Introduction

Laser lithotripsy (LL) has become a first-line modality for treatment of many diagnoses of urinary tract _x000D_ stones. The de facto gold standard laser source for LL systems is a Ho:YAG (Ho) laser emitting at the wavelength of 2.10 µm. _x000D_ Dusting mode of operation (i.e., reduction of stones to fragments < 1÷2 mm in size) has been recognized as the most clinically _x000D_ desired regime. Recently, a high peak power pulsed Tm fiber laser emitting at 1.94 µm has been proposed as a viable alternative to _x000D_ Ho laser. In this work, we present for the first time a detailed in vitro performance comparison between top-of-the line Ho system _x000D_ and the new super-pulse Tm system in the dusting mode._x000D_

Methods

A top-of-the-line Ho system (up to 120 W average power) was compared with a prototype pulsed Tm system capable of _x000D_ operation with up to 50 W average and 500 W peak power. The in vitro experimental setup included a specially designed cuvette _x000D_ allowing quantitative assessment of size distribution of stone fragments. A precisely controlled flow of water was pumped through _x000D_ the cuvette. The setup was also equipped with a high-resolution optical camera and several needle thermocouples. Post-surgery _x000D_ human stones (both bladder and kidney) as well as phantoms were used for the experiments._x000D_

Results

Treatments with the two LL systems were matched in terms of average power (4, 8, 16, 32, 40 W) and/or pulse energy (0.2_x000D_ to 1.0 J), as appropriate. At least three stone specimens were used in each experiment. The following parameters have been _x000D_ evaluated: ablation rate (down to “dust” fragments < 1 mm), magnitude of the retropulsion effect (after a single pulse), temperature _x000D_ rise at water outlet vs inlet, and maximum temperature rise in the cuvette during treatment. For the ablation rate, the following _x000D_ values were measured with Ho laser: 0.62 ± 0.04 mg/s at 8 W, 40 Hz setting; 0.89 ± 0.06 mg/s at 16 W, 80 Hz; and 1.37 ± 0.48 _x000D_ mg/s at 40 W, 50 Hz. The respective numbers with Tm laser, at identical settings, were: 1.0 ± 0.2 mg/s, 2.13 ± 0.13 mg/s, and 3.64 _x000D_ ± 0.29 mg/s. The temperature rise in the cuvette was nearly equal for the two lasers. The average retropulsion distance after a _x000D_ single pulse was substantially shorter with the Tm laser. Similar tendencies were observed for the entire range of tested parameters._x000D_

Conclusions

For all average power levels investigated, Tm laser demonstrated a significantly (~2 times) higher ablation rate than _x000D_ Ho laser, while maintaining equivalent thermal regime. The retropulsion effect of Tm laser was considerably less pronounced than _x000D_ that of Ho laser at equal energy settings._x000D_

Funding

IPG Medical