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.