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125 Cards in this Set

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  • Back
What are x-rays
a form of electromagnetic radiation (EM)
What are other forms of EM?
radio waves, microwaves, visible light, ultraviolet light, and gamma rays
EM forms differ because of
As a wave length decreases the energy
X-rays carry much more _____ than _____ or ____
visible light or
radio waves
What is electrmagnetic radiation?
Alternating electric and magnetic fields that propageat through space.
xrays are ______ radiation
Radio waves and visible light have _____ energy and ______.
low enough energy they are non-ionizing
How are x-rays produced
high energy electrons bombard a substance with a high atmoic number (certain metals) that energy is converted to (released as) x-rays
When high energy electrons hit a metal target the energy released from their deceleration is released as
99% - heat
1% - x-rays
How does an xray machine produce a polychromatic beam?
electrons decelerate differently based on difference in the distance from the nucleus. - most xrays produced this way
Characteristic radiation
energy of the xray is released as the exact amount of energy released when the electron changes shell - specific amount of energy
What is the difference between gamma rays and x-rays
x-rays are made outside the nucleus, gamma rays are emitted from a decaying nucleus.
How does the xray machine produce a beam from electricity?
produces a cloud of electrons
accelreates those electrons with high charge to give high energy
Bombard a metal target with that high energy electron stream to create x-rays
What are the components of the x-ray tube
focusing cup
tube housing
control panel
Cathode function
electron source
current "boils off" the metal due to electrical current.
The electron cloud from the cathode has what charge?
Anode (target, focal spot)
Positive charge applied across the tube (kV)
focusing cup
negatively charge cup that surrounds the cathode filament to keep the electron could tightly packed and prevent electron beam from fanning out.
A bigger cathode filament creates a _____ focal spot.
bigger. small necessary for sharp image detail
A small cathode filament is needed when
a sharp image is curcial (orthopedic)
A large cathode filamen is needed when
a large technique is required (equine abdomen)
Tube housing function
Glass envelope and outer lead housing to shield everything but the window from x-rays.
Filter function
removes low energy x-rays from the beam
Collimator function
adjustable lead shutter device which restricts the size and hsape of the x-ray beam.
Restricting the field of the x-ray beam allows for what
decreases exposure to others and improves image quality by reducing scatter.
mA controls
electrical current to the cathode - number of electrons boiled off - HOW MANY!
mAs is the
number of electrons times the seconds - determines number of electrons in exposure
To adjust the number of x-rays in a the exposure adjust
mA or s
Which mA and s combination is ideal
highets mA and lowest s
Why is a short exposure time important?
reduces chance of movement.
kVp controls
voltage with which the electrons are accelerated - ENERGY of the xrays in the exposure
kVp determines the
penetrating power of the xrays - HOW HARD
The technique of the exposure is determined by
kVP and mAs.
A small kVp charge produces
low energy beam
What are the 3 fates of a single x-ray photon when it enters a body
Complete transmission
Complete absorption
Complete xray transmission is characterized by
black speck on the radiographic film in line with the path of the x-ray photon
Complete absorption is carried out by
patient's body absorping the x-ray and being consumed - this prevents a black speck from forming.
Scatter characteristics
x-ray photon that strikes an outer shell electron and is diverted. Can end up in the patient, on the film or the radiographers
Scatter reduces
radiographic contrast
What 3 factors affect the production of scatter?
Size of the field - larger fields produce larger scatter
kVp - higher kVp produces more scatter
Thickness of body part - thicker body parts create more scatter radiation
What controls contrast?
kVp controls what?
Contrast is what?
differential absorption of x-rays throught the patient
A technique chart should be made each year because...
anode will degrade over time.
The technique chart is set for what 3 parameters?
focus film distance
For portable x-rays machines what needs to be consistent for each exposure
focus film distance
In creating a technique chart what rules should you follow in changing settings
for every cm of body thickness add 2 kVp up to 80 cm
then 3 kVp from 80 - 100 cm
4 kVp over 100 cm
What rules of thumb are there for other body parts when creating a technique chart?
for thorax reduce mAs by 1/2
Extremities/bone - double mAS or increase kVP by 5 - 10
Cat reduce mAs by 1/2
immature dog reduce mAs by 1/2
What is a radiographic filter?
a sheet of metal placed against the window of the x-ray tube, its purpose is to absorb some of the low energy photons.
What is a radiographic grid?
a plate composed of hundred of alternating think lead strips with aluminum or fiber interspaces focues at the x-ray beam anode
A radiographic grid produces
increased contrast by reducing scatter radiation by absorbing it
A radiographic grid DOES NOT
reduce scatter production
A grid should be used when
body part is over 10 cm.
How does a grid effect technique?
it absorbs electrons, so mAs needs to be increased (Bucky Factor)
What is the Bucky Factor?
the amount the mAs must be increased to account for the grid
kVp DOES NOT change
What is an intestifying screen?
thin film of rare earth elements that emit visible light when struck by x-ray radiation
What is the net effect of an intensifying screen?
decreases amount of mAs of the exposure decreasing the amount of radiation the patient is exposed to.
What is the negative effect of intesifying screens?
decreases detail.
The more efficient a screen is at producing light from a certain amount of radiation the more
loss of detail results
When are screens not used?
when fine detail is needed - dental rads. Needs high exposure - 200 mAs
The key ingredient of radiographic film is
siver halide
When silver halide crystals are exposed to radiation they _____ during development.
converted to metallic silver which remains black.
