Neuroimaging Flashcards
what is the age effect
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
A B C S of neurology imaging
- A – Adequacy, Alignment, Artefact
- B – Bones, Blood & Brain
- C – Cisterns & Ventricles
- S – Subcutaneous & Surfaces • Symmetry
types of artefact
- Beam hardening – posterior fossa particularly
- Motion – confused patient, children
- Medical – metal clips, intraventricular shunts
blood
shows up as a biconvex dark shape as the space is limited by the cranial sutures
extradural haematoma
between the skull and the outer layer of the dura
subdural haematoma
between dura and arachnoid
- shaped like a crescent as its only limited by dural reflections (fall/tentorium)
Brain - diffuse axonal injury
- 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
S – Subcutaneous & Soft Tissue
- Skin/subcutaneous lesions
- Orbit
- Sinuses
- Nasopharynx & oropharynx
Ring-enhancing Lesion
- Cystic lesion in right frontal region
- Differential includes tumour or abscess
- MRI required to differentiate further
Meningioma
- Typically benign
- Slow-growing
- Patient often asymptomatic – tumour discovered incidentally
- Good prognosis following surgical removal
- Homogenous, well circumscribed, broad dural base
Haemorrhagic stroke risk factors
- Hypertension
- Ischaemic stroke (haemorrhagic transformation)
- Anticoagulation
- Amyloid angiopathy
Ischaemic Stroke
- Blockage of cerebral arteries causes ischaemia of brain tissue
- Thrombus may be seen as hyperdensity on scan
Monroe-Kellie doctrine:
the sum of volumes of brain, CSF and intracerebral blood is constant
MRI age effect
- Superior soft tissue contrast – much more detail!
* White matter hyperintensities – ‘allowed’ ~1 per decade
what are the safety cautions when taking an MRI
- Pacemakers
- Cochlear implants
- Metal around eyes/head
THINK METAL AND MAGNETS
The physics behind the MRI
- 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)
T1 MRI
best for structural imaging,
• Water is dark, grey matter is darker than
white matter
T2 MRI
good for identifying pathology – inflammation, oedema
• Water is light, white matter is darker than grey matter
ww2 - water is white in t2
DWI: MRI
T2-based sequence that measures diffusion of water within tissues
ADC: MRI
calculated from DWI, shows pure diffusion
strokes and levels of brain perfusion
In acute stroke, cells starved of O2 – membrane channels allow less diffusion
MR Venogram
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!
Multiple Sclerosis
• 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
