011 Comparison of raw hounsfield unit attenuation ratio to dual energy iodine concentration for the evaluation of the hemodynamic significance of coronary stenoses

BACKGROUND: Using rest and stress contrast enhanced dual energy cardiac CT (DECT) we assessed myocardial perfusion distal to coronary stenoses using raw Hounsfield Unit (HU) attenuation and dual energy iodine concentration. METHODS: Subjects received invasive coronary angiography and quantitative coronary artery (QCA) stenoses were grouped in quartiles (Q1, 0-25%; Q2, 25-49%; Q3, 5070%; Q4, 70-99%). DECT rest and hyperaemic stress scans were acquired at 100 and 140 kVp. DECT perfusion was assessed by the AHA radial segment model using 6 mm thick short axis slices of the left ventricle. For raw HU attenuation, perfusion was quantified using the ratio of myocardial HU attenuation divided by LV cavity HU attenuation for rest and stress studies. Vendor supplied software (Dual Energy, Siemens Medical Solutions) calculated iodine concentration maps for rest and stress images. Using individual patient coronary anatomy as a guide, quartile QCA coronary stenosis was compared to polar maps of both raw attenuation and iodine concentration. RESULTS: 278 rest and 282 stress perfusion segments were analysed. QCA identified coronary stenosis ranging from 17 to 91%. Raw HU attenuation perfusion measures in regions of interest (ROI) distal to coronary stenoses for rest and stress (Quartile(rest, stress) showed; Q1 (0.152,0.359), Q2 (0.172,0.345), Q3 (0.206,0.348) & Q4 (0.226,0.325). The mean iodine content (mg/ml) in ROI supplying each quartile were (Quartile(rest, stress)): Q1 (1.58,4.22), Q2 (1.92,4.37), Q3 (1.64,2.95), Q4 (1.63,2.81). There were significant increases in both raw HU attenuation and iodine concentration between rest and stress for all quartiles (P 0.0001). Within the stress studies, HU attenuation was significantly lower between Q3 & Q4 (P 0.001), and iodine content was significantly lower between Q2 & Q3 (P 0.0001). CONCLUSION: For dual energy rest and stress imaging, iodine concentration of the myocardium is a more sensitive discriminator of coronary stenosis compared with raw HU attenuation. Iodine concentration maps may be superior to raw HU attenuation for evaluating the perfusion effect of intermediate coronary stenoses.