title: Inverse Monte Carlo in a multilayered tissue model: merging diffuse reflectance spectroscopy and laser Doppler flowmetry.
abstract: The tissue fraction of red blood cells (RBCs) and their oxygenation and speed-resolved perfusion are estimated 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), allowing for a relative calibration routine, whereas LDF spectra are assessed at 1.2 mm in the same fiber-optic probe. Data are analyzed using nonlinear optimization in an inverse Monte Carlo technique by applying an adaptive multilayered tissue 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 evaluate the method. The absolute root mean square (RMS) deviation between estimated and true oxygenation was 4.1 percentage units, whereas the relative RMS deviations for the RBC tissue fraction and perfusion were 19% and 23%, respectively. Examples of in vivo measurements on forearm and foot during common provocations are presented. The method offers several advantages such as simultaneous quantification of RBC tissue fraction and oxygenation and perfusion from the same, predictable, sampling volume. The perfusion estimate is speed resolved, absolute (% RBC×mm/s), and more accurate due to the combination with DRS.
authors.affiliation: Linköping University, Department of Biomedical Engineering, University Hospital, 581 85 Linköping, SwedenbPerimed AB, Datavägen 9A, 175 43 Järfälla, Sweden.
authors.forename: Ingemar
authors.initials: I
authors.lastname: Fredriksson
authors.affiliation: Linköping University, Department of Mathematics, Division of Optimization, 581 83 Linköping, Sweden.
authors.forename: Oleg
authors.initials: O
authors.lastname: Burdakov
authors.affiliation: Linköping University, Department of Biomedical Engineering, University Hospital, 581 85 Linköping, Sweden.
authors.forename: Marcus
authors.initials: M
authors.lastname: Larsson
authors.affiliation: Linköping University, Department of Biomedical Engineering, University Hospital, 581 85 Linköping, Sweden.
authors.forename: Tomas
authors.initials: T
authors.lastname: Strömberg
mesh_terms: D000328:Adult; D005336:Fiber Optic Technology / Q000379:methods*; D005542:Forearm / Q000098:blood supply; D006801:Humans; D017078:Laser-Doppler Flowmetry / Q000379:methods*; D007866:Leg / Q000098:blood supply; D008297:Male; D008954:Models, Biological; D009010:Monte Carlo Method; D010100:Oxygen / Q000097:blood; D012039:Regional Blood Flow / Q000502:physiology; D012542:Scattering, Radiation; D012867:Skin / Q000098:blood supply; D013057:Spectrum Analysis / Q000379:methods*
chemical_list: D010100:Oxygen