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In Vitro Evaluation of Pulsed Thulium:YAG and High-Power Ho:YAG Lasers with Multiple Pulse Modulations
Alejandra Bravo-Balado1,2, Antoni Sánchez-Puy1,2, Paula Izquierdo2
1Department of Surgery and Morphological Sciences, Universitat Autònoma de Barcelona, Barcelona, Spain.
Objective:
To compare stone ablation volume (AV) and ablation morphology between pulsed thulium:YAG (p-Tm:YAG) and high-power holmium:YAG (Ho:YAG) lasers with different pulse modulation technologies using an in vitro stone model.
Materials And Methods:
BegoStone phantoms (15:6 powder-to-water ratio) were used. A motorized arm applied the laser on the phantoms at a constant speed (0.7 mm/s). Three laser settings were tested: 1.5 J × 5 Hz, 1 J × 20 Hz, and 0.3 J × 50 Hz. For p-Tm:YAG, short pulse (SP) and long pulse (LP) modes were evaluated; for Ho:YAG, SP, LP, Vapor Tunnel™ (VT™), and Virtual Basket™ (VB™) modes were tested. Five 21-mm fissures were created per setting. AV was calculated from fissure width (WOF) and depth (DOF) measured by optical microscopy.
Results:
A total of 555 measurements were analyzed. At 1.5 J × 5 Hz, p-Tm:YAG (SP) produced the deepest fissures (DOF = 1000 µm vs 523.3-734.3 µm, p < 0.05) and was the only modality with a width-to-depth ratio <1, indicating deeper and narrower fissures. In contrast, p-Tm:YAG (LP) showed DOF and width-to-depth ratios comparable with Ho:YAG. At 1 J × 20 Hz, p-Tm:YAG (LP) generated wider, shallower fissures with a lower AV (11.9 mm³ vs 16.9-19.7 mm³, p < 0.05), whereas Ho:YAG (VB™) demonstrated a comparable AV. At 0.3 J × 50 Hz, p-Tm:YAG (LP) and Ho:YAG (VB™) exhibited similar width-to-depth ratios (1.3-1.4), whereas Ho:YAG (LP) and (VT™) achieved greater AV (7.4-8.0 vs 3.4 mm³; p < 0.05), driven by greater DOF.
Conclusions:
p-Tm:YAG and Ho:YAG lasers demonstrated distinct ablation morphologies depending on pulse modulation and laser settings. At intermediate and low-energy settings, p-Tm:YAG (LP) produced wider, shallower fissures, whereas several Ho:YAG modalities achieved greater AV through deeper fissures. Ho:YAG (VB™) showed the most similar ablation morphology to p-Tm:YAG (LP). Whether these differences translate into clinical performance remains to be determined.
