Physics Flashcards
What are x-rays?
aka Photon
Electromagnetic radiation
What determines the energy and the character of an x-ray?
Wave length
**Shorter wavelength = More energy
What properties of x-rays makes them potentially dangerous?
Ionizations (when energy is high enough)
Ionizations can lead to cell death or mutations
T/F: Veterinarians and staff are good about protecting themselves while taking radiographs
FALSE
there is a gerneral disregard for the dangers of radiation exposure in veterinary practice
What is the occupational exposure dose limit of radiation from x-rays?
50 mSv/yr
Must be at least 18 yrs of age
(FYI - the general public/non medical dose is 1 mSv/yr)
How does one reduce their dose of radiation?
ALARA
As Low As Reasonably Achievable
this is a principle protection philosophy - using time, distance, and shedding
How can time to radiation exposure be reduced using ALARA methods?
Rotate personnel taking rads
Avoid repeat x-rays (due to poor technique, lack of training, etc)
Minimize patient holding
What is the inverse square law? Why is it important?
Intensity of radiation decreased with the square of the distance from the source.
**increasing the distance between personnel and radiation source reduces exposure significantly
Doubling the distance between a person and the radiation source will reduce the x-ray intensity to _____
1/4th or a quarter
(1/2)^2
What process is used to protect against scattered radiation?
Shielding:
Protective aprons, thyroid shields, gloves, glasses
T/F: Gloves and gowns protect from the primary beam of radiation
FALSE
These protect only from scatter radiation
Besides shielding, what other technique can be used to reduce scatter?
Contain the beam by using proper collimation
How is the radiation exposure of veterinary staff measured/monitored?
Using exposure badges
Employees should wear their specific badge at work only and outside of the protective x-ray apron
What is a radiograph?
A picture of the pattern of x-rays emerging from the patient. Differential absorption needed to create an image
X rays are produced when high speed ____ strike metal.
Where does this occur?
Electrons
Occurs in an X ray tube
The electrons used to make radiographs come from the ______ and hit the ______.
Electrons are made in the filament (aka Cathode) and will hit the Target (aka anode)
What is the mAs setting?
mAs will control how hot the filament gets and for how long(in seconds)
(the number of electrons produced = the number of x rays produced)
*longer time = more electrons produced
T/F: Doubling the mAs will double the number of x rays produced
TRUE
T/F: A longer time setting of the mAs will produce more electrons and thus more x rays, so we should always try to have a increased time factored into the mAs setting (why or why not)
The first part is true: longer time = more electrons and x rays
But the longer the time = the more time there is for movement to occur and make the radiograph blurry
The goal should be the shortest time possible - to remove error of animal movement
What does the kVp setting represent?
The voltage (potential difference) between anode-cathode that makes the negative cathode attract to the positive anode
*energy of x rays produced
Increasing the kVp will:
- (Increase or decrease) the voltage potential
- Make electrons travel (faster or slower)
- (increase or decrease) kinetic energy
- Create (more or less) energetic x rays
1 - increase
2 - faster
3 - increase
4 - more
What does it mean if your anode is “high frequency”?
The anode will be positive at a constant rate
(rather than having its normal alternating current)
*this is typical of most newer veterinary machines
What percentage of electron energy is converted to heat at the anode?
99%
This is why it is made of tungstun and also spins - to avoid melting
An underexposed film is too _______
LIGHT
not enough x rays were used or there was not enough energy
