Design of a novel antisymmetric coil array for parallel transmit cardiac MRI in pigs at 7 T

• Published in: Journal of magnetic resonance (1997) Vol. 305; pp. 195 - 208
• Main Authors: Elabyad, Ibrahim A., Terekhov, M., Stefanescu, M.R., Lohr, D., Fischer, M., Schreiber, L.M.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.08.2019
• Subjects: Cardiac MRI; Ex-vivo pigs; Multichannel coil arrays; Parallel transmit (pTx); RF shimming; UHF; RF shimming; UHF; Ex-vivo pigs; Multichannel coil arrays; Cardiac MRI; Parallel transmit (pTx)
• ISSN: 1090-7807; 1096-0856
• DOI: 10.1016/j.jmr.2019.07.004

[Display omitted] •The antisymmetric array enhanced the SNR by about two-fold compared to the rectilinear array design.•The novel design demonstrated good decoupling between all neighboring elements of the entire array.•Improved control of the B1+ field distributions using RF shimming was demonstrated in EM-simulations.•The antisymmetric array enabled the application of GRAPPA acceleration factor R = 4 with mean g-factor ± SD of only 1.13 ± 0.07.•High resolution ex-vivo images were acquired using standard clinical protocols (in-plane resolution = 0.3mm × 0.3mm). The design, simulation, assembly and testing of a novel dedicated antisymmetric transmit/receive (Tx/Rx) coil array to demonstrate the feasibility of cardiac magnetic resonance imaging (cMRI) in pigs at 7 T was described. The novel antisymmetric array is composed of eight elements based on mirrored and reversed loop orientations to generate varying B1+ field harmonics for RF shimming. The central four loop elements formed together a pair of antisymmetric L-shaped channels to allow good decoupling between all neighboring elements of the entire array. The antisymmetric array was compared to a standard symmetric rectilinear loop array with an identical housing dimension. Both arrays were driven in the parallel transmit (pTx) mode forming an 8-channel transmit and 16-channel receive (8Tx/16Rx) coil array, where the same posterior array was combined with both anterior arrays. The hardware and imaging performance of the dedicated cardiac arrays were validated and compared by means of electromagnetic (EM) simulations, bench-top measurements, phantom, and ex-vivo MRI experiments with 46 kg female pig. Combined signal-to-noise ratio (SNR), geometry factor (g-factor), noise correlation maps, and high resolution ex-vivo cardiac images were acquired with an in-plane resolution of 0.3 mm × 0.3 mm using both arrays. The novel antisymmetric array enhanced the SNR within the heart by about two times and demonstrated good decoupling and improved control of the B1+ field distributions for RF shimming compared to the standard coil array. Parallel imaging with acceleration factor (R) up to 4 was possible using the novel antisymmetric coil array while maintaining the mean g-factor within the heart region of 1.13.