Abstract
An optical technique based on diffuse reflectance measurement combined with indocyanine green (ICG) bolus tracking is extensively tested as a method for the clinical assessment of brain perfusion at the bedside. We report on multiwavelength time-resolved diffuse reflectance spectroscopy measurements carried out on the head of a healthy adult during the intravenous administration of a bolus of ICG. Intracerebral and extracerebral changes in absorption were estimated from an analysis of changes in statistical moments (total number of photons, mean time of flight and variance) of the distributions of times of flight (DTOF) of photons recorded simultaneously at 16 wavelengths from the range of 650-850 nm using sensitivity factors estimated by diffusion approximation based on a layered model of the studied medium. We validated the proposed method in a series of phantom experiments and in-vivo measurements. The results obtained show that changes in the concentration of the ICG can be assessed as a function of time of the experiment and depth in the tissue. Thus, the separation of changes in ICG concentration appearing in intra- and extracerebral tissues can be estimated from optical data acquired at a single source-detector pair of fibers/fiber bundles positioned on the surface of the head.
Highlights
A variety of optical techniques for brain imaging are tested in clinical diagnostics [1]
We found large amplitudes of changes in the number of photons Ntot, mean time of flight of diffusely reflected photons and variance V of the distributions of times of flight (DTOF) corresponding to the inflow into both deeper and superficially located segments of the tube
The presented signals were adjusted in such a way that the indocyanine green (ICG) inflows into the superficial segment of the tube appear at T ≈70 s in signals acquired at all source-detector separations
Summary
A variety of optical techniques for brain imaging are tested in clinical diagnostics [1] One of such methods is near-infrared spectroscopy (NIRS) [2, 3]. Near-infrared light can penetrate into the human brain through the skin and skull and return to the surface of the head in reflectance geometry. This allows for evaluation of absorption changes in chromophores such as oxy- and deoxyhemoglobin circulating through the tissues because of their different spectral properties in the near infrared range of wavelengths [4]. Three optoelectronic NIRS approaches have been proposed for brain’s hemodynamic changes measurements: continuous wave (CW) [7], frequency-domain [8, 9] and time-resolved (time-domain) [10, 11]
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