NEURORADIOLOGY Flashcards
How does CT work?
A scanner emits x-rays towards a patient from a variety of angles and the detectors in the scanner measure the difference between the x-rays absorbed by the body and x-rays transmitted through the body
The amount of attenuation is determined by the density of the imaged tissue and are individually assigned a Hounsfield Unit
High density tissue e.g. bone absorbs radiation to a greater degree and a reduced amount is detected by the scanner
Low density tissues e.g. lungs absorb radiation to a lesser degree so there is a greater signal detected by the scanner
Can produce 3D images
Differences between CT and MRI?
CT uses X-rays and MRI uses magnetic fields
CT uses radiation and MRI doesnt
CT is cheaper and more available compared to MRI
CT scan time is faster (<7 mins) compared to MRI (30-45 mins)
CT has no absolute contraindications but MRI does (metal implants). Although bear in mind pregnancy is a contraindication for CT
CT shows bone in best detail and MRI shows soft tissue in better detail
Orthogonal planes
Axial plane - cut through head transversely
Coronal plane - like a crown
Sagittal plane - head in half between eyes
What is windowing in CT?
Aka grey-level mapping, contrast enhancement
A process in which CT image greyscale component of an image is manipulated via the CT numbers which will change the appearance of the picture to highlight particular structures
Features of T1 image on MRI?
Grey/white matter is right way around
Fat is bright
Protein, melanin, contrast is also bright
Features of T2 imaging in MRI?
Grey/white matter is wrong e.g. white matter appears grey
Fluid is bright
Fat is not as bright as in T1 imaging
Role of CT in presentation suggestive of stroke?
Acute unenhanced CT head…
To see if its haemorrhagic or ischaemic
To exclude other contraindications to thrombolysis
Identify stroke mimics e.g. subdural haematoma
To identify signs of ischaemia
To identify a treatable cause
To identify a clot and need for CTA or thrombectomy
To assess complications e.g. brain herniation
Role of radiology in presentation suggestive of TIA?
Do a carotid Doppler of the arteries..
Exclude mimics
Identify those requiring surgical treatment e.g. carotid endarterectomy
Identify those require more investigations
Role of acute unenahnced CT in the context of stroke?
It has high sensitivity for identifying whether its an ischaemic or haemorrhagic stroke
Role of MRI in presentation suggestive of stroke?
More sensitive for acute ischameia
Some places e.g. posterior fossa, the CT will not show signs of ischaemia as you get lots of bony artefacts from the skull base. Much better in the MRI
Where does MCA supply?
Lateral and inferior frontal lobe
Anterior lateral parietal lobe
Where does PCA supply?
Occipital lobes
Posteromedial temporal lobes
Where does ACA supply?
Medial superior frontal lobe
Anterior parietal lobe
Oedema vs infarct in brain?
Both appear as low density
If its remains within vascular territory i.e. only in area of brain supplied by MCA then it is likely infarct
If it crosses vascular territory it is likely something else e.g. oedema
Which imaging do we use most often in stroke?
Non-contract CT head
(Sometimes MRI)
CT signs of haemorrhagic stroke?
Bright area of blood (hyper dense)
Have a mass effect - low density around the high density which shows vasogenic oedema
Swelling
Blood may be in ventricles
CT signs of ischaemic stroke?
Thrombus within the vessel - hyper dense
Loss of grey/white matter differentiation
Swelling/closing of sulci
Later on..
Oedema - hypodense (dark)
Mass effect
Intra-axial haemorrhage?
Haemorrhage within the brain parenchyma (cerebral haemorrhage)
Extra-axial haemorrhage?
Outside brain parenchyma e.g.
Extra-dural
Sub-Dural
Sub-arachnoid
What is a extradural haemorrhage and what does it look like on head CT?
Blood that is between skull and dura mater
Almost always caused by trauma.
Often middle meningeal artery e.g. fracture of temporal region
Treated with burr hole
Lens-shaped lesion - does not cross sutures
What is a subdural haemorrhage and what does it look like on head CT?
Haemorrhage between dura and arachnoid mater
Usually caused by tearing of bridging veins that cross the rural space
Usually traumatic and commonly affects the elderly - can be bilateral
Alcoholics are at higher risk because of loss of brain volume as bridging veins extend from inner table of skull onto brain surface and travel through CSF so any trauma = shearing forces
Extends far along complexity of brain as it is in a potential space
Crosses suture lines
What is a sub-arachnoid haemorrhage and what does it look like on head CT?
Between arachnoid and pia matter
Can be traumatic or spontaneous from a ruptured aneurysm
Pia matter is adherent to cortex so blood will go into the sulci
Can also get blood in ventricles as continuous with arachnoid
Age of haemorrhage from appearance of density on CT?
Acute - hyper dense so very bright
Subacute - isodense - grey (similar density to brain so hard to spot)
Chronic - hypo dense so dark
Symptoms of subarachnoid haemorrhage?
Thunderclap headache as blood irritates the meninges
Vomiting
Presentation of extradural haemorrhage?
Lucid interval -> unconsciousness
Hounsfield values of air, fat, water, blood and bone?
Air -1000 (low attenuation - will appear black)
Fat -70
Water 0
Blood +70
Bone +1000 (high attenuation - will appear white)
How does MRI work?
Magnet within the MRI scanner acts on H+ ions in water molecules within cells and causes them to spin. By varying strength and direction of this magnetic field we change the direction of spin of the H+
When the magnet is switched off, H+ will return to their original state (precession). The different tissue types within he body return at different rates and this is what allows us to visualise and differentiate between different tissues
What is a nerve conduction study?
A test that records how fast nerves send messages to the brain and back
Nerves are stimulated using electrodes placed into the surface of a persons skin and then another electrode is placed somewhere else and we record how fast the impulse travels to another point
What is an electromyography?
A test that studies the electrical activity of muscles
Usually recorded using a small needle electrode inserted through the skin and into the muscle. Muscle can be observed at rest and whilst being used
Indications for nerve conduction studies?
Peripheral neuropathy
Nerve injuries
Compressed nerves e.g. Carpal tunnel syndrome
Motor neurone disease
Myasthenia gravis
Myopathy
Radiculopathy
GBS
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