*2.1.2. Calculus phantom*

Calculus phantoms made of Plaster of Paris gypsum employed as tissue phantom for human calculi (UtralCal®30, United States Gypsum Company, Chicago, IL, USA), were broadly utilized for URS investigations by other investigators [40]. The calculus phantoms are made by mixing gypsum powder (500 g) with distilled water (0.23 l) and followed by curing for more than 3 h (preferred overnight). The gypsum was cast to have a dimension of 10‐mm cube as indicated in **Figure 5**. The average weight of the stone phantom is 1.8 g, and with a tensile strength of 2 MPa, which is similar to the tensile strength of a human struvite (0.1–3.4 MPa) [41].

**Figure 4.** Picture of SureFlexTM 273‐ and 365‐μm fibers.

**Figure 5.** 10 × 10 × 10 mm<sup>3</sup> calculus phantom.

#### *2.1.3. Laser system*

The laser systems utilized in this study included a pulsed Ho:YAG laser at 2.13 μm, Holmium 30 W (StoneLightTM 30, American Medical Systems, San Jose, CA, USA), with pulse energy from 0.5 up to 3.0 J, and pulse width from 150 up to 800 μs, as well as a Q‐switched Tm:YAG laser at 2.01 μm with pulse energy of ∼0.02 J. **Figure 6** shows a temporal pulse structure dia‐ gram of StoneLightTM 30 Ho:YAG laser with the pulse duration (*τ*p) of ∼240 μs. This magni‐ tude of pulse duration is known to generate the necessary photothermal effect of fragmenting the stones [42].

A lab‐constructed Q‐switched Tm:YAG laser (2.01 μm) was used for this investigation, as indicated in **Figure 7**. The gain medium Tm:YAG is energized by laser diode pumping beam from a laser diode stack via a delivery system. An optical focusing glass is employed to com‐ pensate the strong thermal lens of Tm:YAG medium to sustain the stability of the resonator cavity. Besides, a lab‐built acoustic Q‐switch is oriented within the resonator to manipulate the output beam in a Q‐switched manor. The laser has a frequency from 1 up to 2 kHz and pulse energy of 20 mJ at the distal end of the beam delivery fiber. Singular light pulse at the far end of the delivery fiber can be dispatched by an extra‐cavity shutter in between the out‐ put window (OC) of laser resonator and the light‐focusing optics system. **Figure 8** displays a light pulse with a pulse length (*τ*p) of 750 ns (FWHM). This magnitude of pulse length is accredited to cause very intense shock wave pressure due to bubble collapse in water [13, 16]. This 2.01‐μm wavelength light source is a suitable tool to study the dependence of water composition in the calculus on fragmentation effectiveness due to its level of water absorp‐ tion constant at 70 cm−1 [43].

#### *2.1.4. Setup*

**Figure 9** shows the schematic diagram and picture of the hydrophone setup: (a) sche‐ matic block diagram; (b) pictures of the setup. From the schematic block diagram, the centerpiece is the blue color water tank that hosts three holders with 3‐D adjustable stages, Investigation of Laser Pulse‐induced Calculus Damage Mechanism by a High‐speed Camera http://dx.doi.org/10.5772/intechopen.69981 87

**Figure 6.** The StoneLightTM 30 Ho:YAG Laser system. (a) laser pulse trace; (b) Laser picture.

*2.1.3. Laser system*

**Figure 5.** 10 × 10 × 10 mm<sup>3</sup>

calculus phantom.

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

the stones [42].

tion constant at 70 cm−1 [43].

*2.1.4. Setup*

The laser systems utilized in this study included a pulsed Ho:YAG laser at 2.13 μm, Holmium 30 W (StoneLightTM 30, American Medical Systems, San Jose, CA, USA), with pulse energy from 0.5 up to 3.0 J, and pulse width from 150 up to 800 μs, as well as a Q‐switched Tm:YAG laser at 2.01 μm with pulse energy of ∼0.02 J. **Figure 6** shows a temporal pulse structure dia‐ gram of StoneLightTM 30 Ho:YAG laser with the pulse duration (*τ*p) of ∼240 μs. This magni‐ tude of pulse duration is known to generate the necessary photothermal effect of fragmenting

