Low-dose, X-ray-based Imaging of Lung Function

Chronic obstructive pulmonary disease (COPD) is characterized by chronic airflow limitation resulting from emphysema and small airway disease. Functional lung imaging of COPD enables early-disease detection, which is crucial for the management of disease. Due to the favorable x-ray interaction characteristics of non-radioactive xenon, it has been proposed as an inhaled contrast agent for x-ray-based imaging of lung ventilation. Current x-ray-based techniques for imaging the lung are based on computed tomography (CT), but the associated high radiation dose potentially precludes their widespread use. Previously, xenon-enhanced dynamic temporal subtraction for lung ventilation study showed sufficient contrast-to-noise ratio of ventilation defects, but motion artifacts compromised the image quality. This thesis focuses on low-dose, low-cost approaches for x-ray-based imaging of lung function, with a specific focus on xenon-enhanced dual-energy (XeDE) radiography and tomosynthesis.

The goals of this project are to (1) develop a mathematical model to quantify the image quality of two-dimensional (2D) XeDE radiography for functional imaging of COPD, (2) experimentally quantify the feasibility of two-dimensional (2D) XeDE radiography for the detection of ventilation defects and investigate the optimal imaging parameters in an experimental phantom study, and (3) investigate the optimal image acquisition and reconstruction parameters of xenon-enhanced tomosynthesis for functional imaging of COPD using an experimental phantom study.

Our theoretical model of the detectability index included the radiological manifestation of the disease, ventilation defect/emphysematous lesion contrast, detector spatial resolution, and image noise power spectrum. The theoretical framework provided a valuable guide to optimizing XeDE imaging of lung function. The experimental validation of the theoretical analysis and the optimization of 2D XeDE radiography and tomosynthesis were investigated using a custom-built chest phantom containing simulated ventilation defects. The experimental feasibility of 2D XeDE radiography and tomosynthesis was investigated using the signal-to-noise ratio (SNR) of a non-prewhitening observer with an eye filter and internal noise.

Our analysis showed that XeDE radiography and tomosynthesis may enable the detection of ventilation abnormalities associated with mild COPD. These important findings indicate that XeDE radiography and tomosynthesis of lung function can be used as low-dose and low-cost alternatives to existing functional imaging approaches for the detection of COPD.