Fig. 7

Simulation of relative image contrast for infarcted myocardium as a function of heart rate and gating factor. For patients with typical heart rates (45–100 bpm, green shading), a gating factor of 2 (orange line) is sufficient to allow for the majority of the longitudinal magnetization to recover between repeated inversion pulses with minimal saturation of magnetization. Thus, differences in image intensity between normal and infarcted myocardium are high and relatively flat across these heart rates with a gating factor of 2. For patients with tachycardia (> 100 bpm, yellow shading), a gating factor of 3 (gray line) is preferred since it maintains the time between repeated inversion pulses and allows longitudinal recovery to occur more fully. Compared to a gating factor of 2, the differences in image intensity between normal and infarcted myocardium are better maintained. The increase in total number of heart beats required to complete the image is partially offset by the increase in heart rate. For patients with significant bradycardia (< 45 bpm, gray shading), a gating factor of 1 (blue line) can be considered since the time between inversion pulses is longer and allows sufficient recovery between inversion pulses to occur. The decrease in number of heart beats required to complete the image reduces the breath hold time (assumes PSIR is not employed). Simulations using the Bloch equations assumed a GRE readout with 23 lines of k-space per heart beat, 19 degree readout flip angle, TI set to null normal myocardium, and an infarct T1 of 300 ms. PSIR = phase sensitive inversion recovery