1. A method of calibrating image data obtained using a medical imaging protocol, comprising: providing a processor with reference image data from a scan of a reference object using the medical imaging protocol; in said processor, comparing the obtained reference image data of the reference object to standard reference image data for the reference object to obtain a comparison result that indicates a degree of deviation of said reference image data with respect to said standard reference image data; in said processor, using said comparison result to set a parameter of a filter that, when applied to filter said reference image data, reduces said degree of deviation so to be within a predetermined range; providing said processor also with subject image data obtained from a scan of subject using the medical imaging protocol, said subject image data comprising at least one visually under-represented part of said subject; in said processor, filtering the subject image data with said filter to obtain filtered obtained filter subject image data; maintaining a set of said subject image data without filtering thereof, as unfiltered subject image data, and making only said unfiltered subject image data, and not said filtered subject image data, available at an output of said processor as a data file in a form allowing display of an image of said subject corresponding to said unfiltered image data; and in said processor, obtaining a value for a variable from said filtered subject image data that represents said degree of under representation of said at least one part of said subject in said unfiltered subject image data, and including an electronic representation of said variable in said data file that contains said unfiltered subject image data for display with said display of said image of said subject corresponding to said unfiltered image data.