Test 2 Flashcards
SID (Source Image Distance) aka
FFD (focal spot film distance)
TFD (target focal distance)
inverse square law
a change in beam intensity varies inversely with the square of the SID
exposure 3 ft from a source is 40 mR/hour; what is exposure rate at 6 ft?
(6^2/ 3^2) * (40/x) or 40*.25 because doubled
= 10 mR/hour
if SID is double, intensity is
1/4 original
if SID is halved, intensity is
4x original
if SID increases, # of x-rays reaching film
decreases
direct square law
old mAs/X = (old SID^2/new SID^2)
if SID doubled, mAs =
4x original
if SID halved, mAs=
1/4 original
classical unit of x-rays in air
Roentgen (R) or mR
classical unit of radiation absorbed dose (patient exposed)
RAD
SI unit for radiation absorbed dose (patient exposed)
Gray (Gy)
___ rad = 1 Gray
100 RAD = 1 Gy
classical unit for radiation equivalent man (occupational exposure)
REM
SI unit for radiation equivalent man (occupational exposure)
Sievert
equation for REM
rad * QF = REM
____ REM = 1 Sievert
100 rem = 1 Sievert
QF for x-ray
1
QF for alpha particles
20
QF for neutrons
5-20 dependent on energy
in x-ray, 1 R = __ RAD = ___ REM
1=1=1
classical unit for quantity of radioactive material
curie
SI unit for quantity of radioactive material
becquerel
important x-ray interactions important for diagnostic level radiography
photoelectric absorption
compton scatter
coherent (not as important)
The unit a physicist will use to name the ionization in air in classical nomenclature:
R
What is the Systems International Unit for REM?
Sievert
Unit used to describe energy absorption into matter
RAD
Milirad converted to RAD
1/1000 of a RAD
What is in the Systems International Unit for R?
Coulombs/kg
Unit of occupational exposure
REM
x-ray interaction that occurs with high atomic #
photoelectric effect (absorption)
x-ray interaction that is related to energy of x-ray photon
all of them (coherent, photoelectric, and compton scatter)
Which x-ray interaction is the most likely to occur at energies below 10 keV?
Coherent Scatter
Which x-ray interaction with matter is most likely to occur at energies between 10-60 keV?
Photoelectric absorption
Which x-ray interaction with matter is most likely to occur at energies greater than 60 keV?
Compton scatter
Which shell level is ionized in the photoelectric absorption interaction?
K
What happens to the original x-ray following the photoelectric interaction?
no longer exists
Which shell level is ionized in the Compton scatter interaction with matter?
outer
What happens to the original x-ray following the Compton scatter interaction?
scatters, then continues to ionize until it loses all it’s energy
What happens to the original x-ray following the Coherent scatter interaction?
scatters and changes direction, does not lose energy
State three other names for the Coherent scatter interaction:
Raleigh
Thompson
Classical
State at least 2 advantages of tissue compression
Decrease patient thickness
Decrease compton scatter
Hold patient to bucky
State at least 2 advantages of performing PA lumbar spine examinations instead of AP.
P-A uses compression and so it decreases mass: less mass less interactions
P-A retains shape so less shape distortion.
How does collimation to the film size or smaller effect the production of scatter radiation?
As collimated field decreases, compton scatter decreases
How does collimation to the smallest field size possible effect radiographic contrast?
Compton scatter decreases contrast, and collimation decreases Compton scatter, so collimation increases contrast
- Decreases density so you increase mAs by 50%
When collimating down “significantly”, what must be done to maintain radiographic density?
- increase mAs by 50% to compensate for decrease in density
How does kVp effect the production of scatter radiation?
compton scatter increases as kVp increases
range of optimum kVp for radiographic examinations of the spine.
70-90
For every 4cm of tissue thickness increase mAs should be
doubled
Another name for radiographic grid
Bucky
Purpose of a radiographic grid
decrease compton scatter;
Causes severe underexposure on both lateral edges of the radiograph?
upside down grid
Grid, in which strips are angled toward the center so that the divergent x-ray beam coincides with the angled strips?
focused grid
Above this energy Compton scatter increases so much that it is necessary to use a radiographic grid?
> 60 kVp
The height of the lead strip in relation to the distance between them (the width of the interspace strip)?
grid ratio
Use of a 12:1 compared to an 8:1 grid causes this to occur?
Increase radiation exposure
Typical grid strip interspace material?
Aluminum, plastic, carbon fiber
The number of grid strips per centimeter or inch?
grid frequency
Photographic factor that improves with the use of a radiographic grid?
contrast
Direction that the x-ray tube can not be angled when using a radiographic grid?
laterally
Must be precise when using a focused grid?
SID
Direction that the x-ray beam may be angled when using a parallel or focused grid?
Direction of strips (Vertical not horizontal)
Causes “fog” density?
compton scatter
Causes the shadows of the grid strips blur out and become almost invisible?
Moving grid
High frequency radiographic grid does this?
decrease visibility of grid lines
Radiographic grid that is not useful in chiropractic because it will not allow an angled central ray (tube tilt)?
cross-hatched
Ratio grid adequate for low amounts of scatter production such as that produced in 8X10” and 10x12” upper cervical techniques?
8:1 or 10:1
This happens when the lead strips absorb the primary radiation on one or both lateral edges of the image?
grid cut off
CM thickness of the patient’s anatomy in which it becomes necessary to use a radiographic grid?
= to or >10cm
This will be indicated on a focused grid?
tube side
3 types of grid movement
Single stroke/manual cocked
Reciprocating
Oscillating
type of chiropractic practice would require a relatively low grid ratio
upper cervical
type of chiropractic practice would require a relatively high grid ratio?
