(Sunday, 7/29/2018) 3:00 PM - 6:00 PM
Room: Exhibit Hall
Purpose: Geometric accuracy is one metric that can be assessed by the American College of Radiology (ACR) Phantom, and can also shift over time. While the ACR criterion is ±2mm, our institution sets the action limits at +1mm as some systems are used for framed and frameless Gamma Knife treatment planning. This work reports the results of our daily geometric accuracy measurements across a large fleet of MRI scanners in a high volume cancer center.
Methods: The large ACR MRI phantom was acquired daily across a diverse platform of scanners (n=33) which included a mix of field strengths, vendors and platforms using the standard ACR phantom protocol. Daily geometric accuracy control charts were generated using an in-house analysis tool written in Python programming language. The automated analysis measured the superior-inferior (SI) phantom length from a sagittal T1-weighted spin echo acquisition and the right-left (RL), anterior-posterior (AP), and two diagonal measurements from the axial T1-weighted acquisition. Physicists reviewed measurements daily and notified local service as needed to resolve geometric accuracy irregularities and failures. Data from 2017 was included in this study and the frequency of failure assessed.
Results: A total 7941 (RL), 8185 (AP), and 8181 (SI) measurements were analyzed. Most failures appeared to be a result of either slow drift in geometric distortion until gradient calibration was necessary, or a sudden change in geometric distortion. Sudden changes were occasionally observed immediately following a vendor periodic maintenance event that involved calibrating the gradients (3 calibration errors over 102 visits). Gradient calibrations were requested >20 times over an annual duration.
Conclusion: Geometric accuracy of better than ±1mm is achievable in a large, diverse MRI fleet with appropriate monitoring. Daily quality assurance captures errors at a higher frequency rate than periodic testing performed specifically for Gamma Knife, which is biannual at our institution.
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