rafast computers to produce images. High performance gradients are necessary to produce the rapid on-off action needed. The Ultrafast computer is required for complex signal data processing and image reconstruction. Echo planar imaging can be performed as a single shot, during which all data is gathered and processed in a single acquisiton, or as a multishot where data is gathered in several individual segments. By virtue of its ultrafast capabilities that eliminate motion artifacts by freezing out macroscopic motion, echo planar imaging is the preferred scanning pulse sequence for DWI. However, gradient induced eddy current effects can occur during echo planar imaging. Eddy currents are the small electrical currents that are generated when the gradients are switched on and off rapidly. If uncompensated, the eddy current effect will cause a decrease in signal and spatial resolution. There also may be a severe chemical shift artifact, a condition that arises when protons from different molecules process at slightly different frequencies. The distinguishing characteristic of EPI is that the spatial frequency domain gets filled after a single RF excitation, producing an entire image.Navigator EchoNavigator echo is a standard spin echo sequence that can be used with any of the above pulse sequences previously described to decrease motion artifact. The navigator echo method was modified to correct phase errors from rotation and translation motions in the diffusion-encoding interval. It uses an additional nonphase encoded echo that is acquired before the imaging echo. It is very effective in improving image quality and eliminating macroscopic motion artifacts in high-resolution diffusion weighted images without the addition of expensive hardware and excessive restraints. However, it does not allow full coverage of the entire brain, and it increases the amount of time to perform the DWI exam.Diffusion-weighted imaging is an effect...