A lab‐constructed Q‐switched Tm:YAG laser (2.01 μm) was used for this investigation, as indicated in **Figure 7**. The gain medium Tm:YAG is energized by laser diode pumping beam from a laser diode stack via a delivery system. An optical focusing glass is employed to com‐ pensate the strong thermal lens of Tm:YAG medium to sustain the stability of the resonator cavity. Besides, a lab‐built acoustic Q‐switch is oriented within the resonator to manipulate the output beam in a Q‐switched manor. The laser has a frequency from 1 up to 2 kHz and pulse energy of 20 mJ at the distal end of the beam delivery fiber. Singular light pulse at the far end of the delivery fiber can be dispatched by an extra‐cavity shutter in between the out‐ put window (OC) of laser resonator and the light‐focusing optics system. **Figure 8** displays a light pulse with a pulse length (*τ*p) of 750 ns (FWHM). This magnitude of pulse length is accredited to cause very intense shock wave pressure due to bubble collapse in water [13, 16]. This 2.01‐μm wavelength light source is a suitable tool to study the dependence of water composition in the calculus on fragmentation effectiveness due to its level of water absorp‐

**Figure 9** shows the schematic diagram and picture of the hydrophone setup: (a) sche‐ matic block diagram; (b) pictures of the setup. From the schematic block diagram, the centerpiece is the blue color water tank that hosts three holders with 3‐D adjustable stages, one for fiber (a 365‐μm core diameter fiber, S‐LLF365 SureFlex Fibre, Boston Scientific Corporation, San Jose, CA, USA, delivers the laser pulse), the second one for calculus phantom and the third one for the hydrophone (Mueller‐Platte Needle Probe 100‐100‐1, Dr. Mueller Instruments, Germany). A ceramic screen is used to reflect the illumination from two high‐intensity LED lamps for a better view of the action center near fiber tip. An SA5 camera from Photron (SA5 16G BW, Photron USA, Inc., San Diego, CA, USA), capable of one million frames per second, is used to record the event and the images are saved to the computer. The oscilloscope (Tektronix DPO 4140 Digital Phosphor Oscilloscope, Tektronix, Inc., Beaverton, OR, USA) is used to monitor and record the optical laser pulses detected by a photodetector (Thorlabs DET10D 2.6 μm InGaAs detector, Newton, NJ, USA) and the transient pressure signal from the hydrophone. In the hydrophone setup picture,

**Figure 7.** Lab built Q‐switched Tm:YAG Laser setup.

**Figure 8.** Q‐switched Tm:YAG Laser Pulse.

it is shown that the tip of the hydrophone is ∼10 mm away from the tip of the fiber. The hydrophone can be located at a different location or orientation if needed.

As a standard data collection convention, the entire test is repeated 10 times and each data point is an average of these 10 measurements.

Investigation of Laser Pulse‐induced Calculus Damage Mechanism by a High‐speed Camera http://dx.doi.org/10.5772/intechopen.69981 89

**Figure 9.** The schematic block diagram and pictures of the test setup. (a) Schematic block diagram; (b) Picture of the hydrophone setup.

#### **2.2. Fiber‐tip damage mechanism**

#### *2.2.1. Laser system*

it is shown that the tip of the hydrophone is ∼10 mm away from the tip of the fiber. The

As a standard data collection convention, the entire test is repeated 10 times and each data

hydrophone can be located at a different location or orientation if needed.

point is an average of these 10 measurements.

**Figure 8.** Q‐switched Tm:YAG Laser Pulse.

**Figure 7.** Lab built Q‐switched Tm:YAG Laser setup.

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

A commercially available Ho:YAG Lumenis VersaPulse® laser (VersaPulse® 100 W, Lumenis Ltd., Yokneam, Israel) was employed for this study. The laser is capable of generating 100 W of laser power at 50 Hz, and up to 3 J of pulse energy at 10 Hz. **Figure 3** shows a temporal pulse structure diagram of a typical 1‐J pulse with a pulse duration (*τ*p) of ∼240 μs. Again, this magnitude of pulse duration is known to generate the photothermal effect necessary to fragment the stones [42].

