1. A method to build a 3D profile of a parameter of interest of an object comprising the steps of: using at least a first radiation source generating a first radiation; positioning a first set of detector elements so as to detect said first radiation; interposing said object in between said first radiation source and said first set of detector elements; representing a region of interest of said object as a first set of voxels, further denoting the value of said parameter of interest within each said voxel by a variable and thereby generating a first set of variables associated with said first set of voxels; representing the signal detected by each element of said first set of detector elements as a ray sum that has contributions from all the voxels of said first set of voxels that intersect with the ray path connecting said first radiation source and said each element of said first set of detector elements; and performing computations on the ray sums representing detected signals from said first set of detector elements to solve for the values of said first set of variables associated with said first set of voxels over said region of interest of said object.