High-speed photographic evaluation of holmium laser

Observation and comparison of gas formation during holmium:YAG laser lithotripsy of cystine, uric acid, and calcium oxalate stones: a chromatographic and electron microscopic analysis

The primary aim of the present in vitro study is to analyze the chemical content of the bubbles occurring during the fragmentation of cystine stones with both the high-power and low-power holmium:YAG (Ho:YAG) lasers. The secondary aim is to discuss their clinical importance. Three types of human renal calculi calcium oxalate monohydrate (COM), cystine, and uric acid were fragmented with both low-power and high-power Ho:YAG lasers in separate experimental setups at room temperature, during which time it was observed whether gas was produced. After laser lithotripsy, a cloudy white gas was obtained, after the fragmentation of cystine stones only. A qualitative gas content analysis was performed with a gas chromatography-mass spectrometry (GC-MS) device. The fragments in the aqueous cystine calculi setup were dried and taken to the laboratory to be examined by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) and X-ray diffraction analysis. No gas production was observed after fragmentation in the COM and uric acid stones. Free cystine, sulfur, thiophene, and hydrogen sulfide gas were produced by both low-power and high-power Ho:YAG laser lithotripsy of the cystine stones. In the SEM-EDX mapping analysis, a free cystine molecule containing 42.8% sulfur (S), 21% oxygen (O), 14.9% carbon (C), and 21% nitrogen (N) atoms was detected in the cystine stone experimental setup. The evidence obtained, which shows that hydrogen sulfide emerges in the gaseous environment during Ho:YAG laser fragmentation of cystine stones, indicates that caution is required to prevent the risk of in vivo production and toxicity.

Plasma formation in holmium:YAG laser lithotripsy

OBJECTIVES

During holmium:yttrium-aluminum-garnet (holmium:YAG) laser lithotripsy to break urinary stones, urologists frequently see flashes of light. As infrared laser pulses are invisible, what is the source of light? Here we studied the origin, characteristics, and some effects of flashes of light in laser lithotripsy.

METHODS

Ultrahigh-speed video-microscopy was used to record single laser pulses at 0.2-1.0 J energy lasered with 242 µm glass-core-diameter fibers in contact with whole surgically retrieved urinary stones and hydroxyapatite (HA)-coated glass slides in air and water. Acoustic transients were measured with a hydrophone. Visible-light and infrared photodetectors resolved temporal profiles of visible-light emission and infrared-laser pulses.

RESULTS

Temporal profiles of laser pulses showed intensity spikes of various duration and amplitude. The pulses were seen to produce dim light and bright sparks with submicrosecond risetime. The spark produced by the intensity spike at the beginning of laser pulse generated a shock wave in the surrounding liquid. The subsequent sparks were in a vapor bubble and generated no shock waves. Sparks enhanced absorption of laser radiation, indicative of plasma formation and optical breakdown. The occurrence and number of sparks varied even with the same urinary stone. Sparks were consistently observed at laser energy >0.5 J with HA-coated glass slides. The slides broke or cracked by cavitation with sparks in 63 ± 15% of pulses (1.0 J, N = 60). No glass-slide breakage occurred without sparks (1.0 J, N = 500).

CONCLUSION

Unappreciated in previous studies, plasma formation with free-running long-pulse holmium:YAG lasers can be an additional physical mechanism of action in laser procedures.

Comparative efficacy and safety of holmium laser enucleation of the prostate (HoLEP) using moses technology and standard HoLEP: A systematic review, meta-analysis, and meta-regression

Purpose

The use of HoLEP was associated with steep learning curve thus prolonging operative procedure. The problem of learning curve could be solved with the invention of Moses HoLEP. This study aimed to evaluate the comparison of efficacy and safety between Moses HoLEP and standard HoLEP in BPH patient.

Materials and methods

Systematic search was carried out using PRISMA guideline. Pubmed, Scopus and Embase were searched to collect randomized controlled trials and observational studies. Quantitative analysis was performed to evaluate the comparison in intraoperative, postoperative and complications characteristics. RevMan 5.4 and STATA were used in data analysis.

Results

Total of 7 studies (1226 patients) were included. Regarding intraoperative characteristics, Moses HoLEP provided significantly shorter enucleation time (MD: 3.00, 95% CI: 5.57 to −0.43, p = 0.02), shorter hemostasis time (MD: 3.79, 95% CI: 5.23 to −2.34, p < 0.00001), and shorter laser use time (MD: 2.79, 95% CI: 5.03 to −0.55, p = 0.01). For postoperative characteristics, Moses HoLEP possessed significantly lower PVR (MD -34.57, 95% CI -56.85 to −12.30, p = 0.002). Overall complication was higher in standard HoLEP although the result was not significant (MD 0.68, 95%CI: 0.38 to 1.21, p = 0.19). Moses HoLEP possessed more superiority over standard HoLEP regarding shorter hemostasis time with the increasing of prostate size (coefficient −0.894, p = 0.044).

Conclusion

Moses HoLEP demonstrated shorter enucleation time, shorter hemostasis time and shorter laser use time. Moses HoLEP also possessed lower PVR. There were no safety issues in Moses HoLEP compared with standard HoLEP.

