Imaging neurochemistry of cerebrovascular disease with PET and SPECT.

Pathophysiology of cerebrovascular disease has been studied by measuring cerebral blood flow and energy metabolism using single photon emission computed tomography (SPECT) and positron emission tomography (PET). These parameters are measures for brain tissue consisting of heterogeneous components such as neurons, glial cells, and blood vessels. It is still difficult to evaluate brain damages specifically involving either neurons or other components. Several trials were recently conducted to visualize neuron-specific injury in cerebrovascular disease by means of 11C flumazenil for PET and 123I-iomazenil for SPECT. These tracers selectively bind to central benzodiazepine receptor which is purely neuronal. A reduced accumulation of these ligands was found in the area surrounding the complete infarction and in the cortex remote from putaminal hemorrhage, indicating the existence of neuron specific injury not visualized by CT and MR. Neurological deficits were well correlated with the loss of cortical accumulation of these ligands. These preliminary studies indicated a potential of neurochemical imaging in cerebrovascular disease. Vulnerability to ischemia which may differ among brain tissue components, among subpopulations of neurons, and among pre-synaptic and post-synaptic functions can be more precisely examined. Neurochemical imaging can be also applied to reveal releases and re-organization of each neurotransmitter-acceptor system after stroke.