Holmium:YAG lithotripsy efficiency varies with energy density

Do Stone Characteristics and Laser Fiber Size Affect Ho: YAG Laser Time and Energy During Ureteroscopy?

Objective

To assess the correlation of attenuation value measured as HU in Non-contrast computed tomography, stone size, location, fibre size and stone composition with Holmium: yttrium-aluminium garnet (Ho: YAG) laser parameters including, cumulative laser energy and final laser time.

Materials and Methods

 We prospectively analyzed 118 patients undergoing flexible/semirigid ureteroscopy and Holmium: YAG laser lithotripsy from October 2022 to October 2023 at Mogadishu Urological Centre. Our study parameters encompass preoperative stone characteristics determined in NCCT (stone size, attenuation value, and stone location), fibre size, cumulative laser energy and time, overall operative time, and postoperative stone composition analysis.

Results

There were 118 patients eligible for our prospective study. In the logistic regression model for retrograde intrarenal surgery with a fibre size of 272 μm, cumulative laser energy showed a significant difference among stone size, location, fibre size, and calcium oxalate stones (P > 0.05). However, no significant difference was noticed in the attenuation value (P = 0.078) (R2 = 0.053). Our analysis showed a positive significance among all the parameters (P < 0.05) for laser time. In logistic regression for a rigid ureteroscope with a fibre size of 365 μm, cumulative laser energy showed a significant difference between the location stone and fibre size (P < 0.05) (R2 = 0.09). However, no significant difference was seen among stone size, attenuation value, and calcium oxalate stones (P > 0.05). For laser time, our analysis showed a positive significance among all parameters except the calcium oxalate stones, which showed no significant difference (P > 0.05).

Conclusion

Our study showed that stone location, hardness, and fibre size are the most critical factors influencing the outcome of Ho: YAG laser parameters. The study revealed that CaOMH stones require more time to disintegrate into smaller ones, while PH-dependent stones such as carbonate apatite may require less time to fragment.

Predicting Urinary Stone Composition in Single-Use Flexible Ureteroscopic Images with a Convolutional Neural Network

Background and Objectives: Analysis of urine stone composition is one of the most important factors in urolithiasis treatment. This study investigated whether a convolutional neural network (CNN) can show decent results in predicting urinary stone composition even in single-use flexible ureterorenoscopic (fURS) images with relatively low resolution. Materials and Methods: This study retrospectively used surgical images from fURS lithotripsy performed by a single surgeon between January 2018 and December 2021. The ureterorenoscope was a single-use flexible ureteroscope (LithoVue, Boston Scientific). Among the images taken during surgery, a single image satisfying the inclusion and exclusion criteria was selected for each stone. Cases were divided into two groups according to whether they contained any calcium oxalate (the Calcium group) or none (the Non-calcium group). From 506 total cases, 207 stone surface images were finally included in the study. In the CNN model, the transfer learning method using Resnet-18 as a pre-trained model was used, and only endoscopic digital images and stone classification data were input to achieve minimally supervised learning. Results: There were 175 cases in the Calcium group and 32 in the Non-calcium group. After training and validation, the model was tested using the test set, and the total accuracy was 81.8%. Recall and precision of the test results were 88.2% and 88.2% in the Calcium group and 60.0% and 60.0% in the Non-calcium group, respectively. The area under the receiver operating characteristic curve of the model, which represents its classification performance, was 0.82. Conclusions: Single-use flexible ureteroscopes have financial benefits but low vision quality compared with reusable digital flexible ureteroscopes. As far as we know, this is the first artificial intelligence study using single-use fURS images. It is meaningful that the CNN performed well even under these difficult conditions because these results can further expand the possibilities of its use.

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.

Evaluation and understanding of automated urinary stone recognition methods

OBJECTIVE

To assess the potential of automated machine-learning methods for recognizing urinary stones in endoscopy.

