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Quantification of the Low Field MRI Image Quality for Deformable Registration

E Boehnke

E Boehnke1*, F Han1 , P Hu1 , Y Yang1 , K Sheng2 , (1) UCLA, Los Angeles, California, (2) UCLA School of Medicine, Los Angeles, CA


TU-L-GePD-J(A)-6 (Tuesday, August 1, 2017) 1:15 PM - 1:45 PM Room: Joint Imaging-Therapy ePoster Lounge - A

Purpose: Low field MRI’s (LFMRI) are currently integrated with select radiation therapy units to offer improved soft tissue imaging in MR guided radiation therapy. A respiratory-resolved, self-gated 4D-MRI was adapted for LFMRI to additionally provide motion information. It is of significant clinical interest to evaluate the quality of LFMRI for gated and motion adaptive radiotherapy in terms of its capability of supporting accurate deformable registration and contour propagation. This study quantitatively compares deformable registration accuracy of 4DMRI at high and low field strengths.

Methods: Six abdominal 4D-MRI series (three healthy volunteers on a 1.5T scanner, and three patients on a 0.35T scanner) with 8 respiratory phases each, were used in this study. All scans were acquired with a recently published Respiratory motion resolved, self-gated 4DMRI sequence. The right kidney was manually contoured in all patients and phases. The contour from the first phase was then propagated to the following phases using demon based freeform deformable registration. The differences between the manual contours (gold standard) and the propagated contours were compared for each phase and series. A two-way ANOVA was performed to compare contour propagation discrepancy between the low and high field strengths, as well as among the different phases.

Results: The contours (1.5T/0.35T) were compared in terms of Mean Distance to Agreement, Dice score and Jaccard index (averages were MDA: 0.65mm/1.3mm, Dice: 0.97/0.93, Jaccard: 0.94/0.87). A statistically significant (p < 0.05) difference between the high and low field strengths was noted in all similarity metrics. This was likely due to the lower tissue contrast in LFMRI (CNR: 2 vs. 7).

Conclusion: The deformable registration and contour propagation accuracy of low field 4D-MRI is statistically lower than the high-field 4D-MRI but the difference is relatively small. The results warrant further investigation of deformable registration methods that are robust to imaging noise.

Funding Support, Disclosures, and Conflict of Interest: DOE DE-SC0017057 NIH R44CA183390 NIH R01CA188300 NIH R43CA183390 NIH U19AI067769

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