1. A method for processing a sequence of a plurality of 2D projection images of an object of interest, acquired with a medical imaging system comprising a source of X-rays adapted to move around the object, the method comprising: obtaining 2D projection images of the object of interest according to a plurality of angulations at a first time when the object is without injection of a contrast product, the 2D projection images being such that R M f M =p M , where p M are the projection images at the first time, f M is the 3D image of the object at the first time and R M , is a projection operator which models acquisition by the imaging system at the first time; obtaining 2D projection images of the object of interest according to a plurality of angulations at a second time when the object is opacified by injection of a contrast product, the 2D projection images being such that R O f O =p O , where p O are the projection images at the second time, f O is the 3D image of the object at the second time and R O is a projection operator which models acquisition by the imaging system at the second time; iteratively treating the projection images by minimizing, relative to a sequence of 3D images, the function: 
 J ({right arrow over ( g )},λ)=λ S ( {right arrow over (g)} )+ Q ( {right arrow over (g)} ), where Q({right arrow over (g)}) is a term of fidelity to the measurements acquired; S({right arrow over (g)})=∥Φ xyz H t {right arrow over (g)}∥ 1 is a restriction where H t is a decomposition time such that {right arrow over (h)}=H t {right arrow over (g)} with {right arrow over (h)}={h α ,h δ } combination of the two constituents of {right arrow over (g)} and where Φ xyz {right arrow over (h)}={Φ α h α ,Φ δ h δ } defines two spatial transforms of compression of both constituents of {right arrow over (h)}, restriction, which will improve the determining of variations linked to the injection, supposedly compressible variations, and select parts common to both images g(t O ) and g(t M ) which will be determined at the same time from the projection images at the first time and the projection images at the second time; and λ is a parameter of compressibility, wherein the minimizing solution is a set of 3D images estimated from: 
 {right arrow over (f)}={f O ,f M }, where {right arrow over (f)} represents the 3D image of the object at both of the first and second time.