MATERIALS AND METHODS

Surface and section images of 123 urinary calculi (109 ex vivo and 14 in vivo stones) were acquired using ureteroscopes. The stones were more than 85% 'pure'. Six classes of urolithiasis were represented: Groups I (calcium oxalate monohydrate, whewellite), II (calcium oxalate dihydrate, weddellite), III (uric acid), IV (brushite and struvite stones), and V (cystine). The automated stone recognition methods that were developed for this study followed two types of approach: shallow classification methods and deep-learning-based methods. Their sensitivity, specificity and positive predictive value (PPV) were evaluated by simultaneously using stone surface and section images to classify them into one of the main morphological groups (subgroups were not considered in this study).

RESULTS

Using shallow methods (based on texture and colour criteria), relatively high sensitivity, specificity and PPV for the six classes were attained: 91%, 90% and 89%, respectively, for whewellite; 99%, 98% and 99% for weddellite; 88%, 89% and 88% for uric acid; 91%, 89% and 90% for struvite; 99%, 99% and 99% for cystine; and 94%, 98% and 99% for brushite. Using deep-learning methods, the sensitivity, specificity and PPV for each of the classes were as follows: 99%, 98% and 97% for whewellite; 98%, 98% and 98% for weddellite; 97%, 98% and 98% for uric acid; 97%, 97% and 96% for struvite; 99%, 99% and 99% for cystine; and 94%, 97% and 98% for brushite.

CONCLUSION

Endoscopic stone recognition is challenging, and few urologists have sufficient expertise to achieve a diagnosis performance comparable to morpho-constitutional analysis. This work is a proof of concept that artificial intelligence could be a solution, with promising results achieved for pure stones. Further studies on a larger panel of stones (pure and mixed) are needed to further develop these methods.

Generated temperatures and thermal laser damage during upper tract endourological procedures using the holmium: yttrium-aluminum-garnet (Ho:YAG) laser: a systematic review of experimental studies

PURPOSE

To perform a review on the latest evidence related to generated temperatures during Ho:YAG laser use, and present different tools to maintain decreased values, and minimize complication rates during endourological procedures.

METHODS

We performed a literature search using PubMed, Scopus, EMBASE, and Cochrane Central Register of Controlled Trials-CENTRAL, restricted to original English-written articles, including animal, artificial model, and human studies. Different keywords were URS, RIRS, ureteroscopy, percutaneous, PCNL, and laser.

RESULTS

Thermal dose (t43) is an acceptable tool to assess possible thermal damage using the generated temperature and the time of laser exposure. A t43 value of more than 120 min leads to a high risk of thermal tissue injury and at temperatures higher than 43 °C Ho:YAG laser use becomes hazardous due to an exponentially increased cytotoxic effect. Using open continuous flow, or chilled irrigation, temperatures remain lower than 45 °C. By utilizing high-power (> 40 W) or shorter laser pulse, temperatures rise above the accepted threshold, but adding a ureteral access sheath (UAS) helps to maintain acceptable values.

CONCLUSIONS

Open irrigation systems, chilled irrigation, UASs, laser power < 40 W, and shorter on/off laser activation intervals help to keep intrarenal temperatures at accepted values during URS and PCNL.

Laser fiber degradation following holmium laser enucleation of the prostate utilizing Moses technology versus regular mode

PURPOSE

We sought to objectively compare laser fiber degradation for holmium laser enucleation of the prostate (HoLEP) cases performed with 550 μm standard fibers versus 550 μm Moses 2.0 fiber in BPH mode on a macroscopic and microscopic level.

METHODS

We prospectively collected outcomes for 50 standardized HoLEP cases using 550 μm Moses fiber with 2.0 BPH mode compared to our historical cohort of 50 patients using 550 μm standard fibers on regular mode. Macroscopic degradation length was the difference in length of exposed fiber at the start and end of each case. Five consecutive 550 μm standard fibers, five 550 μm Moses fibers and their respective controls underwent novel utilization of three objective corroborating imaging techniques: Brightfield high resolution microscopy, high resolution 3-D microCT and Confocal Reflection Surface Analysis. Mann-Whitney U, 2-tailed T tests and Chi-squared tests were used.

