An apparatus to examine a target in a patient includes an x-ray source configured to deliver a first x-ray beam towards the target, a device having an array of openings, the device located at an angle less than 180 degrees relative to a beam path of the first x-ray beam to receive a second x-ray beam resulted from an interaction between the first x-ray beam and the target, and a detector aligned with the device, the detector located at an angle less than 180 degrees relative to the beam path of the first x-ray beam to receive a part of the second x-ray beam from the device that exits through the openings at the device.