test 2 xray physics Flashcards
What is the function of the circulation system of automatic processing systems?
Mixes and filters solutions
What is the function of the replenishment system of automatic processing systems?
Adds fresh chemistry each time a film is processed
What are the lines that are longitudinally orientated in the direction of the transport film called?
guide shoe artifacts (guide lines)
What is the purpose of intensifying screens?
Reduce exposure necessary to make image by converting x-ray energy to visible light
What is the term for visible light emission in response to outside stimulation?
Luminescence
_____% of x-rays incident on x-ray film will interact with the film
_____% of x-rays incident on screen will interact to produce visible light
_____% of x-rays incident on x-ray film will interact with the film
_____% of x-rays incident on screen will interact to produce visible light
Doster: “What protects the intensifying screen from physical damage?”
Answer: _______________
Protective coating
What layer of the intensifying screen produces light?
Phosphor layer
Does the phosphor layer of intensifying screens fluoresce or phosphoresce?
Fluoresce
What layer of the intensifying screen projects light toward film?
Reflective layer
What parts make up intensifying screens?
Protective coating
Phosphor layer
Reflective layer
Base (plastic)
What are some requirements that help the phosphor layer of intensifying screens interact?
High atomic # - increase probability of photoelectric interaction
Spectral matching - produce light in blue/green spectrum
High conversion efficiency
Minimum afterglow
What type of compounds are used for the phosphor layer of of intensifying screens?
Rare earth phosphors such as
Lanthanum
Yttrium
Gadolinium
Rare earth phosphors become more efficient as what increase?
kVp (>60kVp)
What is the formula for intensification factor?
Exposure without screen divided by exposure with screen needed to produce optical density of 1
Exposure without screen divided by exposure with screen needed to produce optical density of 1 is known as what?
Intensification factor
Pertaining to intensifying screens, increased crystal concentration, size, and thickness of phosphor layer will ______ speed and ________ resolution
increase speed and decrease resolution
It is analogous to film
Spatial Resolution of intensifying screens are expressed as what?
Line pairs per millimeter (lp/mm)
Normal spatial resolution regarding line pairs/mm range from what to what?
7 to 15 lp/mm
As screen speed increases, what happens to resolution?
Resolution decreases
What has better resolution? The x-ray film or the screen?
X-ray film has better resolution, the screen has most influence on system speed
Do screens “wear out”?
no
How do you clean cassettes?
Mild soap/water or special cleaning solutions
When putting x-ray film on the screen, should they be in contact?
Yes! They could have complete contact, a blurred area suggest poor film/screen contact
When putting x-ray film on the screen, should they be in contact?
What are the 3 operator control panel settings that are non-physical?
Kilovoltage peak (kVp)
Milliamperage (mA)
Time (fractions of seconds)
What is a physical factor that controls exposure?
Source-image distance
What does kVp control regarding the x-ray beam?
X-ray beam quality
The quality controls the ability to penetrate
and quantity but not a proportional level
As kVp increases, what happens to differential absorption?
Differential absorption decreases, which causes contrast to decrease
What happens to contrast as kVp increases?
Contrast decreases
What does mA determine in relation to x-rays?
X-ray beam quantity
mA and time can be combined as a product called _______.
mAs
When mA or time is changed, what is affected in relation to the x-ray beam?
ONLY the quantity
proportional
What determines the area impacted by the projectile electrons?
Focal spot size - it is on the anode
Does smaller or larger focal spot size affect the quantity or quality of photon production at a given kVp and mAs?
No it does not affect quantity or quality!
BUT
It determines the area over which projectile electron energy is distributed…. It can be a limiting factor for how much kVp and mAs can be safely used without heat damage to the anode
What is the fixed amount of filtering that is built into the x-ray machine to meet government safety standards?
Inherent filtration
What is the additional aluminum or leaded plexiglass filters added to the collimator?
Added filtration
What are the 3 basic types of high voltage generators that are still in use?
Single phase (full wave rectified)
Three phase
High frequency (latest and greatest technology - reduces voltage ripple)
What is the most efficient type of high voltage generator that has the lowest voltage ripple, most efficient x-ray production, and lower patient dose?
High frequency
What are some patient factors that affect x-ray technique?
Body Habitus - radiographic exposure charts correlate patient measurements with correct selection of kVp and mAs
Part thickness - thickness of the tissue to be x-rayed determines the exposure factor setting
Composition of tissue - some tissues have more inherent contrast
Pathology - tissue density can be increased or decreased by disease processes
Why are patient measurements taken in centimeters and not inches?
Because centimeters are smaller than inches and less likely to give you fractional values
What is patient body habitus?
Radiographic exposure charts that correlate patient measurements with correct selection of kVp and mAs
Optical density of x-ray image refers to what?
How much light can pass through
Overexposed x-ray film appears what color?
black
Underexposed x-ray film appears what color?
white
What is the primary control of optical density of the image?
mAs
If a film is over or underexposed enough to have to repeat the x-ray, by how much percentage do you have to change the mAs by in order for it to be a “visible change” to the optical density?
How about if the change needs to be significant?
greater than 30%
If the change needs to be significant, the mAs should be doubled or halved
What is the 15% rule?
15% increase in kVp will approximately double exposure of the image receptor
In order to make a visible change in an image, which requires a greater change? kVp or mAs?
mAs
kVp requires a much SMALLER change to get the same result as changing mAs
If you wanted to double the exposure of the image receptor with a kVp of 80, what would you change the kVp to? why?
92 kVp - the 15% rule states if you increase kVp by 15% it will double the exposure to the image recepto
Resolution has 2 components known as what?
Spatial resolution
Contrast resolution
Spatial resolution of x-ray film is __________ than resolution of the intensifying screens
Greater
What is the undesirable fluctuation or alteration of optical density?
Noise
What are the four components of noise?
Film grain - film crystal size
Structure mottle - screen crystal size
Quantum mottle - distribution of photons
Scatter (most important)
When x-raying the trunk of a larger patient, is it better to have them in a recumbent position or an upright position?
Recumbent position
Source-Image Distance
SID
Distance between the source and the film
Source-Object Distance
SOD
Distance between the source and object you are xraying
Object-Image Distance
OID
Distance of object and xray film
1/2 shadow
Created by objects that are outside of the xray beam and intern does not have edge sharpness
Penumbra
How can you decrease the magnification effect?
Increase SID and decrease OID
