Densitometric analysis of scans: important sources of artefact.

Computed tomography (CT) research in psychiatry often relies on the assessment of minor structural changes. Recently, it has come to encompass changes in regional brain X-ray absorption density. The artefacts prone to be encountered in density measurements are reviewed, and illustrated by a series of studies carried out using a CT 1010 scanner. They are shown to be more important than hitherto assumed in the interpretation of CT scan research.