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191 Cards in this Set
- Front
- Back
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What is electromagnetic radiation?
What is the mass, charge and speed? |
the propagation of energy thru space as oscillating magnetic fields
m=0; c=0; speed=c |
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What is the relationship of energy to wavelength?
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inversely proportional
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X-rays and gamma rays have what type of wavelength and energy?
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short wavelength and high energy
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What is the speed of light equial to?
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c=frequency (v) x wavelength; they are also inversely prop.
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What is ionizing radiation?
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those types of radiation that have sufficient energy to cause ionization of medium thru which they pass
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What are the two types of ionizing radiation and what is the difference between them?
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Particulate: alpha and beta particles that have both mass and charge
Electromagnetic: x-rays, gamma-waves, and uv rays (NOT ALL em is ionizing) |
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What is the difference between x-rays and gamma rays?
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their origin
-gamma - rays: within nucleus of spontaneously decaying atoms -x-rays: from outside the nucleus by interaction of high speed, charged particles |
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What are the basic principles of X-ray production? (3)
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(1) Source
(2) Acceleration (3) Interaction |
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What are the basic components of an x-ray tube?
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Cathode end: glass tube, filament (in a focusing cup)
Anode end: target (focal spot) |
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What is the source of electrons in an x-ray machine?
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the filament (made out of Tungsen because it must be able to withstand high heat)
-part of the cathode |
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What is the process by which electrons are produced?
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Thermionic Emission: low voltage current is passed thru the filament and generates heat and releases a free electron cloud around the filament
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What keeps the electron cloud from dispersing?
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a focusing cup
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What causes electrons to accelerate?
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A high potential difference (voltage) is applied across the tube to pull the electrons toward the target.
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What is the potential different applied when creating a diagnostic range radiograph?
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40-140 kVP
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Where does interaction take place?
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at the target (specifically at the focal spot)
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Why must a vacuum tube be used (pyrex with lead shielding)?
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to prevent interaction of the electron beam with air atoms.
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What are the two processes by which interaction with the target produces X-rays?
Why is this important to know? |
-Transition (characteristic): more specific range
-Bremsstrahlung (general): broader range -X-rays cover a spectrum of energies |
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Is x-ray production efficient? What % is actually converted to x-rays?
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NO
-1%, the rest is heat |
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What is the major limiting factor in x-ray production?
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heat production
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The larger the actual focal spot....
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the greater the heat dissipation
AND greater X-ray output capabilities |
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The smaller the Apparent (effective) focal spot.....
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-the more enhanced is the detail of the image
BUT -limits x-ray output |
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What are the two types of anodes?
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-stationary: fixed target
-rotating: target rotates and filament is offset |
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What are the advantages of a stationary anode?
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-portable
-radiation therapy |
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What are the disadvantages to a stationary anode?
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-heat dissipation limits output capability
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What are the advantages to using a rotating anode?
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-better able to dissipate heat, therefore higher output
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What are the disadvantages to using a rotating anode?
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-low portability
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What is unique about the filaments of a rotating anode machine?
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-some have two filaments to allow a small and large focal spot
-smaller focal spot can provide greater detail, but have limited output capability -THEREFORE, the larger one is usually used |
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How is an x-ray beam characterized?
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(1) quantity: number of x-rays
(2) quality: energy of beam |
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What does quality of the beam mean?
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-the energy of the x-rays; the more energy, the better able to penetrate objects
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What is electron energy determined by?
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tube voltage (kV)
(the kVp selector) |
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If you increase kVP, what do you do to the x-ray beam?
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-increase energy
-secondarily increase number of interactions per electron |
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Quantity refers to what in an x-ray beam?
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number of X-rays in the beam
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What is number of X-rays in the X-ray beam determined by?
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(1) the number of electron interactions with the target
(2) the number of electrons |
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When dealing with quantity, what determines the number of interactions?
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kVp (tube voltage/energy of the electrons)
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When dealing with quantity, what determines the number of electrons?
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current thru the filament (mA Selector)
AND length of time electrons flow across the tube (timer) |
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When you increase mA, what are you doing to the electron beam?
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increasing number of electrons emitted
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What is mA and what does it control?
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mA is the current thru the filament and controls an aspect of X-ray quantity
-specifically controls number of electrons |
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What is kVP and what does it control?
