A method of generating an image data set, describing an object, as the object moves in a scanning space, comprises: a) performing a plurality of scans of the scanning space each scan being arranged to generate a set of samples, each sample including a sample value of at least one parameter associated with a respective point in the scanning space, the plurality of scans generating sample sets relating to a plurality of different parameters b) determining a mapping for each of the samples from the scanning space into an object space which is fixed relative to the object and c) determining object space values for each of the parameters at each of a plurality of points in the object space.
