Frequency-domain near infrared spectroscopy (fd-NIRS) is used to noninvasively characterize in vivo tissue structure and molecular composition by exploiting the deep tissue penetration of red and near-infrared light. However, the size, complexity, expense, and lack of scalability of current fd-NIRS hardware has slowed its translation to clinical applications. Here we present a broad-bandwidth 1.2 x 1.2 mm fd-NIRS application-specific integrated circuit that represents a critical step toward ultrasmall, easily scalable, and wearable fd-NIRS. We present the fd-NIRS integrated circuit design as well as results showing its optical property measurements are comparable to those measured with a standard reference system.
Diffuse optical spectroscopic imaging (DOSI) and diffuse correlation spectroscopy (DCS) are model-based near-infrared (NIR) methods that measure tissue optical properties (broadband absorption, μa, and reduced scattering, μs′) and blood flow (blood flow index, BFI), respectively. DOSI-derived μa values are used to determine composition by calculating the tissue concentration of oxy- and deoxyhemoglobin (HbO2, HbR), water, and lipid. We developed and evaluated a combined, coregistered DOSI/DCS handheld probe for mapping and imaging these parameters. We show that uncertainties of 0.3 mm−1 (37%) in μs′ and 0.003 mm−1 (33%) in μa lead to ∼53% and 9% errors in BFI, respectively. DOSI/DCS imaging of a solid tissue-simulating flow phantom and a breast cancer patient reveals well-defined spatial distributions of BFI and composition that clearly delineates both the flow channel and the tumor. BFI reconstructed with DOSI-corrected μa and μs′ values had a tumor/normal contrast of 2.7, 50% higher than the contrast using commonly assumed fixed optical properties. In conclusion, spatially coregistered imaging of DOSI and DCS enhances intrinsic tumor contrast and information content. This is particularly important for imaging diseased tissues where there are significant spatial variations in μa and μs′ as well as potential uncoupling between flow and metabolism.
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