| 1. |
- Elawa, Sherif, et al.
(författare)
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Skin perfusion and oxygen saturation after mastectomy and radiation therapy in breast cancer patients
- 2024
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Ingår i: Breast. - : Elsevier. - 0960-9776 .- 1532-3080. ; 75
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Tidskriftsartikel (refereegranskat)abstract
- The pathophysiological mechanism behind complications associated with postmastectomy radiotherapy (PMRT) and subsequent implant-based breast reconstruction are not completely understood. The aim of this study was to examine if there is a relationship between PMRT and microvascular perfusion and saturation in the skin after mastectomy and assess if there is impaired responsiveness to a topically applied vasodilator (Methyl nicotinate - MN). Skin microvascular perfusion and oxygenation >2 years after PMRT were measured using white light diffuse reflectance spectroscopy (DRS) and laser Doppler flowmetry (LDF) in the irradiated chest wall of 31 women with the contralateral breast as a control. In the non-irradiated breast, the perfusion after application of MN (median 0.84, 25th-75th centile 0.59-1.02 % RBC × mm/s) was higher compared to the irradiated chest wall (median 0.51, 25th-75th centile 0.21-0.68 % RBC × mm/s, p < 0.001). The same phenomenon was noted for saturation (median 91 %, 25th-75th centile 89-94 % compared to 89 % 25th-75th centile 77-93 %, p = 0.001). Eight of the women (26%) had a ≥10 % difference in skin oxygenation between the non-irradiated breast and the irradiated chest wall. These results indicate that late microvascular changes caused by radiotherapy of the chest wall significantly affect skin perfusion and oxygenation.
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| 2. |
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| 3. |
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| 4. |
- Fredriksson, Ingemar, 1980-, et al.
(författare)
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Inverse Monte Carlo in a multilayered tissue model: merging diffuse reflectance spectroscopy and laser Doppler flowmetry
- 2013
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Ingår i: Journal of Biomedical Optics. - Bellingham, WA, United States : SPIE - International Society for Optical Engineering. - 1083-3668 .- 1560-2281. ; 18:12, s. 127004-1-127004-14
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Fredriksson, Ingemar, 1980-, et al.
(författare)
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Laser doppler flowmetry
- 2012
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Ingår i: Microcirculation imaging. - Weinheim : Wiley-VCH Verlagsgesellschaft. - 3527328947 - 9783527328949 - 9783527651238 ; , s. 67-86
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 6. |
- Fredriksson, Ingemar, 1980-, et al.
(författare)
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Microcirculatory changes in type 2 diabetes assessed with velocity resolved quantitative laser Doppler flowmetry
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 7. |
- Fredriksson, Ingemar, 1980-, et al.
(författare)
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Model-based quantification of skin microcirculatory perfusion
- 2015. - 1
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Ingår i: Computational biophysics of the skin. - Boca Raton : CRC Press. - 9789814463843 - 9789814463850 ; , s. 395-418
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- During the last decades new tools, such as magnetic resonance imaging and Doppler ultra sound imaging, have rapidly been taken into clinical practice for studying the flow dynamics of the macrocirculation. M eanw hile, techniques for quantifying the microcirculation have struggled to become clinically accepted. This includes the use of laser Doppler flow metry (LDF), an optical technique that is capable of monitoring either spatial or temporal changes in the microcirculation by analyzing the backscattered Doppler shifted light from a laser illuminated tissue. Until now , LDF has only been capable of producing non-absolute relative measures, w hich has limited its cl inical acceptance. With a model based analysis approach, as presented here, this can be overcome, and objective diagnosis of the microcirculation may finally be a part of everyday clinical praxis. The most important advantages w ith the proposed method are that a quantitative perfusion estimate (% RBC × mm/ s) can be extracted, and that this measure can be resolved into different speed regions.
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| 8. |
- Fredriksson, Ingemar, 1980-, et al.
(författare)
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Model-based quantitative laser Doppler flowmetry in skin
- 2010
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Ingår i: Journal of Biomedical Optics. - : Society of Photo-optical Instrumentation Engineers. - 1083-3668 .- 1560-2281. ; 15:5
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 9. |
- Fredriksson, Ingemar, 1980-, et al.