Film speed definition
Ability of the film to make an image form a certain number of x-ray photons is referred to as its speed
The greater the ability of a film to make an image of from set number of photons the ____ the speed of the film
Faster speed films have ...
larger silver halide crystals - makes bigger black speck - reduces detail
The speed of a system is dependent on
the film speed and then screen speed
Lower speed systems are used when
very high detail is required - orthopedic
High speed systems are used when
few photons are available - equine abdomen
Medium speed systems are used
for small animal abdomen and pelvis, equine orthopedic exams
Film ____ and ____ ___ must be matched
color sensitivity and intesifying screen
Film fog is produced by
light leaks in the dark room
improper safelight intensity, distance or filter color
loaded cassettes placed too clase to the xray beam when not being used
high heat and humidity
exhausted developer solution
Film id methods
photoprinter - light exposure imprints info from paper
lead letters
x-rite tape
Optical density
how black the film is
What controls optical density?
number of photons that hit the film
mAs - major determinant
Focal distance
subject density
Peripheral film blackness is controlled by
mAs - the number of x-rays
To change film blackness correct the mAs by
to make darker increase mass of 5 to 10. To make lighter decrease mass from 5 to 2.5.
The intesity of the x-ray beam varies by
square of the distance to the film - inverse square law
Decreasing the focal distance 1/2 will be like
quadrupling the mass
If the peripheral film is black but the body part is too light ....
increase the kVp
mAs is correct because the peripheral film is black.
corrections to kVp to affect flim blackness tend to be in what range?
10 - 15 %
Heel Effect is what
xrays beam of lower intensity - fewer photons on the side of the beam toward the anode away from the cathode
The heel effect can be used to
place thicker ends of body parts toward the cathode to even give allow more electrons on that part of the body and evening up the exposure.
What is contrast?
how much black and white
What is lattitude?
how many shades of gray
A film with high contrast will have
low lattitude and will be black and white
A film with low contrast will have
many shades of grady
What type of film should have highest contrast?
What films should have lowest contrast
What setting controls contrast?
kVp - scatter decreases contrast - higher kVp = higher scatter = lower contrast.
Orthopedic studies should have
low kVp and high mAs - high contrast low lattitude
Thoracic studies should have
hight kVp and low mAs
mAs gives --- while kVp distinguishes
tissues within
What are the 5 basic radiographic opacities?
Soft Tissue
Non-fat soft tissues and ___ have the same opacities
fluid - blood urine, transudate, exudate.
A cyst and a tumor will have ____ radiopacities
the same
Can fat and viscera be distinguished?
yes - different opacities
Can fluid and viscera be distinguished?
no - need MRI
Summation means
when 2 sturctures overlay each other and do not touch their radiopacities will combine, preserving their individual margins - there is fluid or gas between them
Silhoutte sign
when two structures are in contact with each other their margins cannot be distinguished. no fluid or gas between them
When placing film on viewer put
patients right on the left for VD and cranial on the left.
Roentgen findings
Describing what you see is
Radiographic finding
saying what you interpret is
Radiographic diagnosis
If film imprinter image is normal, film is _____. If the film imprinter image is too dark ____.
Overexposure can be caused by
incorrect settings
decreased focal film distance
faster film scree combination than normal
mismeasurement of the area of interest
surge in incoming line voltage
Overdevelopment can be caused by
increased developer time
develper temperature too high
Excessive fog is caused by
light leaks
safelight too bright,
darkroom light leask
faulty cassette causing a light leak
chemical fog
Underexposure caused by
incorrect machine settings
lengthened focal film distance
slower film/screen system than normal
mismeasurement of part thickness
failure to hold exposure switch closed for length of the exposure time
Underdevelopment caused by
develper time too short
too low developer temperature
exhausted developer
loading two films in one cassette
Loss of contrast due to
failure to use a grid when indicated
film exposed to back-scatter during an exposure
film out of date
improper film storage
developer time too short/temp high
developer exhausted, contam, dilute
film/screen characteristics
Loss of detail
patient, tube or cassette motion
increased object-film distance
beam not perpendicular to cassette
poor film-sreen contact
fast screens with large crystal size
localized artifact - black artifacts
develper splashed on film
scratch on film
bending of film
static electricity
exposure of edge of film to light while stored
localized artifact - white artifacts
fixer or water splashed on film prior to developing
foreign object on screen
film not develped
crystals not reduced
emulsion scrathes
poor film-screen contac
solarization artifact
Film development steps
Developer solution
reduces all silver atoms within the exposed silver haldie crystals to metallic silver atoms (black) - dependent on time
What three factors effect the amount of development
High temperature of development means
less time needed
What is the purpose of the fixer solution?
stop the development process - remove the undeveloped emulsion
If a small amount of fixer is added to the develper solution it will
inactivate the whole tank
if the fixer is not rinsed off it will cause the film to
brown over time
smell like sulfur
Radiation can unfortunately also cause
malignant cancer
germ cell mutation
ALARA principle
As low as reasonably achievable
With ALARA considerations what 3 variables should be controlled
Reduce the Time you are exposed to radiation
Increase th distance you are from the radiation exposure
Maintain protective shielding
THe maximun permissible dose of radiation from occupational exposure is
5 Rem for whole body
50 Rem for extremities
15 Rem for the lens and eye