Abstract: Motion artefacts are a major hindrance in magnetic resonance (MR) imaging applications, particularly functional imaging and other high-sensitivity applications. The system as disclosed provides a versatile laser ranging method for the measurement of body part rotation and translation, simultaneously in three dimensions. Since optical motion detection and NMR data acquisition are inherently independent, these two systems can function efficiently in parallel. Furthermore, using these optical motion data, real-time image artefact correction can be achieved by passing the appropriate parameters to the pulse programmer to change the acquisition in real time. The system uses three laser diodes mounted on a fixed platform and generating converging beams impinging on three retro-reflectors to generate three parallel but offset reflected beams the positions of which are detected by position sensing detectors providing two output signals indicative of the position of the beam in the plane of the detector.