A Quantitative Comparison of Hemoglobin Concentration and BOLD Signal using Time-Resolved Near-Infrared Spectroscopy

Abstract

Time-Resolved Near-Infrared Spectroscopy (TR-NIRS) is a method of analyzing the time response of the reflected light using a light diffusion equation, and enables us to measure the hemoglobin (Hb) absolute concentration, In this research, we evaluated the applicability of TR-NIRS for the measurement of brain activity. First, we conducted the simultaneous measurement of Continuous Wave Near-Infrared spectroscopy (CW-NIRS) and TR-NIRS in the working memory tasks. The results show the conventional analysis is not applicable, because the fluctuation is larger than the task-related change. Second, we proposed a new signal processing method for suppressing the fluctuation and examined the validity in the original fantom. Finally, by using the proposed method, we conducted the simultaneous measurement of TR-NIRS and functional MRI (fMRI) in the working memory tasks, and verify depth of reach and light path of near infrared light. The result suggests that we can estimate the Hb concentration due to brain activity using the proposed method.