Abstract: A method of determining a three-dimensional motion of a movable ultrasound probe (10) is described. The method is carried out during acquisition of an ultrasound image of a volume portion (2) by the ultrasound probe. The method comprises receiving a stream of ultrasound image data (20) from the ultrasound probe (10) while the ultrasound probe is moved along the volume portion (2); inputting at least a sub-set of the ultrasound image data (20, 40) representing a plurality of ultrasound image frames (22) into a machine-learning module (50), wherein the machine learning module (50) has been trained to determine the relative three-dimensional motion between ultrasound image frames (22); and determining, by the machine-learning module (50), a three-dimensional motion indicator (60) indicating the relative three-dimensional motion between the ultrasound image frames.