Quality control of MR direct application in stereotactic neurosurgery. An experimental and clinical study

Quality control of modern magnetic resonance scanners includes assessment of the geometrical deformations; image distorsion from nonpatient sources is generally well corrected. Nevertheless, magnetic resonance imaging suffers the disadvantage of potential anatomical inaccuracy, due to a multivariate source of spatial distortion of images. This basic error in MRI-direct application in stereotactic neurosurgery, could place critical neural structures in jeopardy. Errors under 5 mm in an MR image, as reported in the literature, might be not harmful in most circumstances (such as in open or free-hand operative approach). However, such inaccuracies undermine the precision of MR stereotactic procedures and invalidate their use for techniques, like functional neurosurgery and brachytherapy, where pinpoint precision is mandatory. To increase the safety and reliability of stereotactic procedures under MRI guidance nonlinear image distortion must be assessed directly on the images used for 'target' location. Our experience has shown that a simple gain correction to a predetermined optimal baseline resonance frequency, and addressed tune setting, with the stereotactical headring inside the head coil is sufficient to provide the desired precision. No targeting reperage vs. operative approach error was recorded in any session of in vitro simulation, or in the clinical series.