canning technique, small flip angle pulses are used to read out a series of stimulated echoes that are separately phase encoded. The high-speed STEAM technique reduces motion artifact without using strong gradients. In fact, high-speed STEAM generally is considered an alternative technique, its main advantage being that it can be used with MRI systems that do not have stronger gradients. However, high-speed STEAM results in lowered SNR and significant T1 relaxation compared to echo-planar, spin echo and gradient echo imaging.Incoherent Gradient Echo (Gradient Spoiled) (MPGR, FLASH, STAGE, GRE, Field Echo, Short)In the gradient echo, the dephasing effects of the pulsed magnetic field gradients are eliminated. This scanning sequence is similar to the standard spin echo sequence without the 180 pulse. Instead, this method uses a smaller flip angle for excitation. In the gradient echo pulse, a bipolar pair of gradients of opposite polarity but equal amplitude are placed in front of the signal acquisition. Gradient echo imaging is much faster than standard spin echo imaging, although there are more pronounced magnetic susceptibility artifacts on gradient echo sequences compared with standard spin echo sequences.Magnetization prepared rapid gradient echo (Turbo FLASH 3-D MP-RAGE). Magnetization prepared rapid gradient echo (MP-RAGE) is an ultrafast technique that uses a combination of small flip angle RF pulses and a centric phase-encoding scheme that minimizes the effect of T1 relazation on image contrast. Data can be acquired in about on second, reducing the SNR and motion artifact. However, if relaxation is not corrected during data acquisition, blurring and edge enhancement may result.Echo-Planar ImagingEcho-planar imaging (EPI) is a technique that uses gradient echoes or combines standard spin echo with a train of gradient echoes. It requires hardware modification to the MRI system, including high-performance gradients and ult...
