Fast Imaging: How Do We Speed Up the Image Acquisition?

Abstract

The key method of faster image acquisition techniques is to acquire more than one line of k-space within each heartbeat. This fills up k-space more rapidly, leading to shorter image acquisition times.

Fast (or turbo) spin echo fills multiple lines of k-space by generating a train of spin echoes with multiple 180° refocusing pulses. Fast (or turbo) gradient echo fills multiple lines of k-space within the same heart beat by the rapid repetition of several TR periods, known as a shot. The number of lines of k-space acquired in each determines the acceleration factor. Image acquisition time can also be shortened by reducing the number of phase encoding steps acquired. This can be done by reducing the image acquisition matrix or the field of view in the phase encoding direction. The symmetry property of k-space also allows image acquisition time to be reduced by sampling only just over one half of k-space, either by omitting phase encoding steps, or by not sampling first part of the echo. Parallel imaging makes use of multi-element array coils to reduce the amount of phase encoding required, resulting in faster image acquisition times.