Absolute optical property extraction through portable near-infrared spectroscopy system: utilizing FDNIRS IC and TDNIRS technique

Abstract

Near-infrared spectroscopy is a non-invasive technology which uses source-detector pair for measuring bio-signal such as hemodynamics. Continuous-wave near-infrared spectroscopy(CWNIRS) was widely used for signal measurement due to its simple implementation and system portability. However, this method is not suitable for absolute optical property measurement which is critical to derive accurate tissue property. Frequency-domain NIRS(FDNIRS) and time-domain NIRS(TDNIRS) are solutions for this problem. FDNIRS and TDNIRS both operate in high speed comparing with CWNIRS, which increases its hardware complexity. To solve the system bulkiness, integrated circuit system design was implemented for FDNIRS. Feasibility of TDNIRS integrated circuit system was also proposed. Fabricated FDNIRS IC used a delay-locked loop (DLL) and a low sampling rate analog-to-digital converter (ADC) to extract amplitude and phase delay information of the NIRS signal. IC system realizes a portable, real-time measurement system.