Ch 1 Filtration of the X-ray Beam
what is Inherent filtration?
refers to any filtering done by components of the x-ray tube assembly
what is added filtration?
is any filtration done by components lying beyond the housing port
How thick is the aluminum plate?
the aluminum plate is either 1-2-mm thick
how thick does the aluminum have to be required by law?
the total amount of filtration (inherent and added filtration combined) must be at equivalent to the filtering done by a 2.5-mm thickness of aluminum
What is the main purpose of filtration?
reduce dose to the patient
what is total filtration?
Inherent plus added filtration
housing port, oil, window
mirror, plastic cover, aluminum sheet
what does the minimum filtration do?
reduces patient radiation dose by eliminating low energy that would otherwise be absorbed by the patients skin
what is a through filter used on?
on the chest
what is wedge filter used for?
use on the foot and t-spine
how are x-rays emitted?
from the focal spot of the anode disk isotropically
what does is isotropically mean?
means in all directions
the only part of the isotropically emitted beam diagnostically useful, however, is the part directed toward the patient through the tube window, the housing port, and the collimator box
the portion of the x-ray beam that exits the patient and strikes the radiographic film
what does increased collimation do to the primary beam?
decreases the size of the primary beam
what two objectives does the radiographer accomplish by limiting the size of the x-ray beam?
patient and personnel radiation dose is reduced, and radiographic image quality is enhanced
cones and cylinders?
another method of limiting the beam size uses either a thick metal cone or a thick metal cylinder. these are either attached to the housing port or the collimator box
diaphragms or aperture?
another device used to limit field size
another important function of collimation is to reduce the amount of scattered radiation, produced within the patient, by limiting the amount of tissue with which the primary x-rays interact
results when primary x-rays interact with the atoms of the irradiated tissues
scattered radiation is AKA?
fog (called supplemental density) either they are absorbed by the patients body or they pass through the patients body without any interaction
what is compton scattered?
is the prominent type contributing to film fog and personnel exposure
aka recoil electron. the primary x-ray loses energy during the collusion and also changes direction.
the direction of travel has changed
both photoelectrons and the characteristic x-rays do what?
may ionize other nearby atoms and do not contribute to personnel exposure or scatter fog on the film
absorption of the primary x-rays depends on what two factors?
the atomic number of the atoms with which the primary x-ray interacts and the energy of the primary x-ray.
what happens as the atomic number increases, which is what happens in the bone?
the likelihood of the photoelectric interaction increases. as the energy of the primary x-ray increases, the likelihood of the photoelectric interaction decreases
what is classical scattering?
AKA coherent scatter, unmodified scatter, rayleigh scatter, and thompson scatter
what happens in classical scattering?
a very low energy x-ray is absorbed after colliding with an atom, causing excitation of the atom
do not contribute to inherent filtration
the total filtration of an x-ray unit is?
2.5-mm Al eq
is not a type of compensating filter
the term used to describe the emission of radiation in all directions is?
the x-rays coming from the x-ray tube, prior to striking the patient are called?
x-rays emitted from areas of the anode disk other than the focal spot are called?
limiting the size of the x-ray beam by adjusting shutters is called?
when an incoming x-ray collides with an orbiting electron in an atom, the electron may be ejected, and this process is called?
this is not a name for scattered radiation having the same energy as the incoming x-ray photon?
the interaction responsible for contrast on an x-ray film and causes complete absorption of the incoming x-rays is called the?
some of this radiation may penetrate the housing
off focus radiation?
refers to x-rays that are produced in areas of the anode other than the focal spot
positive beam limitation. it is important to understand that with a PBL device the beam is not compressed, rather the periphery of the beam is blocked from the patient and the film
unwanted scattered radiation?
absorbed photons, exit and hit IR with info, and scatter