Unit 5 Flashcards
3 definition of spatial resolution:
- the smallest structures that may be seen in an image measured in LP/mm.
- the ability to image adjacent objects as being separate.
- refers to the distinctness or sharpness of structural lines that represent an image.
What is spatial resolution expressed/measured in?
LP/mm
The ____ the number of LP/mm, the _____ the object that can be imaged, and the ____ the spatial resolution.
The higher the number of LP/mm, the smaller the object that can be imaged, and the better the spatial resolution.
What does LP/mm represent?
The smallest size object that the imaging system is capable of representing.
Penumbra:
term that describes the areas of unsharpness around the periphery of the radiographic image
Umbra:
term that describes a lack of unsharpness around the periphery of a radiographic image.
Factors that Affect Spatial Resolution: 8
- OID
- SID
- Filament Size
- Anode Angle Size
- Pt. Motion
- Shape distortion
- Size distortion
- Imaging System/Display
OID:
the distance from the IR to the object being imaged
Increasing OID results in the object being ____
magnified
Decreasing OID =
less mag
What has the largest impact on object mag?
OID
To double the size of a body part (2x mag), move the part 1/2 way between the ______ and the _____
IR and Source
SID:
the distance from the IR to the anode target
When you increase SID, mag ___
decreases
When you decrease SID, Mag _____
increases
Size distortion only alters ___ not shape
size
Size distortion is influenced by ___, ____, and ___.
SID, OID, and SOD
Longer SID = ____ size distortion
less
Shorter SID = ___ size distortion
more
more mag = ___ SR
less
less mag = ___ SR
more
SOD:
source to object distance
distance between the anode target and the object
the source of x-rays:
the target
Actual Focal Spot:
the area of the anode target struck by electrons from the cathode
AFS size is determined by
- Filament size
- Anode Target Angle
The larger the AFS, the ___ the SR
less
The smaller the AFS, the ____ the SR
better
Larger filament size = ____ AFS
larger
Smaller filament size = _____ AFS
smaller
Larger filament size = ____ SR
less
Smaller filament size = ____ SR
better
Smaller the filament = ___ EFS = ___ SR
smaller EFS = better SR
larger the filament = ____ EFS = ____ SR
larger EFS = less SR
smaller AA = ____ EFS= ___ SR
Smaller EFS = better SR
An increase in kVP results in which of the following?
1) Increased photon quantity
2) Increased photon quality
3) increased percentage of photoelectric effect
1 and 2
An increase in kVp will increase photon quality and quantity, but will ____ the percentage of the photoelectric effect.
An increase in kVp will increase photon quality and quantity, but will REDUCE the percentage of the photoelectric effect.
A 15% increase in kVp will double exposure to the ____
IR
A high contrast radiographic image has few shades of gray. It is also known as an image with an ____
Short gray scale
In order to maintain IR exposure, which of the following would be done if kVp was reduced by 15%?
Increase mAs by 100%.
While performing a portable abdominal radiograph, the technologist is satisfied with the IR exposure but would like to increase the subject contrast. What adjustments should be made to their exposure technique in order to improve subject contrast and maintain image receptor exposure?
Decrease kVp 15% and double mAs
Shorter OID = ___ MAG
less
Longer OID = ____ MAG
more
Larger AA = ____ EFS = ____ SR
greater EFS and less SR
EFS:
the area projected onto the pt.
Smaller filament = ___ SR
better
Focal spot blur:
blurred region of a radiograph that tech has little control over
Focal Spot Blur origin:
due to geometric quality of the beam
____ OID helps reduce effects of focal spot blur
reduced
Line Focus Principle:
states that by angling the face of the anode target, a large AFS can be maintained and a small EFS size can be created.
On an angled anode with an angle that is _________, EFS is always smaller than FSS
<45 degrees
a larger AA = ____ EFS size
larger AA = smaller EFS size
Why do we want to make the AFS larger than the filament size?
Heat dissipation.
The larger the angle, the greater ability of the anode to dissipate heat.
What is the line focus principle purpose?
to create a desired small EFS after creating a larger AFS
____ target angles = sharper images
less
____ AA = better heat disspiation
Greater
____ AA = less heat dissipation
Less
Larger filament = ____ AFS
larger
Smaller filament = ___ AFS
smaller
Greater EFS = ____ divergence = _____ SR
Greater EFS = more divergence = less SR
Smaller EFS = _____ divergence = _____ SR
Smaller EFS = less divergence = more SR
Pt. motion always ____ SR
Lowers
Shape distortion:
distortion of object shape
“True distortion”
Shape Distortion
Types of shape distortion:
Foreshortening
Elongation
Shape distortion results from ____
Anatomy, CR, and IR alignment
Which shape distortion is worse, and why?
Foreshortening. Can superimpose anatomy, and miss pathology.
Elongation cause:
Cr angled to anatomy.
- Angle of the CR will project the anatomy.
IR angled but CR and anatomy are perpendicular.
