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


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.
University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, USA.
Yung K
YK
Tan
Stacey L
SL
McLeroy
Stephen
S
Faddegon
Ephrem
E
Olweny
Raul
R
Fernandez
Heather
H
Beardsley
Bruce
B
Gnade
Samuel
S
Park
Margaret S
MS
Pearle
Jeffrey A
JA
Cadeddu
D000497:Alloys; D002129:Calcium Oxalate; D003198:Computer Simulation; D004578:Electron Spin Resonance Spectroscopy / Q000295:instrumentation*; D004867:Equipment Design; D005290:Ferric Compounds; D006801:Humans; D066298:In Vitro Techniques; D008280:Magnetics / Q000295:instrumentation*; D008953:Models, Anatomic; D010316:Particle Size; D014514:Ureteral Calculi / Q000628:therapy*; D018666:Ureteroscopy / Q000295:instrumentation*
D000497:Alloys; D005290:Ferric Compounds; C000499:ferric oxide; D002129:Calcium Oxalate; C013616:nitinol