wk 1-3 Flashcards
what is the difference in visual densities between organs
contrast
changes in mAs can directly control the ___ on an x-ray
density
if a radiograph has been exposed but not developed or fixed it will be what color
purple
how is grid cut off created
when the lead strips, bucky, and tube aren’t lined up
is it true that cassettes placed in a bucky tray require more mAs than a table top exposure
true
to determine KVp for an exposure, you must ____
measure thickness of tissue
the KVp controls the x-ray beams ___
voltage power
the length of time a film is left in the developer depends on what
temperature of developer solution
if a film has been exposed correctly but after going through the darkroom comes out with an image that has purple tinge all over it, what was the problem
the fixer solution washed unsensitized crystals
a film which has been developed and fixed correctly but comes out black was probably a problem with what?
too much exposure to white light, pressure, heat, or radiation - all crystals were sensitized and purple was washed off
the scale of contrast that is desirable on a radiograph of the pelvis Is what?
short scale contrast
a grid is used to do what?
prevent scatter radiation by attracting weak electrons; can affect our safety and cause film fog
intensifying screens allow more or less radiation to be used to expose the film than the same view taken without screen?
less; acts as catalyst and intensifies radiation
radiographs for abdominal tissue require the use of what
base mAs
how many inches is the commonly used animal focal film distance
40 inches
why would the film have come out of the darkroom clear
developer didn’t see any sensitized crystals so fixer washed it all away; or put straight into fixer solution
film is left in the fixer solution for
twice the time it was in the developer solution
the purpose of the collimator
reduce exposure area and scatter radiation
the down leg of the animal will appear smaller or larger than the top leg?
smaller
two things that can cause distortion
magnification
patient movement
tube movement
diagnostic radiology
medical specialization that involves undertaking a range of imaging procedures to obtain images of the inside of the body
ionizing radiation
when radiation carries enough energy to ionize atoms or molecules (ionization is the addition or removal of an electron from an electrically neutral atom)
primary radiation
unaltered radiation existing at the same energy level as when it was created (hand on table in grid)
secondary radiation
scatter radiation; an intersection between primary radiation and matter (bouncing off onto person)
inside the x-ray tube
cathode
anode
heel effect
cathode
negatively charged side of X-ray tube containing filament (coil of tungsten wire) and focusing cup (repels electron cloud towards anode)
anode
positive charged side of X-ray tube containing focal spot (electron beam aimed at spot on target), rotating anode (if it resolves it can withstand more heat and heavier usage), and stationary anode (remains fixed in one place)
heel effect
beam varies in intensity as it comes out of the tube - the thicker end of the animal should be placed at the cathode end
low voltage side/filament circuit
responsible for supplying voltage to the filament in the xray tube so electrons can be boiled off
stepdown transformer
(low voltage) decreases amount of incoming line voltage to the filament in the cathode - heat filament and create electron cloud
MA selector
(low voltage) milampule (density); controls number of electrons produced by filament - regulates the current (more amperage into filament, hotter the tungsten wire gets
xray tube
(low voltage)
high voltage circuit
produces high voltage across the xray tube so the electron cloud created by the cathode moves across the tube
autotransformer (KVP) selector
(high voltage) contrast; provides a variable but predetermined amount of voltage to the step up transformer (determined by thickness, controls contrast of image)
step up transformer
(high voltage) increases voltage to a point high enough to produce xrays
rectification
process of changing alternating current to direct current by blocking or reversing the negative portion of the wave
self rectification
xray tube acts as rectifying unit
half wave rectified
negative portion of current cycle is blocked by installed electrical mechanical apparatus
full wave rectified
xray machine can reverse the negative cycle to utilize the entire wave with additional valve tubes
three phase generators
impose three signal phase currents together so there are no deep valleys between electrical pulses
film composition
- consists of a layer of silver halide emulsion on both sides of polyester sheet
- when exposed to light the crystals are sensitized by heat, light, pressure
latency
always present, needs catalyst to be expressed and visible
speeds of film
high (fast), slow (more detail); film with larger crystals in thicker layer will react quicker
latitude
films ability to produce shades of gray
cassettes
holds xray film and intensifying screens
intensifying screens
increase the efficiency of the xray beam by glowing when struck by radiation; high (regular with thicker crystals), par (medium), detail (slow with smaller crystals)
composition of intensifying screens
crystals will glow when struck by light
technique of intensifying screens
mAs is increased 2 times between high to par; 4 times form par to detail
development process (dark room)
developer solution
water bath
fixer solution
final wash
automatic processor
developer solution
sensitizes the crystals to create black
fixer solution
removes unsensitized crystals and hardens the film
automatic processor
has a set of rollers to push the film through the stages
CR
- uses erasable film in cassette
- cassette is processed
- CR traps image by photostimulable phosphor
- then image appears
*eliminates wet processor and chemicals
*short wait for image display
*reasonable cost for cassettes
BUT
*cassettes need to be serviced and prone to scatter radiaiton
DR
more popular (like camera)
- uses plates
- transfers radiation to digital receptors
- digital data is collected and sent to computer
*fast, good quality, able to manipulate, sends electronically
BUT
*expensive, plates are easily damaged, and software updates are needed
factors affecting the radiographic image (6)
the animal
FFD
distortion
detail
density
contrast
high opacity
bone; absorb most of xray causing less to reach exposed film
low opacity
lungs; allow more X-rays through to exposed film
5 opacity levels
gas (black)
fat (dark gray)
soft tissue and fluid (gray)
bone (light gray - white)
metal (bright white)
focal film distance (FFD)
between focal spot and film; more space = weaker beam
distortion
masking of an objects true shape; closer to tube will be larger - closer to film and table will be more detailed and true to size
object film distance (OFD)
distance from object to film
detail
visual quality of radiograph
factors affecting detail
focal spot size
film and screens
patient motion
tube motion
film fog/scatter radiation
distortion
density
mAs; blackness in the film
short scale contrast
bone; mainly black and white
long scale contrast
soft tissue; black and white with more shades of gray
when an xray beam has a high KVP or penetrating power
there is less difference in the absorption of the beam by tissues of different opacities
collimator
determines area of exposure
cones
restricts the primary beam as it comes out of machine
filters
absorb the lower energy xrays that could not penetrate the patient to expose the film but may still interact with the patients tissues and cause damage or scatter radiation
grids
lead strips that prevent scatter radiation from reaching the film - like a magnet
grid cut off
grid isn’t lined up properly and absorbs rays that you wanted to reach the film
causes of grid cut off
- parallel grid
- not centering grid to the primary beam
- using incorrect FFD
- placing temporary grid upside down
parallel grids
contain strips that are arranged in a parallel fashion
focused grids
contains lead strips that are placed at angles to correspond with the angles go the xray beam
cross hatch grids
two sets of parallel lead strips run perpendicular to each other
temporary grid
taped or attached to cassette independently
