Room: AAPM ePoster Library
Purpose: investigate the image quality of a two-dimensional (2D) xenon-enhanced dual-energy (XeDE) approach for functional imaging of Chronic Obstructive Pulmonary disease (COPD) using a theoretical model.
Methods: used the detectability index of a human observer as a figure of merit to quantify the detectability of ventilation defects associated with COPD. Our theoretical model accounted for quantum noise, electronic noise and anatomic noise, the latter of which accounts for anatomic clutter from soft-tissue and/or bone structures in 2D XeDE images. Our model of quantum noise and defect contrast accounted for patient scatter and assumed an ideal energy-integrating x-ray detector. We calculated the detectability index for a defect present vs. defect absent classification task for emphysematous and non-emphysematous spherical defects of varying diameter in adults. We considered patient entrance exposures ranging from 18 mR to 90 mR (approximate effective radiation doses of 0.02-0.10 mSv), Xe/air concentrations ranging from 0 to 0.75, low-energy tube voltages ranging 50 kV to 70 kV, and a high-energy tube voltage of 140 kV with 1.1 mm of Cu filtration. We used a detectability threshold of 2 to identify whether a defect was detectable or not.
Results: optimal combination of tube voltages was found to be 50/140 kV. For this combination of tube voltage and an 18 mR entrance exposure, the smallest detectable defect was ~2 cm in diameter in XeDE bone-supressed images and ~1.3 cm in XeDE soft-tissue suppressed images, respectively. Increasing the exposure to 90 mR enabled detection of smaller defects.
Conclusion: analysis shows that for a 90 mR exposure, the 2D XeDE approach may enable visualization of defects as small as ~1 cm in diameter. Future work will focus on experimental verification of these results and investigation of tomosynthesis approaches for functional imaging of COPD.