Many neurological and neurosurgical conditions require accurate delineation of both intra-and extracranial vessels. Intra-arterial injection of contrast remains the standard angiographic technique, either imaged directly on X-ray film or by digital subtraction (DSA). Intravenous DSA is of sufficient quality to be of value when investigating certain conditions e.g. carotid stenosis, sagittal sinus thrombosis.

Under local anaesthetic, a catheter is inserted into the femoral artery and manoeuvred up to the carotid or vertebral origin with the help of a 'guide

Series of films taken using an automatic film changer

Contrast injected with a high pressure pump

Series of films taken using an automatic film changer

Contrast injected with a high pressure pump

Subtraction of a pre-injection film from the angiogram eliminates bone densities and improves vessel definition. A general anaesthetic avoids patient movement and aids subtraction but is not essential. Direct vessel puncture is rarely required.

Phase - arterial 1 Most information is now derived from the arterial phase.

- capillary > Prior to the availability of CT scanning, the position of the cerebral

- venous J vessels helped localise intracranial structures.

Digital subtraction angiography (DSA) depends upon high-speed digital computing. Exposures taken before and after the administration of contrast agents are instantly subtracted 'pixel by pixel'. Data manipulation allows enhancement of small differences of shading as well as magnification of specific areas of study.

DSA results in improved contrast sensitivity, permitting the use of much lower concentrations of contrast material.

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