Aubert Sarah, Cunningham Ian A, Tanguay Jesse
Department of Physics, Ryerson University, Toronto, Ontario, Canada.
Imaging Research Laboratories, Robarts Research Institute, Western University, London, Ontario, Canada.
Med Phys. 2022 Nov;49(11):6885-6902. doi: 10.1002/mp.15973. Epub 2022 Oct 4.
X-ray coronary angiography is a sub-optimal vascular imaging technique because it cannot suppress un-enhanced anatomy that may obscure the visualization of coronary artery disease.
The purpose of this paper is to evaluate the theoretical image quality of energy-resolved x-ray angiography (ERA) implemented with spectroscopic x-ray detectors (SXDs), which may overcome limitations of x-ray coronary angiography.
We modeled the large-area signal-difference-to-noise (SDNR) of contrast-enhanced vasculature in ERA images and compared with that of digital-subtraction angiography (DSA), which served as a gold standard vascular imaging technique. To this end, we used calibrated numerical models of the response of cadmium telluride SXDs including the effects of charge sharing, electronic noise, and energy thresholding. Our models assumed zero scatter, no pulse pile up and small signals such that image contrast is approximately linear in the area density of contrast agents. For DSA, we similarly modeled x-ray detection by cesium iodide energy-integrating detectors using validated numerical models. For ERA, we investigated iodine and gadolinium (Gd) contrast agents, two-material and three-material decompositions, analog charge summing for charge sharing correction, and optimized image quality with respect to the tube voltage and energy thresholds assuming cadmium telluride SXDs with three energy bins.
Our analysis reveals that a three-material decomposition using iodine contrast agents will require x-ray exposures that are approximately 400 times those of DSA to achieve the same SDNR as DSA in coronary applications, and is therefore not feasible in a clinical setting. However, three-material decompositions with Gd contrast agents have the potential to provide SDNR that is ∼45% of that of DSA for matched patient air kerma. For two-material decompositions that suppress soft-tissue, ERA has the potential to produce images with SDNR that is 50%-75% of that of DSA for matched patient air kermas but lower levels of tube loading. Achieving these SDNR levels will require the use of analog charge summing for charge sharing correction, which increased SDNR by up to a factor of 1.7 depending on the contrast agent and whether or not a two-material or three-material decomposition was assumed.
We conclude that three-material ERA implemented with Gd contrast agents and two-material ERA implemented with either iodine or Gd contrast agents, should be investigated as alternatives to DSA in situations where motion artifacts preclude the use of DSA, such as in coronary imaging.
X射线冠状动脉造影是一种次优的血管成像技术，因为它无法抑制未增强的解剖结构，而这些结构可能会掩盖冠状动脉疾病的可视化。
本文的目的是评估采用光谱X射线探测器（SXDs）实现的能量分辨X射线血管造影（ERA）的理论图像质量，该技术可能克服X射线冠状动脉造影的局限性。
我们对ERA图像中对比增强血管的大面积信号差与噪声（SDNR）进行建模，并与数字减影血管造影（DSA）进行比较，DSA是一种金标准血管成像技术。为此，我们使用了碲化镉SXDs响应的校准数值模型，包括电荷共享、电子噪声和能量阈值的影响。我们的模型假设零散射、无脉冲堆积和小信号，使得图像对比度在造影剂的面积密度中近似线性。对于DSA，我们使用经过验证的数值模型，类似地对碘化铯能量积分探测器的X射线检测进行建模。对于ERA，我们研究了碘和钆（Gd）造影剂、双材料和三材料分解、用于电荷共享校正的模拟电荷求和，并针对假设具有三个能量 bins 的碲化镉 SXDs，在管电压和能量阈值方面优化图像质量。
我们的分析表明，在冠状动脉应用中，使用碘造影剂的三材料分解需要的X射线曝光量约为DSA的400倍，才能达到与DSA相同的SDNR，因此在临床环境中不可行。然而，使用钆造影剂的三材料分解有可能为匹配的患者空气比释动能提供约为DSA的45%的SDNR。对于抑制软组织的双材料分解，ERA有可能产生SDNR为DSA的50%-75%的图像，但管负载水平较低。要达到这些SDNR水平，需要使用模拟电荷求和进行电荷共享校正，根据造影剂以及假设的是双材料还是三材料分解，这可将SDNR提高高达1.7倍。
我们得出结论，在运动伪影妨碍使用DSA的情况下，如在冠状动脉成像中，应研究使用钆造影剂的三材料ERA和使用碘或钆造影剂的双材料ERA作为DSA的替代方法。
