Antonuk L E, El-Mohri Y, Huang W, Jee K W, Siewerdsen J H, Maolinbay M, Scarpine V E, Sandler H, Yorkston J
Department of Radiation Oncology, University of Michigan Medical Center, Ann Arbor 48109, USA.
Int J Radiat Oncol Biol Phys. 1998 Sep 1;42(2):437-54. doi: 10.1016/s0360-3016(98)00210-7.
The development of the first prototype active matrix flat-panel imager (AMFPI) capable of radiographic and fluoroscopic megavoltage operation is reported. The signal and noise performance of individual pixels is empirically quantified. Results of an observer-dependent study of imaging performance, using a contrast-detail phantom, are detailed and radiographic patient images are shown. Finally, a theoretical investigation of the zero-frequency detective quantum efficiency (DQE) performance of such imagers, using a cascaded systems formalism, is presented.
The imager is based on a 508-microm pitch, 26 x 26 cm2 array which detects radiation indirectly via an overlying copper plate + phosphor screen converter.
Due to its excellent optical coupling, the imager exhibits sensitivity superior to that of video-based systems. With an approximately 133 mg/cm2 Gd2O2S:Tb screen the system is x-ray quantum-noise-limited down to approximately 0.3 cGy, conservatively, and extensions of this behavior to even lower doses by means of reduced additive electronic noise is predicted. The observer-dependent study indicates performance superior to that of conventional radiotherapy film while the patient images demonstrate good image quality at 1 to 4 MU. The theoretical studies suggest that, with a 133 mg/cm2 Gd2O2S:Tb screen, the system would provide DQE performance equivalent to that of video-based systems and that almost a factor of two improvement in DQE is achievable through the incorporation of a 400 mg/cm2 screen.
The reported prototype imager is the first megavoltage AMFPI having performance characteristics consistent with practical clinical operation. The superior contrast-detail sensitivity of the imager allows the capture of high-quality 6- and 15-MV images at minimal dose. Moreover, significant performance improvements, including extension of the operational range up to full portal doses, appear feasible. Such capabilities could be of considerable practical benefit in patient localization and verification.
报道首个能够进行兆伏级射线照相和透视操作的有源矩阵平板成像器（AMFPI）原型的研制情况。对单个像素的信号和噪声性能进行了经验性量化。详细介绍了使用对比细节模型进行的成像性能观察者依赖型研究结果，并展示了射线照相患者图像。最后，使用级联系统形式对这类成像器的零频率探测量子效率（DQE）性能进行了理论研究。
该成像器基于一个间距为508微米、面积为26×26平方厘米的阵列，通过上层铜板+磷光屏转换器间接检测辐射。
由于其出色的光学耦合，该成像器表现出优于基于视频的系统的灵敏度。使用约133毫克/平方厘米的Gd2O2S:Tb屏时，该系统在保守估计下，X射线量子噪声限制低至约0.3厘戈瑞，预计通过降低附加电子噪声，这种性能可扩展到更低剂量。观察者依赖型研究表明其性能优于传统放射治疗胶片，而患者图像在1至4兆伏时显示出良好的图像质量。理论研究表明，使用133毫克/平方厘米的Gd2O2S:Tb屏时，该系统的DQE性能将与基于视频的系统相当，通过采用400毫克/平方厘米的屏，DQE几乎可提高一倍。
所报道的原型成像器是首个具有与实际临床操作一致性能特征的兆伏级AMFPI。该成像器卓越的对比细节灵敏度允许以最小剂量采集高质量的6兆伏和15兆伏图像。此外，包括将操作范围扩展到全门剂量在内的显著性能提升似乎是可行的。这些能力在患者定位和验证方面可能具有相当大的实际益处。
