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112 Cards in this Set
- Front
- Back
Direct Square Law (mAs:SID) |
(mAs1/mAs2)=(SID1/SID2)^2 mAs2=mAs1 * (SID2/SID1)^2 |
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Master Formula |
mAs2=mAs1 * (kVp1/kVp2) * (RS1/RS2) * (SID2/SID2)^2 |
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SID:SOD Ratio |
(SID1/SOD1)= (SID2/SOD2) |
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Inverse Square Law (Intensity:SID) |
(I1/I2)=(SID2/SID1)^2 |
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Define mA |
Measure of quantity of electrical current flowing through a circuit. |
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What does mAs represent? |
A rate representing number of electrons passing through a point in the circuit per second. - Higer mA=more electrons=more x-rays |
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Explain reciprocity with regards to creating an image. |
Light is equal to the product of the intensity of the light and the duration of the exposure. |
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What is mAs directly related to with regards to image quality? |
mAs is directly proportional to radiographic density. |
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In what ways can mAs be changed to adjust radiographic density? |
Either mA (quantity), s (time), or both may be changed. |
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Define density |
The degree of blackness in an area of the image |
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What does density on a film indicate? |
The intensity of the beam of radiation which penetrated the patient and struck the image receptor. |
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If mAs is doubled, what will the result on density be? |
Density will be doubled. |
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What is the minimum change necessary to see a visible change in radiographic density? |
30% |
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What is the minimum change required to see a visible change in most non-optimal radiographs? |
50% |
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What is the correct term for using low mAs values causing an uneven distribution of the photons resulting in a grainy image? |
Quantum Mottle |
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Define kV |
The measurement of electrical force of pressure behind a current of electricity. |
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Where is kV controlled within the circuit? |
kV is controlled by the autotransformer in the high-voltage circuit |
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What does kV measure? |
The quality or energy level of the electrons flowing through the circuit. |
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True/False: All x-rays produced will have the peak kV energy. |
False - The average beam energy will be about 1/3 of the kVp |
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Does kVp affect quantity, or quality of the beam? |
Both because high energy electrons may result in multiple interactions and produce multiple photons. - Higher kV will affect both, but mAs is the primary factor affecting quantity. |
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What will a change in penetration cause with regards to the image quality? |
A change in penetration will directly affect the gray scale (contrast) of the image. Note: kVp will directly affect contrast primarily, and as kVp is increasingly raised, it will also affect the blackness (density) of the image. |
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What determines subject contrast? |
The size, shape, and x-ray attenuating characteristics of the subject being examined and the energy of the beam. |
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What is IR receptor contrast? |
Contrast that inherent to the film and influenced by the processing. |
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Is contrast directly or inversely proportional to gray scale? |
Inversely. - High contrast = Short scale - Low contrast = Long scale |
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True/False: Increasing kVp will result in decreased scatter. |
False - Higher energy x-rays result in a loss of photoelectric interaciotns, leaving high proportions of Compton interactions, resulting in scattered x-rays. |
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What is the most important function of kVp? |
Provide penetration through the patient's tissue. |
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Scatter results in what with regards to image quality? |
Fog or noise |
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What changes in mAs and kVp would result in equal changes to radiographic density? |
Doubling mAs = 15% increase to kVp |
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If the radiographic density of an image was sufficient, but the contrast is too low; what change should be made to technique? |
Double mAs and cut kVp by 15% |
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List the layers of single emulsion film in order from bottom to top. |
Base, adhesive, emulsion, and supercoat |
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List the layers of double emulsion film in order from top to bottom. |
Supercoat, emulsion, adhesive, base, adhesive, emulsion, and supercoat. |
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Define latent image. |
Invisible change to silver halide crystals in the film emulsion resulting from interaction with light or x-ray photons. |
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When does the latent image become the manifest image? |
During processing |
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What are the impurities mixed into the silver halide crystals of the emulsion? |
Sensitivity specks |
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How is the latent image formed? |
- X-ray or light photons interact with atoms in the crystals. - Electrons are freed - The free electrons are attracted to and caught by the sensitivity specks which then have a negative charge, joining positive silver ions to form atomic silver. |
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What causes the exposure in screen film?
