Abstract 19849: Non-invasive Detection of Iron as a New Marker of Unstable Plaques using Dual-energy CT and a New Porcine Plaque Model
Intraplaque hemorrhage is considered a sign of atherosclerotic plaque vulnerability. Subsequent Iron (Fe) deposits could be used as a naturally occurring marker of hemorrhagic plaque. However, non-invasive imaging of Fe is challenging because it often coexists with calcium (Ca) in coronary plaques, yet it is indistinguishable from Ca on standard MR and CT. We have developed a dual-energy CT (DECT) technique to differentiate Fe from Ca, and in this study, validate its performance with an ex-vivo instant plaque model. To create plaques with known quantities of Ca and Fe, mixtures of Fe particles and calcium hydroxyapatite were injected into the wall of swine arteries in vivo. The arteries were then dissected and scanned in an anthropomorphic thorax phantom with a dual-source CT system (Definition Flash, Siemens Healthcare) at 80/140kV, using tin filtration at 140kV. The ratio of CT numbers in the low and high energy images (CTR = CT_low/CT_high) provides material specific information for quantification of tissue composition. The ratio of Fe to Ca mass in each artery wall was calculated based on CTR values measured by DECT. A total of 67 vessels were injected with Fe (n=15), Ca (n=13), or a mixture of both (n=39). For each vessel, a Fe score was calculated based on the ratio of Fe to Ca mass (1 = pure iron, 0 = pure calcium). All 13 samples of pure Ca had Fe scores below 0.2, while 44 of 54 Fe-injected vessels had scores above 0.2. In the remaining 10 Fe-injected vessels, 7 showed neither Fe nor Ca contrast and 3 had a Fe score below 0.2, likely due to the limited spatial resolution of clinical CT (600μm) and very small injected amounts of intramural Fe and Ca. In summary, excluding 7 vessels with no visible plaque at CT, our new DECT technique was able to detect Fe in the arterial wall with 94% sensitivity (44/47) and 100% specificity (13/13), despite the coexistence of Ca similar to the clinical scenario. Ongoing studies will further validate this concept in vivo and in human coronary arteries.
- © 2010 by American Heart Association, Inc.