BIOPSY NEEDLE SUSCEPTIBILITY ARTIFACTS

Understanding the appearance of thin metallic structures in magnetic r esonance imaging is important for evaluating the potential role of MRI in guiding and monitoring percutaneous interventions, As most MR comp atible instruments are made from materials with a susceptibility diffe rent from water, their visibility is enhanced beyond what is expected on the grounds of displaced water alone. Unfortunately, this artifactu ally enhanced visibility is not constant, but instead depends on a var iety of factors. This article presents computer simulations of the ima ge distortion resulting from magnetic susceptibility differences betwe en a needle and the surrounding tissue. The simulations show not only an artifact size that is dependent on needle composition, orientation, and pulse sequence, but also a corresponding shift of the artifact ce nter away from the actual center of the needle. These effects place li mits on the accuracy of MRI-guided needle tip placement.