Ghosting (medical imaging)

Ghosting is a multidimensional artifact that occurs in the MRI in the phase-encoded direction (short axis of the image) after applying the Fourier transform.

Multiple lines of data are created by transmitting RF pulse sequences with a gradient difference of 90° and 180°.

The multi-shot echo planar images tend to capture more data than that of the single shot EPI.

Iterative inverse problem solving is faster than Cardiac gating[2] and doesn't involve the patient too much.

Reference free EPI ghost correction algorithm[3] uses a method called ALOHA (Annihilating filter-based low rank Hankel structured matrix completion approach).

This method was developed based on the fact that the difference between the odd and even virtual k-space data is the Fourier transform of the underlying sparse image.

It is based on the principle that Ghost Nyquists are produced due to the inconsistencies between the odd and even echos of the MR images.

The occurrence of the Ghosts in the images is converted into missing k-space data and is recovered with the help of the ALOHA matrix.

There are 2 types of approaches that are used to remove the Nyquist Ghost artifacts: The odd and the even samples of data are taken from the k-space by means of interpolation.

A high-performance interpolation method would be able to find the missing data from the actual even and odd sequences and remove the ghosting artifacts from the images.

The method of generalized projections (MGP) is based on the fact that discontinuities in the phase form alternating patterns in the k-space, which leads to ghosting.