UROLITHOSCINTIGRAPHY - PRELIMINARY-REPORT OF A NEW IMAGING MODALITY FOR UROLITHIASIS

We investigated the use of bisphosphonates, analogs of pyrophosphate t hat bind to mineralized tissue, to image renal calculi in vivo. Twenty stone-bearing kidneys in 15 patients without urinary obstruction were studied. Technetium-99m-methylene diphosphonate was injected intraven ously followed by 20 mg of furosemide 4 hours later, and images were o btained by gamma counter for 30 minutes. Areas of increased uptake cor responded with the sites of calculi, and even small or radiolucent cal culi were easily seen. Counts in the region of each kidney, the L4 ver tebral body, and a background area were combined to calculate a scinti gram index (SI) for each kidney. The mean SI of the stone-bearing kidn eys was 4.8 +/- 3.5 v 1.3 +/- 0.4 for the normal kidneys. There was co rrelation of the SI with stone composition and size but not with radio graphic density. After correction for size, the SI of stone-bearing ki dneys remained significantly higher than the SI of normal kidneys, but the differences between calculi of different compositions were dimini shed. Nonetheless, high SI values were associated with soft types of c alculi and low values with hard types. Future investigations will reve al if this association is constant and if there is any relation betwee n bisphosphonate uptake and response to lithotripsy. The sensitivity o f urolithoscintigraphy to image small or radiolucent calculi may make it an effective technique for the assessment of residual fragments aft er lithotripsy.