Theoretical optimization of dual-energy x-ray imaging of chronic obstructive pulmonary disease (COPD)

摘要

We propose two-dimensional (2D) dual-energy (DE) x-ray imaging of lung structure and function for the assessment of COPD, and investigate the resulting image quality theoretically using the human observer detectability index (d') as a figure of merit. We modeled the ability of human observers to detect ventilation defects in xenon enhanced DE (XcDE) images and emphysema in unenhanced DE images. Our model of d' accounted for the extent of emphysematous destruction and functional impairment as a function of defect/lesion contrast, spatial resolution, x-ray scatter, quantum and background anatomical noise power spectrum (NFS), and the efficiency of human observers. The effect of x-ray spectrum and exposure allocation factor on d' was also explored. Our results suggest that, the detectability is maximized for exposure allocation factors that minimize quantum NPS. The optimal combination of tube voltage was found to be ～50/140 kV or 60/140 kV depending on the task and patient at an x-ray exposure equal to that of a standard chest x-ray. In 2D DE x-ray imaging of COPD, the detectability is primarily limited by low contrast, x-ray scatter, and anatomic noise, the latter two of which reduce the detectability of individual defects by 30% and ～＞90%, respectively.