A comparison study of different eddy current measurements at low field portable MRI

Motivation: Eddy current results in resolution degradation and unwanted phase variations. However, there have been relatively few eddy-current related studies carried out in low field recently. Goal(s): Our goal was to introduce and compare image-phase based and FID-phase based eddy current measurement techniques in a 64mT MRI system and reduced eddy-current effects. Approach: We employed a large phantom or six field probes to measure eddy-current-induced gradients shift. And we modeled them as sums of exponentially decaying components to compensate the gradient unit. Results: Eddy-current-induced field shift was initially about 350ppm, and reduced to 240ppm and 20ppm by these two methods. Impact: This work develops two methods for measuring eddy current in low-field MRI, especially for portable scanner, which help reducing eddy-current-induced effects and improving the image quality of clinical sequence (e.g. DWI, DTI) in low field scanner.