A cathode for a miniature X-ray device includes an insulating shell, a cathode and an anode. The cathode includes a focusing cup formed into an end. The focusing cup can include a thin metal layer that conforms to an inner surface of the cathode. An emitting material having a low work function, such...http://www.google.com.au/patents/US6771737?utm_source=gb-gplus-sharePatent US6771737 - X-ray catheter with miniature emitter and focusing cup
