EXAM #4 Flashcards
Sensitometry
Expose the film with a step wedge and plot it, measures the response of a system to exposure and processing in a sinusoidal line on the graph
CR/DR is linear line on the graph
applying a histogram corrects linear line to look more like film
applying a histogram
replots the data in sensitometry
Define contrast
Contrast of receptor is _____ proportional to its exposure latitude
the amount of gray shades available
Contrast of receptor is inversely proportional to its exposure latitude
Reciprocity Law
No matter what the mA and time, as long as the mAs is equal, the exposure should be the same, the amount absorbed will be the same
fails under two scenairos: when we use a scintillation at long or short exposure times
Where is your diagnostic range in a sensitometry graph
the straight line portion increasing
Define speed
ability of an IR to respond to low exposure measures, its sensitivity or speed
less exposure to get image = faster
more exposure to get image = slower
What are the primary factors influencing scatter
from most significant to least significant
patient or part thickness (more chance for scatter)
(large) field size
(extremely high) kVp
Increasing kVp INCREASES/DECREASES the percentage of Compton’s vs. Photoelectric interactions.
Increasing kVp INCREASES the percentage of Compton’s vs. Photoelectric interactions.
It would seem from a stand point of scatter reduction, all cases should be done at the HIGHEST/LOWEST possible kVp; however operating in such a manner would cause patient dose to increase due to increases in mAs values.
It would seem from a stand point of scatter reduction, all cases should be done at the LOWEST possible kVp; however operating in such a manner would cause patient dose to increase due to increases in mAs values.
Tools CAN/CANNOT be used to reduce scatter when high kVp values are used.
Tools CAN be used to reduce scatter when high kVp values are used.
_____ determines field size
Collimation determines field size
Increasing field size INCREASES/DECREASES scatter
Increasing field size INCREASES scatter
Increasing the thickness of an object provides for and INCREASE/DECREASE in interactions that create scatter.
Increasing the thickness of an object provides for and INCREASE in interactions that create scatter.
[CLICKER?] Which of the following does not affect the production of scatter?
A. kVp
B. mAs
C. FoV
D. Part thickness
B. mAs
What are four tools that are available to assist in the prevention of scatter and decreasing the affects on image quality?
Aperture Diaphragms
Cones/Cylinders
Collimators
Grids
[*] What is the simplest beam restrictive device?
Aperture Diaphragm
What is an aperture diaphragm ?
lead plate with opening to expose specific area only.
Provides a square, rectangular, circular or oval exposed area.
Whenever we collimate the beam farther from the target or focal spot, the BETTER/WORSE the collimation is going to be.
Whenever we collimate the beam farther from the target or focal spot, the BETTER the collimation is going to be.
Penumbra = _____
Penumbra = blur
two different edges of x-ray creating the same image (focal spot blur)
Benefit of using a cylinder over an aperture diapgragm
tighter collimation and decrease of penumbra
decreases field, brings scatter down, helps with contrast
decreases penumbra = Gives better spatial resolution/detail
[*] As I increase collimation, my field size is getting BIGGER/SMALLER and my scatter goes UP/DOWN
[*] As I increase collimation, my field size is getting SMALLER and my scatter goes DOWN
Collimators _____ radiation field.
Thus _____ the number of interactions possible to make scatter.
Also _____ patient dose by restricting area irradiated.
Collimators reduce radiation field.
Thus reducing the number of interactions possible to make scatter.
Also reduces patient dose by restricting area irradiated.
[CLICKER?] Which of the following is the best beam restrictor?
A. cone
B. collimator
C. cylinder
D. aperture diaphragm
C. cylinder
(always better because farther away from focus)
(Aperture diaphragm is the worst)
(Cones are comparable to aperture diaphragms)
[*] Which of the following does not prevent scattering?
It is always this answer…
Grid
Purpose of grids
Reduce the amount of scatter radiation incident on the IR. Thus decreasing scatter’s affects on image quality.
Are used to increase the contrast displayed on the image.
When do we use a grid?
