Test 2 Flashcards
The recognizability factors in an image depend upon the ____ integrity of the projection
Geometrical
Why is penumbra present to some degree in all practical images?
Because no source of radiation is an infinitely small point, (all consist of areas).
The umbra of very small details in an image can completely disappear by what geometrical process
If the focal spot is significantly larger than the object being projected.
misalignment of the x-ray beam, part and image receptor results in what undesirable image quality
Shape distortion
Given a 2mm focal spot size and SOD of 90 cm and on OID of 30 cm, what is the geometrical unsharpness of the image
0.67 mm
Given an 0.5mm focal spot and SID of 150 cm and an OID of 15 cm what is the geometrical unsharpness of the image
0.055 mm
what is the relative sharpness for an SOD of 90 cm and an OID of 15 cm
6
an original exposure used an SOD of 120 cm and OID of 12 cm. IF the SOD is increased to 150 cm and the OID is reduced to 10 cm by what factor will the sharpness be improved
By 1½ times or 50%
With an SID of 60 cm and an OID of 40 m by what factor will the image be magnified
3 X
an image measures 16cm across. A 60 cm SID was used with an SOD of 40 cm. What is the size of the original object
3 X
what is the percentage magnification for an image with a magnification factor of 1.44
44%
The radiographic image of a particular bone turns out 4 times longer than the real bone, but only 2 times wider. what is the factor of magnification? what is the factor of shape distortion
Magnification = 2 X; Shape distortion = 2 X
The resolution of line pairs from a test template can be reduced by either of which two processes
Blurring or loss of contrast
The ability to distinguish any two adjacent details as separate and distinct details is the definition for what aspect of an image
Resolution
What is the typical range of anode bevel angles fro a general purpose x-ray tube
15-17 degrees
rather than using the line-focus principle, why don’t we just focus down the beam of electrons so that the actual focal spot is 0.5 mm
Because this would damage the anode by concentrating the heat load
the projected focal spot is largest at the end of the ___ image receptor
Cathode
explain why the anode heel effect occurs
Because the anode material itself acts as a filter for x-rays
x-ray tubes are conventionally installed with the anode to your ____ as you approach the x-ray table
left
for a radiograph of the AP foot or femur, it is best to position the patient on the x-ray table with his head to your _____
right
at a shorter SID, the collimator must be opened up to cover the same field size, so the anode heel effect ____
increases
what is the most compelling reason to consider focal spot size as the controlling factor for sharpness in the remnant beam images
The focal spot affects only image sharpness, it does not affect any other image qualities
why is the small focal spot not available when high mA stations are engaged
It is locked out from these high mA stations to prevent overloading the anode with concentrated heat
the actual focal spot is best measured along the
Beveled anode surface
explain how a focal spot which is much larger than an anatomical detail can cause it to disappear from the resolved image
When the focal spot is substantially larger than an image detail, the penumbra can spread so much inward that the umbra portion of the image is completely lost.
If the size of the focal spot is cut exactly in half, the sharpness of the image carried by the remnant x-ray beam will change which way and by precisely how much
Sharpness will increase to precisely double the original
where within the penumbra does the human eye locate the edge of an image detail
At the center of the penumbra
geometrical penumbra is caused by the ____ absorption of xrays as a function of the total absorption which the anatomical structure is capable of
Partial
decreasing the SID _____ penumbra
Increases
list four benefits of increased SID
1) Patient dose is slightly reduced, 2) Spatial resolution (sharpness) is improved,3) Magnification of anatomy is reduced, 4) More anatomy can be included within the field of view
if a change in the SID has resulted in the exposure increasing by 4 times, all other factors equal, the SID must have been changed by what amount?
