Diagnostic Imaging Flashcards
Wavelength and frequency are __ proportional
Inversely
List 3 properties of x-rays
- Short wavelength
- High frequency
- High energy
Which materials can x-rays penetrate?
Materials that absorb or reflect visible light
How do x-rays cause direct tissue damage?
By direct interaction with DNA
How do x-rays cause indirect tissue damage?
By the ionization of water molecules leading the formation of radicals
Which tissues are more affected by x-rays?
List 3
- Bone marrow
- Epithelial cells of the GI tract
- Early stage embryonic cells
What are the 2 classes of biological effects of x-rays?
- Stochastic effects
- Deterministic effects
Define stochastic effects
Give one example
Effects that have a random probability of distribution, and cannot be predicted precisely
Cancer or genetic effects
Define deterministic effects
Give one example
Effects that happen because of certain known conditions
Erythema, hematopoietic damage or cataracts
What does ALARA stand for?
As low as reasonably achievable
What are the units for absorbed radiation?
Gray (Jkg-1)
What are the units for effective dose of radiation?
Sievert
Define radiation exposure
Amount of ionization per mass air
Define absorbed radiation
Amount of energy transferred by radiation per mass
Define effective dose
A measure of radiation and organ system damage in humans
I.e. doses that are NOT received as a patient
What is the annual dose limit of radiation for the public vs a professional?
Public: 1mSv
Professional: 20mSv
What are 3 exceptions for the UK Veterinary Radiation Protection Regulations?
I.e. when can you go in to manually restrain the patient?
- Critical illness in which sedating the animal is dangerous
- Specific radiographic technique is required
- Patient type (i.e., large animal)
List 6 methods of radiation protection
- Filtration of the x-ray tube
- Time
- Distance
- Sheilding
- Collimation
- Personnel monitoring
What is the inverse square law when relating to the distance of radiographic imaging?
If the distance from the primary source is doubled, the intensity will decrease by a factor of four
List 3 ways you can sheild yourself from radiation
- Lead gloves
- Lead aprons
- Lead thyroid collar
What is a collimator?
A light beam diaphragm (like a view finder)
What are 2 types of dosimeters?
- Film badge
- Thermoluminescent (TLD)
How are x-rays produced?
Through conversion of kinetic energy of accelerated electrons into electromagnetic radiation
What is the source of electrons in an x-ray?
A cathode
Define x-ray tube current
Number of electrons flowing per second from the filament to the target
What is the source of deceleration in radiography?
The anode
A high potential difference leads the to __ of the electrons in a vacuum towards the anode
Acceleration
What is the charge of an anode
Positive
What is the function of the actual focal spot of an anode
It reduces over heating
What is the function of the effective focal spot of an anode
Improves detail
Compare small and large filament size in x-ray production
Small: finer detail and concentrates heat
Large: reduced detail but can use higher exposures
An x-ray beam is __
Polychromatic
List 3 things that happen when you increase KVp
(i.e., what else does it increase)
- Increases electron velocity
- Increases number of x-ray photons
- Increases energy
List 2 things that happen when you increase mA
(i.e., what else increases)
- Increases filament heating and tube current
- Increases number of x-rays being produced
Define attenuation
Decrease in intensity of an x-ray beam as it passes through matter
Define transmission
When an x-ray passes through matter without interaction
Define scatter
When the photon changes direction
What creates the image in an x-ray?
I.e., the shadowgram
The attenuation of the x-ray beam by the different tissues in the patient
Describe the photoelectric effect
When the x-ray photon is completely absorbed, and a photoelectron is removed from the shell of the tissue atom (it is ionized)
This gives off some radiation, but not enough to leave the body so it is not a safety hazard
Describe the compton effect
When the x-ray photon ejects an electron from the outer shelll of the tissue atom and the photon is scattered
The scattered photon has a lower energy than the x-ray photon and this may fog the film or be a safety hazard (scatter radiation)
The photoelectric effect is seen with __ radiation, and the compton effect is seen with __ radiation
Photoelectric: low range (up to 30kVp)
Compton: high range
Which form of x-ray absorption provides the best image contrast?
Photoelectric
What are the purpose of grids?
Bonus: when would you use them?
To reduce scatter & improve radiographic contrast
When using high range radiation (producing the compton effect)
What do you need to change about your x-ray when using grids?
Think lighting
Increase exposure
What are the 3 types of radiography?
- Conventional
- Computed
- Digital
Define latent image
The image that reflects the pattern of the part being radiographed
What are the 3 steps in manual film processing?
- Developer
- Fixer
- Wash
When is it recommended to use a grid?
When body part thickness is greater than 10 cm
Why do you need to increase the exposure when using a grid?
Bonus: how much do you need to increase exposure by?
To compensate for the portion of the primary beam absorbed by the grid
Increase exposure by a factor of 2-3
List 3 advantages of using an intensifying screen
- Reduce personnel exposure
- Reduce patient exposure
- Increase image contrast
Where is the image captured in computed radiography?
I.e., what is in the x-ray cassette?
A cassette containing a phosphor storage layer (no film)
List 3 advantages of computed radiography
- Time efficient
- Lower radiation dose
- Cost effective
List 3 disadvantages of computed radiography
- Laser reader is sensitive to dust
- Maintenance
- Manual labour required
How is the image produced in computed radiography?
- Cassette is put into a laser film reader
- Laser beam stimulates phosphor crystals to release stored light energy
- Computer generates a digital image in DICOM format
List 3 advantages of digital radiography
- Quick
- Good quality
- Lower radiation dose
List 2 disadvantages of digital radiography
- More expensive
- Fragile
How is the image produced in digital radiography?
There is an imaging receptor plate containing many small detector elements that transform x-rays into an electrical signal
Explain the difference between direct and indirect digital radiography
Direct: x-ray photon hits a selenium plate and the charges are transmitted to a computer for image construction
Indirect: x-ray photon hits a flat panel that creates visible light, the light photon then stimulates a photocathode which transmits energy to a computer for image construction