FILM FACTORS Flashcards
• The study of the relationship between the intensity of exposure of the
film and the blackness after processing is called
sensitometry
6 types of FILM FACTORS
SPEED, PROCESSING TIME, PROCESSING TEMPERATURE, LATITUDE, DENSITY, CONTRAST
The two principal measurements involved in sensitometry are the
____ and ______
the processed film.
exposure to the film and the percentage of light transmitted through
The two principal measurements involved in sensitometry are the
____ and ______
the processed film.
exposure to the film and the percentage of light transmitted through
It describe the relationship between OD and radiation exposure.
H & D curve
Hurter and Driffield
– low radiation exposure level
Toe
– intermediate radiation exposure level
– the region in which a properly exposed
radiograph appears
Straight line portion
– high radiation exposure level
Shoulder
Apparatus that are needed to construct a characteristic curve:
- Optical step wedge / sensitometer
- Densitometer - a device that measures OD
Apparatus that are needed to construct a characteristic curve:
- Optical step wedge / sensitometer
- Densitometer - a device that measures OD
The degree of blackening on the radiograph.
• It is a logarithmic function.
• Has a precise numeric value that can be calculated if the level of
light incident on a processed film (Io) and the level of light
transmitted through that film (It
) are measured.
OPTICAL DENSITY
is attributable to the composition of the base and the tint
added to the base to make the radiograph more pleasing to the eye.
Base density
Base density has a value of approximately .
0.1
results from inadvertent exposure of film during storage,
undesirable chemical contamination, improper processing, and a
number of other influences.
Fog density
Fog density on a processed radiograph should not exceed .
0.1
The useful range of OD is approximately
0.25 to 2.5.
Base plus fog OD has a range of approximately
0.1 to 0.3.
The ____ states that the OD on a radiograph is proportional
only to the total energy imparted to the radiographic film and
independent of the time of exposure.
reciprocity law
Whether a radiograph is made with short exposure time or long
exposure time, the reciprocity law states that the
OD will be the same
if the mAs value is constant.
The difference in optical density.
High Contrast
Low Contrast
- radiograph that has marked differences in OD
high contrast
- the OD differences are small and are not distinct
low contrast
is the product of image receptor contrast and
subject contrast.
Radiographic contrast
is inherent in the screen-film combination and
is influenced somewhat by processing of the film.
Image receptor contrast
is determined by the size, shape, and x-ray
attenuating characteristics of the anatomy that is being examined and
the energy (kVp) of the x-ray beam.
Subject contrast
The average gradient is the slope of a straight line drawn between two
points on the characteristic curve at ODs __ and __ above base and
fog densities. This is the approximate useful range of OD on most
radiographs.
0.25 and 2.0
Most radiographic image receptors
have an average gradient in the
range of
2.5 to 3.5.
is probably more
important than average gradient for
general radiography because many
clinical ODs appear in the toe region of
the characteristic curve.
Toe gradient
is
more important for mammography.
Midgradient or shoulder gradient
• Fast/high speed IR
• Par speed
• Slow/low/detail IR
• Slow speed → less noise → more patient dose
• Fast speed → more noise → less patient dose
- more than 100
- 100
- less than 100
→ long gray scale → low contrast
Wide latitude
→ short gray scale → high contrast
Narrow latitude
is required for optimal image receptor
contrast because the degree of development has a
pronounced effect on the level of fog density and on the ODs
resulting from a given exposure at a given image receptor
speed.
Proper film processing
FACTORS THAT MAY AFFECT THE FINISHED RADIOGRAPH
-CONCENTRATION OF PROCESSING CHEMICALS
-DEGREE OF CHEMISTRY
AGITATION DURING
DEVELOPMENT
-DEVELOPMENT TIME
-DEVELOPMENT TEMPERATURE
