Characterization of a fluoroscopic imaging system for kV and MV radiography
Characterization of a fluoroscopic imaging system for kV and MV radiography
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DOI：
10.1118/1.598955
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发表时间：
2000-05-01
期刊：
影响因子：
3.8
通讯作者：
Wong, JW
中科院分区：
文献类型：
--
作者：
Drake, DG;Jaffray, DA;Wong, JW
在医用直线加速器上实现了一种在线千伏成像系统，以验证放射治疗场的位置。一个千伏x射线管安装在加速器上，与兆伏（MV）源成90度，并共享相同的等中心。几乎相同的基于ccd的荧光成像仪安装在两个x射线源的对面。这些系统正在用于临床研究患者设置错误，以检查kV成像在线定位的优势。在本文报道的研究中，对kV和MV系统的成像性能进行了表征，为研究设置误差的结论提供了支持。利用空间频率相关的线性系统模型预测了两种系统的探测量子效率。每个都分为一系列增益和扩展阶段。每个阶段的参数要么是测量的，要么是从文献中得到的。该模型预测中压系统增益与实测增益的比值在7%以内，千伏系统增益与实测增益的比值在10%以内。通过测量系统的噪声功率谱（nps）和调制传递函数（MTFs）来构造实测DQEs。利用模拟的多能光谱计算x射线的影响。实测的DQEs与模型预测的DQEs吻合得很好。该模型表明，MV系统得到了很好的优化，并且在低空间频率处x射线量子噪声受到限制。kV系统是次优的，但对于病人定位的目的产生的图像优于MV系统产生的图像。这是由于kV系统的高DQE和固有的高对比度存在于kV能量。(C) 2000年美国医学物理学家协会。
An on-line kilovoltage (kV) imaging system has been implemented on a medical linear accelerator to verify radiotherapy field placement. A kV x-ray tube is mounted on the accelerator at 90 degrees to the megavoltage (MV) source and shares the same isocenter. Nearly identical CCD-based fluoroscopic imagers are mounted opposite the two x-ray sources. These systems are being used in a clinical study of patient setup error that examines the advantage of kV imaging for on-line localization. In the investigation reported here, the imaging performance of the kV and MV systems are characterized to provide support to the conclusions of the studies of setup error. A spatial-frequency-dependent linear systems model is used to predict the detective quantum efficiencies (DQEs) of the two systems. Each is divided into a series of gain and spreading stages. The parameters of each stage are either measured or obtained from the literature. The model predicts the system gain to within 7% of the measured gain for the MV system and to within 10% for the kV system. The systems' noise power spectra (NPSs) and modulation transfer functions (MTFs) are measured to construct the measured DQEs. X-ray fluences are calculated using modeled polyenergetic spectra. Measured DQEs agree well with those predicted by the model. The model reveals that the MV system is well optimized, and is x-ray quantum noise limited at low spatial frequencies. The kV system is suboptimal, but for purposes of patient positioning yields images superior to those produced by the MV system. This is attributed to the kV system's higher DQE and to the inherently higher contrasts present at kV energies. (C) 2000 American Association of Physicists in Medicine.