Abstract
A proton-frequency-transparent (PFT) birdcage RF coil that contains carbon-proton switching circuits (CPSCs) is presented to acquire 13C MR signals, which, in turn, enable 1H imaging with existing 1H RF coils without being affected by a transparent 13C birdcage RF coil. CPSCs were installed in the PFT 13C birdcage RF coil to cut the RF coil circuits during 1H MR imaging. Finite-difference time-domain (FDTD) electromagnetic (EM) simulations were performed to verify the performance of the proposed CPSCs. The performance of the PFT 13C birdcage RF coil with CPSCs was verified via phantom and in vivo MR studies. In the phantom MR studies, 1H MR images and 13C MR spectra were acquired and compared with each other using the 13C birdcage RF coil with and without the CPSCs. For the in vivo MR studies, hyperpolarized 13C cardiac MRS and MRSI of swine were performed. The proposed PFT 13C birdcage RF coil with CPSCs led to a percent image uniformity (PIU) reduction of 1.53% in the proton MR images when compared with the case without it. FDTD EM simulations revealed PIU reduction of 0.06% under the same conditions as the phantom MR studies. Furthermore, an SNR reduction of 5.5% was observed at 13C MR spectra of corn-oil phantom using the PFT 13C birdcage RF coil with CPSCs compared with that of the 13C birdcage RF coil without CPSCs. Utilizing the PFT 13C birdcage RF coil, 13C-enriched compounds were successfully acquired via in vivo hyperpolarized 13C MRS/MRSI experiments. In conclusion, the applicability and utility of the proposed 16-leg low-pass PFT 13C birdcage RF coil with CPSCs were verified via 1H MR imaging and hyperpolarized 13C MRS/MRSI studies using a 3.0 T MRI system.
Highlights
Hyperpolarized 13C MRS/MRSI has been effectively utilized for real-time investigation of cellular metabolism because it increases magnetization of 13C-labeled compounds [1,2]without using invasive radiation treatments [3]
With the exception of the unloaded Q-factor, the swine was loaded inside the 16-leg PFT 13C birdcage RF coil with carbon-proton switching circuits (CPSCs) and 13C birdcage RF coil without CPSCs
We evaluated the performance of the proposed CPSCs by comparing the results of Finite-difference time-domain (FDTD) EM simulations and MR experiments
Summary
Hyperpolarized 13C MRS/MRSI has been effectively utilized for real-time investigation of cellular metabolism because it increases magnetization of 13C-labeled compounds [1,2]without using invasive radiation treatments [3]. The low gyromagnetic ratio (four times lower than that of 1H) and natural abundance (13C for 1.1% and 1H for 99.9% at natural abundance) of the 13C nucleus can weaken the acquired 13C signals when verifying in vivo metabolism. Regional or time-resolved in vivo 13C metabolic information can be acquired via 13C MRI and MRS. A dual-tuned RF coil, which is tuned to both frequencies of nuclei, was utilized to obtain multinuclei MR images containing anatomical and metabolic information of the subject [6,7,8,9]. The most significant advantage of the dual-tuned RF coil is that both nuclei can be MR imaged without changing the RF coil and/or repositioning the subjects. The co-registration of the two types of MR images is straightforward and accurate throughout the dual-tuned RF coil
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