It must have been cut to ½ the original
a technique chart lists 0.05 second for a procedure using 100 cm SID at a new SID of 200 cm, what new time would be required to maintain the exposure at the image receptor
0.2 seconds
for any change greater than ____ percent in the SID, radiographic technique factors should be adjusted to compensate and maintain exposure
15%
when changing from 180 to 100 cm, change the mAs to ____ the original
1/3 (0.31)
image sharpness is directly proportional to which radiographic distance
SOD (source-to-object distance)
in the interest of image sharpness, generally the ____ Feasible SID should be used
Maximum
as a rule-of-thumb, when changing from a 100cm SID to a 125 cm SID, increase the mAs by ______
One step
an SID of 128 cm results in an exposure at the receptor plate of 10 mGy, Using the inverse square law if the SID is changed to 92 cm, what will the new exposure be
19.4 mGy
at an SID of 244cm, 120 ma results in a satisfactory exposure. if the SID is changed to 75 cm what new mA must be sued to maintain the exposure at the receptor plate
11.4 mA (approximately 10 mA)
at an SID of 200 cm, 25 mAs results in a satisfactory exposure. If the SID is changed to 90 cm , what new mAs must be used to maintain the exposure at the receptor plate
5.06 mAs (approximately 5 mAs)
in general radiography, the ____ possible OID should always be used
Minimum
The greater the OID the ___ the subject contrast in the remnant beam image
Greater
The greater the OID the ____ the sharpness of detail in the image
Less
at greater OID, ____ radiation is allowed to spread out more, while ____ radiation remains at the same concentration
Secondary or scatter; primary
magnification is directly proportional to the ____ ratio
SID/SOD
image sharpness is directly proportional to the ____ ratio
SOD/OID
If the SID is 100cm and the SOD is 50cm , the projected image of the object will be magnified by a factor of _____
2
an original technique uses an SID of 100 cm and an OID of 5cm. If the OID were increased to 7.5cm what new SID would be required in order to completely eliminate the blurring effects of the OID change
150 cm
an original magnification ration is 50 percent. if the SID and OID are both tripled, the new magnification ration will be _____
50% (the same)
if both SID and OID are increased by 15 cm, what will be the net effect on the exposure intensity at the image receptor plate
Decrease
If both SID and OID are increased by 20 cm, what will be the net effect on the subject contrast in the image at the receptor plate
Increase
why is off centering of the CR identical in its effects to angling the x-ray beam
Because it places objects into diverging beams which are at an angle to the CR
why do positioning atlases recommend a 15-degree angle for the AP projection of the sacrum, when the sacrum actually lies at 30-35 degree angle
To minimize shape distortion (and to desuperimpose the symphysis pubis)
which of the following would be most distorted by a 30 degree CR angle: the head of the femur, the shaft of the femur, or the sternum
The head of the femur
if a flat object is tilted in relation to the receptor, and the CR is angle perpendicular to the object, what type of distortion if any occurs
Elongation
the distorting effects of off centering are indirectly worsened when the SID is _____
Decreased
If the R is angled 20 degrees, the TTD should be changed from 100 cm to ___ in order to maintain the exposure level
90 cm
List the four aspects of beam part receptor alignment which impact upon shape distortion
1) Shape and size of the object, 2) centering of the object relative to the x-ray beam, 3) angle formed between the object and the x-ray beam, 4) angle formed between the object and the image receptor plate
why does the cranium distort more than the head of the femur with an angled projection
Because of the cranium’s much greater thickness
what is the angle of x-ray beam divergence at a point 10 m cephalic to the CR
7 degrees (cephalic)
for a lateral projection of the lumbar spine, why is it not desirable to build the spine up all the way to a horizontal position
Normal divergence of the x-ray beam lines up with the intervertebral joint spaces when there is slight sag in the spine
what are the four geometrical objectives of radiographic positioning
1) Desuperimpose obstructing anatomy, 2) minimize magnification, 3) minimize distortion, 4) maximize sharpness
why are multiple projections at different angles necessary for fracture radiogrpahy
To fully demonstrate alignment of bones
contrasty anatomy that obscures the anatomy of interest is a form of image ____
Noise
penumbra in the image is ____ by motion of the par, x-ray tube or recptor
Increased (spread)
how might eh x-ray tube accidentally be moving during an exposure
If it is not locked in place
by superimposing various image densities, severe motion can destroy image ___ as well as sharpness
Contrast
streaks or circular artifacts caused by tomographic movement are classified as ____ images
False
list the three methods of minimizing motion during radiographic exposures
1) Minimal exposure time, 2) securing patient cooperation, 3) use of mechanical restraining devices
to freeze motion, exposure time should not exceed ___ second
0.033 (1/30) second
What are the three components of recognizability
sharpness, magnification, shape distortion
what does SID stand for
source to image distance
what does SOD stand for
source to object distance
what does OID stand for
object to image distance
another name for sharpness of detail
spatial resolution
area on the anode where the electrons hit
actual focal spot size
if the angle of the bevel increases the focal spot ____
increases
the clearly defined portion of a projected image
umbra
blur along the edges of an image
penumbra
