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Optical Monitoring of Cerebral Microcirculation
Linköpings universitet, Institutionen för medicinsk teknik, Biomedicinsk instrumentteknik. Linköpings universitet, Tekniska fakulteten. (MINT)ORCID-id: 0000-0003-1869-6387
2017 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

The cerebral microcirculation consists of a complex network of small blood vessels that support nerve cells with oxygen and nutrition. The blood flow and oxygen delivery in the microcirculatory blood vessels are regulated through mechanisms which may be influenced or impaired by disease or brain damage resulting from conditions such as brain tumors, traumatic brain injury or subarachnoid hemorrhage (SAH). Monitoring of parameters relating to the microvascular circulation is therefore needed in the clinical setting. Optical techniques such as diffuse reflectance spectroscopy (DRS) and laser Doppler flowmetry (LDF) are capable of estimating the oxygen saturation (SO2) and tracking the microvascular blood flow (perfusion) using a fiber optic probe. This thesis presents the work carried out to adapt DRS and LDF for monitoring cerebral microcirculation in the human brain.

A method for real-time estimation of SO2 in brain tissue was developed based on the P3 approximation of diffuse light transport and quadratic polynomial fit to the measured DRS signal. A custom-made fiberoptic probe was constructed for measurements during tumor surgery and in neurointensive care. Software modules with specific user interface for LDF and DRS were programmed to process, record and present parameters such as perfusion, total backscattered light, heart rate, pulsatility index, blood fraction and SO2 from acquired signals.

The systems were evaluated on skin, and experimentally by using optical phantoms with properties mimicking brain tissue. The oxygen pressure (pO2) in the phantoms was regulated to track spectroscopic changes coupled with the level of SO2. Clinical evaluation was performed during intraoperative measurements during tumor surgery (n = 10) and stereotactic deep brain stimulation implantations (n = 20). The LDF and DRS systems were also successfully assessed in the neurointensive care unit for a patient treated for SAH. The cerebral autoregulation was studied by relating the parameters from the optical systems to signals from the standard monitoring equipment in neurointensive care.

In summary, the presented work takes DRS and LDF one step further toward clinical use for optical monitoring of cerebral microcirculation.

Ort, förlag, år, upplaga, sidor
Linköping: Linköping University Electronic Press, 2017. , s. 68
Serie
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1807
Nyckelord [en]
optical monitoring, cerebral microcirculation, diffuse reflectance spectroswcopy (DRS), laser Doppler flowmetry (LDF)
Nationell ämneskategori
Annan medicinteknik
Identifikatorer
URN: urn:nbn:se:liu:diva-133781DOI: 10.3384/diss.diva-133781ISBN: 978-91-7685-634-5 (tryckt)OAI: oai:DiVA.org:liu-133781DiVA, id: diva2:1063797
Disputation
2017-02-10, Hugo Theorell, Campus US, Linköping, Norra entrén, Plan 9, Linköping, 09:00 (Svenska)
Opponent
Handledare
Forskningsfinansiär
Vetenskapsrådet, 621-2010-4216Vetenskapsrådet, 621-2013-6078Barncancerfonden, MT2012-0043Tillgänglig från: 2017-01-17 Skapad: 2017-01-09 Senast uppdaterad: 2019-10-11Bibliografiskt granskad
Delarbeten
1. A laser Doppler system for monitoring of intracerebral microcirculation
Öppna denna publikation i ny flik eller fönster >>A laser Doppler system for monitoring of intracerebral microcirculation
2012 (Engelska)Ingår i: Conf Proc IEEE Eng Med Biol Soc., ISSN 1557-170X, s. 1988-1991Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

A two-channel standard laser Doppler perfusion monitor has been adapted for intracerebral measurements. Software developed in Labview makes it possible to present the microvascular perfusion, total light intensity (TLI), heart rate and trend curves in real-time during surgery. A custom-made optical probe was designed in order to enable easy fixation during brain surgery. The constructed brain probe was evaluated and compared to a standard probe. Both probes presented similar feasibility when used for the skin recordings. In addition, evaluation was done in one patient in relation to tumor resection. Stable perfusion and TLI signals were immediately recorded when the probe was positioned in cerebral tissue. Movement artifacts were clearly seen when the probe was moved to a new site. Recordings in cortex and tumor border showed higher perfusion and lower TLI compared to measurements in subcortical white matter. The calculated heart rate estimate agreed well with the noted value from the electrocardiographic patient monitoring system.                                                                                                                                                      

