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Respiratory Motion-Resolved, Self-Gated 4D-MRI Using Rotating Cartesian K-Space (ROCK): Initial Clinical Experience On An MRI-Guided Radiotherapy System

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F Han

F Han1*, Z Zhou1 , D Du2 , Y Gao1 , M Cao2 , N Shaverdian2 , J Hegde2 , M Steinberg2 , P Lee2 , A Raldow2 , D Low2 , K Sheng2 , Y Yang2 , P Hu1 , (1) Department of Radiology, University of California, Los Angeles (2) Department of Radiation Oncology, University of California, Los Angeles


TU-D-601-5 (Tuesday, August 1, 2017) 11:00 AM - 12:15 PM Room: 601

Purpose: Respiratory motion-resolved 4D-MRI provides superior soft-tissue contrast and accurate respiratory motion information for radiotherapy. However, the clinical utility of 4D-MRI is limited primarily because most techniques were developed on diagnostic MRI systems and required prolonged off-line image reconstruction. In this study, we optimize our previously proposed self-gated 4D-MRI using 3D Rotating Cartesian K-space (ROCK-4D-MRI) method in the Viewray 0.35T MRI-guided radiotherapy (MRgRT) system and evaluate its performance in phantoms and patients.

Methods: The ROCK-4D-MRI sequence were optimized to compensate for the SNR loss in 0.35T. An in-line image reconstruction system was implemented, which is integrated with the MRgRT and capable of reconstructing the 4D-image in 10 minutes. The optimized ROCK-4D-MRI was validated in static and dynamic phantoms for geometric integrity and motion quantification. The in-vivo study included seven patients with abdominal tumors treated on the MRgRT system. The MRI exam, including ROCK-4D-MRI and 2D-CINE, was performed immediately after one treatment fraction. Motion quantification were measured and compared between 4D-MRI and 2D-CINE. The subjective image quality of 4D-MRI was evaluated against 4D-CT on a 4-point scale. The tumor volumes were defined on both 4D-MRI and 4D-CT and compared for variability in different respiratory phases.

Results: The ROCK-4D-MRI provided high-resolution (1.3x1.3x1.8mm³) 4D images with superior soft-tissue contrast and less motion artifacts than 4D-CT. The 4D-MRI motion measurements matched well with those based on 2D-CINE, with differences of 1.04±0.52mm in superior-inferior and 0.54±0.21mm in anterior-posterior directions. The image quality scores of 4D-MRI were significantly higher than 4D-CT (3.14±0.89 vs. 1.71±0.95, p=0.025). The tumor volumes were more consistent in 4D-MRI than in 4D-CT, with significantly smaller variability (9.31±4.58% vs. 34.27±23.33%, p=0.022).

Conclusion: Our study demonstrated the clinical feasibility of performing the ROCK-4D-MRI in an MRgRT system. The acquired high-quality 4D-MRI image could provide accurate spatial and dynamic information within the abdomen for radiotherapy.

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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