Quantitative Analysis of Myocardial Iodine Concentration during Stress and Rest Based on Dual-Energy CT – Comparison with Cardiac Perfusion MRI

Note: this paper has won the RSNA Research Trainee Award 2010 in the category Fellow – Cardiac Imaging.

Purpose
Dual-energy CT (DECT) has been proposed for the evaluation of the myocardial blood supply; however, previous investigations used visual, qualitative assessment for detecting myocardial perfusion defects at DECT. We aimed at objectively measuring the myocardial iodine concentration as a surrogate for blood volume during stress and rest based on DECT.

Method and materials
In a pilot phantom experiment we calibrated the DECT iodine signal to known iodine concentrations in a given volume and established the reproducibility of these measurements. We then used the Perfusion Blood Volume software application to perform DECT-based measurements of the iodine concentration in healthy, ischemic, and infarcted myocardium of 9 patients who had undergone rest/stress DECT (Definition Flash, Siemens) of the heart as well as stress/rest cardiac perfusion MRI (CPMRI). The myocardial iodine concentration was then correlated with CPMRI up-slopes during stress and rest as well as with the subjective evaluation of CPMRI.

Results
148/153 myocardial segments could be successfully processed. On CPMRI, 31/148 myocardial segments showed fixed perfusion defects and delayed enhancement indicating chronic infarction. 17/148 segments showed reversible perfusion defects without delayed enhancement indicating ischemia. In healthy myocardium, there was a significant (p<0.001) increase in mean iodine concentration of 0.52 mg/ml tissue between rest and stress measurements. Chronic infarcts showed no significant (p>0.05) differences in mean iodine concentration (0.22 mg/ml) between rest and stress. Ischemic segments showed a significant (p<0.001) decrease of 1.4 mg/ml in mean iodine concentration between rest and stress. These measurements showed fair correlation (r = 0.73-85) with CPMRI up-slopes during stress and rest and fair to excellent correlation (r = 0.87-0.93) with subjective CPMRI evaluation.

Conclusion
DECT measurement of myocardial iodine concentration shows promise for quantifying the extent and severity of ischemic heart disease and for estimating myocardial perfusion reserve in lieu of actual time-resolved perfusion imaging.

Clinical relevance/application
Using iodine concentration as a quantitative surrogate for perfusion could enhance the potential role of DECT as a stand-alone modality for integrative imaging of ischemic heart disease.

Submission Type: Scientific Presentations RSNA 2010

Authors: J D Koonce, MD, Charleston, SC; B Schmidt, PhD; M Weininger, MD; G Bastarrika, MD; T G Flohr, PhD; U J Schoepf, MD