Ingemar Fredriksson, received his M.Sc. in 2004, and his Ph.D. in 2009. He is currently working with research
and development of laser Doppler flowmetry and diffuse reflectance spectroscopy
at Perimed AB and at the Department
of Biomedical Engineering, Linköping University.
Activities and interest:
Publications:
Show/hide year headlines.
Journal papers
2013
Abstract The tissue fraction of red blood cells (RBCs) and their oxygenation and speedresolved 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 fiberoptic 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 flowspeed information.Simulations of 250 tissuelike 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.
Keywords diffuse reflectance spectroscopy; laser Doppler flowmetry; modeling; Monte Carlo simulations; inverse engineering; nonlinear optimization; blood oxygen saturation; speedresolved perfusion, Engineering and Technology
BIBTEX
@article{diva2:681131,
author = {Fredriksson, Ingemar and Burdakov, Oleg and Larsson, Marcus and Strömberg, Tomas},
title = {{Inverse Monte Carlo in amultilayered tissue model: merging diffuse reflectance spectroscopy andlaser Doppler flowmetry}},
journal = {Journal of Biomedical Optics},
year = {2013},
volume = {18},
number = {12},
pages = {127004112700414},
}
2012
Abstract 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 multidetector setup, nonsystematic residual spectrum was only found using the more complex Gegenbauerkernel 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 multidetector setup was also obtained using either two relative calibrated detectors or one absolute calibrated detector at a fiber separation of 0.46 mm.
Keywords Engineering and Technology
BIBTEX
@article{diva2:536040,
author = {Karlsson, Hanna and Fredriksson, Ingemar and Larsson, Marcus and Strömberg, Tomas},
title = {{Inverse Monte Carlo for estimation of scattering and absorption in liquid optical phantoms}},
journal = {Optics Express},
year = {2012},
volume = {20},
number = {11},
pages = {1223312246},
}
Abstract 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 sourcedetector 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 postprocessing. The accuracy of the method was evaluated using Monte Carlo simulations of tissuelike 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 realtime processing.
Keywords Engineering and Technology
BIBTEX
@article{diva2:526996,
author = {Fredriksson, Ingemar and Larsson, Marcus and Strömberg, Tomas},
title = {{Inverse Monte Carlo method in a multilayered tissue model for diffuse reflectance spectroscopy}},
journal = {Journal of Biomedical Optics},
year = {2012},
volume = {17},
number = {4},
pages = {047004},
}
2010
Abstract OBJECTIVETo compare the microcirculatory velocity distribution in type 2 diabetic patients and nondiabetic control subjects at baseline and after local heating. RESEARCH DESIGN AND METHODSThe 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 velocityresolved 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 110 mm/s, and v greater than10 mm/s. RESULTSThe 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 highvelocity blood flow (v greater than10 mm/s). The RBC concentration in diabetic patients increased sevenfold for v between 1 and 10 mm/s, and 15fold 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. CONCLUSIONSThe 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 toetobrachial systolic blood pressure ratio.
Keywords Engineering and Technology
BIBTEX
@article{diva2:342863,
author = {Fredriksson, Ingemar and Larsson, Marcus and Nyström, Fredrik and Länne, Toste and Johan Östgren, Carl and Strömberg, Tomas},
title = {{Reduced Arteriovenous Shunting Capacity After Local Heating and Redistribution of Baseline Skin Blood Flow in Type 2 Diabetes Assessed With VelocityResolved Quantitative Laser Doppler Flowmetry}},
journal = {Diabetes},
year = {2010},
volume = {59},
number = {7},
pages = {15781584},
}
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 modelbased 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 sourcedetector 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 nonlinear 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.
Keywords laser Doppler flowmetry, microcirculation, tissue modeling, inverse Monte Carlo, quantitative measures, flow speed differentiation, Engineering and Technology
BIBTEX
@article{diva2:234423,
author = {Fredriksson, Ingemar and Larsson, Marcus and Strömberg, Tomas},
title = {{Modelbased quantitative laser Doppler flowmetry in skin}},
journal = {Journal of Biomedical Optics},
year = {2010},
volume = {15},
number = {5},
}
2009
Abstract 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 sourcedetector separation) and imaging systems (0.5 and 2.0 mm beam diameter) are considered, at the wavelengths 543 nm, 633 nm, and 780 nm. Nonlinear 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. sourcedetector 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 sourcedetector 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.
