Development of a Novel System for Preclinical Small Animal MR-Guided Radiation Experiments
J Grandinetti*, Y Zhong, Y Peng, C Shen, X Jia, The University of Texas Southwestern Medical Ctr, Dallas, TX
Presentations
TU-D-TRACK 6-6 (Tuesday, 7/27/2021) 2:00 PM - 3:00 PM [Eastern Time (GMT-4)]
Purpose: Small Animal Radiation Research (SARR) serves as a critical counterpart to human radiation therapy (RT). Current SARR platforms use cone-beam CT for image-guidance, which results in poor soft-tissue contrast, additional radiation dose, and lack of real-time imaging. Whereas magnetic resonance-guided RT (MRgRT) has become available for human RT, SARR platforms currently lack on-board MRI capabilities. This study proposes a novel MR-guided SARR platform and reports our on-going progress.
Methods: We propose the use of an inhomogeneous unilateral low-field MR design to ease the integration of MR to a SmART irradiator (Precision X-Ray Inc.). Targeting a 4cm-diameter field of view (FOV), we designed a magnet by optimizing the arrangement of neodymium magnets in a Halbach cylinder using a genetic algorithm. The decaying magnetic field along the axial direction is naturally used for spatial encoding. We constructed the magnet using 3D-printed holders to mount the magnets accurately. We designed and constructed gradient coils with a 4cm gap to allow the beam to pass unobstructed. We designed a 4cm gapped radiofrequency (RF) coil with three resonant circuits to span a wide bandwidth needed to cover the FOV. The inhomogeneous magnetic field allows acquisition of images in a set of curved surfaces, which are resampled to form a volumetric image in Cartesian coordinates. We simulated the MR imaging formation process.
Results: Optimizing magnet orientations was able to increase field strength by 47%, resulting in a 78mT field strength at a distance of 2cm from the surface of the magnet assembly. The measured field strength agreed with our calculations within 3%. The gradient coils achieved linearity through a gapped distance of 4cm. RF coil is under construction.
Conclusion: We proposed a novel approach for MR-guided SARR and are in the process of constructing the system.
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