Functional imaging of vegetative state applying Single Photon Emission Tomography and Positron Emission Tomography

Nuclear medicine techniques, such as single photon emission tomography (SPECT) and positron emission tomography (PET) have been applied in patients in a vegetative state to investigate brain function in a non invasive manner. Parameters investigated include glucose metabolism, perfusion at rest, variations of regional perfusion after stimulation, and benzodiazepine receptor reduction of glucose metabolism and perfusion. While patients post-anoxia exhibit a rather homogenous cortical reduction of glucose metabolism, patients after head trauma often show severe cortical and sub-cortical reductions at the site of primary trauma. To distinguish reduced glucose metabolism due to neuronal inactivation from neuronal loss, flumazenil-PET, and indicator of benzodiazepine receptor density, could add valuable information on the extent of brain damage. Activation studies focus on the evaluation of residual brain network, looking for processing in secondary projection fields. So far the predictive strength concerning possible recovery for the individual patient is limited, and PET und SPECT are not routine procedures in the assessment of patients in a vegetative state.