Fig. 4

Timing diagram of two-dimensional segmented inversion-recovery fast gradient echo pulse sequence. ECG: The ECG tracing is used to trigger the image acquisition in mid-late diastole. Data Acquisition: The dashed box indicates the time during which the data is acquired (“Acquisition window”) which is controlled by the repetition time and the number of lines of k-space being acquired. RF pulses: The sequence begins with a non-selective 180° inversion pulse, followed by the readout pulses. The subsequent heart beat is a “wait beat” to allow for magnetization recovery between inversion pulses. Magnetization: After the detection of the R-wave, there is a time delay (TD) before the inversion pulse is played. The inversion pulse inverts the magnetization, which recovers based on the tissue T1. The recovery curves for infarct and myocardium are shown to highlight the differences in magnetization recovery due to the differences in post-contrast T1. At the time where the center of k-space is acquired, the magnetization of the myocardium is at the zero crossing, while the infarct magnetization is above the zero crossing. The resulting image contrast is that the myocardium has very little signal (magnetization is near zero) while the infarct is bright (significantly above zero). ECG: electrocardiogram. RF: radiofrequency; TD: trigger delay; TI: inversion time delay; α: shallow flip angle excitation