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The intensifying screen gives off light photons when struck by x-ray photons |
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What are the 4 general characteristics of a film? |
Speed Contrast Latitude Recorded Detail |
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What is film speed? |
How fast blackening occurs during exposure. |
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How does crystal size affect speed? |
Larger crystals = Faster speed - Produce larger black area on radiograph |
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How does film speed affect image quality? |
Higher speed = Lower quality (more quantum mottle) |
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Radiographic Contrast Relationship |
Radiographic Contrast = Subject Contrast + Film Contrast |
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What is the difference between high and low-contrast films? |
High - Relatively even grain size Low - Range of grain sizes. |
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What is film latitude? |
The range of exposure that can be used with film to produce diagnostically useful densities. |
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What is the difference between wide and narrow latitude? |
Wide - Exposed over a variety of mAs values and display more shades of gray. Narrow - Smaller range of mAs may be used. Differentiate between differences in tissue densities better. Higher contrast and fewer shades of gray. |
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What is recorded detail? |
The extent to which small anatomical differences can be recorded on film. |
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What is another way to describe an image with good recorded detail? |
Better sharpness, or higher resolution |
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What about crystals affect image sharpness? |
Smaller crystals = smaller image grain = more detail can be seen |
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True/False: Film speed is directly related to recorded detail. |
False. They are inversely related. Higher speed = Lower recorded detail |
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What are the two primary types of film intensifying screens? What type of light do they emit? |
Calcium Tungstate - Blue and blue-violet Rare Earth - UV, blue, green and red |
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All silver halide films respond to what type of light? |
Blue and violet. Note: Dyes are added to sensitize it to other colors of light. |
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Outside of technique factors, what is the primary cause of poor-quality film images? |
Improper storage or handling of film and/or film cassettes |
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What percentage of x-rays interact with film to produce the latent image? |
<1% |
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How do intensifying screens create an image? |
X-ray photons are converted to light photons which expose the film. |
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Intensifying screens have what result on patient dose? |
Lower patient dose. |
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Intensifying screens have what effect on image quality? |
Higher speed = Lower quality |
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What is a luminescent material? |
Any material that emits light in response to outside stimulation. |
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What is luminescence? |
Emitted visible light. |
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What are the 3 primary characteristics of radiographic intensifying screens? |
Screen Speed Image Noise Spatial Resolution |
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What is screen speed? |
Relative number that describes how efficient x-rays are converted to usable light. |
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What type of screens are used as a basis for comparison of all other screens? What is the value assigned to them? |
Par speed calcium tungstate. 100 |
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What is an intensification factor? |
The ratio of the exposure required to produce the same OD with a screen in comparison to that required to produce the same OD w/o a screen. |
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What are the steps in the processing sequence? |
Wetting Developing Stop Bath Fixing Washing Drying |
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What type of chemicals are Phenidone and Hydroquinone? |
Developers |
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What type of chemical is Glutaraldehyde? |
Hardener |
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What does the fixing stage do? |
Stops development and permanently fixes the image to the film. |
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What type of chemical is Acetic Acid and which stage is it used in? |
Activator - Neutralizes the developer and stops the action. |
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What type of chemical is Ammonium Thiosulfate? |
Fixer |
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What are the systems within an automatic processor? |
Transport Temperature-Control Circulation Replenishment Dryer Electrical |
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What is sensitometry? |
The study of the relationship between intensity of exposure of the film and the blackness after processing. |
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What are the two primary measurements involved in sensitometry? |
- Exposure of the film - Percentage of the light transmitted through the processed film |
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What do the measurements used in sensitometry describe? |
The relationship between Optical Density and radiation exposure. |
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How are the OD and radiation exposure expressed graphically? |
As a characteristic curve. AKA: - D log E curve - Sensitometric Curve - H&D Curve (Hurter and Driffield) |
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What are the parts of the characteristic curve and what do they represent with regards to exposure levels? |
Toe - Low levels Straight-Line Portion - Intermediate levels Shoulder - High levels |
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True/False: At the Toe and Shoulder portions of the characteristic curve, large variations in exposure result in large variations in OD. |
False |
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What is base density? |
Inherent OD in the film |