Keywords Laser Doppler flowmetry, Laser Doppler perfusion monitoring, Laser Doppler perfusion imaging, Sourcedetector separation, Measurement volume, Sampling depth, Monte Carlo simulations, Tissue model, Multiple Doppler shifts, Engineering and Technology
BIBTEX
@article{diva2:227221,
author = {Fredriksson, Ingemar and Larsson, Marcus and Strömberg, Tomas},
title = {{Measurement depth and volume in laser Doppler flowmetry}},
journal = {Microvascular Research},
year = {2009},
volume = {78},
number = {1},
pages = {413},
}
Abstract A method for determining a twoparametric Gegenbauerkernel phase function that accurately describes the diffuse reflectance from a polydispersive scattering media at small sourcedetector 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%.
Keywords Engineering and Technology
BIBTEX
@article{diva2:221894,
author = {Lindbergh, Tobias and Fredriksson, Ingemar and Larsson, Marcus and Strömberg, Tomas},
title = {{Spectral determination of a twoparametric phase function for polydispersive scattering liquids}},
journal = {Optics Express},
year = {2009},
volume = {17},
number = {3},
pages = {16101621},
}
Abstract Two forced detection (FD) variance reduction Monte Carlo algorithms for image simulations of tissueembedded 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.
Keywords Monte Carlo simulations, diffuse scattering, variance reduction, Image simulation, Engineering and Technology
BIBTEX
@article{diva2:211823,
author = {Fredriksson, Ingemar and Larsson, Marcus and Strömberg, Tomas},
title = {{Forced detection Monte Carlo algorithms for accelerated blood vessel image simulations}},
journal = {JOURNAL OF BIOPHOTONICS},
year = {2009},
volume = {2},
number = {3},
pages = {178184},
}
Abstract An electrode with adjacent optical fibers for measurements during navigation and radio frequency lesioning in the brain was modeled for Monte Carlo simulations of light transport in brain tissue. Relative reflected light intensity at 780 nm, I_{780}, from this electrode and probes with identical fiber configuration were simulated using the intensity from native white matter as reference. Models were made of homogeneousnative and coagulated gray, thalamus, and white matter as well as blood. Dual layermodels, including models with a layer of cerebrospinal fluid between the fibers andthe brain tissue, were also made. Simulated I_{780} was 0.16 for gray matter, 0.67 forcoagulate gray matter, 0.36 for thalamus, 0.39 for coagulated thalamus, unity forwhite matter, 0.70 for coagulated white matter and 0.24 for blood. Thalamic matterhas also been found to reflect more light than gray matter and less than white matterin clinical studies. In conclusion the reflected light intensity can be used todifferentiate between gray and white matter during navigation. Furthermore,coagulation of light gray tissue, such as the thalamus, might be difficult to detectusing I_{780}, but coagulation in darker gray tissue should result in a rapid increase of _{I780}.
Keywords Brain, Monte Carlo simulations, diffuse reflectance, navigation, radiofrequency lesioning, Medical and Health Sciences
BIBTEX
@article{diva2:128392,
author = {Johansson, Johannes D. and Fredriksson, Ingemar and Wårdell, Karin and Eriksson, Ola},
title = {{Simulation of reflected light intensity changes during navigation and radio frequency lesioning in the brain}},
journal = {Journal of Biomedical Optics},
year = {2009},
volume = {14},
number = {044040},
}
2008
Abstract 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 nonlinear 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 velocityresolved absolute LDF measurements with known sampling volume, and can also be useful for other biooptical modalities.
