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Motion-Compensated Free-Breathing 3D MRI for MR Simulation Using Rotating Stack-Of-Stars Acquisition

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Z Zhou

Z Zhou*, F Han , Y Gao , M Cao , M Steinberg , P Lee , A Raldow , D Low , Y Yang , P Hu , UCLA School of Medicine, Los Angeles, CA


MO-L-GePD-I-5 (Monday, July 31, 2017) 1:15 PM - 1:45 PM Room: Imaging ePoster Lounge

Purpose: MR-based radiotherapy (RT) is gaining momentum in our field. However, due to MR’s intrinsic longer acquisition time comapred to CT, motion compensation is critical for all treatment sites. Current practice is to ask patients remain still w/wo breath-hold. This is sometimes impractical for elderly patients who cannot hold their breath or patients with involuntary movements. In this study, we developed a robust motion-compensated 3D acquisition strategy for free-breathing MR simulation.

Methods: Our method is based on a 3D stack-of-stars radial sequence. The sampling angle of each radial spoke was set to follow a continuous golden angle rotation for both in-plane and through-plane. This strategy allows the 3D k-space to be efficiently sampled, and the artifacts caused by under-sampling and motion are incoherent. A compressed sensing reconstruction algorithm was used to recover high quality artifact-free 3D images. The total acquisition time is 210s. As a feasibility study, the sequence was implemented on a 0.35T MRI-guided RT system (View-Ray) and two patients (one with malignant neoplasm on lower right limb, one with intrahepatic bile duct carcinoma) were imaged with the proposed sequence. As a comparison, a clinical free-breathing, high resolution (1.5 mm³ isotropic) Cartesian sequence (172s) was also used for the extremity patient while a breath-hold, highly-accelerated (7.5X) Cartesian sequence (25s) was used for the bile duct patient.

Results: Images acquired with the proposed radial sequence in both cases have minimal motion artifacts and provide good tumor conspicuity. However, due to involuntary motion (extremity patient) and failure to perform breath-hold (bile duct patient), images from standard Cartesian acquisition have severe artifacts making them not clinically usable.

Conclusion: A motion-compensated free-breathing 3D MR technique has been developed on an MR guide RT system. It could serve as a more robust MR simulation sequence with decreased patient discomfort and higher success rate.

Funding Support, Disclosures, and Conflict of Interest: Dr. Cao reports personal fees from ViewRay Inc., outside the submitted work. Dr. Low reports grants from Siemens Medical, during the conduct of the study. Drs. Lee and Yang report speaking honorarium from Viewray Inc.

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