背景:由于一些挑战,常规的X射线成像和荧光透视在定量方面存在局限性,包括散射,光束硬化,和重叠的组织。双能量(DE)成像,具有量化特定材料面积密度的能力,非常适合解决这些限制,但前提是双能量投影以完美的空间和时间对齐获得并校正散射。
目的:在这项工作中,我们提出了通过结合使用主调制器(PM)和双层(DL)检测器的单发定量成像(SSQI),这使得无运动DE成像与散射校正在一个单一的曝光。
方法:我们的SSQI设置的关键组件包括PM和DL检测器,其中前者能够对后者进行散射校正,而后者能够对前者进行光束硬化校正。SSQI算法允许使用来自PM编码的四个子测量同时恢复两个材料特定图像和两个散射图像。这一概念最初是通过对一名COVID患者的胸部X射线成像模拟来证明的。对于验证,我们在我们的桌面系统上设置SSQI几何形状,并以已知厚度(丙烯酸:0-22.5厘米;铜:0-0.9毫米)成像丙烯酸和铜板,用我们的SSQI算法估计散射,并将两种材料不同组合的材料分解(MD)与地面实况进行了比较。第二,我们对冠状动脉中含有造影剂的拟人化胸部体模进行了成像,并比较了有和没有SSQI的MD。最后,要在动态应用程序中评估SSQI,我们构建了一个流动模型,使碘造影的动态成像成为可能。
结果:我们的模拟研究表明,SSQI导致精确的散射校正和MD,特别是对于较小的焦点模糊和更精细的PM间距。在验证研究中,我们发现SSQI估计的均方根误差(RMSE)对于丙烯酸为0.13cm,对于铜为0.04mm。对于拟人化的幻影,直接MD导致造影剂和软组织的错误解释,虽然SSQI成功地定量区分了它们,将材料特定图像中的RMSE降低38%-92%。对于流动幻像,SSQI能够进行准确的动态定量成像,从背景中分离对比。
结论:我们证明了SSQI用于可靠定量X射线成像的潜力。通过添加PM和升级到DL检测器,SSQI的集成非常简单,这可能使它能够被广泛采用,包括射线照相和动态成像等技术(即,实时图像引导和锥形束CT)。
BACKGROUND: Conventional x-ray imaging and fluoroscopy have limitations in quantitation due to several challenges, including scatter, beam hardening, and overlapping tissues. Dual-energy (DE) imaging, with its capability to quantify area density of specific materials, is well-suited to address such limitations, but only if the dual-energy projections are acquired with perfect spatial and temporal alignment and corrected for scatter.
OBJECTIVE: In this work, we propose single-shot quantitative imaging (SSQI) by combining the use of a primary modulator (PM) and dual-layer (DL) detector, which enables motion-free DE imaging with scatter correction in a single exposure.
METHODS: The key components of our SSQI setup include a PM and DL detector, where the former enables scatter correction for the latter while the latter enables beam hardening correction for the former. The SSQI algorithm allows simultaneous recovery of two material-specific images and two scatter images using four sub-measurements from the PM encoding. The concept was first demonstrated using simulation of chest x-ray imaging for a COVID patient. For validation, we set up SSQI geometry on our tabletop system and imaged acrylic and copper slabs with known thicknesses (acrylic: 0-22.5 cm; copper: 0-0.9 mm), estimated scatter with our SSQI algorithm, and compared the material decomposition (MD) for different combinations of the two materials with ground truth. Second, we imaged an anthropomorphic chest phantom containing contrast in the coronary arteries and compared the MD with and without SSQI. Lastly, to evaluate SSQI in dynamic applications, we constructed a flow phantom that enabled dynamic imaging of iodine contrast.
RESULTS: Our simulation study demonstrated that SSQI led to accurate scatter correction and MD, particularly for smaller focal blur and finer PM pitch. In the validation study, we found that the root mean squared error (RMSE) of SSQI estimation was 0.13 cm for acrylic and 0.04 mm for copper. For the anthropomorphic phantom, direct MD resulted in incorrect interpretation of contrast and soft tissue, while SSQI successfully distinguished them quantitatively, reducing RMSE in material-specific images by 38%-92%. For the flow phantom, SSQI was able to perform accurate dynamic quantitative imaging, separating contrast from the background.
CONCLUSIONS: We demonstrated the potential of SSQI for robust quantitative x-ray imaging. The integration of SSQI is straightforward with the addition of a PM and upgrade to a DL detector, which may enable its widespread adoption, including in techniques such as radiography and dynamic imaging (i.e., real-time image guidance and cone-beam CT).