Neuroimaging

Question 1

What are the technical points of CT imaging?

Answer 1

• age effect:
• normal atrophy with age (shrinkage)
• alcohol/trauma contributes
• if disproportionate to age think neurodegenerative disease
• caudal view
• diagonal image plane
• image generated by absorption (HU units)

Question 2

What is A in ABCS of interpretation of imaging?

Answer 2

A - artefact, alignment and adequancy

• beam hardening: streaks caused by attenuation of rays off of thick bone (esp. posterior fossa)
• medical: things like metal clips can cause distortion of the image
• motion

Question 3

What is B in ABCS of interpretation of imaging?

Answer 3

B - bones, blood, brain

• narrower range of HU can be selected to focus specifically on bone
• extradural haematoma (between skull and outer dura): biconvex
• subdural haematoma (between dura and arachnoid mater): crescent shape (acute - white, hyperintense, chronic - grey, hypointense)

Question 4

What is C in ABCS of interpretation of imaging?

Answer 4

C - cisterns and ventricles

• subarachnoid haemorrhage: blood collects in the cisterns
• obstructive hydrocephalus: obstruction to ventricular system causes enlargement of the lateral ventricles

Question 5

What is S in ABCS of interpretation of imaging?

Answer 5

S - subcutaneous and soft tissue (symmetry)

• skin
• orbit and sinuses
• oropharynx and nasopharynx

Question 6

What is an ischaemic stroke and what to look for in CT scan?

Answer 6

Blockage in cerebral arteries blocking perfusion to the brain causing the tissue to start to die

• cortical hypodensity
• loss of grey-white matter differentiation
• recent scan may show hyperdense thrombus

Question 7

What are the technical points of MRI imaging?

Answer 7

• caudal view
• any plane
• age effect: white matter hyperdensities (1 per decade of patient age)
• safety: pacemaker, cochlear implant, metal around the head and eyes

Question 8

Describe how MRI scanners work

Answer 8

• the body is made up of a lot of protons (hydrogen ions) due to the high water content
• body enters magnetic field and protons line up along magnetic field
• pulses of radiowaves flip protons out of alignment
• when radiowaves halted, realignment of protons sens radio signals to receivers that measure it

Question 9

Describe what MRI sequences are

Answer 9

Different weightings of scan to highlight different features:

T1 (structural):

• water is dark
• grey matter darker than white matter

T2 (pathology):

• water is white
• white matter darker than grey matter

Question 10

Describe MRI variants in the context of a stroke

Answer 10

DWI (diffusion weighted image): T2 sequence that measures the diffusion of water between tissues
ADU (apparent diffusion coefficicent): calculated from DWI - pure diffusion

in the context of a stroke, the tissue is starved of O2 therefore, there is less diffusion.

Question 11

What is an MR venogram?

Answer 11

uses ‘time of flight’ technique which allows contrast imaging without the need to administer a contrast. Focuses on moving particles in contrast to static ones to look for venous thrombosis.