN 1083-3668, E-ISSN 1560-2281, Vol. 22, no 10, article id 106005Article in journal (Refereed)
    Abstract [en]

    Laser speckle-based techniques are frequently used to assess microcirculatory blood flow. Perfusion estimates are calculated either by analyzing the speckle fluctuations over time as in laser Doppler flowmetry (LDF), or by analyzing the speckle contrast as in laser speckle contrast imaging (LSCI). The perfusion estimates depend on the amount of blood and its speed distribution. However, the perfusion estimates are commonly given in arbitrary units as they are nonlinear and depend on the magnitude and the spatial distribution of the optical properties in the tissue under investigation. We describe how the spatial confinement of blood to vessels, called the vessel packaging effect, can be modeled in LDF and LSCI, which affect the Doppler power spectra and speckle contrast, and the underlying bio-optical mechanisms for these effects. As an example, the perfusion estimate is reduced by 25% for LDF and often more than 50% for LSCI when blood is located in vessels with an average diameter of 40 aem, instead of being homogeneously distributed within the tissue. This significant effect can be compensated for only with knowledge of the average diameter of the vessels in the tissue. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License.

  • 12.
    Fredriksson, Ingemar
    et al.
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Nyström, Fredrik
    Linköping University, Department of Medicine and Health Sciences, Internal Medicine . Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Centre for Medicine, Department of Endocrinology and Gastroenterology UHL.
    Länne, Toste
    Linköping University, Department of Medicine and Health Sciences, Physiology . Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart Centre, Department of Thoracic and Vascular Surgery.
    Johan Östgren, Carl
    Linköping University, Department of Medicine and Health Sciences, General Practice. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Local Health Care Services in Finspång, Primary Health Care Centre.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Reduced Arteriovenous Shunting Capacity After Local Heating and Redistribution of Baseline Skin Blood Flow in Type 2 Diabetes Assessed With Velocity-Resolved Quantitative Laser Doppler Flowmetry2010In: Diabetes, ISSN 0012-1797, E-ISSN 1939-327X, Vol. 59, no 7, p. 1578-1584Article in journal (Refereed)
    Abstract [en]

    OBJECTIVE-To compare the microcirculatory velocity distribution in type 2 diabetic patients and nondiabetic control subjects at baseline and after local heating. RESEARCH DESIGN AND METHODS-The skin blood flow response to local heating (44 degrees C for 20 mm) was assessed in 28 diabetic patients and 29 control subjects using a new velocity-resolved quantitative laser Doppler flowmetry technique (qLDF). The qLDF estimates erythrocyte (RBC) perfusion (velocity X concentration), in a physiologically relevant unit (grams RBC per 100 g tissue X millimeters per second) in a fixed output volume, separated into three velocity regions: v less than1 mm/s, v 1-10 mm/s, and v greater than10 mm/s. RESULTS-The increased blood flow occurs in vessels with a velocity greater than1 mm/s. A significantly lower response in qLDF total perfusion was found in diabetic patients than in control subjects after heat provocation because of less high-velocity blood flow (v greater than10 mm/s). The RBC concentration in diabetic patients increased sevenfold for v between 1 and 10 mm/s, and 15-fold for v greater than10 mm/s, whereas no significant increase was found for v less than1 mm/s. The mean velocity increased from 0.94 to 7.3 mm/s in diabetic patients and from 0.83 to 9.7 mm/s in control subjects. CONCLUSIONS-The perfusion increase occurs in larger shunting vessels and not as an increase in capillary flow. Baseline diabetic patient data indicated a redistribution of flow to higher velocity regions, associated with longer duration of diabetes. A lower perfusion was associated with a higher BMI and a lower toe-to-brachial systolic blood pressure ratio.

  • 13.
    Fredriksson, Ingemar
    et al.
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology. Linköping University, Faculty of Health Sciences.
    Salomonsson, Fredrik
    Perimed AB, Järfälla-Stockholm, Sweden.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Improved calibration procedure for laser Doppler perfusion monitors2011In: Optical Diagnostics and SensingXI: Toward Point-of-CareDiagnostics; and Design andPerformance Validation ofPhantoms Used in Conjunctionwith Optical Measurement ofTissue III / [ed] Robert J. Nordstrom; Gerard L. Coté, SPIE - International Society for Optical Engineering, 2011, p. 790602-1-790602-7Conference paper (Other academic)
    Abstract [en]

    Commercial laser Doppler perfusion monitors are calibrated using the perfusion value, i.e. the first order moment of the Doppler power spectrum, from a measurement in a standardized microsphere colloidal suspension under Brownian motion. The calibration perfusion value depends on several parameters of the suspension that are difficult to keep constant with adequate accuracy, such as the concentration, temperature and the microsphere size distribution. The calibration procedure itself may therefore introduce significant errors in the measured values.

    An altered calibration procedure, where the zero order moment is used is described and demonstrated in this paper. Since the above mentioned parameters only affect the frequency content of the Doppler power spectrum and not the total power, the zero order moment will be independent of those parameters. It is shown that the variation in the calibration value, as given by measurements on different scattering liquids with a wide range of scattering properties and temperatures, is only a few percent using the proposed method. For the conventional calibration procedure, this variation corresponds to an error introduced by merely a 1°C variation in the reference liquid temperature. The proposed calibration method also enables absolute level comparisons between measured and simulated Doppler power spectra.

  • 14.
    Fredriksson, Ingemar
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Larsson, Marcus
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Strömberg, Tomas
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Absolute blood flow velocity components in Laser Doppler flowmetry2005In: International Graduate Summer School Biophotonics05,2005, 2005Conference paper (Other academic)
  • 15.
    Fredriksson, Ingemar
    et al.
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Absolute flow velocity components in laser Doppler flowmetry2006In: Proceedings of SPIE, the International Society for Optical Engineering, ISSN 0277-786X, E-ISSN 1996-756X, Vol. 6094, p. 60940A-Article in journal (Refereed)
    Abstract [en]

    A method to separate a Doppler power spectrum into a number of flow velocity components, measured in absolute units (mm/s), is presented. A Monte Carlo software was developed to track each individual Doppler shift, to determine the probability, p(n), for a photon to undergo n Doppler shifts. Given this shift distribution, a mathematical relationship was developed and used to calculate a Doppler power spectrum originating from a certain combination of velocity components. The non linear Levenberg-Marquardt optimization method could thus be used to fit the calculated and measured Doppler power spectra, giving the true set of velocity components in the measured sample. The method was evaluated using a multi tube flow phantom perfused with either polystyrene microspheres or undiluted/diluted human blood (hct = 0.45). It estimated the velocity components in the flow phantom well, during both low and high concentrations of moving scatterers (microspheres or blood). Thus, further development of the method could prove to be a valuable clinical tool to differentiate capillary blood flow.

  • 16.
    Fredriksson, Ingemar
    et al.
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Accuracy of vessel diameter estimated from a vessel packaging compensation in diffuse reflectance spectroscopy2011In: Clinical and Biomedical Spectroscopy and Imaging II / [ed] Nirmala Ramanujam, Jurgen Popp, SPIE - International Society for Optical Engineering, 2011, Vol. 8087, p. 8087 1M-1-8087 1M-8Conference paper (Other academic)
    Abstract [en]

     Light absorption in tissue is generally decreased when chromophores are spatially concentrated rather than being homogeneously distributed. In tissue, this applies to hemoglobin located in blood vessels (vessel packaging). In this paper, the diffusely reflected light from 41 tissue models with discrete blood vessels with diameters ranging from 6.25 to 100 μm were simulated using the Monte Carlo technique. A reverse engineering approach was then utilized to find the model that had an optimal spectral fit to each of the simulated models. The average vessel diameter was one fitting parameter in the adaptive model. The estimated vessel diameter from the optimal fit model was compared to the known diameter from the simulated models. Two different methods to calculate the vessel packaging effect were used, one existing based on a simple analytic expression and a new method based on path length distributions. Both methods had similar performance. For the new method, the absolute RMS deviation of the estimated vessel diameter was 5.5 μm for vessel diameters ≤ 25 μm, and the relative RMS deviation was 21 % for vessel diameters > 25 μm.

