The arrows show the black boundary artifact around the kidneys.
Case Study 2 :
The artificial black boundary is visible for example around the gall bladder (red circle), the kidney (upper arrow) and the spleen (lower arrow).
Case Study 3 :
In this image the same slice of a gradient echo sequence with an in phase (upper image) and an out of phase (lower image) echo time is shown. The black boundary around the kidney (red circle) is not seen (green circle) with in phase echo time.