Magnetic Resonance Imaging Technology Development

National Institute Of Neurological Disorders And Stroke

Investigators

Linked publications, trials & patents

Abstract

We have continued developing technology for RF transmission at high field strength. Specifically, over the last year, we have further developed technology based on voltage-controlled current source amplification integrated with the transmit conductor. This technology is being developed at 7 T with the goal of using it at the 11.7 T system that is expected to come on-line in 2018. This low-cost technology allows improved control over the RF field strength and tissue heating across the brain, which are crucial issues at 11.7 T. During 2017, we have developed and tested a novel 4-channel prototype with a fiber-optic interface and integrated feature to perform a controlled, rapid system shutdown in case of potential tissue over-heating. Excellent performance was observed, and at 7 T, a B1 field strength of 6 microT was achieved. This is in-line with a target field strength of 20 microT for a 16-channel version that will ultimately be built for 11.7 T. Prior to that development, additional improvements will be made to the amplifier in order to minimize cabling and amplifier/interface footprint. In a second project, we have investigated the effect of spatial resolution on fMRI performance. This was done in the context of characterizing the neural representation of movie stimuli, and specifically differences the spatial distribution of brain activity patterns. Somewhat surprisingly, it was found that the highest (1mm) resolution was sub-optimal: rather, both the acquisition at 2 mm resolution, and the post-acquisition blurring to 2 mm effective resolution were found to better allow stimulus discrimination based on activity patterns. This is attributed to the reduced signal-to-noise ratio and increased sensitivity to head motion of high resolution fMRI data. A report of this work has been submitted and is currently under journal review. In a third project, we have explored ways to reduce motion sensitivity in susceptibility weighted MRI. While susceptibility weighted MRI is finding increasing clinical application, and is particularly promising at high field, its motion sensitivity renders image quality unreliable. We are investigating the origin of this motion sensitivity with the goal of developing remediation strategies. So far, we have found that head motion causes a complex change in the magnetic field that results from and interaction from the (static) field patterns of the body and the magnet shims on one hand, and the (head motion dependent) pattern originating from the magnetization of the head. We are currently trying to use reference signals to separate these contributions, with the ultimate goal of being able to correct from motion effects on the quality of susceptibility weighted MRI. Two abstracts of this work were presented at the 2017 ISMRM scientific meeting.