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

Abstract

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. Key words: Magnetic resonance simulation image; Immobilization device material; Imaging quality; Quality assurance