Test 2 Flashcards
what is ionizing radiation?
radiation that has enough energy to remove electrons from atoms (creates ions)
why is ionizing radiation dangerous?
when the electrons are stripped from atoms, they can then interact with other biological molecules in the body; the intensity depends on strength and exposure time
true or false: radiation damage in an individual can be passed onto their offspring
true; damage to the genetic code in reproductive cells can show up in future generations
what is the device used to monitor personal radiation intake called?
dosimeter
how does the dosimeter work?
contains a lithium (calcium fluoride) crystal that absorbs radiation; when crystal is heated the stored energy is released and can be measured in the form of visible light
what is secondary radiation? what leads to it?
is usually “scatter”; radiation that has deflected off of an object and onto the person - caused by increased kVp and/or field size
why are persons under 19 years more likely to develop cancer from radiation exposure?
still have growing tissues; cell division is more frequent and these cells are more susceptible to radiation damage during division
what PPE should be worn when restraining for radiographs?
lead apron
gloves
glasses
thyroid protector
why is the wall colour of the dark room important?
light colour walls reflect less light
why is the safelight colour important?
red light does not affect radiography film due to its wavelength
how do we test a safelight?
expose film in 1/4 increments for 1 minute each; if safelight is working exposure to it will not darken the film
5 basic steps for manual processing
- developer for 5min @ 20*C
- rinse 30sec
- fixer for 10mins
- rinse 20mins
- dry
what does developer do?
converts exposed silver halide crystals to black metallic silver
what are the 2 purposes of fixer?
- clear away unexposed silver halide crystals
2. hardens the emulsion
what is reticulation? what causes it?
wrinkles/cracks in the film; caused by temperature difference between the developer and fixer
what will happen if the radiograph is not rinsed/washed after developing?
the image will darken over time
7 steps to start the automatic processor
- make sure wash, developer, and fixer valves are all closed
- open water tap
- close processor and feed tray covers
- turn on power breaker
- press run
- wait for ready lamp to light up (20min)
- open feed tray cover (insert cleaning sheets one at a time)
identify two differences between manual and automatic processors
- automatic uses a higher temp
2. automatic does not use or require a rinse between developer and fixer
what information must be included on a label?
name address (facility) veterinarian date patient ID
how long must radiographs be kept by law?
5 years
what are x-rays? compare them to visible light
x-rays are electromagnetic radiation; they have greater energy and shorter wavelength than visible light
define and explain excitation
a method of transporting energy through space; a collision with a moving particle excites an atom, it then jumps to a higher energy level; when the electron falls back to its original energy level, the extra energy is released in the form of an electromagnetic photon
true or false: if you have a short wavelength, this means it has less energy
false; a shorter wavelength means there is greater energy
how are x-rays formed? explain
negatively charged electrons are emitted from the heated cathode and accelerated towards the positively charged anode; the electrons collide with nuclei of atoms and start the process of excitation - at the end, an electromagnetic photon is released
what is “brehmsstrahlung” or braking radiation?
the process of electrons slowing down and releasing electormagnetic radiation as they hit the metal anode
what settings affect exposure? how?
HIGHER KVP = faster beam = more penetrating power
HIGHER MAS = longer exposure = more electrons converted to x-rays
SHORTER DISTANCE = more penetrating power
what does milliamperage (mA) do?
heats the cathode; which releases electrons
what is thermoionic emission?
process of heating the cathode to release electrons
how can you assess density and contrast and identify/correct the settings?
- kVp; can you see the details? yes=kVp OK no=kVp too low
if film is overpenetrated bones will look grey; decrease kVp 10-15% - mAs; what is the density like? too low=double mAs too high=decrease mAs by half
what is contrast? how does it apply to radiographs?
contrast is the difference between adjacent densities of the film; you should have high contrast for bones (low kvp) and low contrast for soft tissue (high kvp)
what device can be used for some radiographs to limit scatter? when would we use it?
grid; patient thicker than 10cm
4 basic criteria for patient positioning
- patient welfare
- restraint/immobil
- potential trauma to area of interest
- restrainer exposure
what views are required whenever you take a radiograph?
2 views at right angles to each other; area of interest is closest to the film
where do you measure for thoracic positioning?
caudal border of scapula
what are the peripheral borders for thoracic?
scapulohumeral articulation to L1
should thoracic radiographs be taken on inspiration or expiration?
inspiration; we need to see the gap between heart and diaphragm
where do you measure for abdominal positioning?
thoracolumbar junction
what are the peripheral borders for VD abdominal?
T9 to femoral head
should abdominal radiographs be taken on inspiration or expiration?
expiration; diaphragm should be close/touching the heart
where do you center the beam for an abdominal x-ray? feline? canine?
feline: 2-3 finger widths caudal to 13th rib
canine: over caudal aspect of 13th rib
true or false: legs always need to be straight/perpendicular for VD abdominal x-ray
false; legs do not need to remain straight, only parallel to prevent curving of spine
list four reasons to NOT place a patient in dorsal recumbency for a VD
- trauma to spine
- bloat
- emaciated
- obese/pregnant
what is lateral decubitus?
a VD radiograph taken while patient is in lateral recumbency; beam is positioned horizontally
how would you raise the sternum in a lateral abdominal view? why would you need to?
use a foam wedge under the patient; helps keep sternum parallel to spine
what needs to be included for a lateral abdominal x-ray?
caudal aspect of T7 to femoral head
why are lateral abdominal x-rays taken on expiration?
so the diaphragm doesn’t compress the organs
how should an animal be placed for a proximal(up to and including elbow/stifle) limb x-ray? what are the names of the positions?
