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124 Cards in this Set
- Front
- Back
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What is the purpose of of a technique chart?
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To provide a CONSISTENT way of setting the proper exposures for a diagnostic radiograph.
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Are technique charts AHAA required?
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Yes
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How is a technique chart made?
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A trail and error method that is necessary for each x-ray machine as they all differ somewhat. A radiology log is a key component of keeping track of radiographs and setting up the technique chart according to what worked per the log.
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What is a suggested method for starting a technique chart?
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1) Select a medium size dog or cat with an abdominal measurement of 8-10 cm.
2) Use a trial setting of 65KV at 2.5 mAs 3) Use shortest possible exposure time 4) Write down what worked for that animal and write settings that are proportionate for a larger or smaller animal |
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What is the suggested kVp range for extremities?
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55-65 kVp
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What is the suggested kVp range for abdominal radiographs?
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65-85 kVp
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What is the suggested kVp ranges for the thorax?
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75 - 95 kVp
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When developing a technique chart, a variety of formulas may be used. What are some factors to take into consideration?
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Tissue thickness
grid factor screen type |
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What is a caliper?
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Tool for measuring, in centimeters, the thickness of area to be radiographed for appropriate technique to be developed.
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When measuring for an elbow radiograph, what area should be measured with the calipers?
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the distal humerous, thickest part
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When measuring for a radiograph of the radius/ulna, what area should be measured with the calipers?
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Elbow
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When measuring for a radiograph of the stifle, what area should be measured with the calipers?
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distal femur
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When measuring for a radiograph of the tibia/femur, what area should be measured with the calipers?
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stifle
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When a caliper measurement is less than 10 cm, film tray should be located where?
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Table top
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When a caliper measurement is GREATER than 10cm, the film tray should be located where?
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In the bucky tray
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Why should we know the anatomy of the x-ray machine?
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*So faulty equipment can be detected
*To know when it is necessary to call a repair person *So we can explain to repair person what the problem is * Knowledge of machine helps you understand sales reps *AVMA & National boards questions * To be able to adjust technique |
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What are the 4 types of x-ray units?
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*CONVENTIONAL-large unit with a wide variety of settings (Bel-Rea)
*MOBILE-settings of 100-300 mA, & up to 120 kVp. (Equine) * MOUNTED:may have capacity up to 1000 mA (Dental) * SMALL PORTABLE: Easy to transport, limited to , limited to 20 mA & 90 kVp, Needs long exposure times |
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What are the 5 elements needed for x-ray production?
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1) Source of electrons generated at the cathode.
2) Means for ACCELERATING the electrons (Filament heated, kVp forces electrons across) 3) Free path for passage of high-speed electrons 4) A Target in which the electrons can interact -focal spot on anode 5) A containment area that contains a vacuum |
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What are millamperes?
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A measure of the electron current to the filament, which has a direct relationship to the number of x-rays produced.
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What are milliamperage-seconds (mAs)?
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the number of x-rays produced over a given period. Calculated by multiplying the milliamperage by the time
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What is kilovoltage?
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Related to thousands of volts. Describes the electrical potential (difference) between the cathode and anode. It is responsible for accelerating the electrons from the cathode to the anode and relates to the penatrating power of the x-rays.
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kVp is defined as
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Another term for kilovlatage. Kilovoltage PEAK indicates the maximum energy available at that kilovoltage setting.
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the Higher the kVp
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the faster the electrons are accelerated which increases the energy of the x-rays produced at the electron collision with the anode target.
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What kind of effects does changing the kVp have?
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*Changes the penetrating power of the x-ray beam.
*When kVp is raised, new, shorter wavelength x-rays are produced. * Higher kVp settings produce more penetrating beams, with a higher percentage of radiation reaching the film |
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Higher kVp settings allow for lower
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mAs settings, which generally calls for shorter exposure times
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What is Santes' rule?
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A method of estimating kilovoltage in relation to area thickness. It is a formula
(2 X thickness in centimeters) = kVp |
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What is the function of the cathode?
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It provides the source of electrons by the heating of a filament, which excites electrons, generating an electron cloud, making them available to the anode.
--->Amount of energy generated is called MILLIAMPERAGE --->Acceleration is called KILOVOLTAGE (KV) |
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What is the function of tungsten in an x- ray machine?
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The filament is constructed of this because of its high melting point and high atomic number. (# of protons in the nucleus of an atom)
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What is the function of the anode?
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This is the part of the machine that is bombarded with the electrons that are generated from the cathode. There are 2 types, stationary and rotating.
