Abstract 3406: Fast, Dual-energy, Multi-slice CT Can Discriminate Fe and Ca
Unstable plaque is characterized by intraplaque hemorrhage and subsequent iron deposits. In Dual-Energy (DE) CT, CT values of different elements change disproportionately with change in x-ray energy. This can be exploited to discriminate elements of close atomic numbers, such as Ca (Z=20) and Fe (Z=26), presenting the opportunity to differentiate Ca and Fe in atherosclerotic plaque.
AIM: Demonstrate the sensitivity of DE CT to differentiate Fe and Ca.
METHODS: I: 7 solutions of 100 mg/ml FeNO3, calcium hydroxyapatite, and water (100% of Fe, Ca or H20, 50/50% mixes of Ca/Fe, Ca/H20, Fe/H20, and a 50% Ca, 37.5% H20, 12.5% Fe mix) were placed in cylindrical chambers of an acrylic phantom and imaged at 80 and 140 kV on a 64-slice CT. A linear combination of the 80 and 140 kV images was created to cancel the calcium signal. II: Fe and Ca tablets coated with paraffin were placed in the left ventricle of a pig heart, and 80 and 140 kV data acquired simultaneously using a dual source 64-slice CT. A 3-material decomposition algorithm was applied to the 80 and 140 kV images using changes in CT numbers between the two energy settings to differentiate the materials. Color was assigned according to CT value changes between 80 and 140 kV, and a color mapped DE image used to show material composition.
RESULTS: I: 100% Ca was very bright in the 80 and 140 kV images (670 and 450 HU), but in the DE subtraction image, the pixel value was essentially zero (-5), demonstrating the ability to cancel calcium signal. There was a linear relationship between iron signal and iron concentration even when iron was in solution with Ca or H20.The DE value of 100% Fe was twice that of the 50/50% Fe/Ca mixture, and the Fe/H20 and Fe/Ca/H20 mixtures were the appropriate weighted average of the solution components. II: Color-mapped DE images vividly discriminated iron and calcium based on the changes in CT values, although the tablet composition could not be discriminated in either the 80 or 140 kV image alone.
CONCLUSION: DE CT appears feasible for the discrimination of Fe and Ca, potentially allowing differentiation between hemorrhagic and calcific plaque, both of which appear bright in single energy CT images. Identification of Fe and Ca plaque components might allow for the non-invasive detection of unstable plaques in vivo.