     

  • 17.
    Fredriksson, Ingemar
    et al.
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Forced detection Monte Carlo algorithms for accelerated blood vessel image simulations2009In: JOURNAL OF BIOPHOTONICS, ISSN 1864-063X, Vol. 2, no 3, p. 178-184Article in journal (Refereed)
    Abstract [en]

    Two forced detection (FD) variance reduction Monte Carlo algorithms for image simulations of tissue-embedded objects with matched refractive index are presented. The principle of the algorithms is to force a fraction of the photon weight to the detector at each and every scattering event. The fractional weight is given by the probability for the photon to reach the detector without further interactions. Two imaging setups are applied to a tissue model including blood vessels, where the ID algorithms produce identical results as traditional brute force simulations, while being accelerated with two orders of magnitude. Extending the methods to include refraction mismatches is discussed.

    The principle of forced detection; a part of the photon weight. based on the probability of reaching the detector without further interactions, is forced to the detector at each and every scattering event.

  • 18.
    Fredriksson, Ingemar
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Larsson, Marcus
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Strömberg, Tomas
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Hastighetsupplöst blodflödesmätning med Laserdopplertekniken2005In: Medicinteknikdagar MTF,2005, 2005Conference paper (Other academic)
  • 19.
    Fredriksson, Ingemar
    et al.
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Inverse Monte Carlo method in a multilayered tissue model for diffuse reflectance spectroscopy2012In: Journal of Biomedical Optics, ISSN 1083-3668, E-ISSN 1560-2281, Vol. 17, no 4, p. 047004-Article in journal (Refereed)
    Abstract [en]

    Model based data analysis of diffuse reflectance spectroscopy data enables the estimation of optical and structural tissue parameters. The aim of this study was to present an inverse Monte Carlo method based on spectra from two source-detector distances (0.4 and 1.2 mm), using a multilayered tissue model. The tissue model variables include geometrical properties, light scattering properties, tissue chromophores such as melanin and hemoglobin, oxygen saturation and average vessel diameter. The method utilizes a small set of presimulated Monte Carlo data for combinations of different levels of epidermal thickness and tissue scattering. The path length distributions in the different layers are stored and the effect of the other parameters is added in the post-processing. The accuracy of the method was evaluated using Monte Carlo simulations of tissue-like models containing discrete blood vessels, evaluating blood tissue fraction and oxygenation. It was also compared to a homogeneous model. The multilayer model performed better than the homogeneous model and all tissue parameters significantly improved spectral fitting. Recorded in vivo spectra were fitted well at both distances, which we previously found was not possible with a homogeneous model. No absolute intensity calibration is needed and the algorithm is fast enough for real-time processing.

  • 20.
    Fredriksson, Ingemar
    et al.
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Laser Doppler flowmetry2012In: Microcirculation imaging / [ed] Martin J. Leahy, Weinheim: Wiley-Blackwell, 2012, , p. 411p. 67-84Chapter in book (Other academic)
    Abstract [en]

    Adopting a multidisciplinary approach with input from physicists, researchers and medical professionals, this is the first book to introduce many different technical approaches for the visualization of microcirculation, including laser Doppler and laser speckle, optical coherence tomography and photo-acoustic tomography. It covers everything from basic research to medical applications, providing the technical details while also outlining the respective strengths and weaknesses of each imaging technique. Edited by an international team of top experts, this is the ultimate handbook for every clinician and researcher relying on microcirculation imaging.

  • 21.
    Fredriksson, Ingemar
    et al.
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Measurement depth and volume in laser Doppler flowmetry2009In: Microvascular Research, ISSN 0026-2862, E-ISSN 1095-9319, Vol. 78, no 1, p. 4-13Article in journal (Refereed)
    Abstract [en]

    A new method for estimating the measurement depth and volume in laser Doppler flowmetry (LDF) is presented. The method is based on Monte Carlo simulations of light propagation in tissue. The contribution from each individual Doppler shift is calculated and thereby multiple Doppler shifts are handled correctly. Different LDF setups for both probe based (0.0, 0.25, 0.5, and 1.2 mm source-detector separation) and imaging systems (0.5 and 2.0 mm beam diameter) are considered, at the wavelengths 543 nm, 633 nm, and 780 nm. Non-linear speckle pattern effects are accounted for in the imaging system setups. The effects of tissue optical properties, blood concentration, and blood oxygen saturation are evaluated using both homogeneous tissue models and a layered skin model. The results show that the effect on the measurement depth of changing tissue properties is comparable to the effect of changing the system setup, e.g. source-detector separation and wavelength. Skin pigmentation was found to have a negligible effect on the measurement depth. Examples of measurement depths are (values are given for a probe based system with 0.25 mm source-detector separation and an imaging system with a 0.5 mm beam diameter, respectively, both operating at 780 nm): muscle - 0.55/0.79 mm; liver - 0.40/0.53 mm; gray matter - 0.48/0.68 mm; white matter - 0.20/0.20 mm; index finger pulp - 0.41/0.53 mm; forearm skin - 0.53/0.56 mm; heat provoked forearm skin - 0.66/0.67 mm.

  • 22.
    Fredriksson, Ingemar
    et al.
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Model-Based Quantification of Skin Microcirculatory Perfusion2014In: Computational Biophysics of the Skin / [ed] Bernard Querleux, Singapore: Pan Stanford Publishing, 2014, 1, p. 395-420Chapter in book (Other academic)
  • 23.
    Fredriksson, Ingemar
    et al.
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Model-based quantitative laser Doppler flowmetry in skin2010In: Journal of Biomedical Optics, ISSN 1083-3668, E-ISSN 1560-2281, Vol. 15, no 5Article in journal (Refereed)
    Abstract [en]

    Laser Doppler Flowmetry (LDF) can be used for assessing the microcirculatory perfusion. However, conventional LDF (cLDF) gives only a relative perfusion estimate in an unknown measurement volume. To overcome these limitations a model-based analysis method for quantitative LDF (qLDF) is proposed. The method uses an inverse Monte Carlo technique with an adaptive three layer skin model. By analyzing the optimal model where measured and simulated LDF spectra using two different source-detector separations match, the absolute microcirculatory perfusion for a specified velocity region in a predefined volume is determined. The robustness of the qLDF method and how much it is affected by physiologically relevant variations in optical properties were evaluated using additional Monte Carlo simulations. When comparing qLDF to cLDF, a much smaller deviation from the true perfusion was attained. For physiologically relevant variations in the optical properties of static tissue and blood absorption, qLDF displayed errors <12%. Variations in the scattering properties of blood displayed larger errors (<58%). Evaluations on inhomogeneous models containing small blood vessels, hair and sweat glands displayed errors <5%. For extremely inhomogeneous models containing larger blood vessels, the error increased substantially, but this was detected by analyzing the qLDF model residual. The qLDF algorithm was applied to an in vivo local heat provocation. The perfusion increase was higher with qLDF than cLDF, due to non-linear effects in the latter. The qLDF showed that the perfusion increase was due to an increased amount of blood cells with a velocity > 1 mm/s.

