Real‐time distortion correction of spiral and echo planar images using the gradient system impulse response function

Abstract

Purpose MRI-guided interventions demand high frame-rate imaging, making fast imaging techniques such as spiral imaging and echo planar imaging (EPI) appealing. In this study, we implemented a real-time distortion correction framework to enable the use of these fast acquisitions for interventional MRI. Methods Distortions caused by gradient waveform inaccuracies were corrected using the gradient impulse response function (GIRF), which was measured by standard equipment and saved as a calibration file on the host computer. This file was used at runtime to calculate the predicted k-space trajectories for image reconstruction. Additionally, the off-resonance reconstruction frequency was modified in real-time to interactively de-blur spiral images. Results Real-time distortion correction for arbitrary image orientations was achieved in phantoms and healthy human volunteers. The GIRF predicted k-space trajectories matched measured k-space trajectories closely for spiral imaging. Spiral and EPI image distortion was visibly improved using the GIRF predicted trajectories. The GIRF calibration file showed no systematic drift in 4 months and was demonstrated to correct distortions after 30 minutes of continuous scanning despite gradient heating. Interactive off-resonance reconstruction was used to sharpen anatomical boundaries during continuous imaging. Conclusions This real-time distortion correction framework will enable the use of these high frame-rate imaging methods for MRI-guided interventions.

Correction of B0 eddy current effects in spiral MRI

“…It is possible to instead measure the response of the gradient system to any gradient waveform input . This one time measurement can then be used to predict the eddy current behavior of any acquisition.…”

“…The measurement and correction of both linear and B 0 eddy currents for spiral imaging was previously addressed using a response function based on field probe measurements . A phantom‐based system response measurement, that eliminated the need for additional hardware, was previously used to address linear eddy currents in spiral imaging . However, this approach did not address B 0 eddy currents.…”

Real‐time MRI guidance of cardiac interventions

“…Real-time distortion correction 50 can improve image quality to make application of these techniques in the interventional environment feasible. Iterative parallel imaging reconstructions can be used to achieve fast reconstruction of undersampled non-Cartesian data.…”

Magnetic Resonance Sequences and Rapid Acquisition for MR-Guided Interventions

“…Unfortunately, these additional measurements are impractical in the interventional MR imaging setting. Recently, the gradient system impulse response function (GIRF) has been demonstrated for predicting true gradient waveforms from the nominal waveforms prescribed in the pulse sequence 78 , and a real-time framework using GIRF trajectory correction and interactive off-resonance reconstruction for de-blurring has been applied for distortion correction of spiral images 79 .…”