Optimized (incremented) radio-frequency-angle gradient-echo imaging (ORANGE)

This paper suggests modification of fast low-angle shot (FLASH) gradient-echo imaging. Instead of constant-magnitude flip angles, series of flip angles with increasing amplitude are used for spin excitation, fulfilling two conditions: equal transverse magnetization throughout the sequence and reduction of the longitudinal magnetization to zero with the last excitation. Thus, all available magnetization is used for image formation. In computer simulations, incremented series of flip angles that satisfy conditions 1 and 2 were calculated for a range of TR and T1 values. The resulting tranverse magnetization was compared with that obtainable with Ernst-angle excitations. The effect on image resolution and contrast was investigated and compared with contrast in FLASH imaging