Exposures Test #2
Card Set Information
Exposures Test #2
Flash cards for Exposures Test #2
What are the two photographic properties?
Density and Contrast
What are the two geometric properties?
Recorded detail and Distortion
Definition, sharpness, spatial resolution all mean....
Recorded detail is measured in _______________.
line pairs per millimeter (lp/mm)
True or False: All radiographic images have less recorded detail than the object itself.
As matrix size increases, pixel size decreases, and spatial resolution ______________.
As bit depth increases, spatial resolution ___________.
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?
Measures the accuracy of an image compared to the original object on a scale of 0 to 1.
Moduation Transfer Function (MTF)
What does 1 and 0 represent in MTF?
1 = perfect, image can never be perfect.
0 = no image.
In the Nyquist Theorem, digital imaging requires that the spatial resolution fequency signal be sampled how many time from each cycle?
This occurs when Nyquist Theorem is violated, and the incoming data is sampled less than twice per cycle.
True or False: Ojects smaller then the size of the focal spot cannot be imaged.
As OID decreases, resolution _____________.
As SID increases, resolution ______________.
Sharpness of an image.
The imperfect, unsharp shadow surrounding the umbra.
As focal spot size decreases, penumbra decreases, and resolution _______________.
Radiographic film usually has resolving capabilities in the range ______ lp/mm, far beyond the ability of any screen or human eye.
As phosphor size and layer thickness decrease, resolution ____________.
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 __________.
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?
What is the main cause for loss of resolution in DR?
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?
How does motion affect resolution?
Motion decreases resolution
Motion that is under the direct control of the patient.
Motion that is not under the conscious control of the patient.
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.
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.
As OID increases, magnification ______________.
How is size distortion affected by an increase in SID?
As SID increases, magnification decreases
As OID increases, resolution ______________.
The misrepresentation by unequal magnification of the actual shape of the structure being examined.
The object appears to be longer than it really is.
Object appears shorter than it really is.
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
The part is _____________ to the image receptor.
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
True or False: An optimal diagnostic quality radiograph is always within acceptable limits.
Equipment performance monitoring through a variety of quality assurance and 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
True or False: If an image is outside acceptance limits, it must be repeated.
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
Quality in all aspects of imaging chain is termed...
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)
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?
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?
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...
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
actual KVP needs to be b/w ____% of tested KVP than whats set.
KVP DRIFTS OVER TIME
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
Generator is capable of repeating expsoures accurately
( same dosimeter reading every time)
expose dosimeter w/ different combinations w. mA & time but get same reading
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 ________.
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%