Improving radiofrequency power and specific absorption rate management with bumped transmit elements in ultra‐high field MRI. Issue 6 (23rd June 2020)

• Record Type: Journal Article
• Authors: Sadeghi‐Tarakameh, Alireza; Adriany, Gregor; Metzger, Gregory J.; Lagore, Russell L.; Jungst, Steve; DelaBarre, Lance; Van de Moortele, Pierre‐Francois; Ugurbil, Kamil; Atalar, Ergin; Eryaman, Yigitcan
• Is Part Of: Magnetic resonance in medicine. Volume 84:Issue 6(2020)
• Page Start: 3485
• Page End: 3493
• Publication Date: 2020-06-23
• Subjects: 10.5 Tesla -- bumped transmitter -- MRI -- radiofrequency safety -- ultra‐high field; Nuclear magnetic resonance -- Periodicals; Electron paramagnetic resonance -- Periodicals; 616.07548
• DOI: 10.1002/mrm.28382
• Languages: English
• ISSNs: 0740-3194

Abstract

Abstract : Purpose: In this study, we investigate a strategy to reduce the local specific absorption rate (SAR) while keeping B 1 + constant inside the region of interest (ROI) at the ultra‐high field (B0 ≥ 7T) MRI. Methods: Locally raising the resonance structure under the discontinuity (i.e., creating a bump) increases the distance between the accumulated charges and the tissue. As a result, it reduces the electric field and local SAR generated by these charges inside the tissue. The B 1 + at a point that is sufficiently far from the coil, however, is not affected by this modification. In this study, three different resonant elements (i.e., loop coil, snake antenna, and fractionated dipole [FD]) are investigated. For experimental validation, a bumped FD is further investigated at 10.5T. After the validation, the transmit performances of eight‐channel arrays of each element are compared through electromagnetic (EM) simulations. Results: Introducing a bump reduced the peak 10g‐averaged SAR by 21, 26, 23% for the loop and snake antenna at 7T, and FD at 10.5T, respectively. In addition, eight‐channel bumped FD array at 10.5T had a 27% lower peak 10g‐averaged SAR in a realistic human body simulation (i.e., prostate imaging) compared to an eight‐channel FD array. Conclusion: In this study, we investigated a simple design strategy based on adding bumps to a resonant element to reduce the local SAR while maintaining B 1 + inside an ROI. As an example, we modified an FD and performed EM simulations and phantom experiments with a 10.5T scanner. Results show that the peak 10g‐averaged SAR can be reduced more than 25%.