| PurposeTo prospectively assess the performance of3.0T Cardiac MR imaging using dual-source parallel radiofrequency (RF) transmission with patient-adaptive B1shimming compared with single-source RF transmission in the RF homogeneity, image contrast and image quality.BackgroundIn recent years, higher-field strength MR systems (≥3.0T) 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. However, high-field MR imaging at3.0T also comes with some technical issues, including radiofrequency (RF) field inhomogeneity, local specific energy absorption rate (SAR) peaks and susceptibility artifacts.Materials and MethodsWith institutional review board approval and written informed consent,14healthy volunteers were scanned at3.0T MR equipped with a dual-channel parallel RF transmission technology. B1calibrations (RF shimming) of the area of the whole heart were performed utilizing conventional and dual-source RF transmission respectively, and B1maps of short-axis plane across the left ventricle without and with dual-source were scaled as a percent of the prescribed flip angle (FA), which was used for quantitative assessment of RF homogeneity. Contras ratios (CRs) between ventricular blood pool and septum on short-axis balanced-turbo field echo (B-TFE) ventricular cine images were calculated to evaluate the effect of dual-source versus single-source RF transmission. The off-resonance artifacts were assessed by two radiologists according to a4-point grading scale. Statistical significance was calculated with the Kruskal-Wallis signed rank test. Inter-observer agreement was evaluated with Cohen’s kappa test.ResultsQuantitative B1maps analysis revealed a significantly higher mean percentage of the achieved flip angle (85.38%with dual-source vs76.74%with single source, P=0.0152＜0.05) and a significantly lower mean coefficients of variance (0.066with dual-source vs0.103with single-source, P=0.0094＜0.05). The CRs of short-axis B-TFE ventricular cine images were significantly increased with the use of dual-source RF transmission, as compared with single-source RF excitation (both LV and RV, P<0.05). Overall inter-observer agreement for the off-resonance artifacts of the B-TFE ventricular cine images was good to excellent (K＞0.65). Dual-source RF shimming significantly improved the quality of B-TFE cine images and reduced the off-resonance artifacts (reader A:3.57±0.51vs2.14±0.36, P=0.0002; reader B:3.64±0.49vs2.28±0.46, P=0.0001).ConclusionsDual-source parallel RF transmission with B1shimming significantly improves the homogeneity of RF field and increases image contrast of cardiac B-TFE cine images. An improved B1homogeneity leads to an improved SAR model (shorter TR), which significantly reduces image artifacts. PurposeTo prospectively assess the effect of dual-source radiofrequency (RF) transmission technique on left ventricular (LV) measurements and the reproducibility of these measurements at3.0T magnetic resonance (MR) using balanced steady-state free precession (b-SSFP) cine imaging, compared with the conventional single-source RF transmission reference approach.BackgroundThe b-SSFP cardiac MR imaging has been considered as a preferred method for assessment of LV volume and size at1.5T but may experience B1field inhomogeneity, local SAR (specific absorption rate) peaks and susceptibility off-resonance artifacts at3.0T. Recently, dual-source RF transmission system has been proposed as a means for improving them.Materials and MethodsCardiac MR imaging was performed in19subjects by using a3.0T MR unit equipped with a dual-source RF transmission system. The effect of conventional versus dual-source RF transmission on b-SSFP cine sequences was evaluated. All images were analyzed to obtain LV end-diastolic volume (EDV), end-systolic volume (ESV), stroke volume (SV), ejection fraction (EF), mass, LV end-diastolic inferior wall thickness (LVIW) and interventricular septal thickness (IVS) by using the semiautomated segmentation software. The difference of all LV measurements between the two imaging techniques was tested with the paired t test and the intertechnique agreement was tested through linear regression and Bland-Altman analyses. Additionally, repeated LV measurements were performed to determine intra-and inter-observer variability with the Bland-Altman method, the coefficient of variation (CV) and the