Final Review: image Receptor Exposure Flashcards
Two photographic properties allow detail to be seen on radio graphic images
-IR Exposure
-Contrast
-monitor control
-not the same as density term
-window level controls
Brightness
Window leveling
Moving mouse up and down
-up (blacker image)
Down- (whiter image)
What is your Receptor exposure?
-mAs or kvp?
mAs
What is your contrast?
-mAs or kvp?
kvp
Traditional term “density” no longer applicable in digital world. What was it replaced with?
Image Receptor (IR) exposure
Details not recorded on underexposed image is due to
Due to quantum mottle/noise
What can eliminate excess information on overexposed image?
Digital post processing
This happens when saturation occurs.
Over exposure
When enough photons do not reach the IR. mAs needs to be increased.
Quantum Mottle
Receptor exposure (mAs) + Contrast (kvp) =
Visibility of detail
What percentage is needed in changes in mAs for visible density change?
minimum 30%
Factors Affecting IR Exposure:
Controlling or influencing:
-mAs as controlling factor(in film)
-Multitude of influencing factors
Make changes in doubles or halves:
15% rule
-decrease kvp by 15% and double mAs
-Increase kvp by 15% and reduce mAs by a half
Low Contrast
-Long scale (many grays)
- increase kvp (chest xrays)
-wide window width
-wide latitude
-elephant herd
High Contrast
-short scale (fewer grays)
-decrease kvp (hand xray)
-Narrow window width
- narrow latitude
-zebra
what happens to contrast when you decrease kvp
increase contrast
Intensity of radiation at given distance from point source is inversely related to the square of distance between object and source.
Inverse Square Law
Provides technique correction for change in SID and maintains same image density/ IR Exposure
Direct Square Law
What is being changed in these situations?
The minimum 30 percent for visible density change and making changes in doubles and halaves
Changes in mAs
Image Noise
-Impairs diagnostic acuity
-anything unwanted on an image
Three types of noise
-Quantum noise
-system noise
-ambient noise
what noise is the largest contributor to total noise?
Quantum noise (controlled with mAs)
Regarding image noise what is wanted:
High signal, low noise
what is the primary influencing factor of IR exposure
mAs
This number helps determine how much was reached
e.i. #
Relationship between mAs and IR exposure
directly proportional
Ideal IR exposure
1 mR
a reference point
Exposure index # (e.i.#)
Combination of technical inflencing factors :
mAs
kvp
SID
filtration
grids
collimation
IR sensitivity
Body Part
Heel Effect
Focal spot
Total exposure to the image receptor
Image quality
How is IR exposure best controlled by?
Controlling AEC and technique charts
AEC
Automatic Program Control
APR
Anatomically programmed radiography
increased grid ratio also increases:
patient dose
CR compared to DR
CR- higher technique needed
DR- more sensitive
Is a monitor control function that can change the lightness and darkness of the image on a display monitor but it is not related to IR exposure.
Brightness
Overall blackening that is the result of black metallic silver deposited in the emulsion of film.
Density
Describes digital post processing that produces changes in brightness, so it appropriate to use when controlling the display of an image.
Window Level
Larger focal spots utilize a greater incident electron stream than small focal spots. Small focal spots can not withstand as much heat.
Focal Spot Size
Alters the intensity of radiation and therefore the IR exposure between the anode and cathode ends of the xray tube. (FAT CAT- IR exposure is always greater at the cathode end)
Anode Heel Effect
According to the inverse square law what alters the intensity of the beam reaching the IR?
SID
Relationship with Filtration and IR exposure
Inverse- IR exposure decreases when filtration increases
Restricting the beam, collimating, or reducing the primary beam field size reduces the total photons available what does this reduce overall?
Reduces the amount of scatter radiation and therefore reduces the overall IR exposure.
More matter=
More scatter
Technical factor compensation for changes in IR exposure is required only under the following circumstances:
-large anatomical part
-high kilovoltage
-low grid efficiency
-non-grid examinations
What happens to the IR exposure when tissue thickness, average atomic number of tissue, and/or tissue density increases?
IR exposure decreases
How do you move the window width for contrast
left and right
The more efficient the grid is, how is the IR exposure effected.
The less will be the IR exposure
Grids absorb scatter so how does that affect the IR exposure
It adds exposure to the IR and density to the film
What controls the average energy of xray photons at anode target
kvp
kvp change is not recommended to control?
Image noise
Affects average energy of beam
-only consider when changing from single phase to high frequency, multi-phase
Generator Configuration
When kvp is increased how does that affect quality and quantity
quality and quantity are increased
More matter= more scatter= Compton scatter which is what dose?
Occupational Dose
this number helps determine how much was reached
E.I. #
Built into processing of computer. Pre processing with digital creating picture perfect image. Compares to the image taken.
Histogram
what is the best generator
High frequency- generates more heat
What does Focal Spot Affect
ONLY Resolution
does not affect contrast or receptor exposure
More pronounced with wider collimation
Anode Heel Effect
Alters intensity of beam across cathode/anode axis
Anode Heel Effect
IR exposure up to 45% greater at cathode side of beam
Anode Heel Effect
Words to describe inverse square law:
-Intensity
-mR
-inversely
Words to describe Direct Square Law:
-Maintain
-mAs
-direct
How is filtration related to Ir exposure
Inversely
-Increased filtration will decrease IR exposure
-Increased filtration increases average energy of beam but reduces intensity of beam (quantity)
Relationship between anatomical part and IR exposure
Inversely
How is beam restriction and IR exposure related
inversely
- increased beam restriction decreases IR exposure
- Reduces total amount of remnant radiation striking IR (reduced scatter and secondary)
What can impact the histogram?
Tight collimation
(small field size)
tight collimation works against histogram analysis and equalization
decreased field of view, increase collimation does what to the receptor exposure
decreases
what does increase filtration affect
decreases exposure. (cleans it up, more quality image)
How does the additive pathology affect the IR
Decreases density/ IR exposure
How does Destructive pathology affect the IR
Increases density/ Ir exposure
Is additive pathology radiolucent or radiopaque
radiopaque
is destructive pathology radiolucent or radiopaque
radiolucent
is barium additive or destructive
additive (increase technique)
is iodine additive or destrictive
additive (increase technique)
Is air and gas additive or destructive
destructive ( decrease technique)
what happens to Ir exposure when there is a increase in grid ratio
Decrease receptor exposure
When using positive and negative additives what needs to happen to the contrast material
Double the contrast material
