Measurement of the force required to move a neurosurgical probe through in vivo human brain tissue.

The advent of high-precision magnetic and robotic computer-controlled neurosurgery systems makes it necessary to determine the range of forces that will be encountered by the probes of such devices as they are guided through the brain tissues to intraparenchymal targets. We have measured the penetration forces on 2.5-mm spheres and the drag forces on 3.0-mm ventricular shunt catheters advanced 2.0-3.5 cm deep into in vivo human brain tissues (in patients about to have those tissues resected during epilepsy surgery) at rates of approximately 0.33 mm s-1. Penetration forces of (8 +/- 2) grams were found for the spherical probe once it passed 0.5 cm below the cortical surface, and frictional drags of (2.8 +/- 0.3) grams cm-1 were exerted on the catheters. The variable nature of these forces is discussed and the results are compared with earlier studies on experimental animal tissues and brain phantom gelatins. The implications of these results for magnetic and robotic surgery systems are considered.

An integrated multipurpose lesion-making electrode.

PURPOSE: Although excellent results are reported from centers using microelectrode mapping during stereotactic pallidotomy, the recording methods used are time-consuming and technically cumbersome. We sought to develop a new electrode concept that may, when eventually applied in clinical practice, improve the efficiency and safety of microelectrode-guided functional neurosurgical procedures. CONCEPT: The scout electrode uses a recently developed research technique for simultaneously obtaining multiple microelectrode recordings along the shaft of a macroelectrode. RATIONALE: By positioning recording sites on either side of a lesion-making contact, it is possible to functionally "scout" the brain tissue surrounding the proposed lesion site, thus eliminating the need for serial movements and electrode interchanges. DISCUSSION: The feasibility of the scout electrode concept was tested using prototypes placed into cat medial geniculate nucleus. High-quality unit recordings were simultaneously obtained from different regions within the medial geniculate nucleus. This ability to physiologically map sites above and below the lesion-making contact facilitated precise placement of radiofrequency lesions in the center of the medial geniculate nucleus. These results suggest that it may be possible to develop clinically useful devices based on this novel concept.