Limitations of circulation time in the diagnosis of intracranial disease.

The mode circulation time was measured using intravenously injected technetium 99(m) and a collimation system devised to discriminate between the right and left sides of the head. The results in 21 normal men were used as a basis of assessing the findings in 205 patients, made up of five diagnostic groups (ischaemia, haematoma, subarachnoid haemorrhage, intracranial tumour, and head injury). The average mode circulation time in the affected hemisphere for the three groups with vascular disease was increased, but even in these groups half the patients had a mode circulation time within 1 SD of normal mean; similar results were found for asymmetry between the hemispheres. In serial measurements in 45 patients no correlation was found between change in mode circulation time and the clinical state. That so many results are within the normal range limits the value of this method.