Abstract
A novel mono-surface antisymmetric 16-element transmit/receive (Tx/Rx) coil array was designed, simulated, constructed, and tested for cardiac magnetic resonance imaging (cMRI) in pigs at 7 T. The cardiac array comprised of a mono-surface 16-loops with two central elements arranged anti-symmetrically and flanked by seven elements on either side. The array was configured for parallel transmit (pTx) mode to have an eight channel transmit and 16-channel receive (8Tx/16Rx) coil array. Electromagnetic (EM) simulations, bench-top measurements, phantom, and MRI experiments with two pig cadavers (68 and 46 kg) were performed. Finally, the coil was used in pilot in-vivo measurements with a 60 kg pig. Flip angle (FA), geometry factor (g-factor), signal-to-noise ratio (SNR) maps, and high-resolution cardiac images were acquired with an in-plane resolution of 0.6 mm × 0.6 mm (in-vivo) and 0.3 mm × 0.3 mm (ex-vivo). The mean g-factor over the heart was 1.26 (R = 6). Static phase {B}_{1}^{+} shimming in a pig body phantom with the optimal phase vectors makes possible to improve the {B}_{1}^{+} homogeneity by factor > 2 and transmit efficiency by factor > 3 compared to zero phases (before RF shimming). Parallel imaging performed in the in-vivo measurements demonstrated well preserved diagnostic quality of the resulting images at acceleration factors up to R = 6. The described hardware design can be adapted for arrays optimized for animals and humans with a larger number of elements (32–64) while maintaining good decoupling for various MRI applications at UHF (e.g., cardiac, head, and spine).
Highlights
With the development of ultrahigh field (UHF) strength (B0 ≥ 7 T) magnetic resonance imaging (MRI) scanners, a significant improvement in the signal-to-noise ratio (SNR), and in spatial and temporal resolutions can be achieved compared to conventional lower field strength
We report a novel 8Tx/16Rx pTx cardiac coil array composed of 16-loop elements allocated on the mono-surface of one printed circuit board (PCB) and fixed on half-elliptical housing
The mono-surface array shows a significant improvement in the B1+ field homogeneity after RF-shimming, which proves the high efficiency of the developed array design for using with the pTx-capable MR-system in large animal cardiac studies at UHF
Summary
With the development of ultrahigh field (UHF) strength (B0 ≥ 7 T) magnetic resonance imaging (MRI) scanners, a significant improvement in the SNR, and in spatial and temporal resolutions can be achieved compared to conventional lower field strength For brain imaging at 7 T, different coil array designs and technologies have been introduced to solve the issues of B1+ field inhomogeneity such as microstrip transmission line (MTL) resonators[7,8,9,10,11,12], inverted (MTL) resonators[13], stepped impedance resonators[14,15,16,17,18,19], and by utilizing a high-impedance surfDaceespaisteththeeRnFu-msheieroldustoteicmhpnriocavlecthhaelleefnfigceiesnreclyataenddtopeBn0etarnatdioBn1+offietlhdeiBn1h+ofmielodg2e0,n21e.ities, the application of UHF scanners for cardiovascular research holds significant promise[22,23]. Ra Fu-nsihfoimrmmcinogmobrinBe1+dsBh1+imfimelidndg4i5s–t5r0i.bUutsiionng in the selected region-of-interest (ROI) This process is referred to as eight independent RF power amplifiers (RFPAs) in pTX mode allows driving the individual 8Tx channels of the array dynamically (i.e. to vary the magnitude/phase of each channel or the RF-pulse waveforms), which enables shaping of 2D and 3D excitation profiles based on a wide-range of optimization criteria[51,52]. Half of the tion that the power is divided
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