Neuroradiology Flashcards
what would indicate the need for brain imaging?
headache / raised ICP seizure weakness stroke trauma LOC / neurological deficit post op monitoring
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 (magnet)
not compatible with ICU / emergency equipments
not as quick as CT
patient co-operation 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 (eg 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?
3Fs and 4Ms
- fat
- slow flow (eg partially blocked vessel)
- fluid (containing protein)
- melanin
- methaemoglobin (blood)
- mineralisation (Ca / Mg etc)
- magnevist (gadolinium contrast)
what components of the brain appear as “hypointense” on T1-weighted MRI imaging?
water high flow (eg arteries)
what shows up as hyperintense on T2-weighted MRI imaging?
water or any fluid collections - oedema, demyelination, gliosis, some tumours
fat (this can be suppressed by design)
what shows up as hypointense on T2-weighted imaging?
some blood products (subacute haematoma)
mineral deposition
high flow (eg arteries)
what are some of the basic sequences used in MRI and why are they used?
spin echo: T1, T2, FLAIR (type of T2 where free water = suppressed eg 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 or false?
true
why is gadolinium used as MRI contrast?
patients not allergic to it like iodine CT contrast
has many unpaired electrons which cause an MRI signal to be picked up
what 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