An X-ray apparatus for digital radiography has a rotating arm where the X-ray source and X-ray sensor cassette are oppositely mounted. The source has a primary collimator to adjust the X-ray beam size according to the selected imaging modality. The sensor cassette encloses a first X-ray detector for a first imaging mode, while a second X-ray detector usable for a second imaging mode is detachably mounted on the external side of the sensor cassette. The sensor cassette accommodates a second collimator to create a fan shaped X-ray beam for a third imaging modality. The sensor cassette has a linear motorized movement which is used for: aligning the X-ray beam with respect to the first and second detector； positioning the first detector in the first imaging mode to achieve an extended view； and scanning movement during the third imaging modality synchronized with the horizontal movement of a third X-ray detector.
