Neuroimaging

Question 1

what is the age effect

Answer 1

this is normal atrophy of the brain “cerebral atrophy”
contributing factors include:
- alcohol
- trauma

if this is disproportionate to the patients age then neurodegenerative disorders should be considered

Question 2

A
B
C
S
of neurology imaging

Answer 2

• A – Adequacy, Alignment, Artefact
• B – Bones, Blood & Brain
• C – Cisterns & Ventricles
• S – Subcutaneous & Surfaces • Symmetry

Question 3

types of artefact

Answer 3

• Beam hardening – posterior fossa particularly
• Motion – confused patient, children
• Medical – metal clips, intraventricular shunts

Question 4

blood

Answer 4

shows up as a biconvex dark shape as the space is limited by the cranial sutures

Question 5

extradural haematoma

Answer 5

between the skull and the outer layer of the dura

Question 6

subdural haematoma

Answer 6

between dura and arachnoid

• shaped like a crescent as its only limited by dural reflections (fall/tentorium)

Question 7

Brain - diffuse axonal injury

Answer 7

• wringing out a towel
  • Traumatic brain injury, due to shearing forces
  • Poor grey-white matter differentiation, loss of sulci
  • May be associated with haemorrhage
  • Management largely supportive

Question 8

S – Subcutaneous & Soft Tissue

Answer 8

• Skin/subcutaneous lesions
• Orbit
• Sinuses
• Nasopharynx & oropharynx

Question 9

Ring-enhancing Lesion

Answer 9

• Cystic lesion in right frontal region
• Differential includes tumour or abscess
• MRI required to differentiate further

Question 10

Meningioma

Answer 10

• Typically benign
• Slow-growing
• Patient often asymptomatic – tumour discovered incidentally
• Good prognosis following surgical removal
• Homogenous, well circumscribed, broad dural base

Question 11

Haemorrhagic stroke risk factors

Answer 11

• Hypertension
• Ischaemic stroke (haemorrhagic transformation)
• Anticoagulation
• Amyloid angiopathy

Question 12

Ischaemic Stroke

Answer 12

• Blockage of cerebral arteries causes ischaemia of brain tissue
• Thrombus may be seen as hyperdensity on scan

Question 13

Monroe-Kellie doctrine:

Answer 13

the sum of volumes of brain, CSF and intracerebral blood is constant

Question 14

MRI age effect

Answer 14

• Superior soft tissue contrast – much more detail!

* White matter hyperintensities – ‘allowed’ ~1 per decade

Question 15

what are the safety cautions when taking an MRI

Answer 15

• Pacemakers
• Cochlear implants
• Metal around eyes/head

THINK METAL AND MAGNETS

Question 16

The physics behind the MRI

Answer 16

• Patient enters strong magnetic field
• Hydrogennucleireorient themselves along the magnetic field inside the scanner
• Radio frequency pulse flips nuclei from oriented position and synchronises precession of spin axis
• Receiver measures time until nuclei return to original orientation (structural scans) or desynchronise (functional scans)

Question 17

T1 MRI

Answer 17

best for structural imaging,
• Water is dark, grey matter is darker than
white matter

Question 18

T2 MRI

Answer 18

good for identifying pathology – inflammation, oedema
• Water is light, white matter is darker than grey matter

ww2 - water is white in t2

Question 19

DWI: MRI

Answer 19

T2-based sequence that measures diffusion of water within tissues

Question 20

ADC: MRI

Answer 20

calculated from DWI, shows pure diffusion

Question 21

strokes and levels of brain perfusion

Answer 21

In acute stroke, cells starved of O2 – membrane channels allow less diffusion

Question 22

MR Venogram

Answer 22

MR Venogram
• No contrast required – ‘Time of flight’ technique can be used to track blood as it travels through veins
• Venous sinus thrombosis will cause lack of flow
• Pregnancy and combined oral contraceptive pill increase risk – rare but important differential!

Question 23

Multiple Sclerosis

Answer 23

• Inflammation of myelin sheaths covering axons
T2
• On imaging – white matter ‘plaques’ can appear anywhere in CNS (brain or spinal cord)
• Hyperintense on T2/FLAIR
• Hypointense on T1 (‘black holes’), hyperintense in advanced disease