Disclosed herein is an image sensor comprising: a plurality of packages arranged in a plurality of layers; wherein each of the packages comprises an X-ray detector mounted on a printed circuit board (PCB); wherein the packages are mounted on one or more system PCBs; wherein within an area encompassing a plurality of the X-ray detectors in the plurality of packages, a dead zone of the packages in each of the plurality of layers is shadowed by the packages in the other layers.