A method for correcting breathing‐induced field fluctuations in T2*‐weighted spinal cord imaging using a respiratory trace

Abstract

Purpose Spinal cord MRI at ultrahigh field is hampered by time‐varying magnetic fields associated with the breathing cycle, giving rise to ghosting artifacts in multi‐shot acquisitions. Here, we suggest a correction approach based on linking the signal from a respiratory bellows to field changes inside the spinal cord. The information is used to correct the data at the image reconstruction level. Methods The correction was demonstrated in the context of multi‐shot T2*‐weighted imaging of the cervical spinal cord at 7T. A respiratory trace was acquired during a high‐resolution multi‐echo gradient‐echo sequence, used for structural imaging and quantitative T2* mapping, and a multi‐shot EPI time series, as would be suitable for fMRI. The coupling between the trace and the breathing‐induced fields was determined by a short calibration scan in each individual. Images were reconstructed with and without trace‐based correction. Results In the multi‐echo acquisition, breathing‐induced fields caused severe ghosting in images with long TE, which led to a systematic underestimation of T2* in the spinal cord. The trace‐based correction reduced the ghosting and increased the estimated T2* values. Breathing‐related ghosting was also observed in the multi‐shot EPI images. The correction largely removed the ghosting, thereby improving the temporal signal‐to‐noise ratio of the time series. Conclusions Trace‐based retrospective correction of breathing‐induced field variations can reduce ghosting and improve quantitative metrics in multi‐shot structural and functional T2*‐weighted imaging of the spinal cord. The method is straightforward to implement and does not rely on sequence modifications or additional hardware beyond a respiratory bellows.

Quantitative T1 mapping using multi-slice multi-shot inversion recovery EPI

“…Since multi-shot EPI acquisitions are sensitive to dynamic B 0 -field fluctuations between shots, correction methods using NMR field probes can potentially improve the quality of multi-shot EPI data. A recent method has been proposed to improve image quality and quantitative metrics in multi-shot T 2 *-weighted imaging by retrospectively correcting for respiration induced B 0 -fluctuations with a respiratory trace ( Vannesjo et al., 2019 ).…”

Traumatic and nontraumatic spinal cord injury: pathological insights from neuroimaging

“…On the acquisition side, several improvements have been introduced, such as new receive coil designs for spinal cord 78 , new generation MR systems with stronger diffusion-imaging gradients 79 , or ultra-high field MRI 80 , aiming to maximize signal-tonoise ratio and resolution. Other techniques including tailored pulse sequences for the spinal cord 81 , dynamic 82 and real-time shimming 83 , or retrospective correction for field fluctuations 84 attempt to minimize distortions and other respiratory-related artifacts in DTI.…”

Combining Navigator and Optical Prospective Motion Correction for High-Quality 500 μm Resolution Quantitative Multi-Parameter Mapping at 7T

“…Its potential for resolving thin intra-cortical layers and U-fibers has been demonstrated (6,12,13) but remains limited due to physiological artifacts. Dynamic B0-fluctuation correction has been mainly exploited for acquisitions particularly vulnerable to B0 variations due to long echo times, such as T2*-weighted imaging and mapping (22,63,64), including susceptibility weighted imaging (SWI) and quantitative susceptibility mapping (QSM) (65).…”