X-ray bone densitometry apparatus with variable attenuation, modulation

Abstract

Radiological apparatus, such as a bone densitometry measurement system, utilizes a penetrating radiation source, such as an x-ray source. The apparatus has a multi-position attenuator mechanism for placement of different attenuating materials in the radiation beam. The mechanism includes a rack of attenuating materials which is translated across the radiation beam path by a drive mechanism, such as a linear motor. The mechanism preferably includes a controller for actuating the drive mechanism in response to operator command and monitoring which attenuating material crosses the beam path by way of position signals generated by a position encoder that is coupled to the controller. This attenuator mechanism allows attenuating materials to be stored within the radiological apparatus, enables operator selection of attenuating materials under automatic machine control and self-alignment of the material relative to the radiation beam. Spectral content and intensity of the penetrating radiation beam is modulated in a known an repeatable pattern by a modulating apparatus. In the preferred embodiment one or more concentric, rotating cylinders are interposed between the x-ray beam and the patient support table. Radiation attenuating materials are arrayed in a radial pattern within the rotating cylinders, so that the beam passes through a plurality of layers of attenuating materials. By controlling relative rotational speed of the rotating cylinders through a closed loop control system, a periodic, repetitive pattern of modulating apparent radiation beam intensity and spectral content can be established. The modulation apparatus is useful for dual-energy radiological scans, such as in bone densitometers.