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kVP is the tube voltage
-it controls both aspects of quantity and quality -controls energy of an X-ray beam and -controls # of electron interactions (minor) (quantity) |
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What does the exposure timer do?
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-controls the time that high voltage is applied to the tube - which controls the number of electrons - which thus controls number of X-Rays produced
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How do you get mAs?
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-the product of filament current (mA) and time (seconds)
-the higher the mA, the less time needed for exposure -the lower the mA, the more time needed for exposure |
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When going from a low mA, to a high mA, with kVp constant, what also increases?
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increase
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When going from a low kVp to a high kVp, what increases?
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-intensity (# of x-rays)
AND -energy (get a shorter wavelength) |
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Name some types of accessory equipment.
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-X-ray filters
-collimators -grids -grid artifacts -cassettes intensifying screens X-ray film |
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Where is a filter located?
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between the x-ray tube and the collimator; in the path of the primary beam
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What is a filter normally made out of?
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metal (aluminum)
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What is the purpose of a filter?
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-reduce skin dose to a patient by removing low-energy photons from the primary beam.
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What are the two classifications of X-ray filters? What is the difference?
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(1) inherent: glass tube and oil
(2) added: added metal (aluminum and copper) -both of these make the total filtration |
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What is the NCRP recommendation for X-ray filters?
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2.5 mm Al equivalence filtration for tubes operating above 70kVp
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Other than reducing the dose to the patient, what is an additional good thing that filters do?
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make a cleaner image
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Where are collimators located and what do they do?
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-located outside the tube housing and
-restrict the x-ray beam to a confined region |
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What form do collimators take?
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-fixed as a cone, cylinder, or diaphragm
-better collimators have adjustable shutters |
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What are collimators good for - why would you want to use them?
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-reduces exposure to patient by limiting area of irradiation
-improve image quality by reducing scatter (improves image contrast) |
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Why is scatter radiation bad for image quality?
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- they cause the film to look grey and reduces image quality by decreasing image contrast
-the larger the area, the more scatter |
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Where are grids located?
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usually below the table top of the x-ray unit
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What do grids do?
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absorb scatter radiation before they reach the film
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Any body part thicker than ___ should be using a grid.
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10 cm (the thicker the body part, the greater chance of scatter)
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Scatter radiation is the result of what?
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Compton interactions
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What are grids made of?
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hundreds of alternating lead strips
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Where does primary (not scatter) go? (think about grids)
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passes through the grid interspaces; scatter radiation will not be allowed to pass thru
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What is a focused grid?
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grids that have the lead strips aligned to the divergent pattern of the x-ray beam
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What is the grid ratio?
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height of the grid strip divided by the width of the interspace material
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What type of grid ratio is more effective at removing scatter?
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a high grid ratio
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What would you increase depending on what grid ratio you have?
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mA: have to increase mA with a higher grid ration because less x-rays are reaching the film (have to increase numbers)
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What is critical when using a grid? What happens if this is not done?
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-alignment of the x-ray beam with the grid
-grid cut-off occurs |
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T or F, the number of strips per inch makes a better grid.
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True (103 lines per inch is the BEST)
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What are two features of grid cut off?
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(1) underexposure
(2) accentuation of grid lines |
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What is a cassette?
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rigid, light-tight devices that hold the film in contact with the intensifying screen
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What will happen if the film is not touching the screen (the cassette is not doing its job)?
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loss of contact will result in a light spread that decreases detail
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What is the purpose of the intensifying screen?
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to convert the energy of x-rays into visible light; this light actually exposes the film and is much more efficient
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What do x-ray photons strike in the screen?
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the phosphor crystal - this emits a specific wavelength of light that exposes the film
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The efficiency of the screen is based on what three things?
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(1) thickness of phosphor layer (thinner is better)
(2) type of phosphor (3) size of the phosphor crystal |
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What is better: a ticker or thinner phosphor layer?
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thinner
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When talking about screens, what is the relationship between detail and sensitivity?
What is the measure of sensitivity? |
-inversely proportional
-how much radiation is necessary to expose the film (therefore higher detail will cost you more radiation) |
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What three broad categories are screens classified under?
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-high speed (400-1200)
-par speed (100) -fine detail (50-100) |
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What is screen speed used to define?
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the efficiency of conversion of x-rays to usable light
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What are low screen numbers used for? What is their disadvantage?
