Abstract

The role of cardiac lymphatics in the pathogenesis of myocardial infarction (MI) is unclear. Lymphatic system regulates cardiac physiological processes such as edema and tissue fluid balance, which affect MI pathogenesis. Recently, MI and fibrosis have been assessed using endogenous contrast in magnetic resonance imaging (MRI) based on the relaxation along a fictitious field with rank n (RAFFn). We extended the RAFFn applications to evaluate the effects of lymphatic insufficiency on MI with comparison to longitudinal rotating frame (T_1ρ) and T₂ relaxation times. MI was induced in transgenic (TG) mice expressing soluble decoy VEGF receptor 3 that reduces lymphatic vessel formation and their wild-type (WT) control littermates for comparison. The RAFFn relaxation times with rank 2 (T_RAFF2), and rank 4 (T_RAFF4), T_1ρ and T₂ were acquired at time points 0, 3, 7, 21 and 42 days after the MI at 9.4 T. Infarct sizes were determined based on T_RAFF2, T_RAFF4, T_1ρ and T₂ relaxation time maps. The area of differences (AOD) was calculated based on the MI areas determined on T₂ and T_RAFF2, T_RAFF4 or T_1ρ relaxation time maps. Hematoxylin–eosin and Sirius red stained histology sections were prepared to confirm MI locations and sizes. MI was detected as increased T_RAFF2, T_RAFF4, T_1ρ and T₂ relaxation times. Infarct sizes were similar on all relaxation time maps during the experimental period. Significantly larger AOD values were found together with increased AOD values in the TG group compared to the WT group. Histology confirmed these findings. The lymphatic deficiency was found to increase cardiac edema in MI. The combination of T_RAFF2 (or T_RAFF4) and T₂ characterizes MI and edema in the myocardium in both lymphatic insufficiency and normal mice without any contrast agents.