Portable infrared spectrometer for high-end in-vivo measurements

Near Infrared Spectroscopy (NIRS) can be employed to monitor continuously and noninvasively local changes in hemodynamics and oxygenation of human tissues. In particular, the technique can be used for muscular functional monitoring during physical activity. A portable NIRS acquisition system dedicated to low-noise measurements during muscular exercise is presented. The instrument has been designed for operation in hostile working conditions, such as high altitude or competitive athletic training. The system provides full control of up to eight light sources, two detectors and two non-amplified auxiliary inputs. Such a number of source-detector channels allows for both multipoint measurements and for multi-wavelength spectroscopy of tissue constituents. Moreover, software-configurable input stages allows for flexibility in probe structure and instrument setup. A single-chip mixed-signal RISC microcontroller performs source-to-detector multiplexing using a non-standard digital correlation technique, optimized for computational efficiency and noise rejection. The acquired data are stored on an on-board memory bank, and can be uploaded to a remote personal computer via serial cable or radio link. The resulting instrument is compact, lightweight and efficient. Preliminary tests on a reference clinical protocol show excellent performance.