  • 24.
    Fredriksson, Ingemar
    et al.
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Optical microcirculatory skin model: Assessed by Monte Carlo simulations paired with in vivo laser Doppler flowmetry2008In: Journal of Biomedical Optics, ISSN 1083-3668, E-ISSN 1560-2281, Vol. 13, no 1, p. 14015-Article in journal (Refereed)
    Abstract [en]

    An optical microvascular skin model, valid at 780 nm, was developed. The model consisted of six layers with individual optical properties, and variable thicknesses and blood concentrations at three different blood flow velocities. Monte Carlo simulations were used to evaluate the impact of various model parameters on the traditional Laser Doppler flowmetry (LDF) measures. A set of reference Doppler power spectra was generated by simulating 7,000 configurations, varying the thickness and blood concentrations. Simulated spectra, at two different source detector separations, were compared with in vivo recorded spectra, using a non-linear search algorithm for minimizing the deviation between simulated and measured spectra. The model was validated by inspecting the thickness and blood concentrations which generated the best fit. These four parameters followed a priori expectations for the measurement situations, and the simulated spectra agreed well with the measured spectra for both detector separations. Average estimated dermal blood concentration was 0.08% at rest and 0.63% during heat provocation (44°C) on the volar side of the forearm, and 1.2% at rest on the finger pulp. The model is crucial for developing a technique for velocity-resolved absolute LDF measurements with known sampling volume, and can also be useful for other bio-optical modalities.

  • 25.
    Fredriksson, Ingemar
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Larsson, Marcus
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Strömberg, Tomas
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Separation av shuntat och kapillärt mikrocirkulatoriskt blodflöde med laser Doppler-tekniken2006In: Medicinteknikdagarna,2006, 2006Conference paper (Refereed)
  • 26.
    Henriquez, Pedro
    et al.
    University of Central Lancashire, England.
    Matuszewski, Bogdan J.
    University of Central Lancashire, England.
    Andreu-Cabedo, Yasmina
    University of Central Lancashire, England.
    Bastiani, Luca
    CNR, Italy.
    Colantonio, Sara
    CNR, Italy.
    Coppini, Giuseppe
    CNR, Italy.
    DAcunto, Mario
    CNR, Italy.
    Favilla, Riccardo
    CNR, Italy.
    Germanese, Danila
    CNR, Italy.
    Giorgi, Daniela
    CNR, Italy.
    Marraccini, Paolo
    CNR, Italy.
    Martinelli, Massimo
    CNR, Italy.
    Morales, Maria-Aurora
    CNR, Italy.
    Antonietta Pascali, Maria
    CNR, Italy.
    Righi, Marco
    CNR, Italy.
    Salvetti, Ovidio
    CNR, Italy.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Division of Biomedical Engineering. Linköping University, Faculty of Science & Engineering.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Division of Biomedical Engineering. Linköping University, Faculty of Science & Engineering.
    Randeberg, Lise
    Norwegian University of Science and Technology, Norway.
    Bjorgan, Asgeir
    Norwegian University of Science and Technology, Norway.
    Giannakakis, Giorgos
    Fdn Research and Technology Hellas, Greece.
    Pediaditis, Matthew
    Fdn Research and Technology Hellas, Greece.
    Chiarugi, Franco
    Fdn Research and Technology Hellas, Greece.
    Christinaki, Eirini
    Fdn Research and Technology Hellas, Greece.
    Marias, Kostas
    Fdn Research and Technology Hellas, Greece.
    Tsiknakis, Manolis
    Fdn Research and Technology Hellas, Greece; Technology Educ Institute Crete, Greece.
    Mirror Mirror on the Wall ... An Unobtrusive Intelligent Multisensory Mirror for Well-Being Status Self-Assessment and Visualization2017In: IEEE transactions on multimedia, ISSN 1520-9210, E-ISSN 1941-0077, Vol. 19, no 7, p. 1467-1481Article in journal (Refereed)
    Abstract [en]

    A persons well-being status is reflected by their face through a combination of facial expressions and physical signs. The SEMEOTICONS project translates the semeiotic code of the human face into measurements and computational descriptors that are automatically extracted from images, videos, and three-dimensional scans of the face. SEMEOTICONS developed a multisensory platform in the form of a smart mirror to identify signs related to cardio-metabolic risk. The aim was to enable users to self-monitor their well-being status over time and guide them to improve their lifestyle. Significant scientific and technological challenges have been addressed to build the multisensory mirror, from touchless data acquisition, to real-time processing and integration of multimodal data.

  • 27.
    Hultman, Martin
    et al.
    Linköping University, Department of Biomedical Engineering, Division of Biomedical Engineering. Linköping University, Faculty of Science & Engineering.
    Fredriksson, Ingemar
    Linköping University, Department of Biomedical Engineering, Division of Biomedical Engineering. Linköping University, Faculty of Science & Engineering. Perimed AB, Järfälla-Stockholm, Sweden.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Division of Biomedical Engineering. Linköping University, Faculty of Science & Engineering.
    Alvandpour, Atila
    Linköping University, Department of Electrical Engineering, Integrated Circuits and Systems. Linköping University, Faculty of Science & Engineering.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Division of Biomedical Engineering. Linköping University, Faculty of Science & Engineering.
    A 15.6 frames per second 1 megapixel Multiple Exposure Laser Speckle Contrast Imaging setup2018In: Journal of Biophotonics, ISSN 1864-063X, E-ISSN 1864-0648, Vol. 11, no 2, article id e201700069Article in journal (Refereed)
    Abstract [en]

    A multiple exposure laser speckle contrast imaging (MELSCI) setup for visualizing blood perfusion was developed using a field programmable gate array (FPGA), connected to a 1000 frames per second (fps) 1-megapixel camera sensor. Multiple exposure time images at 1, 2, 4, 8, 16, 32 and 64 milliseconds were calculated by cumulative summation of 64 consecutive snapshot images. The local contrast was calculated for all exposure times using regions of 4 × 4 pixels. Averaging of multiple contrast images from the 64-millisecond acquisition was done to improve the signal-to-noise ratio. The results show that with an effective implementation of the algorithm on an FPGA, contrast images at all exposure times can be calculated in only 28 milliseconds. The algorithm was applied to data recorded during a 5 minutes finger occlusion. Expected contrast changes were found during occlusion and the following hyperemia in the occluded finger, while unprovoked fingers showed constant contrast during the experiment. The developed setup is capable of massive data processing on an FPGA that enables processing of MELSCI data in 15.6 fps (1000/64 milliseconds). It also leads to improved frame rates, enhanced image quality and enables the calculation of improved microcirculatory perfusion estimates compared to single exposure time systems.

  • 28.
    Hultman, Martin
    et al.
    Linköping University, Department of Biomedical Engineering, Division of Biomedical Engineering. Linköping University, Faculty of Science & Engineering.
    Fredriksson, Ingemar
    Linköping University, Department of Biomedical Engineering, Division of Biomedical Engineering. Linköping University, Faculty of Science & Engineering. Perimed AB, Järfälla-Stockholm, Sweden.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Division of Biomedical Engineering. Linköping University, Faculty of Science & Engineering.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Division of Biomedical Engineering. Linköping University, Faculty of Science & Engineering.
    Evaluation of a high framerate multi-exposure laser speckle contrast imaging setup2018In: High-Speed Biomedical Imaging and Spectroscopy III: Toward Big Data Instrumentation and Management / [ed] Kevin K. Tsia, Keisuke Goda, SPIE - International Society for Optical Engineering, 2018Conference paper (Refereed)
    Abstract [en]

