1. A medical data processing method of determining information describing the probable position of a neural fibre in a patient's brain, the method comprising the following steps which are constituted to be executed by a computer: a) acquiring patient-specific medical image data describing the brain of the patient; b) acquiring atlas data defining an image-based model of a human brain; c) determining, based on the patient-specific medical image data and the atlas data, seed region data describing seed regions (A, B) in the patient-specific medical image data in which the ends of neural fibres of the patient's brain may be located; d) determining, based on the patient-specific medical image data and the seed region data, neural fibre tract data describing a plurality of potential tracts (T1, T2, T3) which a specific neural fibre may take through the patient's brain; e) determining, based on the atlas data and the neural fibre tract data, a figure of merit for each one of the potential tracts (T1, T2, T3).