Portable microcontroller-based instrument for near-infrared spectroscopy

Near Infrared Spectroscopy (NIRS) can be employed to noninvasively and continuously measure in-vivo local changes in haemodynamics and oxygenation of human tissues. In particular, the technique can be particularly useful for muscular functional monitoring.
We present a portable NIRS research-grade acquisition system prototype, strictly dedicated to low-noise measurements during muscular exercise.
The prototype is able to control four LED sources and a detector. Such a number of sources allows for multipoint measurements or for multi-wavelength spectroscopy of tissue constituents other than oxygen, such as cytochrome aa3 oxidation.
The LEDs and the detector are mounted on separate probes, which carry also the relevant drivers and preamplifiers. By employing surface-mount technologies, probe size and weight are kept to a minimum. A single-chip mixed-signal RISC microcontroller performs source-to-detector multiplexing with a digital correlation technique. The acquired data are stored on an on-board 64 K EEPROM bank, and can be subsequently uploaded to a personal computer via serial port for further analysis.
The resulting instrument is compact and lightweight. Preliminary tests of the prototype on oxygen consumption during tourniquet-induced forearm ischaemia show adequate detectivity and time response.