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Explain stationary anodes
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A fixed anode that heats up more quickly and unable to withstand large amounts of heat.
*found primarily in dental and small portable machines *biggest disadvantage- limits mA to 100 |
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Explain rotating anodes
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**Shape of a disc in the center of the tube
*composed of tungsten *provides a cooler surface for the electron stream *rotating disc distributes heat over a larger area yet still provides a small spot *rotating anode capabilities are up to 1600 mA (versus 100mA on stationary) |
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What is the focal spot?
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It is the small area of the target where electrons collide on the anode.
-Target is usually angled at about 20 degrees from vertical in an x-ray tube -intensity of the x-ray beam can be changed by altering the angle of the target. |
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What is the heel effect?
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If the anode angle is DECREASED, the intensity on the anode side of the x-ray beam is also decreased---> therefore more x-rays leave the x-ray tube on the cathode side than the anode side causing a variation in exposure to the x-ray film.
--->Less angle--lighter --->more angle--darker |
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What is the penumbra effect?
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*partial outer shadow of an object being imaged by illumination--like a halo.
*having a smaller focal spot produces a smaller penumbra and therefore a sharper image. |
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What are some possible areas of tube failure?
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*cathode/filament failure
*anode failure *anode target failure *glass envelope failure *tube housing anomalies |
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Cathode failure/ filament failure is the most common area of tube failure and these involve:
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*Amount of use. Higher temps and longer length of time in use increases chance of failure.
*No filament=no electrons can be produced=no exposure on film (transparent film results). * if filament has evaporated, no electrons are produced and there will be no movement of the mA. |
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What is the function of the rotor?
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*Prolongs the life of the filament by preheating at a low heat when machine is on
* filament is not heated to sufficient temp to produce an electron cloud until the rotor button is depressed. *Rotor must be sufficiently warmed up before exposures can be taken. **In addition to pre-heating the filament, the rotor also rotates the anode disc for the oncoming electrons. |
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Anode failure can be attributed to
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*damage to target from excessive heat exposure results in a roughening of focal spot on anode, therefore x-ray beam is not uniform and exposures and film density will vary from use to use
--noise on rotating disc will change when bearings wear out, a failed anode will result in no noise being present when pre-exposure button is pushed when the bearing have failed. -->higher kVp and lower mA on the settings can be used to help prevent |
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What is the glass envelope and its functions?
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it is the glass housing for the anode and cathode with the x-ray tube.
*is a glass vacuum tube * Air within the glass tube will interfere with the electrons |
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What is arcing within the glass tube?
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Refers to overheating of the target resulting in metal deposits that act as a secondary anode that attracts electrons from the cathode.
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What are are tube housing anomalies?
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*If glass envelope shifts within the metal housing, the anode target area will be out of alignment with the window, causing a partial exposure.
*oil leak can cause overheating of the bearings and leads to destruction of the tube |
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There are 2 circuits in an x-ray machine, what are they?
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High voltage and low voltage
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What is the action of a low voltage circuit in an x-ray machine?
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*heats up the filament
* the hotter the filament, the more electrons that are produced. *is Measured in milliamperage (mA) |
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In radiology, what is S an abbreviation for?
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time
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What are some important characteristics of mA?
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*it is the energy used to heat up the filament, thus providing more electrons to the anode, thus creating more x-rays. mA is directly involved with time .
* mA x S = mAs |
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The higher the mA, the lower the____
and conversely, the lower the mA, the higher the ____. The shorter the time, the more safe it is for the patient and restrainer. |
S (time)
S |
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The second circuit of the x-ray machine is the high voltage circuit. It has the following properties:
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* Speeds up the electrons
*Sends/propels the electrons from the filament to the target * High voltage is measured in kilovoltage kV or kVp |
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What is the driving force, penetrating power, behind x-rays?
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kVp
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Penetration power of x-rays is linked to
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More electrons --->more energy ---->
----->more x-rays = more penetration |
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What is absorption in relation to x-rays?
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It is the # of x-rays that do not go through the item being x-rayed. They are retained, absorbed by patient.
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What is the definition of a radiograph?
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A visible photographic record on film produced due to the passage of x-rays through an object or body.
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What is the purpose of a radiograph?
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To study inner structures as an aid to diagnosis
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What is the objective of radiography?
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To obtain a radiograph with the best diagnostic info with the least amount of radiation possible.
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What is ionizing radiation?
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radiation capable breaking down body molecules
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What are the 5 tissues most sensitive to ionizing radiation?
