改装高通道线圈实现头颈部放疗模拟定位的可行性研究

A feasibility study on reequipping multi-channel coils for simulation in head and neck radiotherapy

目的:改装两片式16通道(16ch)柔性线圈,建立头颈部模拟定位高通道线圈扫描方案,并评价其可行性。方法:将两片式16ch柔性线圈改装成与头颈部放疗摆位辅助装置相匹配的包绕式设计,进行序列采集,加速因子分别设置为2和3。使用标配的6通道(6ch)线圈,进行相同序列采集,其最大支持加速因子为2,并将其作为参考图像,进行图像质量的比较。对图像各项指标进行定量分析,包括几何畸变百分比(%GD)、层位置(SP)、层厚(ST)、百分图像均匀性(PIU)、伪影比(GR)、信噪比(SNR)和高对比空间分辨率(HCSR);并记录各线圈和不同加速因子时的扫描时间。结果:ACR标准T1加权和T2加权序列,使用16ch线圈PIU较6ch线圈平均提高17.1%,其余各项指标两者差别均较小。加速因子均设置为2且扫描参数相同,16ch较6ch线圈相比,模拟定位序列各序列SNR平均相对提高约21.9%,PIU平均相对提高约10.3%,扫描时间和其它图像参数差别较小。16ch线圈加速因子3与6ch线圈加速因子2比较,时间缩短24.4%,PIU升高8.56%,但SNR下降10.86%。结论:本研究改装的高通道线圈磁共振模拟定位技术可满足临床需要;在不增加扫描时间的前提下,可显著提高图像的信噪比;在保持图像质量相近的前提下,可支持更快的并行采集方案,显著缩短扫描时间。

Objective To propose a scanning scheme based on reequipped two-piece 16-channel(16 ch) flexible coils for the simulation in head and neck radiotherapy, and to evaluate its feasibility. Methods Two-piece 16 ch flexible coils were reequipped with a wrap-around shape that matched the auxiliary positioning device in head and neck radiotherapy for sequence acquisition.The acceleration factors were set at 2 and 3. The image obtained in sequence acquisition using standard 6-channel(6 ch) coils and the maximum support acceleration factor of 2 was used as the reference image for the comparison of image quality. Various indicators were quantitatively analyzed, including percentage of geometric distortion(%GD), slice position(SP), slice thickness(ST), percent image uniformity(PIU), ghosting ratio(GR), signal-to-noise ratio(SNR) and high-contrast spatial resolution(HCSR).Moreover, the scanning time was recorded when adopting different coils and acceleration factors. Results For ACR standard sequences T1 WI and T2 WI, PIU obtained using 16 ch coils was 17.1% higher than that obtained using 6 ch coils, and the differences in the other indicators were trivial. With the same acceleration factor(=2) and the same scanning parameters, SNR and PIU which were obtained using 16 ch coils were higher than those obtained using 6 ch coils, with an increase of about 21.9% and about 10.3%,respectively, and there were small differences in scanning time and other image indicators. Compared with those obtained using6 ch coils with an acceleration factor of 2, the scanning time obtained using 16 ch coil with an acceleration factor of 3 for sequence acquisition was shortened by 24.4%, and PIU was increased by 8.56%, but SNR was decreased by 10.86%. Conclusion The reequipped multi-channel coils for radiotherapy simulation which can meet clinical requirements can significantly improve image SNR without increasing the scanning time and support the parallel acquisition technique while maintaining image quality, thereby greatly shortening scanning time.