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detail, but require more radiation exposure
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Different screens will require an adjustment to what parameter?
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mA
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If your screen is low mA, what type of screen would you use?
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high speed screen
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Your technique using an 800 speed screen is 2.5 mAs. What is the new mA if you change to a 100 speed screen?
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20mAs
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What color will be emitted with the following:
Yttrium Tantalate Barium Lanthanum Gadolinium Calcium Tungsten |
Yttrium Tantalate - violet
Barium - blue Lanthanum - blue Gadolinium - green Calcium Tungsten - blue |
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What is the most important component of the film?
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the emulsion
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What is the emulsion on the radiographic film made of?
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-a homogeneous mixture that contains silver halide crystals
-95% is silver bromide (neg charge) -5% is silver iodide (neg charge) |
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What is a sensitivity speck?
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-a silver sulfide contaminate (pos charge) on the silver halide crystal
-area where the electrons are trapped |
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What happens when electrons are trapped at the sensitivity speck?
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Metallic silver (Ag) is formed
-it is black |
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What is the latent image center?
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-a small group of silver atoms
-developed into black grains during processing |
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What will a high contrast film have?
What will a long lattitude film have? |
-few shades of grey
-multiple shades of grey |
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Which form of radiation has biological implications?
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ionizing
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What are two forms of non-ionizing radiation we use?
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(1) Ultrasound
(2) MRI |
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What are three forms of ionizing radiation we use?
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(1) radiography
(2) computed Tomography (CT) (3) nuclear medicine |
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What are the three sources of your total radiation?
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(1) environment
(2) medical (3) occupational |
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What are three general sources of environmental radiation?
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(1) Cosmic
(2) Earth's Crust (external and internal radon) (3) Human-Made Exposure (TV, tobacco, computers, nuclear power plants) |
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Where is the greatest intensity of cosmic radiation?
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-N and S poles
-higher altitudes |
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What is the source of cosmic radiation?
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protons emitted from solar flares from sun
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What is the main source of radiation from the earth's crust?
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-thorium and uranium (gamma emitters)
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What is radon formed from?
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decay of uranium
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What is the second leading cause of lung cancer?
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breathing high concentrations of radon
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What is the primary cause of occupational exposure?
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accidentally having an extremity in the primary beam; lead does not protect from a primary exposure
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What is a secondary cause of occupational exposure?
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scatter from patient; lead shielding will help
Or tube leakage |
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What is the non-occupational general exposure dose limit?
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dose limit< 100 mrem/year
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What is the non-occupational medical exposure LD50?
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300-400rad (350,000mrem)
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What is the occupational exposure for the following:
-dose limit -hands/feet -fetus |
-dose limit: < or equal to 5 rem/year (5,000mrem/year)
-hands/feet: < or equal to 50 rem/year (50,000 mrem/year) -fetus: (must be declared) < 500 mrem for total gestation |
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What do the following stand for?
-rad -rem -Gy Si Bq |
-rad = radiation absorbed dose
-rem = roentgen equivalent man (or effective dose) -Gy = Gray -Si = Sievert -Bq = Becquerel |
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What is a rad used to measure?
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the amount of energy actually absorbed in tissue - DOES not desribe the biological effects of different radiations
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What is a radiation weighting factor used for?
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-to create a common scale allowing comparisons between different types of radiation easy
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What is radiation dose equivalent (also called Roentgen equivalent man) (rem) equal to?
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absorbed dose (rad) X weighting factor (WR)
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What is radiation dose equivalent expressed in?
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Roentgen equivalent man (rem)
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What is 1 rem equal to in Sieverts?
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1 rem = 10mSV
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What is the weighting Factor value for the following?
X-ray gamma ray alpha particles |
X-ray and gamma ray = 1
alpha particle = 20 |
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What are the most sensitive target organs to radiation?
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-gonads
-breast -GI -BM -Lung -Thyroid -Bone surface |
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What is the most accurate representation of radiation exposure?
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effective dose - takes into account the type of radiation (radiation weighting factor) and target tissue (tissue weighting factor)
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What is the principle target for the biological effect of radiation?
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DNA
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After DNA damage, what three things can occur?
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(1) cell death
(2) enzymatic repair (3) DNA mutation |
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Describe the difference between deterministic and stochastic effects of radiation exposure.
