Time domain optical imaging device based on a commercial time-to-digital converter

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. 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. 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. 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. 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. The linearity and performance of the system are presented, and its potential as the basis for a modular multi-detector imaging system is explored.