AAPM Task Group 333 Report: Quality assurance for MRI‐guided focused ultrasound body systems
A quality assurance (QA) procedure for magnetic resonance‐guided focused ultrasound (MRgFUS) body systems was developed and tested at five institutions. The QA procedure is based on a custom‐designed phantom with tissue‐mimicking acoustic, MR, and thermal properties specific for MRgFUS. The data acquisition includes assessments of maximum temperature rise, targeting error, signal‐to‐noise ratio (SNR), and three‐dimensional thermal ablation spot size, which are to be tracked over longitudinal repetitions of the QA procedure. The procedure is appropriate for intermediate‐level QA, for example, every 20 patients or 6 months, and can be completed in approximately two hours. A subset of the full procedure is recommended for system verification either daily or before each patient (in addition to the vendor‐recommended procedure). The phantom and QA procedure have been tested on a variety of custom and commercially available MRgFUS body systems, including systems with 1.5 and 3.0 T static magnetic fields. Normal variability in measurements based on data from five functional MRgFUS body systems over periods of at least 6 months is reported and establishes quantitative criteria for passing the QA test. This QA procedure may be used to increase confidence in the safety and performance of MRgFUS treatments.