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  • 1.
    Arildsson, Mikael
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Asker, Claes
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Salerud, Göran
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Skin capillary appearance and skin microvascular perfusion due to topical application of analgesia cream2000Inngår i: Microvascular Research, ISSN 0026-2862, E-ISSN 1095-9319, Vol. 59, nr 1, s. 14-23Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Local topical analgesia changes basal skin perfusion and its regulation. In particular, the response induced by local heating, which in nontreated skin comprises a rapidly increased perfusion followed by a normalization within 30 s, is altered to a delayed and persistent perfusion increase. The response dependency to the analgesia cream application time, that is, the intradermal penetration of the analgesics and in which vascular plexa the response occurs, is not known. The aim of this study was to assess changes in the appearance of superficial skin capillaries and skin microvascular perfusion changes due to different application periods of topical analgesia cream (EMLA). Twelve subjects were treated with EMLA and placebo applied to the volar side of each forearm, respectively. The treatment areas were assigned different application times (20 min, 40 min, 1 h, 2 h, and 3 h). The areas were cleared from the creams and shortly thereafter provoked during 9 s with a probe heated to 45°C. To assess capillary number density and skin perfusion, capillary microscopy, and Laser Doppler perfusion imaging (LDPI), respectively, were used. The number density of physiologically active capillary was significantly decreased with longer application times of EMLA (P < 0.005). The LDPI-signal showed a persistent perfusion increase after provocation associated with increasing application time of the cream. This perfusion pattern was not seen after 20 min of treatment, but was present in 9 of 12 subjects after 3 h of treatment. No significant relationship between changes in the capillary number density and the LDF measurement was found. In conclusion, a longer application time and therefore a higher intradermal concentration and a deeper penetration of the analgesics was associated with a delayed and persistent perfusion increase after local heating. There was a discrepancy between changes in capillary number density and skin perfusion, indicating that the perfusion increase does not occur in the capillaries but in the deeper lying vessels. Hence, the contribution of the capillary perfusion to the LDF-signal is smaller than previously anticipated. Capillary number density and presumably their perfusion were decreased with longer application times.

  • 2.
    Arildsson, Mikael
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Nilsson, Gert
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Effects on skin blood flow by provocation during local analgesia2000Inngår i: Microvascular Research, ISSN 0026-2862, E-ISSN 1095-9319, Vol. 59, nr 1, s. 122-130Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Although topical analgesia cream has been used for several years, little is known about its effects on the microcirculation. Previous studies have shown a vasoconstrictive effect after short application times and a vasodilatation after longer application. It has also been shown that vasomotion does not occur in the analgesized skin. The present study was undertaken to investigate the alterations in skin blood perfusion following local cooling, local heating and pin-pricking after the establishment of analgesia. In 11 healthy volunteers, skin analgesia was attained by use of a eutectic mixture of lidocaine and prilocaine (EMLA, Astra Pain Control AB, Sweden) applied to the skin three hours prior to provocation. The changes in skin blood perfusion, after applying three different provocation methods, were studied using the laser Doppler technique. Local cooling and heating to temperatures of +10 and +45°C, respectively, were applied for 9 s by use of a copper probe (Ø12 mm). In the pin-prick provocation method, a combined effect of deflection and penetration of the skin to in total 3 mm was attained. Identical provocation methods were applied to placebo treated and untreated skin areas. After heat provocation, significant differences in the perfusion response between the treatments were seen (P < 0.0001). Skin areas treated with analgesia cream responded with a slow increase in perfusion that persisted beyond the four minute measurement period. Placebo and untreated areas decreased their perfusion over time. After cooling a significant reduction in skin perfusion was seen, irrespective of the treatment. Similarly, after pin-pricking a perfusion increase was seen for all treatments. The findings indicate that topical analgesia influences the myogenic control of the blood flow in those vascular plexa measured by laser Doppler following heat provocation. No differences could be seen in the response to pin-pricking and cooling for the different treatments.