    We present a first evaluation of a new multi-exposure laser speckle contrast imaging (MELSCI) system for assessing spatial variations in the microcirculatory perfusion. The MELSCI system is based on a 1000 frames per second 1-megapixel camera connected to a field programmable gate arrays (FPGA) capable of producing MELSCI data in realtime. The imaging system is evaluated against a single point laser Doppler flowmetry (LDF) system during occlusionrelease provocations of the arm in five subjects. Perfusion is calculated from MELSCI data using current state-of-the-art inverse models. The analysis displayed a good agreement between measured and modeled data, with an average error below 6%. This strongly indicates that the applied model is capable of accurately describing the MELSCI data and that the acquired data is of high quality. Comparing readings from the occlusion-release provocation showed that the MELSCI perfusion was significantly correlated (R=0.83) to the single point LDF perfusion, clearly outperforming perfusion estimations based on a single exposure time. We conclude that the MELSCI system provides blood flow images of enhanced quality, taking us one step closer to a system that accurately can monitor dynamic changes in skin perfusion over a large area in real-time

  • 29.
    Häggblad, Erik
    et al.
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Arildsson, Mikael
    Linköping University, Department of Biomedical Engineering.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Salerud, Göran
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Reflection Spectroscopy of Analgesized Skin2001In: Microvascular Research, ISSN 0026-2862, E-ISSN 1095-9319, Vol. 62, no 3, p. 392-400 Article in journal (Refereed)
    Abstract [en]

    Analgesized skin, when subjected to heat stimuli, responds by increasing skin perfusion. This response does not originate from increased perfusion in superficial capillaries, but rather in the deeper lying vessels. The aim of this study was to assess changes in blood chromophore content, measured by reflection spectroscopy, in relation to the perfusion increase, especially regarding the chromophores oxyhemoglobin and deoxyhemoglobin. Eleven normal subjects were treated with analgesic cream (EMLA) and placebo for 20, 40, 60, 120, and 180 min. Individual reactions to local heating were classified as responses if the change in reflection data or the change in perfusion, as measured by laser Doppler blood flowmetry, exceeded 2 standard deviations of normal variation. The increase in blood perfusion or in blood content gave rise to an increased absorption, interpreted as an increase due mainly to the chromophore oxyhemoglobin. The number of responses increased with increased treatment time for EMLA-treated areas. In general, there was a good agreement between both methods; 44 of 55 classifications coincided for the two methods used. In conclusion, analgesized forearm skin, which had been exposed to local heating, responded with an elevated perfusion consisting of oxygenated blood. This strengthens the hypothesis that the flow increase occurs through dilatation of larger deeper lying skin vessels and not in the capillaries.

  • 30.
    Häggblad, Erik
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Larsson, Marcus
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Arildsson, Mikael
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Salerud, Göran
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Strömberg, Tomas
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Reflektionsspektroskopi på EML-behandlad och värmeprovocerad hud2000In: Svenska läkarsällskapets Riksstämma,2000, 2000, p. 250-250Conference paper (Other academic)
  • 31.
    Häggblad, Erik
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Larsson, Marcus
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Arildsson, Mikael
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Strömberg, Tomas
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Reflectance spectroscopy of analgesized skin after local healing2000In: CNVD,2000, 2000Conference paper (Refereed)
  • 32.
    Häggblad, Erik
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Larsson, Marcus
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Arildsson, Mikael
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Strömberg, Tomas
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Salerud, Göran
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Reflectance spectroscopy2000In: Eight Int Symp CNVD 2000,2000, 2000, p. 45-50Conference paper (Other academic)
  • 33.
    Häggblad, Erik
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Lindbergh, Tobias
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Larsson, Marcus
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Salerud, Göran
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Strömberg, Tomas
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Myocardial blood volume and oxygenation monitoring during thoracic surgery2005Conference paper (Other academic)
  • 34.
    Jonasson, Hanna
    et al.
    Linköping University, Department of Biomedical Engineering, Division of Biomedical Engineering. Linköping University, Faculty of Science & Engineering.
    Bergstrand, Sara
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, Faculty of Science & Engineering.
    Nyström, Fredrik H
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Heart and Medicine Center, Department of Endocrinology.
    Länne, Toste
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Heart and Medicine Center, Department of Thoracic and Vascular Surgery.
    Östgren, Carl Johan
    Linköping University, Department of Medical and Health Sciences, Division of Community Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Primary Care Center, Primary Health Care Center Ödeshög.
    Bjarnegård, Niclas
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences.
    Fredriksson, Ingemar
    Linköping University, Department of Biomedical Engineering, Division of Biomedical Engineering. Linköping University, Faculty of Science & Engineering. Perimed AB, Sweden.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Division of Biomedical Engineering. Linköping University, Faculty of Science & Engineering.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Division of Biomedical Engineering. Linköping University, Faculty of Science & Engineering.
    Skin microvascular endothelial dysfunction is associated with type 2 diabetes independently of microalbuminuria and arterial stiffness2017In: Diabetes & Vascular Disease Research, ISSN 1479-1641, E-ISSN 1752-8984, Vol. 14, no 4, p. 363-371, article id UNSP 1479164117707706Article in journal (Refereed)
    Abstract [en]

    Skin and kidney microvascular functions may be affected independently in diabetes mellitus. We investigated skin microcirculatory function in 79 subjects with diabetes type 2, where 41 had microalbuminuria and 38 not, and in 41 age-matched controls. The oxygen saturation, fraction of red blood cells and speed-resolved microcirculatory perfusion (% red blood cells x mm/s) divided into three speed regions: 0-1, 1-10 and above 10 mm/s, were assessed during baseline and after local heating of the foot with a new device integrating diffuse reflectance spectroscopy and laser Doppler flowmetry. Arterial stiffness was assessed as carotid-femoral pulse wave velocity. Subjects with diabetes and microalbuminuria had significantly higher carotid-femoral pulse wave velocity compared to subjects without microalbuminuria and to controls. The perfusion for speeds 0-1 mm/s and red blood cell tissue fraction were reduced in subjects with diabetes at baseline and after heating, independent of microalbuminuria. These parameters were correlated to HbA1c. In conclusion, the reduced nutritive perfusion and red blood cell tissue fraction in type 2 diabetes were related to long-term glucose control but independent of microvascular changes in the kidneys and large-vessel stiffness. This may be due to different pathogenic pathways in the development of nephropathy, large-vessel stiffness and cutaneous microvascular impairment.

  • 35.
    Jonasson, Hanna
    et al.
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Fredriksson, Ingemar
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology. Perimed AB, Järfälla-Stockholm, Sweden .
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Assessment of the microcirculation using combined model based diffuse reflectance spectroscopy and laser Doppler flowmetry2015In: 16th Nordic-Baltic Conference on Biomedical Engineering: 16. NBC & 10. MTD 2014 joint conferences. October 14-16, 2014, Gothenburg, Sweden, Springer, 2015, p. 52-54Conference paper (Refereed)
    Abstract [en]

    By using a combined inverse model for diffuse reflectance spectroscopy (DRS) and laser Doppler flowmetry (LDF) the tissue fraction of red blood cells (RBCs), their oxygenation and speed-resolved perfusion are estimated in absolute units. DRS spectra (450 to 850 nm) are measured at two source-detector distances; 0.4 and 1.2 mm. LDF spectra are measured at 1.2 mm, integrated in the same fiber-optic probe. Inverse Monte Carlo technique and an adaptive tissue model is used to quantify the microcirculatory parameters. Measurements were done during venous occlusion of the tissue. The model fitting yields a good spectral fit for the two DRS spectra and the LDF spectrum. The physiological responses regarding for example which speed regions respond to provocations follows a priori expectations. The combined model gives quantitative measures of RBC tissue fraction, oxygenation and speed resolved perfusion from the same sampling volume which gives new opportunities to interpret data.

