Traps and Artifacts

Abstract

Artifacts and traps constitute a daily source of difficulties and mistakes when reading MR images of the sellar region. If not recognized they can mimic intrasellar lesions, in particular pituitary microadenomas.Partial volume artifacts occur when a 3-mm-thick section, for instance, includes different anatomical structures such as the anterior pituitary gland and the sphenoid sinus anteriorly, the dorsum sellae posteriorly, or the intracavernous internal carotid arteries laterally. The computer calculates the intensity average of the different components of the section and makes an image that can simulate an intrasellar tumor (Fig. 2.1). Partial volume effects can be eliminated by coupling orthogonal projections or by using 1 mm-thick cuts, for instance with a gradient-echo 3D technique. Magnetic susceptibility artifacts are responsible for geometrical distortion and localized signal intensity changes at the interface of anatomical structures of different signal intensities, mainly in the case of a curved interface. Magnetic susceptibility artifacts are often present at the planum sphenoidale or at the sellar floor level; they are more pronounced at 3.0 T (Fig. 2.2) but can be cleared up with technical ploys. Chemical shift artifacts and ghosting are related to the high signal of fat; they can compromise the visualization of vasopressin storage in the posterior lobe on axial T1W sections when the dorsum sellae is fatty, particularly at 3.0 T. In this case fat saturation is very useful (Fig. 2.3).