Functional imaging of the brain using a portable NIR instrument

摘要

Near Infrared Spectroscopy (NIRS) is a powerful method for non-invasive mapping of cerebral functional activation. We have developed an NIRS instrument that is portable, inexpensive and lightweight consisting of an array of light emitting diodes (LEDs) and photodiodes (PDs) mounted on a flexible printed circuit board (PCB). The flexibility and portability of the instrument makes it easy to apply to subjects ranging from premature babies in intensive care to adults. The flexible PCB array consists of 48 LEDs operating at two different wavelengths (780 nm & 880 nm) together with 14 photodiodes. Transimpedance amplifiers for each of the PDs are also located on the flexible pad to minimise noise pick up. The LEDs are pulsed (10 μs) at a peak optical power of 8 mW, while a sample and hold circuit monitors the voltages at all of the PDs. The array is also encapsulated in black silicone rubber, except for the regions directly above the LEDs and PDs, which have a clear silicone rubber cover. The sensor array is attached to the monitoring electronics by two one metre long flexible ribbon cables. The monitoring circuit provides medical grade electrical isolation between the subject and the controlling computer. Studies have been conducted on phantoms to test the penetration depth of the sensor array for two different separations of LEDs and PDs (11 mm and 27 mm). The maximum depths that can be probed are 5 mm and 11 mm respectively. This makes it suitable for studying cortical activation in babies.