Ort, förlag, år, upplaga, sidor
IEEE, 2012
Nationell ämneskategori
Medicinteknik
Identifikatorer
urn:nbn:se:liu:diva-86150 (URN)10.1109/EMBC.2012.6346346 (DOI)000313296502058 ()23366307 (PubMedID)978-1-4244-4119-8 (ISBN)e-978-1-4244-4120-4 (ISBN)978-1-4577-1787-1 (ISBN)
Forskningsfinansiär
Vetenskapsrådet
Tillgänglig från: 2012-12-07 Skapad: 2012-12-07 Senast uppdaterad: 2017-02-03Bibliografiskt granskad
2. A laser Doppler system for monitoring of cerebral microcirculation: implementation and evaluation during neurosurgery
Öppna denna publikation i ny flik eller fönster >>A laser Doppler system for monitoring of cerebral microcirculation: implementation and evaluation during neurosurgery
2016 (Engelska)Ingår i: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, ISSN 0140-0118, Vol. 54, nr 1, s. 123-131Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The aim of this study was to adapt and evaluate laser Doppler perfusion monitoring (LDPM) together with custom designed brain probes and software for continuous recording of cerebral microcirculation in patients undergoing neurosurgery. The LDPM system was used to record perfusion and backscattered light (TLI). These parameters were displayed together with the extracted heart rate (HR), pulsatility index (PI) and signal trends from adjustable time intervals. Technical evaluation was done on skin during thermal provocation. Clinical measurements were performed on ten patients undergoing brain tumour surgery. Data from 76 tissue sites were captured with a length varying between 10 s to 15 min. Statistical comparisons were done using Mann-Whitney tests. Grey and tumour tissue could be separated from white matter using the TLI-signal (p < 0.05). The perfusion was significantly higher in grey and tumour tissue compared to white matter (p < 0.005). LDPM was successfully used as an intraoperative tool for monitoring local blood flow and additional parameters linked to cerebral microcirculation (perfusion, TLI, heart rate and PI) during tumour resection. The systems stability opens up for studies in the postoperative care of patients with e.g. traumatic brain injury or subarachnoid haemorrhage.

Ort, förlag, år, upplaga, sidor
Springer Berlin/Heidelberg, 2016
Nyckelord
Microcirculation, Brain tumour Laser Doppler perfusion monitoring (LDPM), Pulsatility index (PI), Neurosurgery
Nationell ämneskategori
Medicinsk laboratorie- och mätteknik
Identifikatorer
urn:nbn:se:liu:diva-120632 (URN)10.1007/s11517-015-1332-5 (DOI)000371437900010 ()26105147 (PubMedID)
Forskningsfinansiär
Vetenskapsrådet, 6212-010-4216
Tillgänglig från: 2015-08-20 Skapad: 2015-08-20 Senast uppdaterad: 2017-12-04Bibliografiskt granskad
3. A method for monitoring of oxygen saturation changes in brain tissue using diffuse reflectance spectroscopy
Öppna denna publikation i ny flik eller fönster >>A method for monitoring of oxygen saturation changes in brain tissue using diffuse reflectance spectroscopy
2017 (Engelska)Ingår i: Journal of Biophotonics, ISSN 1864-063X, E-ISSN 1864-0648, Vol. 10, nr 3, s. 446-455Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Continuous measurement of local brain oxygen saturation (SO2) can be used to monitor the status of brain trauma patients in the neurocritical care unit. Currently, micro-oxygen-electrodes are considered as the “gold standard” in measuring cerebral oxygen pressure (pO2), which is closely related to SO2 through the oxygen dissociation curve (ODC) of hemoglobin, but with the drawback of slow in response time. The present study suggests estimation of SO2 in brain tissue using diffuse reflectance spectroscopy (DRS) for finding an analytical relation between measured spectra and the SO2 for different blood concentrations. The P3 diffusion approximation is used to generate a set of spectra simulating brain tissue for various levels of blood concentrations in order to estimate SO2. The algorithm is evaluated on optical phantoms mimicking white brain matter (blood volume of 0.5–2%) where pO2 and temperature is controlled and on clinical data collected during brain surgery. The suggested method is capable of estimating the blood fraction and oxygen saturation changes from the spectroscopic signal and the hemoglobin absorption profile.

Ort, förlag, år, upplaga, sidor
Wiley-VCH Verlagsgesellschaft, 2017
Nyckelord
oxygenation, diffuse reflectance spectroscopy, hemoglobin, optical phantom, human brain
Nationell ämneskategori
Annan medicinteknik
Identifikatorer
urn:nbn:se:liu:diva-127362 (URN)10.1002/jbio.201500334 (DOI)000398216200012 ()27094015 (PubMedID)
Anmärkning

Funding agencies: Swedish Childhood Cancer Foundation; Swedish Research Council [621-2010-4216, 621-2013-6078]

Tillgänglig från: 2016-04-22 Skapad: 2016-04-22 Senast uppdaterad: 2020-12-09Bibliografiskt granskad

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