Abstract
ObjectivesTo prospectively evaluate the impact of 3.0 T Cardiac MR imaging using dual-source parallel radiofrequency (RF) transmission with patient-adaptive B1 shimming compared with single-source RF transmission in the RF homogeneity, image contrast and image quality.MethodsThe study was approved by the local institutional review board, and all subjects provided written informed consent. Fourteen healthy volunteers were examined at 3.0 T MR, with both the conventional single-source and the new dual-source RF transmission. B1 calibrations (RF shimming) of the heart region were performed to acquire a percent of the prescribed flip angle (FA) of B1 maps, which were used for quantitative assessment of RF homogeneity. Contrast ratios (CRs) between ventricular blood pool and septum were calculated on balanced-turbo field echo (B-TFE) cine images. The off-resonance artifacts of cine images were blindly assessed by two radiologists according to a 4-point grading-scale.ResultsA significantly lower mean coefficients of variance of the achieved FA with dual-source revealed better RF homogeneity compared to single-source (P = 0.0094). Dual-source RF shimming significantly increased the CRs (P<0.05) and reduced the off-resonance artifacts of B-TFE cine images (P<0.05). Inter-observer agreement for the off-resonance artifacts of B-TFE cine images was good to excellent (k >0.65).ConclusionsDual-source parallel RF transmission significantly improves the RF homogeneity, increases image contrast and reduces image artifacts of cardiac B-TFE images compared to single-source mode. This may be of value in reducing the observer-dependence of cardiac MR images and enhancing diagnostic confidence for clinical practice using CMR at 3.0 T.
Highlights
In recent years, higher-field strength MR systems ($3.0 T) have been more and more used in both clinical diagnosis and scientific researches by using the balanced steady-state free precession (b-SSFP) imaging, such as cardiac function, cardiac flow analysis and the other imaging techniques [1,2,3]
High-field MR imaging at 3.0 T comes with some technical issues, including radiofrequency (RF) field inhomogeneity, local specific energy absorption rate (SAR) peaks and susceptibility artifacts [1]
The increase in RF power deposition and the presence of off-resonance artifacts are closely related to the nonuniformity of the main magnetic field (B0) and RF field (B1) [1,4]
Summary
Higher-field strength MR systems ($3.0 T) have been more and more used in both clinical diagnosis and scientific researches by using the balanced steady-state free precession (b-SSFP) imaging, such as cardiac function, cardiac flow analysis and the other imaging techniques [1,2,3]. High-field MR imaging at 3.0 T comes with some technical issues, including radiofrequency (RF) field inhomogeneity, local specific energy absorption rate (SAR) peaks and susceptibility artifacts [1]. B0 field uniformity is critical at 3.0 T, while maintaining the homogeneity of the B1 field is more of a challenge. The uniformity of the RF field is associated with a homogeneous distribution of the flip angle (FA) across imaging volume. This factor allows for an optimized SAR distribution and reducing local SAR peaks, which makes it possible at a highfield MR to lower the repetition time (TR) or increase FA of the SSFP sequences [1,5,6,7]. B1 inhomogeneity in turn increases its susceptibility to B0 inhomogeneity
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