BACKGROUND: The goal in the treatment of urolithiasis is not only to remove the stone but also to prevent future stone formation by rendering the patient fragment-free. Surgical treatments for renal and ureteral stones often involves endoscopic techniques which are limited by the ability to visualize the stones well, even when used in conjunction with XRay/US. The purpose of this study is to evaluate the use of fluorescence probes as a novel method of identifying urolithiasis.
METHODS: Calcium oxalate, struvite, uric acid, mixed composition stones and a negative control were incubated with fluorescence probes, Osteosense ^TM 680 and 750 (XXX medical). Imaging was performed with the OV-100 . In addition, the stones were also placed into the renal pelvis of mice, and the probes were injected intravenously. Imaging was performed at various times post injection.
RESULTS: In vitro, the 680 probe demonstrated high binding affinity (Density (D) = 12-14) for calcium oxalate, struvite and uric acid stones and a lower binding affinity for mixed composition stone (D =8). In contrast, the 750 probe demonstrated high binding affinity for calcium oxalate and struvite (D = 17-18) stones and a lower binding affinity for uric acid and mixed composition stones (D = 1-6). In vivo, intravenous administration of the probes were successful in labeling all the stone types. The intensity of the signal from the probes was dependent on time, with a peak intensity at 3-5 days for the 680 probe and 24 hours for the 750 probe. The estimated tissue depth for visualization was approximately 5-6 mm.
CONCLUSIONS: Fluorescence imaging using the Osteosense^TM 680 and 750 probe provides an alternative method of identifying stones in the urinary tract. In addition, it may also help to identify the composition of the stone based upon the differential affinity for the probes. The improved visualization of these stones/fragments would make endoscopic procedures less difficult for the surgeon, decreases the risk of injuring the kidney and adjacent organs, and increases the chance of rendering the patient stone/fragment free after the procedure.