Magnetic resonance imaging versus computed tomography for target localization in functional stereotactic neurosurgery

OBJECTIVE: To determine whether magnetic resonance imaging (MRI), compared with computed tomography (CT), provides consistent and accurate target loca lization for ventrolateral thalamotomy and posteroventral pallidotomy. METHODS: For 93 procedures (78 pallidotomies and 15 thalamotomies) in 83 pa tients, coordinates for the anterior commissure, posterior commissure, and stereotactic target were calculated from MRI- and CT-derived images and com pared. RESULTS: The mean differences for the target were -0.41 mm on the x axis (P < 0.001), 0.06 mm on the y axis (P = 0.412), and -0.34 mm on the taxis (P < 0.01). The mean absolute differences were 0.53 mm on the x axis (median, 0.50 mm; range, 0.00-2.00 mm), 0.46 mm on the y axis (median, 0.50 mm; rang e, 0.00-2.00 mm), and 0.78 mm on the taxis (median, 0.50 mm; range, 0.00-6. 00 mm). The mean three-dimensional distance between MRI- and CT-derived coo rdinates for the anterior commissure was 1.65 mm, with a distance of more t han 4 mm in two cases (2%). The mean three-dimensional distance for the pos terior commissure was 1.65 mm, with a distance of more than 4 mm in two cas es (2%). The mean three-dimensional distance for the target was 1.25 mm (me dian, 1.14 mm; range, 0.00-6.27 mm), with a distance of more than 4 mm in o ne case (1%). CONCLUSION: Statistically significant but relatively small differences betw een MRI- and CT-derived target coordinates were found. In some cases (appro ximately 2% of this series), the differences between MRI- and CT-derived co ordinates may be relatively large (greater than 4 mm and up to 8 mm). Howev er, given the superior anatomic resolution of MRI and the nature of the ste reotactic procedures under consideration, we conclude that MRI, when valida ted within an institution, may be used alone for target localization in pal lidotomy and thalamotomy.