Hypertension is linked to disturbed total-body sodium (Na(+)) regulation; however, measuring Na(+) disposition in the body is difficult. We implemented (23)Na magnetic resonance spectroscopy ((23)Na-MR) and imaging technique ((23)Na-MRI) at 9.4T for animals and 3T for humans to quantify Na(+) content in skeletal muscle and skin. We compared (23)Na-MRI data with actual tissue Na(+) content measured by chemical analysis in animal and human tissue. We then quantified tissue Na(+) content in normal humans and in patients with primary aldosteronism. We found a 29% increase in muscle Na(+) content in patients with aldosteronism compared with normal women and men. This tissue Na(+) was mobilized after successful treatment without accompanying weight loss. We suggest that, after further refinements, this tool could facilitate understanding the relationships between Na(+) accumulation and hypertension. Furthermore, with additional technical advances, a future clinical use may be possible.

The interest in performing vascular interventions under magnetic resonance (MR) guidance has initiated the evaluation of the potential hazard of long conductive wires and catheters. The objective of this work is to present a simple analytical approach to address this concern and to demonstrate the agreement with experimental results. The first hypothesis is that a long conductive structure couples with the electric field of the radio frequency (RF) transmit coil. The second hypothesis is that this coupling induces high voltages near the wire ends. These voltages can cause tissue heating due to induced currents. The experimental results show an increase in coupling when moving a guide wire toward the wall of an RF transmit coil, documented with a temperature increase of a saline solution in close proximity to the tip of the guide wire. The coupling of the wire not only presents a potential hazard to the patient, but also interferes with the visualization of the wire. A safe alternative would be the use of nonconducting guide wires. J. Magn. Reson. Imaging 2001;13:105–114. © 2001 Wiley‐Liss, Inc.

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BackgroundTo demonstrate the applicability of acoustic cardiac triggering (ACT) for imaging of the heart at ultrahigh magnetic fields (7.0 T) by comparing phonocardiogram, conventional vector electrocardiogram (ECG) and traditional pulse oximetry (POX) triggered 2D CINE acquisitions together with (i) a qualitative image quality analysis, (ii) an assessment of the left ventricular function parameter and (iii) an examination of trigger reliability and trigger detection variance derived from the signal waveforms.ResultsECG was susceptible to severe distortions at 7.0 T. POX and ACT provided waveforms free of interferences from electromagnetic fields or from magneto-hydrodynamic effects. Frequent R-wave mis-registration occurred in ECG-triggered acquisitions with a failure rate of up to 30% resulting in cardiac motion induced artifacts. ACT and POX triggering produced images free of cardiac motion artefacts. ECG showed a severe jitter in the R-wave detection. POX also showed a trigger jitter of approximately Δt = 72 ms which is equivalent to two cardiac phases. ACT showed a jitter of approximately Δt = 5 ms only. ECG waveforms revealed a standard deviation for the cardiac trigger offset larger than that observed for ACT or POX waveforms.Image quality assessment showed that ACT substantially improved image quality as compared to ECG (image quality score at end-diastole: ECG = 1.7 ± 0.5, ACT = 2.4 ± 0.5, p = 0.04) while the comparison between ECG vs. POX gated acquisitions showed no significant differences in image quality (image quality score: ECG = 1.7 ± 0.5, POX = 2.0 ± 0.5, p = 0.34).ConclusionsThe applicability of acoustic triggering for cardiac CINE imaging at 7.0 T was demonstrated. ACT's trigger reliability and fidelity are superior to that of ECG and POX. ACT promises to be beneficial for cardiovascular magnetic resonance at ultra-high field strengths including 7.0 T.

The modular 32-channel transceiver cardiac array supports accelerated and high spatial resolution cardiac MRI. The array is compatible with multichannel transmission and provides a technological basis for future clinical assessment of parallel transmission techniques at 7.0T.

Purpose To design, evaluate and apply a two-dimensional 16 channel transmit/receive coil array tailored for cardiac MRI at 7.0 Tesla. Material and Methods The cardiac coil array consists of 2 sections each using 8 elements arranged in a 2 × 4 array. RF safety was validated by SAR simulations. Cardiac imaging was performed using 2D CINE FLASH imaging, T2* mapping and fat-water separation imaging. The characteristics of the coil array were analyzed including parallel imaging performance, left ventricular chamber quantification and overall image quality. Results RF characteristics were found to be appropriate for all subjects included in the study. The SAR values derived from the simulations fall well in the limits of legal guidelines. The baseline SNR advantage at 7.0 T was put to use to acquire 2D CINE images of the heart with a very high spatial resolution of (1 × 1 × 4) mm3. The proposed coil array supports 1D acceleration factors of up to R=4 without impairing image quality significantly. Conclusions The 16 channel TX/RX coil has the capability to acquire high contrast and high spatial resolution images of the heart at 7.0 Tesla.

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Objective: Skin-sodium storage, as a physiologically important regulatory mechanism for blood pressure, volume regulation, and indeed survival, has recently been rediscovered. This prompted the development of MRI methods to assess sodium storage in humans ( 23 Na-MRI) at 3.0 Tesla. This work examines the feasibility of high in-plane spatial resolution 23 Na MRI in skin at 7.0 T. Methods:A two-channel transceiver RF coil array tailored for skin MRI at 7.0 T (f=78.5MHz) is proposed. Specific absorption rate (SAR) simulations and a thorough assessment of RF power deposition were performed to meet the safety requirements. Human skin was examined in an in vivo feasibility study using 2D gradient echo imaging. Normal male adult volunteers (n=17, mean ± SD = 46 ± 18 years, range: 20-79 years) were investigated.Transverse slices of the calf were imaged with 23 Na MRI using a high in-plane resolution of (0.9 x 0.9) mm 2 . Skin Na + content was determined using external agarose standards covering a physiological-range of Na + concentrations. To assess the intra-subject reproducibility, each volunteer was examined three to five times with each session including a 5 min walk and repositioning/preparation of the subject. Age-dependence of skin Na + content was investigated. Results:The 23 Na RF coil provides improved sensitivity within a range of 1 cm from its surface versus a volume RF coil which facilitates high in-plane spatial resolution imaging of human skin. Intra-subject variability of human skin sodium content in the volunteer population was <10.3%. An age-dependent increase in skin Na + content was observed, r = 0.78). Short abstractThis work demonstrates the feasibility of sub-millimeter in-plane spatial resolution 23 Na MRI in skin at clinically acceptable acquisition times at 7.0 T. Intra-subject variability of human skin sodium content in the volunteer population was <10.3%. An age-dependent increase in skin Na + content was observed (r = 0.78). Assigning sodium stores with 23 Na-MRI techniques could be improved at 7.0 T compared to current 3.0 T technology.-6 -