Abstracts

Rationale: This research project investigated the feasibility of using time-dependent diffuse reflectance spectroscopy to improve the outcome of pediatric epilepsy surgery. The spectroscopic technique was used to monitor dynamic optical properties of the cortex that can be associated with its physiological, morphological, and compositional characteristics. Unique features in the recorded dynamic optical properties were identified to differentiate epileptic cortical lesions from normal cortex. Methods: This pilot study was approved by the Western Institutional Review Board, and consent was acquired from all participants. Thirteen pediatric epilepsy patients and seven pediatric brain tumor patients, as normal control, were recruited in this study. Dynamic optical properties were recorded from the cortical surface intraoperatively using a time-dependent diffuse reflectance spectroscopy system. This system consisted of a fiber-optic probe, a tungsten-halogen light source, and a spectrophotometer. It acquired diffuse reflectance spectra with a spectral range of 204 nm to 932 nm at a rate of 33 spectra per second for approximately 12 seconds. Biopsy samples were taken from electrophysiologically abnormal cortex and evaluated by a neuropathologist. Time histories of the diffuse reflectance intensities at two different wavelengths from each investigated site were compared. The time history data was filtered using low-pass filters with various cut-off frequencies to reduce systemic and experimental artifacts. Segments of negative correlation, defined by the opposite slope polarities, between the two time histories were extracted. The total duration of negative correlation, referred as “negative correlation time index”, was calculated by integrating the negative correlation segments. The above comparison procedure was carried out with all possible wavelength combination between 400 nm and 800 nm. The negative correlation time indices from all investigated sites were subgrouped using the corresponding histological identities of the investigated sites. The differences between the mean indices of two subgroups were evaluated statistically. Results: The positive group consisted of seven pathologically abnormal samples, and the negative group consisted of 13 normal controls from non-epileptic tumor patients. Statistical analysis showed the most significant differences between these two groups at the wavelength combination of 700-760 nm versus 550-580 nm and the cut-off frequency of 1.9 to 2.1 Hz. An empirical discrimination algorithm based on the negative correlation time indices in this range produced a 100% sensitivity and a 85% specificity. Conclusions: Time-dependent diffuse reflectance spectroscopy with optimized data analysis methods differentiates epileptic cortical lesions from normal cortex with high sensitivity and specificity; therefore, it may enhance the surgical outcome of pediatric epilepsy surgery. This research was funded by Thrasher Research Fund and Ware Foundation research Endowment.