Abstract：
BACKGROUND: Contrast-enhanced spectral mammography (CESM) with photon-counting x-ray detectors (PCDs) can be used to improve the classification of breast cancers as benign or malignant. Commercially-available PCD-based mammography systems use silicon-based PCDs. Cadmium-telluride (CdTe) PCDs may provide a practical advantage over silicon-based PCDs because they can be implemented as large-area detectors that are more easily adaptable to existing mammography systems.
OBJECTIVE: The purpose of this work is to optimize CESM implemented with CdTe PCDs and to investigate the influence of the number of energy bins, electronic noise level, pixel size, and anode material on image quality.
METHODS: We developed a Monte Carlo model of the energy-bin-dependent modulation transfer functions (MTFs) and noise power spectra, including spatioenergetic noise correlations. We validated model predictions using a CdTe PCD with analog charge summing for charge-sharing suppression. Using the ideal-observer detectability, we optimized CESM for the task of detecting a 7-mm-diameter iodine nodule embedded in a breast with 50% glandularity. We optimized the tube voltage, beam filtration, and the location of energy thresholds for 50 and 100- μ $\\mu$ m pixels, tungsten and molybdenum anodes, and two electronic noise levels. One of the electronic noise levels was that of the experimental system; the other was half that of the experimental system. Optimization was performed for CdTe PCDs with two or three energy bins. We also estimated the impact of anatomic noise due to background parenchymal enhancement and computed the minimum detectable iodine area density in the presence of quantum and anatomic noise.
RESULTS: Model predictions of the MTFs and noise power spectra agreed well with experiment. For optimized systems, adding a third energy bin increased quantum noise levels and reduced detectability by ∼55% compared to two-bin approaches that simply suppress contrast between fibroglandular and adipose tissue. Decreasing the electronic noise standard deviation from 3.4 to 1.7 keV increased iodine detectability by ∼5% and ∼30% for two-bin imaging and three-bin imaging, respectively. After optimizing for tube voltage, beam filtration, and the location of energy thresholds, there was ∼a 3% difference in iodine detectability between molybdenum and tungsten anodes for two-bin imaging, but for three-bin imaging, molybdenum anodes provided up to 14% increase in detectability relative to tungsten anodes. Anatomic noise decreased iodine detectability by 15% to 40%, with greater impact for lower electronic noise settings and larger pixel sizes.
CONCLUSIONS: For CESM implemented with CdTe PCDs, (1) quantitatively-accurate three-material decompositions using three energy bins are associated with substantial increases in quantum noise relative to two-energy-bin approaches that simply suppress contrast between fibroglandular and adipose tissues; (2) tungsten and molybdenum anodes can provide nearly equal iodine detectability for two-bin imaging, but molybdenum provides a modest detectability advantage for three-bin imaging provided that all other technique parameters are optimized; (3) reducing pixel sizes from 100 to 50 μ $\\mu$ m can reduce detectability by up to 20% due to charge sharing; (4) anatomic noise due to background parenchymal enhancement is estimated to have a substantial impact on lesion visibility, reducing detectability by approximately 30%.
OBJECTIVE: The purpose of this work is to optimize CESM implemented with CdTe PCDs and to investigate the influence of the number of energy bins, electronic noise level, pixel size, and anode material on image quality.
METHODS: We developed a Monte Carlo model of the energy-bin-dependent modulation transfer functions (MTFs) and noise power spectra, including spatioenergetic noise correlations. We validated model predictions using a CdTe PCD with analog charge summing for charge-sharing suppression. Using the ideal-observer detectability, we optimized CESM for the task of detecting a 7-mm-diameter iodine nodule embedded in a breast with 50% glandularity. We optimized the tube voltage, beam filtration, and the location of energy thresholds for 50 and 100- μ $\\mu$ m pixels, tungsten and molybdenum anodes, and two electronic noise levels. One of the electronic noise levels was that of the experimental system; the other was half that of the experimental system. Optimization was performed for CdTe PCDs with two or three energy bins. We also estimated the impact of anatomic noise due to background parenchymal enhancement and computed the minimum detectable iodine area density in the presence of quantum and anatomic noise.
RESULTS: Model predictions of the MTFs and noise power spectra agreed well with experiment. For optimized systems, adding a third energy bin increased quantum noise levels and reduced detectability by ∼55% compared to two-bin approaches that simply suppress contrast between fibroglandular and adipose tissue. Decreasing the electronic noise standard deviation from 3.4 to 1.7 keV increased iodine detectability by ∼5% and ∼30% for two-bin imaging and three-bin imaging, respectively. After optimizing for tube voltage, beam filtration, and the location of energy thresholds, there was ∼a 3% difference in iodine detectability between molybdenum and tungsten anodes for two-bin imaging, but for three-bin imaging, molybdenum anodes provided up to 14% increase in detectability relative to tungsten anodes. Anatomic noise decreased iodine detectability by 15% to 40%, with greater impact for lower electronic noise settings and larger pixel sizes.
CONCLUSIONS: For CESM implemented with CdTe PCDs, (1) quantitatively-accurate three-material decompositions using three energy bins are associated with substantial increases in quantum noise relative to two-energy-bin approaches that simply suppress contrast between fibroglandular and adipose tissues; (2) tungsten and molybdenum anodes can provide nearly equal iodine detectability for two-bin imaging, but molybdenum provides a modest detectability advantage for three-bin imaging provided that all other technique parameters are optimized; (3) reducing pixel sizes from 100 to 50 μ $\\mu$ m can reduce detectability by up to 20% due to charge sharing; (4) anatomic noise due to background parenchymal enhancement is estimated to have a substantial impact on lesion visibility, reducing detectability by approximately 30%.
