Department of Radiology, UZ Gasthuisberg, Herestraat 49, Leuven, Belgium.
Med Phys. 2012 Feb;39(2):811-24. doi: 10.1118/1.3675403.
Needle phosphor based computed radiography (CR) systems promise improved image quality compared to powder phosphor based CR units for x-ray screening mammography. This paper compares the imaging performance of needle CR cassettes, powder based CR cassettes and a well established amorphous selenium (a-Se) based flat panel based mammography system, using consistent beam qualities.
Detector performance was assessed using modulation transfer function (MTF), normalized noise power spectrum (NNPS), and detective quantum efficiency (DQE). Mammography system performance was assessed against levels from the European Guidelines, including threshold gold thickness (c-d), relative signal difference to noise (SdNR) and mean glandular dose, for automatic exposure control settings suggested by the manufacturers. The needle based Agfa HM5.0 CR detector was compared against the single sided readout Agfa MM3.0R and dual sided readout Fuji Profect CS powder CR plates using a 28 kV Mo/Rh spectrum, while a 28 kV W/Rh spectrum was used to compare the Agfa HM5.0 against the Siemens MAMMOMAT Inspiration a-Se based system.
MTF at 5 mm(-1) was 0.16 and 0.24 for the needle CR detector in the fast and slow scan directions, respectively, indicating a slight improvement (∼20%) over the two powder CR systems but remained 50% lower than the result at 5 mm(-1) for the a-Se detector (∼0.55). Structured screen noise was lower for the needle phosphor compared to the powder plates. CR system gain, estimated from the measured absorption fraction and NNPS results, was 6.3 for the (single sided) needle phosphor and 5.1 and 7.2 for the single sided and dual sided powder phosphor systems. Peak DQE at ∼100 μGy was 0.47 for the needle system compared to peak DQE figures of 0.33 and 0.46 for the single sided readout powder plates and dual sided readout plates. The high frequency DQE (at 5 mm(-1)) was 0.19 for the needle CR plates, a factor of approximately 3 greater than for the powder CR plates. At 28 kV W/Rh, 2 mm Al, peak DQE for the needle CR system was 0.45 against a value of 0.50 for the a-Se detector. The needle CR detector reached the Acceptable limit for 0.1 mm details in the European Guidelines at a mean glandular dose (MGD) of approximately 1.31 mGy imaged at 28 kV Mo/Rh, compared to figures of 2.19 and 1.43 mGy for the single sided and dual sided readout powder CR systems. The a-Se detector could reach the limit at 0.65 mGy using a 28 kV W/Rh spectrum, while the needle CR system required 1.09 mGy for the same spectrum.
Imaging performance for the needle CR phosphor technology, characterized using MTF and DQE and threshold gold thickness demonstrated a clear improvement compared to both single and dual sided reading powder phosphor based CR systems.
基于针状荧光体的计算机射线照相（CR）系统相较于粉末状荧光体的 CR 系统，有望在 X 射线筛查乳房摄影术中提高图像质量。本文使用一致的光束质量，比较了针状 CR 盒、粉末状 CR 盒和成熟的非晶态硒（a-Se）平板基础乳腺摄影系统的成像性能。
使用调制传递函数（MTF）、归一化噪声功率谱（NNPS）和探测量子效率（DQE）评估探测器性能。使用制造商建议的自动曝光控制设置，评估乳腺摄影系统性能，包括欧洲指南中的阈值金厚度（c-d）、相对信号噪声比（SdNR）和平均腺体剂量。使用 28kV Mo/Rh 光谱比较基于 Agfa HM5.0 的针状 Agfa 与单读取 Agfa MM3.0R 和双读取 Fuji Profect CS 粉末 CR 板，使用 28kV W/Rh 光谱比较基于 Agfa HM5.0 的与 Siemens MAMMOMAT Inspiration a-Se 系统。
在快速和慢速扫描方向上，针状 CR 探测器的 MTF 在 5mm(-1)处分别为 0.16 和 0.24，表明与两种粉末状 CR 系统相比略有改善（约 20%），但仍比 a-Se 探测器在 5mm(-1)处的结果低 50%（约 0.55）。与粉末板相比，针状荧光体的结构屏噪声较低。从测量的吸收分数和 NNPS 结果估计的 CR 系统增益为（单读取）针状荧光体的 6.3，单读取和双读取粉末荧光体系统的增益分别为 5.1 和 7.2。在约 100μGy 时，针状系统的峰值 DQE 为 0.47，而单读取粉末板和双读取粉末板的峰值 DQE 分别为 0.33 和 0.46。在高频 DQE（在 5mm(-1)处），针状 CR 板为 0.19，是粉末 CR 板的约 3 倍。在 28kV W/Rh、2mm Al 处，针状 CR 系统的峰值 DQE 为 0.45，而 a-Se 探测器的值为 0.50。在 28kV Mo/Rh 下，针状 CR 探测器的平均腺体剂量（MGD）约为 1.31mGy 时达到欧洲指南 0.1mm 细节的可接受限制，而单读取和双读取粉末 CR 系统的 MGD 分别为 2.19 和 1.43mGy。使用 28kV W/Rh 光谱，a-Se 探测器可以在 0.65mGy 时达到该限制，而针状 CR 系统在相同光谱下需要 1.09mGy。
基于针状荧光体的 CR 磷光体技术的成像性能，通过 MTF 和 DQE 以及阈值金厚度进行特征描述，与单读取和双读取粉末状荧光体的 CR 系统相比，明显有所改善。
