A system comprising: a non-transitory data storage for storing projection space information, the projection space information in a density domain for an object under observation, and including one or more input projection pixels and one or more predicted projection space pixels; and an image reconstructor computer having at least one processor, the at least one processor operable to: receive the projection space information from the non-transitory data storage; convert the projection space information into projection space data in the density domain; compute preliminary transformed object density update data using the one or more input projection pixels in the density domain, the projection space data, and transformation functions; compute transformed object voxel density update data by re-scaling the preliminary transformed object density update data using slopes derived from a set of non-linear transformations of voxel densities and inverse slopes of a set of non-linear back-transformations of corresponding transformed voxel densities; accumulate the transformed object voxel density update data with a transformed preceding voxel data estimate from a preceding iteration to form transformed object voxel density estimate; compute voxel density data by transforming the transformed object voxel density estimate; compute voxel density estimate data by re-estimating the voxel density data using object structural information; delay the voxel density estimate data by a unit delay to obtain prior voxel density estimate data; transform the prior voxel density estimate data to obtain the transformed preceding voxel data estimate; reconstruct an object space image representing the object under observation using prior voxel density estimate data. a non-transitory data storage for storing projection space information, the projection space information in a density domain for an object under observation, and including one or more input projection pixels and one or more predicted projection space pixels; and an image reconstructor computer having at least one processor, the at least one processor operable to: receive the projection space information from the non-transitory data storage; convert the projection space information into projection space data in the density domain; compute preliminary transformed object density update data using the one or more input projection pixels in the density domain, the projection space data, and transformation functions; compute transformed object voxel density update data by re-scaling the preliminary transformed object density update data using slopes derived from a set of non-linear transformations of voxel densities and inverse slopes of a set of non-linear back-transformations of corresponding transformed voxel densities; accumulate the transformed object voxel density update data with a transformed preceding voxel data estimate from a preceding iteration to form transformed object voxel density estimate; compute voxel density data by transforming the transformed object voxel density estimate; compute voxel density estimate data by re-estimating the voxel density data using object structural information; delay the voxel density estimate data by a unit delay to obtain prior voxel density estimate data; transform the prior voxel density estimate data to obtain the transformed preceding voxel data estimate; reconstruct an object space image representing the object under observation using prior voxel density estimate data. receive the projection space information from the non-transitory data storage; convert the projection space information into projection space data in the density domain; compute preliminary transformed object density update data using the one or more input projection pixels in the density domain, the projection space data, and transformation functions; compute transformed object voxel density update data by re-scaling the preliminary transformed object density update data using slopes derived from a set of non-linear transformations of voxel densities and inverse slopes of a set of non-linear back-transformations of corresponding transformed voxel densities; accumulate the transformed object voxel density update data with a transformed preceding voxel data estimate from a preceding iteration to form transformed object voxel density estimate; compute voxel density data by transforming the transformed object voxel density estimate; compute voxel density estimate data by re-estimating the voxel density data using object structural information; delay the voxel density estimate data by a unit delay to obtain prior voxel density estimate data; transform the prior voxel density estimate data to obtain the transformed preceding voxel data estimate; reconstruct an object space image representing the object under observation using prior voxel density estimate data.