  • 36.
    Jonasson, Hanna
    et al.
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, Faculty of Science & Engineering.
    Fredriksson, Ingemar
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, Faculty of Science & Engineering. Perimed AB, Datavägen 9A, 175 43 Järfälla, Stockholm, Sweden.
    Pettersson, Anders
    Perimed AB, Datavägen 9a, 175 26 Järfälla-Stockholm.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, Faculty of Science & Engineering.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, Faculty of Science & Engineering.
    Oxygen saturation, red blood cell tissue fraction and speed resolved perfusion — A new optical method for microcirculatory assessment2015In: Microvascular Research, ISSN 0026-2862, E-ISSN 1095-9319, Vol. 102, p. 70-77Article in journal (Refereed)
    Abstract [en]

    We have developed a new fiber-optic system that combines diffuse reflectance spectroscopy (DRS) and laser Doppler Flowmetry (LDF) for a multi-modal assessment of the microcirculation. Quantitative data is achieved with an inverse Monte Carlo algorithm based on an individually adaptive skin model. The output parameters are calculated from the model and given in absolute units: hemoglobin oxygen saturation (%), red blood cell (RBC) tissue fraction (%), and the speed resolved RBC perfusion separated into three speed regions; 0–1 mm/s, 1–10 mm/s and above 10 mm/s (% mm/s). The aim was to explore microcirculatory parameters using the new optical method, integrating DRS and LDF in a joint skin model, during local heating of the dorsal foot and venous and arterial occlusion of the forearm in 23 healthy subjects (age 20–28 years). There were differences in the three speed regions in regard to blood flow changes due to local heating, where perfusion for high speeds increased the most. There was also a high correlation between changes in oxygenation and changes in perfusion for higher speeds. Oxygen saturation at baseline was 44% on foot, increasing to 83% at plateau after heating. The larger increase in perfusion for higher speeds than for lower speeds together with the oxygenation increase during thermal provocation, shows a local thermoregulatory blood flow in presumably arteriolar dermal vessels. In conclusion, there are improved possibilities to assess microcirculation using integrated DRS and LDF in a joint skin model by enabling both oxygenation and speed resolved blood flow assessment simultaneously and in the same skin site. Output parameters in absolute units may also yield new insights about the microcirculatory system.

  • 37.
    Jonasson, Hanna
    et al.
    Linköping University, Department of Biomedical Engineering, Division of Biomedical Engineering. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Medical and Health Sciences. Linköping University, Faculty of Medicine and Health Sciences.
    Fredriksson, Ingemar
    Linköping University, Department of Biomedical Engineering, Division of Biomedical Engineering. Linköping University, Faculty of Science & Engineering. Perimed AB, Järfälla, Stockholm, Sweden.
    Bergstrand, Sara
    Linköping University, Department of Medical and Health Sciences, Division of Nursing Science. Linköping University, Faculty of Medicine and Health Sciences.
    Östgren, Carl Johan
    Linköping University, Department of Medical and Health Sciences, Division of Community Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Primary Care Center, Primary Health Care Center Ödeshög.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Division of Biomedical Engineering. Linköping University, Faculty of Science & Engineering.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Division of Biomedical Engineering. Linköping University, Faculty of Science & Engineering.
    In vivo characterization of light scattering properties of human skin in the 475- to 850-nm wavelength range in a Swedish cohort2018In: Journal of Biomedical Optics, ISSN 1083-3668, E-ISSN 1560-2281, Vol. 23, no 12, article id 121608Article in journal (Refereed)
    Abstract [en]

    We have determined in vivo optical scattering properties of normal human skin in 1734 subjects, mostly with fair skin type, within the Swedish CArdioPulmonary bioImage Study. The measurements were performed with a noninvasive system, integrating spatially resolved diffuse reflectance spectroscopy and laser Doppler flowmetry. Data were analyzed with an inverse Monte Carlo algorithm, accounting for both scattering, geometrical, and absorbing properties of the tissue. The reduced scattering coefficient was found to decrease from 3.16 ± 0.72 to 1.13 ± 0.27 mm-1 (mean ± SD) in the 475- to 850-nm wavelength range. There was a negative correlation between the reduced scattering coefficient and age, and a significant difference between men and women in the reduced scattering coefficient as well as in the fraction of small scattering particles. This large study on tissue scattering with mean values and normal variation can serve as a reference when designing diagnostic techniques or when evaluating the effect of therapeutic optical systems.

  • 38.
    Karlsson, Daniel M G
    et al.
    Linköping University, Department of Biomedical Engineering. Linköping University, The Institute of Technology.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering. Linköping University, The Institute of Technology.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering. Linköping University, The Institute of Technology.
    Wårdell, Karin
    Linköping University, Department of Biomedical Engineering. Linköping University, The Institute of Technology.
    Influence of tissue movement on laser Doppler perfusion imaging2002In: Proc. SPIE 4624, Optical Diagnostics and Sensing of Biological Fluids and Glucose and Cholesterol Monitoring II, 106 (May 24, 2002), Vol. 4624 / [ed] Alexander V. Priezzhev and Gerard L. Cote, SPIE , 2002, p. 106-114Conference paper (Refereed)
    Abstract [en]

    The microvascular perfusion can be measured using laser Doppler blood flowmetry (LDF), a technique sensitive to the concentration of moving blood cells and their velocity. However, movements of the tissue itself can cause artifacts in the perfusion readings. In a clinical situation, these movement induced artifacts may arise from patient movements or from movements of internal organs e.g. the intestines or the beating heart. Therefore, we have studied how a well-controlled tissue movement affects the LDF signals during different flow conditions and for different surface structures. Tissue perfusion was recorded non-touch in one point using a laser Doppler perfusion imager. During the measurements the object was placed on a shaker that generated the movement (both horizontal and vertical). Measurements were carried out both on DELRIN® (polyacetal plastic) and the fingertip, for a wide range of velocities (0-3 cm/s). The influence of the microvascular perfusion was evaluated by occluding the brachial artery as well as blood emptying the finger and by using a flow model. The LDF signals were correlated to the movement. In vivo measurements showed that velocities above 0.8 cm/s gave a significant contribution to the perfusion signal. Corresponding velocities for the DELRIN® piece were higher (1.4 – 2.6 cm/s), and dependent on the surface structures and reflecting properties. By reducing the amount of specular reflection the movement influence was substantially lowered.

  • 39.
    Karlsson, Daniel M G
    et al.
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Wårdell, Karin
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Influence of tissue movements on laser Doppler perfusion imaging2002In: Proceedings of SPIE Volume 4624: Optical Diagnostics and Sensing of Biological Fluids and Glucose and Cholesterol Monitoring II / [ed] Alexander V. Priezzhev; Gerard L. Cote, SPIE - International Society for Optical Engineering, 2002, Vol. 4624, p. 106-114Conference paper (Other academic)
    Abstract [en]

    The microvascular perfusion can be measured using laser Doppler blood flowmetry (LDF), a technique sensitive to the concentration of moving blood cells and their velocity. However, movements of the tissue itself can cause artifacts in the perfusion readings. In a clinical situation, these movement induced artifacts may arise from patient movements or from movements of internal organs e.g. the intestines or the beating heart. Therefore, we have studied how a well-controlled tissue movement affects the LDF signals during different flow conditions and for different surface structures. Tissue perfusion was recorded non-touch in one point using a laser Doppler perfusion imager. During the measurements the object was placed on a shaker that generated the movement (both horizontal and vertical). Measurements were carried out both on DELRIN« (polyacetal plastic) and the fingertip, for a wide range of velocities (0-3 cm/s). The influence of the microvascular perfusion was evaluated by occluding the brachial artery as well as blood emptying the finger and by using a flow model. The LDF signals were correlated to the movement. In vivo measurements showed that velocities above 0.8 cm/s gave a significant contribution to the perfusion signal. Corresponding velocities for the DELRIN« piece were higher (1.4 - 2.6 cm/s), and dependent on the surface structures and reflecting properties. By reducing the amount of specular reflection the movement influence was substantially lowered.

