Patent Number: 052280691
Section: summary

FIELD OF THE INVENTION This invention is concerned with computerized tomographic scanners and more particularly with tomographic scanning systems equipped to simultaneously acquire multiple slice data in a single scan. BACKGROUND OF THE INVENTION Early CT scanners that were used for scanning the brain had only a single detector and a single pencil beam X-ray source. The source and detector were repeatedly translated across the head rectilinearly a short distance and then rotated to acquire the plurality of views required to obtain an image. The early scanners required about 300 seconds to complete a 180 degree scan. Historically the next advance in scanners, known as "second generation" scanners also used a two motion system, but improved the data acquisition speed to below 20 seconds through the use of an array of detectors and a fan beam X-ray source. Twenty seconds is a normal breath holding period; and thus, the second generation tomographic scanners managed to reduce motion blurring and artifacts due to respiration. Third generation CT scanners also known as rotate-rotate scanners used fan beam X-ray sources and an array of detectors that rotated simultaneously about the subject. The scan time of the third generation scanners in general is under 5 seconds. The fourth generation CT scanners also use a fan beam X-ray source that rotate within a circle of stationary detectors occupying a full 360 degree circle around the subject. Hence, the successive generations of CT scanners increased the scan speed to decrease the scanning time. Each generation used more detectors in the detector arrays and thereby substantially increased the costs of the system. The increased number of detectors, of course, increased the spatial resolution. Thus in successive gnerations the speed of operation and the cost of the scanners were increased while the spatial resolution was improved. One method used to increase the speed of the earlier scanners; i.e., first generation scan CT scanners was the use of tandem detectors to obtain dual slices in a single scan. This practice was discontinued when detector arrays were used. Thus, after the scan speed improvement of the second generation it was generally assumed by those skilled in the art that there was no longer a need to acquire data for two slices simultaneously. An important factor mitigating against the simultaneous acquisition of dual slice data in a single scan is that to accomplish such dual slice imaging it is necessary to increase the number of detectors. Each detector, of course, normally requires a separate channel with all of the front end electronics and hardware to support the detector. Hence, each added detector substantially increases the cost of the tomographic equipment. Thus, while dual slice equipment saves time it does substantially increase the cost and in the past has increased artifacts caused by the scanning operation. Accordingly, those skilled in the art have not used simultaneous dual slice features since about the time of the introduction of the fan beam; i.e., the second generation scanners and certainly it is not known that any have been used in third generation scanners even though there have been suggestions for using simultaneous dual slice acquisition with fourth generation machines. See, for example, an article entitled "Theoretical Possibilities for a CT Scanner Development" by Dr. D. P. Boyd, which was published in Diagnostic Imaging in December, 1982. In general, the speed of scanning of computerized tomographic systems has increased from something like 5 minutes to less than a second. The increased speed has led to improved image quality; because among other things, of a reduction of motion caused artifacts. In addition the spatial resolution has improved due to increased computer power, and the number and density of the detectors. In the article, the problem of the additional cost of the detectors and hardware required for dual slice acquisition is addressed by the suggestion of the use of a plurality of X-ray sources displaced from each other in the Z direction rather than detectors displaced from each other in the Z direction. The Z direction is transverse to the longitudinal direction of the detector array or where the detector array is arcuate, the longitudinal direction of the top view planar projection of the detector array. As witnessed by the fourth generation scanners, however, those skilled in the art are still searching for methods and apparatus to further decrease motion caused artifacts in addition to increasing the throughput and decreasing the exposure of the subject to radiation. Accordingly, an object of the present invention is to provide a dual slice data acquisition system for use in third generation rotate-rotate computerized tomographic scanners. BRIEF DESCRIPTION OF THE INVENTION In accordance with the present invention a computerized tomographic system is provided, said system comprising: a gantry, PA1 said gantry including means for retaining X-ray source means on one side of a patient and X-ray detector means on the other side of said patient, PA1 means for simultaneously rotating said source means and said detector means about the patient, PA1 said detector means comprising means for simultaneously detecting X-rays that have traversed multiple plane sections in said patient, PA1 means for processing said detected X-rays to provide image data, and PA1 means for displaying images based on said image data. A feature of the present invention provides means for more efficiently using the X-ray beams to obtain dual slice imaging data per scan. This efficient use of the X-ray beams speeds throughput, reduces motion caused artifacts and also reduces the patient's exposure to X-ray radiation without any undue adverse effects on the image quality. The dual slicing can be accomplished at a minimum increase in cost due to extra detectors by using two modes of operation, a single slice mode and a dual slice mode. The dual slice mode may be limited to scans less than whole body scans. A related feature of the present invention provides means for shifting the detector means in the Z direction to assure that artifacts caused by beam divergence is readily correctable by using the familiar single slice scan geometry. A further feature of the invention includes detector means wherein said means for simultaneously detecting X-rays that have traversed multiple plane sections in the patient comprises a pair of abutting detectors extending in the Z direction with means for isolating each of the detectors from affecting the juxtaposed detectors. Where the Y direction is the direction between the source and the detectors and the X direction is the longitudinal direction of a detector array. The Z direction is perpendicular to both the X and the Y direction. A further feature of the invention comprises utilizing a source means that has a dimension in the Z direction and thus is not a point source in the Z direction, said source means providing a fan beam which extends from the source means to the detector means and encompasses the patient in the X direction. Another feature of the invention comprises utilizing multiple detectors extending in the Z direction only for a portion of the array in the X dimension. Thus, this utilization of limited extra detectors in the X direction extending in the Z direction minimizes the costs of extra detectors while providing the benefits of the dual slice capability in critical acquisition procedures, such as head scans.