An imaging system for imaging a region of interest, the imaging system comprising: - a detection values providing unit for providing acquired detection values of the region of interest, wherein the region of interest comprises at least two components, wherein the detection values have been acquired by moving a radiation source emitting radiation and the region of interest relative to each other and by detecting the detection values, which are indicative of the radiation after having traversed the region of interest, while the radiation source and the region of interest move relative to each other, - a reconstruction unit for iteratively reconstructing a final image of the region of interest by performing several iteration steps, in which an intermediate image is updated based on the acquired detection values and based on noise values being variances of the detection values and indicative of the noise of the detection values, wherein the reconstruction unit is adapted to: - determine first component attenuation values and second component attenuation values, wherein the first component attenuation values correspond to elements of a first component within the region of interest and wherein the second component attenuation values correspond to elements of a second component within the region of interest, - determine for each acquired detection value a ratio between a corresponding first component attenuation value and a corresponding second component attenuation value, and - determine the noise values from ratios between corresponding first component attenuation values and corresponding second component attenuation values. - a detection values providing unit for providing acquired detection values of the region of interest, wherein the region of interest comprises at least two components, wherein the detection values have been acquired by moving a radiation source emitting radiation and the region of interest relative to each other and by detecting the detection values, which are indicative of the radiation after having traversed the region of interest, while the radiation source and the region of interest move relative to each other, - a reconstruction unit for iteratively reconstructing a final image of the region of interest by performing several iteration steps, in which an intermediate image is updated based on the acquired detection values and based on noise values being variances of the detection values and indicative of the noise of the detection values, wherein the reconstruction unit is adapted to: - determine first component attenuation values and second component attenuation values, wherein the first component attenuation values correspond to elements of a first component within the region of interest and wherein the second component attenuation values correspond to elements of a second component within the region of interest, - determine for each acquired detection value a ratio between a corresponding first component attenuation value and a corresponding second component attenuation value, and - determine the noise values from ratios between corresponding first component attenuation values and corresponding second component attenuation values.