  • 40.
    Karlsson, Hanna
    et al.
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Fredriksson, Ingemar
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Inverse Monte Carlo for estimation of scattering and absorption in liquid optical phantoms2012In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 20, no 11, p. 12233-12246Article in journal (Refereed)
    Abstract [en]

    A spectroscopic probe with multiple detecting fibers was used for quantifying absorption and scattering in liquid optical phantoms. The phantoms were mixtures of Intralipid and red and blue food dyes. Intensity calibration for the detecting fibers was undertaken using either a microsphere suspension (absolute calibration) or a uniform detector illumination (relative calibration between detectors). Two different scattering phase functions were used in an inverse Monte Carlo algorithm. Data were evaluated for residual spectra (systematic deviations and magnitude) and accuracy in estimation of scattering and absorption. Spectral fitting was improved by allowing for a 10% intensity relaxation in the optimization algorithm. For a multi-detector setup, non-systematic residual spectrum was only found using the more complex Gegenbauer-kernel phase function. However, the choice of phase function did not influence the accuracy in the estimation of absorption and scattering. Similar estimation accuracy as in the multi-detector setup was also obtained using either two relative calibrated detectors or one absolute calibrated detector at a fiber separation of 0.46 mm.

  • 41.
    Karlsson, Hanna
    et al.
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Fredriksson, Ingemar
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Kvantitativa mätningar av mikrocirkulatoriska parametrar med optiska tekniker och en realistisk hudmodell2011Conference paper (Other academic)
  • 42.
    Karlsson, Hanna
    et al.
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Fredriksson, Ingemar
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Perimed AB, Järfälla, Sweden.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Speed resolved assessment of the microcirculation using combined model based diffuse reflectance spectroscopy and laser Doppler flowmetry2014Conference paper (Other academic)
  • 43.
    Karlsson, Hanna
    et al.
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Pettersson, Anders
    Perimed AB, Järfälla-Stockholm.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Can a one-layer optical skin model including melanin and inhomogeneously distributed blood explain spatially resolved diffuse reflectance spectra?2011In: Optical Tomography and Spectroscopy of Tissue IX / [ed] Robert R. Alfano; Bruce J. Tromberg; Arjun G. Yodh; Mamoru Tamura; Eva M. Sevick-Muraca, SPIE - International Society for Optical Engineering, 2011, Vol. 7896, p. 78962Y-78962Y-9Conference paper (Other academic)
    Abstract [en]

    Model based analysis of calibrated diffuse reflectance spectroscopy can be used for determining oxygenation and concentration of skin chromophores. This study aimed at assessing the effect of including melanin in addition to hemoglobin (Hb) as chromophores and compensating for inhomogeneously distributed blood (vessel packaging), in a single-layer skin model. Spectra from four humans were collected during different provocations using a twochannel fiber optic probe with source-detector separations 0.4 and 1.2 mm. Absolute calibrated spectra using data from either a single distance or both distances were analyzed using inverse Monte Carlo for light transport and Levenberg-Marquardt for non-linear fitting. The model fitting was excellent using a single distance. However, the estimated model failed to explain spectra from the other distance. The two-distance model did not fit the data well at either distance. Model fitting was significantly improved including melanin and vessel packaging. The most prominent effect when fitting data from the larger separation compared to the smaller separation was a different light scattering decay with wavelength, while the tissue fraction of Hb and saturation were similar. For modeling spectra at both distances, we propose using either a multi-layer skin model or a more advanced model for the scattering phase function.

  • 44.
    Larsson, Marcus
    Linköping University, Department of Biomedical Engineering. Linköping University, The Institute of Technology.
    Influence of optical properties on Laser Doppler Flowmetry2004Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Laser Doppler flowmetry (LDF) is based on the principle that a Doppler shift occurs when coherent light is scattered by a moving object, i.e. red blood cell (RBC). The magnitude of these frequency shifts affects the optical beating that occurs w hen shifted and non-shifted light is mixed. Based on the optical beating, an LDF perfusion measure is calculated. However, the measure is not only sensitive to the RBC velocity and concentration, but also to the photon path Jength in tissue and the scattering characteristics of the RBC. The Jatter two are both govemed by the optical properties (OP), attributes that differ both within and between individuals.

    The aim of this thesis was to evaluate how the RBC and tissue OP affect the LDF perfusion measure, and to propose methods that partly correct for these errors. Phantom measurements and Monte Carlo simulations showed that the LDF perfusion was significantly affected by variations in OP relevant to skin, especially when comparing individual readings. Simulations revealed that the variations in OP affected the LDF perfusion and the photon path length in a similar manner. This suggests that a path length normalised measure would decrease the OP induced variations, possibly enabling accurate intra and inter-individual comparisons of LDF perfusion measures in different organs.

    A path length estimation technique, based on spatially diffuse reflectance, is proposed and evaluated. Monte Carlo simulations showed that the algorithm predicted the photon path length with an rms error of less than 5%. In vivo measurement (11 subjects) displayed a longer estimated path length (~35%) for the fingertip compared to the forearm. Comparing individual measurements from similar locations, variations up to 40% (max/min) were found. These findings clearly indicate the need for a path length normalization when comparing LDF readings.

    The LDF Doppler spectrum is govemed by the RBC velocity distribution and its phase function. In this thesis, an approach is presented where a measured LDF Doppler spectrum is decomposed using a number of theoretical, single-velocity spectra. As a result, a velocity-resolved perfusion measure is achieved. As the blood flow velocity depends on the dimension of the blood vessel, this approach has the potential to differentiate between arteriole/ venule and capillary activity. In addition, the path length estimation technique and the RBC scattering theory, presented in this thesis, provides a promising step towards an absolute perfusion measure.

    List of papers
    1. Influence Of Optical Properties and Fiber separation on Laser Doppler Flowmetry
    Open this publication in new window or tab >>Influence Of Optical Properties and Fiber separation on Laser Doppler Flowmetry
    2002 (English)In: Journal of Biomedical Optics, ISSN 1083-3668, E-ISSN 1560-2281, Vol. 7, no 2, p. 236-243Article in journal (Refereed) Published
    Abstract [en]

    Microcirculatory blood flow can be measured using a laser Doppler flowmetry (LDF) probe. However, the readings are affected by tissue optical properties (absorption and scattering coefficient; µa and µs) and probe geometry. In this study the influence of optical properties (µa∈[0.053, 0.23] mm-1; µs∈[14.7, 45.7] mm-1) on LDF perfusion and sampling depth were evaluated for different fiber separations. In-vitro measurements were made on a sophisticated tissue phantom with known optical properties, mimicking blood flow at different depths. Monte Carlo simulations were carried out to extend the geometry of the tissue phantom.

    A good correlation between measured and simulated data was found. The

    simulations showed that, for a fixed flow at a discrete depth, the influence of µs or µa on the LDF perfusion increased with increasing flow depth and decreased with increasing fiber separation. For a homogeneous flow distribution, however, the perfusion varied 40% due to the variations in optical properties, almost independent of fiber separation (0.23-1.61 mm). Therefore, the effect in real tissue is likely to vary due to the unknown heterogeneous blood flow distribution. Further, LDF sampling depth increased with decreasing µs or µa and increasing fiber separation. For a fiber separation of 0.46 mm, the e-1 sampling depth ranged from 0.21-0.39 mm.

