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