Resolution of field-emission x-ray sources.

The physical designs of field-emission and conventional x-ray tubes are compared, and the physical and geometric source properties are translated into optical and resolution characteristics using modulation transfer functions calculated for idealized and practical sources and verified by star test pattern measurements. The field-emission design has several advantages: axial symmetry, circular shape, and a relatively favorable intensity distribution of the focal spot; in addition, the focal spot size is independent of the tube current. These advantages greatly enhance uniformity over the field of view and may increase resolution by a factor of 2 for a given nominal source size, thus largely ofsetting the greater physical size of present field-emission sources.