When don’t we?
part is more than 10cm thick
a lot of soft tissue and bone
kVp is above 65
We don’t use grids for extremities or nasal bones
Grid ratio
gives use the most info on how a grid works
(h/d) height of grid strip vs how far apart they are located
increasing the height = higher ratio
increasing the depth = higher ratio
What is the most common grid design?
linear (what we work with)
What is the most specialized grid design
crosshatched
Can crosshatched grids be used with angulation?
no
Can linear grids be used with angulation?
yes
Which grid is more flexible (forgiving)? Linear or crosshatched grids?
linear
If I have taller or more dense grid lines, can I have more or less angulation of the x-ray beam?
less angle
What is a focused grid?
has a set focal range for _____
Always in _____
Not in _____
center grid line is parallel with CR and all other grid lines of grid are congruent with the angulation of the diverging beam
(set focal range for SID)
Always in the table
Parallel in the wall buckey and portables
[*] Higher ratios allow LESS/MORE scatter to reach the film, the STRAIGHTER/ the scatter must be to reach film.
Higher ratios allow LESS scatter to reach the film, the STRAIGHTER the scatter must be to reach film.
[*] Whenever we use grids, we always need to INCREASE/DECREASE technical factors
Whenever we use grids, we always need to INCREASE technical factors
Do grids increase patient dose?
yes because of increased technical factors (increasing mAs)
What is grid frequency?
Common grid frequency?
Number of grid lines per inch/centimeter, 60-196 ln/in
Common frequency = 85-105 ln/in
The more lines per given area, the thiner they are (less noticeable on image = good!)
The less lines per given area, the thicker they are (more noticeable on image = bad!)
[* CLICKER?] Grids reduce the production of scatter
TRUE/FALSE
FALSE (they don’t produce scatter, decrease already produced scatter)
[CLICKER?] Crosshatch grids are acceptable for use on portable examinations
TRUE/FALSE
FALSE (it’s parallel)
[CLICKER?] Grid frequency is the most useful descriptor of a grid
TRUE/FALSE
FALSE (it’s ratio)
Grid cutoff happens in what area of parallel grids
more often in short/long SIDs?
periphery rather than center (grid cutoff = bad!)
happens more often at shorter SIDs
[*]Stationary
Either a grid cassettes or snap on grid. Used for _____ exams.
Grid lines are quite _____ on image, more so with low frequency grids.
Moveable
AKA the Potter-Bucky. The grid moves during exposure in order to _____ _____ grid lines. Movement must be perpendicular to grid lines for _____ to occur.
[*]Reciprocating- moves side-side 2-3cm, uses _____
[*]Oscillating-moves in circular motion, uses _____
[*]Stationary
Either a grid cassettes or snap on grid. Used for PORTABLE exams.
Grid lines are quite evident on image, more so with low frequency grids.
Moveable
AKA the Potter-Bucky. The grid moves during exposure in order to blur out grid lines. Movement must be perpendicular to grid lines for blurring to occur.
[*]Reciprocating- moves side-side 2-3cm, uses motor
[*]Oscillating-moves in circular motion, uses electromagnet
Using a grid requires an increase in mAs, and therefore an increase in dose.
Using a grid requires an INCREASE in mAs, and therefore an INCREASE in dose.
What does a grid conversion factor formula do?
A Grid Conversion Factor formula will assist in selecting the appropriate mAs, this will provide the correct exposure to the IR and prevent noise.
(How the mAs without a grid compares to mAs with a grid)
GCF INCREASE/DECREASE w/ increasing ratios and kVp
GCF INCREASE w/ increasing ratios and kVp
What is selectivity?
If a grid absorbs more scatter vs. primary it is said to have _____.
As scatter is absorbed by grids, so to is primary beam.
If a grid absorbs more scatter vs. primary it is said to have hi-delectability.
[What is contrast improvement factor?]
Grids main purpose is to _____ contrast, it is important to remember that kVp has a controlling influence over contrast as well as the grid used.
Most grid have an improvement factor between __ - __
[What is contrast improvement factor?]
Grids main purpose is to increase contrast, it is important to remember that kVp has a controlling influence over contrast as well as the grid used.
Most grid have an improvement factor between 1.5 - 3.5
What are artifacts?
Unwanted entities in our image
What are off-level grid errors?
What is the result?
Either the tube or grid is angled along so that the beam crosses the parallel grid lines.
Result = decreased density
What are off-center grid errors?
What is the result?
Seen with focused grids. Central ray must be at center of grid.
Result = greater off center = greater cutoff.
What are off-focus grid errors?
What is the result?
Seen with focused grids that are used at greater SIDs than designed.
Result = cut off at periphery
What are upside-down grid errors?
What is the result?
Seen with focused grid that is placed tube side down.
Result = center will be exposed, with ~all being absorbed towards periphery.
[What is the purpose of air-gaps]
Alternative to grid, used in _____ exams. OID is _____, causing air gap between patient and receptor.
Causes the amount of scatter that reaches the film to _____.
