Abstracts

Photoacoustic tomography (PAT) is an emerging imaging modality that has the potential to image the dynamics of brain activity due to its unique ability of imaging biological tissues with both high optical contrast and ultrasound resolution. PAT is sensitive to molecular signatures and may provide real-time functional information including blood oxygenation and blood volume. In this pilot study, PAT was evaluated in an experimental bicuculline methiodide (BMI) animal model of epilepsy., Mechanical scanning PAT with single acoustic transducer was employed for collecting the acoustic signals. The light source was a pulsed Nd:YAG laser with 4ns pulse duration and up to 360mJ pulse power at a wavelength of 532nm. The light power was 15mJ/cm² at the surface of the rat head, which was lower than the maximum permissible exposure for skin to 532nm laser beam (20 mJ/cm²). An immersion acoustic transducer with 1MHz nominal frequency was driven by a motorized rotator to receive acoustic signals over 360[ordm] at an interval of 3[ordm] and thus a total of 120 measurements were performed for one planar scanning. Scanning along z-axis was accomplished by mounting the rotator and the transducer on a platform driven by a linear stage. The complex wave field signal was amplified by a Pulser/Receiver and acquired by a high-speed PCI data acquisition board. PAT data were obtained from 3 young male rats weighing 50[sim]60g using urethane anesthesia (1mg/g). Acute seizure foci were induced by the injection of BMI over the frontal neocortex and confirmed with EEG. The transducer was scanned at a fixed plane for 20 minutes after the BMI injection., PAT images were recovered from data obtained at 1-5, 6-10, 11-15, 6-20 min after the BMI injection. The size of the region with high absorption around the location of BMI injection was observed to be the largest during the 6-10 min scan. The largest increase of absorption is observed in a region around the location of BMI injection between the images of first and second scan. During the following 10 min when the third and fourth scans were applied, the increasing of absorption was slow down in the injection area. The concentration of BMI is high in a small region after the injection and partial seizure has been induced that results in increasing of blood flow in the same area. 3D scanning was also performed to image the epilepsy at different depth. The PAT images reconstructed from the data collected at transverse planes 2 to 5 mm below the skin were displayed., We have identified PAT as a novel laser-based modality tool for epilepsy imaging. Our pilot results indicate that that PAT has the potential to be a powerful tool for real-time imaging of the spatial onset and propagation of seizures., (Supported by National Institutes of Health (R01 AR048122) and Wilder Epilepsy Research Center.)