DQE of direct and indirect digital radiography systems
DQE of direct and indirect digital radiography systems
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直接和间接数字射线照相系统的 DQE
DOI：
10.1117/12.430953
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发表时间：
2001
影响因子：
3.5
通讯作者：
J. Dobbins
中科院分区：
文献类型：
--
作者：
E. Samei;M. Flynn;H. Chotas;J. Dobbins
目前的平板探测器要么直接将X射线能量转换为电子电荷，要么使用中间光学过程的间接转换。本工作的目的是比较直接和间接探测器的调制传递函数（MTF），噪声功率谱（SNR）和探测量子效率（DQE）。使用IEC定义的RQA 5（约75 kVp，21 mm Al）和RQA 9（约120 kVp，40 mm Al）射线照相技术，在Philips Digital Diagnost、GE Revolution XQ/i和Hologic Direct-Ray DR 1000三个平板探测器上进行测量。使用边缘方法测量系统的预采样MTF（Samei等人，Med Phys 25：102，1998）。通过对均匀曝光的射线照片进行2D傅立叶分析，针对一定范围的曝光水平来确定系统的曝光度（Flynn和Samei，Med Phys 26：1612，1999）。使用半经验X射线模型估计每个系统每次暴露的理想信噪比。仅在RQA 5技术下报告的DQE根据测量的MTF、曝光、曝光和理想信噪比进行评估。对于直接系统，MTF被发现是显着高于间接系统，非常接近与探测器像素大小的理想函数。发现直接系统的振幅与频率有关是恒定的。DQE结果反映了基于不同检测器材料的吸收效率的预期差异。使用RQA 5和0.3 mR曝光，XQ/i系统在0.15 mm-1和2.5 mm-1空间频率下测得的DQE值分别为64%和14%，DR-1000为35%和19%。使用RQA 5和所有曝光的平均值，XQ/i系统的相应值为58%和13%，DR-1000为36%和19%。
Current flat-panel detectors either directly convert x-ray energy to electronic charge or use indirect conversion with an intermediate optical process. The purpose of this work was to compare direct and indirect detectors in terms of their modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE). Measurements were made on three flat-panel detectors, Philips Digital Diagnost, GE Revolution XQ/i, and Hologic Direct-Ray DR1000 using the IEC-defined RQA5 (approximately 75 kVp, 21 mm Al) and RQA9 (approximately 120 kVp, 40 mm Al) radiographic techniques. The presampled MTF of the systems was measured using an edge method (Samei et al., Med Phys 25:102, 1998). The NPS of the systems was determined for a range of exposure levels by 2D Fourier analysis of uniformly exposed radiographs (Flynn and Samei, Med Phys 26:1612, 1999). The ideal signal-to-noise ratio per exposure for each system was estimated using a semi-empirical x-ray model. The DQE, reported only at the RQA5 technique, was assessed from the measured MTF, NPS, exposure, and the ideal signal-to-noise ratio. For the direct system, the MTF was found to be significantly higher than that for the indirect systems and very close to an ideal function associated with the detector pixel size. The NPS for the direct system was found to be constant in relation to frequency. The DQE results reflected expected differences based on the absorption efficiency of the different detector materials. Using RQA5 and 0.3 mR exposure, the measured DQE values at spatial frequencies of 0.15 mm-1 and 2.5 mm-1 were 64% and 14% for the XQ/i system and 35% and 19% for DR-1000. Using RQA5 and the averages at all exposures, the corresponding values were 58% and 13% for the XQ/i system and 36% and 19% for DR-1000.