Disadvantage is loss of _____ from increased OID (more magnification)
[What is the purpose of air-gaps]
Alternative to grid, used in magnification exams. OID is increased, causing air gap between patient and receptor.
Causes the amount of scatter that reaches the film to decrease.
Disadvantage is loss of sharpness from increased OID (more magnification)
Common digital imaging systems high-frequency grids
103-200 lines/in
41-80 lines/cm
What is Moire effect?
Scan lines in the image (artifacts/patterns)
When grid lines are parallel to scan lines
High frequency grids can prevent this phenomenon
What is Positive Beam Limitation (PBL)
Sensors in the Bucky that know the size of the IR and collimates to correct size (auto-collimation)
What is tomography
Images the body into slices/planes
Can do different thicknesses
Tomography focuses on one plane within the part thickness, while blurring all other, those above and below.
Tomography employs a moving x-ray tube and image receptor that move in unison.
http://www.youtube.com/watch?v=UZNJ-1v2-f8
What is the most simple and common tomography type?
Linear/curved-linear is most simple and most common
In tomography, more movement in the tube = MORE/LESS blurring
In tomography, more movement in the tube = MORE blurring
[Linear tomography]
Tube movement is in _____ direction(s), with receptor motion _____ to it.
Commonly a general purpose x-ray tube/receptor are connected for use in tomography.
Fulcrum is the _____ _____ or _____ where the imaginary line connecting tube + receptor at start and end positions cross.
Object plain is the area surrounding the pivot point and tissue in this area is imaged ”_____ _____”
[Linear tomography]
Tube movement is in one direction, with receptor motion opposite to it.
Commonly a general purpose x-ray tube/receptor are connected for use in tomography.
Fulcrum is the pivot point or point where the imaginary line connecting tube + receptor at start and end positions cross.
Object plain is the area surrounding the pivot point and tissue in this area is imaged ”in focus”
Adjusting the pivot point or focus may be accomplished by adjusting _____ or _____.
Adjusting the pivot point or focus may be accomplished by adjusting tube height or table height.
[*] Can we use AEC when using tomography?
No, we NEVER use AEC with tomography because we need that 3 - 4 seconds of exposure
Tomographic angle describes the amount of tube movement and the slice _____.
The greater the angle the _____ the slice thickness or less tissue is imaged “_____ _____”.
Tomographic angle describes the amount of tube movement and the slice thickness.
The greater the angle the thinner the slice thickness or less tissue is imaged “in focus”.
The more irregular, or more movement in general the MORE/LESS blur and the GREATER/WORSE contrast enhancement.
Tomography does INCREASE/DECREASE visualized contrast, however, it causes and INCREASE/DECREASE in dose due to the long exposure times.
Grids are employed for tomography, linear with grid lines PARALLEL to tube movement to prevent cutoff.
The more irregular, or more movement in general the MORE blur and the GREATER contrast enhancement. (better the image)
Tomography does INCREASE visualized contrast, however, it causes and INCREASE in dose due to the long exposure times.
Grids are employed for tomography, linear with grid lines PARALLEL to tube movement to prevent cutoff.
[CLICKER?] The _____ the tube movement the _____ the slice thickness
A. greater, greater
B. less, less
C. greater, less
D. greater, no effect on
C. greater, less
[CLICKER?] The tissue of interest in tomography is placed at the fulcrum
TRUE/FALSE
TRUE
Using increased OID, _____ of objects is reached. Often in IR procedures where extremely small objects are being imaged.
Use of small FSS are necessary to combat the loss of _____ due to magnification.
Air gap techniques are also used which eliminates the need for grids.
_____ does have disadvantages- namely increase _____ _____.
Using increased OID, magnification of objects is reached. Often in IR procedures where extremely small objects are being imaged.
Use of small FSS are necessary to combat the loss of detail due to magnification.
Air gap techniques are also used which eliminates the need for grids.
Magnification does have disadvantages- namely increase patient dose.
What are the 3 Prime Factors?
- kVp (primarily quality, but affects quantity. How penetrating the beam is. Higher kVp with denser tissue/material)
- mAs
- SID
[?] If I gave you barium, more or less kVp needed to image?
more kVp
[?] Any time we increase kVp, we _____ the exposure to the patient and the IR (more penetrating and more gets through)
[?] Any time we increase kVp, we increase the exposure to the patient and the IR (more penetrating and more gets through)
[?] If I increase kVp, what happens to the contrast of the image? Scatter? Contrast?
