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132 Cards in this Set
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What are x-rays?
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-a form of electromagnetic radiation (EM)
-as wavelength decreases, energy increases |
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What is electromagnetic radiation?
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-Alternating electric and magnetic fields that propagate through space.
-waves or particles (photons) |
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Are x-rays ionizing radiation or non-ionizing radiation?
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Ionizing = they can knock electrons out of their shells around atoms and break chemical bonds
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How are x-rays produced?
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-When high energy electrons bombard a substance with a high atomic number (metals), that energy is converted to (released as) x rays
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What are the two mechanisms by which x-rays are produced?
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-Bremsstrahlung radiation (breaking radiation)
-Characteristic radiation |
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What is Bremsstrahlung radiation?
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-breaking radiation
1) When a beam of high energy e-s hits a metal target, these e's feel the pull of the + protons in the target nuclei and rapidly decelerate to change course 2) As they slow, energy they carry is released 3)99% heat 1% x-rays *Most of the x-rays produced by a machine are formed by this process |
http://www4.nau.edu/microanalysis/Microprobe-SEM/Images/Bremsstrahlung.jpg
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What is a "polychromatic" beam?
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**Bc e's will slow to dif degrees based on proximity to the nucleus, they give up dif amts of energy and produce x-rays of dif energy.
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What is Characteristic radiation?
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1)e- in a high energy beam strikes an inner shell orbital e- from the metal target, knocking it out of its shell
2)an e' from a higher shell will drop down and takes its place 3)as it drops, it gives off extra energy as an x-ray 4)the energy of the x-ray release is exactly = to the energy dif b2n the 2 shells*, which is a "characteristic" amt for a specific metal* |
http://train-srv.manipalu.com/wpress/wp-content/uploads/2009/11/clip-image00251.jpg
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How does an x-ray machine turn electricity into a beam of x-rays?
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Every x-ray machine has basically the same components which:
-Produce a cloud of e's -Accelerate those e's with extremely high charge to give them high energy -Bombard a metal target with that high energy e' stream to create x-rays |
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What is the x-ray tube?
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A glass (or alloy) tube with all internal air evacuated (vacuum) to keep those high energy e's from colliding with air molecules instead of the metal target.
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What is inside the x-ray tube?
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-cathode
-anode -focusing cup -tube housing -filter -collimator -control panel |
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What is the cathode?
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-The electron source.
-mA (current) passed through -Filament of tungsten -Creates an electron cloud with a strong NEG charge. |
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What is the anode?
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-Target, focal spot
-kV (high voltage) passed through -Disk of tungsten -Develops a strong POS charge -When electrons strike the anode, X-rays are produced. Becomes extremely hot (99%) so rotates. |
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What is the focusing cup?
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- NEG charged cup that surrounds the cathode to keep e' cloud tightly packed and to prevent e' beam from fanning out (want to repel each other)
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What does the size of the cathode filament affect?
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Focal spot size
-bigger filament = bigger focal spot -small better for detail, sharp image -large better for heat dissipation, large techniques to prevent damage to anode or cathode |
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What is the tube housing?
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Glass envelop and outer lead housing to shield everything but the window from x-rays
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What is the filter?
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Removes low energy x-rays from the beam
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What is the collimator?
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An adjustable lead shutter device that restricts the size and shape of the x-ray beam. Most have a light beam to show the center and the limits.
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What is the control panel?
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Allows adjustment of the exposure parameters:
-mA -timer (Adjusting either will adjust the number of x-rays in the exposure.) -kVp |
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What is mA?
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-how many x-rays
-adjusts the electrical current applied to the cathode filament which determines the number of e's boiled off |
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What is the guideline regarding mA?
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Once a desired mAs is determined (based on a technique chart), select the HIGHEST mA possible. This will allow the lowest s (shortest exposure time) for that exposure to help prevent motion artifact.
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What does the timer do?
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Adjusts the length of time (measured in fractions of a second (s)) during which e's are accelerated to the anode (i.e. the length of the exposure)
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What determines the NUMBER of x-rays in the exposure?
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mA x s ---> the mAs
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What is kVp and what does it determine?
