Certain embodiments provide a computer apparatus comprising a display and a processor running a visualization application for visualizing a three-dimensional patient image data set including an anatomical feature of interest. The visualization application is operable to: a) display on the display at least one view of the image data set together with a curve which is intended to follow a path relevant for the anatomical feature of interest, but which may include one or more deviations from the path; and b) initiate an editing session for the curve by selecting a portion of the curve associated with a deviation from the path for correction, the editing session comprising: (i) presenting an MPR view including the selected portion of the curve; (ii) defining a trend line which approximately follows the anatomical path in the vicinity of the selected portion of the curve; (iii) amending under user control any desired part of the selected portion of the curve in the MPR view to make corrections to the curve; (iv) rotating under user control the MPR view about a rotational axis which is parallel to the trend line in order to permit a user to review the corrections in three dimensions in the image data set; (v) iterating under user control the amending and rotating steps as desired to make and review further corrections; and (vi) terminating the editing session under user control by accepting or rejecting the corrections; and c) display at least one view of the image data set together with the curve incorporating amendments from the editing session.