5. Filtration Flashcards
is the process of eliminating undesirable low-energy x-ray photons by the insertion of absorbing materials into the primary beam
Filtration
Filtration is sometimes called ______ since it removes the low-energy (soft) photons.
hardening the beam
At ____ keV, about 45% of the incident photons will penetrate 1 cm of soft tissue but only about 0.0006 percent will penetrate 15cm
20
at ____ keV, 3.5% of the incident photons (a significant percentage) will penetrate 15 cm
50
Significant soft-tissue penetration
occurs between ____ keV
30-40
Any material designed to selectively absorb photons
from the x-ray beam is called a
filter
is the most common filter material used
Aluminum
Other materials : ______ (4) are used to
become filters in various instances.
glass, oil, copper, and tin
is considered the standard filtering material
Aluminum
is also expressed in terms of half-value layer
Filtration
is that amount of absorbing material that will reduce the intensity of the primary beam to one-half its original value
half-value layer (HVL)
TYPES OF FILTRATION
Inherent,
Added,
Compound,
Compensation
occurs at various points between the x-ray
tube and the image receptor
Filtration
Filtration that is a result of the composition of the tube and housing is often called ________ because it is a part of these structures
inherent filtration
The thickness of the glass envelope of the tube, the dielectric oil that surrounds the tube, and the glass window of the housing all contribute to the
inherent filtration
A typical x-ray tube might have a total inherent filtration of ______
0.5-1.0 mm Al/Eq
As the tube ages they become _____, the anode begins to ___ and the glass envelope may gain a mild coating of _______
gassy,
pit,
vaporized metal
Any filtration that occurs outside the tube and housing and before the image receptor is considered _______
added filtration
Filtration materials are selected to absorb as many ____ photons as possible while transmitting a ______ number of high-energy photons
low-energy,
maximum
The collimation device also adds filtration to the beam and is considered to be _______
added filtration
uses two or more materials that
complement one another in their absorbing abilities
Compound filter
Compound filters place the _____ atomic number material closest to the tube and the _____ atomic number material closest to the patient
highest,
lowest
Although aluminum is the most common filtering
material, _____, with an atomic number of 29,
functions well for slightly higher energies
copper
is usually designed to solve a
problem involving unequal subject densities
Compensating filter
The 2 most popular compensating filters are the
wedge filter and the trough filter
sometimes called a double wedge
trough filter
is useful to even the density differences
between the mediastinum and the lungs on a chest
radiograph
Trough filter
can be useful for procedures on the thoracic spine, the feet and the lower extremities (e.g. venography and femoral angiography)
Wedge filter
is equal to the sum of inherent and added filtration and does not include any compound or compensating filters that may be added later
Total filtration
recommends minimum filtration levels for diagnostic radiography
The National Council on Radiation Protection and Measurements
aluminum filters of ____ absorb significant percentages of photons below the diagnostic range while permitting the vast majority to pass
1-3 mm
Below 50 kVp (Minimum Total Filter)
0.5 mm aluminum
50-70 kVp (Minimum Total Filter)
1.5 mm aluminum
Above 70 kVp (Minimum Total Filter)
2.5 mm aluminum
not only does filtration reduce the patient exposure dose by eliminating low-energy photons from the primary beam, it also removes a portion of the
_______ (EFFECT ON OUTPUT)
useful beam
The _____ and _____ has a great impact on recorded detail
overall size,
placement
all filtration can be expressed in terms of the thickness of _________
aluminum equivalency (Al/Eq)
To compensate for the loss of exposure when filtration is increased, technical factors must be _____ to maintain the same image receptor exposure
increased