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What is fog density? |
Density resulting in inadvertent exposure of the film during storage, improper processing or chemical contamination |
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What is the useful range of OD? |
0.25 - 2.5 |
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Radiographic contrast is the result of which two separate factors? |
IR contrast and Subject contrast |
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Film contrast is related to the slope of which portion of the characteristic curve? |
Straight-line portion |
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What is speed with regards to OD? |
The ability of an IR to respond to a low-x-ray exposure |
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How does latitude relate to OD? |
As the range of exposures over which the IR responds OD's in the diagnostically useful range |
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How do latitude and contrast relate proportionally? |
Wide Latitude = Long Scale = Low Contrast Narrow Latitude = Short Scale = High Contrast |
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What is gray scale? |
The range or number of different densities present in the image. |
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What is noise? |
Any unwanted, useless info recorded which obscures the visibility of the desired image |
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What is contrast? |
The ration of differences between two adjacent densities on the image |
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What is fog? |
A form of noise. - A veil of useless density covering portions of the desired image |
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What is recorded detail? |
The abruptness with which the edges of an image stop. - The lack of penumbra in an image |
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What is blur? |
Lack of sharpness, or the presence of penumbra in an image |
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What is penumbra? |
A partial shadow at the edges of an image, causing the transition into the adjacent density to be gradual rather than abrupt |
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What is magnification? |
The difference in size of a real object and the size of its umbral quality on the radiograph |
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What is distortion? |
Difference between the shape of a real object and the shape of its image on the radiography. - Can be elongation or foreshortening |
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What is resolution? |
Ability to distinguish adjacent details as being separate from each other. |
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True/False: Resolution is controlled by both visible and geometric factors |
True |
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How is resolution measured? |
Line pair per millimeter (lp/mm) |
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How does focal spot size relate to the sharpness of the recorded detail? |
Smaller Focal Spot = Sharper Recorded Detail - Inversely proportional |
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How does focal spot size relate to image blur and penumbra? |
Smaller Focal Spot = Less blur or penumbra - Directly proportional |
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Describe Anode Heel Effect |
Intensity of beam is greater towards cathode end of tube. |
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How does anode heel effect relate to positioning of PT? |
Anatomical position of greater tissue density should be placed at cathode end of tube. |
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Where is SID measured from? |
From focal spot to the film or IR |
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How does SID relate to sharpness? |
Sharpness of recorded detail increases as SID increases. - Directly proportional |
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How does OID affect magnification? |
Increased OID = Increased magnification |
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How does SID affect magnification? |
Increased SID = Decreased magnification |
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What is the primary reason for doing a chest x-ray at 72" instead of 40"? |
To decrease magnification of the heart resulting from heart-to-IR OID. |
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True/False: Improper SID will result in distortion of an object. |
False. SID will only affect magnification. Note: Other factors may cause distortion |
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Changes in SID affect image quality in what way? What formula is used to measure this relationship? |
Increased SID = Reduced image density. Inverse Square Law (I1/I2)=(SID2/SID1)^2 |
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How should changes in SID be made to density? |
By a directly proportionate change in mAs. - Changes in SID alter intensity, not penetrability of the x-ray beam |
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What formula is used to adjust mAs for a change in SID? |
Density Maintenance Formula or Direct Square Law (mAs1/mAs2) = (SID1/SID2)^2 |
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What is the full formula for missing factor problems? |
mAs2 = mAs1 * (New Distance/Old Distance)^2 * (New Grid/Old Grid) *(Old kVp Factor/New kVp Factor) * (Old F/S Speed/New F/S Speed |
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How will increasing OID affect image quality? |
- Increased penumbra - Increased magnification - Increased distortion if the part is misaligned. - Decreased density (scatter radiation produced w/i PT diverges more and loses intensity before reaching film.) - Increased contrast (Scatter radiation reaching film is reduced. Primary rays remain at same intensity. Air Gap Technique) |
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Adjusting what ratio is the primary control over image magnification? |
SID:OID Ratio - Magnification and sharpness are both dependent on this ratio. - As long as ratio stays the same, there is no change in part magnification. |
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How is magnification factor found? |
MF = (Image Size/Object Size) * (SOD/SID) Object Size = Image Size * (SOD/SID) |
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How does motion affect an image? |
- Decreased sharpness due to expanding penumbra at image edges. Most destructive effect. - Decreased contrast by superimposition of various densities - No direct relation to overall image density, shape distortion or magnification. |