During 2004-2005, research in AMRI was focused on 2 main projects: 1) the investigation of brain activity patterns during rest and sleep; and 2) the development of MRI techniques on NIH's new 7.0 T human scanner. The investigation of brain activity fluctuations during rest was a continuation of earlier research in AMRI. In the previous year, it was found that in absence of external stimuli, brain blood flow fluctuates in most brain regions. This occurs not only during awake rest, but continues during sleep. To reliably measure the cognitive state of subjects and detect sleep, a method was developed to simultaneously measure BOLD fMRI and EEG signals in the 3.0 T scanner. It was found that blood flow fluctuations occur in both awake resting conditions and stage 1 and stage 2 sleep. This suggest that these fluctuations are not caused by active cognitive processes. To establish that the blood flow fluctuations are not simply a vascular phenomenon without a neuronal component, an MRI method was developed to monitor oxygen consumption changes by simultaneously measuring perfusion and blood oxygen level using BOLD MRI. It was found that the fluctuations during sleep are caused by a metabolic process. The development of the 7.0 T human scanner involved both the optimization of signal detectors as well as development of image acquisition techniques. To optimized signal detectors, computer simulations were performed to study the interaction of electro-magnetic fields with brain tissue. Based on this, and in collaboration with Nova Medical Inc, 8 and 16-channel detectors were designed and developed. Initial measurement with these detectors show a 2-4 fold sensitivity improvement compared to conventional coil designs. These detectors are expected to greatly boost the utility of the 7.0 T system. Furthermore, the simulations and measurements suggest that even higher gains in sensitivity can be obtained with 24 or 32-channel detectors. Based on this, we have ordered addtional receiver channels for the 7.0 T system. The development of acquisition techniques has focused on the suppression of image artifacts related to magnetic susceptibility effects and magnetic field fluctuations caused by respiratory-cycle related chest motion. To reduce susceptibility artifacts, image acquisition speed was improved by using accelerated parallel imaging, which is based on the use of the spatially varying detector sensitivity information in the image acquisition process. This has led to a 2-3 fold reduction in artifact level. To reduce artifacts related to the respiratory cycle, real-time monitoring of the magnetic field was implemented, and used to correct MRI signals during post-processing. This allowed for limited improvement in MRI image quality. For further improvements, we have started a project that aims at real time field correction based on actual chest motion. For this purpose chest position is monitored during MRI acquisition, and a real-time system corrects changes in magnetic field.
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