14X36 FILM, FULL SPINE, GONSTEAD
Is a grid a radiation protection device - for the patient
no
Which ratio grid would require the greatest increase in exposure?
Higher grid ratio = higher mAs
There are 3 types of grids - name them
parallel
focused
cross-hatched
Why would you not want to purchase a crosshatch grid?
Can’t angle beam in any direction
define grid radius
focal range, proper focal range (proper SID)
Describe a radiograph taken at the improper grid radius.
Lateral cut off on both edges
Describe a radiograph that is taken with the central ray off center.
Primary x-rays collide with strips –> grid cut off on lateral edges
Describe a radiograph that is taken with the beam angled to the left or the right.
Cut off on one lateral edge
grid cut off
underexposed, due to scatter and diverging rays
Why are intensifying screens used with x-ray film?
visible light from intensifying screens produce image by stimulating silver halide on film
Film emulsion made of
silver hallide crystals suspended in gelatin
Film base made of
plastic/ mylar
Why does a double-coated film emulsion result in a decrease in sharpness?
The faster the film or screen, the thicker the emulsion, light diverges over emulsion producing pneumbra
Image on the film that is not yet developed
latent image
image actually screen on screen after processing
manifest image
How is film manufactured to increase its’ speed?
Increased thickness= increased speed
Which of these imaging systems would you choose if you were imaging extremities?
100 speed
Which of these imaging systems would result in the most radiation exposure to the patient?
100 speed
Which of these imaging systems would result in the least radiation exposure to the patient?
1200 speed
Which of these imaging systems is the most consistent with the ALARA concept?
1200 speed
What is the cause of quantum mottle? What does it look like?
caused by decreased x-rays used to produce the image
- looks grainy, like low megapixel image
Which of these imaging systems would result in a radiograph with the most quantum mottle?
1200 speed
What is the lowest film-screen system speed that you should consider using for routine spinal radiographs?
400 speed
What does the term film latitude mean?
ability of film screen to allow for error (long latitude is more forgiving); wide range of useful densities
How is film contrast related to film latitude?
as film latitude increases, film contrast decreases – INVERSELY related
What color safelight is safe to use with both green and blue sensitive film?(“Universal”)
red, GBX safelight
How far away from the work surface should a safelight be hung?
4 ft
How do you know that the safelight filter is installed properly?
Writing is on the outside and read from L to R
What is the maximum wattage of a light bulb for the safelight?
What the manufacturer says or less than 15 watts
What color of light do rare earth screens emit? What type of film must be used with them?
green yellow, green sensitive film
What color of light must the intensifying screen emit for orthochromatic film to respond?
green
What color of light do calcium tungstate screens emit? What type film must be used with them?
blue violet, blue sensitive film
If a technique is based on 200 speed imaging system and requires 30 mAs, 80 kVp, 40” SID, what must be done to compensate if a new 600-speed system is used?
USE 1/3 mAs=10 mAs
When an artifact is demonstrated on a film as a result of something on the screen, what color will it appear? Will it be sharp or blurred? Why?
white, sharp, debris blocking light from intensifying screen
What should be used to clean an intensifying screen?
screen cleaner and lint free gauze
What temperature and humidity should film be stored at?
68 degrees and 40-60% humidity
Where is the film’s expiration date located? What is the result of using film that is out of date?
On the box; increase fog, decrease contrast, breakdown silver halide crystals
What may appear on the film if the humidity is too low?
Black artifacts from static
Bending film produces
black crescent moon
in x-ray tube, kVp:
accelerates electrons toward focal spot
As kvP increases, x-ray energy
increases
When kVp decreases by 15%, density ______
density decreases by 1/2
when Kvp increases by 15%, density _____
density increases by 2x
long scale = ___ contrast
low
short scale = _____ contrast
high
15% rule for kVp
- if kVp increases by 15%, mAs decreases by 1/2
if - if kVp decreases by 15%, mAs increases by 2x
(Keeps density the same)
long scale is used for
soft tissue
at long SID, relative _____ x-rays produce image
perpendicular
the use of 40”/72” SID will cause more heat in the tube
72”
___ % change in mAs is required to notice a minimal change in radiographic density
30%
5:1 grid ratio: non-grid mAs
x2
6:1 grid ratio: non-grid mAs
x3
8:1 grid ratio: non-grid mAs
x4
10:1 grid ratio: non-grid mAs
x4
12:1 grid ratio: non-grid mAs
x5
16:1 grid ratio: non-grid mAs
x6
radiographic density can be doubled by (2)
increasing kVp 15%
increasing mAs 50%
if the scale of contrast is too long, it is a ____ scale and the change is ____ to kVp and ___ to mAs
low contrast scale
lower kVp 15%
increase mAs 2x
if the scale of contrast is too high, it is a ____ and the change is ____ to kVp and ___ to mAs
short scale
increase kVp 15%
decrease mAs 1/2
when SID increases, exposure to patient ____
decreases
As SID increases, radiographic density ______
increases
As SID increases, magnification and blur _____
decrease
As OID increases, radiographic density ____
decreases
As OID increases, magnification/blur ______
increase
why does radiographic density change when OID is increased?
decrease in scatter decreases fog density
chiropractic view that uses air gap technique?
lateral cervical
why is air gap technique for lateral cervical better than bucky?
less exposure to patient
if you increase kVp by 15%, and decrease mAs by 1/2, ____ scale of contrast is created
short
low kVp and high mAs relationship results in a ____ scale of contrast
long
short scale of contrast is aka
high contrast
