Experimental investigation on the light transmission of a textile-based over-cap used in functional near-infrared spectroscopy

Abstract

Functional near-infrared spectroscopy as an optical (i.e., light-based) neuroimaging technique is susceptive to ambient light noise. In the daily task scenario experiments, light is required to monitor the movement of patients and to minimize the e ect of this light on the results; the fNIRS optodes are covered with dark materials (e.g., a loose- tting black shower-cap). In our laboratory, over-caps provided by NIRx (produced by EasyCap) have been used to eliminate this con-founder. However, there has been a demand to evaluate their performance by quanti cation. Thus, in this paper, the transmission of light through a fabric over-cap is investigated. The results revealed that the output signal of functional near-infrared spectroscopy could be contaminated signi cantly by the ambient light. Moreover, the noise varies due to the stretch that could be applied due to various head sizes. The changes in the amplitude of the signal, which relates to physiological responses, is about 1-2 % in continuous wave measurement while the result of the investigation notes that the transmission average in the samples varies from 8-46 percent depending on the stretching forces. Therefore, it is suggested that this kind of over-caps would be applied only in a dimmed environment, which is not applicable when subjects have mobility disorders. Under such conditions, other techniques to minimize ambient light should be practiced.