RT202-Chapter 11

Causes of excessive exposure

Unsafe procedures; inaccurate exposure factors

Produced when x-rays interact with body tissue

Scatter radiation

Concern for radiology department personnel as well

Scatter radiation

Increases patient exposure

Scatter radiation

Filtration is the process of eliminating ______ low-energy x-ray photons by insertion of absorbing materials into the primary beam

undesirable

It is also sometimes called hardening the beam because it removes the low-energy (soft) photons

Filtration

Serves to remove the lower-energy photons, making the average energy (quality) higher

Filtration

It results in increased beam quality and reduce patient dose

Filtration

Increasing filtration increases the ____ of an x-ray beam

quality

As filtration is increased, so is the beam quality, but quantity is _______

decreased

Efficient in removing low energy

Aluminum (Z=13)

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

Most of the inherent filtration comes from the ____ of the glass envelope

window

Inherent filtration of a general purpose x-ray tube is approximately _____ Al equivalent

0.5mm

Any filtration that occurs outside the tube and housing and before the image receptor is considered added

Added filtration

A thin sheet aluminium positioned between the protective x-ray tube housing and the x-ray beam collimator

Added filtration

Added filtration results in increased ____

Half-value layer

The amount of absorbing material that will reduce the intensity of the primary beam to one-half its original value

Half value layer

The best method for measuring/specifying x-ray quality

HVL

For equipment operated at 70kVp and above, the minimum HVL should be at least ____

2.5mm

________ is equal to the sum of inherent and added filtration

Total filtration

Designed to solve a problem involving unequal subject densities

Conpensating filters

They are fabricated for many procedures and therefore come in various sizes and shapes

Compensating filters

Designed to be placed under patients body

Boomerang filter

When filtration is increased, technical factors must be _____ to maintain the same OD

increased

The thicker portions of the filter are matched to the _____ patient body parts

less dense

Degrades image quality by creating fog on the film and reducing visibility of detail

Scatter radiation

The area on the patient exposed by the primary x-ray beam

Field size

Created by interactions between primary beam photons and the table or other structures

Backscatter radiation

Occurs when the primary beam strikes the table-top

Backscatter radiation

It is used in some special procedures, usually when a long sections of the anatomy are imaged with the use of two or three separate image receptors

Step wedge filter

Is an adaptation of the wedge filter

Step wedge filter

Is used in digital fluoroscopy, where the image intensifier is round

Conic filter

They are used with Computed Tomography (CT) imaging systems to compensate for the shape of the head or the body

Special bowtie shaped filter

The most common type of compensating filter

Wedge filter

Is used in AP-Femur where the hip end is larger than the knee

Wedge filter

High levels of scatter create radiographs with many _____, reducing contrast

gray tones

Thicker body parts produce more scatter, resulting in a ____ appearance on radiographs

gray

More scatter ______ image detail and contrast

degrades

For abdominal radiographs, positioning the patient ____ can decrease thickness and scatter production

prone

Used to reduce tissue thickness and scatter

Compression bands