Biopsy needle tip artifact in MR-guided neurosurgery

A thorough understanding of both the appearance and origin of metallic biop sy needle tip artifact in magnetic resonance imaging (MRI) as well as its i nteraction with various magnetic resonance (MR) sequence parameters is bene ficial for its application in today's MR-guided therapeutic procedures. In a more practical setting, this investigation has focused on the characteris tics of MR image artifacts associated with a finite-length metallic needle, specifically at the tip of a biopsy needle when it is approximately parall el to the main magnetic field. The image artifact at needle tip, which exhi bits as a blooming ball-shaped signal void, was demonstrated and studied us ing MR imaging and numerical simulation employing the finite difference met hod (FDM). In order to understand the origin of this image artifact, a nume rical model or simulation software based on the FDM has been developed spec ifically to solve for the field disturbance to a uniform magnetic field due to a finite-length metallic needle. The solution for magnetic field shows that the field disturbance Is spatially localized at the needle tip. From t he numerical results, simulated images were generated which were in a very satisfactory agreement MR imaging experiment. Results showed that the MR im age artifacts associated with MR-compatible metallic biopsy needles are not only present due to the magnetic susceptibility difference between the nee dle and its surrounding tissue, but also predictable in routine MR-guided p rocedures, and the size of the image artifacts could be reduced if optimal imaging parameters were used. (C) 2001 Wiley-Liss, Inc.