Abstract
BackgroundThe purpose of this study was to describe targeting accuracy in functional neurosurgery using incisionless transcranial magnetic resonance (MR)-guided focused ultrasound technology.MethodsMR examinations were performed before and 2 days after the ultrasound functional neurosurgical treatment to visualize the targets on T2-weighted images and determine their coordinates. Thirty consecutive targets were reconstructed: 18 were in the central lateral nucleus of the medial thalamus (central lateral thalamotomies against neurogenic pain), 1 in the centrum medianum thalamic nucleus (centrum medianum thalamotomy against essential tremor), 10 on the pallido-thalamic tract (pallido-thalamic tractotomies against Parkinson's disease), and 1 on the cerebello-thalamic tract (cerebello-thalamic tractotomy against essential tremor). We describe a method for reconstruction of the lesion coordinates on post-treatment MR images, which were compared with the desired atlas target coordinates. We also calculated the accuracy of the intra-operative target placement, thus allowing to determine the global, planning, and device accuracies. We also estimated the target lesion volume.ResultsWe found mean absolute global targeting accuracies of 0.44 mm for the medio-lateral dimension (standard deviation 0.35 mm), 0.38 mm for the antero-posterior dimension (standard deviation 0.33 mm), and 0.66 mm for the dorso-ventral dimension (standard deviation 0.37 mm). Out of the 90 measured coordinates, 83 (92.2%) were inside the millimeter domain. The mean three-dimensional (3D) global accuracy was 0.99 mm (standard deviation 0.39 mm). The mean target volumes, reconstructed from surface measurements on 3D T1 series, were 68.5 mm3 (standard deviation 39.7 mm3), and 68.9 mm3 (standard deviation 40 mm3) using an ellipsoidal approximation.ConclusionThis study demonstrates a high accuracy of the MR-guided focused ultrasound technique. This high accuracy is due not only to the device qualities but also to the possibility for the operator to perform on-going real-time monitoring of the lesioning process. A precise method for determination of targeting accuracy is an essential component and basic requirement of the functional neurosurgical activity, allowing an on-going control of the performed therapeutic work indispensable for any target efficiency analysis and the maintenance of a low risk profile.
Highlights
The purpose of this study was to describe targeting accuracy in functional neurosurgery using incisionless transcranial magnetic resonance (MR)-guided focused ultrasound technology
The therapeutic application of any technology to functional neurosurgery requires refined target reconstructions and precise targeting accuracy measurements, which should be within the millimeter domain
As targets are in normal tissue, coordinates have to be established for each target on the basis of a stereotactic atlas of the human brain
Summary
The purpose of this study was to describe targeting accuracy in functional neurosurgery using incisionless transcranial magnetic resonance (MR)-guided focused ultrasound technology. As targets are in normal tissue, coordinates have to be established for each target on the basis of a stereotactic atlas of the human brain. Such an atlas uses internal landmarks to position a coordinate system onto the brain, allowing the placement of any desired target inside the brain. Two steps of the treatment procedure need to be performed with precision inside the millimeter domain: (1) the projection, based on the atlas, of the three coordinates of a chosen target onto the intra-operative magnetic resonance (MR) imaging and (2) the application of heat in the chosen target. The determination of the three-dimensional position of this target on intra-operative images and of the therapeutic lesion on post-operative MR imaging allows to establish the targeting accuracy of the whole therapeutic procedure
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