Accurate localization of needle entry point in interventional MRI

In interventional magnetic resonance imaging (MRI), the systems designed to help the surgeon during biopsy must provide accurate knowledge of the posi tions of the target and also the entry point of the needle on the skin of t he patient. In some cases, this needle entry point can be outside the Bo ho mogeneity area, where the distortions may be larger than a few millimeters. In that case, major correction for geometric deformation must be performed . Moreover, the use of markers to highlight the needle entry point Is Inacc urate. The aim of this study was to establish a three-dimensional coordinat e correction according to the position of the entry point of the needle. We also describe a 2-degree of freedom electromechanical device that is used to determine the needle entry point on the patient's skin with a laser spot . J. Magn. Reson. Imaging 2000; 12:645-649. (C) 2000 Wiley-Liss, Inc.