2. Radiographic Contrast I Flashcards
is the two properties that comprise visibility of
detail
Contrast
Refers to the fact that the image is visible to the human eye only because sufficient contrast (and density) exists to permit the structural details to be perceived
Visibility of detail
is the difference between adjacent densities
Image contrast
Describes the concept of contrast as it is displayed on a soft-copy monitor for digital images
Dynamic range
is the proper term for the range of density/ brightness of the display monitor light emission
Dynamic range
accurately describes the digital processing that produces changes in the range of density/brightness, so its also is appropriate to use when controlling image contrast
Window width
When the differences between adjacent densities that comprise contrast are great, the image is described as ____ contrast and will result in fewer discernible shades of gray
high
when the differences are minimal
Low Contrast
Many shades of gray Decreased contrast High kVp Long scale of contrast Large (wide) dynamic range / window width
Low Contrast
is the number of useful visible densities or shades of gray
Scale of contrast
refers to an image that demonstrates considerable or maximal differences between densities and has a minimal total number of densities
Short scale of contrast
also called high contrast, or increase contrast
SHort scale contrast
Few shades of gray Increased contrast Low kVp Short scale contrast Short (narrow) dynamic range / window width
High Contrast
refers to an image that demonstrates slight or minimal differences between densities but has a maximal total number of densities
Long scale of contrast
also called LOw contrast or decrease contrast
LOng scale contrast
is the total range of density values recorded by the image receptor
Physical contrast
is the maximum contrast possible and its most accurate representation of the varying intensities present in the x-ray beam after it has passed through the subject
Physical contrast
is the total range of density values that can be perceived by the human eye in a single image
Visible contrast
A portion of the physical contrast and comprises the information from which diagnosis is made
Visible contrast
it is the total amount of contrast acquired from both the anatomical part and the image receptor
Image Contrast
are described as subject and image receptor (film) contrast
Image Contrast
the difference between two adjacent densities
Film Contrast
is the range of densities that the film is capable of recording
Image Receptor Contrast / Film Contrast
Film contrast depends on four (4) factors:
- ) Intensifying screens
- ) Film density
- ) the D log E curve
- ) Processing
create an inherently higher contrast image
Intensifying screens
First film
Glass Plates
Highly Flammable
Cellulose Nitrate
Easily Torn
Cellulose Nitrate
Responsible for many fires in hospital basements
Cellulose Nitrate
Types of Films
Glass Film,
Cellulose Nitrate,
Cellulose Triacetate/Polyester
changes dramatically when a film designed for exposure by light is exposed directly to x-rays
The D log E curve
has a negligible effect on contrast
Changing screen speed
controls slope of characteristic curve
Contrast
also changes with changes in Film contrast
Film Density
Excessive or inadequate film density _____ contrast
decreases
radiation and light-sensitive layer
Emulsion
activated by light and radiation to create image
Photographically active layer
Increasing film developer time, temperature or replenishment rate will increase the chemical fog on the film
Film Processing
the primary processing factors that cause objectionable fog levels
Developer temperature
and immersion time, replenishment and developer contamination
Chemical Processing
- Developer
- Stop Bath
- Fixer
Digital contamination by _____ causes increased fog and decreased contrast because the chemical ability of the
developer reducing agents is seriously impaired by the pH change in the solution
Fixer
the primary method for adjusting contrast with digital imaging systems, is through _______
Window Width Manipulations (Digital Image Receptors)
In fact, in most instances ______ provides more information. It provides more differences in density even though the difference between densities is less.
low contrast
The image receptor records many densities that _____ be
seen by the human eye
cannot
________ of the range of densities separates the physical contrast that is actually recorded by
the image receptor from the visible contrast that can be
perceived by the viewer on a single image
Compression or expansion
Exact reason is unknown, contrast is
always ______ for a film exposed to x-rays only than it is for the same film exposed to light from intensifying
screens
lower
The primary determinant of the shape of
the D log E curve is the physical composition of the
film emulsion
