Properties of the x-ray beam: Q3

1. beam quantity

2. beam quality

What are the 2 properties of the x-ray beam

beam quantity (intensity or number of photons produced)

primarily controlled by mA and time (s) or total (mAs), secondarily controlled by kVp, and affected by distance and filtration

beam quality (energy of photons and ability to interact with matter to form radiographic image)

penetration of beam controlled by kVp, affected by filtration

roentgen (R)

traditional unit for exposure

C/kg

SI unit for exposure

Gy_a or J/kg

unit for air KERMA

1. mA

2. exposure time

3. kVp

4. distance

5. filtration

5 factors that affect quantity/intensity/exposure

mA

tube current, made up of electrons flowing per second to heat the filament

exposure time

in seconds, tube is energized and current flowing a certain amt of time

kVp

the force or ‘‘push’’ behind the tube current, higher kVp = more photons due to more energetic e- that can undergo multiple interactions at the anode

distance

affects quantity reaching IR surface due to divergence if the beam

directly

beam quantity is __________ proportional to mAs

I_N/ I_o = mAs_N/ mAs_o

equation for intensity and mAs

4

doubling kVp increases # photons by a factor of ______

I_N/ I_o = kVp_N²/ kVp_o²

intensity and kVp equation

filtration

use of aluminum (Al) or some equivalency, to absorb low energy x-ray photons from the beam as a form of radiation protection for the pt

total filtration

the sum of inherent and added filtration of x-ray tube must be at least 2.5mm Al equivalent

2.5 mm Al

the minimum total filtration required in the x-ray tube is ________

inherent filtration

tube and housing assembly, insulating oil target window is the primary contributor ~0.5 mm Al equivalent

added filtration

1.0 to 2.0mm Al (sheets of Al) between the target window & top of the collimator, usually on the collimator window

compensating filters

vary and adjust for variations in pt thickness or density and create a more uniform exposure to the IR

high-quality (hard) beams

x-ray beams with high energy

low quality (soft) beams

x-ray beams with low energy

primary beam

x-ray beam as it is upon exiting the collimator and exposing the pt

remnant beam

x-ray beam that passes through or interacts w/ the pt reaches the IR