A novel method of imaging calcium urolithiasis using fluorescence

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.

In vitro calcium stones were incubated with each of the Osteosense 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.

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.

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.