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Moses HoLEP is able to divide the laser into 2 waves enabling to increase the efficiency of the HoLEP procedure.

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Moses HoLEP demonstrated superiority intraoperatively with shorter enucleation time, hemostasis time and laser use time.

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Moses HoLEP demonstrated superiority in post operative outcome of lower PVR.

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Moses HoLEP possessed no safety issues compared to standard HoLEP.

Stone retropulsion caused by the pulse-duration adjustable Holmium laser: analysis of the whole-process dynamics with a modified method

INTRODUCTION

Stone retropulsion was shown to be impacted by pulse duration during Holmium laser lithotripsy, while the whole process of retropulsion was troublesome to study. We developed a modified method to analyze retropulsion using a smartphone and video tracking software.

MATERIALS AND METHODS

A Holmium laser system was incorporated with a short (200 μs) and long pulse duration (800 μs), and a 272 μm core fiber was attached. A cross-sectional V-shaped rail was submerged in a tank, on which artificial stones were displaced linearly after lasering. Different combinations of pulse energy, frequency and pulse duration were tested for at least four seconds. An iPhone 11 capable of high-definition videoing and video tracking software were used to analyze the stone's displacement and velocity.

RESULTS

For most settings, the displacement-time graph resembled logarithmic growth and the velocity peaked within the first second after lasering. Higher energy or frequency translated into greater displacement, accompanied by earlier and faster velocity peaks. When the laser power was constant, the stone displacement at the fourth second after lasering was much larger in 0.5 J × 40 Hz than 1.0 J × 20 Hz under the short pulse duration (SP) (13.17 ± 0.92 mm vs. 6.90 ± 1.98 mm, p < 0.05), but this discrepancy was offset by the long pulse duration (LP). The largest stone displacement and velocity were observed in 0.5 J × 40 Hz SP.

CONCLUSION

The pulse duration plays a dominant role in determining the stone retropulsion and velocity, and a long pulse decreases retropulsion and velocity. Given a constant power, the variable combination of frequency and pulse energy contributes to significantly different retropulsion with a short pulse rather than a long pulse. The modified method offers a feasible solution for the study of stone retropulsion by laser lithotripsy.

Comparison of Newly-Optimized Moses Technology Versus Standard Holmium:YAG for Endoscopic Laser Enucleation of the Prostate

INTRODUCTION

The purpose of this study was to describe our initial experience of using a newly-optimized Moses technology that is part of the second generation Moses platform specifically designed for holmium laser enucleation of the prostate M2-HoLEP, and compare it to patients undergoing holmium laser enucleation of the prostate (HoLEP) using standard holmium:YAG technology (S-HoLEP).

METHODS

We retrospectively collected data on patients who underwent M2-HoLEP and compared it to the last 50 patients in whom we performed S-HoLEP. Specifically, we compared preoperative symptom scores for lower urinary tract symptoms (LUTS) and erectile dysfunction (ED), preoperative objective voiding metrics, as well as intraoperative characteristics, perioperative characteristics, postoperative complications, postoperative symptom scores for LUTS and ED, and postoperative objective voiding metrics. Additionally we evaluated the ability for same day discharge following surgery in the M2-HoLEP group.

RESULTS

We included 104 total patients for analysis. We compared the first 54 patients undergoing M2-HoLEP to 50 patients undergoing S-HoLEP. Both groups had similar age, BMI, use of anticoagulation medication, LUTS and ED scores, and objective voiding metrics. Operations performed with M2-HoLEP had faster mean hemostasis time (8.7 vs 10.6 ± 6 minutes, p=0.03) as well as hemostasis rate (0.13 vs 0.30 grams/minute, p=0.01). Same day discharge was successful in 69.4% of patients in the M2-HoLEP group. Postoperatively, both groups also had similar and low rates of urinary retention and complications. At follow-up, both groups had similar symptom scores for LUTS and ED, as well as similar objective voiding metrics.

CONCLUSION

The newly optimized Moses pulse modulation technology is safe and efficient for the treatment of BPH. Such technologic improvements in the laser have greatly enhanced the feasibility of same day discharge of patients undergoing HoLEP.

Dynamic properties of surfactant-enhanced laser-induced vapor bubbles for lithotripsy applications

SIGNIFICANCE

Water is a primary absorber of infrared (IR) laser energy, and urinary stones are immersed in fluid in the urinary tract and irrigated with saline during IR laser lithotripsy. Laser-induced vapor bubbles, formed during lithotripsy, contribute to the stone ablation mechanism and stone retropulsion effects.

AIM

Introduction of a surfactant may enable manipulation of vapor bubble dimensions and duration, potentially for more efficient laser lithotripsy.

APPROACH

A surfactant with concentrations of 0%, 5%, and 10% was tested. A single pulse from a thulium fiber laser with wavelength of 1940 nm was delivered to the surfactant through a 200-μm-core optical fiber, using a wide range of laser parameters, including energies of 0.05 to 0.5 J and pulse durations of 250 to 2500  μs.

RESULTS

Bubble length, width, and duration with surfactant increased on average by 29%, 17%, and 120%, compared with water only.

