Development of a Proton-Frequency-Transparent Birdcage Radiofrequency Coil for In Vivo 13C MRS/MRSI Study in a 3.0 T MRI System

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.

3-T MRI in Patients Received Anterior Cervical Discectomy and Fusion Surgery with MAVRIC SL IR Sequence: A Feasibility Study

Objective: We aimed to investigate the feasibility of multi-acquisition with variable resonance image combination slab selectivity inversion recovery (MAVRIC SL IR) sequence on 3.0 T MRI in patients with anterior cervical discectomy and fusion (ACDF) surgery compared to bandwidth-optimized short tau inversion recovery (STIR) sequence. Methods: Paired sagittal MR images of MAVRIC SL IR and bandwidth-optimized STIR sequences were acquired and analyzed for 21 patients after ACDF surgery with PEEK cage-plate construct. Quantitative comparisons were made on the metal artifact areas of paired mid-sagittal images. In qualitative analysis, the consistency of fat suppression and visibility of anatomic structures (bone-metal interface, surrounding soft tissues, and spinal cord) were independently assessed, based on a five-point scale by two musculoskeletal radiologists, who were blind to the images and patient details. Results: The application of the MAVRIC SL IR sequence resulted in a significant reduction of 48% in the mean area of metal artifacts (t =-7.141, P < 0.001). Based on the comments received from both the reviewers, MAVRIC SL IR sequence showed greater visibility of the bone-metal interface (P < 0.001), considerable visibility of the surrounding soft tissues (P > 0.05) but worse visibility obtained of the spinal cord (P < 0.001), including the consistency of fat suppression (P < 0.001) relative to the bandwidth-optimized STIR sequence. Conclusion: With significantly reduced metal artifacts, the MAVRIC SL IR sequence can be implemented in patients undergoing ACDF surgery with PEEK cage-plate construct for 3.0 T MRI, despite the poor visibility of the spinal cord.

Reproducibility of magnetic resonance fingerprinting-based T1 mapping of the healthy prostate at 1.5 and 3.0 T: A proof-of-concept study

Facilitating clinical translation of quantitative imaging techniques has been suggested as means of improving interobserver agreement and diagnostic accuracy of multiparametric magnetic resonance imaging (mpMRI) of the prostate. One such technique, magnetic resonance fingerprinting (MRF), has significant competitive advantages over conventional mapping techniques in terms of its multi-site reproducibility, short scanning time and inherent robustness to motion. It has also been shown to improve the detection of clinically significant prostate cancer when added to standard mpMRI sequences, however, the existing studies have all been conducted on 3.0 T MRI systems, limiting the technique’s use on 1.5 T MRI scanners that are still more widely used for prostate imaging across the globe. The aim of this proof-of-concept study was, therefore, to evaluate the cross-system reproducibility of prostate MRF T1 in healthy volunteers (HVs) using 1.5 and 3.0 T MRI systems. The initial validation of MRF T1 against gold standard inversion recovery fast spin echo (IR-FSE) T1 in the ISMRM/NIST MRI system revealed a strong linear correlation between phantom-derived MRF and IR-FSE T1 values was observed at both field strengths (R2 = 0.998 at 1.5T and R2 = 0.993 at 3T; p = < 0.0001 for both). In young HVs, inter-scanner CVs demonstrated marginal differences across all tissues with the highest difference of 3% observed in fat (2% at 1.5T vs 5% at 3T). At both field strengths, MRF T1 could confidently differentiate prostate peripheral zone from transition zone, which highlights the high quantitative potential of the technique given the known difficulty of tissue differentiation in this age group. The high cross-system reproducibility of MRF T1 relaxometry of the healthy prostate observed in this preliminary study, therefore, supports the technique’s prospective clinical validation as part of larger trials employing 1.5 T MRI systems, which are still widely used clinically for routine mpMRI of the prostate.

Exposure levels of radiofrequency magnetic fields and static magnetic fields in 1.5 and 3.0 T MRI units

Magnetic resonance imaging (MRI) staff is exposed to a complex mixture of electromagnetic fields from MRI units. Exposure to these fields results in the development of transient exposure-related symptoms. This study aimed to investigate the exposure levels of radiofrequency (RF) magnetic fields and static magnetic fields (SMFs) from 1.5 and 3.0 T MRI scanners in two public hospitals in the Mangaung Metropolitan region, South Africa. The exposure levels of SMFs and RF magnetic fields were measured using the THM1176 3-Axis hall magnetometer and TM-196 3 Axis RF field strength meter, respectively. Measurements were collected at a distance of 1 m (m) and 2 m from the gantry for SMFs when the brain, cervical spine and extremities were scanned. Measurements for RF magnetic fields were collected at a distance of 1 m with an average scan duration of six minutes. Friedman’s test was used to compared exposure mean values from two 1.5 T scanners, and Wilcoxon test with Bonferroni adjustment was used to identify where the difference between exist. The Shapiro–Wilk test was also used to test for normality between exposure levels in 1.5 and 3.0 T scanners. The measured peak values for SMFs from the 3.0 T scanner at hospital A were 1300 milliTesla (mT) and 726 mT from 1.5 T scanner in hospital B. The difference in terms of SMFs exposure levels was observed between two 1.5 T scanners at a distance of 2 m. The difference between 1.5 T scanners at 1 m was also observed during repeated measurements when brain, cervical spine and extremities scans were performed. Scanners’ configurations, magnet type, clinical setting and location were identified as factors that could influence different propagation of SMFs between scanners of the same nominal B0. The RF pulse design, sequence setting flip-angle and scans performed influenced the measured RF magnetic fields. Three scanners were complaint with occupational exposure guidelines stipulated by the ICNIRP; however, peak levels that exist at 1 m could be managed through adoption of occupational health and safety programs.