Basic Physics of MR Signal and Image Generation - Advance Image Processing in Magnetic Resonance Imaging - page 34

RF
Gy
Gx
(a)
k y
k x
(b)
FIGURE 1.18 Timing diagram of (a) spiral sequence and (b) relevant k -space path.
pulse is all that is needed to produce sufficient data for an image. This is called
a single-shot imaging method , which is very popular in functional MRI (fMRI).
There are limits on how fast the gradient fields can be changed and, thus, there
are limits on the spatial resolution that can be achieved with this method.
Another common rapid imaging method is spiral imaging. It exploits the math-
ematics of how k-space trajectories are related to gradient waveforms (Equation
1.48) and that allows nearly any continuous trajectory to be acquired. In particular,
in spiral imaging, gradients are designed to produce a spiral trajectory in k-space
and samples are placed along that pathway (as schematically shown in Figure 1.18).