Exam 2 Flashcards
What does mAs control
The density of the film
What does kVp control
The Contrast and Density of the film
What increase in mAs will cause the first visual change to the film density
30%
Do you retake a film for the 30% rule
no, the difference is so slight it doesn’t make a difference
Other than manually changing the mAs how else can you increase the mAs?
Increase exposure time
What does doubling the mAs do to the density of the film
Doubles the density
If the film is too light but you can see structures what can you do to fix it (using mAs)
Double the mAs
If the film is too dark but you can see structures what can you do to fix it (using mAs)
1/2 the mAs
If the film is too dark or too light and you can see structures how can you fix it using kVp
Dark = decrease kV 15% Light = increase kV 15%
how much kV does it take to increase the density
4 kV
When changing the kV what should you keep in mind
Do not go over or under the optimal kV range
What happens if you need to decrease kV and mA but if you decrease kV it will be under the optimal range
1/2 the mA twice and leave kV alone
What can cause film fogging
Scattered rays
overhead lights
Increasing the developing time/temp
using an expired film
What does film fogging do to the density
increases the density (makes it darker)
If you use a spot shot what will happen to film density if the technique is not increased
The density will decrease (film will get lighter)
What are some factors that will decrease the density of the film
Spot shot without changing technique Too much filtration Wrong film + screen combo patient tissue and body build decreased development time and temp
What type of contrast is black and white
Short
What type of contrast scale has lots of greys
Long scale
How do you fix a film that has too high of contrast (short scale)
decrease kV 15%
double the mAs
How do you fix a film that has too low of contrast (long scale)
Increase kV 15%
1/2 the mAs
If the density of a film is good but there is too much grey how do you fix it
decrease kV 15%
Double the mAs
If the density of the film is good but there is not enough grey how do you fix it
increase kV 15%
1/2 the mAs
What is differential absorption
the differences in x-ray absorption of different tissues
How do the following appear on xrays
Air
Oil
Water
Bone
Air = black Oil = dark grey water = grey bone = white
What is the silhouette sign
If two structures of the same density are in contact you will not be able to see the boarders
How will thinner materials of the same density appear on a film compared to thicker
Thin = less dense thick = more dense
What are the different types of radiographic techniques
Variable kV
fixed kV
High kV
Which radiographic technique should be avoided
Variable kV
Which technique used a constant mAs and a varried kVp
Variable kV
Which technique only changes the kV depending on the size of the part of patient
Variable kV
What technique is most used today
Fixed kV
Which technique changes the mAs depending on the thickness of the part or person
Fixed kV
Which technique has a more constant contrast
Fixed kV
Which technique has a more varied contrast
Variable kV
Is the high kV technique used for bones
no
What is the high kV technique used for
Chest and contrast media studies
What type of Exposure control uses photocells behind the patient that will terminate the exposure once the desired density is achieved
Automatic Exposure Control
When using a technique chart what is something to keep in mind about the values
The values are estimates, you should use your own judgement on whether or not to change these values depending on size and age or patient
What is the name of the calculators used for determining x ray settings
Slide rule calculators
What type of exposure control uses a computer chip that will calculate out the kV and mA depending on what film you are taking and the size of patient
Anatomicl Programmed Chips
When using a chart how much will you decrease the mAs by when xraying a patient under 12 years olf
decrease by 30%-50%
When using a chart how much will you have to decrease the mAs by when xraying an osteoporotic patient
decrease by 30-50%
same as a child under 12
For more muscular or obese patients what will you have to change the mAs by
increase 30-50%
How can you assure that contrast will be good with minimum patient exposure
Stay within the recommended kV ranges
What is Quantum mottle
Visual defects in the film, ie; under/overexposed, too much/too little grey, grainy dots on film
What causes Quantum mottle
Too fast of screens
too high kV and too low mA
dirty/poor screens
old screens
What causes true Quantum mottle
Too high kV and too low mA
What is unsharpness on a film called
Penumbra
what is sharpness on a film called
numbra
An increase or decrease in SID will do what to the film sharpness
Decrease SID = unsharp
increase SID = Sharper
An increase of Decrease in OFD will do what to the film
Decrease OFD = Sharper
Increase OFD = unsharp
What will a large or small focal spot do to the film
Small = Sharper Large = unsharp
What is the order of sharpest to least sharpest Double screen no screen single screen high speed screens
no screen = sharpest
single screen
double screen
high speed screen = least sharp
What can cause motion blur
Patient motion
Equipment motion
What can cause equipment motion
Faulty locks
unstable cassette holder
Heavy construction out side of office
what type of unsharpness does magnification distortion cause
geometric unsharpness
What causes magnification distortion
increased OFD
How should the patient be positioned against the film
The part you want to xray should be as close to the film as possible
a P-A film is best at showing what
Heart, anterior ribs, sinuses, frontal bone
a A-P film is best at showing what
Spine, Occiput, Scapula, posterior ribs
What is another name for Shape distortion
True distortion
What causes Shape distortion/ True distortion
Angulation of the ray, film, or object
What can happen to the X-ray when it enters a patient
Completely absorbed
Partially absorbed/deflected
Pass through patient
X rays that are partially absorbed and pass through make up what type of radiation
Remnant radiation
What are the rays that are deflected back to the tube called
Back scatter
What xrays are undesirable
partially absorbed/deflected
What produces the image on the film
Secondary xrays
Explain secondary xrays
Primary Xrays hit patient and are absorbed, The extra energy sends another electron from the tissue out of its orbit. The secondary xray might hit the film, this will darken it and cause grey
Secondary xrays that leave at a steep angle will do what on the film
No hit it, and create better contrast
What is Comptons scatter effect
When an incoming phtons strikes the outter electron and dispalces it. The greater the angle the photon deflects at the more energy is lost
What type of secondary radiation is more predominant when using recommended kV
Comptons Scatter effect
What causes classic scatter
A weak photon (10keV) causes electrons to vibrate and give off another xray
is there more or less scatter at higher kV
more scatter
why does a higher kV cause more scatter
More penetration = less absorption = more graying from film fog
More x rays penetrate with no interaction
How can you control scatter caused by kV
use optimate kV ranges
How does beam size contribute to scatter
large beam = more scatter from patient tissue
How does patient size affect scatter
More tissue = more scatter
Denser tissue = more scatter
How can you help with removing scatter from patient tissue
Use a Grid infront or behind the patient
What are grids made up of
Thin led or allumnium strips separated by interspacing material
What is the recommended lines per inch grid frequency
103+
What are the different types of grids
Stationany
moving grids
What are the 3 types of stationary grids
Crossed
Parallel
Focused
What is the problem with parallel grids
peripheral rays are attenuated this causes uneven exposure (sides of film are lighter)
What is grid radius
The angle of the strips that match the divergence
What is Grid cut-off
Unequal film density from strips absorbing primary radiation
What causes grid cut-off
Parallel grids Grids that are out of range malalignment of tube backward installation bent/warped grid
What are grid lines
White lines there primary rays hit the led strips
What is a moving grid also called
A reciprocating grid
How can grid lines be avoided
by moving the grid during exposure
What are some problems with a moving/reciprocating grid
They are thicker = increase OFD
can cause motion in film
