Introduction Manganese-enhanced magnetic resonance imaging (MEMRI) is a promising non-invasive imaging tool in viability and cardiomyopathy, quantifying infarct size more accurately than late-gadolinium enhancement, as we previously demonstrated. We aimed to validate MEMRI viability against ¹⁸F-FDG positron emission tomography (PET).

Methods Sprague-Dawley rats (male; 180–300 g) underwent permanent surgical anterior myocardial infarction (n=11), or sham surgery (n=2), with dual MEMRI and 18F-FDG PET assessment at 12 weeks. MEMRI (7 T spectrometer, Agilent, UK) was achieved with intravenous manganese gluconate (EVP1001–1, Eagle-Vision-Pharmaceuticals, USA; n=6, 22 μmol/kg) and mangafodipir (Teslascan, IC-Targets, Norway; n=7, 44 μmol/kg). Anatomical and functional imaging preceded cardiac-gated Modified Look-Locker Inversion recovery (MoLLI) before and 20 min post-contrast (at maximal infarct slice). Commercially available software generated standardised T₁ maps for ROI-contouring. For PET imaging, intravenous ¹⁸F-FDG (20–30 MBq) was administered with PET data acquired for 60 min, followed by cardiac-gated acquisition (10 min). PET/MR images were co-registered and fused for analysis.

Results Infarct size assessed by MEMRI T₁ mapping was smaller than by native T₁ at 12 weeks (mean 23.34 vs 18.68%; p=0.001). Native T₁ mapping consistently overestimated infarct size (bias 25.76; 95% CI: 7.51 to 44.01; p=0.031) but there was excellent agreement between MEMRI T₁ mapping and ¹⁸F-FDG (bias 1.30; 95% CI: −24.98 to 25.57; p=0.7). Post-MEMRI T₁ values showed negative trend with increasing SUV (r²=0.25, p=0.08) whereas native T₁ demonstrated no relationship (r²=0.0001, p>0.9).

Conclusion MEMRI T₁ mapping identifies viable myocardium as well as ¹⁸F-FDG PET and was superior to native T₁ mapping. Post-MEMRI T₁ appears related to SUV where native T₁ does not. This validation data informs the clinical translation of cardiac MEMRI.