Purpose: To develop a figure of merit for the objective evaluation and comparison of tissue-selective images generated from dual-energy (DE) radiography systems.
Methods: The requirements for a successful metric are identified and a metric is proposed based on the spectral transfer of noise, contrast, and resolution properties from the captured (or primary) DE image data to the generated (or secondary) tissue-subtracted images. It combines the relative noise and resolution properties of the tissue-subtracted images with respect to the primary data with the measured quantity and quality of tissue cancellation. An experimental method and an imaging phantom are presented for the capturing all the necessary primary data. Lastly, an analytical method for computing this metric is detailed and verified in a variety of scenarios through first-order X-ray imaging simulations.
Results: The proposed Dual-Energy Subtraction Efficiency (DSE) metric adequately describes a multitude of image properties for all simulated image scenarios, indicating its ability to accurately and objectively evaluate image quality. It is even possible to identify the particulars of the image deficiencies by studying the DSE spectral shape.
Conclusion: The DSE and its measurement method described can become a tool to characterize dual-energy radiographic image quality objectively and quantitatively, allowing for improved system comparison, development, and optimization. We conclude that, alongside quality metrics dedicated to conventional radiography such as detective quantum efficiency, it is now possible to extend objective X-ray system evaluation to include dual-energy subtraction radiography.
Funding Support, Disclosures, and Conflict of Interest: Authors are employed and funded by KA Imaging Inc
Dual-energy Imaging, Resolution, Noise Power Spectrum