A method for calculating pressures in a fluid streaming through a tube section from an upstream end to a downstream end of the tube section, the method comprising scanning the tube section with a scanner and providing a plurality of 2D scanning images along the tube section with an inlet and at least two arms, by a computer program on the basis of the 2D images automatically N calculating a 3D image of the tube section by using interpolating between the 2D images, by a computer program performing a 2D sectional image cut through the 3D image, the image cut following the fluid stream, calculating in the sectional image cut a fluid pressure distribution along multiple locations inside the tube on the basis of given boundary conditions, the boundary conditions including fluid velocity or fluid pressure at the upstream end.