    Place, publisher, year, edition, pages
    Journal of Biomedical Optics, 2002
    Keywords
    Doppler effect, fiber optics, laser Doppler flowmetry, Monte Carlo, simulations, optical properties, sampling depth
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-11717 (URN)10.1117/1.1463049 (DOI)
    Note
    Marcus Larsson, Wiendelt Steenbergen and Tomas Strömberg, Influence Of Optical Properties and Fiberseparation on Laser Doppler Flowmetry, 2002, Journal of Biomedical Optics, (7), 236-243. http://spiedigitallibrary.aip.org/journals/doc/JBOPFO-ft/vol_7/iss_2/236_1.html Copyright 2002 Society of Photo-Optical Instrumentation Engineers. This paper was published in Journal of Biomedical Optics and is made available as an electronic reprint with permission of SPIE. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.Available from: 2002-05-02 Created: 2002-05-02 Last updated: 2017-12-13
    2. Photon pathlength determination based on spatially resolved diffuse reflectance
    Open this publication in new window or tab >>Photon pathlength determination based on spatially resolved diffuse reflectance
    2002 (English)In: Journal of Biomedical Optics, ISSN 1083-3668, E-ISSN 1560-2281, Vol. 7, no 3, p. 478-485Article in journal (Refereed) Published
    Abstract [en]

    A method for the prediction of the average photon pathlength in turbid media has been developed. The method is based on spatially resolved diffuse reflectance with discrete source detector distances up to 2 mm. Light reflectance was simulated using a Monte Carlo technique with a one-layer model utilizing a wide range of optical properties, relevant to human skin. At a source detector separation of 2 mm, the pathlength can vary sixfold due to differences in optical properties. By applying various preprocessing and prediction techniques, the pathlength can be predicted with a root-mean-square error of approximately 5%. Estimation of the photon pathlength can be used, e.g., to remove the influence of optical properties on laser Doppler flowmetry perfusion readings, which are almost linearly related to the average photon pathlength.

    National Category
    Medical and Health Sciences
    Identifiers
    urn:nbn:se:liu:diva-24559 (URN)10.1117/1.1482378 (DOI)6721 (Local ID)6721 (Archive number)6721 (OAI)
    Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2017-12-13Bibliographically approved
    3. In vivo determination of local skin optical properties and photon path length by use of spatially resolved diffuse reflectance with applications in laser Doppler flowmetry
    Open this publication in new window or tab >>In vivo determination of local skin optical properties and photon path length by use of spatially resolved diffuse reflectance with applications in laser Doppler flowmetry
    2003 (English)In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 42, no 7-8, p. 124-134Article in journal (Refereed) Published
    Abstract [en]

    Methods for local photon pathlength and optical properties estimation, based on measured and simulated diffuse reflectance within 2mm from the light source, are proposed and evaluated in vivo on Caucasian human skin. The accuracy of the methods was good (2-7%) for pathlength and reduced scattering but poor for absorption estimation. Reduced scattering and absorption were systematically lower in the fingertip than in the forearm skin (633 nm). A maximum intra-site and inter-individual variation of ~35% in the average photon pathlength was found. The methodology was applied in laser Doppler flowmetry (LDF), where pathlength normalization of the estimated perfusion removed the optical property dependency.

    Place, publisher, year, edition, pages
    Institutionen för medicinsk teknik, 2003
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-11658 (URN)10.1364/AO.42.000124 (DOI)
    Note
    Larsson, M., Nilsson, H. & Strömberg, T., In vivo determination of local skin optical properties and photon path length by use of spatially resolved diffuse reflectance with applications in laser Doppler flowmetry, 2003, Applied Optics, (42), 7-8, 124-134. http://dx.doi.org/10.1364/AO.42.000124. This paper was published in Applied Optics and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://ao.osa.org/abstract.cfm?id=70860. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law. Copyright OSA., http://www.osa.org/Available from: 2008-04-24 Created: 2008-04-24 Last updated: 2017-12-13
    4. Towards a velocity-resolved microvascular blood flow measure by decomposition of the laser Doppler spectrum
    Open this publication in new window or tab >>Towards a velocity-resolved microvascular blood flow measure by decomposition of the laser Doppler spectrum
    2006 (English)In: Journal of Biomedical Optics, ISSN 1083-3668, E-ISSN 1560-2281, Vol. 11, no 1Article in journal (Refereed) Published
    Abstract [en]

    The tissue microcirculation, as measured by laser Doppler flowmetry (LDF), comprises both capillary, arterial and venous blood flow. With the classical LDF approach, it has been impossible to differentiate between different vascular compartments. We suggest an alternative LDF algorithm that estimates at least three concentration measures of flowing red blood cells (RBCs), each associated with a predefined, physiologically relevant, absolute velocity in mm/s. As the RBC flow velocity depends on the dimension of the blood vessel, this approach might enable a microcirculatory flow differentiation. The LDF concentration estimates are derived by fitting predefined Monte Carlo simulated, single velocity, spectra to a measured, multiple velocity LDF spectrum. Validation measurements, using both single and double-tube flow phantoms perfused with a microsphere solution, showed that it is possible to estimate velocity and concentration changes, and to differentiate between flows with different velocities. The presented theory was also applied to RBC flow measurements. A Gegenbauer kernel phase function (αgk = 1:05; ggk = 0:93), with an anisotropy factor of 0.987 at 786 nm, was found suitable for modelling Doppler scattering by red blood cells diluted in physiological saline. The method was developed for low concentrations of RBCs, but can in theory be extended to cover multiple Doppler scattering.

    Place, publisher, year, edition, pages
    Institutionen för medicinsk teknik, 2006
    Keywords
    Doppler effect, biomedical optics, optical properties, anisotropy, laser Doppler
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-11648 (URN)10.1117/1.2166378 (DOI)
    Note
    Copyright 2006 Society of Photo-Optical Instrumentation Engineers. This paper was published in the Journal of Biomedical Optics, (11), 14024 and is made available as an electronic reprint with permission of SPIE. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited. Marcus Larsson and Tomas Strömberg, Towards a velocity resolved microvascular blood flow measure by decomposition of the laser Doppler spectrum, 2006, Journal of Biomdeical Optics, (11), 14024. http://dx.doi.org/10.1117/1.2166378.Available from: 2008-04-23 Created: 2008-04-23 Last updated: 2017-12-13
  • 45.
    Larsson, Marcus
    et al.
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, Faculty of Science & Engineering.
    Favilla, Riccardo
    Institute of Clinical Physiology, Council of National Research, Pisa, Italy.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, Faculty of Science & Engineering.
    Assessment of advanced glycated end product accumulation in skin using auto fluorescence multispectral imaging2017In: Computers in Biology and Medicine, ISSN 0010-4825, E-ISSN 1879-0534, Vol. 85, p. 106-111Article in journal (Refereed)
    Abstract [en]

    Several studies have shown that advanced glycation end products (AGE) play a role in both the microvascular and macrovascular complications of diabetes and are closely linked to inflammation and atherosclerosis. AGEs accumulate in skin and can be detected using their auto fluorescence (AF).A significant correlation exists between AGE AF and the levels of AGEs as obtained from skin biopsies. A commercial device, the AGE Reader, has become available to assess skin AF for clinical purposes but, while displaying promising results, it is limited to single-point measurements performed in contact to skin tissue. Furthermore, in vivo imaging of AGE accumulation is virtually unexplored.We proposed a non-invasive, contact-less novel technique for quantifying fluorescent AGE deposits in skin tissue using a multispectral imaging camera setup (MSI) during ultraviolet (UV) exposure. Imaging involved applying a region-of-interest mask, avoiding specular reflections and a simple calibration. Results of a study conducted on 16 subjects with skin types ranging from fair to deeply pigmented skin, showed that AGE measured with MSI in forearm skin was significantly correlated with the AGE reference method (AGE Reader on forearm skin, R=0.68, p=0.005). AGE measured in facial skin was borderline significantly related to AGE Reader on forearm skin (R=0.47, p=0.078). These results support the use of the technique in devices for non-touch measurement of AGE content in either facial or forearm skin tissue over time.

