Physics and Digital radiography Flashcards
The shorter the wavelength the (more or less)? The energy
Less
All the following are properties of X-rays except..
No mass
Negative charge
Travel in a straight line
Penetrate all matter to some degree
Negative charge is false
X-rays have no charge
What is the dose limit for occupational exposed personnel to X-rays?
50 mSv/yr
General public limit is 1 mSv/yr
How can radiation dose me reduced?
Time
-rotate personnel/fewer repeats
Distance
-inverse square law
Shielding
What is the inverse square law?
Intensity of radiation decreases with he square of the distance from the source
Eg. Double the distance -> 1/4th intensity
If the distance between you and the x-ray source decreases from 40” to 30”, by how much does the radiation intensity change?
(40^2) / (30^2)
T/F: electrons travel from cathode to anode to generate an x-ray
True
The number of X-rays produced is proportional to what properties at the cathode?
Amount of filament current (mA) and time that current is on (s)
T/F: doubling mAs, doubles the number of X-rays produced
True
________ between anode and cathode makes the anode attract electrons.
Voltage (quantified as kVp, kilovolt peak)
What effect will increasing the kVp have on an X-ray?
Greater voltage difference -> electrons travel faster -> higher energy
What is a “high-frequency” X-ray?
Normally a current from the anode alternates positive to negative–> only positive half of the time
High-frequency means the anode is made positive all the time, producing higher yield X-rays
When the electrons interact at the anode, they are converted into heat. How does the target not melt?
Made of tungsten (high melting point - 6191F)
Target spins to dissipate heat
T/F: Exposure =blackness
TRUE
An _______ radiograph is too light
Underexposed
Is you have an image that is cloudy white, how could you improve it?
It is underexposed
- Increase mAs -> more X-rays produced
- Increased kVp-> higher energy and more penetration
If you radiograph image is too dark, how can you improve it?
It is overexposed
- Decrease mAs -> fewer X-rays produced
- Decrease kVp-> lower energy, less through patient
T/F: to increase exposure of a X-ray, kVp can be doubled
False
- mAs are usually doubled
- kVps are usually only changed by 16-20%, which is equivalent to doubling the mAs
A high contrast image has ____kVp and _____mAs
Low; high
A low contrast image has ______kVp and _______mAs
High; low
Is a high or low contrast image used for the thorax
Low
Air in lungs already acts as contrast medium
In a radiograph of a thorax using 5mAs and 100kVp, the image is very cloudy, the you want to correct the image, how should you do so?
A. 2.5mAs, 100kVp
B. 5mAs, 84kvp
C. 10mAs, 100kVp
D. 5mAs, 120kVp
D.
When using a grid to reduce scatter, you need to change the mAs by _________ due to absorption of primary ray beam by lead
2-3x
What is the purpose of an intensifying screen?
Convert X-ray photons to light photons -> expose X-ray film
T/F: intensifying screens reduce movement artifacts, reduce patient exposure, and increase tube life
True
All of these except.. would cause a radiograph to be too dark
KVp or mAs too high X-ray tube to close to film Technique set for grid, but grid not used Underdeveloped Light leak in darkroom
Underdeveloped
Which of the following would cause a radiograph to be too light
KVp or mAs too high X-ray tube to close to film Technique set for grid, but grid not used Underdeveloped Light leak in darkroom
Underdevelopment
The colour in a digital photograph is dependent on??
Wavelength of light striking a pixel
T/F: More pixels mean better detail
True
This means pixels must be small enough to obtain good resolution
What is in a DICOM file?
Image
Header (practice, patient, and device info)
What type of digital radiography has an image plate in cassette-like housing?
Computed radiography (CR)
-cassettes must be processed in a plate reader
What type of digital radiography has a flat panel detector?
Direct digital radiography (DR)
How do DR and film differ?
It appears that detail is better with digital, however the inherent detail of film is better.
It is the contrast of DR that is better
What are the advantages of digital radiography?
Professional image
No darkroom, film, envelope
Post processing
Teleradiology
Exposure latitude
Contrast optimization
What is exposure latitude?
Extent to which a film/ image plate/ flat panel can be over or underexposed and still achieve an acceptable result
T/F: digital imaging has exposure latitude meaning that the exposure factors are not important
False
Underexposure -> grainy images
Sigificant overexposure on a digital X-ray can result in ??
Image dropout
What is contrast optimization ?
Smoothing of the gray scale
-light areas are made darker and dark areas are made lighter
T/F: exposure factors are lower in digital than with film-screen systems
False
Exposure factors are about the same
