Segmented phosphors; MEMS-based high quantum efficiency detectors for megavoltage x-ray imaging
Segmented phosphors; MEMS-based high quantum efficiency detectors for megavoltage x-ray imaging
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DOI：
10.1118/1.1854774
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发表时间：
2005-02-01
期刊：
影响因子：
3.8
通讯作者：
Street, R
中科院分区：
文献类型：
--
作者：
Sawant, A;Antonuk, LE;Street, R
目前基于有源矩阵平板成像仪（AMFPI）技术的电子门静脉成像设备（EPIDs）采用金属板+荧光屏组合进行x射线转换。因此，这些设备面临着x射线量子效率（QE）和空间分辨率之间的严重权衡，从而大大限制了它们的成像性能。在这项工作中，我们提出了一种新的检测器设计，用于基于间接检测的AMFPI EPIDs，旨在规避这种权衡。探测器采用基于微机电系统（MEMS）的制造技术开发，由高达2毫米高的网格组成，光刻胶材料SU-8的光学隔离单元。这些单元在尺寸上与AMFPI阵列的像素相匹配，并填充了闪烁荧光粉。在本文中，研究了这种探测器的各种设计考虑因素。为了研究两个设计参数——电池高度和荧光粉填充密度的影响，对三个小面积（类似于7 x 7 cm(2)）原型探测器进行了经验评估，这两个参数都是成像性能的重要决定因素。在放疗条件下（6 MV）测量了x射线灵敏度、调制传递函数（MTF）和噪声功率谱（NPS），并确定了每个原型SU-8探测器的探测量子效率（DQE）。此外，利用蒙特卡罗模拟进行了理论计算，以确定每个探测器的QE，以及由于吸收能量扩散而产生的固有空间分辨率。本研究的结果与早期研究中发表的相应测量结果进行了比较，该研究使用Lanex Fast-B荧光粉屏幕耦合到相同设计的间接检测阵列。SU-8探测器表现出高达3倍的高QE，同时实现与Lanex Fast-B相当或更好的空间分辨率。然而，由于高水平的光学噪声，这些早期原型的DQE性能明显低于预期。因此，SU-8探测器目前在零空间频率下的DQE值与Lanex Fast-B相当，在更高频率下明显低于Fast-B。最后，讨论了降低Swank噪声的策略，并提出了基于级联系统模型的理论计算，以估计通过这种降噪可以实现的性能改进。(C) 2005年美国医学物理学家协会。
Current electronic portal imaging devices (EPIDs) based on active matrix flat panel imager (AMFPI) technology use a metal plate+phosphor screen combination for x-ray conversion. As a result, these devices face a severe trade-off between x-ray quantum efficiency (QE) and spatial resolution, thus, significantly limiting their imaging performance. In this work, we present a novel detector design for indirect detection-based AMFPI EPIDs that aims to circumvent this trade-off. The detectors were developed using micro-electro-mechanical system (MEMS)-based fabrication techniques and consist of a grid of up to similar to2 mm tall, optically isolated cells of a photoresist material, SU-8. The cells are dimensionally matched to the pixels of the AMFPI array, and packed with a scintillating phosphor. In this paper, various design considerations for such detectors are examined. An empirical evaluation of three small-area (similar to7 x 7 cm(2)) prototype detectors is performed in order to study the effects of two design parameters-cell height and phosphor packing density, both of which are important determinants of the imaging performance. Measurements of the x-ray sensitivity, modulation transfer function (MTF) and noise power spectrum (NPS) were performed under radiotherapy conditions (6 MV), and the detective quantum efficiency (DQE) was determined for each prototype SU-8 detector. In addition, theoretical calculations using Monte Carlo simulations were performed to determine the QE of each detector, as well as the inherent spatial resolution due to the spread of absorbed energy. The results of the present studies were compared with corresponding measurements published in an earlier study using a Lanex Fast-B phosphor screen coupled to an indirect detection array of the same design. The SU-8 detectors exhibit up to 3 times higher QE, while achieving spatial resolution comparable or superior to Lanex Fast-B. However, the DQE performance of these early prototypes is significantly lower than expected due to high levels of optical Swank noise. Consequently, the SU-8 detectors presently exhibit DQE values comparable to Lanex Fast-B at zero spatial frequency and significantly lower than Fast-B at higher frequencies. Finally, strategies for reducing Swank noise are discussed and theoretical calculations, based on the cascaded systems model, are presented in order to estimate the performance improvement that can be achieved through such noise reduction. (C) 2005 American Association of Physicists in Medicine.