99Tcm HMPAO-labelled leucocyte imaging in Crohn's disease: a subtraction technique for the quantification of disease activity.

A new technique for the quantitative analysis of labelled leucocyte images from patients with inflammatory bowel disease is described. The method involves the computer generation of a 'background' image which, after appropriate registration, is subtracted from the patient's image to leave a residue which represents abnormal uptake in the bowel. Quantification of the residual activity yields a scan score which can be related to the level of disease activity in patients with Crohn's disease. In 54 investigations on 33 patients the scan scores correctly agreed with a clinical assessment of disease activity in 16 of 20 cases with inactive disease and 32 out of 34 cases with active disease. Most of the discrepancies reflected inaccuracies in the clinical assessment of activity rather than shortcomings of the imaging technique.