Components and overview of the modified NEMA XR 21-2000 phantom: (a) aluminum plate, (b) custom slot fixture built to allow vessel block insertion in the field of view, (c) plugs for the air cylinders (d) Low contrast artery block 76–715, (e) 15 mg/ml Stenosis/Aneurysm Artery Block- 76–705, (f) phantom containing new inserts, the white arrows indicate aluminum plate positions, the black arrow indicates the slot fixture for the subtraction blocks, (g) modified NEMA phantom with a low contrast vessel subtraction block placed in the slot.