RESULTS

Standard fibers demonstrated greater degradation than the Moses fibers with 2.0 BPH mode [2.9 cm (IQR 1.7-4.3 cm) vs 0.2 cm (IQR 0.1-0.4 cm), p < 0.01]. This difference remained significant when comparing degradation per energy used, per minute enucleation and per gram enucleated (all p < 0.05). None of the cases with Moses fiber and 2.0 BPH mode required intraoperative interruption to re-strip the fiber. Objective fiber degradation by three microscopic techniques confirmed more damage to the standard fibers with regular mode.

CONCLUSION

Overall, use of the 550 μm Moses fiber with 2.0 BPH mode resulted in less fiber degradation compared to a standard 550 μm fiber with regular mode as confirmed using 4 corroborating macroscopic and microscopic techniques.

Comparison of Different Pulse Modulation Modes for Holmium:Yttrium-Aluminum-Garnet Laser Lithotripsy Ablation in a Benchtop Model

Introduction: Manipulation of Holmium:Yttrium-Aluminum-Garnet laser parameters such as pulse energy (PE), frequency, and duration can impact laser lithotripsy ablation efficiency. In 2017, Lumenis introduced Moses™ Technology, which uses pulse modulation to enhance the delivery of energy from fiber to stone as well as to minimize stone retropulsion. Since the introduction of Moses Technology, other companies have brought additional pulse modulation concepts to market. The purpose of this in vitro study is to compare the pulse characteristics and stone ablation efficiency of Lumenis Moses Technology with Quanta's Vapor Tunnel™. Materials and Methods: Submerged BegoStone phantoms were systematically ablated using either the Lumenis Moses Pulse 120H or the Quanta Litho 100 clinical laser system. Two PEs (0.4 and 1 J), three fiber-stone standoff distances (SDs) (0.5, 1, 2 mm), and all available pulse duration and modulation modes for each laser were tested in combination. Fiber speed was adjusted to scan across the stone surface at either 1 or 10 pulses/mm to form single pulse craters or an ablation trough, respectively. Volumes of single craters and 1 mm trough segments were imaged and quantified using optical coherence tomography. Results: Ablation volumes decreased with decreasing PE and increasing SD. Statistically significant variability was seen between pulse types (PT) at every tested parameter set. Among pulse modulation modes, Moses Distance (MD) was superior at 0.5 mm in all testing and at 2 mm in trough testing. Vapor Tunnel (VT) was superior in 2 mm single crater testing. All modulated pulses performed similarly at 1 mm. Conclusions: In this benchtop model of laser lithotripsy, stone ablation was significantly impacted by PT. MD demonstrated superior or noninferior stone ablation at most tested parameters. VT maintained its efficacy the best as SD increased. Future work should focus on the mechanistic differences of these modes relative to other traditional laser pulse modes.

Assessment of Factors Involved in Laser Fiber Degradation with Thulium Fiber Laser

Objectives: To assess the effect of various factors on laser fiber tip degradation with the thulium fiber laser (Tm-fiber): fiber stripping, adjustable laser settings (energy, frequency, peak power), and stone density. Methods: Two hundred seventy-three micrometer fibers were used with a 50W Tm-fiber. First, we assessed the evolution of power transmission with stripped and unstripped fibers submerged in saline. The laser was continuously activated for 5 minutes. The influence of each laser parameter (energy, frequency, and peak power) on fiber degradation was assessed by loss of power transmission and reduction of tip length. Second, we assessed the evolution of power transmission after 150 seconds of lithotripsy in a quasicontact mode against soft and hard BegoStones. The influence of lithotripsy with different laser settings on fiber degradation was assessed by loss of power transmission. Results: Power transmission was close to 100% with stripped fibers, while a power gain appeared for unstripped fibers after 5 minutes of laser emission. Thus, only stripped laser fibers were used during the second series of experiments. Regardless of laser settings, there was a constant loss of measured power transmission after lithotripsy with a significant difference between soft and hard stones, p < 0.0001. Power transmission was 67% and 78% against hard and soft stones, respectively. While there was no influence of peak power on power output against hard stones, there was a significant one against soft stones. Conclusions: The main determinant of loss of power transmission during lithotripsy in contact mode with Tm-fiber is the stone density. Higher loss of power transmission occurs against hard stones than soft stones. All peak powers may be used against hard stones without a difference, while high peak power appears as an additional factor of power loss against soft stones, but this decrease will not the reach the one obtained with hard stones.

