Effects of coregistration of MR to CT images on MR stereotactic accuracy

Abstract

Coregistration of different modality imaging serves to increase the ease and accuracy of stereotactic procedures. In many cases, magnetic resonance (MR) stereotaxis is supplanting computerized tomography (CT). The advantages of increased anatomical detail and multiplanar imaging afforded by MR, however, are offset by its potential inaccuracy as well as the more cumbersome and less available nature of its hardware. A system has been developed by one of the authors by which MR imaging can be performed separately without a stereotactic fiducial headring. Then, immediately prior to surgery, a stereotactic CT scan is obtained and software is used to coregister CT and MR images anatomically by matching cranial landmarks in the two scans. The authors examined this system in six patients as well as with the use of a lucite phantom. After initially coregistering CT and MR images, six separate anatomical (for the patients) and eight artificial (for the phantom) targets were compared. With coregistration, in comparison to CT fiducial scans, errors in each axis are less than or equal to 1 mm using the Cosman-Roberts-Wells system. In fact, the coregistered images are more accurate than MR fiducial images, in the anteroposterior (p = 0.001), lateral (p < 0.05), and vertical (p < 0.03) planes. Three-dimensional error was significantly less in the coregistered scans than the MR fiducial images (p < 0.005). The coregistration procedure therefore not only increases the case of MR stereotaxis but also increases its accuracy.

The Impact of the Reference Imaging Modality, Registration Method and Intraoperative Flat-Panel Computed Tomography on the Accuracy of the ROSA® Stereotactic Robot

“…For the STN-DBS patients, the mean preoperative L -dopa response was 52.55% and the mean L -dopa response status was 14.25 [4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19]. The mean UPDRS III improvement at 6 months was 75% (mean ‘off med' score before surgery = 30.8 [13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45], mean score ‘on stim/on med' = 7.8 [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17], mean ‘on stim/off med' score after 6 months = 14.15 [5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26]). There was neither mortality nor morbidity (permanent nor transient) related to the DBS surgeries.…”

“…In all these cases, there was no remaining error measurable on the planning software. The remaining stereotactic errors are thus mostly linked to errors in image matching between the MRI and the CT scan [16], [35,36,37,38] and, to some extent, a brain shift error when placing the needle or electrode in the brain [39]. Matching between CT and MRI data sets is frequently used in radiosurgery [36], [37] and stereotactic surgery but the potential for residual error must be borne in mind.…”

Investigating the Function of Deep Cortical and Subcortical Structures Using Stereotactic Electroencephalography: Lessons from the Anterior Cingulate Cortex

“…17. Merge the CT images with the MRI images in the stereotactic navigation software 28,29 . Click on the paired volumetric CT and MRI images underneath the "Fusion" tab and then click "Auto Fusion".…”

A Simple Method to Assess Accuracy of Deep Brain Stimulation Electrode Placement: Pre-Operative Stereotactic CT + Postoperative MR Image Fusion

“…MRI scans are more susceptible to spatial distortion due to a number of factors, including inhomogeneities of the constant magnetic field, nonlinearity of the gradient field, linear scale error, instrument imperfections, magnetic susceptibility artefacts and the effects of local magnetization [17,21,[25][26][27]. Several authors have suggested that image fusion with CT scans may improve the accuracy of spatial targeting over that achieved using MRI alone [21,[28][29][30][31]. CT-MR image fusion is increasingly used for stereotactic DBS electrode placement, but we could not find any article underscoring the amount of information that can be derived by the fusion of the postoperative MRI with the pre-operative stereotactic CT.…”