Quantified dual energy computed tomography perfusion imaging using myocardial iodine concentration: Validation using CT derived myocardial blood flow and invasive fractional flow reserve in a porcine model.

BACKGROUND: Myocardial CT perfusion imaging with dual energy (DE-CTP) can produce myocardial iodine perfusion maps. This study evaluated the accuracy of first pass myocardial iodine concentration in DE-CTP compared to CT derived dynamic myocardial blood flow (MBF) to determine regional myocardial ischemia in an animal model of coronary stenosis using invasive Fractional Flow Reserve (FFR).

METHODS: Seven anaesthetised pigs (mean weight 51 ± 4 kg) had a graded coronary artery stenosis produced in six vessels (plus one control animal) using a methacrylate plug with FFR recorded in the target artery (ischemia = FFR<0.80). During adenosine vasodilation, dynamic myocardial CTP and DE-CTP imaging was performed. Using vendor supplied applications, matching regions of interest (ROIs) were drawn in myocardial segments supplied by the target coronary artery to compare the two techniques.

RESULTS: FFR correlated strongly to MBF (r = 0.81) and modestly to myocardial iodine concentration (r = 0.65) and myocardial CT attenuation (r = 0.62) (p < 0.0001 each). The correlation to FFR was stronger using relative ratios (absolute value/reference value of normal segments) than absolute values for MBF (r = 0.86), myocardial iodine concentration (r = 0.80) and CT number (r = 0.79) (p < 0.0001 each). Comparing normal and ischaemic territories there were significant differences in MBF (96 ± 14 vs. 27 ± 18 ml/100 ml of tissue/min, p < 0.0001), myocardial iodine concentration (3.5 ± 1 vs. 1.0 ± 0.7 mg/ml, p < 0.0001) and myocardial CT number (89 ± 9 vs. 73 ± 14 HU, p = 0.002). Myocardial iodine concentration had 91% sensitivity and 98% specificity for detecting FFR <0.8.

CONCLUSION: Quantified myocardial iodine content from first pass DE-CTP correlates with CT derived myocardial blood flow and FFR and accurately discriminates ischemic territories in a porcine model. The accuracy and utility of myocardial iodine content in DE-CTP warrants further investigation in a clinical population with FFR as a reference standard.