X-ray Physics and Circuitry

Concepts and terminology related to x-ray tube physics, electrical circuits, and heat unit calculations.

Actual focal spot

The location on the surface of the anode target.

Effective focal spot

The focal spot directed towards the patient, which decreases in size when the anode angle is decreased.

Off focus radiation

Radiation produced outside the actual focal spot, causing blurred edges or ghost images.

Tube loading

The amount of heat energy generated in the x-ray tube during an exposure, measured in heat units.

Heat Units (HU) Formula

$$HU = kVp \times mA \times \text{time (s)} \times \text{wave form factor}$$

Wave form factor (Single phase)

$$\text{Value} = 1$$

Wave form factor (3 phase 6 pulse)

$$\text{Value} = 1.35$$

Wave form factor (3 phase 12 pulse)

$$\text{Value} = 1.41$$

Wave form factor (High frequency)

$$\text{Value} = 1.45$$

Wave form factor (Average)

$$\text{Value} = 1.4$$

Series circuit

A circuit with only $1$ path where the entire circuit stops if one part breaks.

Parallel circuit

A circuit with multiple paths where other branches continue to work even if one breaks.

Amperes (Amps)

A measure of the flow of electric current in a circuit.

Voltage

The electrical potential difference between two points in a circuit, acting as the pressure that pushes electrons through.

Resistance

Measured in Ohms, it describes how much a material resists or slows down the movement of electrons.

Primary circuit components

Includes the Main power switch, Circuit breaker, Autotransformer, kVp selector, Exposure switch, Timer circuit, and the primary side of the step-up transformer.

Circuit breaker

A component in the primary circuit that protects against electrical overloads.

Autotransformer

A component that adjusts incoming voltage and supplies it to the step-up transformer using self induction.

kVp selector

A device that allows the user to choose the desired kilovoltage.

Secondary circuit components

Includes the secondary side of the step-up transformer, mA meter, rectifiers, and the x-ray tube.

Step-up transformer

Increases voltage to create the potential difference needed for x-ray production by converting low voltage into high voltage.

mA meter

A device that measures the current flowing between the cathode and anode during exposure.

Rectifiers

Components that convert AC to DC so the current flows in only $1$ direction.

Filament circuit components

Includes the Step-down transformer, Filament (Cathode), and mA selector (Rheostat).

Step-down transformer

Reduces voltage while increasing current to heat the filament.

Filament (Cathode)

The heated wire that emits electrons when current passes through it.

mA selector (Rheostat)

Controls the amount of current flowing to the filament to adjust temperature and electron quantity.

Incoming voltage

The supply voltage for the circuit, which is $220\,\text{volts AC}$.

Self induction

Induction occurring in $1$ winding coil, as utilized by the autotransformer.

Mutual induction

Induction occurring in $2$ separate coils, as utilized by the step-up and step-down transformers.

AC-powered components

Includes the Autotransformer, Step up & down transformers, and the incoming power supply.

DC-powered components

Includes the X-ray tube and rectifiers.

Effects of increasing mA

Leads to an increase in filament current, thermionic emission, tube current, quantity of x-rays produced, and patient dose.