NeuroRadiology Flashcards
What are the advantages of CT scans?
Excellent bony details/spatial resolution
Fast
Compatible with emergency/ICU equipment
What are the disadvantages of CT scans?
- Only sensitive to blood EARLY in acute injury
- Poor soft tissue detail
- Grey and white matter show little difference in density
- High radiation dose
What shows up bright and what shows up dark on CT imaging?
Bright = More dense => bone, any metal implants
Dark = Less dense => air
What are the advantages of MRI scanning?
- Excellent contrast/soft tissue resolution
- Excellent depiction of anatomy
- Good for visualising marrow and cord pathologies
- Multiplanar
What are the disadvantages of MRI scanning?
- Less bony detail/spatial resolution
- Not compatible with pacemakers and many implants (due to magnet)
- Not compatible with ICU/emergency equipment
- Not as quick as CT
- Patient cooperation required
Why are different MRI sequences used and give some examples of commonly used sequences.
Multiple sets of MRI images are taken at the one time
(e.g. T1, T2 etc)
=> Different sequences use different combinations of technical parameters
=> Each sequence is unique and gives different information.
What components of the brain enhance as “hyperintense” on T1-weighted MRI imaging?
3 Fs and 4Ms F: fat F: slow flow (e.g. partially blocked vessel) F: fluid (containing protein) M: melanin M: methaemoglobin (blood) M: mineralisation (Ca/Mg etc) M: Magnevist (gadolinium contrast)
What components of the brain appear as “hypointense” on T1-weighted imaging?
Water High Flow (e.g. arteries)
What shows up as hyperintense on T2-weighted MRI imaging?
Water or any fluid collections
- oedema, demyelination, gliosis, some tumors
Fat (this can be suppressed by design)
What shows up as hypointense on T2-weighted imaging?
- Some blood products (subacute hematoma)
- Mineral deposition
- High flow (e.g. arteries)
What are some of the basic sequences used in MRI and why are they used?
T1, T2,
FLAIR (Type of T2 where free water = suppressed e.g. ventricles)
T2* (gradient echo) = highlights blood
T1 (3D): Volumetric
Contrast enhancement = increases density of objects needing to be visualised
Any structure within the blood-brain barrier resists contrast. TRUE/FALSE?
TRUE
Why is gadolinium used as MRI contrast?
- Patients are not allergic to it like iodine CT contrast
- Has many unpaired electrons which cause an MRI signal to be picked up
What vascular pathologies would you expect to see on brain imaging?
- Infarcts
- Haemorrhage
- Vascular anomalies
Describe how a thrombus in a blood vessel of the brain will appear on CT?
Bright
Why is MRI more sensitive to diagnosing stroke?
Grey and white matter differentiation on CT not good enough to outline small infarcts
Why is CT completed first over MRI on presentation of stroke?
Faster
Gives indication of infarct vs haemorrhage and whether pt should receive thrombolysis
An intreparenchymal bleed can break through to the ventricles. TRUE/FALSE?
TRUE
What is a Susceptibility weighted imaging (SWI) MRI sequence used to look for?
- sensitive to venous blood
- especially old venous blood that cannot be picked up on CT
=> looking for haemorrhage and iron storage
what usually causes a subarachnoid haemorrage?
Usually due to aneurysm
How long after an IV injection of CT contrast does it show up in arteries?
8-10s
Describe how a “cavernoma” (type of vascular anomaly) appears on imaging?
Popcorn appearance
Ca2+ present
MRI is more sensitive than CT for small aneurysms. TRUE/FALSE?
FALSE - CT more sensitive due to use of contrast, MRI angiography often doesnt use contrast
What modality of imaging is sensitive for bone injury and ACUTE bleeding in trauma?
CT
