Article Text
PDF
Abstract
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).
Conclusion USPIO are taken up into the infarcted myocardium following acute myocardial infarction and can be quantified by MRI. This approach appears to image infarct-related cellular inflammation and represents an important novel method of assessing recovery following acute myocardial infarction.
In this subject, late gadolinium enhancement had revealed an infarct of the anterior left ventricular wall. Panels A and B are R2 acquisition images of the same subject taken on day 1 (A, pre-USPIO), and day 2 (B post-USPIO) in a patient given ferumoxytol. The white arrow indicates the area of infarction corresponding to the late gadolinium enhancement. In this area there is sequential higher uptake of USPIO as indicated by the red/green colour in this area. This is consistent with neutrophil and macrophage influx. Ferumoxytol is also taken up by the liver reticulo-endothelial system (grey arrow). These findings are confirmed by the quantitative analysis of the R2* signal (Panel C).
Comparison of R2* signal in different tissues. Highest uptake of USPIO is seen in the infarct zone, liver and blood pool. There is a small increase in R2* signal in the remote myocardium. There is no increase in R2* signal in the control group for any tissue.
- MRI
- inflammation
- infarction