Introducing Ultra-Low-Field MRI to Radiation Therapy - Radiofrequency Breast Coil Optimization and Design
T Hornung1,2,3*, N Koonjoo1,4, S Yan1,2, M Rosen1,4,5, T Bortfeld1,2, (1) Harvard Medical School, Boston, MA, (2) Massachusetts General Hospital, Boston, Massachusetts, (3) ETH Zuerich, Zuerich, Switzerland, (4) Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, (5) Harvard University, Cambridge, MA
Presentations
SU-J-202-7 (Sunday, 7/10/2022) 4:00 PM - 5:00 PM [Eastern Time (GMT-4)]
Room 202
Purpose: Ultra-Low-Field MRI guidance inherits not only all benefits of High-Field MRI, but can also introduce lower costs and smaller distortions to guidance in radiation-therapy. As an initial step in the development of a hybrid system, our aim was to optimize a single-breast RF volume coil on an ULF scanner at 6.5 mT. Thereby, we developed a new coil winding optimization method that can be applied to a wide range of coil shapes and image requirements. Finally, two breast coils with different winding patterns (unoptimized, optimized) were constructed and evaluated through imaging.
Methods: The first step of the coil winding optimization method employs Finite-Element-Method simulations as well as Integer-Linear-Programming. It determines for a given coil shape for any inhomogeneity level of the magnetic field in the breast and for any magnetic field fall-off into the chest-wall the minimum wire length needed and thus the maximum possible Signal-to-Noise-Ratio. The second step of the optimization method consists of an algorithm that delivers the optimal combination of those three quantities for any specified imaging goal. To find this optimal combination, the algorithm defines a solution space and finds the optimal combination as tangential intersection of the resulting Signal-to Noise-Ratio band with an empirically defined iso-desire-line.Our optimization method was employed to construct an unoptimized and an optimized close-fitting RF volume coil. The imaging was performed with a 3D-bSSFP-sequence on a self-built conical water-filled breast phantom and on voluteers.
Results: At the expense of a slightly reduced Signal-to-Noise-Ratio, the images obtained with the optimized coil are more homogeneous and have a stronger signal in the chest-wall compared to the images obtained with the unoptimized coil.
Conclusion: We introduced a new coil optimization method and demonstrated its functionality on the example of constructing an optimized breast coil for the use of ULF-MRI guidance in radiation-therapy.
Funding Support, Disclosures, and Conflict of Interest: Susu Yan has a research agreement with RaySearch on proton treatment planning and RayIntelligence
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