Stereotactic ablative neurosurgery with radio frequency current is regularly performed on patients with movement disorders, for instance Parkinson's disease. Even though the technique has been used for ablation in the brain for almost 50 years, nobody has suggested a standardised way of testing the electrodes used for ablative surgery.
Within the framework of this thesis a computer-assisted video system has been developed for a proposed standardised method for in vitro estimation of protein clots generated by radio frequency lesioning electrodes. The system can be used for documentation of lesion growth by video recording, as well as lesion shape and size Oength, width and volume) calculations by use of two perpendicularly captured images of the protein clot. The system has been used for this purpose in a comparative study including two different test solutions (albumin and hen's egg white), three different temperature settings (70, 80 or 90°C) and five different brain electrode configurations, three monopolar (2mm diameter and 4mm tip, 1mm diameter and 2 or 4mm tip) and two bipolar (1 or 2mm diameter). Electrode configurations and parameter settings of the radio frequency generator greatly affect the size and shape of the coagulated lesion. Larger electrodes and higher temperature settings produce larger lesions, while the shape of the lesion is more dependent on the choice between monopolar or bipolar electrodes and the length of the active uninsulated electrode tip. The experiments performed in the albumin solution showed more regular, reproducible and homogeneous shapes and sizes compared to the experiments performed in hen's egg white. Protein clots generated by the electrodes in the albumin solution ranged in width from 2.2±0.1 to 5.3±0.lmm, length from 3.0±0.1 to 8.7±0.3mm and volume from 8.5±1.4 to 133.5±26.8mm3 , (m±s.d.,n=10). By using different test patterns, the video system has been proven to be accurate and precise (random error 2%), giving repeatable and reproducible results.
A method for simulation of the thermal characteristics of brain lesioning electrodes using the finite element method has also been developed. Finite element simulations of thein vitro experiment give valuable information of the lesion growth and final size when using different thermal properties and conditions. No deviation in width and distance from tip was seen when comparing finite element simulations of a power distribution at the distal part of the tip to in vitro experiments. However, the length is somewhat underestimated.
In conclusion, the developed computer-assisted video system can be used as a standard system for evaluation of radio frequency electrodes used in stereotactic ablative neurosurgery. The proposed albumin solution is superior to egg white and should be used as a test substrate. An FEM simulation offers a good approximation for assessment of the size of the in vitro lesion.
Linköping: Linköpings universitet , 1999. , 30 + 3 articles p.