Reverse retrospective motion correction

Abstract

Purpose One potential barrier for using Prospective Motion Correction (PMC) in the clinic is the unpredictable nature of a scan because of the direct interference with the imaging sequence. We demonstrate that a second set of “de-corrected” images can be reconstructed from a scan with PMC that show how images would have appeared without PMC enabled. Theory and Methods For 3D scans, the effects of PMC can be undone by performing a retrospective reconstruction based on the inverse of the transformation matrix used for real time gradient feedback. Retrospective reconstruction is performed using a generalized SENSE approach with continuous head motion monitored using a single-marker optical camera system. Results Reverse retrospective reconstruction is demonstrated for phantom and in vivo scans using an magnetization-prepared rapid gradient echo (MPRAGE) sequence including parallel and Partial Fourier acceleration. Conclusion Reverse retrospective reconstruction can almost perfectly undo the effects of prospective feedback, and thereby provide a second image data set with the effects of motion correction removed. In case of correct feedback, one can directly compare the quality of the corrected with that of the uncorrected scan. Additionally, since erroneous feedback during PMC may introduce artifacts, it is possible to eliminate artifacts in a corrupted scan by reversing the false gradient updates.

Prospective motion correction enables highest resolution time‐of‐flight angiography at 7T

“…Also, compressed sensing (53,54); Controlled Aliasing in Parallel Imaging Results in Higher Acceleration (32); or multiband, multislice imaging (55) could further decrease the scan duration. Potential residual motion artifacts due to large motion (gradient and static magnetic field inhomogeneity, relative changes in coil sensitivity profiles) or imperfect motion correction (crosscalibration errors, latency, pseudo motion) could be addressed retrospectively (35,(56)(57)(58)(59). In less experienced cohorts, large motion could increase residual artifacts due to, for example, relative changes in the receiver sensitivity profiles or gradient nonlinearities, which cannot be corrected by PMC.…”

Prospective motion correction in functional MRI

“…One of the more irksome practical problems is that no “uncorrected” images can be extracted from an experiment if data were acquired with prospective correction. Although an approximation of undoing the effects of prospective correction has been recently proposed (Zahneisen et al, 2016) it can only be used for demonstration purposes and is not relevant to typical fMRI protocols. Therefore, a major constraint exists in performing validation studies, as separate runs are required for scans with and without prospective motion correction, whereas the conditions involving involuntarily motions are not reproducible by definition.…”

Motion correction in MRI of the brain

“…Reverting to uncorrected data is not possible. However, the corrected data may be ‘de-corrected’ by reverse retrospective reconstruction (Zahneisen et al 2015). Higher order effects such as changing B 0 inhomogeneities and gradient imperfections cannot be corrected by PMC.…”