I am Samuel and I am quite new to the domain. In some of the fMRI images that was provided to me, there were some ring or ghosting like artefacts. Could someone help me with understanding the reason behind it and is there an tool which can be used to remove this artefact? I have attached the image below for reference. This is a resting state fMRI and subjects were sedated during the entire procedure (TR = 1.7).