CONCLUSIONS

Our study demonstrated successful manipulation of laser-induced vapor bubble dimensions and duration using a biocompatible and commercially available surfactant. With further study, use of a surfactant may potentially improve the "popcorn" technique of laser lithotripsy within the confined space of the kidney, enable non-contact laser lithotripsy at longer working distances, and provide more efficient laser lithotripsy.

Impact of Laser Fiber Diameter and Irrigation Fluids on Induced Bubble Stream Dynamics with Thulium Fiber Laser: An In Vitro Study

Objectives: The Thulium Fiber Laser (TFL) is studied as an alternative to the holmium:yttrium-aluminium-garnet (Ho:YAG) laser for lithotripsy, with the advantage of an induced bubble stream (IBS). This in vitro study compared the TFL's IBS with 150- and 272 μm-core-diameter laser fiber (CDF) and in four irrigant fluids. Methods: A TFL of 50 W (IPG Photonics^©) and 150 and 272 μm-CDF (Boston Scientific^©) were used, comparing nine energies (in the range from 0.025 to 4 J). An experimental setup consisted of a vertically disposed fiber in a cuvette filled with saline, iodinated contrast agent (IOA), human urine, or deionized water (DW) at ambient temperature. High-speed imaging of three consecutive IBS was performed to determine the influence of energy on their maximum length (ML; μm), width (MW; μm), and duration (MD; μs). Fibers were cleaved with ceramic scissors between each experience. Results: The IBS had higher ML and MW and MD with 150CDF than 272CDF. Maximum pulse rate for 150CDF and 272CDF was 2182 and 2000 Hz, respectively. Every maximum power was higher than the technological limit of TFL (>50 W). At equal energy density, 150CDF was associated with lower dimensions and durations. The IBS had higher maximum dimensions in IOA compared with saline solution (SS). Compared with DW and urine, IBS in IOA were longer beyond 500 mJ. Over 25 mJ, IBS were thinner in DW, urine, and SS. The IBS in DW, urine, and SS had similar maximum dimensions. The IBS's duration was higher in IOA compared with DW, urine, and SS, meaning a lower theoretical maximum pulse rate and power in IOA. Conclusion: Lasering with 150CDF fits with lower pulse energies-higher pulse rates settings than 272CDF, such as fine dusting mode. In IOA, Induced Bubbles Streams present higher dimensions and durations than in other studied fluids, related to its higher viscosity. Safety distance and pulse rate should be increased and decreased, respectively.

Surfactant Enhanced Laser-Induced Vapor Bubbles for Potential use in Thulium Fiber Laser Lithotripsy

The Thulium fiber laser (TFL) is being explored as a potential alternative to the gold standard Holmium:YAG laser for infrared laser ablation of kidney stones. Laser-induced vapor bubbles contribute to both the ablation mechanism and stone retropulsion. In this preliminary study, a biocompatible surfactant with concentrations of 1-5% was used to enhance the vapor bubble dimensions during the laser pulse. Bubble dimensions using surfactant increased on average by 25% compared with water only (control). With further development, introduction of the surfactant into the saline irrigation flow typically delivered through the working channel of the ureteroscope during laser lithotripsy, may contribute to more efficient stone ablation.Clinical Relevance-This preliminary study demonstrates that the dimensions of laser-induced vapor bubbles created during infrared laser lithotripsy can be enhanced by up to 25%, for potential clinical translation into more efficient lithotripsy and use in the "popcorn" ablation method.

Polymer-Mineral Composites Mimic Human Kidney Stones in Laser Lithotripsy Experiments

Despite the widespread use of laser lithotripsy to fragment kidney stones in vivo, there is a lack of robust artificial stone models to replicate the behavior of human stones during lithotripsy procedures. This need for accurate stone models is particularly important as novel laser technologies are introduced in the field of lithotripsy. In this work, we present a method to prepare composite materials that replicate the properties of human kidney stones during laser lithotripsy. Their behavior is understood through the lens of near-IR spectroscopy and helps to elucidate the mechanism of laser lithotripsy in kidney stone materials.

Study of non-contrast helical computed tomography in evaluating holmium laser lithotripsy for urinary calculus

The present study aimed to investigate the correlation between the parameters of non-contrast helical computed tomography (NCHCT) and the total energy of holmium laser lithotripsy, and establish a correlative mathematical model. From March 2016 to February 2017, 120 patients with a single urinary calculus were examined by NCHCT prior to holmium laser lithotripsy. The calculus location was confirmed, the CT value was measured and the volume of the calculus in the established three-dimensional reconstruction model was calculated. The total energy of lithotripsy (TEL) was recorded post-operatively. A significant difference in the TEL between renal calculi and ureteral calculi was identified (P<0.001) and a high and significant correlation between the volume of the calculus and the TEL was determined (Spearman r=0.827, P<0.001). A moderate correlation was identified between the CT value of the calculus and the TEL (Spearman r=0.468, P<0.001). Multivariate linear regression analysis revealed that the location, the volume and the CT value of the calculus were independently associated with the TEL (F=288.858, adjusted R²=0.879, P<0.01). A mathematical model correlating the parameters of NCHCT with the TEL was established, which may provide a foundation to guide the use of energy in holmium laser lithotripsy, and it was possible to estimate the TEL by the location, the volume and the CT value of the calculus.

