Subtraction magnetic resonance for tumours of the skull base and sinuses: a new imaging technique.

A new imaging technique is described, in which photographic subtraction as practised in angiography, is combined with Gadolinium enhanced Magnetic Resonance (GdMR) imaging and applied to the investigation of the paranasal sinuses and skull base. The densities on the subtraction image are dependent upon the blood supply of the tissues examined, thus producing a record of their vascularity: in effect a vasculogram. The method has proved to be technically feasible, and is advantageous in certain situations, particularly those in which the anatomy is complex as in the skull base or where normal structures have been distorted by previous surgery. The technique provides a more accurate record of tumour extent than that shown on unsubtracted GdMR scans.