a First Generation b Second Generation x-ray tube 出 array of detect 图4、直线扫描 图5、平行扫描 c Third Generation d Fourth Generation rotating x-ray tube xraoccccaboobbbbo rotating array of detectors fixed array of detectors 图6、扇形扫描 图7、旋转扫描图4、直线扫描 图5、平行扫描 图6、扇形扫描 图7、旋转扫描