Introduction to Medical Imaging Flashcards
Name two types of medical imaging techniques
Ionising radiation techniques
Non-radiation techniques
What are different types of ionising radiation techniques?
Plain Radiographs (x-rays)
Computer Topography
Fluoroscopy
Nuclear Medicine
What are different types of non-radiation techniques?
Magnetic Resonance Imaging (MRI)
Ultrasonography (Ultrasound)
Which parts of the electromagnetic spectrum is considered to be ionising?
X-rays and gamma rays as they have high energies
Why is ionising radiation harmful?
It carries enough energy to free electrons from atoms or molecules, thereby ionising them
What are the two units of radiation?
Sievert (mainly measured in mSv)
Gray
What are Sieverts used to measure?
Diagnostic doses of radiation
What are Grays used to measure?
Therapeutic doses of radiation
What’s the average background radiation dose for a UK citizen?
2.5 mSv
Why is good image contrast important in imaging procedures?
The imaging technique will emphasize certain contrast characteristics of anatomical structures and allow us to differentiate the structures and determine which structures are abnormal.
What causes the different colours on X-Rays?
Denser materials block rays from reaching the film, leaving it white. X-rays pass through less dense tissue to the film, resulting in more blackening of the film
Positives of x-rays
Fast Non-invasive Painless No special prep required No recovery time
Negatives of x-rays
Radiation risk Image quality can be low Distortion Not good for soft tissues Inappropriate during pregnancy
Positives of CT scans
Fast Non-invasive Painless No special prep required No recovery time Better for soft tissues
Negatives of CT scans
Inappropriate during pregnancy
Contrast Issues
Higher Radiation risk
Why are CT scans able to produce transverse images?
It uses 360° focused X-rays
Why are contrast mediums used?
They are used to examine structures that do not have inherent contrast differences
Define radiopaque
A substance that’s opaque to X-rays or similar radiation.
Define radiolucent
A substance that’s transparent to X-rays
Give two examples of contrast mediums
Barium meal
Angiography
Positives of contrast mediums
Excellent differentiation of tissues
Sequential images – follow through
Negatives of contrast mediums
Special Preparation Adverse Reactions Recovery Time Invasive Slower Transverse
What’s CT short for?
Computer Tomography
Describe the science behind MRIs
Certain atomic nuclei can absorb and emit radio frequency energy when placed in an external magnetic field. Hydrogen atoms exist naturally in people and animals in abundance, particularly in water and fat and have their own magnetic moments
MRI scans map the location of what in the body?
Water and fat
Positives of MRI scans
Excellent differentiation of tissues Sequential images – follow through Any plane Images structures better without contrast Non invasive Detect abnormal tissues No risk to “normal” patient No radiation
Negatives of MRI scans
Scans take longer
Remain completely still (hold breath)
Bowel movements and heart always in motion
Distortion from metallic implants, fillings
Cost
What do ultrasound scans use to create the images?
High frequency sound waves, which create echoes/reflections
Positives of ultrasound
Quick Low cost Portable No radiation Risk free Use on “high risk” patients Live feedback – not static Biopsy
Negatives of ultrasound
Varying quality
Unable to cross tissue-gas or tissue-bone boundary
Gas containing structures can obscure deeper tissues
High degree of technical skill
Define the term ‘stochastic effects’
Effects of radiation that occur on a random basis, independent of the size of the radiation size
Define the term ‘non-stochastic effects’
Effects of radiation that have a clear relationship between the exposure and the effect. The magnitude of the effect is directly proportional to the size of the dose