Keywords laser Doppler velocimetry, simulations, biomedical optics, Doppler, Engineering and Technology
BIBTEX
@article{diva2:18124,
author = {Fredriksson, Ingemar and Larsson, Marcus and Strömberg, Tomas},
title = {{Optical microcirculatory skin model: Assessed by Monte Carlo simulations paired with in vivo laser Doppler flowmetry}},
journal = {Journal of Biomedical Optics},
year = {2008},
volume = {13},
number = {1},
pages = {14015},
}
2007
Abstract The^{ }reduced scattering coefficient, µ_{s}, was determined using oblique angle illumination^{ }and imaging backscattered light intensity. The distance r between the^{ }point of light incidence (hotspot) and the circular symmetric diffuse^{ }reflectance centre, is ~1/µ. Previously, r was obtained analyzing a^{ }1D strip aligned with the laser beam. We improved this^{ }method by calculating a 2D intensity image with extended dynamic^{ }range by assessing camera linearity, superimposing images with multiple integration^{ }times, and compensating for lens vignetting. The hotspot algorithm utilises^{ }several images to minimize speckle variations and account for laser^{ }beam shape. Diffuse centre position is obtained by filtering the^{ }superimposed image with decreasing thresholds using momentum analysis to determine^{ }circular symmetry. The method was evaluated on 18 optical liquid^{ }phantoms with µ_{s}[1.5, 3.0] mm^{1} and µ_{s}[0.01, 0.16] mm^{1}. The^{ }2D method had better linearity with µ_{s} and smaller variations^{ }due to more stable hotspot detection, than the 1D method.^{ }The anisotropy factor g was obtained by fitting measured and^{ }Monte Carlo simulated spatially resolved intensity decays and verified with^{ }a laser Doppler flowmetry technique. With an optimal compensation for^{ }the µ_{a} dependence, the rms error in µ estimation was^{ }2.9%.
Keywords Reduced scattering coefficient, absorption coefficient, anisotropy factor, optical properties, oblique angle illumination, optical phantoms, Monte Carlo simulations, Engineering and Technology
BIBTEX
@article{diva2:246007,
author = {Lindbergh, Tobias and Larsson, Marcus and Fredriksson, Ingemar and Strömberg, Tomas},
title = {{Reduced scattering coefficient determination by noncontact oblique angle illumination: methodological considerations}},
journal = {Proceedings of SPIE, the International Society for Optical Engineering},
year = {2007},
volume = {6435},
pages = {64350I164350I12},
}
2006
Abstract 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 LevenbergMarquardt 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.
Keywords Laser Doppler flowmetry, LDF, Monte Carlo simulations, flow phantom, blood perfusion, scattering phase, Engineering and Technology
BIBTEX
@article{diva2:18125,
author = {Fredriksson, Ingemar and Larsson, Marcus and Strömberg, Tomas},
title = {{Absolute flow velocity components in laser Doppler flowmetry}},
journal = {Proceedings of SPIE, the International Society for Optical Engineering},
year = {2006},
volume = {6094},
pages = {60940A},
}
Book chapters
2012
Ingemar Fredriksson, Marcus Larsson, Tomas Strömberg,
"Laser Doppler Flowmetry",
Microcirculation Imaging,
6784, 2012.
Keywords Doppler effect, microcirculation, light scattering, theory, measurement depth, measurement volume, monte carlo simulations, Engineering and Technology
BIBTEX
@incollection{diva2:571143,
author = {Fredriksson, Ingemar and Larsson, Marcus and Strömberg, Tomas},
title = {{Laser Doppler Flowmetry}},
booktitle = {Microcirculation Imaging},
year = {2012},
pages = {6784},
publisher = {WileyBlackwell},
address = {Weinheim},
}
Conference papers
2013
Abstract We have previously presented an inverse Monte Carlo algorithm based on a threelayer semiinfinite skin model for analyzing diffuse reflectance spectroscopy (DRS) data. The algorithm includes presimulated 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 postprocessing. Recorded DRS spectra at sourcedetector 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 nonlinear 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 rmserror < 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 2fold 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.
Keywords Microcirculation, diffuse reflectance spectra, Monte Carlo simulations, skin modeling, laser Doppler flowmetry, Engineering and Technology
BIBTEX
@inproceedings{diva2:645355,
author = {Strömberg, Tomas and Karlsson, Hanna and Fredriksson, Ingemar and Larsson, Marcus},
title = {{Experimental results using a threelayer skin model for diffuse reflectance spectroscopy}},
booktitle = {Optical Tomography and Spectroscopy of Tissue X},
year = {2013},
series = {Proceedings of SPIE},
volume = {8578},
pages = {85783418578348},
publisher = {SPIE  International Society for Optical Engineering},
}
2011
Abstract 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.
