Silicon Photomultipliers for Diffuse Optical Tomography

Abstract: Optical neuroimaging stands as a promising potential surrogate for fMRI, capable of achieving comparable imaging of brain activity near the cortical surface. High-density diffuse optical tomography (HD-DOT) systems, which rely on the optical properties of oxygenated and deoxygenated blood, face trade-offs between the high performance of fiber-based systems that require large opto-electronic consoles and bulky head-restricting fiber optics, and wearable fiberless systems which have worse noise characteristics. These differences stem from the difficulty of miniaturizing the avalanche photodiodes (APDs) in fiber-based systems, but recent advancements in silicon-photomultipliers (SiPMs) in the near-infrared range present an opportunity to combine the improved noise characteristics of fiber-based APDs with the small form factor of wearable systems.

The characteristics of SiPMs are modeled in the context of an HD-DOT system, and then physically evaluated in a hybrid APD/SiPM system, showing potential to significantly expand the number of system channels. Complicating factors of SiPMs, including nonlinearity and temperature variability are quantified and managed. A miniaturized dual source/detector module is designed and evaluated, showing a noise floor even lower than what can be achieved with APDs, while remaining small enough to support the development of a high-density (13mm-nearest neighbor spacing) wearable DOT system.