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With growing clinical acceptance of dual-energy chest radiography, there is increased interest in the application of dual-energy techniques to other clinical areas. This paper describes the creation and experimental validation of a poly-energetic signal-propagation model for technique optimization of new dual-energy clinical applications. The model is verified using phantom experiments simulating typical abdominal radiographic applications such as Intravenous Urography (IVU) and the detection of pelvic and sacral bone lesions or kidney stones in the presence of bowel gas.
The model is composed of a spectral signal propagation component and an image-processing component. The spectral propagation component accepts detector specifications, X-ray spectra, phantom and imaging geometry as inputs, and outputs the detected signal and estimated noise. The image-processing module performs dual-energy logarithmic subtraction and returns figures-of-merit such as contrast and contrast-to-noise ratio (CNR), which are evaluated in conjunction with Monte Carlo calculations of dose.
Phantoms assembled from acrylic, aluminum, and iodinated contrast-agent filled tubes were imaged using a range of kVp's and dose levels. Simulated and experimental results were compared by dose, clinical suitability, and system limitations in order to yield technique recommendations that optimize one or more figures-of-merit.
The model accurately describes phantom images obtained in a low scatter environment. For the visualization of iodinated vessels in the abdomen and the detection of pelvic bone lesions, both simulated and experimental results indicate that dual-energy techniques recommended by the model yield significant improvements in CNR without significant increases in patient dose as compared to conventional techniques. For example the CNR of iodinated vessels can be doubled using two-thirds of the dose of a standard exam. Alternatively, in addition to a standard dose image, the clinician can obtain a dual-energy bone image with greater than 8-fold increase in CNR, with the addition of just 15% higher dose. It is expected that this tool will enable the rapid clinical utilization of new applications of dual-energy radiography.
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