Radiographic technique Flashcards
The combination of the radiation quantity (mR/mAs) and radiation quality (HVL)
Exposure factors
What are the 4 main exposure factors?
KVP, mA, Exposure time, SID
controls how fast the electrons are sent across the tube
kVp
Controls Quality
KVP
Controls Quantity
mAs (directly proportional)
Beam penetrability of KVP
high energy, greater penetrating ability, more compton effect(scatter)
KVP
- controls scale of contrast
* increasing image noise production
* reducing image contrast
affects number of x-rays produced (not energy)
mA
mA, quantity, and patient dose are ____ proportional
directly
determines the number of photons radiation quantity, OD and patient dose
mA
mA stations are usually
50, 100, 200, 300, 400 & 600
Three phase exposure time
1 ms
single phase exposure time
<8ms
Short exposure time ______ image blur.
reduces
Must ________ mA when using short exposure times to maintain x-ray intensity
mA
Formula for mAs
mAs= (mA) x (S)
key factor of optical density
mAs
mAs
changes the number of electrons
states the OD will be constant for any combination of mA and exposure time that results in constant mAs
Reciprocity Law
Distance affects x-ray ________ not _______
intensity; quality
Determine required change in mAs after a change in SID to maintain OD
square law
half-wave rectification
drops to zero
Full wave rectification
consistent but always drops to zero
3 phase power
6 or 12 pulse, energy higher, nearly constant output
high frequency
less 1% ripple, much better overall
Hypersthenic
5% population, massive type, chest and abdomen are very broad, lungs are short and wide, stomach is high and transverse
Sthenic
average body type, represents 50% of population, active or strong, stomach is more J-shape and lower, more slender version of hypersthenic
Asthenic
opposite of hypersthenic, 10% of population, very frail and of poor muscle tone, narrow, long, shallow
diaphragm is low, heart is long and slender,
abdominal cavity rests mainly in the pelvic region
Hyposthenic
35% of population, modification of the asthenic build, stomach is j-shaped and extends into the iliac crest region, high splenic flexure
As thickness increases, ______ radiation is necessary for penetration.
more
soft tissue technique
low kvp and high mAs
Extremity technique (soft tissue and bones)
low kvp
Chest technique (high contrast)
high kvp
Abdomen (low contrast)
middle kvp
Pathology
the destructive decrease or constructive increase in mass or composition has a direct effect on technical consideration
image quality factors
Optical density, contrast, image detail, distortion
The degree of blackening of the finished radiograph
Optical density
when OD is high…
took dark, over exposed
when OD is low…
too light, under exposed
OD and mAs are _______ proportional.
directly
when only mAs is changed it is either………
halfed or doubled
___% increase required for visible change in OD for mAs.
30%
____% increase is required for visible change in OD for kvp
4
square law formula
mAs2/mAs1=(SID2)^2/(SID1)^2
15% rule: To maintain OD a ___ increase in kvp would require a reduction of ____ the mAs
15%; half
variation in OD between adjacent atomic structures
Contrast
Contrast is controlled by
KVP (penetrability of the primary beam)
The range of OD from the whitest portion to the blackest portion of the radiographic image
scale of contrast
Short scale
low kvp, short scale, high contrast, “bone work”
high contrast radiographs
used when an increase in contrast is desired
produces greater differences in black and white
short scale
Long scale contrast
low contrast, many shades of grey, high kvp, “chest images”
radiographs having optimal radiographic density and contrast to visualize area of interest
photographic properties
5% rule
an increase in kvp by 5% may be accompanied by reduction in mAs by 30% to produce the same OD at a slightly reduced contrast scale.
Sharpness of small structures or spatial resolution of the image
image detail
image detail is evaluated by
sharpness and visibility
the amount of clarity or blur in the visualization of the structural lines or borders of tissues in the image
sharpness
Sharpness controlled by
FFS, SID, OID, intensifying screen
The contrast resolution of ability to see the detail of the radiographic image
Visibility
Loss of Visibility
refers to any factor that causes a deterioration or obscuring of the image detail (fog)
The misrepresentation of object size and shape due to position of the tube, the anatomic part, and or image receptor
Distortion
disadvantage of distortion
elongation, foreshortening
advantage of distortion
allow better visualization of anatomy
technique charts based on
- variable kvp
- fixed kvp
- high kvp
- AEC
VARIABLE KVP CHART
- varies according to thickness of anatomic part
- provides radiographic with shorter scales of contrast
- Ma and time stays the same, but you measure for kvp
Fixed kVp chart
- developed by arthur fuchs
- kVp stays constant, mAs varies
- provide radiographs with longer scale of contrast
- seen group small, average, large
high kvp chart
- Used for barium exams, contrast exams, cxr,
- ensures adequate penetration
- requires a decrease in mAs
- reduces patient dose
AEC
- the use of computer assisted automatic/electric timers and photocells
- needs selection of kvp and od settings
- patient positioning must be accurate
- terminated when the image receptor has received the appropriate radiation exposure to correspond with OD settings
- most AECs have 2s override