  • 3.
    Arildsson, Mikael
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Nilsson, Gert
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Spectral signature and heterodyne efficiency for different wavelengths in laser Doppler flowmetry2002Inngår i: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 40, nr 1, s. 85-89Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Laser Doppler perfusion monitoring and imaging technologies generate time traces and two-dimensional flow maps of the microcirculation. With the goal of reaching different tissue depths, these technologies are equipped with lassers operating at different wavelengths λ. The fact that the average scattering angle, at a single scattering event, between a photon and a red blood cell increases with λ is compensated for by a 1/λ effect in the scattering vector, rendering the average frequency shift virtually independent of the choice of wavelength. Monte Carlo simulations showed that the corresponding spectral signature of the Doppler signals for λ=632.8nm and 780nm were close to identical. The theoretical predictions were verified by calculating the centre-of-gravity (COG) frequency of the laser Doppler power spectral density for the two wavelengths from forearm and finger skin, representing a low and high perfusion area, respectively (forearm COG=123 against 121Hz, finger COG=220 against 212 Hz). When the wavelength changes from 632.8nm to 780nm, the heterodyne efficiency of the detector and, thereby, the inherent system amplifcation increase. For tissues with identical microvascular flow conditions, the output signal therfore tends to increase in magnitude when shifting to longer wavelengths.

  • 4.
    Arildsson, Mikael
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Strömberg, Tomas
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Perfusion responses after local provocation of EMLA analgesized skin1999Inngår i: Congress of the International Society for Skin Imaging,1999, 1999Konferansepaper (Annet vitenskapelig)
  • 5.
    Asker, Claes
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Arildsson, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Salerud, Göran
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Strömberg, Tomas
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Compartmental skin perfusion resposes affected by analgesia1999Inngår i: Congress of the International Society for Skin Imaging,1999, 1999Konferansepaper (Annet vitenskapelig)
  • 6.
    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
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Steenbergen, Wiendelt
    University of Twente, Netherlands .
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Thompson, Oliver B.
    Callaghan Innovat, New Zealand .
    Laser speckle contrast imaging: theoretical and practical limitations2013Inngår i: Journal of Biomedical Optics, ISSN 1083-3668, E-ISSN 1560-2281, Vol. 18, nr 6Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 7.
    Ewerlöf, Maria
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Salerud, E. Göran
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Larsson, Marcus
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Estimating skin blood saturation by selecting a subset of hyperspectral imaging data2015Inngår i: Imaging, Manipulation, and Analysis of Biomolecules, Cells, and Tissues XIII / [ed] Daniel L. Farkas; Dan V. Nicolau; Robert C. Leif, SPIE, 2015, Vol. 9328Konferansepaper (Fagfellevurdert)
    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.

  • 8.
    Fredriksson, Ingemar
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan. Perimed AB, Järfälla, Sweden.
    Burdakov, Oleg
    Linköpings universitet, Matematiska institutionen, Optimeringslära. Linköpings universitet, Tekniska högskolan.
    Larsson, Marcus
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Inverse Monte Carlo in a multilayered tissue model: merging diffuse reflectance spectroscopy and laser Doppler flowmetry2013Inngår i: Journal of Biomedical Optics, ISSN 1083-3668, E-ISSN 1560-2281, Vol. 18, nr 12, s. 127004-1-127004-14Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 9.
    Fredriksson, Ingemar
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Larsson, Marcus
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Nyström, Fredrik
    Linköpings universitet, Institutionen för medicin och hälsa, Internmedicin. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Medicincentrum, Endokrin- och magtarmmedicinska kliniken US.
    Länne, Toste
    Linköpings universitet, Institutionen för medicin och hälsa, Fysiologi. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Hjärtcentrum, Thorax-kärlkliniken.
    Johan Östgren, Carl
    Linköpings universitet, Institutionen för medicin och hälsa, Allmänmedicin. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Närsjukvården i Finspång, Vårdcentralen.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    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 Flowmetry2010Inngår i: Diabetes, ISSN 0012-1797, E-ISSN 1939-327X, Vol. 59, nr 7, s. 1578-1584Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 10.
    Fredriksson, Ingemar
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Larsson, Marcus
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Nyström, Fredrik
    Linköpings universitet, Institutionen för medicin och hälsa. Linköpings universitet, Institutionen för medicin och hälsa, Kardiologi.
    Länne, Toste
    Linköpings universitet, Institutionen för medicin och hälsa. Linköpings universitet, Institutionen för medicin och hälsa, Kardiologi.
    Östgren, Carl Johan
    Linköpings universitet, Institutionen för medicin och hälsa, Allmänmedicin. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Närsjukvården i västra Östergötland, Primärvården i västra länsdelen.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Microcirculatory changes in type 2 diabetes assessed with velocity resolved quantitative laser Doppler flowmetryManuskript (Annet vitenskapelig)
    Abstract [en]

