CHAPTER 6 Flashcards
It is a combination of both the visibility and the sharpness of recorded detail
Radiographic quality
Combine to make up the overall or radiographic contrast
Detector contrast
Due to the patient and the film
SUBJECT CONTRAST
Often called image density or simply density which describes the degree of darkness or blackening of the x-ray image
OD (optical density)
It is the logarithm of the ratio of the incident light intensity on the film the intensity transmitted through the film
Optical density
The OD of the film is equal to ______
2
OD is measured using an ___________
Optical densitometer
Images in diagnostic radiology have ODs that range from ___________
0.2-3.0
The most useful information of ODs range at
0.5 to 1.5
Technical factors which affects density
Controlling (primary)
Influencing
When a change is necessary to the overall density of an image, the ___________ and ___________ should be change before any other changes is made
Controlling/primary factor. And mAs
Is the controlling or primary technical factor used to control image density?
mAs
mAs is defined as the product of ___________ and ___________
mA and Exposure time
The ___________ controls the number of x-ray protons in the beam or the quantity of x-rays
mA
It controls the duration of the exposure
Exposure time
What is the factor of when it is necessary to control the amount of density on an image
mAs
To create visible , increase in density the mAs must be increased by at least
30%
It controls the energy of the x-ray photons, and when it is increased, the quality of the beam is increased and x-ray photons are able to penetrate the tissue of interest
Kilovoltage
It is a general rule states that a 15% in increase in KVP will equate to doubling the MAS on the image and 15% decrease will halve the MAS on the image.
15% rule
The intensity of the x-ray photons striking the film depends on the ________
Source-to-image receptor distance (SID)
It is the distance between the image receptor and the focal spot or x-ray photon source
SID
Increasing the SID decreased the number of x-ray photon, striking the film, and this is a result of the ________
Inverse square law
Doubling the SID, DECREASES the intensity to ________ of the original intensity
1/4
Reducing the SID to one half, INCREASES the intensity to ________ the original value
4 times out of
This formula is similar to inverse square law, but is reversed to a direct square law because as already stated, the MAS must increase when the distance is increased or vice versa to maintain the image density
Exposure maintenance formula or density maintenance formula
It changes the beam by removing soft x-ray photons and hardening the beam which decreases the image density
Filtration
Restricting the beam size by using collimation reduces the total number of photons available, which reduces the amount of scatter radiation, reaching the image receptor
Beam restriction
The use of this changes the atomic number of the tissue and affects the image density
Contrast media
As tissue thickness, atomic number and tissue density INCREASE, the image density
Decreases
It absorbs Scott there before it can reach the film and deposit unwanted density on the image
Grids
The type of emit receptor, whether FILM or INTENSIFYING SCREEN used to produce an image will alter the ________
Image density
It is a decrease in primary beam on the Cathode side of the tube more intense in comparison
Anode heel effect
The anode heel effect is more visible in radiographs that use a ________
short SID and LARGE xray filed size
The visibility of the anode heel effect on a radiographic image depends on the
SID used
x-ray beam field size
An atomic area of interest
It states that the density produced on the radio graph will be equal for any combination of milliamperage and exposure time, as long as the product of MAS is equal
Reciprocity law
This law holds true for direct exposure radiography
Reciprocity law
It times to bloom, more higher milliamperages and may occasionally reach a point where they alter the image receptor exposure
Large focal spot
This adjusts the exposure time to produce acceptable image densities.
Automatic exposure control (AEC)
This measures the amount of exit radiation striking the image receptor and terminates the exposure when the proper number of x-ray photons has reached the film to provide OPTIMAL DENSITY.
Automatic exposure control AEC
This are used as AEC detectors
Ion Chambers
Scintillation detectors
Solid – state detectors
When an AEC circuit is operating changing the KVP will change the image contrast but notthe
Image density
Is this designed to prevent catastrophic tube damage by terminating exposure after a maximum time if AEC fails
Backup timer
It is always set in case something goes wrong with AEC circuit
Backup timer
A typical back up timer setting is approximately at
5000 ms
This changes the exposure time to maintain the same density following changes in MA kVp or distance
AEC circuit