(författare)
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On the equivalence and differencesbetween laser Doppler flowmetry andlaser speckle contrast analysis
- 2016
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Ingår i: Journal of Biomedical Optics. - : SPIE - International Society for Optical Engineering. - 1083-3668 .- 1560-2281. ; 21:12
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Tidskriftsartikel (refereegranskat)abstract
- Laser Doppler flowmetry (LDF) and laser speckle contrast analysis (LASCA) both utilize the spatiotemporalproperties of laser speckle patterns to assess microcirculatory blood flow in tissue. Although the techniquesanalyze the speckle pattern differently, there is a close relationship between them. We present atheoretical overview describing how the LDF power spectrum and the LASCA contrast can be calculatedfrom each other, and how both these can be calculated from an optical Doppler spectrum containing variousdegrees of Doppler shifted light. The theoretical relationships are further demonstrated using time-resolvedspeckle simulations. A wide range of Monte Carlo simulated tissue models is then used to show how perfusionestimates for LDF and LASCA are affected by changes in blood concentration and speed distribution, as well asby geometrical and optical properties. We conclude that perfusion estimates from conventional single exposuretime LASCA are in general more sensitive to changes in optical and geometrical properties and are less accuratein the prediction of real perfusion changes, especially speed changes. Since there is a theoretical one-to-onerelationship between Doppler power spectrum and contrast, one can conclude that those drawbacks with theLASCA technique can be overcome using a multiple exposure time setup.
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| 10. |
- Fredriksson, Ingemar, 1980-
(författare)
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Quantitative Laser Doppler Flowmetry
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Laser Doppler flowmetry (LDF) is virtually the only non-invasive technique, except for other laser speckle based techniques, that enables estimation of the microcirculatory blood flow. The technique was introduced into the field of biomedical engineering in the 1970s, and a rapid evolvement followed during the 1980s with fiber based systems and improved signal analysis. The first imaging systems were presented in the beginning of the 1990s.Conventional LDF, although unique in many aspects and elegant as a method, is accompanied by a number of limitations that may have reduced the clinical impact of the technique. The analysis model published by Bonner and Nossal in 1981, which is the basis for conventional LDF, is limited to measurements given in arbitrary and relative units, unknown and non-constant measurement volume, non-linearities at increased blood tissue fractions, and a relative average velocity estimate.In this thesis a new LDF analysis method, quantitative LDF, is presented. The method is based on recent models for light-tissue interaction, comprising the current knowledge of tissue structure and optical properties, making it fundamentally different from the Bonner and Nossal model. Furthermore and most importantly, the method eliminates or highly reduces the limitations mentioned above.Central to quantitative LDF is Monte Carlo (MC) simulations of light transport in tissue models, including multiple Doppler shifts by red blood cells (RBC). MC was used in the first proof-of-concept study where the principles of the quantitative LDF were tested using plastic flow phantoms. An optically and physiologically relevant skin model suitable for MC was then developed. MC simulations of that model as well as of homogeneous tissue relevant models were used to evaluate the measurement depth and volume of conventional LDF systems. Moreover, a variance reduction technique enabling the reduction of simulation times in orders of magnitudes for imaging based MC setups was presented.The principle of the quantitative LDF method is to solve the reverse engineering problem of matching measured and calculated Doppler power spectra at two different source-detector separations. The forward problem of calculating the Doppler power spectra from a model is solved by mixing optical Doppler spectra, based on the scattering phase functions and the velocity distribution of the RBC, from various layers in the model and for various amounts of Doppler shifts. The Doppler shift distribution is calculated based on the scattering coefficient of the RBC:s and the path length distribution of the photons in the model, where the latter is given from a few basal MC simulations.When a proper spectral matching is found, via iterative model parameters updates, the absolute measurement data are given directly from the model. The concentration is given in g RBC/100 g tissue, velocities in mm/s, and perfusion in g RBC/100 g tissue × mm/s. The RBC perfusion is separated into three velocity regions, below 1 mm/s, between 1 and 10 mm/s, and above 10 mm/s. Furthermore, the measures are given for a constant output volume of a 3 mm3 half sphere, i.e. within 1.13 mm from the light emitting fiber of the measurement probe.The quantitative LDF method was used in a study on microcirculatory changes in type 2 diabetes. It was concluded that the perfusion response to a local increase in skin temperature, a response that is reduced in diabetes, is a process involving only intermediate and high flow velocities and thus relatively large vessels in the microcirculation. The increased flow in higher velocities was expected, but could not previously be demonstrated with conventional LDF. The lack of increase in low velocity flow indicates a normal metabolic demand during heating. Furthermore, a correlation between the perfusion at low and intermediate flow velocities and diabetes duration was found. Interestingly, these correlations were opposites (negative for the low velocity region and positive for the mediate velocity region). This finding is well in line with the increased shunt flow and reduced nutritive capillary flow that has previously been observed in diabetes.
