The dual‐mode dipole: A new array element for 7T body imaging with reduced SAR. Issue 2 (5th September 2018)

• Record Type: Journal Article
• Authors: Solomakha, Georgiy; Leeuwen, Carel van; Raaijmakers, Alexander; Simovski, Constantin; Popugaev, Alexander; Abdeddaim, Redha; Melchakova, Irina; Glybovski, Stanislav
• Is Part Of: Magnetic resonance in medicine. Volume 81:Issue 2(2019)
• Page Start: 1459
• Page End: 1469
• Publication Date: 2018-09-05
• Subjects: coil -- Dipole -- modes -- parallel transmit -- SAR; Nuclear magnetic resonance -- Periodicals; Electron paramagnetic resonance -- Periodicals; 616.07548
• DOI: 10.1002/mrm.27485
• Languages: English
• ISSNs: 0740-3194

Abstract

Abstract : Purpose: To design and test an RF‐coil based on two orthogonal eigenmodes in a pair of coupled dipoles, for 7 Tesla body imaging with improved SAR, called dual‐mode dipole . Methods: The proposed coil consists of two dipoles and creates two orthogonal field distributions in a sample (the even and odd modes). A coupler used to excite the modes was miniaturized with the conductor track routing technique. Numerical simulations of the dual‐mode dipole in the presence of a homogeneous phantom were performed. Moreover, an array of such coils was simulated with a voxel body model. For comparison, a fractionated dipole combined with a surface loop coil was also simulated. Both coils were tested in a 7 Tesla MRI system on a phantom. Subsequently four dual‐mode dipoles or dipole/loop combinations were used for a comparison of imaging performance in a human volunteer. Results: Using the even mode of the dual‐mode dipole showed 70% SAR reduction in comparison to the fractionated dipole while having the same B 1 + in the prostate region. The odd mode of the dual‐mode dipole showed a performance comparable to the surface loop both for SAR and B 1 efficiency. The obtained results showed that the proposed coil while creating lower SAR gave images of the same quality as the reference coil. Conclusions: It was demonstrated that the array of dual‐mode dipoles provided the same SNR and prostate imaging quality as the reference array, while demonstrating lower SAR. This is due to a smoother current distribution over a sample surface.