SignificanceContinuous-wave functional near-infrared spectroscopy has proved to be a valuable tool for assessing hemodynamic activity in the human brain in a non-invasively and inexpensive way. However, most of the current processing/analysis methods assume the head is a homogeneous medium, and hence do not appropriately correct for the signal coming from the scalp. This effect can be reduced by considering light propagation in a layered model of the human head, being the Monte Carlo (MC) simulations the gold standard to this end. However, this implies large computation times and demanding hardware capabilities.AimIn this work, we study the feasibility of replacing the homogeneous model and the MC simulations by means of analytical multilayered models, combining in this way, the speed and simplicity of implementation of the former with the robustness and accuracy of the latter.ApproachOxy- and deoxyhemoglobin (HbO and HbR, respectively) concentration changes were proposed in two different layers of a magnetic resonance imaging (MRI)-based meshed model of the human head, and then these changes were retrieved by means of (i) a typical homogeneous reconstruction and (ii) a theoretical layered reconstruction.ResultsResults suggest that the use of analytical models of light propagation in layered models outperforms the results obtained using traditional homogeneous reconstruction algorithms, providing much more accurate results for both, the extra- and the cerebral tissues. We also compare the analytical layered reconstruction with MC-based reconstructions, achieving similar degrees of accuracy, especially in the gray matter layer, but much faster (between 4 and 5 orders of magnitude).ConclusionsWe have successfully developed, implemented, and validated a method for retrieving chromophore concentration changes in the human brain, combining the simplicity and speed of the traditional homogeneous reconstruction algorithms with robustness and accuracy much more similar to those provided by MC simulations.
In this work we introduce an analytical way of computing the photon measurement density functions in multilayered flat and spherical media. Comparisons with Monte Carlo simulations in the particular case of two-layered media show very good agreement (differences below 10%), with the additional advantage that the time taken by the theoretical calculations is several orders of magnitude (more than 6) lower than the corresponding Monte Carlo calculations.
In this work we derive general equations for the analytical calculation of photon mean partial pathlengths (MPPLs) in turbid media with an arbitrary number of layers. Comparisons with their Monte Carlo (MC) counterpart show excellent agreement. These quantities can now be used to retrieve haemoglobin concentrations changes in cerebral blood in real-time and with minimal computing requirements.
KEYWORDS: Spherical lenses, Data modeling, Near infrared, Head, Multilayers, Monte Carlo methods, Magnetic resonance imaging, Absorption, Skull, Photons
We compare flat and spherical models of the human head using Bayesian inference. Monte Carlo simulations are used to obtain the photons times of flight. Results suggest that the spherical model better represents the data.
Ultrasound is widely used as an inexpensive, real-time method for imaging vascular tissue. However, sonographs often lack automatic or semi-automatic software for measuring vascular diameter precisely, especially in low- and mid-income countries or institutions. Tools can be developed to perform this task, but they must be validated before being accepted for clinic use. For that purpose, in this work we present low-cost phantoms that resemble vascular tissue when subjected to ultrasound. Several materials are analysed and a step-by-step recipe for building a simple phantom is presented. Qualitatively, models were imaged by an ultrasound expert physician, and several characteristic are assessed. Quantitatively, a comparison between ultrasound and caliper measurements of the phantoms is presented. Finally, a discussion about the results and the recommended materials for low-cost vascular phantoms is carried out.
Near Infrared diffuse transmission of light through tissue is a tool for noninvasive imaging for diagnostic purposes. Most
of the research has been focused over breast cancer imaging; however, major efforts have been done in cerebral
tomography and topography imaging, as well as small animal organs imaging systems. In this work, we investigate the
transmitted light profiles when scattering and absorbing cylindrical inhomogeneities are submerged at different depths
inside slabs of turbid media. We analyze the transilluminance profiles when the phantom is scanned using both, CW and
time resolved detection. The study of the spatial profiles obtained with CW light, shows an apparently contradictory
effect when the absorption coefficient of the inclusion is higher than that of the bulk. In this case, the intensity profiles
displays a peak of higher intensity where the inclusion is located, as it would be expected for a less absorbing inclusion.
The experiments were compared and analyzed with a theoretical model for cylindrical inclusions and Monte Carlo
simulations implemented in a Graphic Processing Unit (GPU).
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