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-Kilovoltage PEAK
-voltage with which the e's are accelerated toward the anode ***kVp determines the max ENERGY of x-rays in the exposure --- the PENETRATING POWER of the x-rays |
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What is termed the "technique"?
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selection of the kVp and mAs for a radiographic exposure
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What are the 3 possible fates of a single x-ray photon when it enters a patient's body?
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1) COMPLETE TRANSMISSION - passes straight through p and results in a black speck
2) COMPLETE ABSORPTION - strikes an e' in the p and all of the E is consumed. NO black speck. 3) SCATTER - strikes an outer shell e' in the p's body and is diverted from path. May travel out or strike a part of the film creating a black speck in a different location. |
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What is the enemy of radiography?
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Scatter radiation. It reduces radiographic contrast (incr gray, decr b/w). Degrades the usable image.
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What 3 factors affect the production of scatter?
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1) SIZE of the COLLIMATED FIELD of the primary x-ray beam
2) kVp -- CONTROLS CONTRAST. Higher kVp creates more scatter! 3) THICKNESS of the body part. Thicker = more scatter. |
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What is a techniques chart?
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A table with predetermined x-ray machine settings that enables the radiographer to select the correct machine setting based on the thickness of the tissue and anatomical portion of the body to be radiographed.
*Every machine is dif and a chart must be made for every machine, for ea body part* |
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Flow chart for dev of technique chart?
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1)select model dog
2)x-ray machine, set tube film distance dep on mA 3)cassette and film 4)grid 5)darkroom processing 6)test exposure 7)test - underexposed 8)test - overexposed 9)correct exposure 10) rules |
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What are rule of 2's, 3's and 4's?
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To create a complete abdominal chart for each cm of body thickness:
-add 2 kVp up to 80 -add 3 kVp up to 80-100 -add 4 kVp over 100 |
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What is a grid?
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A thin plate composed of hundreds of alternating thin lead strips with aluminum or fiber interspaces focused at the x-ray beam anode.
-Placed directly in front of the cassette |
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What is the purpose of a grid?
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-To increase contrast of the film by reducing the amount of scatter radiation that hits the film
-The thin lead septa placed b2n p and film are focused to the anode, so they allow primary x-ray photons traveling along their original path pass. Scattered photons, originating in the patient, travel in other directions and many will be absorbed as they hit the lead septa obliquely. |
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When should a grid be used?
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Anytime a body part over 10cm is radiographed.
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Does the use of a grid affect technique settings?
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YES! Since some x-rays are absorbed by the grid, fewer x-ray photons can make the image. More photons are needed so you need to increase the mAs.
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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.
Effected by the grid ratio. A BF 3 means that the mAs must be 3 times higher to achieve the same film blackness. **The kVp does NOT change! |
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What is the "grid ratio"?
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The height of the lead strips divided by the distance between them.
Commonly 5:1 BF 2, 8:1 BF 3, 12:1 BF 4 |
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What are intensifying screens?
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Thin sheets lining the inside of a cassette which emit visible light when struck with x-ray radiation. The film is sandwiched between these screens.
***They decrease the amount of radiation the patient is exposed to (mAs can be 1/10 of what would be needed w/o one) -produce many light photons for every x-ray photon that hits. **Rad film is actually exposed by VISIBLE light NOT x-rays |
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What is the down side to intensifying screens?
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Radiographic detail is slightly reduced.
-bc light photons diffuse a small distance from their creation point in the screen -the more efficient a screen is at producing light from a certain amount of radiation (the "speed" of the screen), the more loss of detail -i.e. the faster the film/screen comb (the lower the rad exp needed to prod a useful image), the more loss of fine detail in the image |
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What is radiographic film made of?
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A sheet of plastic with a coating of photographic emulsion -- SILVER HALIDE CRYSTALS.
Sensitive to light and x-rays. Altered by excitation of electrons. In development, silver ions in exposed crystals convert to METALLIC SILVER WHICH IS BLACK! |
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What is the "speed" of a rad film?
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-Ability of film to make an image from a certain # of x-ray photons
-greater ability to do this, greater spd -Faster speed film has larger crystals -tradeoff for incr speed = DECR detail **combination of the FILM AND the SCREEN! can be changed by changing the film or the screen or both. |
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What is film "fog"?