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deterministic: a threshold dose for injury exists (ex. radiation burns)
stochastic: no threshold dose because effect can occur at any dose (severity of effect is not dose related, but probability of effect increases with absorbed dose) |
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What is more applicable to those who are performing diagnostic imaging - stochastic or deterministic effects?
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stochastic (ex. cancers or heritable mutations)
-a concern at all doses (<50rad) |
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Fetal effects of radiation are dependent on what factors (3)?
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(1) dose
(2) dose rate (3) stage of gestation (50mrem/month) |
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What is the effect of fetal exposure to radiation during:
preimplantation (0-2 weeks) |
fetal death
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What is the effect of fetal exposure to radiation during:
organogenesis (2-8 weeks) |
congenital malformations and carcinogenesis (later on)
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What is the effect of fetal exposure to radiation during:
organogenesis (8-15 weeks) |
mental retardation and carcinogenesis (later on)
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What is the effect of fetal exposure to radiation during:
fetal period (>25 weeks) |
carcinogenesis (later in life)
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What does ALARA stand for?
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As Low as Reasonable Achievable
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What are the basic principles of ALARA?
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(1) time
(2) distance (3) shielding |
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What is the inverse square law?
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-if double distance from radiation, than the dose is decreased by 4
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What is the minimum distance you want to be from your patients during a radiograph?
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2 meters
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How much can apron and gloves reduce scatter radiation?
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1/20th of dose
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How thick of lead do you want in shielding?
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0.5 mm lead
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Monitoring of personnel is required if they will exceed what level in a year?
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1/10th of their annual maximum
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Which is the more accurate badge - radiation sensitive film or optically sensitive luminescence?
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optically sensitive luminescence
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What are disadvantages to a film badge?
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(1) less precise
(2) delay between exposure and results |
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What are advantages to a film badge?
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(1) inexpensive
(2) premanent record |
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How many badges to you wear if you are pregnant?
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2
1 is under lead apron at level of abdomen to measure fetal exposure second is outside lead apron |
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Is a radiation exposure badge worn inside or outside the lead apron?
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outside
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What is radiographic contrast?
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the difference in film blackness (optical density) between adjacent structures within an image
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What three things is radiographic contrast influenced by?
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(1) subject contrast
(2) film contrast (3) fog = scatter and light leakage |
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What three things contribute to subject contrast? These can not be manipulated.
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(1) tissue density
(2) thickness (3) anatomic number |
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What are the 5 tissue densities from the most radiolucent to the most radioopaque?
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(1) air
(2) fat (3) soft tissue/water (4) bone/mineral (5) metal |
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Do tissues with a high atomic number cause more or less electrons to be absorbed?
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more - look radioopaque
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What is the largest contributer to fog? What are three other minor contributers?
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Scatter
(1) light leak artifacts (2) film exposure (3) developing |
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What exposure factors can be adjusted to change or optical density (film blackness) and contrast to be optimized?
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(1) Focal film distance
(2) mA (3) time (4) kVp |
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What is focal film distance?
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distance between the x-ray tube focal spot and film
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If FFD is decreased, what happens to the intensity of the beam?
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increases
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What is the typical FFD?
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40 cm
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What two things, when talking about radiographic technique, can you change to alter how many x-rays will reach the patient?
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FFD and mA
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What will doubling the FFD do to area of coverage and x-ray intensity?
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--covers 4x the area
-x-ray beam is 1/4 as intense |
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What do you need to do with mAs if you increase your FFD?
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increase mAs - more scatter and more exposure
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In leymans terms, what does mAs and kVp mean for the patient?
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mAs - exposure to patient
kVp - penetration (also increases the number of x-rays) |
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How much of a percentage increase in kVp do you need to double the film's blackness?
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10-15% increase in kVp
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What does doubling the mAs do to film blackness?
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-doubles it
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What would you change to adjust the blackness of the film?
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mAs
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What would you change to adjust the scale of contrast?
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kVp
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What kind of contrast will a film have with low kVp?
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high contrast
-more blacks and whites |
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What kind of contrast will a film with high kVp have?
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lower film contrast (more shades of grey)
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What kVp would you want to use in the thorax or for musculoskeletal system? Why?