    The response to local heating (44oC for 20 min) was evaluated in 28 type 2 diabetes patients (DM) and 29 non-diabetes controls (ND). Microcirculatory perfusion was assessed using conventional and quantitative Laser Doppler flowmetry (cLDF and qLDF), respectively. The qLDF estimates perfusion in a physiological relevant unit (g RBC / 100 g tissue × mm/s) in a fixed output volume, separated into three velocity regions, v < 1 mm/s, 1 - 10 mm/s, and v > 10 mm/s. Perfusion in cLDF is given in arbitrary units with unknown velocity distribution and measurement volume.

    A significantly lower response in DM than in ND was found after heat provocation both for the initial peak and the plateau response, while no significant differences were found at baseline. The qLDF showed increased perfusion for the velocity regions 1-10 mm/s and above 10 mm/s, while no significant increase was found for v < 1 mm/s. In conclusion, we found a lowered LDF response to local heating in DM. The new qLDF method showed that the increased blood flow occurs in vessels with a velocity above 1 mm/s. Baseline qLDF-data indicated that a redistribution of flow to higher velocity regions was associated with longer DM duration and for DM a negative correlation between perfusion and BMI.

  • 11.
    Fredriksson, Ingemar
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Larsson, Marcus
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan. Linköpings universitet, Hälsouniversitetet.
    Salomonsson, Fredrik
    Perimed AB, Järfälla-Stockholm, Sweden.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Improved calibration procedure for laser Doppler perfusion monitors2011Inngår i: 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, s. 790602-1-790602-7Konferansepaper (Annet vitenskapelig)
    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.

  • 12.
    Fredriksson, Ingemar
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Larsson, Marcus
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Strömberg, Tomas
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Absolute blood flow velocity components in Laser Doppler flowmetry2005Inngår i: International Graduate Summer School Biophotonics05,2005, 2005Konferansepaper (Annet vitenskapelig)
  • 13.
    Fredriksson, Ingemar
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Larsson, Marcus
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Absolute flow velocity components in laser Doppler flowmetry2006Inngår i: Proceedings of SPIE, the International Society for Optical Engineering, ISSN 0277-786X, E-ISSN 1996-756X, Vol. 6094, s. 60940A-Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 14.
    Fredriksson, Ingemar
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Larsson, Marcus
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Accuracy of vessel diameter estimated from a vessel packaging compensation in diffuse reflectance spectroscopy2011Inngår i: Clinical and Biomedical Spectroscopy and Imaging II / [ed] Nirmala Ramanujam, Jurgen Popp, SPIE - International Society for Optical Engineering, 2011, Vol. 8087, s. 8087 1M-1-8087 1M-8Konferansepaper (Annet vitenskapelig)
    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.