formula to calculate for penumbra
penumbra = Fs x OID/ SOD
Smaller focal spot sizes produce ____ penumbra which in turn produces better ____ _____
less, spatial resolution
Why do we not use a small focal spot size for all images
it burns out the anode due to too much heat
If we increase SID what does it do to spatial resolution
increases
if we increase SID what does it do to magnification
decreases
what is the formula for magnification factor
image size/ object size or SID/SOD
what is the formula for object size
image size (SOD/SID)
what two types of distortion are there
magnification and shape
Changes in SID changes on the ___ on the x-ray beam
intensity
Changes in SID do not affect the ____ or the ____ of the x-ray beam
energy or penetrability
What ratios of interactions are unchanged by the change in SID
absorption, transmitted and scatter
True or false. Changes in SID affect subject contrast of an image
false
Principle that exposure at the image receptor can be maintained for difference SIDs by changing the mAs by the square of distance changed
square law
An increase in OID ____ magnification
increases
and increase in OID _____ spacial resolution
decreases
an increase in SID ___ patient skin exposure
reduces/decreases
what geometrical component should be maximized in an exposure
sharpness
what geometrical component should be minimized in an exposre
magnification and shape distortion
relative sharpness in a radiographic image is proportional to the ratio:
SOD/OID
True or false: high contrast is the same has high spatial resolution
false
true or false: blur is the same as low contrast
false
Radiographic magnification is proportional to the ratio:
SID/SOD
In order for magnification to be present, the ____ of the image must be expanded
umbra
the overall quality of an image, and the ability to distinguish adjacent details as being separate and distinct from one another
resolution
when one dimension of the image is changed by a different amount than the other this is considered
shape distortion
the two most important components or resolution are
contrast and sharpness of detail
what principle uses steep anode bevel angles to project an effective focal spot that is much smaller than the actual focal spot
line-focus principle
Because of the line-focus principle the projected focal spot is smaller toward the ___ end of the x-ray tube
anode
the ___ end of the x-ray tube produces a sharper image
anode
which end of the x-ray tube produces less radiation
anode
what effect results in less radiation being emitted at the anode end of the x-ray tube
anode heel effect
the thinnest portion of the anatomy should be at what end of the x-ray tube
anode
the thickest portion of the anatomy should be at what end of the x-ray tube
cathode
what 4 things affect the anode heel effect
steeper anode bevels, larger focal spots, shorter SID, longer field size
the size of the projected focal spot is directly proportional to ____ and inversely proportional to the _______ produced in the remnant beam image
penumbra, sharpness
produced by rays from different portions of the focal spot recording the same detail edge in different locations at the recptor
penumbra
penumbra causes ____ to shrink
umbra
if an anatomical detail of interest is significantly smaller than the focal spot used, what happens to it?
It may not be resolved in the image and will disappear from view
True or false: Focal spot size has no effect upon image magnification
true
true or false : Focal spot size has an effect on distortion
false
The focal spot affects image ____ exclusively
sharpness
what effects image sharpness exclusively and is the only radiographic variable that does so?
focal spot
what is the controlling factor at the detector for image sharpness
focal spot
what focal spot should always be engaged for smaller anatomical parts?
small
what portion of the human body can be used to estimate an SID if a tape measure it not available
wingspan
a longer SID ____ penumbra
reduces/ decreases
A longer SID_____ the sharpness of recorded detail
increases / enhances
increasing the SID _____ the SOD
increases
A longer SID ____ magnification
reduces/decreases
increased SID allows for a ____ field of view to be included with the area of the image receptor
larger
the inverse square of the distance reduces the exposure _____ at the receptor plate
intensity
x-rays spread out _____
isotropically
any changes great than ___ percent in SID should be compensated for by adjusting technique
15 percent
The adjustment of radiographic technique for changes in SID follows the _____ _____
square law
True or false. The SID has no direct impact upon image contrast or shape distortion
true
What does SSD stand for
source to skin
True or false SSD changes by a greater ratio than the SID
True
true or false. Increased SID can be used to reduce patient skin dose
true
True or false. OID impacts shape distortion
false
true or false. OID impacts every image quality except shape distortion
true
Increasing the OID enhances ______ _____ in the remnant beam image
subject contrast
Increasing OID ______ the total exposure at the image receptor
lessens
Increasing OID causes the spread of ______ and reduces ______
penumbra, sharpness
Increasing OID ____ magnification
increases
magnification is proportional to the _____ ratio
SID/SOD
Sharpness of recorded detail in the image is proportional tot he ____ Ratio
SOD/OID
Misalignment of the CR, part or receptor can produce what kind of error
part distortion
____-____ results in identical effects as angling the beam
off-centering
angling or off-centering on spherical or cuboidal objects will often cause ____
elongation
flat, tubular, or wedge shaped objects tilted in relation to the CR and receptor will undergo _____ distortion
foreshortening
