X-Ray Source without Moving Parts for Ultra-High Speed Tomography

A method for producing a sequence of intense X-ray focal sources, by azimuthally sweeping apulsed electron beam around a large diameter target path circumscribing the patient, was demonstrated during the Spring of 1977 in laboratory tests at Palo Alto using the full scale geometry of a whole body scanner, at electron energies in the range of 130 to 200 kV and with peak currents of 200 to 400 mA. A low emittance electron gun together with a multi-element beam handling system was employed to overcome a variety of beam optic problems and to provide small X-ray focal sources of controllable and reproducible shape and position. Some of the initial test results illustrating the effectiveness of this technique will be discussed. Also discussed are alternative, more recently investigated methods, in which immediately prior to executing an X-ray scan, the HV system is energy stabilized by loading the azimuthally fast sweeping high power electron beam into a radiation shielded, annular collector located contiguous to the target. With this method, a rapid sequence of X-ray sources is produced (a) in the case of a pulsed electron beam, by using a low intensity dc field to kick the beam onto the annular target, and (b) in the case of a dc electron beam, by using a programmed low perturbing field to radially oscillate the beam on and off the target during the azimuthal sweep.