Tungsten Alloy X-ray Tube in Various Generations of CT-2

Fourth generation of CT scanner uses Rotate-Fixed Ring geometry where a ring of fixed detectors completely surrounds the patient. Tungsten alloy X-ray tube rotates inside the detector ring through a full 360 degrees with a wide fan beam producing a single image. Due to the elimination of translate-rotate motion the scan time is reduced comparable with third generation scanner, initially, to 10 seconds per slice but the radiographic geometry is poor because the X-ray tube must be closer to the patient than the detectors, i.e. the geometric magnification is large also scatter artifact is more than third generation since they cannot use anti-scatter grid. -The disadvantages of poor geometry noted above have been alleviated very neatly by the so called nutating geometry. Tungsten alloy X-ray tube is external to the detector ring but slightly out of the detector plane, this change resulted in increasing both the acquisition speed, and image resolution. The method of scanning was still slow, because the X-ray tube and control components interfaced by cable, limiting the scan frame rotation. Further, they were more sensitive to artifacts because the non-fixed relationship to the x-ray source made it impossible to reject scattered radiation.