A radiation detector (24) includes a two-dimensional array of upper scintillators (30t) which is disposed facing an x-ray source (14) to convert lower energy radiation events into visible light and transmit higher energy radiation. A two-dimensional array of lower scintillators (30<SUB>B</SUB>) is disposed adjacent the upper scintillators (30t) distally from the x-ray source (14) to convert the transmitted higher energy radiation into visible light. Upper and lower photodetectors (38t, 38<SUB>B</SUB>) are optically coupled to the respective upper and lower scintillators (30t,30<SUB>B</SUB>) at an inner side (60) of the scintillators (30t,30<SUB>B</SUB>). An optical element (100) is optically coupled with the upper scintillators (30t) to collect and channel the light from the upper scintillators (30t) into corresponding upper photodetectors (38t).