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| 11. |
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| 12. |
- Fredriksson, Ingemar, 1980-, et al.
(författare)
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Vasomotion analysis of speed resolved perfusion, oxygen saturation, red blood cell tissue fraction, and vessel diameter : Novel microvascular perspectives
- 2022
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Ingår i: Skin research and technology. - : Wiley-Blackwell Publishing Inc.. - 0909-752X .- 1600-0846. ; 28:1, s. 142-152
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Tidskriftsartikel (refereegranskat)abstract
- BackgroundVasomotion is the spontaneous oscillation in vascular tone in the microcirculation and is believed to be a physiological mechanism facilitating the transport of blood gases and nutrients to and from tissues. So far, Laser Doppler flowmetry has constituted the gold standard for in vivo vasomotion analysis.Materials and methodsWe applied vasomotion analysis to speed-resolved perfusion, oxygen saturation, red blood cell tissue (RBC) tissue fraction, and average vessel diameter from five healthy individuals at rest measured by the newly developed Periflux 6000 EPOS system over 10 minutes. Magnitude scalogram and the time-averaged wavelet spectra were divided into frequency intervals reflecting endothelial, neurogenic, myogenic, respiratory, and cardiac function.ResultsRecurrent high-intensity periods of the myogenic, neurogenic, and endothelial frequency intervals were found. The neurogenic activity was considerably more pronounced for the oxygen saturation, RBC tissue fraction, and vessel diameter signals, than for the perfusion signals. In a correlation analysis we found that changes in perfusion in the myogenic, neurogenic, and endothelial frequency intervals precede changes in the other signals. Furthermore, changes in average vessel diameter were in general negatively correlated to the other signals in the same frequency intervals, indicating the importance of capillary recruitment.ConclusionWe conclude that vasomotion can be observed in signals reflecting speed resolved perfusion, oxygen saturation, RBC tissue fraction, and vessel diameter. The new parameters enable new aspects of the microcirculation to be observed.
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| 13. |
- Hultman, Martin, et al.
(författare)
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A 15.6 frames per second 1 megapixel Multiple Exposure Laser Speckle Contrast Imaging setup
- 2018
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Ingår i: Journal of Biophotonics. - : Wiley-VCH Verlagsgesellschaft. - 1864-063X .- 1864-0648. ; 11:2
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 14. |
- Hultman, Martin, 1992-, et al.
(författare)
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Comprehensive imaging of microcirculatory changes in the foot during endovascular intervention - A technical feasibility study
- 2022
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Ingår i: Microvascular Research. - Maryland Heights, MO, United States : Academic Press. - 0026-2862 .- 1095-9319. ; 141
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Tidskriftsartikel (refereegranskat)abstract
- Chronic limb-threatening ischemia (CLTI) has a major impact on patient's lives and is associated with a heavy health care burden with high morbidity and mortality. Treatment by endovascular intervention is mostly based on macrocirculatory information from angiography and does not consider the microcirculation. Despite successful endovascular intervention according to angiographic criteria, a proportion of patients fail to heal ischemic lesions. This might be due to impaired microvascular perfusion and variations in the supply to different angiosomes. Non-invasive optical techniques for microcirculatory perfusion and oxygen saturation imaging have the potential to provide the interventionist with additional information in real-time, supporting clinical decisions during the intervention. This study presents a novel multimodal imaging system, based on multi-exposure laser speckle contrast imaging and multi-spectral imaging, for continuous use during endovascular intervention. The results during intervention display spatiotemporal changes in the microcirculation compatible with expected physiological reactions during balloon dilation, with initially induced ischemia followed by a restored perfusion, and local administration of a vasodilator inducing hyperemia. We also present perioperative and postoperative follow-up measurements with a pulsatile microcirculation perfusion. Finally, cases of spatial heterogeneity in the observed oxygen saturation and perfusion are discussed. In conclusion, this technical feasibility study shows the potential of the methodology to characterize changes in microcirculation before, during, and after endovascular intervention.
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| 15. |
- Hultman, Martin, 1992-, et al.
