Functional brain imaging.

Abstract

Recent advances in brain imaging have allowed a regional examination of brain function using multiple-probe inert gas studies of cerebral blood flow, positron or single photon tomography. Inert gas blood flow methods using inhalation or injection of 133xenon have been used with multiple-probe systems to measure blood flow in 1 to 2 cm regions of lateral cortex. The sensitivity of these systems to neurophysiological stimuli and neurological diseases have been demonstrated in numerous studies of the normal resting state, memory and learning, motor activity and sensory input, dementia, and aphasia, to name some. Positron tomography utilizes cyclotron-produced, short-lived positron-emitting isotopes to label biologically active radiopharmaceuticals. Using positron tomographs capable of quantitative three-dimensional imaging and appropriate tracer-kinetic models, regional metabolic function, including glucose, oxygen, amino acid metabolism, and receptor-binding can be regionally studied throughout the brain. Clinical studies have been performed in dementia, schizophrenia, affective disorders, resting states, and sensory stimulation. Positron tomography offers potentially the greatest variety of studies and highest temporal and spatial resolution of any of the presently available functional brain-imaging modalities. Its principal drawback is the very high cost. Single photon tomography uses gamma-emitting isotopes such as 123iodine and 133xenon to image regional cerebral blood flow and recently receptor function. Although at present it does not have the variety of studies or the technical capabilities of positron tomography, it does provide three-dimensional studies with 1 to 2 cm resolutions throughout the brain at a considerably lower cost than positron tomography. In the future, magnetic resonance studies of blood flow or phosphorus metabolism may add a fourth modality.