If kVp is doubled, intensity hitting IR is _____
High kVp = more scatter = lower contrast
kVp and contrast are inversely related
If kVp is doubled, intensity hitting IR is quadrupled (exponential)
[Increased kVp]
Increases beam _____
Is used with _____ _____
_____ patient and IR exposure
If kVp is doubled, intensity _____
2x kVp, is __X the intensity or exposure
[Increased kVp]
Increases beam penetrability
Is used with denser tissue
Increases patient and IR exposure
If kVp is doubled, intensity quadruples
2x kVp, is 4X the intensity or exposure
[Increased mAs]
If mAs goes up, quantity goes _____
If I double mAs, intensity is _____
mAs and intensity are _____ proportional
being changed for _____
_____ patient and IR exposure
If mAs goes up, quantity goes up
If I double mAs, intensity is doubled
mAs and intensity are directly proportional
being changed for thickness
Increases patient and IR exposure
What is the 15% Rule
Increasing kVp by 15% = 2x mAs
Scenario A: If I shoot 70 kVp at 10 mAs and I’m just looking at what got through to the IR = 80 kVp at 5 mAs
[SID]
__ or __ inches are standards
Increased SID:
_____ magnification
_____ detail
Requires the use of _____ _____ law to maintain exposure at IR
If SID is doubled, intensity _____ to a _____
2X the distance, exposure is decreased by __X
40 or 72 inches are standards
Increased SID:
Decreases magnification
Increases detail
Requires the use of inverse square law to maintain exposure at IR
If SID is doubled, intensity decreases to a quarter
2X the distance, exposure is decreased by 4X
What is direct square law
As the distance increases, the mAs increases
mAs1 / mAs2) = (SID1^3 / SID2^3
Less technique used for these pathologies
COPD and emphysema
If a patient only has one lung and you’re using AEC, which cell should be turned on?
the one under the side with the lung
OD is synonymous with…
brightness (how dark or light an image is)
Is it overexposed (dark) or underexposed (white)
Exposure is synonymous with… lightness/darkness
how dark the image is
[Exposure (Optical Density or Brightness)]
Can be described as the _____ visualized in an image
Overexposed is too “_____” and underexposed too “_____” in most systems. Exposure indicators will tell you for sure, we have to rely on the data and not just the image in CR/DR.
_____ and _____ control exposure. Generally the SID used is set so exposure issues are resolved via mAs changes. 2x or 1/2 mAs values are used to make changes
[Exposure (Optical Density or Brightness)]
Can be described as the blackness visualized in an image
Overexposed is too “dark” and underexposed too “light” in most systems. Exposure indicators will tell you for sure, we have to rely on the data and not just the image in CR/DR.
mAs and SID control exposure. Generally the SID used is set so exposure issues are resolved via mAs changes. 2x or 1/2 mAs values are used to make changes
What are the 2 controls for exposure
mAs and SID
Define contrast
number of gray shades in an image
or how black/white an image is
What controls subject contrast?
kVp, which is responsible for the penetrability of the beam
Thus affecting attenuation
CR/DR detectors have a _____ response, so the receptor contrast is _____ or _____.
We can manipulate it later with _____/______
CR/DR detectors have a linear response, so the receptor contrast is linear or wide.
We can manipulate it later with histograms/postprocessing
[*] _____ contrast, _____ contrast and _____ affect the final contrast see in an image.
Subject contrast, receptor contrast and processing affect the final contrast see in an image.
[*] What can improper density affect
Appearance of contrast
If picture is really white or dark, we cannot adjust/fix contrast
What is detail
Spatial resolution, how crisp or small the object can be seen
Measured in Line Pairs
CR 15, DR 10
What is distortion
misrepresentation of an objects size or shape
Elongation = appears larger
Foreshortening = appears smaller
Can be used as a technique for better visualization (like scaphoid deviation)
[CLICKER?] When doubling the kVp, the intensity of the beam will ____?
A. Double
B. Half
C. Quadruple
D. Quarter
C. Quadruple
[CLICKER?] When selecting a technique for a patient with excessive musculature, one would increase which factor?
A. mAs
B. kVp
C. SID
D. No change
B. kVp
they are denser than baseline
If someone is fatter, more kVp or mAs?
mAs because fat is less dense
What are technique
3 types?
developed for each piece of equipment to provide the necessary information to produce high quality radiographs with little variation among technologists
Charts provide for consistent IR exposure and contrast
Three types are available, generally a facility selects one type for use throughout the facility.