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Gonads
thyroid lens of the eye skin & intestinal epithelium blood-forming organs |
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What is primary radiation?
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Radiation from the primary beam
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What is secondary radiation?
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Scatter radiation produced from primary beam interacts with objects in its path
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What is background radiation?
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made up of cosmic rays, sunlight, lights
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What are the 4 beams and rays we are most concerned with in radiography?
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* Primary beam
* Central ray * Primary ray * Secondary rays |
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What is the primary beam?
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A group of rays that make up the beam
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What is the central ray?
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The central most ray
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What is the primary RAY?
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rays on either side of the central ray that makes up the primary beam
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What are the secondary rays?
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rays that don't contain enough energy to pass into the object--- scatter results from these
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What are beam filters?
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they filter out the beams with longer wavelengths
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What are 2 beam limiting devices?
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Cones and collimators
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A cone is a beam limiting device that
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slides on the tube underneath the filter to limit the size of the x-ray beam, concentrates the size of the beam and limits it
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A collimator is a
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lead shutter beam limiting device that adjusts down to decrease the size of the beam. Wide open is 17" x 17"
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What are the advantages of collimation?
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* Decrease amount of radiation to the patient and the radiographer/restrainer
* The smaller the size of primary beam , the BETTER DETAIL on radiograph |
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Detail in radiography refers to:
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Sharpness & Clarity on a radiograph
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Object Density in radiography refers to:
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The density of the object that affects the amount of radiation that penetrates subject being radiographed.
* More density-->less penetration =white on film ex-bones ***conversely--- Less density-->more penetration = black on film ex: air |
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Contrast in radiography refers to:
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*Differences between 2 densities of adjacent structures/areas
*short scale contrast *ex-bones versus abdominal structures |
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What is the purpose of x-ray film?
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To provide a permanent record that contains vital diagnostic information
*Usually kept for 7 years past death of patient or 7 years past when they are no longer a patient at that clinic |
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What are the 2 parts of the x-ray film?
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* BASE - a transparent polyester that provides flexible support
* EMULSION - a geletin suspension of silver halide crystals that coat the film evenly |
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What is silver halide composed of?
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It is a compound made up of silver and either bromine (most common), chlorine or iodine.
**Silver bromide crystals are most common type of silver halide crystals |
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In regards to film sensitivity, sensitivity refers to
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how sensitive the film is to x-rays and therefore how sensitive the silver halide crystals are
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In regards to film sensitivity, the film can be sensitive to which spectrums of light?
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Blue or green
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In regards to film sensitivity, the more sensitive the film, the __________ the speed of the film.
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faster
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Fast film tends to be used for ______,
has _________ silver halide crystals, requires less exposure to x-rays and has increased __________ but produces film with poorer detail. |
body cavities
larger sensitivity |
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Slow film tends to be used for ______,
has _______ silver halide crystals, needs more x-ray exposure, has decreased sensitivity and produces greater detail than faster film. |
bones and joints
smaller |
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What speed film is most commonly used?
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Medium speed
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When a crystal changes on an x-ray film, does the whole thing change?
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yes
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Qualities of slow speed film:
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* Increased film detail
* Increased amount of radiation used * decreased sensitivity to radiation * decreased crystal size |
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Qualities of fast speed film:
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*Decreased film detail
* less radiation needed/used * increased sensitivity to radiation * increased crystal size |
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How should film be stored?
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*in a vertical position
**DARK, COOL, DRY** * at 10 - 15 degrees Celsius * Humidity at 40-60% |
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Film is least sensitive to _____light and most sensitive to _____ light.
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red
white |
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What is the purpose of film holders?
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* To protect film from being exposed to white light
* To protect film from being scratched or bent |
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What are two types of film holders?
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Cassettes
cardboard |
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What are 4 ways to INCREASE/affect radiographic density?
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1) Increase # of x-rays that reach film (increase mA)
2) Increase penetrating power (increase kVp) 3) Change developing time, long enough? 4) Temperature of developer can affect |
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5 ways to affect radiographic contrast
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1) Object density needs to be taken into consideration at set-up
2) Adjust kVp 3) Scatter radiation needs to be controlled 4) Film speed use will affect 5) Film fog can affect (a darkroom artifact) |
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What is an intensifying screen?
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A part of the cassette that is composed of sheets of luminescent phosphor crystals that are bound together. Purpose is to reduce the amount of radiation exposure necessary to produce a radiograph.
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What is the purpose of intensifying screens?
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Thye convert x-rays into visible light when the phosphor crystals fluoresce when struck by x-rays and produce visible light.
