Transcranial Doppler
- A non-invasive imaging technique that measures flow velocity in the basal cerebral arteries
- Offers moderate sensitivity but is highly specific
- Vasospasm is identified by increased flow velocity within a vessel:
- Flow velocity >120 cm/s
- Flow velocities increase >50 cm/s/day from baseline in 2 vessels
- Lindegaard ratio >3 (ratio of flow velocity in ipsilateral MCA and internal carotid artery)
Digital subtraction Angiography
- Invasive investigation requiring specialist neuroradiology staff
- The gold standard but is rarely used with increasing availability of CT
CT Angiography
- Non-invasive investigation widely used to diagnose vasospasm
- Highly specific but may overestimate the degree of spasm
CT Perfusion
- Can be used to identify regions of possible brain ischemia in patients who have a new neurologic deficit