X-ray Tubes in CT Scanners

X-ray Tubes in CT Scanners

• CT scanners exert significantly higher thermal loads on X-ray tubes compared to other diagnostic X-ray applications.

• Early CT scanners used lower power levels due to longer scan times, allowing for sufficient heat dissipation.

• Later CT models with shorter scan times necessitated high-power X-ray tubes and oil-cooled rotating anodes for effective heat dissipation.

Helical CT and X-ray Tube Design

• The introduction of helical CT with continuous scanner rotation presented new challenges for X-ray tubes.

• Significant design advancements were implemented to increase power levels and address target temperature, heat storage, and dissipation problems in tubes.

• These advances include redesigned tube envelopes, cathode assemblies, and anode assemblies (including anode rotation and target design).

Increased Heat Capacity and Efficiency

• Shorter scan times have led to a five-fold increase in anode heat capacities, eliminating the need for cooling delays in most clinical procedures.

• Modern X-ray tubes possess heat capacities ranging from 5 to 8 million heat units.

• Improved heat dissipation rates (kilo-heat units per minute) are another factor that enhanced heat storage capacity in modern tubes.

• Increased heat capacity is facilitated by thick graphite backing on target disks, increased anode diameters (200 mm or more), superior high-temperature rotor bearings and metal housings with ceramic insulators.

Tube Lifespan and Mass Considerations

• The working life of modern X-ray tubes ranges from 10,000 to 40,000 hours, far exceeding the 1,000-hour lifespan of conventional CT tubes.

• Design efforts were also focused on reducing the tube's mass to accommodate higher gantry rotational rates demanded by faster scan times.