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)