     

  • 15.
    Fredriksson, Ingemar
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Larsson, Marcus
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Forced detection Monte Carlo algorithms for accelerated blood vessel image simulations2009Inngår i: JOURNAL OF BIOPHOTONICS, ISSN 1864-063X, Vol. 2, nr 3, s. 178-184Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 16.
    Fredriksson, Ingemar
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Larsson, Marcus
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Strömberg, Tomas
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Hastighetsupplöst blodflödesmätning med Laserdopplertekniken2005Inngår i: Medicinteknikdagar MTF,2005, 2005Konferansepaper (Annet vitenskapelig)
  • 17.
    Fredriksson, Ingemar
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Larsson, Marcus
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Inverse Monte Carlo method in a multilayered tissue model for diffuse reflectance spectroscopy2012Inngår i: Journal of Biomedical Optics, ISSN 1083-3668, E-ISSN 1560-2281, Vol. 17, nr 4, s. 047004-Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 18.
    Fredriksson, Ingemar
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Larsson, Marcus
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Laser Doppler flowmetry2012Inngår i: Microcirculation imaging / [ed] Martin J. Leahy, Weinheim: Wiley-Blackwell, 2012, , s. 411s. 67-84Kapittel i bok, del av antologi (Annet vitenskapelig)
    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.

  • 19.
    Fredriksson, Ingemar
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Larsson, Marcus
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Measurement depth and volume in laser Doppler flowmetry2009Inngår i: Microvascular Research, ISSN 0026-2862, E-ISSN 1095-9319, Vol. 78, nr 1, s. 4-13Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 20.
    Fredriksson, Ingemar
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Larsson, Marcus
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Model-Based Quantification of Skin Microcirculatory Perfusion2014Inngår i: Computational Biophysics of the Skin / [ed] Bernard Querleux, Singapore: Pan Stanford Publishing, 2014, 1, s. 395-420Kapittel i bok, del av antologi (Annet vitenskapelig)
  • 21.
    Fredriksson, Ingemar
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Larsson, Marcus
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Model-based quantitative laser Doppler flowmetry in skin2010Inngår i: Journal of Biomedical Optics, ISSN 1083-3668, E-ISSN 1560-2281, Vol. 15, nr 5Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 22.
    Fredriksson, Ingemar
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Larsson, Marcus
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Optical microcirculatory skin model: Assessed by Monte Carlo simulations paired with in vivo laser Doppler flowmetry2008Inngår i: Journal of Biomedical Optics, ISSN 1083-3668, E-ISSN 1560-2281, Vol. 13, nr 1, s. 14015-Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 23.
    Fredriksson, Ingemar
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Larsson, Marcus
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Strömberg, Tomas
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Separation av shuntat och kapillärt mikrocirkulatoriskt blodflöde med laser Doppler-tekniken2006Inngår i: Medicinteknikdagarna,2006, 2006Konferansepaper (Fagfellevurdert)
  • 24.
    Hultman, Martin
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Avdelningen för medicinsk teknik. Linköpings universitet, Tekniska fakulteten.
    Fredriksson, Ingemar
    Linköpings universitet, Institutionen för medicinsk teknik, Avdelningen för medicinsk teknik. Linköpings universitet, Tekniska fakulteten. Perimed AB, Järfälla-Stockholm, Sweden.
    Larsson, Marcus
    Linköpings universitet, Institutionen för medicinsk teknik, Avdelningen för medicinsk teknik. Linköpings universitet, Tekniska fakulteten.
    Alvandpour, Atila
    Linköpings universitet, Institutionen för systemteknik, Elektroniska Kretsar och System. Linköpings universitet, Tekniska fakulteten.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik, Avdelningen för medicinsk teknik. Linköpings universitet, Tekniska fakulteten.
    A 15.6 frames per second 1 megapixel Multiple Exposure Laser Speckle Contrast Imaging setup2018Inngår i: Journal of Biophotonics, ISSN 1864-063X, E-ISSN 1864-0648, Vol. 11, nr 2, artikkel-id e201700069Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 25.
    Hultman, Martin
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Avdelningen för medicinsk teknik. Linköpings universitet, Tekniska fakulteten.
    Fredriksson, Ingemar
    Linköpings universitet, Institutionen för medicinsk teknik, Avdelningen för medicinsk teknik. Linköpings universitet, Tekniska fakulteten. Perimed AB, Järfälla-Stockholm, Sweden.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik, Avdelningen för medicinsk teknik. Linköpings universitet, Tekniska fakulteten.
    Larsson, Marcus
    Linköpings universitet, Institutionen för medicinsk teknik, Avdelningen för medicinsk teknik. Linköpings universitet, Tekniska fakulteten.
    Evaluation of a high framerate multi-exposure laser speckle contrast imaging setup2018Inngår i: 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, 2018Konferansepaper (Fagfellevurdert)
    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

