Preliminary study of near infrared (NIR) light detection of water content in two models of brain edema

Currently, the detection of brain edema in patients or laboratory experiments is not ideal. For patients, MRI is not convenient for continuous monitoring or quantitation, while intracranial pressure monitoring is indirect and relatively invasive. Both methods have a cost disadvantage. Most quantitative water content determinations are made post mortem, preventing real time measurements. We have performed preliminary experiments on two models of brain edema to determine the validity of Differential NIR Spectroscopy as a real-time, convenient and noninvasive method of monitoring brain edema. As an in vitro model, we prepared serial dilutions of Lyposin ffl, a fat emulsion, to simulate varying degrees of brain water content In 4 preparations, with 703nm and 957nm NIR light, we obtained a correlation coefficient of 0.927±0.016 over the water content range of 76.5% to 96.2%. An in vivo model was developed using dog brain tissue slices, dried in steps to approximate changing levels of brain edema. In 4 preparations, with 695nm and 957nm NIR light, we obtained a correlation coefficient of 0.957±0.027 over a total water content range of 67.6% to 83.5%. We evaluated the depth of interrogation of NIR light into the fat emulsion. At a depth of 3 cm of Lyposin m, 20% of the NTR absorption signal remains. Our preliminary results suggest NIR spectroscopy as new technique for monitoring brain edema in both clinical and laboratory settings.