High-Performance Gradient Coil for 7 Tesla MRI

Massachusetts General Hospital, Boston MA

Investigators

Abstract

PROJECT SUMMARY/ABSTRACT This application seeks to upgrade an existing 7 Tesla human MRI scanner at the Athinoula A. Martinos Center for Biomedical Imaging. The proposed upgrade consists of newly available high-performance head gradient coil, the most powerful of its kind—with maximum slewrate of 700 T/m/s and strength of 200 mT/m, more than twice that of the most advanced gradient coils in regular use today. This innovative gradient coil, the "Impulse", was designed exclusively for 7T by Siemens with input from Martinos investigators, and has overcome the performance limits of previous-generation gradient coils. It is currently in use only at one 7T site (UC Berkeley). The key advantage provided by this gradient coil’s added performance is faster image encoding for brain imaging. This can be utilized to improve image quality in many techniques, in particular echo planar imaging (EPI), which is the workhorse method for functional imaging studies as well as diffusion, and perfusion MR imaging. The higher performance will help reduce artifacts such as distortion and blurring, which are present in EPI at these higher magnetic field strengths, and thereby enhance data quality for a broad range of applications. The faster imaging speeds can also provide the necessary encoding for high-resolution functional MRI (fMRI) within the limited time-window afforded by T2* signal decay. Although 7T provides a substantial boost in fMRI sensitivity, and mounting evidence indicates that the intrinsic biological resolution of fMRI is well below the millimeter scale, existing hardware platforms cannot achieve the imaging resolution desired for many experiments—thus today, 7T fMRI is known to be “encoding limited”. This gradient coil will help surpass these encoding limits to help reap the full potential of 7T fMRI. The high gradient strength combined with the high slew rate of this gradient coil will also help enable diffusion MRI at 7T by reducing both the diffusion encoding duration and image encoding times, which is typically challenged by rapid T2 decay at ultra-high field. The high slew rate will also boost performance of advanced anatomical imaging methods like our “wave-CAIPI” method that can achieve even higher acceleration factors with faster slew rates for high-resolution anatomical imaging. The Martinos Center has vast experience with similar previous-generation head gradient coils. We have the technical expertise to optimize performance of this powerful new gradient coil, and a team of engineers to support the instrument and develop—and invent—new applications. Overall, this proposed upgrade will benefit the broad user base within the Martinos Center and the many affiliated researchers within the Boston area who use our facilities, providing investigators with a technological edge required for innovative clinical, translational, and basic research. This exciting technology will enable new experiments and thus will likely generate new funding support, and attract talented developers and new investigators. Finally, the success of this instrumentation upgrade will help pave the way for other PHS-funded research centers to adopt this next- generation gradient coil and help launch a community of researchers using this transformative new technology.