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QuestionAnswer
How many centimeters are equal to 1 inch? 2.5 cm
How many cm are in 40"? 100 cm
How many cm are in 72"? 180 cm
What does distance affect? density, size distortion and sharpness
What does FFD mean? focal film distance
What does TFD mean? target film distance
If you increase SID what happens to magnification? decreases
If you increase SID what happens to density? decreases
If you increase SID what happens to sharpness of detail? increases
What affect does SID contrast? SID does NOT affect contrast
In order for image contrast to change, what has to happen? The ratio between compton and photoelectric interactions has to change
If you have a large body part, do you have more or less penumbra? more penumbra
Does penumbra increase or decrease when SID is decreasd? increases
For magnification to change, what has to happen? Umbra and penumbra have to grow at the same rate.
How does SID affect shape distortion? SID NEVER affects Shape distortion
How do you prevent shape distortion? beam/ part/ film alignment
How much change in SID do you need in order to get a visible change in density? 20% or 10"
How much change in distance do you need to require an adjustment in technique? 20% or 10"
The intensity of the radiation is inversely proportional to the square of the distance is what law? Inverse Square Law
What does the inverse square law predict? density
The change in technique should be equal to the square of the change in distance is what law? Square Law
What is another name for the Square Law? Density Maintainance Formula
mAs is directly related to the square of the distance is what law? Square Law also called the density maintainance formula
What is the Air Gap Technique used for? Combat image fog
How many inches of OID are used for the Air Gap Technique? 6"-8"
If you increase OID, what happens to contrast? Contrast increases
If you increase OID, what happens to density? Density decreases
When OID is increased, what should you do to SID? increase SID to decrease magnification
Does OID affect distortion? yes, size distortion
What factor should be adjusted when you have large OID or long SID mAs
what is the formula to determine magnification? magnification= SID/ SOD
Which has a greater affect on magnification SID or OID? OID
What does AEC mean? Automatic Exposure Control
What are the two types of AEC? Photo-multiplier and Ionization Chamber
What is the more connon type of AEC? Ionization chamber
What year was AEC developed? 1942
What are the advantages of AEC? reduce inconsistancy, provides uniform density, radiologists are able to read uniform and consistant radiographs
What is the variable in AEC machines? time mA and KVp are set
What does photomultiplier use to terminate the exposure? Light
What does Ionization chamber use to terminate the exposure? radiation
Is photomultiplier entrance type or exit type? Exit
What tells where to center with AEC? photo cells
Is Ionization chamber measured before or after the intesifying screens? Before
Is ionization chamber entrance or wxit type? entrance
Sufficient density is obtained when these fill and terminate the exposure. Thyristor capacitator
What are modern ionization chambers formed from? aluminum sheets
Why is higher KVP used in AEC? the give a wider lattitude (which decreased the amount of repeats)
What is responsible for averaging out density? photo cells
Where do you need to center for AEC? must be centered over photo cells (choosing the proper cell is crucial)
The time it takes for the exposure to teminate is called? reaction time
What is the typical minimum exposure time? .002 seconds for new units .02 seconds for older units
What is it called when the AEC unit first detects radiation and then responds? Minimun Response Time ( the shortest exposure time)
What is the longest amount of time an exposure can last before it is terminated? Backup Time (patient protection)
How is the backup time determined? Double the time used for an ideal radiograph (takes the reaction time and doubles it)
What is the most common error when using AEC? Choosing the wrong IR (wall bucky vs. table)
What are the limitations of AEC? selection of cell, can not use on extremities, can not use on table top exposures
What is AEC best for? Trunk of body, femur, neck and cranium with the exception of the sinuses
Who is the biggest jerk in the class? Joe
What are the 2 main factors of resolution? Contrast and sharpness
What is resolution? The ability to see 2 adjacent structures as separate structures within the image.
What are other terms that mean sharpness? geometrical detail, recorded detail, sharpness of detail, definition
How are resolution and sharpness related? directly proportional
How are distance and definition related? They are inversely proportional
If you increase divergence, what happens to sharpness? decreases
What are the visibilty factors? density, contrast and noise
What are the recognizability factors? Shape distortion (elongation and foreshortening) Size distortion (magnification) and Sharpness (detail)
How is FFD related to sharpness? directly.. Increase FFD (also called SID) you increase sharpness
How is OFD related to sharpness? indirectly.. Increase OFD (also called OID) you decrease sharpness
Do intensifying screens increase or decrease detail? decrease
Do intensifying screens increase or decrease patient dose? decrease
Is film sentitive to light or x-rays? light
How does blur affect density? NEVER affects density
What is the only thing focal spot size affects? DETAIL (sharpness)
How do you know if you have motion of poor screen contact? Motion would show all over the radiograph, poor screen contact shows as a localized blur that usually starts at the corners.
What are 4 types of motion? Peristalsis, heart motion, breathing, and voluntary.. breathing can be voluntary or involuntary
What is the average respirations per minute for the average adult? 16-18/ min
How do you minimize motion? short exposure time, communication, and use of restraints
What affect does motion have on sharpness? decreases it
How does slight motion show on the radiograph? blur along the peripheral edges of the anatomy
How does severe motion show on the radiograph? blur accross the whole image
What affect does motion have on contrast? decreases contrast
Is motion considered a primary controller of image contrast? No.. it is the only variable that reduces contrast without the affect of scatter
How does motion affect shape distortion? gives a false image categorized as noise not shape distortion.
Does motion increase or decrease penumbra? increase
What is the highest time you should use for a child? 1/30th of a second
What type of patient is the most likely to cause motion? pediatrics
Created by: 100001225073119