  • 46.
    Larsson, Marcus
    et al.
    Linköping University, Department of Biomedical Engineering. Linköping University, The Institute of Technology.
    Nilsson, Henrik
    Linköping University, Department of Biomedical Engineering. Linköping University, The Institute of Technology.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering. Linköping University, The Institute of Technology.
    In vivo determination of local skin optical properties and perfusion using a pathlength compensated spatially resolved laser Doppler flowmetry approachManuscript (preprint) (Other academic)
    Abstract [en]

    The laser Doppler flowmetry (LDF) perfusion estimate is almost linearly related to the pathlength of the detected photons, and, consequently, sensitive to the optical properties of the tissue. Therefore, we propose an in vivo pathlength and optical property estimation method, based on diffuse reflectance and Monte Carlo simulations, that minimizes the influence of optical properties on the LDF perfusion estimate. Caucasian human skin displayed a maximrun variation of -35% in the photon pathlength between individuals in similar locations, and within individuals comparing fingertip and forearm skin. The results suggest that, using the proposed method, it is possible to minimize the influence of optical properties, thus enabling intraw and inter-individual compatisons ofLDF perfusion estimates in different organs.

  • 47.
    Larsson, Marcus
    et al.
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Nilsson, Henrik
    Linköping University, Department of Biomedical Engineering.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    In vivo determination of local skin optical properties and photon path length by use of spatially resolved diffuse reflectance with applications in laser Doppler flowmetry2003In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 42, no 7-8, p. 124-134Article in journal (Refereed)
    Abstract [en]

    Methods for local photon pathlength and optical properties estimation, based on measured and simulated diffuse reflectance within 2mm from the light source, are proposed and evaluated in vivo on Caucasian human skin. The accuracy of the methods was good (2-7%) for pathlength and reduced scattering but poor for absorption estimation. Reduced scattering and absorption were systematically lower in the fingertip than in the forearm skin (633 nm). A maximum intra-site and inter-individual variation of ~35% in the average photon pathlength was found. The methodology was applied in laser Doppler flowmetry (LDF), where pathlength normalization of the estimated perfusion removed the optical property dependency.

  • 48.
    Larsson, Marcus
    et al.
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Steenbergen, Wiendelt
    University of Twente, Faculty of Applied Physics, Enschede, The Netherlands.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Influence Of Optical Properties and Fiber separation on Laser Doppler Flowmetry2002In: Journal of Biomedical Optics, ISSN 1083-3668, E-ISSN 1560-2281, Vol. 7, no 2, p. 236-243Article in journal (Refereed)
    Abstract [en]

    Microcirculatory blood flow can be measured using a laser Doppler flowmetry (LDF) probe. However, the readings are affected by tissue optical properties (absorption and scattering coefficient; µa and µs) and probe geometry. In this study the influence of optical properties (µa∈[0.053, 0.23] mm-1; µs∈[14.7, 45.7] mm-1) on LDF perfusion and sampling depth were evaluated for different fiber separations. In-vitro measurements were made on a sophisticated tissue phantom with known optical properties, mimicking blood flow at different depths. Monte Carlo simulations were carried out to extend the geometry of the tissue phantom.

    A good correlation between measured and simulated data was found. The

    simulations showed that, for a fixed flow at a discrete depth, the influence of µs or µa on the LDF perfusion increased with increasing flow depth and decreased with increasing fiber separation. For a homogeneous flow distribution, however, the perfusion varied 40% due to the variations in optical properties, almost independent of fiber separation (0.23-1.61 mm). Therefore, the effect in real tissue is likely to vary due to the unknown heterogeneous blood flow distribution. Further, LDF sampling depth increased with decreasing µs or µa and increasing fiber separation. For a fiber separation of 0.46 mm, the e-1 sampling depth ranged from 0.21-0.39 mm.

  • 49.
    Larsson, Marcus
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Steenbergen, Wiendelt
    Faculty of Applied Physics University of Twente, Enschede, NL.
    Strömberg, Tomas
    Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation.
    Influence of tissue phantom optical properties and emitting - receiving fiber distance on Laser Doppler flowmetry2000In: Progress in Biomedical Optics and Imaging,2000, San José: SPIE , 2000, p. 56-63Conference paper (Refereed)
    Abstract [en]

    The influence of emitting - receiving fiber distance on the perfusion signal in laser Doppler flowmetry (LDF) for a range of optical properties has been studied. A custom made LDF probe with eight 230 μm fibers arranged in a row was used. Measurements were made on a tissue phantom with three different sets of optical properties (P={μs; μa} [mm-1]; P1={14.7; 0.212}, P2={44.9; 0.226} and P3=(45.6; 0.0532}). A single moving disc simulated flow at four different depths. The noise-corrected perfusion for a given set of optical properties (P), fiber distance (l) and disc depth (d) is defined as Perf(ν,P,d,l)=k(P,d,l) v, where v is the speed of the rotating disc. The relative difference between two slopes, Δk(Pa,Pb,l,d), indicates how sensitive the LDF readings are to changes in optical properties (Pb → Pa) for given disc depth and fiber distance. Evaluation of Δk(P1,P2,d,l) (reflects changes in scattering coefficient, μs) and Δk(P3,P2,d,l) (reflects changes in absorption coefficient, μa) indicated that LDF perfusion was more sensitive to the changes in μs than in μa. The sensitivity also increased with increasing disc depth. A fiber distance of 920 [μm] was found to minimize these effects. E.g. the sensitivity due to the variations in μs, for fiber distance l1=920, l2=230 [μm] and for all disc depths, was Δk(P1,P2,l1)=[0.76, 1.06, 1.58, 2.40] and Δk(P1,P2,l2)=[1.61, 2.98, 5.04, 7.67].

  • 50.
    Larsson, Marcus
    et al.
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Strömberg, Tomas
    Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
    Towards a velocity-resolved microvascular blood flow measure by decomposition of the laser Doppler spectrum2006In: Journal of Biomedical Optics, ISSN 1083-3668, E-ISSN 1560-2281, Vol. 11, no 1Article in journal (Refereed)
    Abstract [en]

    The tissue microcirculation, as measured by laser Doppler flowmetry (LDF), comprises both capillary, arterial and venous blood flow. With the classical LDF approach, it has been impossible to differentiate between different vascular compartments. We suggest an alternative LDF algorithm that estimates at least three concentration measures of flowing red blood cells (RBCs), each associated with a predefined, physiologically relevant, absolute velocity in mm/s. As the RBC flow velocity depends on the dimension of the blood vessel, this approach might enable a microcirculatory flow differentiation. The LDF concentration estimates are derived by fitting predefined Monte Carlo simulated, single velocity, spectra to a measured, multiple velocity LDF spectrum. Validation measurements, using both single and double-tube flow phantoms perfused with a microsphere solution, showed that it is possible to estimate velocity and concentration changes, and to differentiate between flows with different velocities. The presented theory was also applied to RBC flow measurements. A Gegenbauer kernel phase function (αgk = 1:05; ggk = 0:93), with an anisotropy factor of 0.987 at 786 nm, was found suitable for modelling Doppler scattering by red blood cells diluted in physiological saline. The method was developed for low concentrations of RBCs, but can in theory be extended to cover multiple Doppler scattering.

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