(författare)
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Evaluation of a high framerate multi-exposure laser speckle contrast imaging setup
- 2018
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Ingår i: High-Speed Biomedical Imaging and Spectroscopy III. - : SPIE - International Society for Optical Engineering. - 9781510614963
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Konferensbidrag (refereegranskat)abstract
- 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
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| 16. |
- Hultman, Martin, 1992-
(författare)
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Real-time multi-exposure laser speckle contrast imaging of skin microcirculatory perfusion
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The microcirculation, the blood flow in the smallest blood vessels in the body, has a vital function as this is where oxygen and nutrients diffuses from the blood to to the surrounding cells. An important quantity is the tissue perfusion, a measure of the microcirculation’s capacity to provide oxygen and nutrients to the cells. Laser speckle contrast imaging (LSCI) is a non-invasive optical technique that captures images of the microcirculatory perfusion by analysing the local contrast in the laser speckle pattern that forms when tissue is illuminated by a laser. LSCI has seen extensive use in clinical research due to the easy and cheap measurement setup, and high spatial and temporal resolution. Despite this, clinical acceptance and routine use remains low. Some of the drawbacks of the technique is a limitation to relative measurements in arbitrary units, as well as high susceptibility to measurement noise and confounding properties of the tissue. This makes comparisons difficult, especially between patients. An extension of LSCI called multi-exposure laser speckle contrast imaging (MELSCI) was proposed to deal with some of these issues, although the more complicated data acquisition and models prevented real-time use. MELSCI has in-stead been used exclusively as an offline technique where data is post-processed, and the clinical use has been non-existent. Furthermore, existing models for LSCI and MELSCI are designed for tissues where individual vessels are visible, such as the surface of the brain or on the retina. For measurements in the diffuse regime, such as on skin tissue, these models are no longer physiologically accurate, resulting in incorrect perfusion estimates.This thesis presents a MELSCI-based perfusion imaging instrument that is simultaneously fast and physiologically accurate for measurements of skin. There are three main parts to this work; development of a real-time MELSCI system, development of perfusion models for skin, and demonstration of the system in a clinical feasibility study.A real-time MELSCI instrument was developed based on a high-speed CMOS camera tightly integrated with algorithms in a field programmable gate array (FPGA). The algorithm was based on synthetic multi-exposure, where a set of 64 individual 1-ms images were digitally added to create multi-exposure images at 1, 2, 4, 8, 16, 32, and 64 ms. The resulting multi-exposure data was demonstrated to have high quality and less susceptibility to measurement noise than previous models. The instrument enabled continuous acquisition and analysis of MELSCI data in real-time at 15.6 frames per second, sufficiently fast to capture the temporal dynamics of the skin perfusion.To enable real-time estimation of accurate and physiologically relevant perfusion from the MELSCI data, two artificial neural networks were trained on synthetic data from a mathematical model of skin. The first estimated perfusion as computed by conventional laser Doppler flowmetry (LDF), demonstrating a high correlation between the two methods. The second estimated true perfusion in absolute units %RBC × mm/s separated into three distinct speed components, 0-1 mm/s, 1-10 mm/s and >10 mm/s. The ANNs removed the need for iterative optimization algorithms, resulting in more than 1000x speed-up over previous methods, and enabled real-time use in an imaging setting.The instrument was demonstrated in controlled experiments on healthy volunteers, using standardized occlusion-release provocations, and in a clinical feasibility study where the foot perfusion was monitored during endovascular interventions in patients with chronic limb-threatening ischemia. The instrument enabled continuous imaging of perfusion, with sufficiently high framerate to capture the pulsatile dynamics, or lack thereof, at each point in time. The necessity for both high spatial and temporal resolution to properly asses the microcirculation was demonstrated.The advancements to MELSCI proposed in this thesis has the potential to improve the clinical viability of the technique, increase interpretability of the results, and might lead to improved treatments based on a better understanding of the complex processes in the microcirculation.
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| 17. |
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| 18. |
- Meyerson, Amanda, et al.
(författare)
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Effects of daylight and darkness at daytime versus nighttime on driver sleepiness : A driving simulator study
- 2024
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Ingår i: Transportation Research Interdisciplinary Perspectives. - : Elsevier. - 2590-1982. ; 24
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Tidskriftsartikel (refereegranskat)abstract
- The study explores the impact of light conditions on driver sleepiness. In a driving simulator experiment, 20 drivers drove both during daytime in an alert condition and then later at night after being awake since early morning. Light conditions were manipulated by driving in a simulated nighttime scenario in a dark room (1 lx) versus driving in simulated daylight in a room lit with light emitting diodes combining blue light with a yellow phosphor giving a two peaked spectrum (212 lx). Both the daylight and the darkness scenarios were driven daytime and nighttime in a 2 × 2 design. Sleepiness was measured during the four 1-hour drives in terms of subjective sleepiness ratings, divided attention ability, driving performance, heart rate variability and blink behaviour. Significant differences were found in all measured sleepiness indicators between the daytime and nighttime drives, and in most indicators for time-on- task. No significant main effects were found between simulated daylight and darkness. A psychomotor vigilance test conducted before and after each drive also showed no significant effects for lighting condition. Further research, preferably using longitudinal studies in more realistic settings on real roads, is needed to determine which behaviours and which cognitive processes that are affected when driving in daylight versus darkness.
