*2.1.1. Fiber*

A commercially available pulsed Ho:YAG laser at 2.13 with a 365‐μm core diameter fiber impinging on calculus phantoms (Plaster of Paris, white gypsum cement, 10‐mm cube) was employed to simulate the URS process. Laser power‐caused pressure wave, cavitation bubble dynamics, and calculus particles scattering were videotaped by a high‐speed camera with 10,000–930,000 frames per second (fps). The pressure wave is captured by the Schlieren method. The contribution of ejected stone particles in fiber‐tip degradation is also investi‐ gated. The study concluded that using a high‐speed camera combining with the Schlieren technique is a powerful tool to study the movement of the pressure wave and its relationship with bubble dynamics and stone damage. More study in pressure wave shaping by the geo‐ metric shape of the fiber tip and the detailed mechanisms of shock waves, cavitation bubble

During the treatment of urolithiasis, the urinary calculus is subjected to retropulsion forces induced by the combined effects of ablated particle ejection, interstitial water vaporization, and bubble dynamics [25–27]. Therefore, because of the retropulsion, the stone has moved away from the fiber tip. This can cause longer procedure time because of additional steps of finding the dislocated stone and repositioning the fiber tip to it. Recoil motion investigations in the past revealed the relation between retropulsion displacement and laser power, fre‐ quency, and fiber core size [28–31]. Recoil motion is proportional to the laser power and the fiber core size. Furthermore, another research claimed that the recoil motion decreased with a

The amplitude of stone recoil motion (retropulsion) during kidney stone treatment depends mainly on the power source or instrument. The pneumatic or electrohydraulic lithotripters cause a much bigger recoil motion than laser lithotripters [30, 33–34]. Nevertheless, the laser lithotripters can cause noticeable dislocation of the stone during the procedure. A few inves‐ tigations of the URS treatment of upper ureteral calculi have revealed that the main reason for calculus‐free failures can be due to recoil motion and less frequently to inability to track or seek the stones [35–37]. Recoil‐dislocated calculus could lead to longer operation period, the necessity for another process to deal with recoiled parts and as such reduced stone‐ free level. The stone recoil motion results in additional patient morbidity and health‐care expenses [30, 33]. Besides, left‐behind stone debris can act as a seed for calculus growing

The previous studies on stone retropulsion often employed a holder, like a test tube or a "V" shape groove. These approaches, however, have shown large uncertainty and low accu‐ racy, most likely due to the friction between the stone phantom and the holder on which the stone phantom stationed. For instance, stone phantoms (Plaster of Paris, 10‐mm cube) were employed to simulate the URS process, with the previous methodology resulted in <0.5‐mm entire recoil movement (either with a "V" grove or a test tube). When scaling down the stone size to 5‐mm cube (1/8 in volume), the recoil movement was very unpredictable. Our ear‐ lier study of recoil movement on a 5‐mmcube resulted in a 59% standard deviation [38], for

example, a peak‐to‐peak recoil movement range of ∼3–10 times as much.

dynamics, and calculus debris ejection will be investigated in a future study.

84 Updates and Advances in Nephrolithiasis - Pathophysiology, Genetics, and Treatment Modalities

longer laser pulse without compromising dusting effectiveness significantly [32].

**1.3. Calculus migration/retropulsion**

back, renal colic, and persistent infection.

**Figure 4** shows a picture of SureFlexTM fibers, Model S‐LLF273/365, 273/365‐μm core diameter fibers (S‐LLF273/365 SureFlex Fibre, Boston Scientific Corp., San Jose, CA, USA) that are used in the test of this study.
