A novel method of imaging calcium urolithiasis using fluorescence

Purpose: In the surgical management of urolithiasis the goal of treatment is not only to remove calculi, but also prevent future stone formation by rendering the patient stone-free/fragment-free. Achieving this goal is often difficult with endoscopic procedures due to the inability to visualize small calculi well even with x-ray or ultrasound. We evaluated fluorescence probes as a novel method of identifying calculi in the urinary tract. Materials and Methods: In vitro calcium stones were incubated with each of the Osteosense (TM) 680 and Osteosense 750 calcium binding fluorescence probes, and imaged with a near infrared fluorescence imaging system. Using a mouse model calculi were placed in the renal pelvis and the probes were injected intravenously. Imaging was performed at various times after injection. Results: In vitro the Osteosense 680 probe demonstrated high binding affinity for calcium oxalate-struvite, calcium phosphate-struvite and ammonium urate-calcium oxalate-calcium phosphate stones, and lower binding affinity for the calcium phosphate stone. In contrast, the Osteosense 750 probe demonstrated high binding affinity for calcium oxalate-struvite and calcium phosphate-struvite stones, and lower binding affinity for calcium phosphate and ammonium urate-calcium oxalate-calcium phosphate stones. In vivo intravenous administration of the probes was successful in labeling all calcium stone types tested. Conclusions: Fluorescence imaging provides a new method for identifying calculi in the urinary tract. The improved visualization of these stones/fragments would make endoscopic procedures less difficult, decrease the risk of complications and increase the chance of rendering the patient stone-free/fragment-free.