Fragmentation targeted at preferred discontinuities: A new concept in endolithotripsy with Holmium laser:YAG

INTRODUCTION

There are currently 3holmium laser, YAG (Ho:YAG) endolithotripsy procedures that are considered basic (fragmentation, pulverisation, "pop-corn" technique). We present the technique of fragmentation targeted at preferred discontinuities (FTPD), a new concept of endolithotripsy by Ho:YAG laser.

MATERIAL AND METHODS

The FTPD technique is based on the selective application of energy (targeting a specific preselected point) to an area that is visually prone to the formation of a fracture line or preferred discontinuity (conditioned by the anisotropy of the urolithiasis). The ideal energy regimen (setting) is a high range of working energy (2-3J) with a very low frequency range (5-8Hz) and short pulse width. Between January 2015 to February 2017, the FTPD technique was used in 37 procedures (7 NLP, 16 RIRS, 12 URS, 2 cystolithotomies), with a Ho:YAG laser (Lumenis Pulse 120H^®, Tel-Aviv, Israel). Maximum power used: 24W (3J/8Hz) with fibres of 365μ and 273μ (URS, RIRS), and 32W (4J/8Hz) with fibres of 550μ (NLP, cystolithotomy).

RESULTS

Strategic improvement was achieved in all cases using the TFPD technique to continue the endolithotripsy or remove fragments. No complications were recorded after the use of this method.

CONCLUSIONS

FTPD can be considered a complementary option in combination with the basic methods of fragmentation and pulverisation. In our experience, it constitutes significant progress in optimising the performance of Ho:YAG laser endolithotripsy.

Analysis of thulium fiber laser induced bubble dynamics for ablation of kidney stones

The Thulium fiber laser (TFL) is being explored as an alternative to the Holmium : YAG laser for lithotripsy. TFL parameters differ in several fundamental ways from Holmium laser, including smaller fiber delivery, more strongly absorbed wavelength, low pulse energy/high pulse rate operation, and more uniform temporal pulse structure. High speed imaging of laser induced bubbles was performed at 105,000 frames per second and 10 μm spatial resolution to determine influence of these laser parameters on bubble formation and needle hydrophone data was also used to measure pressure transients. The TFL was operated at 1908 nm with pulse energies of 5-65 mJ, and pulse durations of 200-1000 μs, delivered through 105-μm-core and 270-μm-core silica optical fibers. Bubble dynamics using Holmium laser at a wavelength of 2100 nm with pulse energies of 200-1000 mJ and pulse duration of 350 μs was studied, for comparison. A single, 500 μs TFL pulse produced a bubble stream extending 1200 ± 90 μm and 1070 ± 50 μm from fiber tip, with maximum bubble widths averaging 650 ± 20 μm and 870 ± 40 μm (n = 4), for 105 μm and 270 μm fibers, respectively. These observations are consistent with previous studies which reported TFL ablation stallout at working distances beyond 1.0 mm. TFL bubble dimensions were four times smaller than for Holmium laser due to lower peak power and smaller fiber diameter used. The maximum pressure transients measured 0.6 bars at 35 mJ pulse energy for TFL and 7.5 bars at 600 mJ pulse energy for Holmium laser. These fundamental studies of bubble dynamics as a function of specific laser and fiber parameters may assist with optimization of the TFL parameters for safe and efficient lithotripsy in the clinic. Image of bubble formation during fiber optic delivery of Thulium fiber laser energy in saline (35 mJ, 500 μs).

Holmium Laser Lithotripsy in the New Stone Age: Dust or Bust?

Modern day holmium laser systems for ureteroscopy (URS) provide users with a range of settings, namely pulse energy (PE), pulse frequency (Fr), and pulse width (PW). These variables allow the surgeon to choose different combinations that have specific effects on stone fragmentation during URS lithotripsy. Contact laser lithotripsy can be performed using fragmentation or dusting settings. Fragmentation employs settings of low Fr and high PE to break stones that are then extracted with retrieval devices. Dusting is the utilization of high Fr and low PE settings to break stones into submillimeter fragments for spontaneous passage without the need for basket retrieval. Use of the long PW mode during lithotripsy can reduce stone retropulsion and is increasingly available in new generation lasers. During non-contact laser lithotripsy, stone fragments are rapidly pulverized in a calyx in laser bursts that result in stones breaking into fine fragments. In this review, we discuss the effect of different holmium laser settings on stone fragmentation, and the clinical implications in a very much evolving field.

