Evaluation of imaging performance of a taper optics CCD 'FReLoN' camera designed for medical imaging
Evaluation of imaging performance of a taper optics CCD 'FReLoN' camera designed for medical imaging
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DOI：
10.1107/s0909049506008983
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发表时间：
2006-05-01
影响因子：
2.5
通讯作者：
Bravin, A
中科院分区：
文献类型：
--
作者：
Coan, P;Peterzol, A;Bravin, A
本工作的目的是从调制传递函数(MTF)、归一化噪声功率谱(NNPS)和探测量子效率(DQE)三个方面来评估间接转换探测器(锥形光学CCDFREON相机)的成像性能。用同步辐射层流光束在20-51.5keV范围内对不同厚度的格拉基荧光屏进行了不同单色能量的测量；数据采集和分析是通过适应用于传统锥形光束的这种光束几何协议进行的。使用边缘方法测量了系统的预采样MTF。通过对均匀曝光的X线片进行二维傅立叶分析，确定了系统在一定曝光水平范围内的NNP。根据测量的MTF、NNPS、曝光和入射光子数来评估DQE。对于给定的屏幕，MTF被发现几乎与能量无关，并且对于给定的能量，对于最薄的屏幕，MTF更高。在33keV和40(100)mm屏幕上，在10%时，MTF为9.2(8.6)线对mm(-1)。NNPS被发现在两个分析方向上与频率相关不同。在100 mm和25keV(0.5)的组合下，DQE值最高；在51.5keV(在Gd K边缘上方)时，DQE值仍然等于0.4。DQE受荧光屏转换效率和电荷耦合器件效率的限制。在手稿的最后，将frelon表征的结果与文献中提出的选定数量的探测器的结果进行了比较。
The purpose of this work was to assess the imaging performance of an indirect conversion detector (taper optics CCD 'FReLoN' camera) in terms of the modulation transfer function (MTF), normalized noise power spectrum (NNPS) and detective quantum efficiency (DQE). Measurements were made with a synchrotron radiation laminar beam at various monochromatic energies in the 20-51.5 keV range for a gadolinium-based fluorescent screen varying in thickness; data acquisition and analysis were made by adapting to this beam geometry protocols used for conventional cone beams. The presampled MTFs of the systems were measured using an edge method. The NNPS of the systems were determined for a range of exposure levels by two-dimensional Fourier analysis of uniformly exposed radiographs. The DQEs were assessed from the measured MTF, NNPS, exposure and incoming number of photons. The MTF, for a given screen, was found to be almost energy independent and, for a given energy, higher for the thinnest screen. At 33 keV and for the 40 ( 100) mm screen, at 10% the MTF is 9.2 (8.6) line-pairs mm(-1). The NNPS was found to be different in the two analyzed directions in relation to frequency. Highest DQE values were found for the combination 100 mm and 25 keV (0.5); it was still equal to 0.4 at 51.5 keV ( above the gadolinium K-edge). The DQE is limited by the phosphor screen conversion yield and by the CCD efficiency. At the end of the manuscript the results of the FReLoN characterization and those from a selected number of detectors presented in the literature are compared.