Mechanisms of Pulse Modulated Holmium:YAG Lithotripsy

Introduction: This study aimed at answering three research questions: (1) Under the experimental conditions studied, what is the dominant mechanism of Holmium:YAG lithotripsy with or without pulse modulation? (2) Under what circumstances can laser pulse modulation increase crater volume of stone ablation per joule of emitted radiant energy? (3) Are BegoStone phantoms a suitable model for laser lithotripsy studies? Materials and Methods: The research questions were addressed by ablation experiments with BegoStone phantoms and native stones. Experiments were performed under three stone conditions: dry stones in air, hydrated stones in air, and hydrated stones in water. Single pulses with and without pulse modulation were applied. For each pulse mode, temporal profile, transmission through 1 mm water, and cavitation bubble collapse pressures were measured and compared. For each stone condition and pulse mode, stones were ablated with a fiber separation distance of 1 mm and crater volumes were measured using optical coherence tomography. Results: Pulses with and without pulse modulation had high (>80%) transmission through 1 mm of water. Pulses without pulse modulation generated much higher peak pressures than those with pulse modulation (62.3 vs 11.4 bar). Pulse modulation resulted in similar or larger craters than without pulse modulation. Trends in BegoStone crater volumes differed from trends in native stones. Conclusions: This results of this study suggest that the dominant mechanism is photothermal with possible photoacoustic contributions for some stone compositions. Pulse modulation can increase ablation volume per joule of emitted radiant energy, but the effect may be composition specific. BegoStones showed unique infrared ablation characteristics compared with native stones and are not a suitable model for laser lithotripsy studies.

Comparison of Holmium:YAG and Thulium Fiber Lasers on the Risk of Laser Fiber Fracture

Objectives: To compare the risk of laser fiber fracture between Ho:YAG laser and Thulium Fiber Laser (TFL) with different laser fiber diameters, laser settings, and fiber bending radii. METHODS: Lengths of 200, 272, and 365 μm single use fibers were used with a 30 W Ho:YAG laser and a 50 W Super Pulsed TFL. Laser fibers of 150 µm length were also tested with the TFL only. Five different increasingly smaller bend radii were tested: 1, 0.9, 0.75, 0.6, and 0.45 cm. A total of 13 different laser settings were tested for the Ho:YAG laser: six fragmentation settings with a short pulse duration, and seven dusting settings with a long pulse duration. A total of 33 different laser settings were tested for the TFL. Three laser settings were common two both lasers: 0.5 J × 12 Hz, 0.8 J × 8 Hz, 2 J × 3 Hz. The laser was activated for 5 min or until fiber fracture. Each measurement was performed ten times. Results: While fiber failures occurred with all fiber diameters with Ho:YAG laser, none were reported with TFL. Identified risk factors of fiber fracture with the Ho:YAG laser were short pulse and high energy for the 365 µm fibers (p = 0.041), but not for the 200 and 272 µm fibers (p = 1 and p = 0.43, respectively). High frequency was not a risk factor of fiber fracture. Fiber diameter also seemed to be a risk factor of fracture. The 200 µm fibers broke more frequently than the 272 and 365 µm ones (p = 0.039). There was a trend for a higher number of fractures with the 365 µm fibers compared to the 272 µm ones, these occurring at a larger bend radius, but this difference was not significant. Conclusion: TFL appears to be a safer laser regarding the risk of fiber fracture than Ho:YAG when used with fibers in a deflected position.

