Abstracts

Rationale: Surgical removal of epileptogenic brain lesions, when applicable, remains an important therapeutic modality for pediatric patients with intractable epilepsy. Yet, there are currently no effective means to determine the true resection margin prior to and during epilepsy surgery. Optical spectroscopy such as fluorescence and diffuse reflectance spectroscopy can be used as a non-destructive tool to effectively measure physiological features, including hemodynamics and metabolism, of the brain in vivo. In addition, it has been demonstrated that optical spectroscopy can detect intraoperatively certain in vivo biochemical and structural alterations in the brain induced by cancer development and injuries. In this pilot in vivo human study, the feasibility of using combined fluorescence and diffuse reflectance spectroscopy to assist epilepsy surgery in children was investigated. Methods: Pediatric patients receiving epilepsy surgery were recruited to participate in this pilot study. Static and dynamic fluorescence and diffuse reflectance characteristics of the in vivo brain were measured using a portable, high-speed spectroscopic system developed by our research group. The optical recordings were performed on the cortical surface within and outside the resection zone, determined by the subdural EEG and imaging studies, as well as on the lesion itself when feasible. Biopsy samples were taken from the recording sites situated within the resection zones. The dynamic diffuse reflectance signals were also converted to the local hemodynamic characteristics use an analytical model of photon migration. The optical and hemodynamic data were analyzed along with their corresponding pathology, subdural EEG, and imaging study records to identify unique spectral and hemodynamic characteristics of epileptogenic brain lesions. Results: The optical characterization study was performed on 30 pediatric patients (15 static and 15 dynamic studies). Elevated static diffuse reflectance signals between 500 and 600 nm and between 650 and 850 nm were observed in the investigated sites with histological abnormalities. This suggests that cortical malformation would lead to an increase in the scattering properties of the cortex. A unique fluorescence spectral change, marked by the appearance of the 400 nm fluorescent peak, was observed in some investigated sites. This fluorescence peak may be originated from biological fluorophores such as collagen and tryptophan; it indicates unique compositional alterations in these brain tissues. In the dynamic studies, unsynchronized fluctuations in both local blood oxygenation and local blood volume were observed in the cortical areas with abnormal EEG features. Conclusions: The results of this study demonstrate that pediatric epileptogenic lesions possess unique static optical features and dynamic interictal hemodynamic features that differ from normal brain parenchyma. This, in turn, implies that optical spectroscopy may used intraoperatively to aid epilepsy surgery.