A method of obtaining a volumetric image, the method carried out by a processor (54, 700, 1204), the method comprising: obtaining a plurality of volumetric images, the volumetric images reconstructed using respective sets of projection images, wherein the volumetric images and the respective sets of projection images correspond with different respective bins for a physiological cycle; and determining an additional volumetric image using one or more of the projection images from two or more sets that correspond with different respective bins for the physiological cycle, and by obtaining data regarding registrations of the respective volumetric images; wherein: the act of determining the additional volumetric image comprises modifying the one or more of the projection images from the two or more of the sets, by iteratively modifying one of the projection images from one of the sets using at least some of the data regarding two or more of the registrations; and using the modified projection images to reconstruct the additional volumetric image; wherein: (i) each of the registrations of the corresponding volumetric image comprises a registration between the corresponding volumetric image and a reference image, the reference image being any one of the plurality of volumetric images; or: (ii) each of the registrations of the corresponding volumetric image comprises a registration between the corresponding volumetric image and another one of the volumetric images that is adjacent to the corresponding volumetric image in bin order. obtaining a plurality of volumetric images, the volumetric images reconstructed using respective sets of projection images, wherein the volumetric images and the respective sets of projection images correspond with different respective bins for a physiological cycle; and determining an additional volumetric image using one or more of the projection images from two or more sets that correspond with different respective bins for the physiological cycle, and by obtaining data regarding registrations of the respective volumetric images; wherein: the act of determining the additional volumetric image comprises modifying the one or more of the projection images from the two or more of the sets, by iteratively modifying one of the projection images from one of the sets using at least some of the data regarding two or more of the registrations; and using the modified projection images to reconstruct the additional volumetric image; the act of determining the additional volumetric image comprises modifying the one or more of the projection images from the two or more of the sets, by iteratively modifying one of the projection images from one of the sets using at least some of the data regarding two or more of the registrations; and using the modified projection images to reconstruct the additional volumetric image; wherein: (i) each of the registrations of the corresponding volumetric image comprises a registration between the corresponding volumetric image and a reference image, the reference image being any one of the plurality of volumetric images; or: (ii) each of the registrations of the corresponding volumetric image comprises a registration between the corresponding volumetric image and another one of the volumetric images that is adjacent to the corresponding volumetric image in bin order. (i) each of the registrations of the corresponding volumetric image comprises a registration between the corresponding volumetric image and a reference image, the reference image being any one of the plurality of volumetric images; or: (ii) each of the registrations of the corresponding volumetric image comprises a registration between the corresponding volumetric image and another one of the volumetric images that is adjacent to the corresponding volumetric image in bin order.