放疗体位固定板材料对MR定位图像质量影响

目的 检测7种不同放疗体位固定板(体板)材料对MR定位图像质量的影响,为临床选择提供数据指导。方法 使用西门子MR定位机相同T1、T2序列扫描置于7种体板材料(Orfit碳纤维板、PC板、HP板;济南华宇新BR、WR、KP、SP材料)上的ACR LargePhantom模体,以直接置于扫描床上图像质量(无体板)为参照,分别分析:(1)高对比度空间分辨率(高对比):观察3对阵列小孔清晰度,分别代表左右、上下方向分辨率为1.1、1.0或0.9 mm;(2)图像灰度均匀性(PIU):PIU=100×[(1-(高-低)/(高+低)];(3)低对比度分辨率(低对比):记录对比度分别为5.1%、3.6%、2.5%和1.4%的4层面图像可分辨轮辐数。依据ACR模体指南判断图像质量是否满足临床需求,即高对比1.0 mm,T1WI及T2-PIU>82%,低对比轮辐数差≤3。结果 无体板、PC板、HP板及KP材料T1WI、T2WI图像高对比均为0.9 mm,其余>0.9 mm;无体板T1WI及T2-PIU值>87%,碳纤维板PIU值均下降>25%,其余相差不到±4%。低对比除碳纤维板其余轮辐数与标准相差在3以内。结论 实际治疗采用碳纤维板对MR图像质量影响最大,不宜用于MR定位。PC板和HP板基本与对比标准一致,BR及KP对MR信号影响甚微。其余材料也具有用于MR体位固定及附属部件制作的潜在价值。

Impact of immobilization base plates composed of various materials on the imaging quality of MR simulation during radiotherapy

Objective To compare the impact of immobilization base plates composed of 7 types of materials on the MR-simulation imaging quality used for radiotherapy, aiming to provide reference data for clinical applications. Methods Using identical T1 and T2 sequences of Siemens MR-simulator, the MR images of ACR Large Phantom were acquired on the Orfit carbon fiber laminate,polycarbonate (PC),high precision base plate (HP),Jinan Huayuxin BR,WR,KP and SP materials, respectively. The imaging quality without any plate was used as the baseline data. The following metrics were compared:1.High-contrast spatial resolution:the sharpness of 3 pairs of hole arrays was observed, which represented resolutions of 1.1 mm,1.0 mm and 0.9 mm on the LR and AP directions;2.Image intensity uniformity in terms of percent integral uniformity (PIU):PIU=100×[1-((high-low)/(high+low)];3. Low-contrast resolution:distinguishable spokes representing resolutions of 5.1%, 3.6%, 2.5% and 1.4% were recorded. According to ACR recommendations, high-contrast resolution of 1.0 mm, PIU of T1WI and T2>82%and low-contrast spoke difference<3 were considered as clinically acceptable. Results High-contrast T1WI and T2WI resolutions of no plate, PC plate, HP plate and KP material were all 0.9 mm, and those of the remaining materials were worse than 0.9 mm. The T1WI and T2WI PIU of no plate was>87%, and the PIU of carbon fiber plate was reduced by> 25%. The PIU decrease of remaining materials was within ±4%. Except the carbon fiber plate, the low-contrast spokes of the remaining materials were within ±3 compared with the reference. Conclusions
In clinical settings, carbon fiber plate exerts the most significant effect upon the MR-simulation imaging quality, which is unsuitable for MR simulation. Imaging quality of PC and HP plates are consistent with that of no plate. BR and KP materials exert slight effect upon MR signal. The remaining materials are of potential values for the manufacture of immobilization devices and accessories.