Free-breathing pediatric MRI with nonrigid motion correction and acceleration

Abstract

Purpose To develop and assess motion correction techniques for high-resolution pediatric abdominal volumetric MR images acquired free breathing with high scan efficiency. Materials and Methods First, variable-density sampling and radial-like phase-encode ordering are incorporated into the 3D Cartesian acquisition. Second, intrinsic multi-channel Butterfly navigators are used to measure respiratory motion. Lastly, these estimates are applied for both motion-weighted data-consistency in a compressed sensing and parallel imaging reconstruction, and for nonrigid motion correction using a localized autofocusing framework. With Institutional Review Board approval and informed consent/assent, studies were performed on 22 consecutive pediatric patients. Two radiologists independently scored the images for overall image quality, degree of motion artifacts, and sharpness of hepatic vessels and the diaphragm. The results are assessed using paired Wilcoxon test and weighted kappa coefficient for inter-observer agreements. Results The complete procedure yielded significantly better overall image quality (mean score of 4.7 out of 5) when compared to using no correction (mean score of 3.4, P value < 0.05) and to using motion-weighted accelerated imaging (mean score of 3.9, P value < 0.05). With an average scan time of 28 s, the proposed method resulted in comparable image quality to conventional prospective respiratory-triggered acquisitions with an average scan time of 91 s (mean score of 4.5). Conclusion With the proposed methods, diagnosable high-resolution abdominal volumetric scans can be obtained from free breathing data acquisitions.

Compressed sensing for body MRI

“…The non-rigid motion can also be approximated as localized linear translations, and a method called localized autofocusing has been proposed for respiratory motion correction by applying the appropriate linear-phase correction in k-space (72). This imaging technique has been demonstrated in free-breathing pediatric imaging in sedated patients where respiration patterns are largely predictable (64). Some approaches, such as motion-guided L+S reconstruction (73), are able to learn the motion fields to guide the image reconstruction, not only correcting for motion but also providing access to motion information.…”

“…The sparse imaging techniques described in the previous section have been applied for a number of clinical applications in body MRI, in order to increase imaging speed and improve performance (61,64,75–86). These studies include accelerated 3D abdominal MRI, free-breathing DCE-MRI, abdominal 4D flow imaging.…”

Sparse Reconstruction Techniques in Magnetic Resonance Imaging

“…Children have particular difficulty in providing the long breath-holds required; these patients are scared and often sedated or anesthetized. Thus application to pediatric abdominal imaging is one of the first areas where early application of sparse reconstructions such as compressed sensing has been particularly promising, for improved delineation of key structures in the abdomen with significantly shortened acquisition times 14,20,79,139,140 .…”

Clinical performance of a free-breathing spatiotemporally accelerated 3-D time-resolved contrast-enhanced pediatric abdominal MR angiography

“…For each free-breathing MR angiography dataset, respiratory motion in the superior/inferior direction was calculated and assumed to be the dominant motion. Soft-gating weights were calculated based on the estimated motion and applied to the acquired data for motion compensation [37]. Soft gating effectively reduces motion artifacts by assigning a motion-weighted data consistency in the reconstruction: k-space data with very little motion corruption were assumed to be motion-free and assigned to a weighting of 1; k-space data with significant motion corruption were assigned to a weighting close to zero.…”

“…Respiratory triggering/gating can achieve good image quality, but the spatiotemporal resolution is usually reduced by at least three-fold compared to breath-holding acquisition [30]. Free-breathing acquisition with advanced retrospective motion compensation, including respiratory binning and soft gating, can achieve higher scan efficiency and image quality comparable to respiratory-triggered acquisition [31–37]. Acquisition trajectory can also be modified to mitigate motion artifacts [38–41].…”