Neuroradiology Flashcards
What are some indications to perform a CT scan?
Head trauma: NICE guidelines
Acute stroke: NICE guidelines
Headache: SIGN guidelines, red flags for suspected tumour or subarachnoid haemorrhage
Cancer: looking for metastatic brain tumours in patients with symptoms
Post-surgical: hydrocephalus, haemorrhage
What are some reasons not to perform a CT scan?
Minor head trauma exclusion criteria: NICE and SIGN guidelines
Seizure: NICE guidelines (pg 16), usually choose MRI
- primary idiopathic generalised epilepsy – no imaging
- complete recovery after a first seizure is not epilepsy
What are some indications to perform a MRI scan?
Mostly done by specialist physicians:
Neurologists:
Demyelination
CNS tumours
Spine - for intervertebral disc prolapse
Transient ischaemic attacks
Epilepsy
Paediatric neurology
Headache
Surgeons:
Spine: Intervertebral disc degeneration causing neural compression
Cancer: clarifying the number, location and aggressiveness of brain tumours
What are some contraindications to perform an MRI scan?
Implanted electronics (check with manufacturer):
- Cardiac pacemakers, implantable defibrillators, cochlear implants
- Relative contraindication for programmable shunts, insulin pumps
Moveable metallic implants (check make and model):
• Aneurysm clips, heart valves, recent intra-abdominal clips
Relative contraindications:
• Claustrophobia, pregnancy, tattoos
What are some uses of angiography in the diagnosis of neurological pathology?
Used for large vascular (arterial and venous) abnormalities Used for diagnosis and treatment
- Aneurysm
- Arteriovenous malformation - an abnormal connection between arteries and veins, bypassing the capillary system
- Carotidocavernous fistula
- Unstoppable epistaxis
What is perfusion?
Perfusion is defined as the volume of blood passing through a defined volume of tissue per unit time
Units: ml blood/100g tissue/min
Can be a CT or MRI technique
What are some disorders of abnormal perfusion?
Stroke - decreased perfusion
Tumour - increased perfusion indicates angiogenesis and a more aggressive tumour
WHat are PET scans used for?
PET is usually used to map out glucose usage
Increased metabolism is seen in:
- Tumour
- Inflammation
- Infection
Useful after brain tumour resection for differentiating granulation tissue (low energy usage) from leftover tumour (high energy usage)
How are plain radiographs recognised?
Multiple superimposed bones, bones are white
Immediately recognisable body parts
Soft tissue is grey
Air is black
How do you indetify a CT scan?
White circle of skull
Black CSF in sulci and ventricles
Air is black
Grey brain with subtle grey-white matter difference
Image quality:
- reconstructed by back projection from a rotating fan beam of X-rays
- beam hardening from radiodense objects
Metal produces white starbust artefacts, slightly grainy
How do you indentify a MRI scan?
White CSF is the best clue, but only true for T2- weighted MRI - Same anatomy with different sequences often shown
Better grey-white matter differentiation than CT
Image quality:
- reconstructed from Fourier transforms of radio signals
- has a JPEG-like quality, usually not grainy
How do you identify radionuclide radiology/nuclear medicine/PET?
Images often have bright and varied colours
The image is fuzzy
How do you identify ultra sound?
(not as important)
Wedge-shaped image with the edges of the image diverging away from top to bottom
Often has a curve at the top matching the ultrasound probe (exception: flat probes)
Very noisy image (like an old un-tuned TV)
Objects which block the ultrasound beam (air, bone, stones) cast shadows cast downwards
What colour is CSF is CT and MRI?
CT - black
MRI - white
What are the advantages of ultrasound?
- No radiation
- Less expensive equipment
- Can be performed in the neonatal unit
- Movement tolerant
What are the disadvantages of ultrasound?
• Requires a wide enough open fontanelle
i.e. up to about 1 year of age
• Image quality and interpretation based on operator skill
What are the advantages of plain radiographs?
- Almost universal availability
- Fast
- Sequential images in subtraction angiography
What are the disadvantages of plain radiograph?
• Lacks soft tissue detail
What are the advantages of a CT scan?
- Rapid
- Metal and pacemaker tolerance
- Good for demonstrating acute haemorrhage
What are the disadvantages of a CT scan?
- Radiation 2mSv
- More expensive cumbersome equipment
What are the advantages of radionuclide radiology?
It gives you physiological information such as:
- Glucose metabolism
- Perfusion
- Dopamine reuptake receptors
What are the disadvantages of radionuclide radiology?
- Unclear anatomical information
- Medium cost of equipment
- Radiotracers can be expensive
What are the advantages of MRI?
- No radiation
- Soft tissue differentiation
Gives you physiological information:
- blood flow
- diffusion restriction
- metabolite concentrations
What are the disadvantages of MRI?
- Poor tolerance of metalwork
- Magnetic sensitive electronics may fail or are contraindicated:
- Pacemakers!
- Cochlear implants absolutely contraindicated
- Least movement tolerance
- Slow, must limit sequences
- Most expensive equipment
- Danger of metallic objects becoming projectiles
