In vitro comparison of prototype magnetic tool with conventional nitinol basket for ureteroscopic retrieval of stone fragments rendered paramagnetic with iron oxide microparticles.

PURPOSE: We developed a prototype magnetic tool for ureteroscopic extraction of magnetized stone particles. We compared its efficiency for retrieving magnetized calcium oxalate monohydrate stone particles with that of a conventional nitinol basket from the pelvi-collecting system of a bench top ureteroscopic simulator. MATERIALS AND METHODS: Iron oxide microparticles were successfully bound to 1 to 1.5, 1.5 to 2 and 2 to 2.5 mm human calcium oxalate monohydrate stones. Several coated fragments of each size were implanted in the collecting system of a bench top ureteroscopic simulator. Five-minute timed stone extraction trials were performed for each fragment size using a back loaded 8Fr magnetic tool mounted on a 0.038-inch guidewire or a conventional basket. The median number of fragments retrieved per timed trial was compared for the magnetic tool vs the basket using the Mann-Whitney U test. RESULTS: For 1 to 1.5 mm fragments the median number retrieved within 5 minutes was significantly higher for the prototype magnetic tool than for the nitinol basket (9.5 vs 3.5, p = 0.03). For 1.5 to 2 mm fragments the magnetic tool was more efficient but the difference in the number of fragments retrieved was not statistically significant (9.5 vs 4.5, p = 0.19). For 2 to 2.5 mm fragments there was no difference between the instruments in the number retrieved (6 per group, p = 1.0). CONCLUSIONS: The prototype magnetic tool improved the efficiency of retrieving stone particles rendered paramagnetic that were less than 2 mm but showed no advantage for larger fragments. This system has the potential to decrease the number of small retained fragments after ureteroscopic lithotripsy.

Rendering stone fragments paramagnetic with iron-oxide microparticles improves the efficiency and effectiveness of endoscopic stone fragment retrieval.

OBJECTIVES: To develop peptide-coated iron oxide-based microparticles that selectively adhere to calcium stone fragments, thereby enabling magnetic manipulation of human stone fragments. METHODS: In phase 1, human stone fragments were coated overnight with iron oxide-based microparticles. Groups of 10 coated stones (1.5-3 mm) were placed into a bladder simulator and removed cystoscopically with either an 8 Fr magnetic extraction device or a 2.4 Fr nitinol basket. In phase 2, the peptide coating was optimized and 2 stone fragment sizes (1-2 mm and 2-3 mm) were exposed to 3 separate concentrations of microparticles for 3 different incubation times. In each trial, 10 fragments were placed into a glass vial and removed using the 8 Fr magnetic device. RESULTS: In phase 1, mean total time for removal of all fragments was 53% shorter using the magnetic instrument compared with basket extraction. An average of 3.7 extractions was required to magnetically remove all fragments versus 9.4 for basket extraction. In phase 2, 18 different combinations of particle concentrations, fragment sizes, and incubation times were tested; 91% of small fragment trials and 43% of large fragment trials yielded successful fragment extraction. Of the small fragments, 100% were successfully extracted at both the middle and high particle concentrations after 2 minutes, and of the large fragments 70% and 100% were successfully extracted after 10 minutes of incubation at the lowest and highest concentrations, respectively. CONCLUSIONS: Rendering stone fragments paramagnetic with novel microparticles allows manipulation and removal using a novel magnetic device in vitro, potentially improving surgical efficacy and efficiency.