Exhibit Hall | Forum 5
Purpose: This work investigates how much a low-profile, hands-free ultrasound probe moves with the patient during free-breathing imaging in preparation for ultrasound-based IGRT.
Methods: Simultaneous ultrasound and MR images were collected from 11 healthy volunteers using an MR-compatible ultrasound probe. The ultrasound probe was placed on the volunteer to image the liver intercostally. It was secured in position with a nylon strap. Surface markers were attached to the probe for localization in the MR images. Multi-phase sagittal 2D MR slices (200 frames/slice) were acquired and utilized in this work. For MR slices that captured the probe surface markers, the markers were tracked over time as a surrogate for probe motion. In this way, probe motion during free-breathing imaging was obtained. From the tracked motion, we evaluated the average breathing cycle range of motion in both superior-inferior (SI) and anterior-posterior (AP) directions. In a subset of the data, liver vessels were also tracked in the MR images. Using the vessel tracking as an indication of breathing motion, we analyzed the motion correction between the breathing cycle and the probe.
Results: We analyzed 31 instances where a probe surface marker was visible in the MR slices. The average range of motion in the AP and SI directions was 0.78±0.56 mm and 0.28±0.13 mm, respectively. When considering the pixel size of the MR images is 1.56 mm, these values correspond to less than a pixel of motion. We found that the probe motion had some correlation with the vessel motion, with average correlation values of 0.67±0.17 and -0.55±0.25 for AP and SI, respectively.
Conclusion: When positioned for intercostal liver imaging and secured with a strap, the ultrasound probe showed good stability with less than 1 mm of motion. Therefore, this setup may be suitable for real-time ultrasound imaging during 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).
Not Applicable / None Entered.