Department of Radiology, UZ Gasthuisberg, Herestraat 49, B-3000 Leuven, Belgium.
Med Phys. 2013 Aug;40(8):081920. doi: 10.1118/1.4816309.
This work characterizes three candidate mammography phantoms with structured background in terms of power law analysis in the low frequency region of the power spectrum for 2D (planar) mammography and digital breast tomosynthesis (DBT).
The study was performed using three phantoms (spheres in water, Voxmam, and BR3D CIRS phantoms) on two DBT systems from two different vendors (Siemens Inspiration and Hologic Selenia Dimensions). Power spectra (PS) were calculated for planar projection, DBT projection, and reconstructed images and curve fitted in the low frequency region from 0.2 to 0.7 mm(-1) with a power law function characterized by an exponent β and magnitude κ. The influence of acquisition dose and tube voltage on the power law parameters was first explored. Then power law parameters were calculated from images acquired with the same anode∕filter combination and tube voltage for the three test objects, and compared with each other. Finally, PS curves for automatic exposure controlled acquisitions (anode∕filter combination and tube voltages selected by the systems based on the breast equivalent thickness of the test objects) were compared against PS analysis performed on patient data (for Siemens 80 and for Hologic 48 mammograms and DBT series). Dosimetric aspects of the three test objects were also examined.
The power law exponent (β) was found to be independent of acquisition dose for planar mammography but varied more for DBT projections of the sphere-phantom. Systematic increase of tube voltage did not affect β but decreased κ, both in planar and DBT projection phantom images. Power spectra of the BR3D phantom were closer to those of the patients than these of the Voxmam phantom; the Voxmam phantom gave high values of κ compared to the other phantoms and the patient series. The magnitude of the PS curves of the BR3D phantom was within the patient range but β was lower than the average patient value. Finally, PS magnitude for the sphere-phantom coincided with the patient curves for Siemens but was lower for the Hologic system. Close agreement of doses for all three phantoms with patient doses was found.
Power law parameters of the phantoms were close to those of the patients but no single phantom matched in terms of both magnitude (κ) and texture (β) for the x-ray systems in this work. PS analysis of structured phantoms is feasible and this methodology can be used to suggest improvements in phantom design.
本研究旨在针对二维（平面）乳腺 X 线摄影和数字乳腺断层合成（DBT）中的低频区域的功率谱，对具有结构背景的三种候选乳腺 X 线摄影体模进行幂律分析。
本研究使用三个体模（水中球体、Voxmam 和 BR3D CIRS 体模），在两个来自两个不同供应商（西门子 Inspiration 和豪洛捷 Selenia Dimensions）的 DBT 系统上进行。对平面投影、DBT 投影和重建图像进行功率谱（PS）计算，并在低频区域（0.2 至 0.7mm^-1）用幂律函数进行曲线拟合，该函数由指数β和幅度κ来描述。首先探索采集剂量和管电压对幂律参数的影响。然后，计算了三个测试对象在相同的阳极/滤过组合和管电压下采集的图像的幂律参数，并相互比较。最后，将基于测试对象乳腺等效厚度由系统选择的自动曝光控制采集（阳极/滤过组合和管电压）的 PS 曲线与患者数据的 PS 分析（西门子 80 和豪洛捷 48 张乳腺 X 线照片和 DBT 系列）进行比较。还检查了三个测试对象的剂量学方面。
发现平面乳腺 X 线摄影的幂律指数（β）与采集剂量无关，但球体体模的 DBT 投影的β变化更大。管电压的系统增加并不影响β，但降低了平面和 DBT 投影体模图像中的κ。BR3D 体模的 PS 曲线更接近患者的 PS 曲线，而 Voxmam 体模的κ值高于其他体模和患者系列。BR3D 体模的 PS 曲线幅度在患者范围内，但β低于患者平均值。最后，球体体模的 PS 曲线幅度与西门子患者曲线吻合，但与豪洛捷系统的曲线相比则较低。所有三个体模的剂量与患者剂量非常吻合。
体模的幂律参数与患者的参数接近，但在本研究中的 X 射线系统中，没有一个体模在幅度（κ）和纹理（β）方面都匹配。结构体模的 PS 分析是可行的，这种方法可以用于建议改进体模设计。