Combining ultrasonography and noncontrast helical computerized tomography to evaluate Holmium laser lithotripsy

The purpose of the study was to establish a mathematical model for correlating the combination of ultrasonography and noncontrast helical computerized tomography (NCHCT) with the total energy of Holmium laser lithotripsy.In this study, from March 2013 to February 2014, 180 patients with single urinary calculus were examined using ultrasonography and NCHCT before Holmium laser lithotripsy. The calculus location and size, acoustic shadowing (AS) level, twinkling artifact intensity (TAI), and CT value were all documented. The total energy of lithotripsy (TEL) and the calculus composition were also recorded postoperatively. Data were analyzed using Spearman's rank correlation coefficient, with the SPSS 17.0 software package. Multiple linear regression was also used for further statistical analysis.A significant difference in the TEL was observed between renal calculi and ureteral calculi (r = -0.565, P < 0.001), and there was a strong correlation between the calculus size and the TEL (r = 0.675, P < 0.001). The difference in the TEL between the calculi with and without AS was highly significant (r = 0.325, P < 0.001). The CT value of the calculi was significantly correlated with the TEL (r = 0.386, P < 0.001). A correlation between the TAI and TEL was also observed (r = 0.391, P < 0.001). Multiple linear regression analysis revealed that the location, size, and TAI of the calculi were related to the TEL, and the location and size were statistically significant predictors (adjusted r = 0.498, P < 0.001).A mathematical model correlating the combination of ultrasonography and NCHCT with TEL was established; this model may provide a foundation to guide the use of energy in Holmium laser lithotripsy. The TEL can be estimated by the location, size, and TAI of the calculus.

Ureteroscopic holmium:YAG laser endopyelotomy is effective in distinctive ureteropelvic junction obstructions

AIM

To evaluate the effectiveness and safety of holmium:YAG (Ho:YAG) laser endopyelotomy in distinctive ureteropelvic junction obstructions (UPJO) with distinctive aetiologies.

MATERIAL AND METHODS

Thirty-one patients diagnosed with UPJO of distinctive causes were included. Aetiology consisted of 7 congenital UPJO, 10 post-pyeloplasty UPJO, 7 post-lithotomy obstructions, 4 ureteropelvic junction obstructions post-extracorporeal shockwave lithotripsy stenoses and 3 post-ureteroscopic lithotriptic UPJO. Retrograde ureteroscopic Ho:YAG laser endopyelotomy was performed in all patients. Operation related parameters were studied

RESULTS

Average procedure duration was 46 min. Mean discharge was 1.81 days. There was no notable complication such as perforation or haemorrhage. All patients were followed for at least 12 months. The single success rate was 80.6%, leaving 6 patients undergoing secondary endopyelotomy, among whom 4 were successful while 2 required an open approach. The overall success rate was 93.5%. Failed pyeloplasty UPJO is more disposed to restenosis (p = 0.0075). Inversely implanted ureteral stent yielded a higher success rate (p = 0.0158).

CONCLUSIONS

Ho:YAG laser endopyelotomy is a safe, minimally invasive approach effective in both primary and secondary UPJO treatments. Implantation of inversed ureteral stents can be more beneficial.

Use of laser lithotripsy for fragmentation of uroliths in dogs: 73 cases (2005-2006)

OBJECTIVE

To describe use of transurethral cystoscope-guided laser lithotripsy for fragmentation of cystic and urethral uroliths and determine procedure duration and short-term and long-term outcome in dogs.

DESIGN

Retrospective case series.

ANIMALS

73 dogs with naturally occurring uroliths in the urinary bladder, urethra, or both.

PROCEDURES

Transurethral cystoscope-guided laser lithotripsy was performed in all dogs, and medical records were reviewed for short-term and long-term outcome and complications.

RESULTS

Laser lithotripsy resulted in complete fragmentation of all uroliths in all 28 female dogs and a majority of male dogs (39/45 [86.7%]). Dogs with urethroliths had shorter median laser time than dogs with cystic uroliths. Basket extraction and voiding urohydro-propulsion were successful for removal of the urolith fragments following laser lithotripsy. Complications related to cystoscope-guided laser lithotripsy occurred in 5 of 28 (17.9%) female dogs and 6 of 45 (13.3%) male dogs.

CONCLUSIONS AND CLINICAL RELEVANCE

Transurethral cystoscope-guided laser lithotripsy was successful in female dogs and most male dogs for fragmentation of cystic and urethral uroliths. Short-term complications were most commonly related to urethral swelling and resolved with placement of an indwelling urinary catheter. There were no long-term complications.

Is the holmium:YAG laser the best intracorporeal lithotripter for the ureter? A 3-year retrospective study

PURPOSE

To study the efficiency and safety of holmium:YAG laser lithotripsy for ureteral stones.

PATIENTS AND METHODS

A series of 188 patients with 208 ureteral stones were treated with semirigid ureteroscopy and holmium:YAG laser lithotripsy from January 2003 to December 2005. Of the stones, 116 were lower ureteral, 37 middle ureteral, and 55 upper ureteral.

RESULTS

The success rate was 92.7% at the time of ureteroscopy and 96.7% at 3 months. The failures were secondary to retropulsion of the stones (3.3%). There were no perforations and one stricture. Stenting was done in 90% of patients.

CONCLUSIONS

The Holmium:YAG laser is an ideal intracorporeal lithotripter for ureteral calculi, with a high success rate and low morbidity.

Ureteroscopic treatment of ureteral calculi with holmium: YAG laser lithotripsy

PURPOSE

We evaluated the effectiveness and safety of holmium: YAG laser lithotripsy with a semirigid ureteroscope for ureteral calculi in a prospective cohort of 697 patients.

