Enhancing MRI contrast between sub-chronic myocardial infarct, remote and healthy myocardium using periodic irradiation in the rotating frames

Relaxations Along a Fictitious Field in the rotating frame of rank 2 (RAFF2) was used to characterize fibrosis-related myocardial diseases with MRI. RAFF2 can be sensitized to molecular dynamics processes by changing the durations of the RAFF2 pulses. Here, we studied the effect of altering the RAFF2 pulse durations for characterization of myocardial infarction (MI). 10 mice underwent myocardial infarct surgery, and the hearts were collected 7 days after the operation. 3 mice hearts were served as healthy control. We tested the influence of stretching factor (TL) on relaxations, where TL was between 0.6 and 2.0, and TL = 1 corresponds to the duration of the RAFF2 pulses TL = 2.25 ms with α₂ = 45°. Here, α₂ = 45° indicates location of the fictitious field in the second rotating frame. The contrast between MI and remote areas were measured as Relative Relaxation Time Difference (RRTD). Significant increase in relaxation time constants between MI and remote areas with relatively high RRTD were found in RAFF2 TL0.6, TL0.8, TL1.8 and TL2.0. With protein analysis, fibronectin was upregulated in MI area and histology showed area of fibrosis. By altering durations RAFF2 pulse, MI areas can be captured from the myocardium, which provides a novel way to evaluate molecular dynamics in MI area. The findings were validated by the results of other MRI methods, protein analyses and histological sections. Enhancement of MRI contrast between MI, remote and healthy myocardium without using any contrast agents can be achieved by changing the duration RAFF2 pulse.