Purpose Cardiorenal syndrome describes disorders of the heart and the kidneys in which a dysfunction of 1 organ induces a dysfunction in the other. This work describes the design, evaluation, and application of a 4/4‐channel hydrogen‐1/sodium (1H/23Na) RF array tailored for cardiorenal MRI at 7.0 Tesla (T) for a better physiometabolic understanding of cardiorenal syndrome. Methods The dual‐frequency RF array is composed of a planar posterior section and a modestly curved anterior section, each section consisting of 2 loop elements tailored for 23Na MR and 2 loopole‐type elements customized for 1H MR. Numerical electromagnetic field and specific absorption rate simulations were carried out. Transmission field (B1+) uniformity was optimized and benchmarked against electromagnetic field simulations. An in vivo feasibility study was performed. Results The proposed array exhibits sufficient RF characteristics, B1+ homogeneity, and penetration depth to perform 23Na MRI of the heart and kidney at 7.0 T. The mean B1+ field for sodium in the heart is 7.7 ± 0.8 µT/√kW and in the kidney is 6.9 ± 2.3 µT/√kW. The suitability of the RF array for 23Na MRI was demonstrated in healthy subjects (acquisition time for 23Na MRI: 18 min; nominal isotropic spatial resolution: 5 mm [kidney] and 6 mm [heart]). Conclusion This work provides encouragement for further explorations into densely packed multichannel transceiver arrays tailored for 23Na MRI of the heart and kidney. Equipped with this technology, the ability to probe sodium concentration in the heart and kidney in vivo using 23Na MRI stands to make a critical contribution to deciphering the complex interactions between both organs.

Diffusion-weighted imaging (DWI) provides information on tissue microstructure. Single-shot echo planar imaging (EPI) is the most common technique for DWI applications in the brain, but is prone to geometric distortions and signal voids. Rapid acquisition with relaxation enhancement [RARE, also known as fast spin echo (FSE)] imaging presents a valuable alternative to DWI with high anatomical accuracy. This work proposes a multi-shot diffusion-weighted RARE-EPI hybrid pulse sequence, combining the anatomical integrity of RARE with the imaging speed and radiofrequency (RF) power deposition advantage of EPI. The anatomical integrity of RARE-EPI was demonstrated and quantified by center of gravity analysis for both morphological images and diffusion-weighted acquisitions in phantom and in vivo experiments at 3.0 T and 7.0 T. The results indicate that half of the RARE echoes in the echo train can be replaced by EPI echoes whilst maintaining anatomical accuracy. The reduced RF power deposition of RARE-EPI enabled multiband RF pulses facilitating simultaneous multi-slice imaging. This study shows that diffusion-weighted RARE-EPI has the capability to acquire high fidelity, distortion-free images of the eye and the orbit. It is shown that RARE-EPI maintains the immunity to B inhomogeneities reported for RARE imaging. This benefit can be exploited for the assessment of ocular masses and pathological changes of the eye and the orbit.

Shortened dipole antennas based on rectangular dielectric blocks play an important role in ultrahigh field magnetic resonance imaging (UHF-MRI) radio frequency (RF) coil design. However, the generally assumed direct contact with the subject is difficult to maintain in typical in vivo settings. We have previously observed that certain dielectrically shortened dipole antennas can produce a substantially altered transmit field distribution with a very low transmit efficiency when the block and the sample are physically separated. Therefore, the aim of this study was to determine a) why certain designs of dielectrically shortened dipole antennas can produce an inefficient transmit field when the block and the sample are physically separated and b) how this depends on key parameters such as rectangular block geometry, dielectric constant, loading geometry, and RF feeding. In this work, two main types of quasi-transverse dielectric modes were found in different rectangular block geometries and interpreted as TE11δz (MR efficient) and TE1δδy (MR inefficient), and their impact on in vivo MRI experiments involving the human head, calf, and wrist was explored. This study shows, for the first time, why certain antennas preserve their transmit field efficiency despite physical separation from the sample. We conclude that the proposed approach has the potential to provide new insights into dipole antenna design for UHF-MRI.

Three most important eye compartments in the context of sodium physiology were clearly delineated in all of the images: the vitreous humor, the aqueous humor, and the lens. Our results provide encouragement for further clinical studies. The implications for research into eye diseases including ocular melanoma, cataract, and glaucoma are discussed. Magn Reson Med 80:672-684, 2018. © 2018 International Society for Magnetic Resonance in Medicine.