1. Calibration phantom for a medical imaging system, comprising: a plurality of separate detection elements arranged in a determined pattern, each detection element containing a product that is visible by the medical imaging system, each detection element comprising an envelop delimiting an internal volume filled with the product, and a support made of a material that is invisible by the medical imaging system so as to contrast with the product in an image of the medical imaging system, the support comprising a plurality of housings arranged according to the determined pattern, each housing being adapted to receive at least a part of one of the detection elements, the support comprising a plurality of plates provided with the housings, which housings are arranged along first and second directions, the plates being stacked along a third direction perpendicular to the first and second directions, said calibration phantom being characterised in that each plate presents opposed first and second surfaces, the respective first and second surfaces of two adjacent plates resting against each other, the envelope of each detection element has an external surface and each housing is adapted to receive entirely one of the detection elements so that a part of the external surface of said detection element is flush with the first surface of the plate.