Takatsu Yasuo, Nakamura Masafumi, Suzuki Yuichi, Miyati Tosiaki
Molecular Imaging, School of Medical Sciences, Fujita Health University, 1-98, Dengakugakubo, Kutsukake-cho, Toyoake, Aichi 470-1192, Japan; Division of Health Sciences, Graduate School of Medical Sciences, Kanazawa University, 5-11-80 Kodatsuno, Kanazawa, Ishikawa 920-0942, Japan.
Division of Health Sciences, Graduate School of Medical Sciences, Kanazawa University, 5-11-80 Kodatsuno, Kanazawa, Ishikawa 920-0942, Japan; Department of Radiology, Otsu City Hospital, 2-9-9, Motomiya, Otsu-City, Shiga 520-0804, Japan.
Magn Reson Imaging. 2023 Jun;99:41-47. doi: 10.1016/j.mri.2023.01.009. Epub 2023 Jan 20.
The position dependence of the apparent diffusion coefficient (ADC) in magnetic resonance imaging (MRI) by echo-planar imaging (EPI)- and turbo spin echo (TSE)-diffusion-weighted imaging (DWI) was assessed using phantoms.
Six pure water-filled containers were placed parallel to the direction of the static magnetic field from the center of the magnetic field to the foot direction (five containers) and the head direction (one container). Six slice positions were set, and a cross-section image was scanned at the center of each container using a 1.5-T MRI scanner. Diffusion times for both EPI- and TSE-DWI were matched as much as possible. The slice thickness was adjusted to match the signal-to-noise ratio (SNR) at the center of the magnetic field for both sequences. A B map was analyzed. The ADC and SNR at each position of both sequences were tested using the Wilcoxon signed-rank test (P = 0.05) and compared using Friedman and Steel-Dwass multiple comparison tests (P = 0.05). Pearson correlation coefficients between ADC and SNR and between ADC and flip angle (FA) were calculated.
ADC decreased significantly with distance from the center of the magnetic field for both EPI-DWI and TSE-DWI (P < 0.05). TSE-ADC was significantly higher than EPI-ADC for all combinations (P < 0.01). Based on the Friedman test, the SNR of EPI- and TSE-DWI was significantly different and depended on the slice position (P < 0.01). The Pearson correlation coefficient between ADC and SNR was 0.78 in EPI-DWI and 0.60 in TSE-DWI, whereas that between ADC and FA was 0.97 in EPI-DWI and 0.94 in TSE-DWI. The FA decreased by 0.048 and 0.047° per mm from the center of the magnetic field to head and foot directions, respectively.
ADC depends on the slice position and decreases with an increase in distance from the magnetic field center. Caution should be taken when comparing and quantitatively evaluating the ADC at sites shifted in the long-axis direction.
使用体模评估回波平面成像（EPI）和快速自旋回波（TSE）扩散加权成像（DWI）在磁共振成像（MRI）中表观扩散系数（ADC）的位置依赖性。
将六个装满纯水的容器平行于静磁场方向放置，从磁场中心向足部方向（五个容器）和头部方向（一个容器）。设置六个切片位置，并使用1.5-T MRI扫描仪在每个容器的中心扫描横断面图像。EPI-DWI和TSE-DWI的扩散时间尽可能匹配。调整切片厚度以匹配两个序列在磁场中心的信噪比（SNR）。分析B图。使用Wilcoxon符号秩检验（P = 0.05）测试两个序列每个位置的ADC和SNR，并使用Friedman和Steel-Dwass多重比较检验（P = 0.05）进行比较。计算ADC与SNR之间以及ADC与翻转角（FA）之间的Pearson相关系数。
对于EPI-DWI和TSE-DWI，ADC均随距磁场中心距离的增加而显著降低（P < 0.05）。在所有组合中，TSE-ADC均显著高于EPI-ADC（P < 0.01）。基于Friedman检验，EPI-DWI和TSE-DWI的SNR存在显著差异，且取决于切片位置（P < 0.01）。EPI-DWI中ADC与SNR之间的Pearson相关系数为0.78，TSE-DWI中为0.60，而EPI-DWI中ADC与FA之间的Pearson相关系数为0.97，TSE-DWI中为0.94。从磁场中心向头部和足部方向，FA分别以每毫米0.048°和0.047°的速度下降。
ADC取决于切片位置，并随距磁场中心距离的增加而降低。在比较和定量评估长轴方向偏移部位的ADC时应谨慎。
