Department of Radiology, Charité-Universitätsmedizin Berlin, Charitéplatz 1, Berlin, Germany.
Radiology. 2010 Oct;257(1):80-6. doi: 10.1148/radiol.10092489. Epub 2010 Aug 2.
To analyze the dynamics of the shear modulus of the liver to assess the optimal driving frequency and to determine the diagnostic accuracy of generalized frequency-independent elasticity cutoff values for staging hepatic fibrosis.
This institutional review board-approved prospective study included 16 healthy volunteers and 72 patients with biopsy-proved liver fibrosis. After obtaining written informed consent, imaging was performed at 1.5-T by using a motion-sensitized echo-planar imaging sequence. Wave excitation was performed by an actuator introducing a superposition of four frequencies (25.0, 37.5, 50.0, 62.5 Hz) of shear waves. The elasticity µ value and the structure geometry parameter α were calculated by using the two-parameter springpot model. The performance of magnetic resonance (MR) elastography in staging liver fibrosis was assessed with area under the receiver operating characteristic curve (AUROC) analysis and Spearman correlation analysis.
Elasticity increased with stage of fibrosis, with mean values as follows: for volunteers, 2.25 kPa ± 0.43 (standard deviation); stage F1, 2.61 kPa ± 0.43; stage F2, 3.00 kPa ± 0.63; stage F3, 3.86 kPa ± 0.61; and stage F4, 5.86 kPa ± 1.22. Frequency-independent cutoff values derived for fibrosis and AUROC values, respectively, were as follows: stage F1 or higher, 2.84 kPa and 0.9128; stage F2 or higher, 3.18 kPa and 0.9244; stage F3 or higher, 3.32 kPa and 0.9744; and equivalent to stage F4, 4.21 kPa and 0.9931. The geometry of the tissue (α value) did not correlate with fibrosis. Frequencies of 50.0 Hz and 62.5 Hz displayed the highest diagnostic accuracy.
The diagnostic performance of multifrequency MR elastography in determining the degree of hepatic fibrosis increases with stage of fibrosis. Metrics obtained at the higher frequencies provide better diagnostic performance compared with the lower frequencies. Results of the AUROC analysis demonstrate the high accuracy of frequency-independent cutoff values for staging higher grades of hepatic fibrosis.
分析肝脏剪切波弹性模量的动力学，以确定最佳驱动频率，并确定广义频率无关弹性截断值在肝纤维化分期中的诊断准确性。
本研究经机构审查委员会批准，为前瞻性研究，纳入 16 名健康志愿者和 72 名经肝活检证实的肝纤维化患者。在获得书面知情同意后，采用运动敏感型 echo-planar 成像序列在 1.5-T 磁共振扫描仪上进行成像。通过致动器引入四个频率（25.0、37.5、50.0、62.5 Hz）的剪切波进行波激发。通过双参数弹簧模型计算弹性µ值和结构几何参数α。采用受试者工作特征曲线（ROC）下面积（AUROC）分析和 Spearman 相关分析评估磁共振弹性成像在肝纤维化分期中的性能。
弹性随纤维化程度的增加而增加，平均值如下：志愿者组为 2.25 kPa±0.43（标准差）；F1 期为 2.61 kPa±0.43；F2 期为 3.00 kPa±0.63；F3 期为 3.86 kPa±0.61；F4 期为 5.86 kPa±1.22。为纤维化和 AUROC 分别推导的频率无关截断值如下：F1 期或更高，2.84 kPa 和 0.9128；F2 期或更高，3.18 kPa 和 0.9244；F3 期或更高，3.32 kPa 和 0.9744；F4 期相当，4.21 kPa 和 0.9931。组织的几何形状（α 值）与纤维化无关。50.0 Hz 和 62.5 Hz 的频率显示出最高的诊断准确性。
多频磁共振弹性成像在确定肝纤维化程度方面的诊断性能随纤维化程度的增加而提高。与较低频率相比，较高频率获得的指标具有更好的诊断性能。ROC 分析结果表明，频率无关截断值在肝纤维化较高分期中的准确性较高。
