Date(s) - 04/01/2014
Epilepsy is a most common serious brain disease, of which, however, the understanding is limited. In epileptic seizures, intensive hemodynamic changes are induced as a result of the synchronized electrical discharges from groups of neurons in the brain, and there is a growing trend to detect these hemodynamic changes for epilepsy diagnosis. Compared to other existing hemodynamic detection methods, photoacoustics features the vascular imaging and hemodyamic signal tracking in small animal brains, thus is a promising tool for epilepsy research on small animals.
We here present a real-time three-dimensional (3D) photoacoustic system for the study of epilepsy in small animals. The system is based on a spherical array containing 192 transducers with a 5MHz central frequency, offering an isotropic resolution about 0.2mm. With the 64-channel data acquisition system and the 10Hz laser, it can record a complete set of 3D data in 0.3s. Phantom experiments and in-vivo experiments were conducted to demonstrate the high imaging quality and real time imaging ability of the system.
Neurovascular coupling in generalized seizures was studied using the proposed system with simultaneous electroencephalography (EEG). Two groups of rats were imaged with two different wavelengths for the signals of oxy-hemoglobin (HbO2) and deoxy-hemoglobin (HbR) respectively. Hemodynamic changes in different regions of the brain are extracted and analyzed with correlation and Granger Causality methods. Study shows that the change of HbR is less significant than that of the HbO2 during the seizure, and hyperoxygenation were concentrated around the hippocampus following the seizure onset. It is also noticed that the hemodynamic connections between different brain regions were found to be closer as the seizure evolved.
To study the neuro-hemodynamic activities in seizure in freely moving rats, we built a photoacoustic sensor with EEG electrodes that can be attached on the rat head. Experiments showed that both the neural and vascular responses to seizure in freely moving rats have characteristics, which are observed to be different and more diverse from that of anesthetized rats, and this calls for more detailed study in future. This technology also promises for other hemodynamic related research study in freely moving small animals.