Abstract: To enhance the capability of functional near-infrared spectroscopy in quantitative acquisition of cerebral optical parameters, a frequency-domain near-infrared brain imaging detection circuit system was designed and implemented. A direct digital synthesizer (AD9959) was employed in the system as the high-frequency modulation signal source, while an STM32 microcontroller was used for light source driving and data acquisition control. Additionally, a heterodyne demodulation circuit was applied to extract amplitude attenuation and phase delay information of the detected optical signals, enabling quantitative inversion of tissue absorption and scattering coefficients. The hardware system consists of light source modulation, signal reception, amplification and filtering, mixing and demodulation, and embedded processing modules, which were integrated into a 16 cm × 10 cm standard circuit board with high integration and low power consumption. Experimental results show that the system can operate stably at 110 MHz frequency and can successfully acquire and process signals from polyformaldehyde phantoms at source-detector distances of 1.8 cm and 3.0 cm. The measured absorption coefficient of polyformaldehyde phantoms is 0.11 cm−1 , and the scattering coefficient is 8.75 cm−1 . These measurement results are consistent with the typical optical characteristics of the phantom material, verifying the feasibility and stability of the designed circuit system in retrieving optical parameters. This study provides hardware support for the implementation of portable frequency-domain near-infrared brain imaging systems in neural monitoring and brain function research.

Key words: biomedical optics, frequency-domain near-infrared brain imaging detection system, heterodyne demodulation method, optical parameters of biological tissues, circuit system design