1. A method of generating an image data set, describing an object, as the object moves in a scanning space relative to a scanner, the method comprising: 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 sample parameter associated with a respective point in the scanning space, the plurality of scans generating sample sets relating to a plurality of different sample 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 sample parameters at each of a plurality of points in the object space.