Manganese-enhanced MRI during remotely induced myocardial ischemia reperfusion injury in male mice

Abstract

Early assessment of myocardial viability post-ischemia is crucial to mitigate adverse remodeling and optimize therapy. Current noninvasive methods like late gadolinium enhancement (LGE) MRI may overestimate infarct size. Manganese-enhanced MRI (MEMRI) emerged as a promising alternative, offering greater specificity in assessing myocardial damage. We evaluated MEMRI alongside LGE and histology in a murine ischemia-reperfusion model using a novel "in-scanner" remote occlusion technique for real-time imaging during acute ischemia. Male C57BL/6 mice (n = 16) underwent left anterior descending artery occlusion (n = 7), sham surgery (n = 6), or no intervention (n = 3). MEMRI (0.1 mmol/kg MnCl₂) during ischemia (0-60 min) and LGE (0.1 mmol/kg Gd-DOTA, 24 h post-surgery) quantified perfusion deficits and infarct size. MEMRI detected acute hypo-perfusion (lateral wall signal reduction: p < 0.01 vs. septal), confined to the occluded territory, while LGE overestimated infarct size (p = 0.0225 vs. histology). Ischemic mice showed adverse remodeling with reduced ejection fraction (61.37% vs. 71.92%, p < 0.01). MEMRI-derived perfusion deficits correlated with functional decline and histology-confirmed infarcts. Pre-occlusion T₁ times did not differ between ischemic and sham groups (p = 0.85), confirming technique specificity. MEMRI enables early, accurate ischemic injury detection and predicts cardiac dysfunction, outperforming LGE in infarct size determination. Our remote occlusion technique facilitates real-time perfusion assessments, enhancing preclinical myocardial ischemia studies.

Keywords: ischemia–reperfusion injury; left anterior descending artery; manganese enhanced magnetic resonance imaging; myocardial perfusion; myocardial remodeling.

FIGURE 1

MEMRI during remotely induced ischemia outlines the hyperperfused area. (a) Short‐axis mid‐ventricular slice is shown (raw signal intensity; a.u.) at 30 min of LAD occlusion. White arrow points to the lack of increased signal intensity observed in the lateral region of the myocardium, depicted as the ischemic zone. Yellow arrow points to the suture placement. (b) ROI analysis revealed difference in contrast dynamics in the lateral regions compared to septal regions in ischemic animals. (c) Linear regression analysis of signal intensities between the start and end of ischemia. (d) Linear regression analysis of signal intensities between the start and the initial 30 min of reperfusion. ROI, region of interest; SI, signal intensity.

FIGURE 2

Volumetric mapping of ischemic perfusion deficit during LAD occlusion using MEMRI. Representative 3D perfusion maps of the delineated myocardium in an ischemic animal (left) and a sham animal (right), acquired during remote temporary LAD ligation. Perfusion deficit was quantified using the slope criterion (ΔSI = SI _t=30min–SI _t=0min). The volumetric overlay highlights the spatial extent of perfusion impairment in the ischemic animal, localized to the LAD territory. Data are displayed in short‐axis orientation (ant, anterior; inf, inferior; lat, lateral; sep, septal; SI, signal intensity).

FIGURE 3

Comparative assessment of ischemic burden across imaging and histological metrics. (a) MEMRI‐derived perfusion deficit quantified via the linear slope metric demonstrated significant differences between ischemic animals and both sham and naïve groups, reflecting ischemia‐specific Mn²⁺ uptake impairment. (b) Similarly, threshold‐based MEMRI analysis distinguished ischemic animals from sham and naïve groups, corroborating the linear slope findings. (c) Late gadolinium enhancement (LGE)‐defined area at risk (AAR) confirmed elevated ischemic injury in the IRI group versus sham controls. (d) Histological assessment (Sirius red staining) validated significant myocardial damage in ischemic animals compared to sham. (e) In the IRI group LGE‐AAR overestimated infarct size relative to SR, while MnCl₂‐derived perfusion deficits showed no significant discrepancy from LGE or SR. Sham animals exhibited significant overestimation of injury by LGE versus MnCl₂ threshold‐based perfusion deficits and linear slope versus LGE, despite limited histological evidence of scar formation versus LGE.

FIGURE 4

Correlation of early imaging metrics with histological and functional outcomes. (a) Early assessment of myocardial damage using MnCl₂ perfusion deficit (linear slope and threshold‐based methods) and LGE‐derived area at risk was correlated with histologically quantified infarct size (SR) and long‐term cardiac dysfunction (ΔESV: End‐systolic volume at 4 weeks vs. baseline). (b) Correlation of myocardial damage between both imaging markers of acute myocardial injury (LGE vs. MEMRI) with simple linear regression line fit (dotted lines mark the 95% fitting confidence).

FIGURE 5

Longitudinal assessment of cardiac remodeling and functional outcomes. (a) Cardiac cine MRI revealed significant left ventricular (LV) remodeling 4 weeks after remote LAD occlusion. While baseline end‐systolic (ESV; p = 0.7768) and end‐diastolic (EDV; p = 0.8025) volumes did not differ between groups, ischemic animals exhibited marked systolic dysfunction at follow‐up, whereas sham‐operated animals maintained stable function. (b) Serum cardiac troponin I levels 24 h post‐surgery were significantly elevated in the IRI group versus sham. (c) Pre‐occlusion native T₁ relaxation times showed no difference between IRI and sham groups. (d) Segmental fractional wall thickening (fWT) at 4 weeks demonstrated impaired contractility in the IRI group (red dotted line), particularly in the lateral wall (histologically confirmed infarct zone), versus sham (solid line). Data are presented as segmental averages with shaded 5% error bands, highlighting regional dysfunction.