Department of Clinical Radiology, Institute of Clinical Radiology, University Hospitals Munich, Campus Grosshadern, Munich, Germany.
Invest Radiol. 2010 May;45(5):245-54. doi: 10.1097/RLI.0b013e3181d83abc.
The purpose of this study was to evaluate the feasibility of diffusion tensor imaging of the kidney at a field strength of 3T. We assessed fractional anisotropy (FA) and apparent diffusion coefficients (ADC) of various acquisition protocols and determined the reproducibility of these measurements. FA, ADC, signal-to-noise ratios (SNR), and contrast-to-noise ratios (CNR) were compared with those acquired at 1.5T.
Ten healthy volunteers were examined with a respiratory-triggered echo-planar imaging sequence (TR: 1800 ms, TE: 58 ms, b = 0, 300 s/mm(2)) on a 3-Tesla whole-body MR scanner. Protocol variations included diffusion measurements during free-breathing, in 6 or 12 directions, and an additional b-value of 50 s/mm(2). A breath-hold protocol was also integrated (TR: 820 ms, TE: 58 ms, b = 0, 300 s/mm(2)). Measurements with 2 b-values and 6 diffusion directions were also acquired at 1.5 T. SNR was calculated with the difference-image method. Statistical analysis was performed with Wilcoxon signed-rank tests. Intrareader correlation was assessed with weighted kappa coefficients and reproducibility with the root-mean-square-average and the Bland-Altman-method.
At 3T, SNR of cortex and medulla and CNR of cortex/medulla were significantly higher than at 1.5T, leading to improved corticomedullary discrimination. There were no significant FA- and ADC differences with 2 b-values and 6 diffusion directions between measurements at 1.5T and 3T. FA of the medulla was significantly higher than that of the cortex in all measurements. Tractography visualized a typical radial diffusion direction in the medulla. Best image quality was achieved with a respiratory triggered protocol with 12 acquisition directions. Measurements with 3 b-values led to decreased ADCs. Acquisition in 12 directions resulted in decreased cortical FA. FA and ADC of breath-hold and free-breathing acquisitions were significantly higher than that of the respiratory-triggered protocol. Intrareader correlation ranged from kappa 0.60 to 0.96. Variance of the respiratory-triggered protocol was smaller than that of breath-hold and free-breathing protocols. Variance was highest for medullary FA in all protocols with reproducibility coefficients ranging from 0.36 to 0.46.
Diffusion tensor imaging of the kidney at 3T is feasible and yields significantly higher SNR and CNR. FA and ADCs do not significantly differ from 1.5T. Number of b-values influences ADC-values. Acquisitions in 12 directions provide lower cortical FA-values. We recommend a respiratory-triggered protocol because of improved image quality and reproducibility.
本研究旨在评估在 3T 场强下进行肾脏弥散张量成像的可行性。我们评估了各采集方案的各向异性分数（FA）和表观扩散系数（ADC），并确定了这些测量的可重复性。FA、ADC、信噪比（SNR）和对比噪声比（CNR）与 1.5T 时的测量值进行了比较。
10 名健康志愿者在 3T 全身磁共振扫描仪上使用呼吸触发的回波平面成像序列（TR：1800ms，TE：58ms，b=0、300s/mm²）进行检查。方案变化包括自由呼吸、6 个方向和 12 个方向以及附加 b 值为 50s/mm²的弥散测量。还整合了一个屏气协议（TR：820ms，TE：58ms，b=0、300s/mm²）。在 1.5T 时还采集了 2 个 b 值和 6 个扩散方向的测量值。SNR 采用差分图像法计算。统计分析采用 Wilcoxon 符号秩检验。采用加权 kappa 系数评估内部读者相关性，采用均方根平均和 Bland-Altman 法评估重复性。
在 3T 时，皮质和髓质的 SNR 和皮质/髓质的 CNR 均显著高于 1.5T，从而改善了皮质/髓质的区分。在 1.5T 和 3T 时，2 个 b 值和 6 个扩散方向的测量值之间没有显著的 FA 和 ADC 差异。在所有测量中，髓质的 FA 均显著高于皮质。弥散张量成像显示在髓质中存在典型的放射状扩散方向。使用具有 12 个采集方向的呼吸触发协议可获得最佳图像质量。使用 3 个 b 值会导致 ADC 值降低。在 12 个方向采集会导致皮质 FA 降低。屏气和自由呼吸采集的 FA 和 ADC 显著高于呼吸触发协议。内部读者相关性在 kappa 0.60 至 0.96 之间。呼吸触发协议的方差小于屏气和自由呼吸协议的方差。在所有协议中，髓质 FA 的方差最高，重复性系数在 0.36 至 0.46 之间。
3T 下的肾脏弥散张量成像可行，可获得显著更高的 SNR 和 CNR。FA 和 ADC 与 1.5T 时无显著差异。b 值的数量会影响 ADC 值。12 个方向的采集会降低皮质 FA 值。我们推荐使用呼吸触发协议，因为其具有改善的图像质量和可重复性。