should be in dorsal recumbency;
forelimbs = CdCr, rear limb = CrCd
how should an animal be placed for a distal(including elbow/stifle and below) limb x-ray? what are the names of the positions?
should be in sternal recumbency;
forelimbs = DPa or CrCd, rear limb = PLD or CdCr
technical term for a lateral limb x-ray?
mediolateral
what needs to be included in a long bone x-ray?
include both proximal and distal to the joint; including the joint
what needs to be included with a joint x-ray?
include 1/3 of limb distal and proximal to joint
where do you measure for a limb x-ray?
mid-diaphysis
where do you measure for a joint x-ray?
articulation
what needs to be included in a scapular lateral x-ray?
dorsal aspect of scapula and 1/3 of the humerus
true or false: the trachea and ET should be ventral to scapulohumeral articulation
false; should be dorsal
why would you take a radiograph of a flexed elbow?
useful if there is laxity of joint; carpal articulation is visible
what does a true lateral pelvis x-ray look like? what are some possible issues with this view?
affected and contralateral limbs are superimposed; cannot see hip luxation or femur differentiation
what does a pelvis-obliques lateral position look like? positives of this view?
affected limb is pulled cranially while contralateral is pulled caudal; hip luxation and/or differentiation of femurs is visible
why would you perform a VD extended view of a hip?
to check for hip displasia
5 key points for a proper hip x-ray
- legally labelled
- femurs parallel
- patellae between femoral condyles
- no rotation of bones
- must include entire pelvis, femurs and stifles
5 things we can assess on the femoral head
- angle of femoral head
- cranial 1/3 joint space of equal width
- at least 1/2 of femoral head in acetabulum
- rounded and smooth femoral heads
- smooth femoral neck
what are the 3 views for Penn HIP?
- standard extended view
- compression view w/ neutral position
- distraction view w/ same neutral hip position
why would you choose Penn HIP over OFA?
Penn HIP is certifiable sooner at 4 months and uses mathematical measurements to diagnose hip displasia; OFA is certifiable at 18 months and uses a panel of three veterinarians to diagnose
true or false: any vet can do a Penn HIP diagnosis
false; must be certified
what are 3 requirements for cassettes?
- light tight but allows penetration
- may have lead blocker in one corner
- back lined with lead to absorb backscatter
what is an intensifying screen and how does it work?
sheet of luminescent phosphor crystals which emit fluorescent light when excited by x-ray radiation; intensifies the effect of x-rays on film during exposure
6 steps of intensifying screen
- 2 screens in cassette sandwich film
- x-rays hit the phosphor crystals
- crystals fluoresce
- x-rays convert into visible light
- latent image forms on film from visible light
- > 95% of film exposure comes from light emitted from crystals and not the beam
what is the primary purpose of the intensifying screen?
t oreduce the amount of radiation exposure required
true or false: the intensifying screen lowers the required mAs by 5x
true; the mAs would be 5x higher without the intensifying screen
benefits of using an intensifying screen?
lower radiation to patient/personnel
lower chance of movement
lower scatter radiation
what are the 4 layers of the intensifying screen?
- base
- reflective layer
- phosphor layer
- protective coating
true or false: light photons are more readily absorbed by film than x-rays
true
true or false: a good intensifying screen should have low absorption, high conversion and high afterglow
false; should have high absorption, high conversion, and low afterglow
define screen speed
how efficient the screen is; how much exposure is required to produce visible film image
what 3 factors effect the screen speed?
- calcium tungstate
- rare earth elements (lanthanide)
- crystal size; larger=faster
(4) phosphor layer thickness
(5) reflective layer efficiency
why does calcium tungstate effect the screen speed?
emits in blue region
silver halide film must be sensitive to blue light
4x slower than rare earth film; requires more exposure factors
how does lanthanide effect screen speed?
emits light in green spectrum; need green light sensitive film
4x faster at light conversion; less exposure
uses different film (purple)
why do rare earth film grains have higher resolution and absorption?
they are tubular grains
6 benefits of using rare earth film
- higher speed, lower mAs
- greater absorption and conversion
- less scatter
- less exposure for patient/personnel
- less chance of movement
- less tube load/extension of machine
3 disadvantages of rare earth film
- more expensive
- limited film selection
- more complex technique chart
how does crystal size effect screen speed?
smaller = slower screen, more mAs, more detail, low grain medium = mid speed, mid range exposure, good resolution, medium grain larger = faster screen, less mAs, less detail, high grain
how are non-screen films exposed?
by direct action of radiation; they need more exposure to make up for the lack of intensifying screen
why would a non-screen film be used?
used in bone/dental radiographs; increased exposure and small interest
5 reasons a film would turn out too dark
- over exposure
- over development
- over measurement of anatomy
- too short SID
- machine not calibrated properly
how might developing chemicals turn a film foggy?
temp too high
too long
exhausted
poor fixing
6 contributing factors to low contrast
- scatter
- light exposure
- old film/poor storage
- no grid
- kVp/mAs too high
- poor film/screen combo
why might an image appear too white?
under exposure
under measurement
too long SID
underdevelopment
why might a film come out with a sepia tone?
inadequate rinsing inadequate fixation too short a time exhausted fixer film stuck together during fixing
2 reasons film may have green or purple areas
- processing solutions are low
2. film stuck together through whole process
define penumbra
lack of detail, unsharpness; animal moves and image is blurry
how do you prevent foreshortening and elongation?
foreshortening: keep entire subject parallel
elongation: keep beam parallel
what happens if the central beam is not directed at the centre of film or subject is not parallel?
geometric distortion