Keywords Inverse Monte Carlo, tissue model, absorption, pigment packaging, blood, Engineering and Technology
BIBTEX
@inproceedings{diva2:425943,
author = {Fredriksson, Ingemar and Larsson, Marcus and Strömberg, Tomas},
title = {{Accuracy of vessel diameter estimated from a vessel packaging compensation in diffuse reflectance spectroscopy}},
booktitle = {Clinical and Biomedical Spectroscopy and Imaging II},
year = {2011},
series = {Proceedings of SPIE (Progress in biomedical optics and imaging)},
volume = {Vol. 8087},
pages = {8087 1M18087 1M8},
publisher = {SPIE  International Society for Optical Engineering},
}
Ingemar Fredriksson, Marcus Larsson, Fredrik Salomonsson, Tomas Strömberg,
"Improved calibration procedure for laser Doppler perfusion monitors",
Optical Diagnostics and SensingXI: Toward PointofCareDiagnostics; and Design andPerformance Validation ofPhantoms Used in Conjunctionwith Optical Measurement ofTissue III, Proceedings of SPIE (Progress in biomedical optics and imaging),
Vol. Vol. 7906,
79060217906027, 2011.
Abstract 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.
Keywords Laser Doppler flowmetry, calibration, Brownian motion, optical phantoms, Engineering and Technology
BIBTEX
@inproceedings{diva2:401575,
author = {Fredriksson, Ingemar and Larsson, Marcus and Salomonsson, Fredrik and Strömberg, Tomas},
title = {{Improved calibration procedure for laser Doppler perfusion monitors}},
booktitle = {Optical Diagnostics and SensingXI: Toward PointofCareDiagnostics; and Design andPerformance Validation ofPhantoms Used in Conjunctionwith Optical Measurement ofTissue III},
year = {2011},
series = {Proceedings of SPIE (Progress in biomedical optics and imaging)},
volume = {Vol. 7906},
pages = {79060217906027},
publisher = {SPIE  International Society for Optical Engineering},
}
2009
Keywords Engineering and Technology
BIBTEX
@inproceedings{diva2:271469,
author = {Johansson, Johannes and Fredriksson, Ingemar and Wårdell, Karin and Eriksson, Ola},
title = {{Monte Carlo simulations of reflected light intensity for navigation in the brain}},
booktitle = {World Congress 2009, 11th International Congress of the IUPESM, Medical Physics and Biomedical Engineering},
year = {2009},
}
2008
Keywords Medical and Health Sciences
BIBTEX
@inproceedings{diva2:265189,
author = {Johansson, Johannes and Fredriksson, Ingemar and Eriksson, Ola and Wårdell, Karin},
title = {{Simulering av ljusreflektion i hjärnan under navigation och radiofrekvensablation}},
booktitle = {Medicinteknikdagarna 2008,2008},
year = {2008},
pages = {7070},
}
2006
Keywords Medical and Health Sciences
BIBTEX
@inproceedings{diva2:258062,
author = {Fredriksson, Ingemar and Larsson, Marcus and Strömberg, Tomas},
title = {{Separation av shuntat och kapillärt mikrocirkulatoriskt blodflöde med laser Dopplertekniken}},
booktitle = {Medicinteknikdagarna,2006},
year = {2006},
}
2005
Keywords Medical and Health Sciences
BIBTEX
@inproceedings{diva2:251024,
author = {Fredriksson, Ingemar and Larsson, Marcus and Strömberg, Tomas},
title = {{Hastighetsupplöst blodflödesmätning med Laserdopplertekniken}},
booktitle = {Medicinteknikdagar MTF,2005},
year = {2005},
}
Keywords Medical and Health Sciences
BIBTEX
@inproceedings{diva2:250706,
author = {Fredriksson, Ingemar and Larsson, Marcus and Strömberg, Tomas},
title = {{Absolute blood flow velocity components in Laser Doppler flowmetry}},
booktitle = {International Graduate Summer School Biophotonics05,2005},
year = {2005},
}
Theses
2009
Abstract Laser Doppler flowmetry (LDF) is virtually the only noninvasive 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 nonconstant measurement volume, nonlinearities 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 lighttissue 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 proofofconcept 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 sourcedetector 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 mm^{3} 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.
Keywords Engineering and Technology
BIBTEX
@phdthesis{diva2:234437,
author = {Fredriksson, Ingemar},
title = {{Quantitative Laser Doppler Flowmetry}},
school = {Linköping University},
type = {{Linköping Studies in Science and Technology. Dissertations No. 1269}},
year = {2009},
address = {Sweden},
}
