A medical data processing method for determining an orientation of nerve fibres relative to a non-physiological electric field, the method comprising the following steps which are constituted to be executed by a computer: a) acquiring patient medical image data describing a patient medical image of an anatomical body part of a patient's body, the anatomical body part including nerve tissue comprising white matter nerve fibres; b) acquiring diffusion image data describing a diffusion-enhanced image of the anatomical body part; c) acquiring atlas data describing a spatial distribution of grey value-based tissue classes in a model body part representing a model of the anatomical body part; d) determining, based on the patient image data and the diffusion image data and the atlas data, fibre orientation data describing an orientation of the white matter nerve fibres, wherein the atlas data serves as a comparison for determining the area inwhich the nerve fibres are positioned in the diffusion image data, and the diffusion image data is used to reconstruct a diffusion tensor which describes the orientation of the nerve fibres and determining the fibre orientation data includes determining a transformation between a positionof the anatomical body part in the diffusion-enhanced image and a position of the anatomical body part in the patient medical image, wherein the patient medical image is defined by greyvalues and wherein the position of the white matter in the patient medical image is determined by comparing the grey values of the patient medical image to the tissue classes described by the atlas data; e) acquiring electric field orientation data describing an orientation of the non-physiological electric field which is an electric field simulated around a simulated electrode virtually placed in a predetermined spatial relationship relative to the anatomical body part; f) determining, based on the fibre orientation data and the electric field orientation data, relative orientation data describing a relative orientation between the orientation of the white matter nerve fibres and the orientation of the electric field; g) determining indication signal data describing an indication signal to be output to a user using the information content of the relative orientation data, wherein the indication signal data comprises relative orientation visualization data describing a visualization of the relative orientation between the white matter nerve fibres and the electric field, wherein the visualization comprises a coloured display of the patient medical image or the diffusion-enhanced image, wherein the relative orientation is represented by an orientation angle between the orientation of the white matter nerve fibres and the orientation of the electric field, and wherein angular threshold data is acquired describing a threshold angle. a) acquiring patient medical image data describing a patient medical image of an anatomical body part of a patient's body, the anatomical body part including nerve tissue comprising white matter nerve fibres; b) acquiring diffusion image data describing a diffusion-enhanced image of the anatomical body part; c) acquiring atlas data describing a spatial distribution of grey value-based tissue classes in a model body part representing a model of the anatomical body part; d) determining, based on the patient image data and the diffusion image data and the atlas data, fibre orientation data describing an orientation of the white matter nerve fibres, wherein the atlas data serves as a comparison for determining the area inwhich the nerve fibres are positioned in the diffusion image data, and the diffusion image data is used to reconstruct a diffusion tensor which describes the orientation of the nerve fibres and determining the fibre orientation data includes determining a transformation between a positionof the anatomical body part in the diffusion-enhanced image and a position of the anatomical body part in the patient medical image, wherein the patient medical image is defined by greyvalues and wherein the position of the white matter in the patient medical image is determined by comparing the grey values of the patient medical image to the tissue classes described by the atlas data; e) acquiring electric field orientation data describing an orientation of the non-physiological electric field which is an electric field simulated around a simulated electrode virtually placed in a predetermined spatial relationship relative to the anatomical body part; f) determining, based on the fibre orientation data and the electric field orientation data, relative orientation data describing a relative orientation between the orientation of the white matter nerve fibres and the orientation of the electric field; g) determining indication signal data describing an indication signal to be output to a user using the information content of the relative orientation data,