  • 26. Humeau, A
    et al.
    Nilsson, Henrik
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för datavetenskap, PELAB - Laboratoriet för programmeringsomgivningar.
    Steenbergen, W
    Strömberg, Tomas
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Laser Doppler perfusion monitoring and imaging: Novel approaches2007Inngår i: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 45, nr 5, s. 421-435Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Laser Doppler flowmetry (LDF) is a non invasive method enabling the monitoring of microvascular blood flow, a very important marker of tissue health. This article gives an overview on the concept of LDF for microvascular perfusion monitoring and imaging. It first describes the theoretical background of the technique. Then, the benefits of LDF signal processing are shown through clinical examples: use of time-frequency representations and wavelets. Afterwards, the paper introduces novel approaches of velocity components. For that purpose, a work providing the determination of the velocities relative contribution in physiologically relevant units (mm/s) is presented. Imaging perfusion is also reviewed through methods based on laser speckle. The most prominent disadvantage of the latter devices being the time needed to produce a perfusion image, solutions are proposed in the last part of the paper. © International Federation for Medical and Biological Engineering 2007.

  • 27.
    Häggblad, Erik
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Larsson, Marcus
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Arildsson, Mikael
    Linköpings universitet, Institutionen för medicinsk teknik.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Salerud, Göran
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Reflection Spectroscopy of Analgesized Skin2001Inngår i: Microvascular Research, ISSN 0026-2862, E-ISSN 1095-9319, Vol. 62, nr 3, s. 392-400 Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 28.
    Häggblad, Erik
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Larsson, Marcus
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Arildsson, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Salerud, Göran
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Strömberg, Tomas
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Reflektionsspektroskopi på EML-behandlad och värmeprovocerad hud2000Inngår i: Svenska läkarsällskapets Riksstämma,2000, 2000, s. 250-250Konferansepaper (Annet vitenskapelig)
  • 29.
    Häggblad, Erik
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Larsson, Marcus
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Arildsson, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Strömberg, Tomas
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Reflectance spectroscopy of analgesized skin after local healing2000Inngår i: CNVD,2000, 2000Konferansepaper (Fagfellevurdert)
  • 30.
    Häggblad, Erik
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Larsson, Marcus
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Arildsson, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Strömberg, Tomas
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Salerud, Göran
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Reflectance spectroscopy2000Inngår i: Eight Int Symp CNVD 2000,2000, 2000, s. 45-50Konferansepaper (Annet vitenskapelig)
  • 31.
    Häggblad, Erik
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Lindbergh, Tobias
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Karlsson, M. G. Daniel
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Medicinsk informatik.
    Casimir-Ahn, Henrik
    Linköpings universitet, Institutionen för medicin och hälsa, Thoraxkirurgi. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Hjärtcentrum, Thorax-kärlkliniken.
    Salerud, Göran
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Strömberg, Tomas
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Myocardial tissue oxygenation estimated with calibrated diffuse reflectance spectroscopy during coronary artery bypass grafting2008Inngår i: Journal of Biomedical Optics, ISSN 1083-3668, E-ISSN 1560-2281, Vol. 13, nr 5, s. 054030-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a study using a method able to assess tissue oxygenation, taking into account the absorption and the level of scattering in myocardial tissue using a calibrated fiber optic probe. With this method, interindividual comparisons of oxygenation can be made despite varying tissue optical properties during coronary artery bypass grafting (CABG). During CABG, there are needs for methods allowing continuous monitoring and prediction of the metabolism in the myocardial tissue. 14 patients undergoing CABG are investigated for tissue oxygenation during different surgical phases using a handheld fiber optic spectroscopic probe with a source-detector distance of less than 1 mm. The probe is calibrated using a light transport model, relating the absorption and reduced scattering coefficients (mu(a) and mu()(s)) to the measured spectra. By solving the inverse problem, absolute measures of tissue oxygenation are evaluated by the sum of oxygenized hemoglobin and myoglobin. Agreement between the model and measurements is obtained with an average correlation coefficient R-2 of 0.96. Oxygenation is found to be significantly elevated after aorta cross-clamping and cardioplegic infusion, as well as after reperfusion, compared to a baseline (p < 0.05). Tissue oxygenation decreases during cardiac arrest and increases after reperfusion.

