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 to obtain sample values of each of a plurality of sampled parameters, each of the scans being arranged to generate a sample set comprising a plurality of the sample values; wherein each of the sampled parameters relates to a plurality of different parameters of the object; b) registering the sample sets from the scanning space with a reference data set defining a 3D volume in an object space which is fixed relative to the object to form a scattered data set which comprises sample values mapped to scattered points in the object space, thereby correcting for motion of the object in the scanning space; and c) determining object space values for each of the parameters of the object at each of a plurality of points in the object space from the scattered data set.