Room: Stars at Night Ballroom 2-3
Purpose: MRI presents several unique safety considerations not typically encountered in a radiotherapy treatment setting. Chief among these concerns is the exclusion of ferromagnetic materials from all aspects of machine use. This presents a challenge when implementing quality assurance programs, particularly those that traditionally include the use of motion stages.
Methods: Any phantom for use in an MR setting must either completely eliminate ferromagnetic materials from the construction or isolate those ferromagnetic materials from the imaging space. The phantom we describe chooses the latter approach. Motors, control systems, and electronics remain outside the imaging space. All motion generated by the ferromagnetic components is transferred via a hydraulic line through a waveguide into the RF cage of the room to a non-ferromagnetic motion platform.
Results: The motion stage of the phantom consists of a 12â€? x 6â€? 3D printed platform to which is affixed a 2 oz syringe, a NEMA-17 bi-polar stepper with a threaded lead screw, limit switches, two 3/8â€? diameter ceramic coated aluminum rods for motion guidance, and the requisite power supplies. The motion is controlled by a C# written UWP-app on Windows IoT Core running on a Raspberry Pi 3B. Motion traces loaded on the controller drive the stepper to oscillate the syringe plunger which is connected to a 25â€™ length of nylon tubing running into the imaging space. This tubing connects to a similar platform without ferromagnetic components that is placed into the bore of the MRI. On the imaging platform sits a 3 cm spherical water-filled target volume that oscillates at the same frequency and amplitude as the controlling platform outside the imaging space.
Conclusion: The hydraulic design isolates the ferromagnetic components from the magnetic field while providing a reproducible motion trace in the magnet bore.