  • 32.
    Häggblad, Erik
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Lindbergh, Tobias
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Larsson, Marcus
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Salerud, Göran
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Strömberg, Tomas
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Myocardial blood volume and oxygenation monitoring during thoracic surgery2005Konferansepaper (Annet vitenskapelig)
  • 33.
    Johansson, Anders
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik.
    Strömberg, Tomas
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Influence of tidal volume and thoraco-abdominal separation on the respiratory induced variation of the photoplethysmogram2000Inngår i: Journal of clinical monitoring and computing, ISSN 1387-1307, E-ISSN 1573-2614, Vol. 16, nr 8, s. 575-581Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Objective. The present study was aimed at determining the relative influences of tidal volume and thoraco-abdominal separation (relative thoracic and abdominal contribution to the tidal volume) on the respiratory induced intensity variation (RIIV) of the photoplethysmographic signal. The effects were studied in two body positions. Methods. Respiratory inductive plethysmography was used or quantifying thoraco-abdominal separation and for assessing tidal volumes. 10 subjects were trained to perform widely varying degrees of thoraco-abdominal separation at different tidal volumes. The relationship between the RIIV signal peak-to-peak value (measured at the forearm), and the tidal volume and thoraco-abdominal separation was investigated in two body positions with the use of multiple linear regression. Results. Larger tidal volume and more thoracic contribution to respiration were found to increase the RIIV peak-to-peak value (p < 0.0005). In the supine position, the tidal volume influence was stronger than that of thoraco-abdominal separation, and in the sitting position, the opposite was seen. Conclusions. The effects on the RIIV signal following changes in thoraco-abdominal separation and tidal volume are of the same order of magnitude. In the supine position, the influence of thoracic versus abdominal contribution to the tidal volume is not as significant as in the sitting position. Photoplethysmography is a promising technique for combined monitoring of several respiratory parameters, including tidal volume. In situations where the relative thoracic and abdominal contribution are likely to vary, the tidal volume information becomes less reliable.

  • 34.
    Johansson, Anders
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    The influence of breathing pattern in ventilation monitoring using photoplethysmographyManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Objective. The present study aimed at determining the relative influences of tidal volume and thoraco-abdominal separation (relative thoracic and abdominal contribution to the tidal volume) on the respiratory induced intensity variations (RIIV) of the photoplethysmographic (PPG) signal. The effects were studied in two body positions.

    Methods. Respiratory inductive plethysmography (RIP) was used for quantifying thoracoabdominal separation and for assessing tidal volumes. 10 subjects were trained to perform widely varying degrees of thoraco-abdominal separations at different tidal volumes. The relationship between the RIIV signal peak-to-peak value (measured at the forearm), and the tidal volume and separation was investigated in two body positions with the use of multiple linear regression.

    Results. Larger tidal volume and more thoracic contribution to respiration were found to increase the RIIV peak-to-peak value (p<0.0005). In the supine position, tidal volume had a stronger influence than separation, and in the sitting position, the opposite was seen.

    Conclusions. The effects on the RIIV signal from changes in thoraco abdominal separation and tidal volume are of similar magnitude. In the supine position, the influence of separation is less than in the sitting position, but the regression model fit is reduced. PPG is a promising technique for monitoring tidal volumes. However, in situations where the relative thoracic and abdominal contributions are likely to vary, the tidal volume information is less reliable.

