Abstract
We modeled retropulsion during holmium:YAG lithotripsy on the conservation of momentum, whereby the force of ejected fragment debris off of the calculous surface should equal the force of retropulsion displacing the stone. We tested the hypothesis that retropulsion occurs as a result of ejected stone debris. Uniform calculous phantoms were irradiated with holmium:YAG energy in air and in water. Optical fiber diameter and pulse energy were varied. Motion of the phantom was monitored with high speed video imaging. Laser induced crater volume and geometry were characterized by optical coherence tomography. To determine the direction of plume laser burn paper was irradiated at various incident angles. Retropulsion was greater for phantoms irradiated in air versus water. Retropulsion increased as fiber diameter increased and as pulse energy increased (p <0.001). Crater volumes increased as pulse energy increased (p <0.05) and generally increased as fiber diameter increased. Crater geometry was wide and shallow for larger fibers, and narrow and deeper for smaller fibers. The ejected plume propagated in the direction normal to the burn paper surface regardless of the laser incident angle. Retropulsion increases as pulse energy and optical fiber diameter increase. Vector analysis of the ejected plume and crater geometry explains increased retropulsion using larger optical fibers. Holmium:YAG lithotripsy should be performed with small optical fibers to limit retropulsion.
Highlights
Retropulsion increases as pulse energy and optical fiber diameter increase
Holmium:YAG lithotripsy should be performed with small optical fibers to limit retropulsion
In lasers with a short pulse duration of less than 1 microsecond retropulsion occurs mainly due to strong pressure waves or laser induced shock waves caused by symmetrical collapse of a spherical cavitation bubble.[5, 6]
Summary
Uniform calculous phantoms were irradiated with holmium:YAG energy in air and in water. Optical fiber diameter and pulse energy were varied. Laser induced crater volume and geometry were characterized by optical coherence tomography. Uniform calculous phantoms were prepared using plaster of Paris. Mm.[3] The calculous phantom was placed in an in vitro ureteral model consisting of a clear glass tube with an inner diameter of 12.5 mm. A clinical and a scientific holmium:YAG laser were used in our study. Holmium: YAG energy was delivered to a calculous phantom in contact mode with low OHϪ quartz fibers 272, 365, 550 and 940 m. Before and after ablation laser energy out of the distal end of the fiber was measured with an energy meter equipped with a pyroelectric joulemeter
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