Ullman Gustaf, Sandborg Michael, Dance David R, Yaffe Martin, Alm Carlsson Gudrun
Department of Radiation Physics, IMV, Linköping University, SE-581 85 Linköping, Sweden.
Phys Med Biol. 2005 Jul 7;50(13):3143-52. doi: 10.1088/0031-9155/50/13/012. Epub 2005 Jun 22.
The aim of this work was to search for the optimal x-ray tube voltage and anode-filter combination in digital iodine contrast media mammography. In the optimization, two entities were of interest: the average glandular dose, AGD, and the signal-to-noise ratio, SNR, for detection of diluted iodine contrast medium. The optimum is defined as the technique maximizing the figure of merit, SNR2/AGD. A Monte Carlo computer program was used which simulates the transport of photons from the x-ray tube through the compression plate, breast, breast support plate, anti-scatter grid and image detector. It computes the AGD and the SNR of an iodine detail inside the compressed breast. The breast thickness was varied between 2 and 8 cm with 10-90% glandularity. The tube voltage was varied between 20 and 55 kV for each anode material (Rh, Mo and W) in combination with either 25 microm Rh or 0.05-0.5 mm Cu added filtration. The x-ray spectra were calculated with MCNP4C (Monte Carlo N-Particle Transport Code System, version 4C). A CsI scintillator was used as the image detector. The results for Rh/0.3 mmCu, Mo/0.3 mmCu and W/0.3 mmCu were similar. For all breast thicknesses, a maximum in the figure of merit was found at approximately 45 kV for the Rh/Cu, Mo/Cu and W/Cu combinations. The corresponding results for the Rh/Rh combination gave a figure of merit that was typically lower and more slowly varying with tube voltage. For a 4 cm breast at 45 kV, the SNR2/AGD was 3.5 times higher for the Rh/0.3 mmCu combination compared with the Rh/Rh combination. The difference is even larger for thicker breasts. The SNR2/AGD increases slowly with increasing Cu-filter thickness. We conclude that tube voltages between 41 and 55 kV and added Cu-filtration will result in significant dose advantage in digital iodine contrast media mammography compared to using the Rh/Rh anode/filter combination at 25-32 kV.
这项工作的目的是在数字碘造影剂乳腺摄影中寻找最佳的X射线管电压和阳极-滤过组合。在优化过程中，关注两个指标：平均腺体剂量（AGD）和用于检测稀释碘造影剂的信噪比（SNR）。最佳条件定义为使品质因数SNR²/AGD最大化的技术。使用了一个蒙特卡罗计算机程序，该程序模拟光子从X射线管穿过压迫板、乳房、乳房支撑板、反散射栅格和图像探测器的传输过程。它计算压迫乳房内碘细节的AGD和SNR。乳房厚度在2至8厘米之间变化，腺体组织占比为10 - 90%。对于每种阳极材料（铑、钼和钨），管电压在20至55千伏之间变化，并结合25微米的铑或0.05 - 0.5毫米的铜附加滤过。使用MCNP4C（蒙特卡罗N粒子输运代码系统，版本4C）计算X射线光谱。使用碘化铯闪烁体作为图像探测器。铑/0.3毫米铜、钼/0.3毫米铜和钨/0.3毫米铜的结果相似。对于所有乳房厚度，铑/铜、钼/铜和钨/铜组合在约45千伏时品质因数达到最大值。铑/铑组合的相应结果给出的品质因数通常较低，且随管电压变化较缓慢。对于4厘米厚的乳房，在45千伏时，铑/0.3毫米铜组合的SNR²/AGD比铑/铑组合高3.5倍。对于更厚的乳房，差异甚至更大。SNR²/AGD随着铜滤过厚度的增加而缓慢增加。我们得出结论，与在25 - 32千伏使用铑/铑阳极/滤过组合相比，在数字碘造影剂乳腺摄影中，41至55千伏的管电压和附加铜滤过将带来显著的剂量优势。
