Basharat Fateen, Belli Michael, Kirby Miranda, Tanguay Jesse
Department of Physics, Ryerson University, Toronto, ON, Canada.
Med Phys. 2020 Dec;47(12):6191-6206. doi: 10.1002/mp.14530. Epub 2020 Nov 2.
Chronic obstructive pulmonary disease (COPD) affects ∼200 million people worldwide. 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.
We investigated xenon-enhanced DE (XeDE) radiography for functional imaging of COPD and unenhanced DE radiography for structural imaging of COPD. We modeled the ability of human observers to detect ventilation defects in XeDE images and emphysema in (unenhanced) DE images using the detectability index ( ) as a figure of merit. We accounted for the extent of emphysematous destruction and functional impairment as a function of disease severity, defect/lesion contrast, spatial resolution, x-ray scatter, quantum noise, anatomic noise, and the efficiency of human observers. Whether or not disease was detectable was determined based on a detectability threshold of two. For (unenhanced) DE imaging of emphysema, we compared detectability with that of single-energy (SE) imaging. Models of signal and noise were compared to published data.
Models of signal and noise agreed well with published data, and model predictions of the detectability of emphysema by SE radiography were consistent with poor sensitivity (i.e., ) to mild to moderate COPD but moderate sensitivity (i.e., ) to severe COPD. The detectability of emphysema by DE radiography was greater than that of SE radiography, but did not cross the threshold of detectability for mild to moderate COPD. The detectability index for XeDE imaging exceeded the detectability threshold for mild, moderate, and severe COPD.
Dual-energy radiography may offer modest improvements in the detection of emphysema relative to SE imaging, but will unlikely enable detecting mild and moderate COPD. However, XeDE radiography may enable detection of functional abnormalities associated with mild, moderate and severe COPD at x-ray exposures typical of those used in conventional chest radiography, thus warranting further investigation as a low-dose, low-cost alternative to CT- and MRI-based approaches for functional imaging of COPD.
慢性阻塞性肺疾病（COPD）影响着全球约2亿人。我们提出采用二维（2D）双能（DE）X线成像来评估肺结构和功能，以用于COPD的评估，并从理论上研究所得图像的质量。
我们研究了用于COPD功能成像的氙增强双能（XeDE）射线照相术以及用于COPD结构成像的非增强双能射线照相术。我们使用可探测性指数（ ）作为衡量标准，对人类观察者检测XeDE图像中的通气缺陷和（非增强）DE图像中的肺气肿的能力进行了建模。我们考虑了肺气肿破坏程度和功能损害程度与疾病严重程度、缺陷/病变对比度、空间分辨率、X线散射、量子噪声、解剖噪声以及人类观察者效率之间的函数关系。根据可探测性阈值为2来确定疾病是否可被检测到。对于肺气肿的（非增强）DE成像，我们将其可探测性与单能（SE）成像的可探测性进行了比较。将信号和噪声模型与已发表的数据进行了比较。
信号和噪声模型与已发表的数据吻合良好，SE射线照相术对肺气肿可探测性的模型预测表明，其对轻度至中度COPD的敏感性较差（即 ），而对重度COPD的敏感性为中度（即 ）。DE射线照相术对肺气肿的可探测性高于SE射线照相术，但未超过轻度至中度COPD的可探测性阈值。XeDE成像的可探测性指数超过了轻度、中度和重度COPD的可探测性阈值。
相对于SE成像，双能射线照相术在肺气肿检测方面可能会有适度改善，但不太可能检测出轻度和中度COPD。然而，XeDE射线照相术可能能够在传统胸部X线摄影典型的X线照射剂量下检测出与轻度、中度和重度COPD相关的功能异常，因此有必要作为一种低剂量、低成本的替代方法，进一步研究其用于COPD功能成像，以替代基于CT和MRI的方法。