- fixed kVp (manipulate mAs, fixed kVp)
- variable kVp (manipulate kVp, fixed mAs)
- AEC
Radiolucency
vs.
Radioopaque
getting through (dark)
vs.
not getting through (white)
How does one make a technique chart?
Usually a chart accompanies new radiographic equipment; however, this chart is meant as a starting point from which a facility will make adjustments.
Equipment must be calibrated by a medical physics and the processors must be working within their prescribed parameters.
What are variable kVp charts?
SHORT/LONG scale contrast?
HIGHER/LOWER patient dose?
NARROW/WIDE exposure latitude?
ADVANTAGES?
DISADVANTAGES?
A fixed mAs is used and kVp is varied to accommodate differences in thickness (historic, not used much anymore)
SHORT scale contrast
HIGHER patient dose
NARROW exposure latitude
ADVANTAGES:
• Allows for small changes in exposure for small changes in part thickness
• Higher contrast
DISADVANTAGES:
• More patient dose
• Higher repeat rate
• Increased Tube wear
What are fixed kVp chart s?
SHORT/LONG scale contrast?
HIGHER/LOWER patient dose?
NARROW/WIDE exposure latitude?
_____ or _____ the mAs for every __cm of part thickness
ADVANTAGES?
DISADVANTAGES?
kVp is selected to provide proper penetration of the part, mAs is varied to provide adequate density.
LONG scale contrast
LOWER patient dose
WIDER exposure latitude
Double or half the mAs for every 5cm of part thickness
ADVANTAGES:
• Reduction in patient dose
• Provides more information within the image
• Increased consistency in density and contrast
• Lengthens exposure latitude
• Reduces x-ray tube wear
• Allows for shorter exposure times, thus reduces patient motion
• Easier to memorize
DISADVANTAGES:
• Lower overall contrast when compared to variable kVp systems
• Perceived as less pleasing to the eye
• Higher optimal kVp results in more scatter
Images have more gray
What are AEC charts ?
- Appropriate kVp must be selected for the part.
- Proper cell configurations must be selected.
- Density control selections are also available, 2,1,0, -1,-2. These adjust the set point of radiation intensity needed to activate the system. (generally a decrease in mAs)
What is imperative to measure a patient when using which of the following?
A. High kVp chart
B. Variable kVp chart
C. Fixed kVp chart
D. AEC chart
B. Variable kVp chart
Which system allows for a more conservative dose to the patient?
A. Fixed kVp
B. Variable kVp
A. Fixed kVp
[PRACTICE QUIZ]
The amount of darkening from the black metallic silver deposited in the film is termed.
contrast
density
attenuation
base fog
density
The radiographic density or the amount of blackness in the image is directly proportional to the exposure of the film’s silver bromide crystals to the light emitted by the intensifying screens and the direct action of the x-rays. The action of the development solution speeds the conversion of the exposed silver bromide crystals into the black metallic silver components of the radiographic image.
[PRACTICE QUIZ]
A technique of 400 mA 100 ms and 75 kVp is employed to produce an image with the desired radiographic density using the principles stated in the 15% kVp rule. What mA setting would produce a similar radiographic density at 50 ms sec. and 86 kVp?
800 mA
400 mA
200 mA
100 mA
400 mA
This problem is based on the principle stated in the 15% kVp rule. The first step in solving the problem is to determine that 20 mAs will be required at 86 kVp to maintain a similar density. The second step uses the formula mA=mAs/time to obtain the appropriate mA station at a 50 ms (.05 sec.) timer setting.
[PRACTICE QUIZ]
The primary function of mAs during a radiographic exposure is to:
improve resolution
increase penetration
provide a higher contrast
regulate density
regulate density
The milliampere - seconds value determines the number or quantity of photons produced in the x-ray beam. This factor has a strong direct relationship to the patient’s dose and the radiographic density of the image.
[PRACTICE QUIZ]
The primary exposure factor that is used for regulating radiographic contrast is:
distance
focal spot size
kVp
mAs
kVp
[PRACTICE QUIZ]
A satisfactory radiograph is made at a 160 cm (64”) source-to-image receptor distance (SID) using 40 mAs at 87 kVp. What new factors will produce a similar density if a 80 cm (32”) source-to-image distance (SID) is employed?
5 mAs at 87 kVp
10 mAs at 87 kVp
20 mAs at 87 kVp
40 mAs at 87 kVp
10 mAs at 87 kVp
The problem can be solved by using the formula New mAs = Original mAs x New SID2/Original SID2
[PRACTICE QUIZ]
A film is said to possess excessive radiographic density. This would appear:
lighter than normal
darker than normal
to have excessive contrast
to have poor recorded detail
darker than normal
A radiograph with excessive density appears darker than desired due to excessive amounts of radiation that have reached the imaging receptor.
