# Drawbacks of parallel imaging

by Denis Hoa

The use of parallel imaging to speed up acquisition reduces the signal-to-noise ratio, due to:

• the decrease in the number of k-space lines (of a ratio equal to the square root of the acceleration factor)
• the geometric factor (g factor) which depends on the number, size and orientation of the different coil elements, resulting in a heterogeneous signal-to-noise ratio within the slice
• slice position, the acceleration factor and k-space filling trajectory

In image domain reconstruction technique, noise in the image will be heterogeneously distributed within the image, whereas in frequency domain reconstruction technique it is more homogeneously distributed (because the errors relate to k-space data).

In the case of foldover artifacts related to a reduced field of view, additional artifact images will appear in image domain reconstruction technique because these foldover artifacts produce errors in sensitivity mapping, which perturb the reconstruction of the image.