1．5TMR不同b值的扩散加权成像（DWI）在肺内实性病变鉴别中的优化

Optimization of Different b Value in Diffusion-weighted MRI at 1.5T for the Differential Diagnosis of Solid Pulmonary Lesions

目的探讨MR扩散加权成像（DWI）中不同b值在肺内实性病变鉴别诊断中的应用及优化。方法收集我院肺内病变60例。其中恶性病变32例，良性病变28例。应用呼吸门控技术，在相同扫描参数下，激励次数（NEX）8次，采用三组不同b值分别等于（500s／mm2；800s／mm2；1000s／mm2）进行胸部DWI序列扫描。测量并分析三组ADC值特点及不同b值对影像质量、信噪比（SNR）、对比噪声比（CNR）的影响。结果在复杂的肺内病变影像中，采用不同b值时，ADC值测量结果呈现出逐步下降趋势，影像质量、信噪比、对比噪声比存在差异，ADC值测量结果均具有诊断价值。其中选择b=1000s／mm2时，最具有临床诊断意义。结论在1．5T场强下，应用上述参数及呼吸门控技术，在激励次数为8次，b=1000s／mm2时，操作特征（ROC）曲线下面积最大为0．636，其敏感度为61．5％，特异度为71．9％，最具有临床诊断意义，优于其它两种方案，未产生严重的磁敏感性伪影，但信噪比有所下降，仍可以清晰显示感兴趣区域的组织及病变形态。

Objective To investigate the utility and optimization of b value in diffusion-weighted MR imaging for differential diagnosis of solid pulmonary lesions. Methods 60 cases of pulmonary lesions were collected, consisting of 32 malignant cases and 28 benign cases. With respiratory gating techniques and number of excitation （NEX） of 8, chest DWI sequence scannings were operated at four different groups of b-value under the same scan parameters. ADC values were measured and the impacts of b value on imaging quality and signal-to-noise ratio （SNR） were analyzed. Results Of the complex images of pulmonary lesions, the ADC value and imaging quality varied with different b-value. When b value was 1000 s/mm2, the highest clinical diagnostic significance could be obtained. Conclusions In diffusion-weighted imaging （1.5T） of pulmonary lesions with respiratory gating techniques and the number of excitation （NEX） of 8, the ADC values in three groups of b value （500, 800 and 1000 s/mm2） were stable and diagnostically significance. When b value was 1000 s/mm2, the maximal area under curve that was the most clinically diagnostically significant was acquired, of which the sensitivity was 61.5% and the specificity was 71.9%, without serious magnetic susceptibility artifacts, with signal-to-noise ratios and contrast-to-noise ratios in accepted range.