Introduction
This topic covers the main imaging methods used to examine the brain, spinal cord and their coverings, and vessels supplying them. The key skill in the exam is knowing which modality answers which clinical question, what each one shows best, and what its limitations are.
Principles of choosing a method
The choice depends on the clinical question, the urgency, the patient's condition and contraindications. In an emergency, speed and availability matter most. For detailed soft-tissue characterisation, magnetic resonance imaging (MRI) is usually preferred. Ionising radiation exposure should always be kept as low as reasonably achievable, which is why repeated CT scans in the same patient need justification.
- Acute trauma or suspected acute haemorrhage: non-contrast CT first.
- Suspected acute ischaemia: non-contrast CT to exclude haemorrhage, then MRI with diffusion-weighted imaging or CT angiography as needed.
- Tumours, demyelinating disease, infections, epilepsy and most chronic neurological disorders: MRI with and without gadolinium.
- Vascular stenosis, aneurysm or malformation: CT angiography, MR angiography or digital subtraction angiography.