Magnetic Resonance Imaging Technology Development

National Institute Of Neurological Disorders And Stroke

Investigators

Linked publications, trials & patents

Abstract

As part of its efforts to improve MRI methodology, the AMRI section at NINDS carries the main responsibility for the development of NIHs 11.7T human MRI scanner, a uniquely powerful system that will allow in-vivo neuroimaging with unprecedented clarity. Over the last year, AMRI has continued preparation for re-installation of the 11.7T human MRI system, which got first delayed because of the COVID-19 crisis, followed in January 2022 by the Helium crisis. This has led us to postpone the energization of the magnet. Together with the clinical trials unit at NINDS, AMRI has continued to plan for the scanning of human subjects at 11.7T. This requires obtaining an investigational device exemption (IDE) from the FDA. Our initial draft proposal for this IDE was reviewed by the FDA and came back with significant comments regarding cognitive testing of human subjects, as well as the proper control of tissue heating by the RF transmission required for MRI. We have further worked on this cognitive testing plan, and have collaborated with scientists of the Engineering Core (EC) in LFMI/NINDS to evaluate tissue heating. On human head mimicking phantoms, we were able to achieve good correspondence between measured heating, and heating predicted with RF field simulations. Together with EC, we have also continued developing RF transmission and detection hardware for operation at 11.7T. Over the years, AMRI has played a substantial role in developing high field MRI systems, and has contributed to developing 7T detector and signal acquisition technology to improve sensitivity. Current 7T MRI scanners (of which 3 are in the NMR center at NIH) are uniquely sensitive to brain iron and myelin, both of which are important indicators of neurodegeneration. Together with TNU of Danny Reich, AMRI has worked to develop robust iron and myelin measurement techniques to characterize brain lesions in multiple sclerosis. Previously AMRI developed a unique approach to render MRI robust in the presence of head motion. The approach simultaneously corrects for spatial encoding errors associated with head motion as well as accompanying magnetic field changes. Over the last year, we demonstrated the effectiveness of this approach for lesion detection and visualization in MS patients. Applications based on this work were published in NMR in Biomedicine and Multiple Sclerosis. MRI measurement of brain perfusion is another application that benefits strongly from high field, potentially allowing spatial resolutions that resolve the cortical ribbon (<<2mm). This is important because perfusion, and its change with brain activity, is predominantly localized to grey matter. Perfusion MRI furthermore allows the detection of brain activity with superior spatial fidelity compared to conventional techniques based on blood oxygen level dependent (BOLD) contrast. To overcome its inferior sensitivity relative to BOLD fMRI, we implemented a background-suppressed perfusion technique that improves sensitivity by two-fold. Evaluation of normal human volunteers showed competitive performance relative to BOLD fMRI at 2mm resolution, but a loss in sensitivity at 1mm resolution. This was only recoverable when increasing scan time by 3-fold. Therefore, the practical resolution limit for perfusion MRI is about 2mm.