Patent Number: 
Section: claims

1. Device limiting the appearance of decoding artefacts for a gamma camera with a coded mask (1) comprising a gamma radiation detector (3) opposite the coded mask and having a field of view with an area partially coded (20) by the coded mask, characterised in that it comprises a recessed part (30), which is opaque to the gamma radiation, to be arranged opposite the detector (3) with respect to the coded mask (1), with said recessed part (30) obscuring the partially coded area (20) of the field of view for the detector (3) and having a thickness that varies over its length, so that a gamma photon is stopped by the same thickness of material, regardless of its path between the partially coded area (20) of the field of view and the detector (3). 2. Device according to claim 1, characterised in that the recessed part (30) has a substantially cylindrical, frusto-conical, pyramid-shaped, or even polyhedral internal wall. 3. Device according to claim 2, characterised in that the recessed part (30) borders the coded mask (3). 4. Device according to claim 1 characterised in that the recessed part (30) is made of metal with a density greater than 7 g/cm3. 5. Device according to claim 4, characterised in that the recessed part (30) can be made of stainless steel, lead or a lead-based alloy, tungsten or a tungsten-based alloy such as DENAL, or copper or a copper-based alloy. 6. Device according to claim 1, characterised in that the recessed part (30) has a threaded end (30a) so as to be attached by screwing to a support part (53) of the coded mask (1). 7. Device according to claim 1, for a gamma camera with a coded mask with a field of view having an area totally coded (10) by the coded mask (1), limited by a casing (10.1) and adjacent to the partially coded area (20), characterised in that the recessed part (30) comprises a free end (30b) opposite the detector (3) when it is mounted on the camera so that the casing (10.1) of the totally coded area (10) passes through the free end (30b). 8. Device according to claim 1, for a gamma camera with a coded mask with a field of view having an area totally coded (10) by the coded mask (1), limited by a casing (10.1) and adjacent to the partially coded area (20), characterised in that the recessed part (30) has a wall that engages with the casing (10.1) of the totally coded area (10). 9. Device according to claim 1, characterised in that the recessed part (30) has a free end (30b) opposite the detector (3) when it is mounted on the camera, which free end (30b) is substantially rounded. 10. Device according to claim 9, characterised in that the rounded end corresponds to a radius (R) centred in a central portion of the detector (30). 11. Gamma camera characterised in that it comprises a device (30) limiting the appearance of decoding artefacts according to claim 1.