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An increase in background film density (blackness) due to exposure of film to extraneous light and x-rays
-reduces contrast |
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What are sources of film fog?
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-light leaks in the dark room
-improper safelight intensity, distance or filter color -loaded cassettes placed too close to the x-ray beam when not being used -high heat and humidity -pressure -exhausted (old) developer soln |
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What identification needs to be on a radiograph?
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Permanently imprinted with
-Hospital name -date -owner -animal ID Can use: -photoprinter -lead letters -x-rite tape |
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What does optical density mean?
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Film blackness
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What controls optical density?
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The number of photons that hit the film.This is determined by:
-mAs (MAJOR) -focal distance (focus-film distance) -kVp -subject density |
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What is the major determinant of film blackness/optical density?
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mAs
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What is the inverse square law?
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mAs new = (FFD new)sq
------------------------------------ mAs orig = (FFD orig)sq so moving away will will result in fewer photons hitting the film. Changing the FFA acts just like changes the mAs. But beam intensity changes with the square of the distance. So decr the focal distance to 1/2 of the original acts like 4X the mAs. **kVp does not change! |
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How does kVp affect film blackness?
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Increasing will increase the # of x-rays getting through the patient to expose the film.
If periphery is black but the body part is too light, kVp needs to be increased. Corrections usually 10-15% (mAs 100%) |
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What is the heel effect?
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The phenomenon in which the x-ray beam is of lower intensity (fewer photons) on the side of the beam toward the anode (away from the cathode).
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Why does the heel effect happen, what does it look like, is it apparent on all films, and how do we use this info?
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Why: x-rays are absorbed as they pass through the anode metal, so fewer photons are avail to make the film black on the anode end.
Film will be slightly lighter (less black) on one end than the other No, Most apparent when a low level of exposure (low kVp&mAs) is made on a long, thin body part When rad a part that is thick on one end and thin on the other, place the thicker end toward the cathode to make the relative exposure even. |
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What is contrast?
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How much black and white
High contrast = low latitude with black and white and few shades of gray. |
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What is latitude?
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How many shades of gray
High latitude = low contrast with many shades of gray. |
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Guideline for contrast?
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Orthopedic rads: highest contrast
- low kVp, high mAs Thoracic rads: lowest contrast - high kVp, low mAs Abdominal rads: in between To increase contrast w/o changing overall exposure: -decr kVp by 10-15%, double the mAs and vice versa |
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How is contrast adjusted?
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kVp!!! and mAs
Higher kVp produces more scatter, more scatter = less contrast. mAs must be adjusted to counterbalance this effect. |
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What are the 5 basic radiographic opacities?
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-Air (gas)
-Fat -Soft tissue (solid and fluid filled look the same!!) -Mineral (or bone) -Metal |
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What is needed to ID the true shape and orientation of a 2D version of a 3D object? (loss of depth perception)
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A minimum of 2 rad projections
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What is summation?
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When 2 structures overlay the same path of the x-ray beam and DO NOT TOUCH each other, their radiopacities will COMBINE while PRESERVING VISIBILITY OF THEIR INDIVIDUAL MARGINS
ex, kidneys on a lateral view like a vin diagram |
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What is silhouette sign?
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AKA "border effacement," this sign is in direct contrast to summation. When two structures of the same radiopacity are IN CONTACT (touch), their MARGINS CANNOT BE DISTINGUISHED
ex. Heart with attached lung mass. Looks like a snowman. |
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What causes distortion in rads?
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It is the artificial change in shape of an image due to one aspect of the object being a different distance from the cassette than another aspect.
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What happens if the object is elevated (evenly)?
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Magnification and blurriness
think shadows smaller sharper object is the one closest to the cassette |
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What are the rules for naming rad projections?
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-base on the PATH of the x-ray beam, ENTRY and EXIT surfaces
-proper descriptive VET anatomic terminology -exception with lateral views, ok to just say Left lateral if in left lateral recumbency with cassette beneath, etc |
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Common rad projections for extremities
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CrCd or CdCr - if proximal to the antebrachiocarpal joint
DPa or DPl - distal to antebrachiocarpal joint |
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What are radiographic findings?
