Recognition of the superscan in prostatic bone scintigraphy.

Widespread bone metastases can occasionally give rise to a uniform distribution of 99Tcm methylene diphosphonate resulting in a superficially normal appearance on the bone scan. The scans are recognizable by the high ratio of bone to soft tissue activity, the absence of focal lesions in the axial skeleton, and there are usually no renal images. These "superscans" can occasionally be misinterpreted as normal. An index of image quantitation related to the ratio of bone to soft tissue uptake is shown to be capable of clearly distinguishing these patients from patients in other categories. The condition is thought to be more frequently associated with prostatic carcinoma than with other aetiologies.