  • 35.
    Jonasson, Hanna
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Fredriksson, Ingemar
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan. Perimed AB, Järfälla-Stockholm, Sweden .
    Larsson, Marcus
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Assessment of the microcirculation using combined model based diffuse reflectance spectroscopy and laser Doppler flowmetry2015Inngår i: 16th Nordic-Baltic Conference on Biomedical Engineering: 16. NBC & 10. MTD 2014 joint conferences. October 14-16, 2014, Gothenburg, Sweden, Springer, 2015, s. 52-54Konferansepaper (Fagfellevurdert)
    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.
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska fakulteten.
    Fredriksson, Ingemar
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska fakulteten. Perimed AB, Datavägen 9A, 175 43 Järfälla, Stockholm, Sweden.
    Pettersson, Anders
    Perimed AB, Datavägen 9a, 175 26 Järfälla-Stockholm.
    Larsson, Marcus
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska fakulteten.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska fakulteten.
    Oxygen saturation, red blood cell tissue fraction and speed resolved perfusion — A new optical method for microcirculatory assessment2015Inngår i: Microvascular Research, ISSN 0026-2862, E-ISSN 1095-9319, Vol. 102, s. 70-77Artikkel i tidsskrift (Fagfellevurdert)
    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.
    Karlsson, Daniel M G
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Larsson, Marcus
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Wårdell, Karin
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Influence of tissue movement on laser Doppler perfusion imaging2002Inngår i: 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, s. 106-114Konferansepaper (Fagfellevurdert)
    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.

  • 38.
    Karlsson, Daniel M G
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Larsson, Marcus
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Wårdell, Karin
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Influence of tissue movements on laser Doppler perfusion imaging2002Inngår i: 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, s. 106-114Konferansepaper (Annet vitenskapelig)
    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, Hanna
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Fredriksson, Ingemar
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Larsson, Marcus
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Inverse Monte Carlo for estimation of scattering and absorption in liquid optical phantoms2012Inngår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 20, nr 11, s. 12233-12246Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 40.
    Karlsson, Hanna
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Fredriksson, Ingemar
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Larsson, Marcus
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Kvantitativa mätningar av mikrocirkulatoriska parametrar med optiska tekniker och en realistisk hudmodell2011Konferansepaper (Annet vitenskapelig)
  • 41.
    Karlsson, Hanna
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Fredriksson, Ingemar
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Perimed AB, Järfälla, Sweden.
    Larsson, Marcus
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Speed resolved assessment of the microcirculation using combined model based diffuse reflectance spectroscopy and laser Doppler flowmetry2014Konferansepaper (Annet vitenskapelig)
  • 42.
    Karlsson, Hanna
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Pettersson, Anders
    Perimed AB, Järfälla-Stockholm.
    Larsson, Marcus
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Can a one-layer optical skin model including melanin and inhomogeneously distributed blood explain spatially resolved diffuse reflectance spectra?2011Inngår i: 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, s. 78962Y-78962Y-9Konferansepaper (Annet vitenskapelig)
    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.

  • 43.
    Larsson, Marcus
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Nilsson, Henrik
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska högskolan.
    In vivo determination of local skin optical properties and perfusion using a pathlength compensated spatially resolved laser Doppler flowmetry approachManuskript (preprint) (Annet vitenskapelig)
    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.

  • 44.
    Larsson, Marcus
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Nilsson, Henrik
    Linköpings universitet, Institutionen för medicinsk teknik.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    In vivo determination of local skin optical properties and photon path length by use of spatially resolved diffuse reflectance with applications in laser Doppler flowmetry2003Inngår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 42, nr 7-8, s. 124-134Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 45.
    Larsson, Marcus
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Steenbergen, Wiendelt
    University of Twente, Faculty of Applied Physics, Enschede, The Netherlands.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Influence Of Optical Properties and Fiber separation on Laser Doppler Flowmetry2002Inngår i: Journal of Biomedical Optics, ISSN 1083-3668, E-ISSN 1560-2281, Vol. 7, nr 2, s. 236-243Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 46.
    Larsson, Marcus
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Steenbergen, Wiendelt
    Faculty of Applied Physics University of Twente, Enschede, NL.
    Strömberg, Tomas
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Influence of tissue phantom optical properties and emitting - receiving fiber distance on Laser Doppler flowmetry2000Inngår i: Progress in Biomedical Optics and Imaging,2000, San José: SPIE , 2000, s. 56-63Konferansepaper (Fagfellevurdert)
    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].

