CH 21 Film Sensitometry Flashcards
Film Sensitometry
The measurement of the characteristic responses of the film to exposure and processing.
Penetrometer
Step wedge, series of increasingly thick, uniform absobers.
Penetrometer is usually made out of:
Aluminum, sometimes plastic.
Penetrometer is not recommended for?
Quality Control testing equipment purposes.
Uses for a penetrometer is to?
Monitor x ray equipment, including intensifying screens.
Sensitometer
Used to expose a reproducible, uniform, optical step wedge onto a film.
A sensitometer uses a
Controlled intensifying light source and a pulsed stroboscopic light.
Sensitometers are available in:
11 to 21 step versions.
11 step increases intensity by
100%
21 step increases intensity by
41%
Densitometer
An instrument that provides a read out of the amount of blackening on a film.
Densitometer properties are:
1)Calibrated light source 2)Stage for placing film 3)A light aperature 4)Sensor arm with optical sensore 5)Read out display 6)Calibration control
Calibrating the Densitometer prepares it for:
it’s reading, it will measure the differences of density between the calibration intenisty and the intensity of the light the beam is transmitting.
Optical Density Numbers
The logarithmic number range displayed by the Densitometer.
Optical Density Formula
OD=Log10(Io/It) Io=Intensity of the incident light It+Intensity of transmitted light
An increment of .3 on the logarithmic scale represents a
Doubling of exposure
Films ability to stop light:
Opacity
Opacity formula
Io/It
The D log E curve is AKA
Log exposure, H&D Curve (Hurter and Driffield), Characteristic Curve, Sensitometric Curve
Base Plus Fog
The area of film w/no exposure, the density at no exposure.
Density is always ____ on film.
Inherant
Radiographic film base densities range from OD:
0.05-0.10
Base Plus fog should not exceed?
0.22
On a D log E curve the bottom of the curve represents:
The Base Plus Fog
Above the Base plus fog on the D log E curve the
Toe is found.
What portions is between the Toe and the Shoulder?
The body, usually straight line due to linear reactions.
The shoulder aread of the curve represents the:
Darker more dense areas. (Hydroquinone)
The darkest aspect of the curve is found at the
Dmax
The toe is controlled by
Phenidone
D log E curve low ranges
OD 0.25-0.50
D log E curve high ranges
OD 2.0-3.0
Most OD diagnostic quality densities are between
OD 0.5 and 1.25
Curve reversal or solarization occurs when:
OD has reached Dmax however exposure continues, ionizing the silver atoms attached on the speck causing them to repel. This produces less density.
Hydroquinone controls what color tones?
Black tones
Phenidone controls what tones?
Gray tones
Dmax
max density a film is capable of recording
4 Film Characteristics
1)Resolution 2)Speed 3)Contrast 4)Latitude
A change in density will only affect contrast when=>
Above or below the straight line portion of the curve
Latitude
A range of exposures that will produce densities with in the diagnostic scale
Latitude formula
Eh-El=Latitude, Eh=high exposure, El- low exposure point.
