Test #2 Flashcards
This refers to the overall blackening of the finished radiograph
Radiographic/Optical density
As the mAs is increased, the quantity of radiation is _______ & the optical density is ______
Increased: Increased
Increasing kVp does what to density?
Increases it
What is the 15% rule?
A 15% increase in kVp will have the same effect on density as doubling the mAs. A 15% decrease in kVp will have the same effect on density as decreasing the mAs by 1/2
What is the Inverse Square Law?
The intensity of the x-ray beam is inversely proportionate to the square distance from the source
Increase in SID requires that what is increased to maintain density?
mAs
A faster film-screen system speed does what to density?
Increases it
What is the variation in densities on the radiograph called?
Radiographic contrast
Radiographic contrast is the product of what 2 major factors?
Film contrast
Subject contrast
What is a controlling factor of contrast?
kVp
What are controlling factors of density?
Milliamperage
Time
How do influencing factors affect contrast?
By controlling the amount of scatter that reaches the film
How do grids affect contrast?
By absorbing much of the scatter that exits the pt before it reaches the film
How does collimation affect contrast?
Less collimation irradiates more tissue causing more scatter which causes less contrast
How does tissue thickness affect contrast?
Increase the thickness of tissue increases scatter causing decrease in contrast
What is geometric unsharpness along the edges of the film called? It’s greatest on the cathode side of the tube.
Penumbra
What effect does an increase in focal spot size have on recorded detail?
Increases unsharpness which decreases in recorded detail
What does increasing the SID do to recorded detail?
Decreases unsharpness which increases recorded detail
What does increasing the OID do to recorded detail?
Increases unsharpness which decreases recorded detail
Misrepresentation of either the size or shape of the anatomical part
Distortion
Distortion is caused by what?
d/t inaccurate alignment of the central ray w/ the part being images or the film
What is the function of beam restrictors?
Changes the size & shape of the primary beam
What are the types of beam restrictors?
Aperture diaphram
Cones & cylinders
Variable aperture diaphragm/collimator
This type of beam restrictor has fixed field sizes, is heavy, and is used for dental & skull xrays
Cones & cylinders
This is the M/C’ly used beam restricting device. It has 2 adjustable sets of shutter leaves.
Variable aperture diaphragm/collimator
This is the simplest of beam restrictors. Only produces one field size. Used in dedicated chest equipt., tomo., & CT
Aperture diaphram
When the film is clamped into the tray, this sensing device in the tray sends a signal to the collimator & it automatically restricts the beam to film size & provides unexposed borders all around the film
Positive Beam Limiting Device (PBL)
This device is placed b/w the pt & the film to decrease the amount of scatter reaching the film
Grid
Grids w/ “good clean-up” will attenuated what % of scatter?
80-90%
A higher grid ratio does what to scatter?
More effectively cleans scatter
A 5:1 grid cleans up what % of scatter?
85%
A 16:1 grid cleans up what % of scatter?
97%
This is the number of lead strips per inch or cm.
Grid frequency
What is the M/C grid frequency?
60-110 lines per inch
What are the 3 types of grids?
Linear
Cross Grid (Cross hatched)
Focused grid
This type of grid is commonly used. It allows for t.t. w/o attenuation of the primary beam
Linear grid
This type of grid cleans up more scatter than the linear type. Central axis of the beam must be in the center of the grid. Can’t use t.t.
Crossed grid
This type of grid must be used at specific focal film distances. The required distance is marked on the grid but you can vary the distance 10cm either way & still maintain qulaity
Focused grid
These are undesirable images of lead strips on the film
Grid lines
This is a moving grid/Bucky grid
Potter Bucky diaphram
What type of grids can a potter bucky diaphram be used w/?
Linear & focused grids only
This is undesirable absorption of the primary beam by the grid. Causes the edges of the film to be light
Grid cut off
What is the M/C film size to see grid cut off?
14x17 or larger
What are 3 types of grid cutoff?
Upside down focused grid
Lateral decentering
Distance decentering
Type of grid cutoff caused by the tube side of the grid not facing the tube. Causes a plus density (dark stripe) down the center of the film.
Upside down focused grid cutoff
What are the 3 causes of lateral decentering?
Grid is off level
Tube is angled against the lead lines
Central ray is not in the center of a focused grid
Type of grid cutoff caused by using the focused grid outside of the recommended SID
Distance decentering
When light strikes the silver halide crystals in the emulsion it creates what type of image?
Latent image (metallic silver)
When the film is chemically processed, the latent images b/co what?
Manifest image (elemental silver)
Transparent plastic that provides support for the emulsion. Light blue tint which makes it easy on the eyes & enhances contrast
Film base
This geltin is clear, gives structure, & holds the silver halide crystals
Emulsion
What is the primary active ingredient in silver halide crystals?
Silver bromide
This is the gelatinous covering that protects the emulsion from scratching, pressure, & contamination
Supercoat
What are the 3 types of film?
Screen film
Direct exposure film
Duplicating film
What is the M/C type of film used in medical imaging? It’s designed to be used w/ intensitfying screens & usually has double emulsion
Screen film
Type of film primarily used for extremities. Doesn’t use screens, has a cardboard cassette, is thicker. & has a high concentration of silver halide crystals
Direct exposure film
Type of film has emulsion on one side that is exposed to UV light through the existing radiograph
Duplicating film
Increasing the ______ or _____ of silver halide crystals increases film speed/sensitivity
Number; size
The color of light to which a particular film is most sensitive is called what?
Spectral sensitivity
This is a silver halide film that responds to blue & violet light. Uses calcium tunstate screens
Blue sensitive
This is an orthochromatic film that responds to blue & green light. Uses rare earth screens
Green sensitive
Lights w/ a colored filter that provide some illumination in the dark room
Safe lights
The safe light filter must be based on what?
Spectral sensitivity of the film
The wavelength of the safe light must be what?
Above the spectral response of the film (If not, it leaves a fog on the film
What is the closest distance a safelight can be to film?
4ft
What is the watt range a safelight can be?
7.5-15 watts
Type of safelight used for blue sensitive film?
Amber Filter/Wratten 6B filter
Type of safelight used for blue or green sensitive film
Red filter/GBX filter
Type of safelight used for green sensitive film
Wratten 1A filter
What temp, should you store films in?
<68F
How long can you refrigerate films for?
Up to 1yr at 50F
What does a humidity level >60% do to the films?
Decrease contrast