  • 47.
    Larsson, Marcus
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Towards a velocity-resolved microvascular blood flow measure by decomposition of the laser Doppler spectrum2006Inngår i: Journal of Biomedical Optics, ISSN 1083-3668, E-ISSN 1560-2281, Vol. 11, nr 1Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 48.
    Lindbergh, Tobias
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Fredriksson, Ingemar
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Larsson, Marcus
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Spectral determination of a two-parametric phase function for polydispersive scattering liquids2009Inngår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 17, nr 3, s. 1610-1621Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A method for determining a two-parametric Gegenbauer-kernel phase function that accurately describes the diffuse reflectance from a polydispersive scattering media at small source-detector separations (0.23 to 1.2 mm), is presented. The method involves spectral collimated transmission measurements, spatially resolved spectral diffuse reflectance (SRDR) measurements, and inverse Monte Carlo technique. Both absolute calibration (using a monodispersive polystyrene microsphere suspension) and relative calibration (eliminating differences between fibers) of SRDR spectra yielded comparable results. When applied to water dilutions of milk, simulated and measured spectra deviated less than 6.5% and 2.5% for the absolute and relative calibration case, respectively, even for the closest fiber separation. Corresponding values for milk including ink as an absorber, were 13.4% and 7.3%.

  • 49.
    Lindbergh, Tobias
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Häggblad, Erik
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Ahn, Henrik Casimir
    Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Institutionen för medicin och vård, Thoraxkirurgi. Östergötlands Läns Landsting, Hjärtcentrum, Thorax-kärlkliniken.
    Salerud, Göran
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Strömberg, Tomas
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik.
    Lokal spektroskopisk bestämning av blodmängd och saturation i hjärtmuskeln under och efter bypasskirurgi på människa2006Inngår i: Medicinteknikdagarna,2006, 2006Konferansepaper (Fagfellevurdert)
  • 50.
    Lindbergh, Tobias
    et al.
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Häggblad, Erik
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Ahn, Henrik
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Salerud, Göran
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Larsson, Marcus
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Strömberg, Tomas
    Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska högskolan.
    Improved model for myocardial diffuse reflectance spectra by including mitochondrial cytochrome aa3, methemoglobin, and inhomogenously distributed RBC2011Inngår i: Journal of Biophotonics, ISSN 1864-063X, Vol. 4, nr 4, s. 268-276Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hemo- and myoglobin oxygen saturation and cytochrome aa3 oxidation was locally assessed using calibrated diffuse reflectance spectroscopy in fourteen patients undergoing coronary artery bypass grafting. Diffuse spectral reflectance data, recorded with a handheld fiberoptic probe with a single source-detector separation, was analyzed using an empirical light transport model relating the absorption and reduced scattering coefficients to the measured spectrum. The absorption coefficient has previously been modeled as a sum of hemoglobin and myoglobin, fat, and water. In this study, inclusion of cytochrome aa3 and the sum of methemoglobin and metmyoglobin improved the spectral fit, especially in the wavelength regions where their absorption is prominent. On average, the extended model increased the mean R2 from 0.96 to 0.99 and displayed 4% units higher saturation levels. After aorta cross-clamping, the sum of hemo- and myoglobin oxygen saturation increased while cytochrome aa3 oxidation decreased slightly. Opposite trends were observed during cardiac arrest. At reperfusion, the saturation increased compared to the levels found at cardiac arrest, and the cytochrome aa3 oxidation was restored. The estimated tissue chromophore fractions, saturation and oxidation, were in agreement with other studies.

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