Ablation Efficiency of a Novel Thulium Fiber Laser: An In Vitro Study on Laser Setting and Fiber Usage

Introduction: To investigate the ablation efficiency of super-pulse thulium fiber laser (SPTFL) with different laser settings and fiber usage. Materials and Methods: SPTFL machine was attached with different fibers. Artificial stones were fixed in water, whereas laser fiber was driven on a platform for ablation. Pulse energy, frequency, fiber-moving speed, fiber-to-stone distance, and fiber size were adjusted in each trial. The cross-sectional area of craters on the lateral stone surface was measured for comparison of ablation rate, combined with fiber-moving speed. Results: There was a trend that the ablation rate increased as pulse energy or frequency increased. When pulse energy was set as 0.2 J and frequency was increased from 50 to 150 Hz, the cross-sectional area of the crater was enlarged from 0.21 to 0.37 mm² (p < 0.05); when the frequency was set as 100 Hz and pulse energy was increased from 0.1 to 0.3 J, the crater was enlarged from 0.10 to 0.45 mm² (p < 0.05). Furthermore, energy demonstrated greater impact on ablation rate and the crater was enlarged from 0.20 mm² in the 0.1 J × 300 Hz group to 0.44 mm² in the 0.3 J × 100 Hz group (p < 0.05). Then fiber was set at different moving speeds with the same laser setting; the ablation rate of 3 mm/second group was 3.64 times higher than 0.5 mm/second group (p < 0.05). Ablation diminished as fiber-to-stone distance grew. A 200 μm fiber produced thinner and deeper fissure than 272 and 550 μm fibers, and the ablation rate was the highest for the 200 μm fiber. Conclusion: Pulse energy is a more important factor in influencing ablation efficiency compared with frequency. Closer fiber-to-stone distance, faster fiber movement, and smaller fiber size increase ablation efficiency.

A prospective evaluation of high- and low-power holmium laser settings for transurethral lithotripsy in the management of adults with large bladder calculi

PURPOSE

To prospectively investigate the efficacy and safety of high-power (100 W) vs low-power (20 W) laser settings for transurethral laser lithotripsy in the management large vesical calculi (> 4 cm).

METHODS

All patients with vesical calculi > 4 cm in the maximum dimension and scheduled for transurethral holmium laser lithotripsy were invited to participate in the study. Every alternate patient was treated with either the low- or high-power laser settings. We used a continuous irrigation resectoscope with laser bridge or a laser working element (Karl Storz) for laser lithotripsy of bladder stones. We compared the operative time, intra-operative/post-operative complications (up to 1 year), and stone-free rates between the treatment groups using IBM SPSS Statistics 24 software. Comparisons between treatment groups for continuous variables were assessed using the Welch test, while categorical variables were compared with either the Chi-square or Fisher's exact test. A p value < 0.05 was considered statistically significant.

RESULTS

Twenty patients with ten in each cohort were recruited. Preoperative data and mean bladder stone size were comparable in both groups. The duration of surgery was significantly reduced from 70.80 ± 25.28 min in low-power cohort to 40.90 ± 15.01 min in the high-power group (p = 0.005). There were no significant intra-operative complications in either group. All patients were stone-free following the procedure.

CONCLUSION

High-power laser setting of up to 100 W results in a significant reduction in duration of surgery without any increase in the complication rate for treatment of large bladder stones.

The optimal settings of holmium YAG laser in treatment of pediatric urolithiasis

The aim of this study is to present our experience on the use of the holmium:yttrium-aluminum-garnet (Ho:YAG) laser in pediatric patients for pediatric urolithiasis and describe the optimal settings. A total of 116 children who underwent urolithiasis treatment (percutaneous nephrolithotomy (PNL), ureterorenoscopy (URS), retrograde intrarenal surgery (RIRS)) were included. The mean age of the patients was 8.4 ± 5.2 years (1-18). The mean follow-up was 26 ± 8.8 months (9-45). There was no difference between the mean stone sizes of PNL and RIRS patients (p = 0.816). Operations were performed with 200, 272, and 365-μm fibers. In mini-URS, stone fragmentation was achieved with the energy settings set between 0.5 and 1 J and frequency set to > 8 Hz. In RIRS, fragmentation was achieved with the setting of 0.5-0.8 J at 10-20 Hz. Stone fragmentation was performed with energy settings of 0.8 to 2 J between 5 and 15 Hz for PNL. There was no significant difference between the stone-free rates of the PNL and RIRS (p = 0.150). Four postoperative complications occurred (Clavien II), which included febrile urinary infections in two patients who underwent mini-URS, one patient who underwent PNL, and one patient who underwent RIRS. Our results confirmed that Ho-YAG laser can be effectively used in children for stone treatment by using low-energy high-frequency settings for URS and RIRS and a high energy setting for PNL.

