Test 4 Chapters 10-11 Flashcards
Ability to image small objects
Spatial Resolution
Distinguish anatomy with similar subject contrast
Contrast Resolution
OID refers to
Size, magnification
You want OID as small or large as possible?
Small
Most CR/DR systems run between speeds of what?
200-400
Direct exposure means what in regard to patient exposure and intensifying screens?
No intensifying screens and TONS of patient exposure
Speed number is directly or indirectly related to patient exposure?
Directly
1-50 is a reduction by 50. 100-200 is a reduction by 100
Noise looks like what on an image?
Fuzzy, grainy
Noise is what?
Film graininess-actual piece of film NOT image
Structure Mottle
Quantum Mottle-number of photons controlled by mAs
Scatter
Image quality speed
How efficiently photons are converted to light. The faster the speed, the faster the conversion, the less mAs needed to convert, thus less exposure to patient
Spatial resolution improves as…
Screen blur decreases
Motion blur decreases
Geometric blur decreases
The random fluctuation in the OD (optical density) of the image
Radiographic Noise
The use of high-mAs, low-kVp and of slower image receptors reduces…
Quantum mottle
Fast image receptors have…
High noise
Low spatial resolution
Low contrast resolution
High spatial resolution and high contrast resolution require
Low noise
Slow image receptors
Low noise accompanies slow image receptors with
High spatial resolution
High contrast resolution
Exposure to film and the percentage of light transmitted through the processed film is
Sensitometry
Optical Density is referring to
How much % of light that gets through
-Degree of darkening of the image
Measurements in film exposure and % of light transmitted through describe what relationship?
Between OD (optical density) and Radiation Exposure
The relationship between OD and Exposure is called what?
Characteristic Curve
At low and high radiation exposure levels, what kind of variations in exposure result in only a small change in OD?
Large variations
At intermediate radiation exposure levels, what kind of changes in exposure result in large changes in OD?
Small variations
The portions of the characteristic curve that represent the large variations in exposure are called?
Toe and Shoulder
The region in which properly exposed radiographs appear is the
Straight-line portion
A densitometer
measures OD
Already on the film, built in density even with no exposure
Base and Fog
A characteristic curve that is more horizontal
Is a slower speed and has long scale contrast-more shades of gray-therefore higher kVp and higher mAs
A characteristic curve that is more vertical
Is a faster speed and has short scale contrast-fewer shades of gray-therefore lower kV and lower mAs
Latitude is referencing
Margin of error
Wide latitude means
Have room to play with, long scale contrast-more shades of gray, slower speed
Narrow latitude means
Less room to play with, short scale contrast-fewer shades of gray, faster speed
Optical density + 0.3 LRE does what to image?
Twice as much density, image will appear twice as dark
Base + Fog =
Base= 0.1 Fog= 0.1
Base + Fog = 0.10-0.30
How much density is already built into the film
Where do useful radiographic densities lie?
0.25-2.5
The HD curve (rise over run) is telling you what?
Numerical number for contrast
When does the reciprocity law fail for screen film?
When the mAs difference is extreme in either faster time or slower time:
less than 10 ms or greater than 2 seconds
Reciprocity law ALWAYS works for what kind of exposure of film?
Direct exposure
Inherent system (film/IR) contrast is designed to be what in relation to grey scale?
Shorter scale
Screen film or Digital systems ALWAYS have shorter scale than what?
Direct exposure
Contrast scale gets (blank) the faster the system (goes clear to black fast)
Shorter
Subject contrast is determined by what?
Size
Shape
Attenuating characteristics of subject
Latitude and contrast are (blank) related
Inversely
Wide latitude means you have long scale contrast
The wider the latitude the wider…
The range of acceptable exposures
Processing includes:
Chemical concentration (strength)
Agitation
Time
Temperature
What happens if the temperature is too hot during processing?
The image is going to convert to dark quicker-temperature will effect density AND contrast
What happens during the fixing stage of processing?
You stop the image from processing-turning dark,and you remove the silver crystals that weren’t exposed
If an image measures at the “toe” of an HD curve chart what does your image look like?
Light, way underexposed
If an image measure at the “shoulder” of an HD curve chart what does your image look like?
Dark, way overexposed
Objects will always be (blank) than my image if lined up properly. If object size is (blank) than image size-something is wrong. (especially in math problems)
Smaller
Bigger
Shape distortion is what?
Unequal magnification of object
If you have foreshortening/elongation this means what in relation to the object?
Object was not parallel to the image receptor
How do you minimize distortion?
Keep you anatomy of interest in the center of your IR and keep the CR on the area of interest.
If I decrease SID (get closer with the tube) I will do what with magnification?