This in vitro study again utilized a 365‐μm core diameter fiber, and a calculus phantom (Plaster of Paris, 10 × 10 × 10 mm<sup>3</sup> cube) to mimic laser lithotripsy procedure. The test setup for laser‐ induced shock wave by the Schlieren imaging technique is depicted in **Figure 10**. The illumi‐ nating laser is a He‐Ne beam at 543.5‐nm wavelength. The two telescopes used for laser beam expansion each has a three times amplification. They enlarge the He‐Ne beam size from ∼1.7 to a 15 mm in diameter. The water box contains two handles with 3‐D adjustable stages, one is for the fiber (a 365‐μm core diameter fiber, S‐LLF365 SureFlex Fibre, Boston Scientific Corp., San Jose, CA, USA) and the other is for the stone phantom. The focusing optics is a 100‐mm plano‐convex optics with a 2" OD. The razor blade edge is positioned at the focus of the focus‐ ing optics. Besides, a high‐speed camera was employed to videotape the laser‐stone interac‐ tion. The SA5 camera from Photron has a frame rate of up to one million frames per second.

#### **2.3. Calculus migration/retropulsion**

#### *2.3.1. Laser system*

The laser system used for calculus migration/retropulsion is the same as that in Section 2.2.1.

#### *2.3.2. Experimental setup*

In this investigation, a commercial flash lamp pumped Ho:YAG laser at 2.13 μm, a 365‐μm core diameter fiber, and a stone phantom (Plaster of Paris, 10 mm cube) were employed to simulate URS treatment process. An in‐water pendulum is setup for recoil motion investigation, which

**Figure 10.** Schematic picture of test setup.

is composed of a calculus phantom with the size of 10 × 10 × 10 mm<sup>3</sup> as depicted in **Figure 11**. The calculus phantom is hung underwater by a string of ∼200‐mm long. In order to control the rotational motion of the stone in case the laser pulse from the fiber is not exactly pointed at the center of the mass of the stone phantom, the stone is held in a clear plastic basket and two threads with a separation of ∼10 mm are used to hang the phantom (**Figure 11b**). Since water has a relatively low viscosity (1.002 mPa\*s), the suspended phantom pendulum under water has virtually no friction and is free to move in the direction perpendicular to the thread. A 365‐μm core diameter fiber (S‐LLF365 SureFlex Fibre, Boston Scientific Corp., San Jose, CA, USA) was used to deliver the laser pulse to the stone phantom. Furthermore, a high‐speed camera was used to study the movement of the calculus. The SA5 camera from Photron (SA5 16G BW, Photron USA Inc., San Diego, CA, USA) is capable of one million frames per second as shown in **Figure 11(c)**. In contrast to a conventional camera, the high‐speed camera can be used to video tape and to fully characterize the kinetic motion of the stone phantom retropul‐ sion. These dynamic details include the displacement, speed, and acceleration parameters of the stone phantom during laser lithotripsy.

This in vitro study again utilized a 365‐μm core diameter fiber, and a calculus phantom (Plaster

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

induced shock wave by the Schlieren imaging technique is depicted in **Figure 10**. The illumi‐ nating laser is a He‐Ne beam at 543.5‐nm wavelength. The two telescopes used for laser beam expansion each has a three times amplification. They enlarge the He‐Ne beam size from ∼1.7 to a 15 mm in diameter. The water box contains two handles with 3‐D adjustable stages, one is for the fiber (a 365‐μm core diameter fiber, S‐LLF365 SureFlex Fibre, Boston Scientific Corp., San Jose, CA, USA) and the other is for the stone phantom. The focusing optics is a 100‐mm plano‐convex optics with a 2" OD. The razor blade edge is positioned at the focus of the focus‐ ing optics. Besides, a high‐speed camera was employed to videotape the laser‐stone interac‐ tion. The SA5 camera from Photron has a frame rate of up to one million frames per second.

The laser system used for calculus migration/retropulsion is the same as that in Section 2.2.1.

In this investigation, a commercial flash lamp pumped Ho:YAG laser at 2.13 μm, a 365‐μm core diameter fiber, and a stone phantom (Plaster of Paris, 10 mm cube) were employed to simulate URS treatment process. An in‐water pendulum is setup for recoil motion investigation, which

cube) to mimic laser lithotripsy procedure. The test setup for laser‐

of Paris, 10 × 10 × 10 mm<sup>3</sup>

**2.3. Calculus migration/retropulsion**

*2.3.1. Laser system*

*2.3.2. Experimental setup*

**Figure 10.** Schematic picture of test setup.

**Figure 11.** Schematic picture of the pendulum setup. (a) Schematic; (b) Picture of actual setup; (c) the experimental setup including the pendulum and high‐speed camera.
