A computed tomography (CT) imaging technique called variable resolution x-ray (VRX) detection provides variable image resolution ranging from that of clinical body scanning (1 cy/mm) to that of microscopy (100 cy/mm). In this paper, an experimental VRX CT scanner based on a rotating subject table and an angulated storage phosphor screen detector is described and tested. The measured projection resolution of the scanner is > or = 20 lp/mm. Using this scanner, 4.8-s CT scans are made of specimens of human extremities and of in vivo hamsters. In addition, the system's projected spatial resolution is calculated to exceed 100 cy/mm for a future on-line CT scanner incorporating smaller focal spots (0.1 mm) than those currently used and a 1008-channel VRX detector with 0.6-mm cell spacing.
A new technique called Variable-Resolution X-ray (VRX) detection that dramatically increases the spatial resolution in computed tomography (CT) and digital radiography (DR) is presented. The technique is based on a principle called "projective compression" that allows the resolution element of a CT detector to scale with the subject or field size. For very large (40-50cm) field sizes, resolution exceeding 2 cy/nun is possible and for very small fields, microscopy is attainable with resolution exceeding 100 cy/mm. Several effects that could limit the performance of VRX detectors are considered. Experimental measurements on a 16-channel, CdWO, scintillator + photodiode test array yield a limiting MTF of 64 cy/mm (8.t) in the highest-resolution configuration reported. Preliminary CT images have been made of small anatomical specimens and small animals using a storage phosphor screen in the VRX mode. Measured detector resolution of the CT projection data exceeds 20 cy/mrn (<25 pt); however, the final, reconstructed CT images produced thus far exhibit 10 cy/mm (5O.t) resolution because of non-flatness of the storage phosphor plates, focal spot effects and the use of a rudimentary CT reconstruction algorithm.A 576-channel solid-state detector is being fabricated that is expected to achieve CT image resolution in excess ofthat of the 16-channel test array.
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