X-ray Tube & Generator Circuits Review (4)

Name the two circuits feeding the x-ray tube and what each controls.

Filament circuit: sets filament current (heats filament). Tube (high-tension) circuit: sets tube current (mA) across tube.

How does filament current relate to tube current?

A small change in filament current can produce a large change in tube current.

What are the three generator sections?

Low voltage (primary), high voltage (secondary), and tube sections.

Where is the autotransformer and what does it do?

Primary (low-voltage) side; adjusts incoming voltage and sets kV to be sent to the step-up transformer.

What does the kVp meter measure, and where is it wired?

Prereads voltage to the step-up transformer; wired in parallel on the primary side.

What does the rheostat (mA selector) do and where is it?

Variable resistor that sets current to the filament; in the primary circuit of the filament (step-down) transformer.

Where is the mAs timer located?

On the secondary side of the step-up transformer (the only manual timer there).

Where is the rectification circuit located?

High-voltage section between the step-up transformer and the x-ray tube.

List the main components of the x-ray tube.

Cathode (filament[s] and focusing cup), anode (stationary or rotating target), envelope, rotor/induction motor, and tube window.

What fraction of electron kinetic energy becomes x-rays vs heat at the anode?

Less than 1% becomes x-rays; more than 99% becomes heat.

How can you extend x-ray tube life?

Use appropriate warm-up procedures and the lowest kVp/mA/time consistent with image quality; avoid excessive heat loading.