Background:Medical and diagnostic applications of near infrared spectroscopy (NIRS) areincreasing, especially in operating rooms (OR). Since NIRS is anoptical technique, radio frequency (RF) interference from other instruments isunlikely to affect the raw optical data, however, NIRS dataprocessing and signal output could be affected. Methods: We investigatedthe potential for three common OR instruments: an electrical cautery,an orthopaedic drill and an imaging system, to generate electromagneticinterference (EMI) that could potentially influence NIRS signals. The timeof onset and duration of every operation of each devicewas recorded during surgery. To remove the effects of slowchanging physiological variables, we first used a lowpass filter andthen selected 2 windows with variable lengths around the momentof device onset. For each instant, variances (energy) and meansof the signals in the 2 windows were compared. Results:Twenty patients were studied during ankle surgery. Analysis shows nostatistically significant difference in the means and variance of theNIRS signals (p < 0.01) during operation of any ofthe three devices for all surgeries. Conclusion: This method confirmsthe instruments evaluated caused no significant interference. NIRS can potentiallybe used without EMI in clinical environments such as theOR. ©2010 COPYRIGHT SPIE–The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.