1. A method of compensating for motion artefact of a portion of a subject, wherein signal intensity data representing movement of the portion of the subject is recorded and plotted on a display, the method comprising the steps of: selecting on a computer a region of interest (ROI) covering an edge of the moving portion to maximize detection of motion artefacts; said computer calculating and plotting data points representing an average signal intensity of the selected ROI at specific time instances; said computer smoothing the data points to produce a smoothed curve representing the mean of the plotted data points; said computer measuring the difference between the plotted data points and the smoothed curve at particular time instances to produce a difference curve; said computer detecting a set of critical points on the difference curve; and said computer interpolating the detected set of critical points to form a curve of equal time intervals for subsequent processing.