Pulse modulation with Moses technology improves popcorn laser lithotripsy

PURPOSE

Moses™ technology has been developed to improve holmium laser fragmentation at 1-2 mm distance from the stone. Because popcorn lithotripsy is a non-contact technique, we compared short pulse (SP) and Moses distance (MD) modes in an in vitro model.

METHODS

BegoStones were fragmented using a 120 W Ho:YAG laser (P120 Moses) and a 230 μm core fiber introduced through a ureteroscope. 20 W (1 J × 20 Hz; 0.5 J × 40 Hz) and 40 W (1 J × 40 Hz; 0.5 J × 80 Hz) settings (total energy 4.8 kJ) were tested using SP and MD modes. We assessed fragment size distribution and mass lost in fluid (initial mass-final dry mass of all sievable fragments). High-speed video analysis of fragmentation strike rate and vapor bubble characteristics was conducted for 1 J × 20 Hz and 0.5 J × 80 Hz. Laser strike rate (number of strikes divided by frequency) was categorized as: (1) direct-a visual plume of dust ejected from stone while in contact with fiber tip; (2) indirect-a visual plume of dust ejected with distance between stone and fiber tip.

RESULTS

For 1 J × 20 Hz (20 W), MD resulted in more mass lost in fluid and a lower distribution of fragments ≥ 2 mm compared to SP (p < 0.05). 0.5 J × 80 Hz (40 W) produced no fragments ≥ 2 mm, and there were no significant differences in fragment distribution between MD and SP (p = 0.34). When using MD at 1 J × 20 Hz, 96% of strikes were indirect vs 61% for SP (p = 0.059). In contrast to the single bubble of SP, with MD, there was forward movement of the collapsing second bubble, away from the fiber-tip.

CONCLUSIONS

For lower frequency and power popcorn settings, pulse modulation results in more fragmentation through true non-contact laser lithotripsy.

Deep learning computer vision algorithm for detecting kidney stone composition

OBJECTIVES

To assess the recall of a deep learning (DL) method to automatically detect kidney stones composition from digital photographs of stones.

MATERIALS AND METHODS

A total of 63 human kidney stones of varied compositions were obtained from a stone laboratory including calcium oxalate monohydrate (COM), uric acid (UA), magnesium ammonium phosphate hexahydrate (MAPH/struvite), calcium hydrogen phosphate dihydrate (CHPD/brushite), and cystine stones. At least two images of the stones, both surface and inner core, were captured on a digital camera for all stones. A deep convolutional neural network (CNN), ResNet-101 (ResNet, Microsoft), was applied as a multi-class classification model, to each image. This model was assessed using leave-one-out cross-validation with the primary outcome being network prediction recall.

RESULTS

The composition prediction recall for each composition was as follows: UA 94% (n = 17), COM 90% (n = 21), MAPH/struvite 86% (n = 7), cystine 75% (n = 4), CHPD/brushite 71% (n = 14). The overall weighted recall of the CNNs composition analysis was 85% for the entire cohort. Specificity and precision for each stone type were as follows: UA (97.83%, 94.12%), COM (97.62%, 95%), struvite (91.84%, 71.43%), cystine (98.31%, 75%), and brushite (96.43%, 75%).

CONCLUSION

Deep CNNs can be used to identify kidney stone composition from digital photographs with good recall. Future work is needed to see if DL can be used for detecting stone composition during digital endoscopy. This technology may enable integrated endoscopic and laser systems that automatically provide laser settings based on stone composition recognition with the goal to improve surgical efficiency.

