University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
Med Phys. 2010 Nov;37(11):5896-907. doi: 10.1118/1.3490556.
Dual-energy (DE) iodine contrast-enhanced x-ray imaging of the breast has been shown to identify cancers that would otherwise be mammographically occult. In this article, theoretical modeling was performed to obtain optimally enhanced iodine images for a photon-counting digital breast tomosynthesis (DBT) system using a DE acquisition technique.
In the system examined, the breast is scanned with a multislit prepatient collimator aligned with a multidetector camera. Each detector collects a projection image at a unique angle during the scan. Low-energy (LE) and high-energy (HE) projection images are acquired simultaneously in a single scan by covering alternate collimator slits with Sn and Cu filters, respectively. Sn filters ranging from 0.08 to 0.22 mm thickness and Cu filters from 0.11 to 0.27 mm thickness were investigated. A tube voltage of 49 kV was selected. Tomographic images, hereafter referred to as DBT images, were reconstructed using a shift-and-add algorithm. Iodine-enhanced DBT images were acquired by performing a weighted logarithmic subtraction of the HE and LE DBT images, The DE technique was evaluated for 20-80 mm thick breasts. Weighting factors, w(t) that optimally cancel breast tissue were computed. Signal-difference-to-noise ratios (SDNRs) between iodine-enhanced and nonenhanced breast tissue normalized to the square root of the mean glandular dose (MGD) were computed as a function of the fraction of the MGD allocated to the HE images. Peak SDNR/ mean square root of MGD and optimal dose allocations were identified. SDNR/ mean square root of MGD and dose allocations were computed for several practical feasible system configurations (i.e., determined by the number of collimator slits covered by Sn and Cu). A practicalsystem configuration an d Sn-Cu filterpair that accounts for the trade-off between SDNR, tube-output, and MGD were selected.
w(t) depends on the Sn-Cu filter combination used, as well as on the breast thickness; to optimally cancel 0% with 50% glandular breast tissue, w(t) values were found to range from 0.46 to 0.72 for all breast thicknesses and Sn-Cu filter pairs studied. The optimal w(t) values needed to cancel all possible breast tissue glandularites vary by less than 1% for 20 mm thick breasts and 18% for 80 mm breasts. The system configuration where one collimator slit covered by Sn is alternated with two collimator slits covered by Cu delivers SDNR/ mean square root of MGD nearest to the peak value. A reasonable compromise is a 0.16 mm Sn-0.23 mm Cu filter pair, resulting in SDNR values between 1.64 and 0.61 and MGD between 0.70 and 0.53 mGy for 20-80 mm thick breasts at the maximum tube current.
A DE acquisition technique for a photon-counting DBT imaging system has been developed and optimized.
双能（DE）碘对比增强 X 射线乳房成像已被证明可识别否则在乳房 X 线摄影中隐匿的癌症。在本文中，进行了理论建模，以使用 DE 采集技术为光子计数数字乳腺断层合成（DBT）系统获得最佳增强的碘图像。
在检查的系统中，使用与多探测器相机对准的多狭缝预患者准直器对乳房进行扫描。在扫描过程中，每个探测器在独特的角度采集投影图像。通过分别用 Sn 和 Cu 滤波器覆盖交替的准直器狭缝，在单次扫描中同时获取低能（LE）和高能（HE）投影图像。研究了 0.08 至 0.22 毫米厚的 Sn 滤波器和 0.11 至 0.27 毫米厚的 Cu 滤波器。选择了 49 kV 的管电压。使用移位和添加算法重建断层图像，此后称为 DBT 图像。通过对 HE 和 LE DBT 图像进行加权对数相减来获得碘增强的 DBT 图像。评估了 DE 技术对于 20-80 毫米厚的乳房。计算了最佳抵消乳房组织的加权因子 w(t)。将碘增强和非增强乳房组织之间的信号差异与噪声比（SDNR）除以均方根腺体剂量（MGD），作为分配给 HE 图像的 MGD 分数的函数进行计算。确定了峰值 SDNR/均方根 MGD 和最佳剂量分配。为几种实际可行的系统配置（即由 Sn 和 Cu 覆盖的准直器狭缝数量决定）计算了 SDNR/均方根 MGD 和剂量分配。选择了一种实用的系统配置和 Sn-Cu 滤波器对，以平衡 SDNR、管输出和 MGD。
w(t)取决于使用的 Sn-Cu 滤波器组合以及乳房厚度；为了最佳地抵消 0%至 50%的乳腺组织，发现 w(t)值在研究的所有乳房厚度和 Sn-Cu 滤波器组合下的范围为 0.46 至 0.72。用于抵消所有可能的乳腺组织腺性的最佳 w(t)值在 20 毫米厚的乳房中变化小于 1%，在 80 毫米厚的乳房中变化小于 18%。一个 Sn 覆盖的准直器狭缝与两个 Cu 覆盖的准直器狭缝交替的系统配置提供最接近峰值的 SDNR/均方根 MGD。一个合理的折衷方案是 0.16 毫米 Sn-0.23 毫米 Cu 滤波器对，对于 20-80 毫米厚的乳房，在最大管电流下可获得 1.64 至 0.61 的 SDNR 值和 0.70 至 0.53 mGy 的 MGD。
已经开发并优化了用于光子计数 DBT 成像系统的 DE 采集技术。
