Accuracy of MRI-Directed Frame-Based Stereotaxis

06/09/2011

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BACKGROUND: Accurate placement of a probe to the deep regions of the brain is an important part of neurosurgery. In the modern era, magnetic resonance image (MRI) based target planning with frame-based stereotaxis is the most common technique.

OBJECTIVE: To quantify the inaccuracy in MRI-guided frame-based stereotaxis and assess the relative contributions of frame movements and MRI distortion.

METHODS: The MRI-directed implantable guide-tube technique was used to place carbothane stylettes prior to implanting deep brain stimulation (DBS) electrodes. The coordinates of target, dural entry point and other brain landmarks were compared between pre- and intra-operative MRI to determine the inaccuracy.

RESULTS: The mean three-dimensional inaccuracy of the stylette at the target was 1.8mm (95% CI: 1.5mm, 2.1mm). In DBS surgery, the accuracy in the x and y (axial) planes are important; the mean axial inaccuracy was 1.4mm (95% CI: 1.1mm, 1.8mm). The maximal mean deviation of the head-frame compared to brain over 24.1 +/- 1.8 hours was 0.9 mm (95% CI: 0.5mm, 1.1mm). The mean three-dimensional inaccuracy of the dural entry-point of the stylette was 1.8mm (95% CI: 1.5mm, 2.1mm), which is identical to that of the target.

CONCLUSION: Stylette positions did deviate from the plan, albeit by 1.4 mm in the axial plane and 1.8 mm in three-dimensional space. There was no difference between the accuracies at the dura and the target approximately 70 mm deep in the brain, suggesting potential feasibility for accurate planning along the whole trajectory.

Full article access for Neurosurgery subscribers at Neurosurgery-Online.com.