A method, apparatus, medium and signal for producing a representation of a
measurable property which varies in time and space are disclosed. The
apparatus includes a receiver for receiving a plurality of sets of values
representing measurements of the property across the object at respective
measurement times, each set being associated with a respective
measurement time. The apparatus further includes a processor circuit in
communication with the receiver. The processor circuit is programmed to
produce a plurality of sets of values representing the property at a
plurality of locations throughout the object at the respective
measurement times, by minimizing a figure of merit function relating the
values representing the measurements with the values representing the
property at the plurality of locations, with a shape constraint imposed
on the values representing the property at the plurality of locations.