PURPOSE
Spin density-weighted (SDW) and inversion recovery (IR) 23Na MRI provide different sodium contrasts with complementary information. Therefore, the aim was to develop a time-efficient sequence scheme capable of providing both contrasts by acquiring SDW and IR 23Na MRI data within a single sequence without additional measurement time.
METHODS
In the developed pulse sequence, the conventional 180° inversion pulse was divided into two successive 90° pulses, with an additional readout inserted between them. The sequence was initially evaluated in simulations and phantom measurements. Afterwards, it was applied in calf muscle measurements of six healthy volunteers to assess its practical feasibility and signal characteristics. All 23Na measurements were acquired at 7 T and compared to standard SDW and IR sequences.
RESULTS
The interleaved SDW/IR sequence yielded image quality and contrast comparable to standard SDW and IR sequences. Phantom experiments showed slightly higher remaining T1-weighting in the interleaved sequence compared with standard SDW, resulting in only minor changes in image contrast. Fluid suppression was effective across all IR approaches, though efficiency decreased modestly with longer effective inversion pulse lengths. Spin dynamic simulations for IR 23Na MRI indicated slightly increased sensitivity to fluid suppression artifacts arising from B0 inhomogeneities in the interleaved sequence. In vivo calf muscle measurements did not reveal significant differences in the mean muscle signal between the interleaved SDW/IR sequence and the corresponding standard sequences.
CONCLUSION
The proposed interleaved sequence enables simultaneous acquisition of 23Na SDW and IR contrasts, thereby reducing overall scan time and eliminating the need for co-registration.
Tobias Wilferth, Fiona Meyer, Jordan M Höhn et al.· Magnetic Resonance in Medici...· 0 citations
To evaluate the repeatability and consistency of rapid quantitative 23Na MRI of the human calf, an acquisition‐weighted stack‐of‐stars (AW‐SOSt) sequence was implemented on a 7T MRI system and used for all measurements. Three variants, differing only in nominal in‐plane spatial resolution (2.5, 5.0, and 7.5 mm) and corresponding acquisition times (8:04, 4:02, and 2:41 min), while maintaining a constant slice thickness of 15 mm, were employed for imaging the calf skeletal muscle. Quantitative consistency across resolutions and repeatability was evaluated in simulations and consecutive measurements of 10 healthy volunteers. The apparent tissue sodium concentration (aTSC) was determined using a postprocessing pipeline consisting of a B0, B1, relaxation, and partial volume correction (PVC). Deviations of the determined aTSC from simulated ground truth were below 6.0%. The simulated coefficient of variation (CV) improved with decreasing spatial resolution from 1.1% to 0.9%. The in vivo findings matched the simulation results. The CV improved with increasing voxel size, decreasing from 2.7% at 2.5‐mm resolution to 2.0% at 7.5‐mm resolution. Measurements remained highly consistent across different in‐plane resolutions, with a small increase in aTSC (≈0.2 mM) observed as a difference between lower resolutions (7.5 mm) and the highest resolution (2.5 mm). All applied protocols showed good repeatability and high consistency between the protocols. aTSC quantification using low‐resolution 23Na MRI showed improved repeatability, whereas in vivo measurements showed no effect on quantitative accuracy. This study demonstrates that low‐resolution 23Na MRI with short acquisition times combined with PVC could be a practical alternative to commonly used “high‐resolution” techniques with long acquisition times for quantifying aTSC in calf muscle tissue.
Jordan M Höhn, Tobias Wilferth, L. Gast et al.· NMR in Biomedicine· 0 citations
