The FSE Cusp Artifact: A Phase Wrap-In Artifact Seen on Routine Clinical MR Images of the Knee

In the course of routine fast spin echo (FSE) magnetic resonance (MR) imaging of knees, we have noticed a distinct and recurrent artifact on MR sagittal knee images. The artifact usually appears as a focal dot of high signal intensity and/or c-shaped ripples at a non-orthogonal angle (Figure 1). The technical features of this artifact have been previously described in an ISMRM abstract in 1995, when the artifact was termed the FSE “cusp” artifact [ 11. In the course of our investigation, we have found that the FSE cusp artifact has a high prevalence in clinical MR images of the knee and that it can occasionally obscure anatomic detail that is required for clinical evaluation and diagnosis. We have additionally noted a similar FSE artifact in the presence of metal implants (Figure 2). Despite its prevalence, however, the FSE cusp artifact is still not well known. In this abstract, we describe the origin, nature, clinical prevalence, and methods for management of the FSE cusp artifact when it is encountered clinically.