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What YOU SEE!
-identification and description of abnormalities within the patient you can evaluate a structure's: -size -shape -number -location -margination -opacity ex: The left atrium is enlarged. |
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What is radiographic diagnosis?
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What YOU INTERPRET. The DISEASE or name of the lesion.
ex. Mitral valve insufficiency (likely due to endocardiosis) or can be a list of ddx's |
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What is the first step in classifying a radiographic artifact?
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Decide if the error is focal in location or general throughout the film. Next, note if it is + density (black) or - density (white)
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What can cause general artifact - dark film?
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Overexposure:
-incorrect settings (too high, too long) -decreased FFD -using faster film-scree combo -mismeasurement -surge in incoming voltage Over development: -incr dev time -dev temp too high |
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What can cause excessive fog - add'l unwanted darkness which causes gray film with overall loss of contrast and detail?
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-Fog, due to light leaks
-Fog due to scatter radiation -Chemical fog (exh dev or incr temp) |
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What can can cause general artifact - light film?
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Underexposure:
-incorrect machine settings (too low, too short) -lengthened FFD -slower film-screen system -mismeasurement -failure to hold exposure switch closed for length of exposure time Underdevelopment: -dev time too short -too low dev temp -exhausted dev -2 films in one cassette grid cutoff |
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What can can cause general artifact - loss of contrast?
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-fog
-failure to use grid -film exposed to back scatter -film out of date -improper storage -combo of dev time too short and temp too high -dev exhausted, contam, dil -comb overexp and under dev -film-screen combo |
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What can can cause general artifact - loss of detail?
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-patient, tube, or cassette in motion
-incr obj-film distance -beam not perp to cassette -poor film-screen contact -fast screens with lg crystal sz |
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What can can cause localized artifact (black artifacts)?
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-dev splashed on film
-scratch -bending -static -exposure of edge of film to light while being stored or while in cassette |
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What can can cause localized artifact (white artifacts)?
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-fixer or water splashed on film prior to dev
-FO on screen (screen artifact) -film not dev bc stuck to other film or wall of tank -crystals not red bc of air bubbles next to film while in fixer soln -emulsion scratches -poor film-screen contact -solarization artifact |
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What are grid artifacts?
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Heavy parallel lines across the rad.
-inverted grid -not centered properly -used outside of its focal range -off-level -upside down |
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What are the 4 stages of film development?
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1) DEVELOPED in developer soln
2) FIXED in fixer soln 3) RINSED in water 4) DRIED |
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What is the purposed of the developer soln?
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To reduce all silver atoms within the exposed silver halide crystals to metallic silver atoms (which are black)
-can also occur in unexposed crystals, so goal is to remove from developer when exposed ones have developed but before unexposed have |
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What 3 factors affect the amt of development (i.e. film blackness achieved by the dev process)?
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1) TIME the film spends in dev soln
2) TEMP of dev soln 3) CONC of dev soln Given a certain temp, the film should dev for a fixed length of time. *Higher temp = less time needed* |
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What is the purpose of the fixer soln?
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To STOP the development process (maintain rad contrast) and REMOVE the undeveloped emulsion
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What are the risks with radiation?
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A form of ionizing radiation that wan cause MALIGNANT CANCER and GERM CELL MUTATION
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What does the ALARA principle suggest (3 variables)?
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"As Low As Reasonably Achievable"
1)Reduce TIME you are exposed 2) Increase DISTANCE you are from the radiation exposure (inverse square law) 3) Maintain protective SHIELDING b2n yourself and the radiation source |
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What unit is used in rad safety for describing radiation exposure to the indvl?
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The Rem (old) or the Sievert (SV, new)
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What are the advantages of digital radiography?
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-prompt image viewing (improves quality control)
-improved patient throughput -ability to perform image processing (such as grayscale optimization) -ability to perform digital measurements -automatic filing -automatic image backup -enhanced ability to perform remote consultation -electronic distribution |
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What are the disadvantages of digital radiography?
