A Fast and Reliable Eddy Current Measurement Method in Portable Low-Field MRI

Portable permanent low-field magnetic resonance imaging (MRI) is gaining increasing attention due to its low cost, safer scanning, and broad range of applications, such as emergency. However, frequent relocation of portable systems may alter their eddy current performances, which can degrade image quality unless timely recalibration is performed. Conventional eddy current measurement method relies on image-phase analysis and typically require several hours in low-field MRI due to low signal-to-noise ratios (SNR). In this work, a fast eddy current measurement method using field probes, which consists of an array of six1H probes, is presented. The acquisition time was reduced by a factor of 100, from 9 hours to 5 minutes, while successfully reducing residual eddy currents to within ± 0.03% of the applied gradient amplitude over whole measurement. To overcome the poor SNR, the probe size was increased by leveraging the reduced susceptibility effects in low-field. Measurement sequences were optimized to address challenges such as field inhomogeneity and residual magnetism effects in low-field. Gradient pre-emphasis parameters were adjusted according to the derived eddy current parameters. To evaluate correction efficiency, phantom and volunteer experiments were conducted by acquiring eddy current maps, fast spin-echo, and diffusion-weighted echo-planar imaging images. It was found that corrections obtained using the field probe method outperformed those obtained by image-phase based method within the same measurement iterations, providing more stable reduction of eddy-current-induced artifacts. These results demonstrate the potential of the proposed method as a reliable timely solution for eddy currents correction in portable permanent low-field MRI.