[PRACTICE QUIZ]
A reduction of scattered radiation on a radiographic film is likely to occur with an:
increased kVp
increased collimation
increased part thickness
decreased focal spot size
increased collimation
Scattered radiation is an unavoidable consequence of x-radiation’s interaction with matter. The scattered radiation produced in the tissue can be reduced by using a lower kVp setting, reducing the thickness of the tissue, increasing the degree of beam limitation.
[PRACTICE QUIZ]
An example of a pathological change in a patient which requires an increase in penetration are:
- Pagets disease
- Acromegaly
- Aseptic necrosis
1 + 2 only
1 + 3 only
2 + 3 only
1, 2 + 3
1 + 2 only
Many pathological conditions have a considerable effect on the overall density of a tissue and the resulting radiographic density. Conditions associated with excessive bone growth (acromegaly) and bone repair (Paget’s disease) would require an increase in technique.
[PRACTICE QUIZ]
The dose a patient receives during a diagnostic exposure is directly proportional to the:
- mAs employed
- kVp employed
- Focal spot size selected
1 only
2 only
3 only
1, 2 + 3
1 only
The amount of radiation absorbed in a patient (dose) is directly proportional to the number of x-ray photons to which the patient is exposed; i.e., the milliampere - seconds (mAs) value.
[PRACTICE QUIZ]
Which of the primary exposure factors has the greatest effect on beam quality, attenuation, and exposure latitude?
mA
time
mAs
kVp
kVp
The kilovoltage peak is perhaps the single most important technical factor since its modification effects beam quality, penetrability, attenuation, image contrast and density, as well as the exposure latitude.
[PRACTICE QUIZ]
A radiographic image is produced with insufficient contrast and excessive radiographic density. Which of the following changes in the technical factors will best correct for this error?
increase the mAs, decrease the kVp
increase the mAs, increase the kVp
decrease the mAs and increase the kVp
decrease the mAs and kVp
decrease the mAs and kVp
[PRACTICE QUIZ]
An increase in technique to maintain the radiographic density is often required for patients with:
emphysema
pulmonary edema
osteoporosis
leprosy
pulmonary edema
Any pathological condition associated with excessive fluid production (pulmonary edema) and its build up in tissues will require a 30 - 50% increase in mA’s value to compensate for the increased attenuation of fluid and maintain the appropriate radiographic density.
[PRACTICE QUIZ]
Radiographic contrast can be defined as the:
difference in blackening between adjacent areas of the radiograph
overall blackening of the radiograph
base plus fog blackening of the radiograph
ratio of film speed to screen speed
difference in blackening between adjacent areas of the radiograph
The relative difference in density between adjacent areas of a radiograph is termed radiographic contrast.
[PRACTICE QUIZ]
The percentage of scatter reaching the radiographic film during a non-grid exposure of an abdomen comprises about ___ of the image.
10%
20%
50%
90%
90%
[PRACTICE QUIZ]
A radiograph is produced of a high tissue density structure. The area of the film corresponding to this structure will show a:
high radiographic density
low radiographic density
tissue density in not related to radiographic density
low radiographic density
Since bone has the highest tissue density in the body, the radiographic densities corresponding to bone tissue will posses a low radiographic density.
[PRACTICE QUIZ]
A radiograph that shows a short scale of contract often results from the use of:
breathing techniques
tilted anode techniques
low kilovoltage techniques
failing load techniques
low kilovoltage techniques
A high contrast image consisting of a small number of density shades (short scale) with a wide density difference between them is most commonly seen when low kVp techniques are employed.
[PRACTICE QUIZ]
The utilization of high kVp (above 90 kVp) for radiographs of the abdomen will result in:
high exposure latitude and short scale contrast
high exposure latitude and long scale contrast
low exposure latitude and short scale contrast
low exposure latitude and long scale contrast
high exposure latitude and long scale contrast
[PRACTICE QUIZ]
A radiograph that shows a small differential attenuation is best described as having a:
low contrast
high density
high resolution
poor definition
low contrast
A small difference in the attenuation properties of a tissue will provide only small differences in the radiographic densities and produce a low or long scale contrast.
[PRACTICE QUIZ]
In order to see a noticeable change in radiographic density, a change of ___ in the mAs is required.
