兆伏级锥形束CT影像质量定量分析  

Quantitative analysis of the image quality in megavoltage cone-beam computed tomography

作　　者：胡伟刚[1] 章真[1] 常熙[1] 朱骥[1] 徐志勇[1] 唐劲天[1] 蒋国梁[1] 

机构地区：[1]复旦大学上海医学院肿瘤学系肿瘤医院放疗科,上海200032

出　　处：《中华放射肿瘤学杂志》2009年第3期226-229,共4页Chinese Journal of Radiation Oncology

摘　　要：目的定量分析不同成像条件下兆伏级锥形束CT（MVCBCT）的影像质量，为临床应用提供参考。方法采用西门子ONCOR直线加速器上的MVCBCT设备，在不同的成像条件下扫描影像质量模体。通过分析影像均匀性、噪声、空间分辨率、对比度分辨率及成像剂量来评估其影像质量，并与常规大孔径CT影像进行定量比较。结果MVCBCT影像噪声随加速器出束跳数（MU）增加而减少。均匀性指数与成像MU数及重建矩阵无线性关系。空间分辨率上采用256×256重建矩阵除5MU条件下为0．25lp／mm，其他皆为0．4lp／mm。随MU数增加对比度分辨率增加。成像剂量上头颈患者接受最大剂量为1．2cGy／MU，中心位置剂量为0．8—0．9cGy／MU，腹部最大和中心处分别为1．3cGy／MU和0．7cGy／MU。结论MVCBCT的噪声、均匀性、空间分辨率及对比度分辨率都差于常规扇形束CT。通过选择恰当成像参数和重建参数，可在患者接受尽量低成像剂量的同时获得足够分辨率来分辨骨组织、空腔及部分软组织用于影像引导放疗。Objective To quantitatively analyze the image quality of megavoltage cone-beam CT （MVCBCT） under different scanning conditions to provide reference in clinical applications. Methods Siemens ONCOR linear accelerator with MVCBCT was used to scan the phantom under different conditions. The image quality was evaluated in terms of image noise, uniformity, spatial resolution, contrast resolution, the number of Monitor Units（MUs） used in imaging,and the size of the reconstruction matrix. The comparison of the image quality between MVCBCT and conventional simulator CT was also analyzed. Results The image noise was decreased with the increase of the number of MUs. The uniformity index showed that the system uniformity was weakly dependent on MU numbers or the size of the reconstruction matrix. Except for the images with 5 MUs, all other images had the spatial resolution of 0.4 lp/mm with a reconstruction matrix of 256 × 256. Better low contrast resolution was achieved by using more MUs. For typical pelvis and head-and- neck patients, the imaging dose at the center was 0.8 cGy/MU and 0.7 cGy/MU,respectively, and the maximum dose was about 1.2 cGy/MU. For typical abdomen patients ,the image maximum dose and center dose was 1.3 cGy/MU and 0.7 cGy/MU, respectively. Conclusions The image quality of MVCBCT is inferior to the conventional kilo-voltage CT. However,with the optimization of the parameters in imaging,we can achieve sufficient image contrast in the bone, air and some soft-tissue structures with low imaging dose to patients. Such images can be used for IGRT.

关 键 词：断层摄影术 X线计算机 兆伏级锥形束 影像质量 定量分析 

分 类 号：R686[医药卫生—骨科学]