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-$$$
-technical expertise requirements -pot'l for increased rad exposure to workers and patients (dose creep) |
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What are the methods of digital image acquisition?
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-Computed radiography (CR)
-digital radiography (DR) -charge coupled device (CCD) |
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What is CR?
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-x-rays interact with a PSP detector
-the detector is read in a machine analogous to film dev *DA bc prolongs time -machine creates a digital image, which is a matrix of grayscale values for ea pixel |
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What is DR?
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-x-rays interact with excitable molecules in the detector elements of the flat panel plate.
-this prod an electrical current that is converted directly into a digital image -the image can be viewed seconds after exposure and the plate can be removed from the table |
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What is CCD?
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-x-rays interact with fluorescent detectors that give off light which is focused through a lens and then captured by the CCD chip
-similar to DR, the image can be viewed seconds after exposure -also used on digital cameras -can have image degradation, esp in thicker parts "veiling glare" -detector cannot be removed from the table |
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Which digital image system has the best image quality?
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DR is best, but they tend to be more expensive.
Diagnostic image quality can be reached with all of them. |
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What is the benefit of digital image processing?
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-improved lesion conspicuity
-radiographic viewing efficiency -automated image optimization no need for manual adjustment (bright light) -automatic trimming less need for zooming and roaming -improved lesion detection vs false positives |
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What is ultrasound?
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Ultrasonography is an imaging modality based on the interaction of ultrasound with tissues.
Ultrasound is the acoustic energy with a frequency above human hearing (20khz) |
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What is the piezoelectric effect?
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Makes US possible.
-Electricity interacts with a crystal producing ultrasound. -The US interacts once more with the crystal producing an electrical current that is used to construct an image based on the magnitude and timing of the electrical signals. |
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What are the advantages of US?
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-eval of fluid and soft tissue structures
-eval of blood flow, real-time movement, guidance of needles -uses no ionizing radiation -widely available -relatively inexpensive -portable -typically w/o anesthesia -non-invasive -cross-sectional imaging modality -images become part of med rec |
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What are the disadvantages of US?
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-accuracy highly dep on competency of the USer
-takes a great deal of time, effort, and mentorship to master -limited in regions with mineral or gas and in large patients due to limited penetration of the US beam |
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What does US provide information about?
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Number
Size Shape Location Margination Position Echotexture Echogenicity |
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What is echogenicity?
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Relative brightness or darkness of a tissue or organ
-typically used to compare one organ to another or to compare an organ to the ultrasonographer's subjective opinion of normal |
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What is speckle pattern?
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The inherent "texture" of tissue displayed in the image.
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How can you differentiate images made by a CT from an MRI?
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CT = cortical bone is white
MRI = bones are black |
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What are the advantages of CT vs MRI?
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CT
-superior spatial resolution -improved detail of cortical and trabecular bone -less time to perform -less expensive -eliminates problems asso with summation -provides excellent eval of bones, lungs, nasal cavity -fair eval of soft tissue structures MRI -excellent for soft tissue lesions (much better than CT) -good not great for bone lesions -no ionizing radiation |
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What are the disadvantages of CT vs MRI?
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CT
-inferior soft tissue contrast resolution -high dose of ionizing radiation -anesthesia -limited availability -field of view limitations -cost MRI -anesthesia -spatial resolution < CT -limited availability -field of view limitations -COST!! -lack of data correlating findings to clin dz |
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CT vs MR soft tissue contrast resolution?
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MR
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CT vs MR spatial resolution
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CT
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CT vs MR eval of bones
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CT
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CT vs MR time req for study
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MR takes longer
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CT vs MR exposure to ionizing radiation
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CT
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CT vs MR field of view limitations
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MR slightly more limited, both though
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CT vs MR
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CT $$ MR $$$$
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What is CT?
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an x-ray based imaging modality in which a computer creates a slice based (tomographic) image based on numerous x-ray projections.
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What is attenuation?
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The brightness or darkness on the CT image
Can be quantified in terms of Hounsefield units Brightness or darkness is relative so "hyperattenuating" or "hypoattenuating" should be used when comparing two structures to one another or comparing an organ or tissue to know normal values |
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What are Hounsfield units?