Foreshortening cause:
Anatomy not parallel with the IR
Examples of using shape distortion:
1) AP Axial Towne Skull
- better images occipital and parietal bones
2) PA Axial Projection (Tunnel View)
- elongation of intercondyloid fossa
3) PA Projection of OS Calcis
- elongation of calcaneous
Image distortion types:
Size and Shape
Size distortion causes:
Increased OID
Decreased SID
Increased Mag = more penumbra = less SR
Shape distortion causes:
Elongation from angling CR or IR
Foreshortening from angling the anatomy
3 primary geometric factors affecting image quality:
1) Magnification
2) Distortion (shape and size)
3) Focal spot blur: has to do w/ divergence
- all cause blur
Prime exposure factor and Pt. dose:
1) kVp
2) mA
3) Time
4) SID (distance)
Increasing kVp increases the quality and penetrability of the beam.
The creation of a _____ # of photons is created at the target when kVp increases.
Greater
X-ray quantity varies _______ w/ changes in kVp
Exponentially
Changes in x-ray quantity is _____ to the square of the ratio of the kVp
Proportional
When kVp is doubled, the beam quality increases by ______
a factor of 4
kVp x2 = Quantity x
4
Increasing kVp = increasing beam quantity along the entire spectrum of the x-ray beam = _____ pt. dose
increased
Bigger beam = ____ dose
more
There are more lower energy photons created that will be absorbed as dose, along with a greater number of higher energy photons that pass through the pt.
Increased dose = ____ transmission
increased
There is a greater proportional increase in the # of high energy photons that will pass through the pt., therefore there is a ____ in image contrast
Decrease
15% rule:
creates a 30% increase of photons hitting the pt.
Increasing kVp by 15% is equivalent to the mAs being ____
doubled
a 15% increase in kVp does not double ______
X-ray intensity
a 15% increase in kVp is equivalent to ______ ____ to the IR
doubling mAs
Radiographically, only a 15% increase in kVp is necessary to double IR exposure for two reasons:
1) increased # of photons created
2) increased # of photons penetrating the pt. and reaching the IR (other 70%)
Increasing kVp is better than increasing ____
Increasing mAs
kVp increased 15% = _x photons hitting the IR = _x mAs
kVp increased by 15% = 2x photons hitting the IR = 2x mAs
Decreasing kVp by 15% is equivalent to _____ the mAs
halving
a 15% decrease of kVp does not half the ____ ____
x-ray intensity
a 15% decrease in kVp is the equivalent to halving the ____ to the IR.
mAs
Radiographically, only a 15% decrease in kVp is necessary to half IR exposure for two reasons:
1) decreased # of photons created
2) decreased # of photons penetrating the pt. and reaching the IR
Quantum Noise
Umbrella term?
Underexposed means:
kVp or mAs is insufficient
If you increase kVp 15%, but don’t touch mAs = _x photons will strike the IR and fix the image
2x
To increase the exposure to the IR, ____ kVp by 15%
increase
To decrease the exposure to the IR, ____ kVp by 15%
decrease
Decrease contrast and maintain exposure by ___ kVp 15% and ___ mAs
increase kVp 15% and 1/2 mAs
Increase contrast and maintain exposure by ____ kVp 15% and ___ mAs
decrease kVp 15% and double mAs
15% rule can ____ pt. dose
decrease
Increasing kVp 15% and 1/2 mAs 50% = _____ less dose
20%
Increasing kVp 15% without adjusting mAs will increase pt. dose by ____
30%
mAs and dose relationship:
proportional
As mA increases, so does the # ________ crossing the tube to reach the anode
Electrons
2x mA = 2x electrons = 2x xrays emitted
1/2 mA = 1/2 electrons = 1/2 xrays emitted
Time (S):
the amount of time that potential difference (voltage) is applied to the tube.
Changes in the length of time a tube is energized will effect the total # of ____ flowing from C to A
electrons
exposure time is directly proportional to the # of electrons crossing the tube, and is also directly proportional to the # of ____
x-rays generated
2x time = 2x # of electrons = 2x xrays generated
2x time = 2x dose
1/2 time = 1/2 dose
2x time = 2x # of electrons = 2x xrays generated
2x time = 2x dose
1/2 time = 1/2 dose
Beam Intensity:
the measurement of the concentration of photons in the primary beam measured at a single point.
Factors affecting beam intensity:
1) mA
2) exposure time
3) kVp
4) distance:
5) target material
6) target angle
7) generator type
8) filtration
Intensity of the beam and exposure to the IR varies greatly w/ changes in distance because:
the beam diverges as it travels from the anode target.
X-ray intensity and exposure to the IR will decrease as distance ___
increases
X-ray intensity and exposure to the IR will increase as distance ____
decrease
What illustrates the relationship between distance and beam intensity?
Inverse Square Law
If you double distance = Dose _____ x4
decreases
If you half distance = dose ____ x4
increases
A ____ SID requires mAs to increase to maintain exposure to the IR
Increased
A _____ SID requires mAs to decrease to maintain exposure to the IR
decreased