intra-class correlation coefficient (ICC).ResultsCompared with conventional single-source reference, dual-source technique slightly overestimated EDV, ESV and SV volumes (mean differences,3.9mL±9.7,1.1mL±2.6and2.8mL±9.1, respectively; P＞0.05), resulting in a small but significant positive bias in the calculated EF (1.5%±2.6; P=0.021). The calculated LV mass was significantly smaller with dual source than with conventional single-source (mean difference,-4.0g±6.5, P=0.001). Dual-source slightly underestimated IVS (-0.29mm±0.6, P=0.067) and significantly underestimated LVIW (-0.55mm±0.4, P＜0.0001). However, the percentage difference of all LV measurements was within4.0%level with the exception of LVIW (8.1%) between the two imaging techniques and the two techniques correlated highly, as reflected by r2values (0.81to0.96, P＜0.0001). Intra-and inter-observer variability in the dual-source measurements was much lower than that in single-source values, and all variability values were＜14.0%.ConclusionsImproved image quality of b-SSFP cine imaging performed by using dual-source RF transmission technique at3.0T MR may provide more reproducible and accurate measurements of LV compared with conventional single-source reference approach. The superior reproducibility of LV measurements with dual-source favors this technique for clinical use. PurposeThe aim of this study was to prospectively evaluate the diagnostic performance of cardiac MR (CMR) in children with suspected acute myocarditis (AMC) and chronic myocarditis (CMC) after respiratory or gastrointestinal tract viral infection, as well as to follow the course of myocatditis.BackgroundOn the basis of published data, CMR has recently emerged as a noninvasive tool to diagnosis myocarditis. With this technique, it is possible to visualize the changes of myocardial inflammation (oedema, necrosis and fibrosis). However, the majority of these studies were focused on adult myocarditis. The need for accurate diagnosis of pediatric viral myocarditis arises from the low diagnostic accuracy of routine clinical tests.Materials and MethodsOur study design was adapted from the "Lake Louise criteria" and approved by the local ethics committee. We examined73childhood and adolescent patients with clinically suspected AMC (defined by symptoms≤14days; n=25) and CMC (symptoms＞14days; n=48). We compared these patients to17controls. All subjects underwent CMR, including function analyses, T2-weighted imaging for assessment of myocardial edema (regional or global T2ratio), T1-weighted imaging before and after contrast administration for evaluation of hyperemia (global early gadolinium enhancement ratio, EGEr), and assessment of late gadolinium enhancement (LGE).9patients with severe (fulminant) myocarditis out of AMC returned for the follow-up CMR＞4weeks after presentation.ResultsIn the acute phase (AMC), the T2ratio was elevated in56%, EGEr in68%, and LGE was present in52%of the patients. In group AMC,19patients (76%) were any2of3MR parameters (T2ration, EGEr and LGE) abnormal. We found a significant difference between patients with suspected AMC and controls in LVEF (51.2%vs.61.3, P＜0.001), LV mass (130.2±14.0vs.120.5±13.9g, P=0.035), mean T2ratio (1.96±0.2vs.1.69±0.13, P＜0.001), and mean EGEr (4.1±0.27vs.3.4±0.39, P＜0.001). For group CMC, the T2ratio was elevated in35.4%, EGEr in43.7%, and LGE was present in31.3%of the patients. In group CMC,26patients (54.1%) were any2of3MR parameters abnormal. There was no statistically significant difference between CMC and controls in LVEF and mass (P＞0.05), but mean T2ratio (1.88±0.18vs.1.69±0.13, P=0.005) and EGEr (3.93±0.22vs.3.4±0.39, P＜0.001). However, the mean T2ratio and EGEr in CMC were less than the proposed cut-off values. At follow-up, there was an increase in LVEF (48.6%vs.59.7%, P＜0.001) while both T2ratio (2.04±0.16vs.1.8±0.11, P＜0.001) and EGEr (4.34±0.43vs.3.85±0.17, P=0.013) significantly decreased. The LGE persisted in4patients.ConclusionsA comprehensive CMR is able to visualize the location and extent of inflammation over the course of paediatric myocarditis and may serve as a powerful noninvasive diagnostic tool in suspected AMC. In contrast, the diagnostic performance of CMR in children with suspected CMC may be valuable, but never satisfactory in clinical practice. |
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