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quantify attenuation
higher = tissues with higher x-ray attenuation, such as bone these appear brighter on the image Lower = lung or fat, appear darker on the image |
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What is window width?
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the range of Hounsfield units displayed in an image, these are analogous to the contrast and brightness controls on a TV monitor
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What is window level?
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The mean value of Hounsfield units displayed in an image.
Window width and level can be adjusted to optimize eval of bone (bone window) or soft tissue (soft tissue window) |
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What is MR?
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a tomographic imaging modality based on the relaxation properties of tissues.
A strong magnetic field is applied to orient the hydrogen atoms within the patient parallel to the field These atoms spin or precess at a known freq Radio waves at the same freq interact with these atoms in a resonance phenom causing them to absorb the rel energy. The process of energy release is termed "relaxation" The released energy is captured and converted into an image through a series of complicated math computations. By modifying the timing of radio wave appl, images can be "weighted" to emph diff tissue relaxation characteristics |
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What is signal intensity?
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The relative brightness or darkness on MR images.
High signal intense (hyperintense) = bright white |
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What is nuclear scintigraphy?
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A radiopharmaceutical is given, which may have a specific target.
A gamma camera detects emitted photons. A computer converts data into an image. Movement through the body can be observed real-time |
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What are the disadvantages of scintigraphy?
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-limited availability
-poor spatial res -use of ionizing radiation -animals must remain in radiation isolation until they are cleared |
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What are the clinical applications of scintigraphy?
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-bone scans
-thyroid scans -scintigraphic determination of GFR -dx of portosystemic shunts -pulmonary perfusion imaging |
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What is the skyline view?
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A type of oblique view, made in a proximal to distal direction.
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What is the stressed technique?
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Indicates applying stress to a joint in an attempt to angulate, hyperflex, hyperextend, or rotate the alignment of the joint
-used to indirectly assess the integrity of the supporting soft tissues of the joint |
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What is the flexed technique?
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-flexing the joint allows other osseous surfaces to be exposed
-common in LA, esp eq carpus |
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What is the weight bearing technique?
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-the p is standing and placing some weight on the limb
-allows assessment of the joint space size -common in LA |
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What is the non weight bearing technique?
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-the p is in a recumbent position
-the jt space sz cannot be evaluated -common in SA |
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What is a compression view?
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-made by placing a radiolucent paddle over the area of interest
-aids in removing various overlying soft tissue planes -can also be used to move small animal phalanges closer to the cassette/imaging plate |
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What is a cross table?
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-denotes using the x-ray beam in a horizontal direction to obtain a "standard" view, on a recumbent patient
-ex: to obtain a cr-cd view of a femur on which remained in laterally recumbent position |
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What is an epiphysis?
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end or ends of a long bone, often forming the articular portion of a long bone
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What is a physis?
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the growth plate of a long bone; resides b2n the epiphysis and the metaphysis
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What is a metaphysis?
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the often wide part of the bone residing b2n the physis and the diaphysis
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What is the diaphysis?
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the longest central portion of the shaft of a long bone; resides between the proximal and distal metaphyses
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What is the apophysis?
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A portion of some long bone, often residing near the end of the bone, which has its own growth center, but does not contribute to the growth in length of the long bone; only a few long bones have an apophysis, e.g. a process, a tubercle, or a tuberosity
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What is the periosteum?
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The fibrous osteoblastic layer of cells forming a membrane over much of the cortical surface of a long bone; this tissue is too think to be normally distinguished rad'lly.
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What is the nutrient foramen?
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a small hole through the cortex of a bone, allowing for the penetration of an artery into the medullary cavity of the bone.
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What is the articular cartilage?
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The cartilage on the articular surface of the epiphysis of a long bone
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What is the "joint space"?
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an apparent space rather than an actual space; appears to be a "space" bc the adjacent articular cartilages, the intervening jt fluid, and the peri-articular soft tissues are all the same radiographic opacity (i.e. fluid or soft tissue), and thus a radiographic "silhouette sign" results (i.e. the artic carts, fluid and peri-artic soft tissue become indistinguishable from ea other, mimicking a "jt space")
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