X-ray emission

rad elect

X-ray Exposure

Number of x-ray photons, aka radiation quantity or radiation
intensity

X-ray Exposure measured in…

roentgens (R ) (mR ) (Gyₐ) or C/kg

Factors contribute to x-ray quantity:

– mAs (primary)
– kVp
– distance
– filtration

mAs is the Primary control for…

radiographic density. Density is the overall degree of darkness of an x-ray film

Increase mAs…

increase quantity

Double mAs = double exposure

kVp controls the…

penetration power of the beam,

quality of the beam (primarily) but
affect quantity as well(secondary)

Increase kVp…

quality increases

15% rule

15% increased kV will double the density (equivalent to double mAs), kV decrease by 15 % will decrease density by ½
(equivalent to halving mAs)

X-RAY QUALITY

its ability to penetrate through tissue, Penetrability of the X-ray beam will also affect radiographic contrast

Factors of Quality

– kilovoltage potential (kVp)

– filtration

low contrast, wide latitude

high contrast, narrow latitude

Increase kV…

INCREASE quality, exposure rate, penetration, scatter radiation, DECREASE contrast

Beam Filtration reduces…

patient exposure

Increase filtration…

increase quality

Half Value Layer (HVL)

thickness of absorbing material that will reduce intensity to ½ the original value

HVL increases, quality increases

4 types of filtration

inherent, added, total, compensating

Filtration - inherent

Tube construction

0.5 mm Al equivalent

Filtration - Added

• Al filters at port
• 2.0 mm Al equivalent

Filtration - Total

• Inherent + added
• 2.5 mm Al

Filtration - Compensating

• Compensates for differences in tissue thickness
• Examples: wedge, trough