CT devices and methods thereof are disclosed. The CT device comprises a circular electron gun array including a plurality of electron guns, each of the electron guns is configured to emit electron beams along the radial direction of the circular electron gun array in sequence according to a predetermine pulse sequence; an acceleration cavity disposed inside of a circle on which the circular electron gun array is positioned, including a plurality of nested concentric coaxial cavities that operate in π mode for accelerating electron beams emitted from the respective electron guns of the circular electron gun array; a circular transmission target disposed inside of a circle on which the acceleration cavity is positioned and being bombarded by the accelerated electron beams to generate X-rays; and a circular detector configured to receive the X-rays after they have passed through an object to be detected.