5 Manganese enhanced MRI can quantify myocardial infarct size earlier than gadolinium enhanced MRI

IntroductionLate gadolinium enhanced MRI (LGE-MRI) can quantify infarct size after myocardial infarction (MI) but is non-specific and reflects the increased membrane rupture and extracellular space that develop post MI.1 Mn is a potent T1-contrast agent that enters myocytes through active calcium channels, thus reducing T1 in viable myocardium.2 This active process rapidly ceases under ischemia. Hence, we hypothesised that Mn-enhanced MRI (MEMRI) could quantify final infarct size earlier than LGE-MRI.MethodsMyocardial infarction was induced in 7 mice which then underwent MEMRI (n=4, 0.1 mmol/kg MnCl2) or LGE-MRI (n=3, 0.5 mmol/kg Gd-DTPA) at 1 hour post MI. All animals then underwent both MEMRI and LGEMRI at ∼24 hours post MI with a contrast washout period of at least 5 hours between scans. Imaging was performed using a 9.4T Agilent MRI system and a multi-slice inversion recovery sequence in the short-axis orientation covering the whole left ventricle TE/TR=3.04/1.11 ms, TI=∼600 ms for MEMRI and ∼350 ms for LGE-MRI, 900 excitation pulse, slice thickness=1.0 mm, FOV=25.6 × 25.6 mm, matrix size=128 × 128) as described.3 ResultsAt 1 hour post MI, viable myocardium was enhanced in MEMRI, allowing early delineation of the occlusion zone as 41%±8% of the myocardium, whereas only subtle enhancement was seen on LGE-MRI, yielding a significantly lower value of 12%±2% (p=0.03. Figure 1). At ∼24 hours post MI, the MEMRI measure of infarct size remained constant (41%±5%) whilst LGE-MRI significantly increased to a level comparable with MEMRI (37%±3%). Figure 2 shows a direct comparison of MEMRI and LGE-MRI acquired in the same animal at 22 and 27 hours after MI, respectively, with matching histological TTC staining for infarct size.Abstract 5 Figure 1MEMRI and LGE-MRI acquired at 1 and 24 hours post MIAt 1 h post MI, Mn uptake in viable myocardium allowed the estimated final infarct area to be distinguished, whilst only subtle enhancement was seen in LGE-MRI resulting in a smaller measure of occlusion zone. At 24 h post MI the infarct shows hypoenhancement in MEMRI and hyperenhancement in LGE of similar sizesAbstract 5 Figure 2Direct comparison of MEMRI and LGE-MRIDirect comparison of MEMRI and LGE-MRI acquired in the same animal at 22 and 27 hours after MI, respectively. Arrowhead shows hypoenhancement of the infarct in the MEMRI image and hyperenhancement of the infarct in LGE. In vivo data corresponded with TTC histological staining for infarctDiscussionEffected my