National Coordinating Centre for the Physics of Mammography (NCCPM), Royal Surrey NHS Foundation Trust, Guildford, UK.
Department of Physics, University of Surrey, Guildford, UK.
Med Phys. 2021 Nov;48(11):6859-6868. doi: 10.1002/mp.15216. Epub 2021 Sep 18.
The purpose of this study was to measure the threshold diameter of calcifications and masses for 2D imaging, digital breast tomosynthesis (DBT), and synthetic 2D images, for a range of breast glandularities. This study shows the limits of detection for each of the technologies and the strengths and weaknesses of each in terms of visualizing the radiological features of small cancers.
Mathematical voxel breast phantoms with glandularities by volume of 9%, 18%, and 30% with a thickness of 53 mm were created. Simulated ill-defined masses and calcification clusters with a range of diameters were inserted into some of these breast models. The imaging characteristics of a Siemens Inspiration X-ray system were measured for a 29 kV, tungsten/rhodium anode/filter combination. Ray tracing through the breast models was undertaken to create simulated 2D and DBT projection images. These were then modified to adjust the image sharpness, and to add scatter and noise. The mean glandular doses for the images were 1.43, 1.47, and 1.47 mGy for 2D and 1.92, 1.97, and 1.98 mGy for DBT for the three glandularities. The resultant images were processed to create 2D, DBT planes and synthetic 2D images. Patches of the images with or without a simulated lesion were extracted, and used in a four-alternative forced choice study to measure the threshold diameters for each imaging mode, lesion type, and glandularity. The study was undertaken by six physicists.
The threshold diameters of the lesions were 6.2, 4.9, and 6.7 mm (masses) and 225, 370, and 399 μm, (calcifications) for 2D, DBT, and synthetic 2D, respectively, for a breast glandularity of 18%. The threshold diameter of ill-defined masses is significantly smaller for DBT than for both 2D (p≤0.006) and synthetic 2D (p≤0.012) for all glandularities. Glandularity has a significant effect on the threshold diameter of masses, even for DBT where there is reduced background structure in the images. The calcification threshold diameters for 2D images were significantly smaller than for DBT and synthetic 2D for all glandularities. There were few significant differences for the threshold diameter of calcifications between glandularities, indicating that the background structure has little effect on the detection of calcifications. We measured larger but nonsignificant differences in the threshold diameters for synthetic 2D imaging than for 2D imaging for masses in the 9% (p = 0.059) and 18% (p = 0.19) glandularities. The threshold diameters for synthetic 2D imaging were larger than for 2D imaging for calcifications (p < 0.001) for all glandularities.
We have shown that glandularity has only a small effect on the detection of calcifications, but the threshold diameter of masses was significantly larger for higher glandularity for all of the modalities tested. We measured nonsignificantly larger threshold diameters for synthetic 2D imaging than for 2D imaging for masses at the 9% (p = 0.059) and 18% (p = 0.19) glandularities and significantly larger diameters for calcifications (p < 0.001) for all glandularities. The lesions simulated were very subtle and further work is required to examine the clinical effect of not seeing the smallest calcifications in clusters.
本研究旨在测量不同乳腺密度的二维成像、数字乳腺断层合成（DBT）和合成二维图像的钙化和肿块的阈值直径。本研究显示了每种技术的检测极限，并展示了在可视化小癌症的放射学特征方面，每种技术的优缺点。
创建了具有 9%、18%和 30%体积乳腺密度、厚度为 53mm 的数学体素乳腺模型。在一些乳腺模型中插入了具有不同直径的模拟边界不清晰的肿块和钙化簇。使用西门子 Inspiration X 射线系统测量了 29kV、钨/铑阳极/滤波器组合的成像特性。通过对乳腺模型进行射线追踪，创建了模拟的二维和 DBT 投影图像。然后对这些图像进行修改，以调整图像锐度，并添加散射和噪声。对于二维和 DBT，三种乳腺密度的平均腺体剂量分别为 1.43、1.47 和 1.47 mGy，1.92、1.97 和 1.98 mGy。对所得图像进行处理，以创建二维、DBT 平面和合成二维图像。提取有或没有模拟病变的图像块，并在四项选择强制选择研究中使用，以测量每种成像模式、病变类型和乳腺密度的阈值直径。这项研究由六名物理学家进行。
对于乳腺密度为 18%的情况，2D、DBT 和合成二维图像的病变阈值直径分别为 6.2、4.9 和 6.7mm（肿块）和 225、370 和 399μm（钙化）。对于所有乳腺密度，DBT 中边界不清晰的肿块的阈值直径明显小于 2D（p≤0.006）和合成二维（p≤0.012）。乳腺密度对肿块的阈值直径有显著影响，即使在 DBT 中，图像中的背景结构也减少了。2D 图像的钙化阈值直径明显小于 DBT 和合成二维图像，对于所有乳腺密度。乳腺密度对钙化的阈值直径影响较小，表明背景结构对钙化的检测影响不大。我们测量到合成二维成像的阈值直径比二维成像略大，但无统计学意义，在 9%（p=0.059）和 18%（p=0.19）乳腺密度下，肿块的情况如此。对于所有乳腺密度，合成二维成像的钙化阈值直径均大于二维成像（p<0.001）。
我们已经表明，乳腺密度对钙化的检测只有很小的影响，但对于所有测试的模式，较高的乳腺密度导致肿块的阈值直径显著增大。我们发现，在 9%（p=0.059）和 18%（p=0.19）乳腺密度下，合成二维成像的肿块阈值直径比二维成像略大，但无统计学意义，而在所有乳腺密度下，钙化的阈值直径明显更大（p<0.001）。模拟的病变非常细微，需要进一步研究才能观察到不显示最小钙化簇的临床效果。
