This invention is related to a method to adjust the starting position of an acquisition trajectory of a mobile X-ray device that is to perform a portable X-ray tomography acquisition sequence. The invention supports an operator in positioning a mobile X-ray device such that it can subsequently successfully and autonomously perform a digital tomosynthesis exam. Alternatively may an operator provide visual input on a camera image on where he desires the tomosynthesis acquisition to be performed, allowing the mobile X-ray device to adjust its initial starting position autonomously.