摘要：
背景：具有光子计数X射线探测器（PCD）的对比增强光谱乳房X线照相术（CESM）可用于改善乳腺癌的良性或恶性分类。市售的基于PCD的乳房X线照相术系统使用基于硅的PCD。碲镉(CdTe)PCD可以提供优于基于硅的PCD的实际优势,因为它们可以被实现为更容易适应现有乳房X线照相术系统的大面积检测器。
目的：这项工作的目的是优化使用CdTePCD实施的CESM，并研究能量仓数量的影响，电子噪声级,像素大小,和阳极材料对图像质量的影响。
方法：我们开发了与能量仓相关的调制传递函数（MTF）和噪声功率谱的蒙特卡罗模型，包括空间能量噪声相关性。我们使用具有模拟电荷求和的CdTePCD验证了模型预测，以抑制电荷共享。利用理想观察者的可检测性，我们对CESM进行了优化,以检测乳腺腺体浓度为50%的直径为7毫米的碘结节.我们优化了管电压，光束过滤，以及50和100μm像素的能量阈值的位置，钨和钼阳极，和两个电子噪声水平。电子噪声水平之一是实验系统的电子噪声水平；另一个是实验系统的一半。对具有两个或三个能量箱的CdTePCD进行优化。我们还估计了由于背景实质增强引起的解剖噪声的影响，并计算了在存在量子和解剖噪声的情况下可检测的最小碘面积密度。
结果：MTF和噪声功率谱的模型预测与实验吻合良好。对于优化的系统，与简单地抑制纤维腺体和脂肪组织之间的对比的两仓方法相比，增加第三能量仓增加了量子噪声水平，并降低了55%的可检测性。将电子噪声标准偏差从3.4keV降低到1.7keV，对于两箱成像和三箱成像，碘可检测性增加了5%和30%，分别。对管电压进行优化后,光束过滤，以及能量阈值的位置，对于两箱成像，钼和钨阳极之间的碘可检测性差异为3%，但是对于三箱成像，相对于钨阳极，钼阳极的可检测性提高了14％。解剖噪声使碘检测能力降低15%至40%，对更低的电子噪声设置和更大的像素尺寸具有更大的影响。
结论：对于使用CdTePCD实施的CESM，（1）相对于简单地抑制纤维腺和脂肪组织之间的对比的两能量仓方法，使用三个能量仓的定量精确的三材料分解与量子噪声的大幅增加相关；（2）钨和钼阳极可以为两仓成像提供几乎相等的碘检测能力，但是钼为三箱成像提供了适度的可检测性优势，前提是所有其他技术参数都得到了优化；（3）由于电荷共享，将像素尺寸从100μm减小到50μm可以将可检测性降低多达20％；（4）由于背景实质增强导致的解剖噪声估计对病变的可见度有重大影响，将可检测性降低约30%。
目的：这项工作的目的是优化使用CdTePCD实施的CESM，并研究能量仓数量的影响，电子噪声级,像素大小,和阳极材料对图像质量的影响。
方法：我们开发了与能量仓相关的调制传递函数（MTF）和噪声功率谱的蒙特卡罗模型，包括空间能量噪声相关性。我们使用具有模拟电荷求和的CdTePCD验证了模型预测，以抑制电荷共享。利用理想观察者的可检测性，我们对CESM进行了优化,以检测乳腺腺体浓度为50%的直径为7毫米的碘结节.我们优化了管电压，光束过滤，以及50和100μm像素的能量阈值的位置，钨和钼阳极，和两个电子噪声水平。电子噪声水平之一是实验系统的电子噪声水平；另一个是实验系统的一半。对具有两个或三个能量箱的CdTePCD进行优化。我们还估计了由于背景实质增强引起的解剖噪声的影响，并计算了在存在量子和解剖噪声的情况下可检测的最小碘面积密度。
结果：MTF和噪声功率谱的模型预测与实验吻合良好。对于优化的系统，与简单地抑制纤维腺体和脂肪组织之间的对比的两仓方法相比，增加第三能量仓增加了量子噪声水平，并降低了55%的可检测性。将电子噪声标准偏差从3.4keV降低到1.7keV，对于两箱成像和三箱成像，碘可检测性增加了5%和30%，分别。对管电压进行优化后,光束过滤，以及能量阈值的位置，对于两箱成像，钼和钨阳极之间的碘可检测性差异为3%，但是对于三箱成像，相对于钨阳极，钼阳极的可检测性提高了14％。解剖噪声使碘检测能力降低15%至40%，对更低的电子噪声设置和更大的像素尺寸具有更大的影响。
结论：对于使用CdTePCD实施的CESM，（1）相对于简单地抑制纤维腺和脂肪组织之间的对比的两能量仓方法，使用三个能量仓的定量精确的三材料分解与量子噪声的大幅增加相关；（2）钨和钼阳极可以为两仓成像提供几乎相等的碘检测能力，但是钼为三箱成像提供了适度的可检测性优势，前提是所有其他技术参数都得到了优化；（3）由于电荷共享，将像素尺寸从100μm减小到50μm可以将可检测性降低多达20％；（4）由于背景实质增强导致的解剖噪声估计对病变的可见度有重大影响，将可检测性降低约30%。