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| 19. |
- Strömberg, Tomas, 1966-, et al.
(författare)
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Experimental results using a three-layer skin model for diffuse reflectance spectroscopy
- 2013
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Ingår i: Optical Tomography and Spectroscopy of Tissue X. - : SPIE - International Society for Optical Engineering. - 9780819493477 ; , s. 857834-1-857834-8
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We have previously presented an inverse Monte Carlo algorithm based on a three-layer semi-infinite skin model for analyzing diffuse reflectance spectroscopy (DRS) data. The algorithm includes pre-simulated Monte Carlo data for a range of physiologically relevant epidermal thicknesses and tissue scattering levels. The simulated photon pathlength distributions in each layer are stored and the absorption effect from tissue chromophores added in the post-processing. Recorded DRS spectra at source-detector distances of 0.4 and 1.2 mm were calibrated for the relative intensity between the two distances and matched to simulated spectra in a non-linear optimization algorithm. This study evaluates the DRS spectral fitting accuracy and presents data on the main output parameters; the tissue fraction of red blood cells and local oxygenation (SO2). As a reference, the microcirculatory perfusion (Perf) was measured simultaneously in the same probe using laser Doppler Flowmetry. Data were recorded on the volar forearm of three healthy subjects in a protocol involving a 5 min systolic occlusion. The DRS spectra were modeled with an rms-error < 2%. In two subjects, SO2 decreased during occlusion to <10%, and increased to above baseline after hyperemia, while Perf increased >7 times compared to baseline. In the third subject the SO2 decreased less during occlusion and increased to baseline values at hyperemia with only a 2-fold increase in Perf. The observed difference could be due to different microvascular beds being probed. It is concluded that integrating DRS and LDF enables new possibilities to deduce microcirculation status.
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| 20. |
- Strömberg, Tomas, 1966-, et al.
(författare)
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Spatial frequency domain imaging using a snap-shot filter mosaic camera with multi-wavelength sensitive pixels
- 2018
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Ingår i: Proceedings Volume 10467, Photonics in Dermatology and Plastic Surgery 2018; 104670D (2018). - : SPIE - International Society for Optical Engineering.
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Konferensbidrag (refereegranskat)abstract
- Spatial frequency domain imaging (SFDI) utilizes a digital light processing (DLP) projector for illuminating turbid media with sinusoidal patterns. The tissue absorption (μa) and reduced scattering coefficient (μ,s) are calculated by analyzing the modulation transfer function for at least two spatial frequencies. We evaluated different illumination strategies with a red, green and blue light emitting diodes (LED) in the DLP, while imaging with a filter mosaic camera, XiSpec, with 16 different multi-wavelength sensitive pixels in the 470-630 nm wavelength range. Data were compared to SFDI by a multispectral camera setup (MSI) consisting of four cameras with bandpass filters centered at 475, 560, 580 and 650 nm. A pointwise system for comprehensive microcirculation analysis was used (EPOS) for comparison. A 5-min arterial occlusion and release protocol on the forearm of a Caucasian male with fair skin was analyzed by fitting the absorption spectra of the chromophores HbO2, Hb and melanin to the estimatedμa. The tissue fractions of red blood cells (fRBC), melanin (/mel) and the Hb oxygenation (S02 ) were calculated at baseline, end of occlusion, early after release and late after release. EPOS results showed a decrease in S02 during the occlusion and hyperemia during release (S02 = 40%, 5%, 80% and 51%). The fRBC showed an increase during occlusion and release phases. The best MSI resemblance to the EPOS was for green LED illumination (S02 = 53%, 9%, 82%, 65%). Several illumination and analysis strategies using the XiSpec gave un-physiological results (e.g. negative S02 ). XiSpec with green LED illumination gave the expected change in /RBC , while the dynamics in S02 were less than those for EPOS. These results may be explained by the calculation of modulation using an illumination and detector setup with a broad spectral transmission bandwidth, with considerable variation in μa of included chromophores. Approaches for either reducing the effective bandwidth of the XiSpec filters or by including their characteristic in a light transport model for SFDI modulation, are proposed.
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