Introduction to Imaging Flashcards
Why is imaging used?
Physical examination is unreliable
Different tests are good for different things
Faster diagnosis
Assess response to treatment
What is triage?
Identify who is going to benefit most from surgery and other treatment
What is screening?
Identify diseases at an early stage to intervene
What is an X-ray?
Electromagnetic packet of energy with a short wavelength between 0.1 and 10nm
What can an atom be defined by?
Mass number A
Atomic number Z
Nucleus
Electrons
What is the mass number?
Amount of protons and neutrons
What is the atomic number?
Amount of protons
Where do gamma rays come from?
The nucleus
What are the layers of electrons around the nucleus known as?
Inner and outer shell
What causes the electrical and chemical properties of an atom?
Outer shell of electrons
What is responsible for the production of X rays?
Inner shell of electrons
How does an X ray work?
- Cathode heated to 2200oC to produce a stream of electrons
- Travel to T which is positively charged, crossing a vacuum
- 0.1% of energy creates X rays, rest is heat, rotar (r) and S makes sure the disk spins quick
- O and E controls the heat and B allows it to expand
- X rays travel down the LED glass/window
What does the intensity of the X ray depend on?
Tube current
Atomic number of target
Tube voltage
What are the 3 paths of an X ray once it interacts with matter?
Absorption
Transmission
Scatter
What is attenuation?
Process by which radiation loses power as it travels through matter and interacts with it
What does attenuation depend on?
Atomic number
Density
Thickness
How do X rays interact with air?
Travel all the way through
How do X rays interact with a tooth?
Most absorbed, some travels straight through
How to X rays interact with the abdomen?
Complex due to gas, tissue and bone
What is X ray film composed of?
Luminescent screen
Film emulsion
Luminescent screen
What does the film emulsion contain?
Silver halide which clumps after exposure to light generated on luminescent screen
What speed and frequency does ultrasound travel through the body at?
Speed of 1540m/s
Frequency of 1-20MHz
How does ultrasound generate an image?
Some waves are reflected which is detected and used to generate an image
Why is jelly used with ultrasound?
Because you need tight acoustic coupling
What are the advantages of ultrasound?
Cheap
Portable
No radiation
How do lower frequency and higher frequency ultrasound waves differ?
Lower frequency travels further but is less detailed
What is barium?
A radio opaque contrast agent used for outlining the GI tract
Why does barium absorb more X rays than the surrounding tissues?
High atomic number
When is barium dangerous?
When it leaks out of the bowel
How does a CT scan work?
Rotating X ray tube
Uses multiple beams
What are CT scans great for?
Bony detail
What is a disadvantage of a CT scan?
Exposure to radiation
What is radiation?
Process of emitting energy in the form of particles or waves
What is ionising radiation?
Particle or wave with sufficient energy to ionise a neutral molecule
What are different types of radiation?
Alpha particle (2n and 2p)
Beta particle (e- or +)
Photons (X or gamma ray)
What are alpha particles stopped by?
Paper
What are beta particles stopped by?
Hand
What are photons stopped by?
Concrete
What is a seivert?
A unit used for describing the absorption of radiation by the human body
How much radiation do we typically absorb per year?
2.4mSv/year
What kinds of cell damage does ionising radiation lead to?
Repair
Cell death
Transformation
How can exposure to radiation be reduced?
Reducing time exposed
Increasing distance
Using protection
What can you say about types of tests and the increased risk of developing cancer?
Different tests have different risks of developing cancer in your lifetime
Body CT has the most and dental X ray has the least
