Myocardial Edema as Detected by Pre-Contrast T1 and T2 CMR Delineates Area at Risk Associated With Acute Myocardial Infarction

Abstract

Objectives To determine whether cardiac magnetic resonance (CMR) in vivo T1-mapping can measure myocardial area at risk (AAR) compared with microspheres or T2-mapping CMR. Background If T2-weighted CMR is abnormal in the AAR due to edema related to myocardial ischemia, then T1-weighted CMR should also be able to detect and accurately quantify AAR. Methods Dogs (n=9) underwent a 2 hour coronary occlusion followed by 4 hours of reperfusion. CMR of the left ventricle was performed for mapping of T1 and T2 prior to any contrast administration. AAR was defined as regions which had a T1 or T2 value (ms) greater than 2SD from remote, and regions with microsphere blood flow (ml/min/g) during occlusion less than 2SD from remote. Infarct size was determined by triphenyltetrazolium chloride staining. Results The relaxation parameters T1 and T2 were increased in the AAR compared to remote myocardium (T1: 1133±55 vs. 915±33ms, T2: 71±6 vs. 49±3 ms; mean±SD). On a slice-by-slice basis (n=78 slices), AAR by T1- and T2-mapping correlated (R2=0.95, p<0.001) with good agreement (0.4±16.6 % of slice, mean±2SD). On a whole-heart analysis, T1 measurements of left ventricular mass, AAR and myocardial salvage correlated to microsphere measures (R2=0.94) with good agreement (−1.4±11.2 g of myocardium; mean±2SD). Corresponding T2 measurements of left ventricular mass, AAR, and salvage correlated to microsphere analysis (R2=0.96, agreement 1.6±9.2 g of myocardium; mean±2SD). Median infarct size was 30% of the AAR (range 12–52). Conclusions For determining area at risk after acute myocardial infarction, non-contrast T1-mapping and T2-mapping sequences yield similar quantitative results, and both agree well with microspheres. The relaxation properties T1 and T2 both change in a way that is consistent with the presence of myocardial edema following myocardial ischemia/reperfusion.

T 1 mapping for assessment of myocardial injury and microvascular obstruction at one week post myocardial infarction

“…In the current work we show similar findings in myocardial infarction patients; namely, the extent of oedema identified by our optimised ROC threshold method, one week post-MI, is significantly larger than that measured by T2W-SPAIR, except in MVO+ patients where the difference is not statistically significant. This builds on the preclinical findings of O h-Ici et al [29] and Ugander et al [23], who have already demonstrated that T1 mapping can identify the area-at-risk, and the region so measured shows excellent correlation with microspheres. In the context of human studies, our work provides an interesting counterpoint to the findings of Dall'Armellina et al [3] who noted that T1 mapping and T2W-SPAIR detected similar oedema volumes in STEMI patients 24 hours post-MI.…”

“…Several oedema imaging methods exist-single-photon emission computed tomography, [26] T2W CMR, [19] LGE endocardial surface area, [27] T1 mapping CMR, [3,4,23] and T2 mapping CMR[13, 23]-but this study represents the first application of T1 mapping with a quantitative ROC-threshold optimised to a STEMI population. The precedent for such an approach was set by Ferreira et al [28], in a recent study on myocarditis.…”

“…For T2W-SPAIR volumetric analysis, pixels with signal intensities 2SD higher than the mean signal intensity of remote myocardium were considered oedematous, [23] and oedema volume was expressed as a percentage of the total myocardial volume. For T1 mapping, two methods were used to measure the oedema volume: 1) a 2SD threshold, equivalent to that described for T2W-SPAIR; 2) a pre-set threshold, where pixels were considered oedematous if their T1 values fell between the ROC-derived threshold and the mean blood pool T1 minus 2SD.…”

Ecto-5′-Nucleotidase on Immune Cells Protects From Adverse Cardiac Remodeling

“…This MRI approach is known to identify cardiac edema formation, and in the acute setting, this is equivalent to the myocardial area at risk. 17 As shown in Figure 2F and in representative midventricular short-axis MRI slices ( Figure 2G), myocardial edema determined 1 day after I/R was not different between CD73-null and WT mice. Thereafter, however, cardiac edema continuously decreased to baseline values within 28 days in the WT animals, whereas the respective values in CD73 −/− mutants tended to further increase.…”

Native Myocardial T1 Mapping, Are We There Yet?

“…35) Native T1 mapping was also helpful in determining the area at risk (AAR) and yielded similar quantitative results, agreeing well with microspheres. 36) In reperfusion injury, the values at areas of microvascular obstruction (MVO) have been found to be slightly higher than those of remote myocardium, but lower than the surrounding infarcted area (Figure 2). 32,33) These T1 changes may persist for two months after the onset of the infarction.…”