Background Inflammation following myocardial infarction has detrimental effects on reperfusion, myocardial remodelling and left ventricular function. MRI using ultrasmall superparamagnetic particles of iron oxide (USPIO) can be used to detect cellular inflammation in tissues.
Methods 15 patients were recruited up to 5 days after ST-segment elevation myocardial infarction. Nine patients underwent cardiac MRI (3 Tesla) at baseline, and at 24 and 48 h following infusion of USPIO (4 mg/kg; Ferumoxytol, AMAG). Six control patients underwent the same scanning protocol without infusion of USPIO. T2*-weighted multi-gradient-echo sequences were acquired and R2* maps (inverse of T2*) were generated to assess USPIO accumulation. Baseline scans were registered to subsequent 24 and 48 h scans and the infarct zone was defined on Gadolinium-enhanced T2-weighted images. An “object map” was created that defined corresponding regions of interest (ROI) on all scans for each subject. The ROIs included infarct zone, peri-infarct zone, remote myocardium, liver, blood pool and skeletal muscle. The R2* values for each ROI was calculated.
Results In the control group, the R2* value in the infarct zone remained constant: baseline, 0.047 s−1 (95% CI 0.034 to 0.059); 24 h, 0.043 s−1 (95% CI 0.035 to 0.052) and 48 h, 0.040 s−1 (95% CI 0.024 to 0.056). In the infarct zone, the R2* value increased from a baseline of 0.041 s−1 (95% CI 0.029 to 0.053) to 0.164 s−1 (95% CI 0.125 to 0.204) at 24 h and 0.128 s−1 (95% CI 0.097 to 0.158) at 48 h following USPIO administration (p<0.01; non-parametric repeated measure one-way ANOVA, Dunn's post test comparison).