angling the CR perpendicular to an object which is tilted in relation to the receptor will cause ____ distortion
elongation
flat or linear objects kept ______ to the receptor may not be visibly distorted by CR angles
parallel
True or false CR angulation has no effect upon subject contrast
true
T or F CR angulation has an effect on magnification
false
t OR f CR has no effect on sharpness of detail
true
what is the most destructive factor for sharpness of recorded detail in the remnant beam image
motion
severe motion can destroy subject contrast by
superimposing various densities
t or f motion can create false images
true
t or f motion has a direct relationship to brightness
false
t or f motion has no direct relationship to magnification
true
t or f motion has no direct relationship to shape distortion
true
To freeze motion, exposure times should not exceed ____ seconds
.033
what three factors affect the anode heel effect
SID, cassette size, focal spot size
what three components make up the geometrical integrity or recognizability of an image
sharpness, magnification, shape distortion
abruptness with which the edges of a particular image stops
sharpness
another name for sharpness
spatial resolution
The ARRT definition for the sharpness of the structural edges recorded in the images
spatial resolution
what source of light produce edges with no blur, and there are few in nature
point source
what source of light is an example of sunlight
disk source
what source of light is an example of headlights and flashlights
area sources
inner portion of a shadow that hos a uniform darkness
umbra
pure portion of a shadow
umbra
blurry fading partial shadow projected at each edge
penumbra
blurriness, unsharpness
penumbra
as penumbra increases, umbra _____
decreases
When penumbra from two adjacent objects overlap and deceptively appear as the shadow of one object
geometrical penumbra
motion of the source of light, the object or the recording surface
motion penumbra
motion penumbra spreads penumbra ______ such that its ____ is expanded
laterally, width
another name for magnification is
shape distortion
difference between the size of the real object and the size of its projected image
magnification
For magnification to be present what portion of the image must be larger?
umbra
If the penumbra is enlarged is this considered magnification?
no, just more blurring
difference between the shape of the real object and the shape of its projected image
shape distortion
what must be altered for shape distortion to have occured
the length and width of the object by different degrees
what two variation of shape distortion can occur
foreshortening and elongation
what can cause shape distortion
off-centering, angulation, misalignment
sharpness can only be measured by what method
indirectly by directly measuring the unsharpness
unsharpness is controlled b what three things
SOD, OID, and focal spot size
What is the formula to calculate penumbra
penumbra = fsxoid/sod
T or F high contrast is equal to better sharpness
false
T or F Scatter radiation does not affect sharpness
True
what two factors control sharpness
Prevention of motion, use of optimum geometry (OID, SID, SOD and focal spot)
When both the length and the width of the image will measure larger than the real object by equal proportions
magnification
what ratio is SID/SOD
magnification
If the length of the image measures longer than that of the real object it is considered to have what kind of shape distortion
elongation
if the width of the image measures wider than that of the real object it is considered to have what kind of shape distortion
foreshortening
the total amount of useful information present in an image
resolution
The angle of the target surface of the anode in relationship to a vertical line drawn perpendicular to the long axis of the x-ray tube.
Anode Bevel
Effects the size of the effective focal spot and the distribution of x-ray intensity within the beam
anode bevel
The smaller the focal spot size the ____ the sharpness
greater/ better
the _______ focal spot can be made smaller than the actual stream of electron
effective
where is the true actual focal spot measured
along the beveled anode surface
In terms of the line-focus principle, what aspects effect the sharpness of the radiograph?
the size of the filament, the angle of the anode bevel
The area available for the dispersion of heat generated in teh anode from the colliding electrons
actual focal spot
achieve goal of very small effective focal spot while allowing at the same time the anode heat to disperse over a sufficient area
line-focus principle
which end of the x-ray tube produce sharper images
anode end
a variation in the x-ray intensity along the longitudinal tube axis
anode heel effect
The anode heel effect is more pronounced with what field and focal spot sizes
large
The thinner size of anatomy should be place at what end of the x-ray tube
anode
the lower back corner of the anode disc
heel
what diminishes toward the anode side of the x-ray beam
the intensity of the beam
The anode acts as a for of ____ filtration
inherent
______ the SID spreads out the effects of the anode heel effect
increasing
Shorter SID _____ the effects of the anode heel effect
and ____ the effects
Concentrates, amplifies
what three things have an affect on the anode heel effect
cassette size, focal spot size, and SID
focusing of the electron beam in the x-ray tube down onto a small area on the anode target surface
focal spot
spot “seen” from the viewpoint of the image receptor (1mm)
effective focal spot
the smaller the focal spot the ______ the recorded detail
sharper
focal spot is ______ proportional to recorded detail
inversely
The three variables that control the projected geometrical sharpness of details in the image:
- SOD
- OID
- Focal Spot Size
