Wong Oi Lei, Yuan Jing, Yu Siu Ki, Cheung Kin Yin
Medical Physics and Research Department, Hong Kong Sanatorium & Hospital, Happy Valley, Hong Kong, Hong Kong SAR, China.
Quant Imaging Med Surg. 2017 Apr;7(2):205-214. doi: 10.21037/qims.2017.02.08.
A flexible RF coil setting has to be used on an MR-simulator (MR-sim) in the head and neck simulation scan for radiotherapy (RT) purpose, while the image quality might be compromised due to the sub-optimized flexible coil compared to the normal diagnostic radiological (DR) head coil. In this study, we assessed the image quality of an MR-sim by conducting the standard American College of Radiology (ACR) MRI phantom test on a 1.5T MR-sim under RT-setting and comparing it to DR-setting.
A large ACR MRI phantom was carefully positioned, aligned and scanned 9 times for each under RT- and DR-setting on a 1.5T MR-sim, following the ACR scanning instruction. Images were analyzed following the ACR guidance. Measurement results under two coil settings were quantitatively compared. Inter-observer disagreements under RT-setting between two physicists were compared using Bland-Altman (BA) analysis and intra-class correlation coefficient (ICC).
The MR-sim with RT-setting obtained sufficiently good image quality to pass all ACR recommended criteria. No significant difference was found in phantom length accuracy, high-contrast spatial resolution, slice thickness accuracy, slice position accuracy, and percent-signal ghosting. RT-setting significantly under-performed in low-contrast object detectability, while better performed in image intensity uniformity. BA analysis showed that 95% limit of agreement and biases of phantom test measurement under RT-setting between two observers were very small. Excellent inter-observer agreement (ICC >0.75) was achieved in all measurements except for slice thickness accuracy (ICC =0.42, moderate agreement) under RT-setting.
Very good and highly reproducible image quality could be achieved on a 1.5T MR-sim with a flexible coil setting as revealed by the standard ACR MRI phantom test. The flexible RT-setting compromised in image signal-to-noise ratio (SNR) compared to the normal DR-setting, and resulted in reduced low-contrast object detectability.
在用于放疗（RT）目的的头颈部模拟扫描的磁共振模拟机（MR-sim）上，必须使用灵活的射频线圈设置，然而，与普通诊断放射学（DR）头部线圈相比，由于灵活线圈的优化不足，图像质量可能会受到影响。在本研究中，我们通过在1.5T MR-sim上进行标准的美国放射学会（ACR）MRI体模测试，并将其与DR设置进行比较，来评估MR-sim的图像质量。
按照ACR扫描说明，在1.5T MR-sim上，将一个大型ACR MRI体模小心放置、对齐，并在RT设置和DR设置下各扫描9次。按照ACR指南对图像进行分析。对两种线圈设置下的测量结果进行定量比较。使用Bland-Altman（BA）分析和组内相关系数（ICC）比较两名物理学家在RT设置下的观察者间差异。
采用RT设置的MR-sim获得了足够好的图像质量，能够通过所有ACR推荐标准。在体模长度精度、高对比度空间分辨率、切片厚度精度、切片位置精度和百分比信号鬼影方面未发现显著差异。RT设置在低对比度物体可检测性方面表现明显较差，而在图像强度均匀性方面表现较好。BA分析表明，两名观察者在RT设置下的体模测试测量的95%一致性界限和偏差非常小。除了RT设置下的切片厚度精度（ICC = 0.42，中等一致性）外，所有测量均实现了出色的观察者间一致性（ICC > 0.75）。
标准的ACR MRI体模测试表明，在1.5T MR-sim上使用灵活的线圈设置可实现非常好且高度可重复的图像质量。与正常DR设置相比，灵活的RT设置在图像信噪比（SNR）方面有所妥协，并导致低对比度物体可检测性降低。