PATIENTS AND METHODS

Holmium: YAG laser lithotripsy was performed with a semirigid ureteroscope in 697 inpatients between September 2002 and January 2006. Calculi were located in the distal ureter in 382 patients (54.8%), the midureter in 143 (20.5%), and the proximal ureter in 172 (24.7%). Patients were assessed 2 to 24 weeks postoperatively with repeat plain radiography, ultrasonography, intravenous urography, or some combination.

RESULTS

The overall stone-free rate was 92.2%, the rate being 100% for calculi in the distal ureter (N = 382), 97.9% for calculi in the midureter (N = 140), and 70.3% for calculi in the proximal ureter (N = 121). Complications occurred in 13 patients (1.9%). Postoperative ureteral stricture developed in five patients (0.72%) and was managed surgically.

CONCLUSIONS

Holmium: YAG laser lithotripsy with a semirigid ureteroscope is a highly effective and safe treatment for ureteral calculi, especially those in the distal ureter and midureter.

Holmium laser for stone management

The efficiency and safety profile of the holmium laser has made this tool a versatile multi-purpose instrument for use in the endoscopic treatment of a wide variety of urologic disorders, in particular urinary calculi. Herein we review holmium laser physics, current endourologic laser lithotripsy applications, and the performance of new low power holmium laser devices.

Plasma bubble formation induced by holmium laser: an in vitro study

OBJECTIVES

To use the elementary physical measurements of temperature and size to prove that the thermal effects produced by the holmium laser's pulses are due to the formation of a plasma bubble. The physical phenomenon related to high temperatures generated during procedures with the holmium laser (holmium:yttrium-aluminum-garnet) was the object of our interest.

METHODS

Using a double micrometric slide attached to a 550-microm optic fiber and two thermocouples submerged in water, a series of pulses of 0.8 J at 10 to 30 Hz was delivered from a holmium:yttrium-aluminum-garnet laser, and we recorded temperatures on both frontal and lateral planes. Subsequently, samples of prostatic tissue and small stones were treated with 1.5 J at 20 Hz on both frontal and lateral planes.

RESULTS

Treatment with 1.5 J at 30 Hz (frontal plane) and with 1.5 J at 20 Hz (lateral plane) produced the ablation of the structure of the thermocouple at 2 mm and 1 mm, respectively, indicating plasma formation. The dimensions of the bubble after the delivery of 1.5 J at 20 Hz was 2 x 1.5 mm. Coagulation of the prostatic tissue took place at 1 mm from the plasma bubble, on both frontal and lateral planes.

CONCLUSIONS

The plasma bubble that forms at the tip of the fiber connected to the holmium:yttrium-aluminum-garnet laser makes it possible to work on stones and soft tissues. The coagulation of the prostatic tissue is caused by the hot water-vapor bubble that forms on the edge of the plasma bubble. During lithotripsy, guidewires and baskets within the expansion area of the plasma bubble risk damage.

In vitro effects of pulsed holmium laser energy on canine uroliths and porcine cadaveric urethra

BACKGROUND AND OBJECTIVES

To assess the effect of holmium laser energy on canine uroliths and porcine urethra.

STUDY DESIGN/MATERIALS AND METHODS

Uroliths of known composition and fresh cadaveric urethra were exposed to holmium laser energy. Urolith fragmentation times and depth of urethral lesions were determined.

RESULTS

Overall mean fragmentation time was 11.8 +/- 8.01 seconds. Magnesium ammonium phosphate (MAP) and urate uroliths had significantly shorter fragmentation times compared to other uroliths. Fragmentation time of MAP uroliths irradiated with 1.2 J/pulse was significantly longer than the fragmentation time of MAP uroliths irradiated with 0.3 J/pulse. Overall mean lesion depth for urethral specimens treated with 90 degrees contact mode irradiation was significantly greater than overall mean lesion depth for specimens treated with 30 degrees non-contact mode.

CONCLUSIONS

Holmium laser energy effectively fragmented canine uroliths and caused minimal urethral damage in vitro. Dogs with urolithiasis may represent a useful animal model for developing human lithotripsy procedures.

New concepts in the treatment of ureteral calculi

The management of patients with ureteral stones remains under debate in several areas. The ability to predict spontaneous passage has improved but remains imprecise, whilst the range of therapeutic options continues to widen. Excellent results can be obtained by both shockwave lithotripsy and ureteroscopic methods, with relatively minimal complications. Routine ureteral stenting is not warranted whichever treatment is chosen. In future, directly comparative studies should be designed to incorporate quality-of-life parameters rather than just stone-free status, to improve our understanding of the effect of treatment decisions on patients.

A perspective on laser lithotripsy: the fragmentation processes

This paper describes in simple terms the physics of laser-calculus interactions and introduces a method with which physicians can understand or evaluate the application of any new laser technique for use in lithotripsy or other medical fields. Tissue optical properties and laser parameters govern the mechanism(s) of fragmentation of urinary or biliary calculi. Laser pulse energies for clinical lithotripsy range from Q0 = 20 mJ to 2 J for short-pulsed lasers to long-pulsed lasers, respectively. Lasers with short pulse durations (i.e., less than a few microseconds) fragment calculi by means of shockwaves following optical breakdown and plasma expansion of ionized water or calculus compositions or by cavitation collapse, thus manifesting a photoacoustical effect. Laser-tissue interactions involving dominant photomechanical or photoacoustical effects are usually stress confined. Long-pulsed lasers (i.e., >100 microsec), on the other hand, generate minimal acoustic waves, and calculi are fragmented by temperatures beyond the thresholds for vaporization of calculus constituents, melting, or chemical decomposition.

