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What are the two photographic properties?
Density and Contrast
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What are the two geometric properties?
Recorded detail and Distortion
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Definition, sharpness, spatial resolution all mean....
Recorded detail
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Recorded detail is measured in _______________.
line pairs per millimeter (lp/mm)
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True or False: All radiographic images have less recorded detail than the object itself.
True
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As matrix size increases, pixel size decreases, and spatial resolution ______________.
Increase
-
As bit depth increases, spatial resolution ___________.
Increases
-
Lots of line pairs per millimeter, tiny object size.
High spatial frequency
-
Few line pairs per millimeter, large object size.
Low spatial frequency
-
High signal to noise ratio means what in terms of resolution?
Good Resolution
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Measures the accuracy of an image compared to the original object on a scale of 0 to 1.
Moduation Transfer Function (MTF)
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What does 1 and 0 represent in MTF?
- 1 = perfect, image can never be perfect.
- 0 = no image.
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In the Nyquist Theorem, digital imaging requires that the spatial resolution fequency signal be sampled how many time from each cycle?
Twice
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This occurs when Nyquist Theorem is violated, and the incoming data is sampled less than twice per cycle.
Aliasing
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True or False: Ojects smaller then the size of the focal spot cannot be imaged.
True
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As OID decreases, resolution _____________.
Increases
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As SID increases, resolution ______________.
Increases
-
Sharpness of an image.
Umbra
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The imperfect, unsharp shadow surrounding the umbra.
Penumbra
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As focal spot size decreases, penumbra decreases, and resolution _______________.
Increases
-
Radiographic film usually has resolving capabilities in the range ______ lp/mm, far beyond the ability of any screen or human eye.
100
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As phosphor size and layer thickness decrease, resolution ____________.
Increases
-
As gray scale bit depth increases, what happens to resolution?
As gray scale bit depth increases, resolution increases.
-
As concentration of phosphor layer increases, resolution __________.
Increases
-
As film/screen speed increases, what happens to resolution?
As speed increases, resolution increses
-
What is the main cause for loss of resolution in CR?
Light scattering
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What is the main cause for loss of resolution in DR?
The monitor
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Why does motion reduce recorded detail?
Anatomy does not stay in place long enough for image to form, this creates blurriness
-
What is the only way to correct quantum mottle?
Increase mAs
-
How does motion affect resolution?
Motion decreases resolution
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Motion that is under the direct control of the patient.
Voluntary
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Motion that is not under the conscious control of the patient.
Involuntary
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What are some ways to reduce voluntary motion?
Provide clear patient instructions and immobilization
-
What are some ways to reduce involuntary motion?
Decrease time and increase mAs
-
The misrepresentation of size or shape of the structures being examined.
Distortion
-
Why is size distortion always magnification in film/screen radiography?
The divergence of the beam.
-
True or False: Size distortion is always minification in film/screen radiography.
False
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As OID increases, magnification ______________.
Increases
-
How is size distortion affected by an increase in SID?
As SID increases, magnification decreases
-
As OID increases, resolution ______________.
Decreases
-
The misrepresentation by unequal magnification of the actual shape of the structure being examined.
Shape distortion
-
The object appears to be longer than it really is.
Elongation
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Object appears shorter than it really is.
Foreshortening
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When does elongation occur?
When the tube or the image receptor is improperly aligned.
-
When does foreshortening occur?
When the part is improperly aligned.
-
CR is ____________ to the part and the image receptor
Perpendicular
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The part is _____________ to the image receptor.
Parallel
-
If the CR is not centered to the part, how is the image formed?
The image is formed by angled photons and shape distortion occurs.
-
The application of scientific knowledge to an analysis of the image.
Art of image critique
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True or False: An optimal diagnostic quality radiograph is always within acceptable limits.
True
-
Equipment performance monitoring through a variety of quality assurance and quality control.
Quality control.
-
True or False: An non-optimal diagnostic quality radiograph is always within acceptable limits.
True. Film is still passable, just learn from this exam
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True or False: If an image is outside acceptance limits, it must be repeated.
True
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What are the three major categories for determining the cause of image problems?
- Technical factors - denstiy and contrast or recorded detail and distortion
- Procedural factors - patient positioning and/or patient prep
- Equipment malfunction - x-ray machine or processor
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Quality in all aspects of imaging chain is termed...
Quality Assurance
-
Quality Control controls....
Equipment and performance standards
-
what is the largets hosptial accredidation agency?
JCAHCO (joint commission of accredidation of health care organization)
-
How often is the processor senistometric monitored? Why is it monitored?
It is monitored daily. This is done to determine if it is operating w/i limits
-
What equipment is necessary for processor senisitometric monitoring?
- control box of film (all films come out of same box)
- sensitometer (puts densities on the film)
- densitometer (reads densities)
- digital thermometer (bc it doesnt break, wont contaminate)
-
contrast index
speed index
b+f
developer temp
- be w/i + or - .1
- be w/i + or - .1
- be w/i + or - .5
- be w/i + or - .1 (f) or + or - .5 (c)
-
how often are dark room safe lights tested?
semiannually (every 6 mo.)
-
what are some reasons why safe lights can fog film?
- cracked/ worn filter (cause fading)
- wrong bulb wattage
- too many safe lights
- safe lights are too close to work area
-
too much fog on film...
low contrast, high density
-
film that is exposed or unexposed to safe lights has to be..
less than or equal too .02 OD
-
focal spot size test is done how often?
semiannually
-
what are 3 tools used to measure FSS and how are they used?
- lp/mm tool- image piece on equipment then read it compared to a key
- star test pattern- image piece on equipment then read it compared to a key
- pin hole camera- creates a density on film, indicating the FS (creates image of affected FS)
-
How is HVL measured?
mm/Al
-
if the beam is filtered too little, half vaule layer is....
half value layer is low ( soft/ low energy photons still in the beam= increase pt. dose)
-
when checking collimator, central ray, and bucky tray accuracy what two tools can be used?
- collimator template- place table top, collimate to square on template
- beam alignment tool- place on collimator template and align steel ball to bullseye
-
if the light field is larger than xray field....
if the light field is smaller than xray field...
- clip anatomy
- increased pt. dose
-
distance and angulator accuracy acceptance limits
calculated SID = + or - 2% of actual SID
-
If tube angulation is + or - actual angle on angle indicator ___________ results
distortion
-
actual KVP needs to be b/w ____% of tested KVP than whats set.
5
-
-
timer accuracy is determinded by
- spinning top test = pulses, should be a certain # of dots to match up (single phase)
- synchronized spinning top test= done for 3 phase and high frequency
-
what are the acceptance limits for timer accuracy?
+ or - 5% of actual time compared to set time
-
shorter exposure time = _____ density
less
-
Generator is capable of repeating expsoures accurately
- Reproducibility
- ( same dosimeter reading every time)
-
expose dosimeter w/ different combinations w. mA & time but get same reading
Linearity
-
if linearity is out of limits...
density increases all the time OR density is decreased all the time
-
display monitors are adjusted until
- all shades of gray are visible
- (this is seen on a SMPTE test pattern)
-
Display monitors are tested for...
-
PACS system is checked to...
make sure HIS & RIS is all working w/ data accurately
-
what is Fix Q
where innaccuracy on file goes and is MANUALLY changed (human is neeeeded!)
-
Repeat image studies are done _____ & to determine ________.
- quarterly
- amount and cause of repeats
-
If the repeat rate is too low...
Repeate rate should be..
- techs are passing poor quality films for fear of repercussions
- b/w 3 & 10%
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