Exhibit Hall | Forum 2
Purpose: Utilizing a novel e4D, MR-compatible ultrasound transducer, this work aimed to establish a registration between simultaneously acquired ultrasound and MR datasets to transform ultrasound feature tracking results into the MR coordinate system in preparation for use during radiotherapy.
Methods: A simultaneous MR and ultrasound liver imaging protocol was conducted on nine healthy volunteers. A T1-weighted end-exhale 3D MR dataset was acquired followed by simultaneous multi-phase 2D sagittal MR slices and 3D ultrasound volumes of the liver. Liver vessels were tracked in the 3D ultrasound volumes and 2D MR slices as indicators of breathing motion. From this, we identified an ultrasound volume acquired during end-exhale. A manual landmark-based approach was taken to initialize the 3D ultrasound to 3D MR registration. Based on this initialization, the MR field of view was masked downed to the field of view of the ultrasound plus a buffer radius of 8 pixels. The registration was then rigidly optimized using mutual information. The resulting transformation matrix was applied to the dataset of tracked points in ultrasound. The registration was evaluated using the center-of-mass distance-to-agreement (COMD) between feature contours in both the 3D MR and registered 3D ultrasound. Breathing motion analysis was conducted as the correlation between the registered ultrasound tracking data and MR tracking data.
Results: Seven datasets were successfully registered using this method. Two datasets could not be registered as the ultrasound imaging window was unsuitable from rib shadowing or bowel gas. The average COMD was 4.19±1.85 mm. The vessel motion correlation between the MR and ultrasound data was 0.91±0.05 and 0.56±0.55 for superior-inferior and anterior-posterior directions, respectively.
Conclusion: With appropriate ultrasound imaging quality, we were able to establish a registration between ultrasound and MR datasets. Once refined, this work will provide the necessary pre-treatment imaging information to accomplish real-time ultrasound guidance for radiotherapy.
Funding Support, Disclosures, and Conflict of Interest: This work was also supported by the University of Wisconsin - Madison Pandemic-Affected Research Continuation Initiative (PARCI).
Image-guided Therapy, Registration, Vessel Tracking