X-ray Physics: Prime Factors, Quantity, Quality, and Exposure Control

List the prime factors.

mAs, kVp, distance

What is meant by x-ray quantity?

Number of photons in the beam.

List three terms that refer to x-ray quantity.

Output, intensity, exposure

What is meant by x-ray quality?

Penetration power of the beam.

Define mAs.

Product of mA and time; it is the number of electrons available to cross from cathode to anode and for how long.

What is the primary controller of x-ray quantity?

mAs

What happens inside the tube when mAs is increased?

More electrons burned off through thermionic emission, creating more target interactions and more x-ray photons.

Define kVp.

Kilovoltage peak; it is the maximum possible energy for any photon exiting the tube.

What happens inside the tube when kVp is increased?

Electrons have more energy (faster), producing higher energy x-ray photons and more photons due to increased target interactions.

Explain what happens to the intensity of the beam as distance is increased.

Intensity decreases because of the divergence of the beam.

Explain what happens to the intensity of the beam as filtration is increased.

Intensity decreases because filtration removes the low-energy x-ray photons.

As kVp is increased, what happens to the average energy of the beam?

Increases

As filtration is increased, what happens to the average energy of the x-ray beam?

Increases

What is the numerical representation of x-ray quality?

HVL (Half-Value Layer)

What is the primary controller of IR exposure?

mAs

If mAs is doubled, what happens to IR exposure?

It doubles.

If kVp is increased by 15%, what happens to IR exposure?

It doubles.

If distance is increased, what happens to IR exposure?

It decreases.