Neuroradiology 1 Flashcards
What determines the colour of something on a CT scan and what type of technique is a CT scan ?
It is a X-ray technique
The contrast/ colour (black, grey or white) is determined by the electron density of something
What is seen on this CT scan and describe its characteristic appearance
It is a extradural haematoma
Radiological features:
- Typically bi-convex (or lentiform) in shape
- Usually limited by cranial sutures because of their location
- Most frequently seen beneath the squamous part of the temporal bone because most commonly due to rupture of middle meningeal artery
- Depending on their size, secondary features of mass effect (e.g. midline shift, subfalcine herniation, uncal herniation) may be present.
(Recall that this is a collection of blood that forms between the inner surface of the skull and outer layer of the dura - why they are limited by sutures usually)
What is the appearance of contrast (Injected iodine based material ‘contrast agents’) on CT in the brain? and what other uses does it have?
Iodinated contrast does not normally pass into the brain because of the ‘blood brain barrier’ however this can be disrupted by tumours or inflammation and a CT scan 5mins after contrast injection will show ‘enhancement’ ( whiteness) where BBB is disrupted
Such as the pic shown
Can also be used to produce a CT venogram
What are the 3 main different sequences of MRI scans ?
- Proton density weighted
- T1 weighted
- T2 weighted
T1 and 2 are measurements of the molecular and chemical environments of protons
What is the appearance of different tissues on T1 sequence MRI scans ?
- fluid (e.g. urine, CSF): low signal intensity (black)
- muscle: intermediate signal intensity (grey)
- fat: high signal intensity (white)
- Air and cortical bone (black)
brain:
- grey matter: intermediate signal intensity (grey)
- white matter: hyperintense compared to grey matter (white-ish)
What is the appearance of different tissues on T2 sequence MRI scans ?
- fluid (e.g. urine, CSF): high signal intensity (white) and/or less tissue e.g. fluid collections, edema, demyelination, gliosis, some tumors etc (obv these ones one be as white as fluid tho)
- muscle: intermediate signal intensity (grey)
- fat: high signal intensity (white)
- Air and cortical bone as they have a paucity of water (black)
- Some blood products e.g. subacute haematomas (black) hence MRI not good for acute setting of investigating haematomas
Brain:
- grey matter: intermediate signal intensity (grey)
- white matter: hypointense compared to grey matter (dark-ish)
Pic shows the appearance of T2 MRI on the brain
What is the appearance of different tissues on proton density sequence MRI scans ?
- fluid (e.g. joint fluid, CSF): high signal intensity (white) (darker than in T2 tho)
- muscle: intermediate signal intensity (grey)
- fat: high signal intensity (white)
- White matter - darker than bright gray
- Gray matter - bright gray
- Bone - dark
- Air - dark
What are the main contraindications to use of MRI scans ?
Strict contraindications
- Implanted electric and electronic devices are a strict contraindication to the magnetic resonance imaging, and in particular:
- heart pacemakers (especially older types)
- insulin pumps
- implanted hearing aids
- neurostimulators
- intracranial metal clips
- metallic bodies in the eye
Relative contraindications (radiologist makes decision for these)
- Metal hip replacements, sutures or foreign bodies in other sites are relative contraindications to the MRI.
- The first trimester of pregnancy is also a relative contraindication against the examination.
What type of contrast can be used in T1 weighted MRI scans (basically the same concept in CT scans but different contrast used) and what are they used for ?
- Gadolinium compounds
- Can enhance blood and demonstrate disruption of the blood brain barrier on T1 weighted images.
Pic shows
What are some of the other sequences of MRI scans ?
- Diffusion weighted (DWI)
- Flow weighted
- Functional MRI
- MR spectroscopy
Describe what each of the different MRI sequences look at:
- Diffusion weighted (DWI)
- Flow weighted
- Functional MRI
- MR spectroscopy
- Diffusion weighted (DWI) - assess the ease with which water molecules move around within a tissue (mostly representing fluid within the extracellular space) and give insights into cellularity (e.g. tumours), cell swelling (e.g. ischaemia) and oedema. Acute pathology (ischaemic stroke, cellular tumour, pus) usually appears as increased signal denoting restricted diffusion.
- Flow weighted - image physiological flow (e.g. blood flow) often without the need for intravenous contrast. This allows for the imaging of arteries, veins and CSF flow.
- Functional MRI - technique used to obtain functional information by visualising cortical activity. fMRI detects subtle alteration in blood flow in response to stimuli or actions. i.e. Good to see which parts of your brain are active for different functions e.g. speech, movement etc
- MR spectroscopy - allows tissue to be interrogated for the presence and concentration of various metabolites.
Go over the differences in CT vs MRI
Describe angiography used in neurology and its indications
Investigation of spontaneous subarachnoid haemorrhage (after diagnosis has been made to help determine the cause and therefore treatment required)
What are the 3 markers commonly assessed on MR spectroscopy and what do each of the 3 signify ?
- NAA is predominantly intra-neuronal marker of neuronal density Also correlated to the rate of mitochondrial phosphorylation Generally regarded as a marker of neurometabolic fitness
- Cho peak is a sum of free choline, acetylcholine, glycerophorycholine, phosphocholine Rate limiting precursor to cell membrane Phosphatidylcholine
- Cr peak is a sum of Cr and PCr Reserve for high energy phosphates, buffers cellular ATP/ADP ratios Cr signal generally reflects the health of systemic energy use and storage
