Department of Radiology, Children's Medical Center of Dallas, Dallas, Texas 75235, USA.
Med Phys. 2011 Jul;38(7):4415-21. doi: 10.1118/1.3595111.
To propose a quality assurance procedure for routine clinical diffusion tensor imaging (DTI) using the widely available American College of Radiology (ACR) head phantom.
Analysis was performed on the data acquired at 1.5 and 3.0 T on whole body clinical MRI scanners using the ACR phantom and included the following: (1) the signal-to-noise ratio (SNR) at the center and periphery of the phantom, (2) image distortion by EPI readout relative to spin echo imaging, (3) distortion of high-b images relative to the b= 0 image caused by diffusion encoding, and (4) determination of fractional anisotropy (FA) and mean diffusivity (MD) measured with region-of-interest (ROI) and pixel-based approaches. Reproducibility of the measurements was assessed by five repetitions of data acquisition on each scanner.
The SNR at the phantom center was approximately half of that near the periphery at both 1.5 and 3 T. The image distortion by the EPI readout was up to 7 mm at 1.5 T and 10 mm at 3 T. The typical distortion caused by eddy currents from diffusion encoding was on the order of 0.5 mm. The difference between ROI-based and pixel-based MD quantification was 1.4% at 1.5 T and 0.3% at 3 T. The ROI-based MD values were in close agreement (within 2%) with the reference values. The ROI-based FA values were approximately a factor of 10 smaller than pixel-based values and less than 0.01. The measurement reproducibility was sufficient for quality assurance (QA) purposes.
This QA approach is simple to perform and evaluates key aspects of the scanner performance for DTI data acquisition using a widely available phantom.
提出一种使用广泛可用的美国放射学院（ACR）头部体模对常规临床扩散张量成像（DTI）进行质量保证的程序。
在 1.5T 和 3.0T 全身临床 MRI 扫描仪上使用 ACR 体模对采集的数据进行分析，包括以下内容：（1）体模中心和周边的信噪比（SNR），（2）EPI 读出相对于自旋回波成像的图像失真，（3）扩散编码引起的高 b 图像相对于 b=0 图像的失真，以及（4）使用感兴趣区（ROI）和像素的方法测量各向异性分数（FA）和平均扩散系数（MD）。通过在每台扫描仪上重复五次数据采集来评估测量的可重复性。
在 1.5T 和 3T 时，体模中心的 SNR 约为周边的一半。EPI 读出引起的图像失真在 1.5T 时最大可达 7mm，在 3T 时最大可达 10mm。扩散编码引起的典型涡流失真约为 0.5mm。基于 ROI 和基于像素的 MD 定量之间的差异在 1.5T 时为 1.4%，在 3T 时为 0.3%。基于 ROI 的 MD 值与参考值非常吻合（在 2%以内）。基于 ROI 的 FA 值约为基于像素值的十分之一，小于 0.01。测量的可重复性足以满足质量保证（QA）的目的。
这种 QA 方法简单易行，使用广泛可用的体模评估了 DTI 数据采集的扫描仪性能的关键方面。
