![]() ![]() ![]() Until recently, such technology has been very expensive, bulky, and power-consuming. This limitation can be overcome if the distances traveled by the photons in the tissue are measured, and this can be achieved using ultrafast technology, which records the flight times of photons with a picosecond resolution. However, because the light is highly scattered, simple measurements of transmitted intensity are insufficient to quantify absolute hemoglobin concentrations. ![]() Because the technology is both safe and relatively portable, DOT has been a popular tool for studying the developing brains of infants and babies. ![]() Tachtsidis, “ Clinical brain monitoring with time domain NIRS: A review and future perspectives,” Appl. Torricelli, “ New frontiers in time-domain diffuse optics, a review,” J. Arridge, “ Recent advances in diffuse optical imaging,” Phys. This approach, known as diffuse optical tomography (DOT), has been widely used to study the human brain and, especially, the response of the brain to sensory stimuli and cognitive tasks. A combination of measurements made at multiple locations on the tissue surface enables images to be generated, which display the variation in blood volume and oxygenation in the underlying tissues. The oxygenated and deoxygenated forms of hemoglobin have different optical absorption characteristics, and consequently, measurements of the transmission of near-infrared (NIR) light at two or more wavelengths across human tissue (such as a region of the head) can be used to monitor their relative concentrations. The linearity and performance of the system are presented, and its potential as the basis for a modular multi-detector imaging system is explored. The system is able to generate histograms of photon flight times at a rate of 81–90 kS/s and with a sampled bin width of 54 ps. While such technology usually depends on customized circuits, in this article, we present a system assembled from commercially available components, including a low-cost time-to-digital converter and a silicon photomultiplier detector. Recent advances in silicon electronics have enabled the development of time-domain systems, which are lightweight and low cost, potentially enabling the imaging technique to be applied to a far greater cohort of subjects in a variety of environments. Measuring the times of flights of photons provides information on the photon pathlengths in tissue, which enables absolute concentrations of the oxygenated and deoxygenated forms of hemoglobin to be estimated. Time-domain diffuse optical imaging is a noninvasive technique that uses pulsed near-infrared light as the interrogation source to produce quantitative images displaying the variation in blood volume and oxygenation in the human brain. ![]()
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