3.0 T MR多源射频发射技术在心脏平衡式快速场回波序列中的应用价值

The value of multi-source RF-transmission in balanced fast field echo cardiac cine imaging at 3.0 T magnetic resonance imaging

目的 探讨多源射频发射（MT）技术在改善心脏平衡式快速场回波（BFFE）电影序列图像中的作用.方法 15名志愿者进行3.0 TMR心脏成像,用和不用MT技术分别采集B1图.用不同的采集方法单源射频发射技术（ST）、MT、短TR多源射频发射技术（MTS）采集左室短轴面及四腔心位BFFE心脏电影图像.对B1场均匀性和对比噪声比（CNR）进行定量分析,B1均匀性用感兴趣区内像素值表示,采用Student t检验进行比较.CNR=（SI心室-SI室间隔）/0.5×（SD心室＋SD室间隔）,采用单因素方差分析比较3组CNR,用LSD方法进行两两比较.按4分值对图像质量进行评分,采用Friedman秩和检验比较3组评分结果,用Wilcoxon秩和检验进行两两比较.2名医师双盲法阅片,采用Kappa检验比较2名医师间评分的一致性.结果 在其他扫描参数不变的情况下,采用MT技术的图像B1场均匀性明显高于传统单源射频（ST）技术的图像均匀性（t=21.632,P＜0.01）.使用ST、MT和MTS技术时,左心室CNR分别为10.8±2.2、14.4±2.4和14.1±2.2,右心室CNR分别为7.7±1.2、12.2±1.4及12.0±1.2,差异均有统计学意义（F值分别为11.617、61.472,P值均＜0.01）.两两比较,多源组均高于单源组,差异有统计学意义,而2个多源组间CNR差异无统计学意义.医师1、2使用ST、MT和MTS技术的图像评分分别为（4.60±1.18）、（6.53±1.19）、（6.73±1.03）和（4.73±1.10）、（6.67±1.29）、（6.73±0.88）分,3组间评分结果差异有统计学意义（x2分别为23.577、24.275,P值均＜0.01）.与ST组相比较,MT组和MTS组的图像质量明显改善,差异有统计学意义.2位医师的评分结果一致性较好,ST、MT及MTS时的K值分别为0.643、0.722及0.814（P值＜0.05）.结论 采用MT技术可以明显提高CNR及B1均匀性,明显改善图像质量,减少伪影,还可以在正常特殊吸收率（SAR）范围内缩短TR值,增加扫描速度.

Objective To assess the advantages of multi-source RF transmission（MT） for balanced fast field echo（BFFE） cardiac cine imaging.Methods Fifteen volunteers were scanned on a clinical 3.0 T MR system equipped with MT.Acquisition of B1 maps with and without MT were followed by axial and four chambers BFFE cine imaging for all subjects with different transmission modes[single source RF transmission （ST）,MT and MT with allowable shortest TR（MTS）].The B1 field uniformity and contrast to noise ratio （CNR） were quantitatively analyzed.The B1 field uniformity was evaluated by the pixel values within the ROI and was compared with Student t test.CNR was defined as follows：（SIblood-SImyocardium）/ 0.5 ×（SDblood ＋ SDmyocardium）.CNR were tested with one-way ANOVA for three groups comparision and with LSD for inter-group comparison.Image qualities were blindly assessed by 2 readers with a 4-score scale.Global image quality scores were tested for statistical significance by using the nonparametric paired sample Friedman rank test for three groups and the Wilcoxon signed rank test for further inter-group comparison.The Kappa statistics was used to assess interreader agreement.Results B1 homogeneity was significantly improved for images with MT compared with ST under the condition of other parameters unchanged （t =21.632,P 〈0.01）.In left ventricular,CNR of blood and myocardium was improved from 10.8 ±2.2 for ST to 14.4 ± 2.4 for MT and 14.1 ± 2.2 for MTS.In fight ventricular,it was improved from 7.7 ± 1.2 for ST to 12.2 ± 1.4 for MT and 12.0 ± 1.2 for MTS.The differences were statistically significant （F =11.617,61.472,P 〈0.01）.The images of MT and MTS groups demonstrated greater CNR versus the ST images.There was no statistical difference between latter two groups.The image scores of Reader 1 and 2 were 4.60 ± 1.18 and 4.73 ± 1.10 for ST,6.53 ± 1.19 and 6.67 ± 1.29 for MT and 6.73 ± 1.03 and 6.73 ± 0.88 for MTS respectively.There were statistically differences among three groups （x2 =23.577,24.275,P 〈 0.01）.The image quality was improved on BFFE images using MT and MTS technology compared to ST technology,and there were also significant differences.The interreader agreement between two readers was good [K=0.643,0.722 and 0.814（P 〈0.05） for ST,MT,and MTS group respectively].Conclusions MT technology significantly improves B1 field uniformity,increases CNR and reduces artifact on BFFE cardiac cine images.The TR is decreased within the normal SAR ranges,and thus scanning speed is increased.