Embodiments of the present invention provide phantoms, and associated methods of calibration which are suitable for use in both medical resonance imaging and radiographic imaging systems. A phantom for calibration of a medical imaging system, comprises a first component having a first outer shape, a portion of which defines part of at least one pocket; and a second component coupled to the first component and having a second outer shape, a portion of which defines another part of the at least one pocket. At least one of the first and second components comprises a reservoir, the reservoir having a shape at least a portion of which locates a center of the at least one pocket.