How about the abdomen? |
thorax/muscles- use a high kVp because want more shades of grey to tell the structures apart
-abdomen - use low kVp because you want more black and whites for the same reason (there is not a lot of inherent contrast in the abdomen) |
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If the peripheral film is not black, what does this mean?
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the film was underexposed
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What happened if the film you are looking at has structures that are too black?
too white? |
-overexposed/overpenetrated
-underpenetrated |
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If you already have good contrast, what should you manipulate?
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mAs
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If you do not have good contrast, what do you manipulate?
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kVp
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If a film is underexposed, what should you change next time?
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increase mAs
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If a film is underpenetrated, what would you change next time?
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increase kVp
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What would you change id your radiograph is overpenetrated or overexposed?
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-if above optimal kVp contrast range, then decrease kVP, OTHERWISE decrease mAs
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What are the steps to film processing?
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developing, rinsing, fixing, rinsing, drying
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What occurs during the fixing process of film processing?
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unexposed silver crystals are removed from the film - leaving those areas appear white
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What happens if you leave chemicals on the film during the rinsing process?
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the thiosulfate will oxidize and turn the film brown
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What is light leak artifact caused by?
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an improperly closed or broken cassette
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Name two positive density artifacts (black)?
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(1) static electricity - tree branch
(2) pressure marks - black cresent shaped |
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Name a negative density artifact.
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dirty screen - leaves a white mark due to being underexposed (in the shape of dirt or debris)
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What three radiographic geometric phemomena degrade image accuracy?
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(1) magnification
(2) distortion (3) unsharpness |
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What three factors affect the size of the radiographic image?
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(1) object size
(2) Subject-film distance (3) tube-film distance |
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What happens when the subject film distance is increased?
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image becomes magnified (enlarged)
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What happens if the tube-film distance is decreased?
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the image is magnified
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How do you minimize magnification?
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minimize subject film distance (SFD) and maximize tube-film distance (TFD)
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What is the down to maximizing tube film distance?
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greater output by the equipment
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What are causes of distortion?
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-unequal magnification (size and shape)
-location of the beam (location) |
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What is distortion?
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misrepresentation of size, shape and location of an object
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Distortion of position is due to what?
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unequal magnification of distances
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How do you minimize distortion?
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-magnification (minimize)
-position: keep linear objects parallel to the film and perpendicular to x-ray beam -location: center objects in the x-ray beam -views: use 2 as a minimum |
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What is unsharpness influenced by?
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(1) recording system
(2) penumbra (3) absorption (4) motion |
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What is penumbra?
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it is a partial shadow of the object at the edge of the actual image (umbra); this results in unsharpness (blurring of the edge of an image).
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What is penumbra caused by?
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caused by the projection of the edge of an object by x-rays coming from different angles
-b/c the focal spot is not a point sourc, instead it has multiple point sources of x-rays |
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How can penumbra be minimized?
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(1) decreases magnification (magnification also increases the penumbra)
(2) decrease the focal spot |
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How do magnification and penumbra relate to affect image detail?
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loss of detail with penumbra is due to magnification of penumbra
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What is absorption unsharpness?
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it is due to the shape of an object with absorption at the edge of the object.
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How do you control absorption unsharpness?
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you can't, just know it happens
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Motion unsharpness is most affected by what factor?
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time - exaggerated with longer exposure times
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How can motion unsharpness be minimized?
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-patient restraint (chemical is best)
-shorter exposure time |
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Is penumbra or motion a more significant factor - why does this matter?
|
motion - therefore must select for a larger focal spot to increase mA and decrease time exposed
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Which focal spot is more routinely used and why?
Is a faster or slower screen routinely used? |
-the larger one, because it better deals to reduce motion unsharpness (not as concerned with penumbra)
-faster for the reason above |
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Exposure Geometry refers to what two phenomena?
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-inverse square law
-heel effect |
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What is the relationship between the intensity of the X-ray beam and mAs?
What is the relationship between the intensity of the X-ray beam and the square of the distance? |
-directly proportional
-inversely proportional |
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What is the significance of the Inverse Square Law?
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to convert a known exposure at a know distance to a new exposure at a new distance if the TFD is changed
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What is the heel effect?
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it refers to the uneven intensity of the x-ray beam within the field; has greater intensity on the cathode side and less intensity on the anode side
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What is the true significance of the Heel effect?
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must position patients in the x-ray field properly; thicker portions should be closer to the cathode
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