Corrections of myocardial tissue sodium concentration measurements in human cardiac ²³Na MRI at 7 Tesla

Abstract

Purpose: To quantify the tissue sodium concentration (TSC) in cardiac 23 Na MRI.To evaluate the influence of different correction methods on the measured myocardial TSC. Methods: 23 Na MRI of four healthy subjects was conducted at a whole-body 7T MRI system using an oval-shaped 23 Na birdcage coil. Data acquisition was performed with a density-adapted 3D radial pulse sequence using a golden angle projection scheme. 1 H MRI data were acquired at a 3T MRI system to generate a myocardial mask. Retrospective cardiac and respiratory gating were used to reconstruct 23 Na MRI data in the diastolic phase and exhaled state. B 0 and B 1 inhomogeneity and partial volume (PV) effects were corrected. Relaxation times and TSC of ex vivo blood samples and calf muscle were determined. These values were used in the PV correction to estimate myocardial TSC, which was compared with the measured TSC of calf muscle. Results: Without any correction the measured myocardial TSC was (54 ± 5) mM.The applied correction methods reduced these values by (48 ± 5)% to (29 ± 3) mM, where PV correction had the largest effect (reduction of (34 ± 1)%). Respiratory and cardiac motion gating decreased the concentrations by (11 ± 1)%. With the applied setup, the corrections of B 0 and B 1 inhomogeneity (reduction of (3 ± 2)%) had negligible influences on TSC values. The resulting myocardial TSC was approximately 1.4-fold higher than the measured TSC of calf muscle tissue of the same healthy subjects ((20 ± 3) mM). |LOTT eT aL. |LOTT eT aL. F I G U R E 1Schematic outline of the measurements and the post-processing workflow. The process can be divided into a main path and a side path. The main part contains the cardiac 23 Na and 1 H MR measurements, all applied corrections and the determination of the myocardial TSC. In the side path, parameters, that are required for the corrections, such as relaxation times and sodium concentration of whole blood were determined for each volunteer individually F I G U R E 2 Retrospectively gated cardiac 23 Na in vivo data in a diastolic cardiac phase for one volunteer as an example. The not sorted 23 Na data (A) were reconstructed with the full set of projections. 49% of the projections were used to conduct the diastolic 23 Na image reconstruction (B). The measured sodium concentration in the diastolic image (C, red) is slightly reduced compared with the not sorted data (C, blue). Cardiac 23 Na data and line plots for the other three volunteers are shown in the Supporting Information Figure S3

Assessing the variability of 23Na MRI in skeletal muscle tissue: Reproducibility and repeatability of tissue sodium concentration measurements in the lower leg at 3 T

“…In previous work concerning quantitative cardiac 23 Na MRI, B 0 correction had only a negligible influence on the measured TSC. 29 The larger influence of the B 0 correction on measured TSC values that was observed in our work might be caused by the relatively high off-resonance values of the reference tubes (mean off-resonance of up to 32 Hz). By contrast, Lott et al 29 used blood as an internal reference, avoiding high susceptibility differences.…”

“…29 The larger influence of the B 0 correction on measured TSC values that was observed in our work might be caused by the relatively high off-resonance values of the reference tubes (mean off-resonance of up to 32 Hz). By contrast, Lott et al 29 used blood as an internal reference, avoiding high susceptibility differences. Here, our B 0 inhomogeneity correction can minimise the distortion in the calibration vials to improve the efficacy of quantification as well as to increase the SNR in the muscles.…”

Cardiorenal sodium MRI at 7.0 Tesla using a 4/4 channel 1H/23Na radiofrequency antenna array

“…Efficient and uniform RF excitation of the heart and kidney is essential for accurately assessing tissue sodium concentration . For the proposed surface RF array, the antenna elements (for both resonant frequencies) are placed close to the cardiorenal targets.…”

Radiofrequency excitation–related 23Na MRI signal loss in skeletal muscle, cartilage, and skin

“…While considerable effort has been applied to the facilitation of quantitative 23 Na MRI through correction of B 0 and B 1 inhomogeneity with field mapping, correction for excitation‐related signal loss requires accurate knowledge of spin‐3/2 relaxation and ω Q values in the tissue of interest. These values may change with pathology and would likely need to be measured in each volunteer.…”