Currently, methods for the detection of brain edema in patients or laboratory experiments are invasive or inconvenient for continuous monitoring. We have performed experiments on two models of brain edema to determine the validity of differential near infrared spectroscopy (NIR) as a real-time, low cost and noninvasive method of monitoring brain edema. As a chemical in-vitro model, we prepared serial dilutions of Liposyn III, a fat emulsion, to simulate varying degrees of brain water content. NIR light at two wavelengths (703 nm and 957 nm) was used to assess water content of Liposyn solutions. We demonstrated a strong relation between wavelength specific light interactance and water content, for (n equals 4) serial dilutions from 97.6% to 80.0% water, R2 equals 0.985 plus or minus 0.017. Secondly an in vitro brain tissue model was developed to test the NIR method against wet-to-dry water content measurements. A total brain water content range of from 83.5 to 67.6 water was investigated (n equals 4). Using 695 nm and 957 nm NIR light, a correlation between NIR interactance and brain water content was again obtained, R2 equals 0.957 plus or minus 0.027. Our preliminary results suggest differential NIR spectroscopy may serve as an accurate and useful technique for monitoring surface brain edema in clinical and laboratory settings.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.