QUANTITATIVE IMAGING OF CEREBRAL BLOOD FLOW AND OXYGEN CONSUMPTION

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Cerebral blood flow and oxygen consumption can be used to investigate regional cerebral metabolism and physiology. The goals of this project are, first to develop non-invasive magnetic resonance (MR) approaches for quantitative imaging of cerebral blood flow and oxygen consumption, and, second, to apply these approaches to study regional cerebral metabolism and physiology in schizophrenic patients. Positron Emission Tomography (PET) approaches use radioactive tracers to image cerebral blood flow and oxygen consumption. MR approaches can provide the same information using MR-detectable "tracers". However, one of the problems with MR (and PET) approaches that follow the time-course of tracers in the brain is that the need for good time resolution compromises the spatial resolution of the image. This problem can be circumvented (in both MR and PET) using steady-state tracer approaches. "Arterial spin tagging" techniques provide a steady-state MR tracer approach for imaging cerebral blood flow. Our initial spin tagging experiments with cats demonstrated a number of theoretical and technical problems. One of the most important problems was the need for fast acquisition of the arterial spin tagging images. We have now involved this problem using single-shot echo planar imaging (EPI), and have extended the arterial spin tagging approach to humans. Initial studies indicate that, using EPI version of arterial spin tagging approaches, quantitative cerebral blood flow images with a voxel size of ? cc can be obtained in approximately 15 minutes. Optimization of the approach, using higher magnetic field strengths and different data acquisition paradigms, should reduce this imaging time significantly.