Exposure Factors

kVp

controls the voltage difference across the x-ray tube.

kVp Main Function

Controls x-ray beam quality, energy, and penetration.

Lower kVp Effects

Less penetration and higher subject contrast.

High kVp

A ___ KVP decreases subject contrast and produces more shades of gray.

mA (Tube Current)

Controls how many electrons flow from the cathode to the anode.

mAs

controls total x-ray photon quantity.

Underpenetrated Anatomy

Increase kVp when you have

increase mAs

You ___ mAs when you have Too Few Photons / Quantum Mottle

15% Rule (Increasing kVp)

Increasing kVp by 15% approximately doubles receptor exposure.

15% Rule Compensation

Increase kVp by 15% and halve mAs to maintain similar receptor exposure.

Decreasing kVp by 15%

Approximately halves receptor exposure.

SID

Source-to-image receptor distance.

Short SID

More beam divergence.

Long SID

Less beam divergence across the receptor.

Higher kVp

Photon energy increases

Photon energy increases

Higher kVp

Penetration increases

Higher kVp

Scatter increases

Higher kVp

Subject contrast decreases

Higher kVp

More shades of gray are produced

Higher kVp

X-ray photons have more energy

Higher kVp increases penetration because

Higher kVp increases scatter because

More penetrating photons interact through Compton scatter

More scatter causes

Lower subject contrast

More shades of gray and less black-and-white difference

Lower subject contrast