A miniature x-
ray tube capable of intra vascular use, has a micro
cathode preferably formed by MEMS techniques. The very fine wire of the
cathode filament is formed on a
semiconductor base and draws a current sufficiently low that lead wires in a
cathode heater circuit, passing through a probe line connected to the x-
ray tube, can be very small wires, which helps maintain sufficient
dielectric spacing in the
high voltage circuit handled by the same probe line. In a preferred embodiment the probe line comprises a
glass fiber, held at a small
diameter to allow flexibility for navigating small-
radius turns within the vessels. In a preferred embodiment the
fiber is overcoated with a high-
dielectric polymer to significantly increase the
dielectric strength of the overall cable, without adding significantly to stiffness. The
high voltage ground conductor is a coaxial sheath on the outside of the
polymer. Exterior to the ground conductor is a further flexible layer having paths for
coolant.