The present invention relates to an apparatus for destroying a predetermined defined volume (10) in a tissue, such as generating controlled coagulation, so-called lesion, in the brain. More particularly, the apparatus comprises a main unit (1) for transmitting a tissue-destroying medium comprising a control unit (3) for controlling the medium transmission, and a transferring means (4), such as an electrode, which is connected to said main unit and adapted to be inserted into the predetermined volume for transferring the transmitted medium to the volume. The apparatus according to the invention is characterised in that it further comprises a measuring means (5-8) for measuring at least one optical characteristic of the predetermined volume, the optical characteristic varying with the size of the destroyed volume, the measuring means being connected to said control unit for controlling the supply of the tissue-destroying medium on the basis of the measured optical characteristic.

A method and a device for testing a brain lesion electrode (1) which is intended for use in treatment of a specified area in the brain, for instance, by controlled coagulation or lessening. The device comprises a transparent container (2) which in adapted to accommodate a solution of coagulatable protein with a predetermined salt content, a seal (6), which the brain lesion electrode (1) can penetrate and which is adapted to seal the container (2) containing the solution, a heating device (3) for heating the solution to a selected temperature, a power unit (23) for supplying, during a selected period, current of a predetermined intensity and frequency between the electrode (1) and a backplate electrode (18) in the container (2) to increase the temperature of the solution in the area at the tip of (21) of the electrode when the electrode (1) is introduced into the solution and positioned therein.