A novel EPID design for enhanced contrast and detective quantum efficiency.
A novel EPID design for enhanced contrast and detective quantum efficiency.
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DOI：
10.1088/0031-9155/61/17/6297
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发表时间：
2016-09-07
影响因子：
3.5
通讯作者：
Berbeco R
中科院分区：
文献类型：
--
作者：
Rottmann J;Morf D;Fueglistaller R;Zentai G;Star-Lack J;Berbeco R
目前临床使用的电子门静脉成像设备（EPID）固有的低图像对比度阻碍了实时软组织运动估计等光束眼视图成像应用。我们介绍并描述了一种新的EPID设计，该设计提供了大幅提高的探测量子效率（DQE），对比噪声比（CNR）和灵敏度，而不会降低空间分辨率。原型设计的特点是四个传统EPID层叠加在一起，结合了低噪声集成读出电子设备。每一层由一块铜板、一个闪烁体（GdO2S2: T b）和一个光电二极管/ tft开关（aSi:H）组成。我们根据调制传递函数（MTF）、DQE和噪比（CNR）表征了原型对6 MV光子束的信号响应。预采样MTF使用斜狭缝技术估计，DQE由测量的归一化噪声功率谱（nNPS）计算，MTF和CNR使用拉斯维加斯对比度模体估计。在尺寸和数据输出规格方面，该原型的设计和制造可与瓦里安TrueBeam平台（AS-1200）上当前的临床EPID互换。使用瓦里安as -1200 EPID作为参考检测器，以绝对值和相对值进行性能评估。与AS-1200参考探测器相比，使用四层设计观察到DQE(0)增加了五倍，达到约6.7%。在每一层的单个MTF和所有四层联合工作的MTF之间没有观察到实质性的差异，表明由于光束发散引起的散焦可以忽略不计。此外，使用四层而不是一层将信噪比（SNR）提高了1.7倍。分层EPID设计提高了辐射灵敏度，同时保持了单层传统EPID的空间分辨率和饱和度水平。第一个4层原型的实验表征表明，在保持高分辨率的同时，大幅度提高了DQE和CNR。除了整体提高图像质量和剂量灵敏度外，我们预计这种新型探测器设计将在放射治疗过程中实现更准确的软组织运动估计。
Beams-eye-view imaging applications such as real-time soft-tissue motion estimation are hindered by the inherently low image contrast of electronic portal imaging devices (EPID) currently available for clinical use. We introduce and characterize a novel EPID design that provides substantially increased detective quantum efficiency (DQE), contrast-to-noise ratio (CNR) and sensitivity without degradation in spatial resolution. The prototype design features a stack of four conventional EPID layers combined with low noise integrated readout electronics. Each layer consists of a copper plate, a scintillator (GdO2S2: T b) and a photodiode/TFT-switch (aSi:H). We characterize the prototype’s signal response to a 6 MV photon beam in terms of modulation transfer function (MTF), DQE and contrast-to-noise ratio (CNR). The presampled MTF is estimated using a slanted slit technique, the DQE is calculated from measured normalized noise power spectra (nNPS) and the MTF and CNR is estimated using a Las Vegas contrast phantom. The prototype has been designed and built to be interchangeable with the current clinical EPID on the Varian TrueBeam platform (AS-1200) in terms of size and data output specifications. Performance evaluation is conducted in absolute values as well as in relative terms using the Varian AS-1200 EPID as a reference detector. A fivefold increase of DQE(0) to about 6.7% was observed by using the four-layered design versus the AS-1200 reference detector. No substantial differences are observed between each layer’s individual MTF and the one for all four layers operating combined indicating that defocusing due to beam divergence is negligible. Also, using four layers instead of one increases the signal to noise ratio (SNR) by a factor of 1.7. A layered EPID design improves the radiation sensitivity while maintaining the spatial resolution and saturation level of a single layer conventional EPID. Experimental characterization of this first 4-layered prototype demonstrates substantially improved DQE and CNR while maintaining a high resolution. Besides overall improved image quality and dosimetric sensitivity, we anticipate that this novel detector design will enable more accurate soft-tissue motion estimations during radiation therapy procedures.
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