wk4: ND - Medical Imaging and VEPs Flashcards
Are X-rays mutagenic or non-mutagenic?
Mutagenic
Define mutagenic
a mutagen is a physical or chemical agent that changes the genetic material, usually DNA, of an organism and thus increases the frequency of mutations above the natural background level.
What kind of exposure does tissue and bone give in an X-ray?
Tissue: high exposure
Bone: little to no exposure
What kind of exposure does dense tissue such as muscle give in an X-ray
Little to moderate exposure
List 5 applications of X-rays
Visualise orbital bones/sinuses:
- After injury or trauma
- Changes to structure
- FBs
- Brain stem-spine/CNS
- Screening tool for metal foreign bodies prior to orbital MRI
What is the first 3D imaging technique?
CT scans
Which is cheaper: X-rays or CT scans?
X-rays
How are CT scans carried out and with what kind of beam?
X-rays in a fan beam, rotating around the patient
Like X-rays, what are CT scans best at detecting?
Bony structures (however they can also image soft tissues too)
What kind of resolution is given by an MRI scan and what kind of tissue is it good for?
High resolution. Great for non-calcified tissue
List the basic principles behind how MRI works (7)
- Body is made up largely of water
- Hydrogen nuclei (protons) become aligned in magnetic field
- MRI applies a very strong magnet (typically 1.5 or 3T) to align the proton “spins”
- Also apply a radio frequency (RF) current that varies the magnetic field
- Protons absorb energy from this variable current and flip their “spins”
- When turned off,the protons return to normal state but this process varies depending on tissue density and results in the emission of RF energy
- The emitted RF energy is used to create 2D images
In brief terms, describe how MRI works. How can you see tissue density?
Protons aligned in a magnetic field absorb some energy and misallign slightly. When you turn off the magnetic field: the protons re-allign. The time taken to reallign is based on the RF energy, which is what is collected. Because there is differences in RF energy, you can see tissue density
Define the two components of a structural MRI. Explain what they describe. Do they vary between tissues?
T1 - longitudinal relaxation time
T2 - transverse relaxation time
Both describe different aspects of how the protons return to equilibrium after the applied radio frequency pulse.
T1 and T2 signals vary between tissues resulting in different image qualities
Define Repetition Time (TR)
amount of time between successive pulse sequences applied to the same slice
Define Time to Echo (TE)
the time between the delivery of the RF pulse and the receipt of the echo signal
What structures have the following colours on a T1 weighted MRI image: Black (3) Dark (3) Grey (1) Bright/White (2)
Black: air, bone, calcium
Dark: CSF, oedema, most lesions
Grey: White and grey matter
White: Fat, blood
What structures have the following colours on a T2 weighted MRI image:
Black (3)
Dark (1)
Bright/White (4)
Black: air, calcium, bone
Dark: white matter, grey matter
Bright: CSF, blood, oedema, most lesions
What does FLAIR stand for and what does it consist of? (2)
Fluid attentuation inverted recovery. Consists of a long TE (echo time) and a long TR (repetition time)
Woo
