Abstract: Methods and apparatus for reconstructing an image of an object utilizing an imaging system, in which a limited width beam of radiation is emitted towards the object, the limited width beam of radiation having a fan beam angle extent selected to encompass a perimeter of a region of interest (ROI) within the object and to encompass less than a perimeter of the object itself; a set of truncated projection data of the object, including projection data of the ROI, is obtained by detecting the radiation from the limited width beam of radiation passing through the object; low frequency components of the set of truncated projection data are estimated; and an image of the ROI within the object is reconstructed utilizing the set of truncated projection data and the estimated low frequency components. Information from a limited set of complete projection data can be used to estimate the low frequency components of the set of truncated projection data, but such information is not required.

Abstract: A spectral correction algorithm for correcting dense object-induced spectral artifacts is described. In one embodiment, a calibration object, representative of typical head scanning conditions is scanned and the data reconstructed to provide an image. A water or water-equivalent cylinder of about the same diameter also is scanned and reconstructed, on the same display field of view (DFOV). These two images are designated respectively by BWEQ and WEQ. The ratio of images BWEQ and WEQ is then evaluated, and a region of interest extracted by multiplying the ratio by a function II(r), to obtain a calibration pattern CP. The calibration pattern is then averaged in azimuth to obtain a calibration vector. This calibration vector is fitted with low--order polynomial, and then divided by the fitting polynomial, to take out from the vector the low frequency components that, for instance, would be introduced on an "ideal" scanner. By subtracting 1.