Get MORE magnification.
Chose a small focal spot for
Detail ie bone work
Chose a large focal spot for
Heat loading capability concern
If you’re using a small focal spot, do you use more or less mAs than with a large focal spot?
Less mAs for a small focal spot
Unsharpness and loss of detail are worse with larger or smaller focal spots, shorter SID and longer OID
Larger
think of lateral c-spine:
You back tube up to 72 inches to reduce magnification, and because there’s an air gap between the neck and the image receptor.
Focal spot blur is worse on Anode or Cathode side?
Cathode
More photons on the cathode side
What is good to reduce magnification, is also good to reduce…
Focal Spot Blur
In relation to focal spot blur you want to Minimize (blank) and Maximize (blank)
Min- OID
Max- SOD
Most important influence on subject contrast is
kVp
Low kVp gives what kind of scale
Short scale (absorption)
High kVp gives what kind of scale
Long scale (scatter)
Iodine gives us…
Differential Absorption
You can enhance subject contrast with…
Contrast Media that has a relatively high atomic number-gives you photoelectric absorption
What would a low atomic number contrast media be and what would it give you image wise?
Air, it’s radiolucent so blackness
To help reduce motion blur what can you do?
Good instructions Immobilization devices Comfortable positions Short exposure times Long SID Short OID
In screen film scenarios, image density is Directly or Indirectly proportional to mAs?
Directly
In order to see a change in screen film density from one set of technical factors to another, what must you do?
Have a 30% change in mAs
Between Direct exposure, Screen film and CR/DR-which has the longest scale of contrast, and then the next etc
Direct has longest scale of contrast, then Screen film, then CR/DR
Which type of imaging has the highest patient dosage and therefore is unacceptable?
Direct exposure
Contrast results from attenuation differences…which is
Differential Absorption
As grid ratio increases, scale of contrast…
Decreases
What happens to patient does when using a grid?
Goes up
Increased collimation is a smaller or larger light field?
Smaller
What makes detail visible?
Contrast
What attributes to image sharpness?
Recorded detail: Small focal spot Short OID Long SID Eliminate motion Slowest acceptable imaging system
What attributes to image visibility?
Reduce fog and scatter by restricting the beam, use grids
What attributes to Distortion?
Control with tube, image receptor, part alignment and patient positioning
What is scatters relationship with density?
It adds to Density
If you remove scatter you do what to image density?
Decrease the image density
Ways to reduce scatter
Beam restriction
Grids
kVp
Beam restriction does what?
Remove off direction photons
Better image clarity and shorter scale of contrast
When you use beam restriction you have to do what to mAs?
Increase, need more quantity to maintain image density.
Low kVp gives you more of what kind of reaction?
More Photoelectric
High kVp gives you more of what kind of reaction?
More Compton
PBL stands for and does what?
Positive Beam Limitation
Automatic beam collimation, detects image receptor size and automatically collimates to that size.
In relation to soft tissue, which interaction is most likely at less than 20 keV?
Mostly photoelectric
In relation to soft tissue, which interaction is most likely at more than 20 keV?
Mostly compton
In relation to bone, which interaction is most likely at less than 40 keV?
Mostly photoelectric
In relation to bone, which interaction is most likely at more than 40 keV?
Compton
How does grid use influence patient dose?
It increases it because you have to use more mAs to get the image you need
What are the different grid parts usually made of and why?
Lead strips-to absorb the lower quality photons that produce scatter
Interstrip material that is radiolucent to allow photons to pass through to the IR
Grid ratio is
Height divided by distance
The higher the grid ratio…
The more sensative, more grid cut off etc. You must be more precise with positioning.
As you go up in grid ratio the lead strips are packed more tightly giving you what kind of contrast scale? And causing what with patient exposure?
Shorter Scale
Go up
Two most common grid patterns
Parallel and Focused
What kind of a grid is in the wall bucky or table?
Reciprocating grid-moves to blur the lead lines.
Focused-Grid misalignments:
Off Level
Cutoff across image; underexposed, light image
Focused-Grid misalignments:
Off Center
Cutoff across image; underexposed, light image
Focused-Grid misalignments:
Upside down
Severe cutoff toward edge of image
Focused-Grid misalignments:
Off Focus
Cutoff toward edge of image
The need for a grid is reduced with …
Increased OID
Keep SID and SOD as (blank) as possible and OID as (blank) as possible
Long
Short
Noise, what can you control?
Quantum Mottle
Very small amounts of mAs is when this comes into play
Structure mottle is what?
Screen inherent-the way it’s made,nothing you can do about it
Faster imaging systems have (blank) structure mottle
Worse
