Samei Ehsan
Department of Radiology, Duke University, DUMC 3302, Durham, North Carolina 27710, USA.
Med Phys. 2003 Jul;30(7):1747-57. doi: 10.1118/1.1578772.
Two general types of phosphor screens are currently used in indirect digital radiographic systems: structured phosphor screens and turbid phosphor screens. The purpose of the study was to experimentally compare the image quality characteristics of two flat-panel digital radiography detectors with similar electronics and pixel sizes (0.127 mm), but otherwise equipped with the two types of screens (0.6-mm-thick structured CsI and Lanex Regular). The presampled modulation transfer functions (MTFs) of the detectors were assessed using an edge method. The noise power spectra (NPS) were measured by two-dimensional Fourier analysis of uniformly-exposed radiographs at 50-100 kVp with 19 mm added Al filtration. The detective quantum efficiencies (DQEs) were assessed from the MTF, the NPS, and estimates of the ideal signal-to-noise ratio. The MTF measures of the two detectors were generally similar above a spatial frequency of 2 mm(-1), with approximately 2.5 and approximately 3.8 mm(-1) spatial frequencies corresponding to 0.2 MTF and 0.1 MTF, respectively. Below 2 mm(-1), the MTF for the CsI-based detector was slightly higher by an average of 0.07. At 70 kVp, the measured DQE values in the diagonal (and axial) direction(s) at spatial frequencies of 0.15 mm(-1) and 2.5 mm(-1) were 78% (78%) and 26% (20%) for the CsI-based detector, and 20% (20%) and 7% (6%) for the Lanex-based detector, respectively. The comparative findings experimentally confirm that in indirect flat-panel detectors, structured phosphor screens provide a more favorable tradeoff between resolution and noise compared to turbid-phosphor screens, effectively increasing the detection efficiency of the detector without a negative impact on the detector's spatial resolution response.
目前，间接数字射线照相系统中使用两种类型的荧光屏：结构化荧光屏和散射荧光屏。本研究的目的是通过实验比较两种平板数字射线照相探测器的图像质量特性，这两种探测器具有相似的电子元件和像素尺寸（0.127毫米），但分别配备了两种类型的荧光屏（0.6毫米厚的结构化碘化铯和Lanex Regular）。使用边缘法评估探测器的预采样调制传递函数（MTF）。通过对添加19毫米铝滤过、在50 - 100 kVp下均匀曝光的射线照片进行二维傅里叶分析来测量噪声功率谱（NPS）。从MTF、NPS以及理想信噪比的估计值评估探测量子效率（DQE）。在空间频率高于2毫米⁻¹时，两种探测器的MTF测量值总体相似，对应于0.2 MTF和0.1 MTF的空间频率分别约为2.5毫米⁻¹和约3.8毫米⁻¹。在2毫米⁻¹以下，基于碘化铯的探测器的MTF平均略高0.07。在70 kVp时，基于碘化铯的探测器在空间频率为0.15毫米⁻¹和2.5毫米⁻¹时，对角线（和轴向）方向上测得的DQE值分别为78%（78%）和26%（20%），而基于Lanex的探测器分别为20%（20%）和7%（6%）。这些比较结果通过实验证实，在间接平板探测器中，与散射荧光屏相比，结构化荧光屏在分辨率和噪声之间提供了更有利的权衡，有效提高了探测器的探测效率，而不会对探测器的空间分辨率响应产生负面影响。
