Abstract
Diffuse optical spectroscopy (DOS) and diffuse optical imaging (DOI) are emerging non-invasive imaging modalities that have wide spread potential applications in many fields, particularly for structural and functional imaging in medicine. In this article, we review time-resolved diffuse optical imaging (TR-DOI) systems using solid-state detectors with a special focus on Single-Photon Avalanche Diodes (SPADs) and Silicon Photomultipliers (SiPMs). These TR-DOI systems can be categorized into two types based on the operation mode of the detector (free-running or time-gated). For the TR-DOI prototypes, the physical concepts, main components, figures-of-merit of detectors, and evaluation parameters are described. The performance of TR-DOI prototypes is evaluated according to the parameters used in common protocols to test DOI systems particularly basic instrumental performance (BIP). In addition, the potential features of SPADs and SiPMs to improve TR-DOI systems and expand their applications in the foreseeable future are discussed. Lastly, research challenges and future developments for TR-DOI are discussed for each component in the prototype separately and also for the entire system.
Highlights
Diffuse optical spectroscopy (DOS), known as near infrared spectroscopy (NIRS), is an optical technique to investigate the interaction between light and matter within the optical window of 600 to 1000 nm
We discussed how silicon solid state detectors have contributed in developing the field of TR-DOS and diffuse optical imaging (DOI) into a new era of affordability, portability, and compactness
In the first section of this paper, we introduced the physical principles of diffuse optical spectroscopy in the biological window (600–1000 nm), and the time-resolved diffuse optical imaging (TR-DOI) prototypes categorized based on geometry and methods of illumination and detection
Summary
Diffuse optical spectroscopy (DOS), known as near infrared spectroscopy (NIRS), is an optical technique to investigate the interaction between light and matter within the optical window of 600 to 1000 nm. The light propagation inside a highly scattering target is mathematically described by a forward problem solver based on the radiative transfer equation (RTE), or its simplified version, the diffusion equation (DE) [5,6] These re-emitted photons can be collected using photodetectors in either reflectance geometry or transmittance geometry. The terms DOI and DOT are used to describe any prototype that utilizes an inverse problem solver to reconstruct images from raw data obtained from DOS. DOT systems can produce 2D or 3D images (slices) in transmittance geometry (detectors and sources are not on the same side) for thin targets (less than 8 cm thickness) such as muscles, breasts, and heads of newborn babies [21,22]. TG TR-DOIofand the FR vs. TG and the potential features, and possible future developments potential usage, features, and possible future developments of using each mode are presented
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