Radiographic Technique Flashcards
What controls quantity?
mAs
What influences and determines the quantity and quality of x-rays ?
Exposure Factors
Radiation quality refers to x-ray beam penetrability, best measured by what?
HVL (Half Value Life)
What are the (4) prime exposure factors?
- kVp
- mA
- Exposure time
- SID
High kVp _____ image contrast.
Reduces
What controls how fast the electrons are sent across the tube?
Kilovolts
What controls beam quality?
kVp
What controls beam penetrability?
kVp
What controls the radiographic scale of contrast?
kVp
What determines the # of photons, radiation quantity, OD and patient dose?
mA
What affects the number of x-rays produced?
mA
What are the available mA stations?
50, 100, 200, 300, 400 & 600
Does changing the mA change the kinetic energy of e-?
No
What relationship does mA quantity and patient dose have?
They are directly proportional
Short exposure time _____ image blur
Reduces
What must you do when using short exposure times to maintain x-ray intensity?
Increase mA
Single phase can not produce an image under…
8ms
Three phase can produce an image under…
1ms
mAs=
(mA)x (s)
What does mAs control?
- Radiation quantity
- Changes the number of electrons
- Optical density
- Patient dose
Does mAs change the energy of x-rays produced?
No, just the number
mAs is a key factor in the control of ________ ________.
Optical Density
What is the reciprocity law?
OD will be constant for any combination of mA and exposure time that results in constant mAs
Does distance have much affect on quality?
No
Does distance have an affect on density?
Yes
Does distance affect x-ray intensity?
Yes
What does the square law do?
Determines the required change in mAs after a change in SID to maintain OD
What are some patient factors when determining technique?
- Body habitus
- Thickness of part
- Body composition
- Pathology
What are the (4) types of body habitus?
- Hypersthenic
- Sthenic
- Hyposthenic
- Asthenic
Define:
Hypersthenic
- Short & wide
- Chest and abdomen are broad
- 5%
- Lungs are short and wide
- Stomach is high and transverse
Define:
Sthenic
- Average body type
- 50% of population
- Active or strong
- Slender version of Hypersthenic
Define:
Asthenic
- Opposite of Hypersthenic
- 10% of population
- Frail, poor muscle tone
- Narrow, long, shallow
- Diaphragm is low
- Abdominal cavity rests in pelvic region
Define:
Hyposthenic
- 35%
- High splenic flexure
- Stomach is J shaped and extends into iliac crest region
In general, what kind of technique does a soft tissue neck require?
Low kVp & high mAs
In general, what kind of technique do extremities require?
Low kVp
In general, what kind of technique does a chest require?
High kVp
In general, what kind of technique does an abdomen require?
Middle kVp
What are the (4) image quality factors?
Key word DICO
- Disorientation
- Image Detail
- Contrast
- Optical Density
What is OD?
The degree of blackening of the finished radiograph
When OD is high=
- Too dark
- Overexposed
When OD is low=
- Too light
- Underexposed
OD can be controlled by mAs and SID? T/F
True
Quantity=
mAs
Quality=
HVL
What is more efficient, a single phase or a three phase?
3 phase
When SID is shortened, what happens to your mAs?
It goes down
When SID is increased, what happens to your mAs?
It goes up
What are the (4) types of generators?
- Half wave rectification
- Full wave rectification
- 3 phase power
- High frequency generator
Half Wave:
- Only produces x-rays half the time
- Drops to zero every time
- x-rays are not produced on negative side
- Rarely used
Full Wave:
-Consistant, but drops to zero
3 phase power:
- 6 & 12 pulse
- Nearly constant output & exposure
- energy is higher
- Higher quantity & quality
High frequency:
- Less than 1% ripple
- Constant output
- Great efficiency
What are the effects of a destructive disease?
- Destroying part of tissue, bone, ligaments
- Taking away, making more lucent
What are the effects of a constructive disease?
- Growing
- Dense
How much of in increase is required for a visible change in OD?
30%
When mAs is doubled, you get…
Double the density
When only mAs is changed it is either ____ or ____.
Halved or doubled
When mAs is doubled=
Your density is doubled
When kVp is changed it must be increased by __% to produce a visible change in OD.
4%
The 15% rule is the same as?
Doubling the mAs
To maintain OD a 15% increase in kVp would require a reduction of ____ the mAs.
Half
Does the 15% rule apply to kVp or mAs?
kVp
A strip that goes from black to white quickly would have a…
- Short scale
- High contrast
- Lower kVp
- Black and white
A strip that goes from black to white slowly would have a…
- Long scale
- Low contrast
- High kVp
- Many shades of gray
What is contrast?
Differences between things that are adjacent to one another
Contrast is controlled by…
kVp
A result of the differences in attenuation of the x-ray beam as it penetrates various structures.
Contrast
The variation in OD between adjacent anatomic structures.
Contrast
A chest would have what scale of contrast?
Long scale of contrast
Short scale contrast gives you ___ contrast radiographs.
High
High contrast radiographs would have…
- Short scale contrast
- Fewer shades from white to dark
Bone work would have short scale ____ contrast
High
Long scale contrast produces _____ shades of gray.
Many
How much kVp is requited to see a difference in contrast?
4 kVp
At low kVp, how much change is needed to see a difference?
2 kVp
At high kVp, how much kVp is needed to see a difference?
10 kVp
High kVp will give you ___ contrast.
Low
A chest has ___ subject contrast.
High
High subject contrast has ____ variations in tissue composition
Greater
A hand has ____ subject contrast.
Low
An abdomen has ____ subject contrast.
Low
What is the 5% rule?
An increase in kVp by 5% requires a reduction in 30% mAs
What is image detail?
Sharpness of small structures or spatial resolution of the image
How is image detail evaluated?
Sharpness of image detail
Visibility of image detail
What is sharpness?
Clarity or blur of the structural lines
What is visibility?
Seeing that there is anatomy
Sharpness is controlled by…
- Focal spot size (FSS)
- SID
- OID
- Intensifying screen
What can reduce visibility?
Fog
What is distortion?
Misrepresentation of an object and shape due to position of the tube or anatomic part
What are disadvantages of distortion?
- Elongation
- Foreshortening
What is an advantage of distortion?
Allows for better visualization of anatomy
Variable kVp chart:
- kVp varies according to thickness of anatomic part
- Provides radiographs with shorter scales of contrast
- Other factors stay the same
Fixed kVp chart:
- kVp stays constant
- mAs varies
- Developed by Arthur Fuchs
- Provides longer scales of contrast
High kVp chart:
- Used for barium exams, contrast exams, CXR
- Ensures adequate penetration
- Decrease in mAs
- Reduces patient dose
AEC:
- Use of computer assisted automatic/ electric timers and photocells
- Patient positioning must be accurate
- Terminated when the image receptor has received the appropriate radiation exposure
- Most have 2s override
An increase of 15% in kVp is equivalent to…
Doubling the mAs in terms of density
Long scale contrast:
- Low contrast
- Many shades of gray
- Higher kVp
Short scale contrast:
- High contrast
- Black and white
- Lower kVp
What controls contrast?
kVp
What controls density?
mAs
A high grid ratio will produce a short scale contrast? T/F
True
