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.