Endoscopic management of urologic disease with the holmium laser

The efficiency and safety profile of the holmium laser have made this tool a versatile multipurpose instrument for use in the endoscopic treatment of a wide variety of urologic disorders. Herein are reviewed holmium laser physics and current endourologic applications, as well as the performance of new low-power holmium lasers.

Free electron laser lithotripsy: threshold radiant exposures

PURPOSE

To determine the threshold radiant exposures (J/cm2) needed for ablation or fragmentation as a function of infrared wavelengths on various urinary calculi and to determine if there is a relation between these thresholds and lithotripsy efficiencies with respect to optical absorption coefficients.

MATERIALS AND METHODS

Human calculi composed of uric acid, calcium oxalate monohydrate (COM), cystine, or magnesium ammonium phosphate hexahydrate (MAPH) were used. The calculi were irradiated in air with the free electron laser (FEL) at six wavelengths: 2.12, 2.5, 2.94, 3.13, 5, and 6.45 microm.

RESULTS

Threshold radiant exposures increased as optical absorption decreased. At the near-infrared wave-lengths with low optical absorption, the thresholds were >1.5 J/cm2. The thresholds decreased below 0.5 J/cm2 for regions of high absorption for all the calculus types. Thresholds within the high-absorption regions were statistically different from those in the low-absorption regions, with P values much less than 0.05.

CONCLUSIONS

Optical absorption coefficients or threshold radiant exposures can be used to predict lithotripsy efficiencies. For low ablation thresholds, smaller radiant exposures were required to achieve breakdown temperatures or to exceed the dynamic tensile strength of the material. Therefore, more energy is available for fragmentation, resulting in higher lithotripsy efficiencies.

Holmium: YAG lithotripsy: optimal power settings

PURPOSE

We tested the hypothesis that holmium:YAG laser lithotripsy speed is best maximized by using low pulse energy at high pulse frequency.

MATERIALS AND METHODS

To demonstrate that optical fiber damage increases with pulse energy and irradiation, the 365-microm optical fiber irradiated calcium hydrogen phosphate dihydrate (CHPD), calcium oxalate monohydrate (COM), cystine, magnesium ammonium phosphate hexahydrate (MAPH), and uric acid calculi at pulse energies of 0.5 to 2.0 J. Optical energy output was measured with an energy detector after 10 J to 200 J of total energy. To demonstrate that lithotripsy efficiency varies with power, fragmentation was measured at constant power settings at total energies of 200 J and 1 kJ with the 365-microm optical fiber. Fragmentation was measured for the 272-microm optical fiber at pulse energies of 0.5 J to 1.5 J at 10 Hz. To demonstrate that low pulse energy produces smaller fragments than high pulse energy, fragment size was characterized for COM and uric acid calculi after 0.25 kJ of irradiation using the 272-microm to 940-microm optical fibers at 0.5 J to 1.5 J.

RESULTS

Damage to the 365-microm optical fiber was greatest for irradiation of CHPD, followed by MAPH, and COM (P<0.001). There was no significant optical fiber damage after cystine and uric acid lithotripsy. For the 365-microm optical fiber and CHPD, fragmentation after 200 J was greatest for pulse energies < or =1.0 J (P< 0.001). For other compositions, fragmentation was not statistically different among the power settings for constant irradiation. No significant difference was noted in fragmentation for any composition at different pulse energies (1.0 v. 2.0 J) for 1-kJ irradiation. However, for all compositions, the calculated lithotripsy speed was greatest at high power settings (P<0.001). For the 272-microm optical fiber, CHPD fragmentation was greatest for the 1.0-J pulse energy. The mean fragment size and relative quantity of fragments > or =2 mm both increased as pulse energy increased.

CONCLUSIONS

Optical fiber degradation varies with stone composition, irradiation, and pulse energy. Holmium:YAG lithotripsy speed is maximized with higher power (either increased pulse energy or higher pulse frequency). Because low pulse energy may be safer and yields smaller fragments than high pulse energy, holmium:YAG lithotripsy speed is best increased by using pulse energies < or =1.0 J at a high repetition rate.

Holmium:YAG laser lithotripsy: A dominant photothermal ablative mechanism with chemical decomposition of urinary calculi

BACKGROUND AND OBJECTIVE

Evidence is presented that the fragmentation process of long-pulse Holmium:YAG (Ho:YAG) lithotripsy is governed by photothermal decomposition of the calculi rather than photomechanical or photoacoustical mechanisms as is widely thought. The clinical Ho:YAG laser lithotriptor (2.12 microm, 250 micros) operates in the free-running mode, producing pulse durations much longer than the time required for a sound wave to propagate beyond the optical penetration depth of this wavelength in water. Hence, it is unlikely that shock waves are produced during bubble formation. In addition, the vapor bubble induced by this laser is not spherical. Thus the magnitude of the pressure wave produced at cavitation collapse does not contribute significantly to lithotripsy.

