Physics

Question 1

What are x-rays?

Answer 1

aka Photon

Electromagnetic radiation

Question 2

What determines the energy and the character of an x-ray?

Answer 2

Wave length

**Shorter wavelength = More energy

Question 3

What properties of x-rays makes them potentially dangerous?

Answer 3

Ionizations (when energy is high enough)

Ionizations can lead to cell death or mutations

Question 4

T/F: Veterinarians and staff are good about protecting themselves while taking radiographs

Answer 4

FALSE

there is a gerneral disregard for the dangers of radiation exposure in veterinary practice

Question 5

What is the occupational exposure dose limit of radiation from x-rays?

Answer 5

50 mSv/yr

Must be at least 18 yrs of age

(FYI - the general public/non medical dose is 1 mSv/yr)

Question 6

How does one reduce their dose of radiation?

Answer 6

ALARA

As Low As Reasonably Achievable

this is a principle protection philosophy - using time, distance, and shedding

Question 7

How can time to radiation exposure be reduced using ALARA methods?

Answer 7

Rotate personnel taking rads
Avoid repeat x-rays (due to poor technique, lack of training, etc)
Minimize patient holding

Question 8

What is the inverse square law? Why is it important?

Answer 8

Intensity of radiation decreased with the square of the distance from the source.

**increasing the distance between personnel and radiation source reduces exposure significantly

Question 9

Doubling the distance between a person and the radiation source will reduce the x-ray intensity to _____

Answer 9

1/4th or a quarter

(1/2)^2

Question 10

What process is used to protect against scattered radiation?

Answer 10

Shielding:

Protective aprons, thyroid shields, gloves, glasses

Question 11

T/F: Gloves and gowns protect from the primary beam of radiation

Answer 11

FALSE

These protect only from scatter radiation

Question 12

Besides shielding, what other technique can be used to reduce scatter?

Answer 12

Contain the beam by using proper collimation

Question 13

How is the radiation exposure of veterinary staff measured/monitored?

Answer 13

Using exposure badges

Employees should wear their specific badge at work only and outside of the protective x-ray apron

Question 14

What is a radiograph?

Answer 14

A picture of the pattern of x-rays emerging from the patient. Differential absorption needed to create an image

Question 15

X rays are produced when high speed ____ strike metal.

Where does this occur?

Answer 15

Electrons

Occurs in an X ray tube

Question 16

The electrons used to make radiographs come from the ______ and hit the ______.

Answer 16

Electrons are made in the filament (aka Cathode) and will hit the Target (aka anode)

Question 17

What is the mAs setting?

Answer 17

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

Question 18

T/F: Doubling the mAs will double the number of x rays produced

Answer 18

TRUE

Question 19

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)

Answer 19

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

Question 20

What does the kVp setting represent?

Answer 20

The voltage (potential difference) between anode-cathode that makes the negative cathode attract to the positive anode

*energy of x rays produced

Question 21

Increasing the kVp will:

1. (Increase or decrease) the voltage potential
2. Make electrons travel (faster or slower)
3. (increase or decrease) kinetic energy
4. Create (more or less) energetic x rays

Answer 21

1 - increase
2 - faster
3 - increase
4 - more

Question 22

What does it mean if your anode is “high frequency”?

Answer 22

The anode will be positive at a constant rate

(rather than having its normal alternating current)

*this is typical of most newer veterinary machines

Question 23

What percentage of electron energy is converted to heat at the anode?

Answer 23

99%

This is why it is made of tungstun and also spins - to avoid melting

Question 24

An underexposed film is too _______

Answer 24

LIGHT

not enough x rays were used or there was not enough energy

Question 25

An overexposed film is too ____

Answer 25

DARK

Too many x rays were used or the energy was too high

Question 26

How should you correct an underexposed film (in regards to mAs and kVp)?

Answer 26

Increase the mAs (this will increase time and could potentially make a poor rad if motion is involved)

or

Increase the kVp

**one or the other - do not increase both at the same time

Question 27

What is a good “go to” for how much you should increase/decrease your mAs and kVp?

Answer 27

mAs: usually halved or doubled

kVp: changed by 16-20% (this is the equivalent to halving or doubling the mAs)

Question 28

What mAs/kVp combo will produce a high contrast image?

Answer 28

High mAs
Low kVp

High contrast images have TRUE blacks and whites

*x-rays are less penetrable so they are either absorbed or not

Question 29

What mAs/kVp combo will produce a low contrast image?

Answer 29

Low mAs
High kVp

Low contrast images have no or few pure black and whites but rather many shades of grey

*x rays are more penetrable and absorption is more uniform

Question 30

What part of the body will naturally produce a high contrast image? why? What should your mAs/kVp settings be then?

Answer 30

The thorax is naturally high contrast due to the amount of air in the lungs

For this reason - you should set your machine up for a LOW contrast image = Low mAs and High kVp

Question 31

What settings should be used to take an abdominal rad? Why?

Answer 31

You should use a low kVp and high mAs = high contrast

you want to shoot for high contrast since the abdomen naturally has a low contrast; organs have similar consistency and only fat is there for contrast

Question 32

What is the purpose of grids in the x ray table?

Answer 32

These are used to intercept scatter from the patient before it reaches film

Grid = alternating strips of lead and aluminum - need to increase the mAs when using a grid

Question 33

What are the two methods available for converting the x ray pattern exiting the patient into a visible image?

Answer 33

Analog conversion (film/screen systems)

Digital conversion