OBJECTIVE Diffusion-weighted imaging (DWI) in the liver suffers from signal loss due to the cardiac motion artifact, especially in the left liver lobe. The purpose of this work was to improve the image quality of liver DWI in terms of cardiac motion artifact reduction and achievement of black-blood images in low b-value images. MATERIAL AND METHODS Ten healthy volunteers (age 20-31 years) underwent MRI examinations at 1.5 T with a prototype DWI sequence provided by the vendor. Two diffusion encodings (i.e. waveforms), monopolar and flow-compensated, and the b-values 0, 20, 50, 100, 150, 600 and 800 s/mm2 were used. Two Likert scales describing the severity of the pulsation artifact and the quality of the black-blood state were defined and evaluated by two experienced radiologists. Regions of interest (ROIs) were manually drawn in the right and left liver lobe in each slice and combined to a volume of interest (VOI). The mean and coefficient of variation were calculated for each normalized VOI-averaged signal to assess the severity of the cardiac motion artifact. The ADC was calculated using two b-values once for the monopolar data and once with mixed data, using the monopolar data for the small and the flow-compensated data for the high b-value. A Wilcoxon rank sum test was used to compare the Likert scores obtained for monopolar and flow-compensated data. RESULTS At b-values from 20 to 150 s/mm2, unlike the flow-compensated diffusion encoding, the monopolar encoding yielded black blood in all images with a negligible signal loss due to the cardiac motion artifact. At the b-values 600 and 800 s/mm2, the flow-compensated encoding resulted in a significantly reduced cardiac motion artifact, especially in the left liver lobe, and in a black-blood state. The ADC calculated with monopolar data was significantly higher in the left than in the right liver lobe. CONCLUSION It is recommendable to use the following mixed waveform protocol: Monopolar diffusion encodings at small b-values and flow-compensated diffusion encodings at high b-values.

中文翻译：

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用于减少肝脏黑血弥散加权成像中心脏运动伪影的混合波形协议。

目的由于心脏运动伪影（尤其是在左肝叶中），肝脏中的弥散加权成像（DWI）会遭受信号丢失的困扰。这项工作的目的是通过减少心脏运动伪影和实现低b值图像中的黑血图像来改善肝脏DWI的图像质量。材料与方法十名健康志愿者（年龄在20-31岁之间）接受了供应商提供的原型DWI序列的1.5 T MRI检查。使用了两种扩散编码（即波形），即单极性和流量补偿，b值分别为0、20、50、100、150、600和800 s / mm2。由两名经验丰富的放射科医生定义并评估了两个描述脉动伪影的严重程度和黑血状态质量的李克特量表。在每个切片的右肝叶和左肝叶中手动绘制感兴趣区域（ROI），并合并到感兴趣的体积（VOI）。计算每个归一化VOI平均信号的平均值和变异系数，以评估心脏运动伪影的严重性。ADC的计算使用两个b值，一次用于单极性数据，一次使用混合数据，对于低b值使用单极性数据，对高b值使用流量补偿数据。使用Wilcoxon秩和检验比较单极性数据和流量补偿数据获得的Likert得分。结果在b值从20到150 s / mm2的情况下，与流补偿扩散编码不同，单极性编码在所有图像中产生黑血，由于心脏运动伪影而产生的信号损失可忽略不计。在b值600和800 s / mm2时，流量补偿编码可显着减少心脏运动伪影，尤其是在左肝叶和黑血状态下。用单极数据计算的ADC在左肝叶中明显高于在右肝叶中。结论建议使用以下混合波形协议：b值小的单极性扩散编码和b值高的流量补偿扩散编码。