(Wednesday, 8/1/2018) 7:30 AM - 9:30 AM
Room: Room 202
Purpose: Gastrointestinal (GI) motion such as peristalsis and segmental contractions can alter shape and position of stomach and intestines with respect to other organs during radiation therapy. However, these GI deformations are concealed by respiratory 4D MRI techniques. We present a method to reconstruct breathing-compensated images showing the phases of GI motion.
Methods: Fourteen DCE-MRI examinations were performed with a 3D golden-angle stack-of-stars gradient-echo sequence as part of a pilot study of individualized adaptive radiation therapy. Each scan collected 2000 radial spokes that were reconstructed into a time series of 3D images with high temporal but low spatial resolution. From this series, a respiratory motion signal was extracted indicating the superior-inferior movement of the liver, and used to sort spokes according to respiratory phase. The sorted spokes were reconstructed using view sharing into 21 respiratory motion state images. These were aligned using deformable image registration and the resulting deformation vector fields were used to correct projection images reconstructed from acquired spokes. Deformed projection images were combined using view sharing into a dynamic time series without any visible respiratory motion. A GI motion signal was extracted from the time–intensity curves in an ROI covering the GI tract by temporal filtering and PCA. Breathing-corrected projection images were sorted according to the GI motion signal and reconstructed into 21 gastrointestinal motion state images showing the phases of GI motion.
Results: Reconstructed image volumes showed varying gastric states clearly with no visible breathing motion or related artifacts. The mean frequency of the GI motion signal was 2.9 cycles/min with a standard deviation of 0.3 cycles/min.
Conclusion: Periodic GI motion can be visualized without confounding respiratory motion using the presented GI 4D MRI technique. Therefore, GI 4D MRIs could help define internal target volumes for treatment planning, or support gastrointestinal motion tracking during irradiation.
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