STUDY DESIGN/MATERIALS AND METHODS

A fast-flash photography setup was used to capture the dynamics of urinary calculus fragmentation at various delay times following the onset of the Ho:YAG laser pulse. These images were concurrently correlated with pressure measurements obtained with a piezoelectric polyvinylidene-fluoride needle-hydrophone. Stone mass-loss measurements for ablation of urinary calculi (1) in air (dehydrated and hydrated) and in water, and (2) at pre-cooled and at room temperatures were compared. Chemical and composition analyses were performed on the ablation products of several types of Ho:YAG laser irradiated urinary calculi, including calcium oxalate monohydrate (COM), calcium hydrogen phosphate dihydrate (CHPD), magnesium ammonium phosphate hexahydrate (MAPH), cystine, and uric acid calculi.

RESULTS

When the optical fiber was placed perpendicularly in contact with the surface of the target, fast-flash photography provided visual evidence that ablation occurred approximately 50 micros after the initiation of the Ho:YAG laser pulse (250-350 micros duration; 375-400 mJ per pulse), long before the collapse of the cavitation bubble. The measured peak acoustical pressure upon cavitation collapse was negligible (< 2 bars), indicating that photomechanical forces were not responsible for the observed fragmentation process. When the fiber was placed in parallel to the calculus surface, the pressure peaks occurring at the collapse of the cavitation were on the order of 20 bars, but no fragmentation occurred. Regardless of fiber orientation, no shock waves were recorded at the beginning of bubble formation. Ablation of COM calculi (a total of 150 J; 0.5 J per pulse at an 8-Hz repetition rate) revealed different Ho:YAG efficiencies for dehydrated calculus, hydrated calculus, and submerged calculus. COM and cystine calculi, pre-cooled at -80 degrees C and then placed in water, yielded lower mass-loss during ablation (20 J, 1.0 J per pulse) compared to the mass-loss of calculi at room temperature. Chemical analyses of the ablated calculi revealed products resulting from thermal decomposition. Calcium carbonate was found in samples composed of COM calculi; calcium pyrophosphate was found in CHPD samples; free sulfur and cysteine were discovered in samples composed of cystine samples; and cyanide was found in samples of uric acid calculi.

CONCLUSION

These experimental results provide convincing evidence that long-pulse Ho:YAG laser lithotripsy causes chemical decomposition of urinary calculi as a consequence of a dominant photothermal mechanism.

Ureteroscopic lithotripsy

The indications for ureteroscopic lithotripsy have increased with endoscope miniaturization and powerful, precise endoscopic lithotrites like the holmium: yttrium-aluminum-garnet laser. Successful ureteropyeloscopic treatment with the currently available instrumentation and techniques is independent of the size, composition, and location of stones in the upper urinary tract. Extracorporeal shockwave lithotripsy maintains a major role in treating uncomplicated, moderately sized upper urinary tract calculi. Complex upper urinary tract calculi, however, are best treated endoscopically. In addition, the endoscopic treatment of ureteral calculi is efficacious and definitive, albeit more invasive than extracorporeal shock wave lithotripsy.

Holmium: YAG lithotripsy: photothermal mechanism

OBJECTIVE

A series of experiments were conducted to test the hypothesis that the mechanism of holmium:YAG lithotripsy is photothermal.

METHODS AND RESULTS

To show that holmium:YAG lithotripsy requires direct absorption of optical energy, stone loss was compared for 150 J Ho:YAG lithotripsy of calcium oxalate monohydrate (COM) stones for hydrated stones irradiated in water (17+/-3 mg) and hydrated stones irradiated in air (25+/-9 mg) v dehydrated stones irradiated in air (40+/-12 mg) (P < 0.001). To show that Ho:YAG lithotripsy occurs prior to vapor bubble collapse, the dynamics of lithotripsy in water and vapor bubble formation were documented with video flash photography. Holmium:YAG lithotripsy began at 60 microsec, prior to vapor bubble collapse. To show that Ho:YAG lithotripsy is fundamentally related to stone temperature, cystine, and COM mass loss was compared for stones initially at room temperature (approximately 23 degrees C) v frozen stones ablated within 2 minutes after removal from the freezer. Cystine and COM mass losses were greater for stones starting at room temperature than cold (P < or = 0.05). To show that Ho:YAG lithotripsy involves a thermochemical reaction, composition analysis was done before and after lithotripsy. Postlithotripsy, COM yielded calcium carbonate; cystine yielded cysteine and free sulfur; calcium hydrogen phosphate dihydrate yielded calcium pyrophosphate; magnesium ammonium phosphate yielded ammonium carbonate and magnesium carbonate; and uric acid yielded cyanide. To show that Ho:YAG lithotripsy does not create significant shockwaves, pressure transients were measured during lithotripsy using needle hydrophones. Peak pressures were <2 bars.

CONCLUSION

The primary mechanism of Ho:YAG lithotripsy is photothermal. There are no significant photoacoustic effects.