A method of reconstructing an image of a colon, including receiving scan data of a colon taken by an imaging capsule that traverses the colon； wherein the imaging capsule emits X-ray radiation inside the colon and includes detectors that detect photons that are returned toward the imaging capsule from X-ray fluorescence and Compton back scattering interactions responsive to the radiation； and wherein the scan data includes counts of photons detected by each detector from X-ray fluorescence and Compton back scattering interactions； defining an initial guess of a geometry of a contour of a slice of the colon； calculating count values for each detector responsive to the geometry using a forward model； comparing the calculated count values of each detector with the values from the scan data； if the results of the comparison do not indicate reaching an optimal match then adjust the defined geometry and repeat the calculating and comparing.
