Abstracts

Rationale: Along with hemoglobin changes, cerebral blood flow (CBF) and oxygen consumption (OC) changes resulting from functional activations are all important components of the hemodynamic response in epileptic seizure disorders. Malformations of cortical development (MCD) have been considered significantly as a major cause of seizures, which would demonstrate imaging contrast in cellular morphology imaging. Diffuse optical tomography (DOT) is able to retrieve 3D tissue functional and molecular properties noninvasively [Q. Wang et. al., 2008, Med. Phys. 35:216-224], which distinguishes it from intrinsic optical signal imaging where incision is required for imaging [S. Bahar et. al., 2006, NeuroReport 17:499-503]. Besides, DOT is able to reach a temporal resolution >1Hz, which gives this technology advantage over fMRI [Y. Aghakhani et. al., 2004, Brain 127:1127-1144] where important temporal information could be lost despite the fast varying brain activities. Methods: A multispectral continuous-wave (CW) DOT system was applied in this study. Generally, filtered light (700nm and 750nm) from a white light source was delivered to multiple source points consequently on surface of the scalp area above the hippocampus. The screening site was imaged onto a CCD camera (CoolSNAP EZ, Photometrics) yielding a raw image of a 6x10mm area. Data acquisition time was about 750nm per frame (25 source points, single wavelength). A total of four rats were used in this study. For EEG control and source localization, 8 electrodes were implanted surrounding the imaging area for each rat. Anesthetized rats were mounted on a headset with ear bars and all hair on the scalp was shaved. Seizures were induced by intraperitoneal injection of pentyleneterazol (PTZ). DOT measurements made before the PTZ injection were used as calibration data and scans were conducted continuously for up to an hour after the PTZ injection, along with whole course EEG monitoring. A regularized nonlinear iterative reconstruction algorithm is applied for image recovery and analysis [C. Li et. al., 2007, App. Opt. 46:8229-8236]. Results: Figure 1 shows the reconstructed in vivo volume normalized CBF where the localized seizure focus has increased CBF (indicated by arrow). This is consistent with the general observation that epileptic seizures increase cerebral metabolism dramatically coupled with cerebral vessels dilations, while cerebral OC and CBF also increase secondary to the enhanced metabolic rate. For the reconstructed in vivo mean particle size images, significant quantitative changes over time have also been observed at the seizure focus. Conclusions: In summary, we have developed effective system and models that are capable of estimating hemoglobin change, scattering particle size and volume fraction, as well as the CBF of biological tissues.