Effects of RAFF2 periodicity enhance the contrast between sub-chronic myocardial infarction and remote myocardium

Introduction One dangerous cardiovascular disease is myocardial infarction (MI). Relaxation Along a Fictitious Field in the rotating frame of rank n (RAFFn) and rotating frame longitudinal T1r relaxation has demonstrated to characterize fibrosis-related myocardial diseases. The RAFF2-45° method can be further tuned to be sensitive for specific freuencies and pathological changes by changing the durations of the RAFF2-45° pulses, potentially measure more accurately tissue alterations and microstructural features of the myocardium after MI. Purpose To study the effect of periodicity of irradiation by changing the durations of RAFF2-45° pulses at 9.4T ex vivo. Materials and Methods The hearts of C57BL (n = 10) mice 7 days after occlusion of LAD and healthy hearts (n=3) were imaged. Study followed the "Principles of laboratory animal care". Stretching factor (TL) defines how much P-packet in RAFF2-45° pulse are either compressed or stretched. Here, we used TLs between 0.6-2.0. The original duration of P-packet in RAFF2-45° pulse is marked as TL1.0, with the angle α2 = 45° between the fictitious field and the z″ axis of the second rotating frame. Due to variation in RAFF2-45° pulse duration, maximum number of pulses in pulse train varied from 4 to 32 and 2D fast-spin echo readout was used. RAFFn-45° measurements were performed by detecting signal intensity evolution from +Z and -Z. Relaxation time maps were calculated using monoexponential decay function taking into account steady state (SS) formation. The contrast between remote and infarcted areas was measured as Relative Relaxation Time Difference (RRTD). The RRTD was calculated as (T(infarct)-T(remote))/T(remote)*100%, where T refers for the relaxation time in specific area. Results Higher relaxation times are associated with MI (indicated as a red oval) as compared to the rest of the myocardium (Figure 1). Significant differences between infarction and remote areas with relatively high RRTD were found in the steady state (SS-TRAFF2-45°) maps with TL0.6 and in SS-TRAFF2-45° with TL0.8 (Figure 2). Statistically significant differences in RRTD-values were also found in the SS-TRAFF2-45° TL2.0 and SS-TRAFF2-45° TL1.8 methods (Figure 2). Conclusion By altering durations of the P-packets in RAFF2-45° pulse one can capture the MI areas from the rest of the myocardium. This finding has the potential to provide a novel way to evaluate molecular dynamics in the MI area. The finding is supported by the results of other rotating frame relaxation measurements by being increased in the same regions as TRAFF2-45° TL0.6-TL2.0 relaxation time constants. The results were further validated by histological sections. Thus, enhancement of contrast between the MI area and the rest of the myocardium can be achieved by changing the duration of the P-packets of the original RAFF2-45° pulse, which can be used for generating novel contrast to reveal MI areas in the myocardium.