5%
10%
15%
30%
30%
A significant change in radiographic density will require a change of 25-30% in the mAs value or about 6% change in the kVp.
[PRACTICE QUIZ]
When a substance is exposed to diagnostic x-rays, the amount of attenuation is primarily dependent upon the ___ of the attenuator.
atomic number
electron density
viscosity
proton-neutron ratio
atomic number
The principal factors effecting the amount of attenuation of a tissue are its effective atomic number and thickness.
[PRACTICE QUIZ]
The use of 15% kilovoltage rule in the maintenance of radiographic density as mAs is halved offers the advantage of:
- smaller patient dose
- greater exposure latitude
- shorter exposure times
1 only
2 only
3 only
1, 2 + 3
1, 2 + 3
The mAs can be reduced by 1/2 by a 15% increase in the kVp without a significant effect on radiographic density. This technical modification can be used to reduce the patient dose and the exposure time while increasing the exposure latitude and penetration of the beam.
[PRACTICE QUIZ]
When developing a variable-kilovoltage technique chart, an increase of ___ should be used for every centimeter of thickness difference.
2 kVp
15% in kVp
39% of mAs
50% of mAs
2 kVp
[PRACTICE QUIZ]
The principal controlling factor for the number of photons produced during an exposure is:
- timer setting
- milliampere setting
- kilovoltage
1 + 2 only
1 + 3 only
2 + 3 only
1, 2 + 3
1 + 2 only
The combination of the milliampere station and the timer value (mAs) is used to give an estimate of the amount of radiation used during the imaging process.
[PRACTICE QUIZ]
A radiograph of an obstructed patient is performed showing an excessive radiographic density. The probable cause is due to ___ of the intestinal gas.
excessive scatter
excessive absorption
excessive density
excessive penetration
excessive penetration
Large amounts of intestinal gas which may be present in obstructed patients often causes a decrease in the average tissue density. The resulting image will show excessive penetration and in increase in radiographic density.
[PRACTICE QUIZ]
An exposure of 40 mAs can be accomplished by using which of the following set of factors?
200 mA, 100 ms
10 mA, 250 ms
400 mA, 100 ms
400 mA, 50 ms
400 mA, 100 ms
The problem is solved by using the formula mAs = mA x time.
[PRACTICE QUIZ]
If you halved the time of exposure, how much would you change the milliampere to obtain the same density on the radiograph?
double the milliampere
add 10 milliamperes
use 4 times the milliampere
use half the milliampere
double the milliampere
The problem is solved using the formula mA = time/mAs
[PRACTICE QUIZ]
When an air gap technique is employed, the amount of scatter reaching the film is decreased because:
of the filtering effects of the air
more scatter misses the film
less scatter is produced at a longer SID
scatter consists only of primary radiation
more scatter misses the film
[PRACTICE QUIZ]
A technique of 160 mAs and 60 kVp has been employed in producing a satisfactory radiograph. In order to reduce this to 80 mAs, a new kVp of ___ should be employed.
51 kVp
69 kVp
74 kVp
86 kVp
69 kVp
The 15% kVp rule is used to equate the change required in the amount of kVp which results in the same change in radiographic density as a doubling or halving (50%) of the mA’s value.
[PRACTICE QUIZ]
The principal controlling factor for scale of contrast is:
kilovoltage
milliampere
focal spot size
distance
kilovoltage
Contrast and scale contrast are primarily controlled by changes in the kilovoltage peak (kVP).
[PRACTICE QUIZ]
During a manual radiographic exposure, if the kilovoltage is increased from 80 kVp to 90 kVp, with no other changes made, an increase in the ___ will occur.
- radiographic contrast
- exposure latitude
- scatter produced
1 + 2 only
1 + 3 only
2 + 3 only
1, 2 + 3
2 + 3 only
[PRACTICE QUIZ]
The visualization of a single tomographic section involves the motion of the tube and image receptor movement:
at right angles to each other
in the same direction as each other
in opposite directions of each other
vertical to each other
in opposite directions of each other
[PRACTICE QUIZ]
During tomography, all tissue planes ___ the focus plane will show a marked degree of blurring.
above
below
both of the above
neither of the above
both of the above
Tomography provides the visualization of a single tissue plane by causing a motion blur in all tissues above and below a desired plane.
[PRACTICE QUIZ]
Which of the following tomographic movements is generally employed to provide the most uniform blur pattern?
circular
rectilinear
elliptical
hypocycloidal
hypocycloidal
The movement pattern called hypocycloidal which looks similar to a clover leaf involves the formation of 3 overlapping ellipses providing a very long amplitude. This pattern is associated with a thin tomographic section and exceptional uniformity of blurring.
