Three weeks postoperatively, rats first underwent DEMRI scanning, under isoflurane anaesthesia as described above.
At 12 weeks after surgery, DEMRI and MEMRI (48 h apart) were repeated using the identical protocols described above.
For infarct quantification, DEMRI inversion recovery, DEMRI [T.sub.1] mapping, MEMRI [T.sub.1] mapping, and MTC assessments were compared using Wilcoxon signed-rank test (2-tailed), with post hoc multiple comparison Bonferroni testing.
After surgery, infarct size at the maximal infarct slice was smaller when assessed by MEMRI than DEMRI at 3 weeks (17.4 [+ or -] 8% versus 28.5 [+ or -] 13%, P < 0.05), although the differences were less marked by 12 weeks (20.4 [+ or -] 9% versus 28.6 [+ or -] 8%, P = 0.067, Figure 4).
At 12 weeks, DEMRI inversion recovery, DEMRI [T.sub.1] mapping, and MEMRI [T.sub.1] mapping of infarct size all correlated independently with histologically quantified infarct size by MTC (all P < 0.05).
This novel combination of imaging techniques has been employed to directly compare two distinct manganese contrast agents with conventional DEMRI in the assessment of viability by infarct size, as well as examine altered calcium handling in remodelling myocardium over time, building on previous pilot data in myocardial infarction.
We have further shown that MEMRI [T.sub.1] mapping provides a better estimate of infarct size than DEMRI using both inversion recovery and [T.sub.1] mapping and correlates with left ventricular remodelling within the remote myocardium following myocardial infarction.
In myocardial infarction, both DEMRI inversion recovery and [T.sub.1] mapping consistently overestimated infarct area 3 weeks after surgery in comparison with MEMRI [T.sub.1] mapping.
In the imaging of an infarct, it is possible to select an inversion time following manganese administration whereby the infarct is nulled and the myocardium enhances, in an opposite fashion to DEMRI with gadolinium.
Abbreviations DEMRI: Delayed enhancement magnetic resonance imaging DPDP: Dipyridoxyl diphosphate ETL: Echo train length FOV: Field of view MEMRI: Manganese-enhanced magnetic resonance imaging MoLLI: Modified Look-Locker inversion recovery MRI: Magnetic resonance imaging MTC: Masson's trichrome NMR: Nuclear magnetic resonance ROI: Region of interest TE: Echo time TR: Repetition time.