Abstract: A method and system for reconstructing an x-ray image from a partial orbit through the use of a “virtual” fan angle. The virtual fan angle is determined based upon the range of angular positions spanned by a source in a CT instrument or a selected smaller angle. Exposure data is obtained and he virtual fan angle is used to weight the exposure data. Image reconstruction can then proceed using the weighted exposure data. The described methods and system also function for data collected over a complete orbit.

Abstract: A method and system for reconstructing an x-ray image from a partial orbit through the use of a “virtual” fan angle. The virtual fan angle is determined based upon the range of angular positions spanned by a source in a CT instrument or a selected smaller angle. Exposure data is obtained and he virtual fan angle is used to weight the exposure data. Image reconstruction can then proceed using the weighted exposure data. The described methods and system also function for data collected over a complete orbit.

Abstract: A method and system for reconstructing an x-ray image through mapping. The system rotates an x-ray source and an x-ray detector in an irregular path. A calibration factor matrix for each position of a source and detector is calculated using a calibration phantom and then stored for use during reconstruction. The image is reconstructed by mapping a reprojected image point from a known coordinate using the calibration factors. The mapping takes into consideration the non-idealities in the irregular path, improving the image reconstruction.

Abstract: An x-ray computed tomography device and method where backprojection is performed with pixels each having their own back projection range. The range is determined using a two-dimensional completeness condition such that every line through a reconstructed slice must intercept the projection of the source orbit onto the plane of the slice. The completeness condition provides an adequate amount of data for the back projection to maintain quality of the reconstructed image while allowing a higher helical pitch ratio. This is advantageous in situations where fast scanning is desired, such as patient screening and CT-angiography. The method and device are preferably applied to a helical cone beam system. The backprojection can be performed using cone-beam projection data obtained with a helical scan or after sorting the projection data into parallel-beam ray-sums in the transverse plane while maintaining the cone angle.

Abstract: A method and apparatus to calibrate and correct magnetic and geometrical distortions in an imaging system, specifically a computed tomography (CT) system, includes a distortion measuring object which is placed on the surface of an image intensifier. An image frame of the distortion measuring object is generated, and a correction table is generated to correct the image frame. Once the correction table has been generated using the distortion measuring object, subsequent image frames are corrected using the correction values in the correction tables. A method and apparatus to calibrate and correct offsets, veiling glare and scatter in an imaging system, specifically a computed tomography system. An image frame is generated and areas not directly impinged by direct radiation are used to correct areas of the detector that are directly impinged. A method and apparatus for correcting and calibrating an imaging system, specifically a computed tomography system.

Abstract: A method and apparatus to calibrate and correct magnetic and geometrical distortions in an imaging system, specifically a computer tomography (CT) system, includes a calibration object which is placed on the surface of an image intensifier. An image frame of the calibration object is generated, and a vertical correction table is generated corresponding to the amount of image distortion caused to the image frame of the calibration object. The image frame is corrected using the vertical correction table, and the corrected image frame data is summed or averaged and either stored for further transformation into a slice image or used to generate a horizontal correction table to correct distortions in the horizontal direction. Once the vertical and horizontal correction tables have been generated using the calibration object, subsequent image frames are corrected using the correction values in the correction tables.