Article
Error in indirect stereotactic target planning with MRI caused by frame positioning
Ausmaß der Fehler stereotaktischer indirekter Zielpunktplanung durch verkippte Positionierung des stereotaktischen Ringes
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Authors
Published: | April 23, 2004 |
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Outline
Text
Objective
Some targets in functional neurosurgery can not be visualized in imaging studies. Their coordinates are determined by their previously established relative position to well defined landmarks. Generally the position of the stereotactic frame is assumed to be parallel to the anatomical coordinate system of the brain. We examined the deviation of the target points caused by angles between the frame coordinate system and the anatomical coordinate system.
Methods
In 49 of our patients who underwent functional procedures the Radionics MRI compatible UCLF frame was placed. It was our goal to position the frame parallel to the AC-PC axis and its vertical axis parallel to the falx and septum pelucidum. In the stereotactic MRI images coordinates for AC, PC and points in the falx and septum pelucidum were determined. With these reference points, using vector-mathematical procedures for coordinate transformation in all geometrical axis, the deviation between the anatomical and the frame coordinate system could be determined. The resulting corrections for the coordinates for the target STN were recorded.
Results
The distances between the coordinates for the corrected and uncorrected targets were from 0.3 to 4 mm (median 1.7 mm) for the left STN. In 40% of cases the distance was greater or equal than 2 mm and in 6% greater or equal than 4 mm. The deviation for the right STN was similar.
Conclusions
The error occurring in indirect stereotactic target planning can lead to missing the anatomical target in a considerable number of cases. Appropriate steps should be taken to correct for errors occurring through deviation of frame and anatomical coordinate systems due to frame placement.