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Comparison of free-breathing motion-resolved radial imaging with standard breath-hold imaging on liver MRI: a feasibility study1Department of Radiology, Memorial Sloan Kettering Cancer Center, New York, NY, United States, 2Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, NY, United States, 3GE Healthcare, Waukesha, WI, United States
Synopsis
Respiratory motion remains a major challenge in clinical abdominal MRI. Recent technical advances using continuous radial imaging during free-breathing and motion-resolved compressed sensing-based image reconstruction have demonstrated improvements in motion robustness over conventional motion-gated or motion-corrected techniques, but they were not validated for liver imaging. This work implemented extra-dimensional (XD) reconstruction for free-breathing RadialLAVA acquisitions and compared it against conventional breath-held CartesianLAVA. We demonstrate that the XD technique matches that, and in some instances, is superior to that of standard breath-hold technique in terms of overall image quality in the evaluation of post-contrast liver images.
INTRODUCTION
MRI is an essential clinical tool in the detection and characterization of liver lesions, but image quality on post-contrast T1 weighed imaging is dependent on patient cooperation and their breath-holding capabilities, especially in unwell patients, as well as the elderly and pediatric population (1). Recent technical advances using continuous free-breathing radial imaging and compressed sensing-based motion-resolved image reconstruction, such as XD-GRASP (2), have demonstrated significant improvements in motion robustness over navigators or registration techniques. However, they have not been validated against routine clinical techniques for liver MRI. In this work, we have implemented the XD-GRASP reconstruction approach for Radial Liver Advanced Volumetric Acceleration (RadialLAVA) acquisitions for free-breathing liver imaging and compared it against routine breath-held LAVA in terms of motion robustness on patients undergoing imaging of the liver.METHODS
Patient population: This HIPAA-compliant prospective single institution study was performed after obtaining approval from our institutional review board. Five patients who were undergoing routine liver imaging as part of disease surveillance were recruited.
Data acquisition: Data were acquired on a 3T MRI scanner (MR750w, GE Healthcare) after contrast injection during the delayed phase. Breath-held Cartesian LAVA (BHLAVA) was performed during a breath-hold of ~20 seconds with a voxel size of 1.125x1.125x3mm3. Free-breathing RadialLAVA (3) was performed using 600 spokes with a voxel size of 1.4x1.4x3mm3 in 4 patients (scan time = 90 seconds) and 1.125x1.125x3mm3 in 1 patient (scan time = 110 seconds).
Image reconstruction: BHLAVA data were reconstructed online on the scanner and free-breathing RadialLAVA data were reconstructed using the XD-GRASP approach (2). With a respiratory signal extracted directly from the data, radial k-space were sorted into 4 undersampled respiratory states and temporal multicoil compressed sensing reconstruction was performed on the 4D data (3D+respiratory dimension) – see Figure 1. XDRadialLAVA images from the end-expiration phase were employed for comparison to BHLAVA.
Image evaluation: Two radiologists with 10 and 2 years of abdominal MRI experience respectively evaluated the images and scored each patient MRI for overall image quality, liver edge sharpness, hepatic vessel clarity and the presence of motion artifact. If a lesion was present, the lesion was also scored on conspicuity and edge sharpness. Each parameter was scored on a scale of 1 to 5, with the highest score reflecting optimal image quality.
RESULTS
In all patients, images reconstructed with the XDRadialLAVA technique were scored as either good or excellent in terms of overall image quality and clarity. In one case, XDRadialLAVA performed better than the standard breath-hold LAVA in terms of image quality and clarity as scored by both radiologists. One radiologist felt that the overall image quality of XDRadialLAVA was superior to breath-hold LAVA in an additional two cases. The second radiologist rated both these cases as comparable in terms of image quality but rated XDRadialLAVA above breath hold LAVA for liver edge sharpness and vessel clarity in one of these cases. The presence of motion artifact was rated as comparable in two subjects. Both radiologists agreed that there was more motion artifact on free-breathing XDRadialLAVA than the breath hold LAVA in one case, however overall image quality and clarity remained equal between the two sequences. In one case, one reader rated breath hold LAVA to have more motion artifact than XDRadialLAVA, the second reader felt the artifact was comparable. Liver lesions were detected in two subjects. Lesion conspicuity and edge sharpness were comparable on both sequences, with both radiologists in agreement.DISCUSSION
We demonstrate that image quality from XDRadialLAVA, a continuous motion-resolved radial MRI technique performed during free-breathing, is equivalent to, and in some instances superior to, standard breath-hold techniques on post-contrast imaging of the liver in a small cohort of patients. Further studies with a larger patient population are required to build on these findings. A potential positive clinical impact from this technique may be seen in improved image quality of patients undergoing abdominal imaging who have limited breath-holding capabilities.Acknowledgements
NoneReferences
1. Korin HW, Ehman RL, Riederer SJ, Felmlee JP, Grimm RC. Respiratory kinematics of the upper abdominal organs: a quantitative study. Magn Reson Med. 1992;23(1):172-8.
2. Feng L, Axel L, Chandarana H, Block KT, Sodickson DK, Otazo R. XD-GRASP: Golden-angle radial MRI with reconstruction of extra motion-state dimensions using compressed sensing. Magn Reson Med. 2016;75(2):775-88.
3. Zhang T, Wang K, Fisher, Bayram E, Fast motion robust abdominal stack of stars imaging using coil compression and soft gating. ISMRM; 2017; Hawaii.
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