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What are the 4 parts to an intensifying screen?
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* base support-cassette holder
* Reflective layer - bounces light back to film * Phosphor crystal layer-causes fluorescing *protective coat |
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What are 2 types of screen crystals?
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* Calcium tungstate screens
-invented by Edison in 1896 - Emits lights in blue spectrum - does NOT convert light very efficiently *Rare Earth phosphor Screens -More efficient -Has a significantly greater x-ray to light conversion -Emits light in the green OR blue spectrum -Advantage: reduced radiation dose |
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What are screen speeds?
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Refers to screen's ability to convert absorbed x-ray energy to visible light.
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What qualities do cassettes with fast screen speeds have?
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Less exposure time needed
Has larger crystals Poorer detail radiographs More efficient at light conversion |
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What qualities do cassettes with Slow screen speeds have?
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More exposure time needed
Has Smaller crystals Better detailed radiographs Less efficient at light conversion |
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What cassette screen speed is most commonly used in practice?
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Medium
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What are the layers of a cassette?
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CASSETTE TOP
-top padding -intensifying screen ***FILM*** -intensifying screen -bottom padding -lead foil cassette bottom (clips) |
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What is radiographic density?
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The degree of blackness or darkness on a radiograph. This is different than object density which refers to the density of the object being radiographed, which has an effect on radiographic density. More object density means less radiographic density.
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What is a grid in reference to radiography?
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It is a device made of lead strips embedded in a spacing material, placed between the patient and the film, designed to absorb non-image forming radiation.
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What is a grid cutoff?
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a progressive decrease in transmitted intensity caused by absorption of primary x-rays by the grid lines.
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What is grid efficiency?
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Ability of a grid to absorb non-image forming radiation in the production of a quality radiograph.
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What is grid factor?
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The amount the exposure needs to be increased to compensate for grids absorption of a portion of the primary beam.
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What is grid focus?
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The distance between the source of x-rays and the grid in which the grid is effective without grid cutoff.
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What is grid ratio?
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Relation of height of lead strips to distance between them.
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What is backscatter?
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Rays that bounce off film holder or table after penetrating patient.
**Grids are used to reduce this |
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A grid is a device that
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sits between the patient and the film on top of the cassette or may be built into the cassette.
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Grid composition refers to
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the pattern of lead strips and spacer material. Can be linear or cross patterns
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What is the most common lead strip to spacer ratio?
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8:1
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For an 8:1 ratio on grid factor, it is recommended that you increase mAs by ____ or increase kVp by _____.
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3-4 times
15 |
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Moving grid was invented by
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Dr. Bucky
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Radiographic quality is dependent on what 3 qualities?
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*Density
*Contrast *Factors affecting detail |
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What are the 5 main object densities?
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* Air--black
* Fat- white to light gray * Tissues of water density-shades of grey * Bone- white * Enamel & Metal -white |
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What are 4 factors that affect radiographic density?
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*mA
*kVp *Object density *thickness and type of tissue |
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What are 4 ways to increase radiographic density?
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* increase mA
* increase kVp * increase developing time * increase temperature of developer |
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What is radiographic contrast?
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The varying shades of gray on a radiograph-density difference between 2 adjacent areas on a radiograph
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What 5 things influence contrast?
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* Subject contrast/object contrast
* kVp *scatter radiation * film type, speed * film fog ( developing artifact that can be caused by too much red light and electrical equipment next to film. |
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What are 2 types of contrast?
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*Short scale contrast (high contrast) -white to black'
*long scale contrast- (low contrast) shade of grey |
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What are 3 causes of decreased radiographic detail?
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1) geographic unsharpness
2) Geometric distortion 3) radiographic noise |
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In regards to decreased radiographic detail, geometric unsharpness refers to:
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-fog (fuzziness) on a particular area of a radiograph caused by:
-poor screen/film contrast & contact -Focal spot size - focal film distance - Motion -geometric distortion |
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In regards to radiographic detail, geometric distortion refers to:
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A variation in normal size and shape of anatomical structures due to their position in relation to x-ray source and film.
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In relation to geometric distortion on a radiograph, what is elongation?
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Distortion of anatomical structures so that the image appears longer than the actual size owing to the x-ray beam not being placed perpendicular to film surface
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In relation to geometric distortion on a radiograph, what is foreshortening?
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Distortion of anatomical structures when the image appears shorter than actual size due to the plane of interest not being parallel to film surface.
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What is radiographic noise?
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*Graininess or artifact attributed to variations in density not associated with normal differences in desnisty between bone, air, fat, etc.
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