Program Information
Analysis of Temporal Patient-Specific MR Distortions:A Per-Organ Assessment
S Nejad-Davarani1*, S Weiss2 , P Sevak1 , S Renisch2 , C Glide-Hurst1 , (1) Henry Ford Health System, Detroit, MI, (2) Philips GmbH Innovative Technologies, Hamburg, Germany
Presentations
TU-D-FS4-6 (Tuesday, August 1, 2017) 11:00 AM - 12:15 PM Room: Four Seasons 4
Purpose: As we move toward MR-only patient models for treatment planning, a need exists to fully quantify distortions. However, the stability of patient-level distortion corrections is not currently known for changing anatomy (e.g., bladder/rectal filling), particularly over long MRI acquisitions. This work quantifies organ-specific distortions and explores the need for temporal corrections in pelvis.
Methods: Nine healthy male volunteers were scanned for 3-6 timepoints/subject (34 timepoints) at 1T, 1.5T and 3T following a fixed bladder filling protocol. At each timepoint, T2-weighted images (delineation) and dual-echo gradient-recalled echo images (B0-mapping) were acquired. Distortion maps were generated from B0 field maps based on bandwidth and T2-weighted acquisition pixel size. Prostate, seminal vesicles (SVs), bladder, rectum, and penile bulb were delineated by a physician to assess distortions on an organ-by-organ basis. To quantify temporal local distortion changes due to filling, distortion difference maps were generated and segmented by organ. Magnet stability was assessed.
Results: Baseline organ-specific distortions [P5, P95] in full bladder conditions were as follows: [-0.61, 0.4] mm for prostate, [-0.38, 0.37] mm for bladder, [-0.66, 0.65] mm for rectum, and [-0.16, 0.33] mm for seminal vesicles. To evaluate local target regions, CTV-PTV ring distortions were [-0.61, 0.52] mm. Assessment of temporal displacement maps (full to empty bladder) revealed that patient-specific distortions changed <±0.5 mm for 99% of voxels in bladder, prostate, and SVs. In rectum, ~5% of voxels displaced >0.5 mm. In the CTV-PTV ring, only 1% of voxels displaced >0.5 mm. Magnets were stable over the imaging sessions (-0.10 to 0.16 mm).
Conclusion: Temporal patient-specific distortion changes for pelvic organs were <1mm for >99% of all voxels. Distortions were larger near air-filled organs, suggesting that bladder/bowel preparation is warranted for MR-only pelvis planning. Results suggest the magnitude may be larger in anatomies with higher tissue/air ratios (e.g., head and neck).
Funding Support, Disclosures, and Conflict of Interest: Research supported by the National Cancer Institute of the National Institutes of Health under Award Number R01CA204189. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH. C. Glide-Hurst acknowledges funding from HFHS Internal Mentored Grant and Philips Healthcare.
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