Dual-energy (DE) for quantitative material discrimination has emerged as a promising application of microCT to increase contrast discrimination in preclinical studies. Here we present a protocol designed to optimize DE image subtraction for contrast enhanced studies in rodents, employing iodine-based contrast medium (CM). Our investigation used an Albira ARS commercial unit, not specifically designed for quantitative CT tasks. DE subtraction was divided into stages that were independently analyzed: acquisition, volume reconstruction, image registration and image weighting. The DE radiological techniques (low- and high- energy) had been previously optimized to enhance the visualization of iodine-based CM. An independent reconstruction was needed to guarantee linearity between iodine intensity and its concentration for high energy acquisition; it also reduced structured noise occasionally produced by the microCT reconstruction software over uniform regions and improved bone visualization. Image registration was optimized combining an affine transformation with a non-linear transformation determined with the Free-Form Deformation algorithm. Two subtraction weight factors were determined: one that maximized the contrast-to-noise ratio (CNR) of iodine mixed with soft-tissue-equivalent resin and another that minimized CNR between bone-like rods and soft-tissue-equivalent material. A pilot test of the optimized protocol was performed on a rat injected with a continuous flow of CM.
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