Patent ID: 7358479

Claim:
An x-ray computed tomography gantry comprising: a stator; a rotor mounted for rotation relative to said stator through a rotation angle; an x-ray tube that emits an x-ray beam and a radiation detector on which said x-ray beam is incident, said x-ray tube and said radiation detector being mounted on said rotor for co-rotation therewith and being configured to irradiate a subject, disposed between said x-ray tube and said radiation detector, to generate detector data representing said x-ray beam attenuated by the subject; a disc comprising a plurality of circumferentially disposed, spaced markings; a detection device that detects said markings, one of said disc or said detection device being co-rotatable with said rotor and said detection device generating electrical signals at an output thereof representing relative movement between said markings and said detection device while said detector data are being generated; a low-pass filter connected to the output of said detection device that low-pass filters said electrical signals, to produce a low-pass filtered signal at an output thereof; an evaluation device connected to the output of said low-pass filter that converts said low-pass filtered signal into a measurement signal representing said rotation angle; and an image reconstruction computer supplied with said measurement signal and supplied with said detector data, that reconstructs an image of the subject by executing an image reconstruction algorithm employing said detector data and said rotation angle.