[PRACTICE QUIZ]
During a tomographic study, if the fulcrum setting is changed from 5 cm to 9 cm with the exposure angle remaining the same for both exposures, the result will be a:
- different cut level
- thicker cut
- improved resolution
1 only
2 only
3 only
1, 2 + 3
1 only
What is the four centimeter rule?
For every four centimeters of thickness, adjust technique by a factor of 2. (in mAs) (if kVp, remember 15% rule)
(4cm thicker than avg. = double technique)
(4cm thinner than avg. = half the technique)
(applied in steps, if 8cm thicker, double, then double again)
(if 2cm thicker than avg. = half-way double (50%))
p. 286
What is the minimum change rule?
Technique should be increased to at least one-third (+35% mAs, +5% kVp) to bring about any significant alteration in the final exposure
p. 286
[Contrast]
Can be described as the number of _____ _____ in an image or how _____/_____ an image is.
Subject contrast is controlled by _____, which is responsible for the _____ of the beam. Thus affecting _____.
CR/DR detectors have a _____ response, so the receptor contrast is _____ or _____.
Subject contrast, receptor contrast and processing affect the final contrast see in an image.
Improper _____ can affect the appearance of contrast
[Contrast]
Can be described as the number of gray shades in an image or how black/white an image is.
Subject contrast is controlled by kVp, which is responsible for the penetrability of the beam. Thus affecting attenuation.
CR/DR detectors have a linear response, so the receptor contrast is linear or wide.
Subject contrast, receptor contrast and processing affect the final contrast see in an image.
Improper density can affect the appearance of contrast
[*] What pathological conditions require an INCREASE in technique? (Additive diseases)
Acromegaly Actinomycosis Ascites Carcinomas Cardiomegaly Cirrhosis Pulmonary edema Hydrocephalus Hydropneumothorax Osteoarthritis Osteochondroma Osteopetrosis Paget's Disease Pleural Effusion Pneumoconiosis Pneumonia Syphilis Tuberculosis
Scatter is _____ proportional to the x-ray beam area
Scatter is DIRECTLY proportional to the x-ray beam area
Scatter radiation INCREASES/DECREASES the density of an image
Scatter radiation INCREASES the density of an image
Interspace materials are generally made from _____ or _____
Interspace materials are generally made from ALUMINUM or PLASTIC
A stationary grid produces VISIBLE/INVISIBLE grid lines on an image
A stationary grid produces VISIBLE grid lines on an image
Grids may _____, move side to side, or _____, move in a circular pattern
Grids may RECIPROCATE, move side to side, or OSCILLATE, move in a circular pattern
Increasing grid ratios INCREASES/DECREASES the amount of scatter that is absorbed
Increasing grid ratios INCREASES the amount of scatter that is absorbed
Increased grid ratios will result in increased _____ and will result in an INCREASE/DECREASE in patient dose
Increased grid ratios will result in increased mAs and will result in an INCREASE in patient dose
The higher the grid frequency, the MORE/LESS obvious the grid lines on an image
The higher the grid frequency, the LESS obvious the grid lines on an image
What is the Bucky Factor/Grid Conversion Factor?
The higher the grid ratio, the HIGHER/LOWER the factor
Using a grid has the disadvantage of increasing dosage to the patient, this is the Bucky Factor/Grid Conversion Factor
The higher the grid ratio, the HIGHER the factor
What is differential absorption?
It results in…
The difference in what is transmitted through the patient is differential absorption
It results in image contrast
As kVp increases, the probability of interactions, whether PE or Compton, INCREASES/DECREASES
As kVp increases, the probability of interactions, whether PE or Compton, DECREASES
Air kerma of __uGY (__ mR) is normally required for a reasonable image
Air kerma of 5uGY (0.5 mR) is normally required for a reasonable image
Most used beam restrictor is…
Most used beam restrictor are collimators
What is the most common technique chart?
Fixed kVp
For denser parts, we increase kVp/mAs
For thicker parts, we increase kVp/mAs
For denser parts, we increase kVp
For thicker parts, we increase mAs
The OID affects every image quality except _____
The OID affects every image quality except shape distortion
p. 357
Increasing the OID INCREASES/DECREASES subject contrast
Increasing the OID INCREASES subject contrast
p. 357
What is bit depth?
how many shades of gray I can assign to a pixel