Are We Cutting Ourselves Short? Laser Lithotripsy Performance Based on Differences in Fiber-tip Preparation

OBJECTIVE

To better understand the impact of laser fiber-tip configuration on lithotripsy performance, we undertook an in vitro study comparing 3 fiber-tip configurations: (1) new (single-use), (2) cleaved (reusable), and (3) coated (cut with scissors).

METHODS

Lithotripsy was performed using a Ho:YAG laser utilizing fragmentation (1 J × 10 Hz) and dusting (0.5 J × 20 Hz) settings. BegoStones were fragmented with a laser fiber advancing at a speed of 1 mm/s (220 seconds of activation). Three fiber-tip configurations were tested: new single-use standard (242 μm core) and cleaved (272 μm core), compared to the same fiber-tip coated/cut flush with scissors, respectively. Study outcome was difference in stone mass before and after each experiment. Power output was measured using a power meter.

RESULTS

Fragmentation for new or cleaved fibers was greater than the coated/cut flush fiber-tip (P <.05). For 1 J × 10 Hz and 0.5 J × 20 Hz settings, fragmentation was 59% and 75% higher with new fiber-tip compared to the coated/cut flush fiber-tip, respectively. For 1J × 10 Hz and 0.5 J × 20 Hz settings, fragmentation was 51% and 45% higher with cleaved fiber-tip compared to the coated/cut flush fiber-tip, respectively. Power output at the end of laser activation was higher for new and cleaved fiber-tips.

CONCLUSION

New and cleaved laser fibers demonstrated superior lithotripsy performance compared to fibers that were coated/cut flush with scissors. Cutting single-use laser fibers risks damaging the fiber-tip which can disperse the energy and reduce lithotripsy efficiency.

Preclinical comparison of superpulse thulium fiber laser and a holmium:YAG laser for lithotripsy

PURPOSE

A superpulse (500 W peak power) thulium fiber laser operating at a 1940 nm wavelength, suitable for lithotripsy, has recently been developed. The goal of this study was to compare stone fragmentation and dusting performance of the prototype superpulse thulium fiber laser with leading commercially available, high-power holmium:YAG lithotripters (wavelength 2100 nm) in a controlled in vitro environment.

METHODS

Two experimental setups were designed for investigating stone ablation rates and retropulsion effects, respectively. In addition, the ablation setup enabled water temperature measurements during stone fragmentation in the laser-stone interaction zone. Human uric acid (UA) and calcium oxalate monohydrate (COM) stones were used for ablation experiments, whereas standard BegoStone phantoms were utilized in retropulsion experiments. The laser settings were matched in terms of pulse energy, pulse repetition rate, and average power.

RESULTS

At equivalent settings, thulium fiber laser ablation rates were higher than those for holmium:YAG laser in both dusting mode (threefold for COM stones and 2.5-fold for UA stones) and fragmentation mode (twofold for UA stones). For single-pulse retropulsion experiments, the threshold for onset of stone retropulsion was two to four times higher for thulium fiber laser. The holmium:YAG laser generated significantly stronger retropulsion effects at equal pulse energies. The water temperature elevation near the laser-illuminated volume did not differ between the two lasers.

CONCLUSIONS

Distinctive features of the thulium fiber laser (optimal wavelength and long pulse duration) resulted in faster stone ablation and lower retropulsion in comparison to the holmium:YAG laser.

Clinical efficacy and safety of flexible ureteroscopic lithotripsy using 365 μm holmium laser for nephrolithiasis: a prospective, randomized, controlled trial

PURPOSE

To compare the clinical efficacy and safety between the FURL with 365 μm and 200 μm holmium laser for treating nephrolithiasis.

MATERIALS AND METHODS

A prospective randomized controlled trial was performed including analysis of data from 200 patients with nephrolithiasis. A total of 180 patients were randomized into two groups according to 1:1 ratio. In the 365 μm holmium laser group, kidney stones were disintegrated into less than 2 mm fragments with a 365 µm holmium laser fiber with the settings of 30-45 W under direct visualization; in the control group, the conventional 200 μm holmium laser was used. Descriptive statistics and logistic regression analyses tested the association among operation time, stone-free rate (SFR) and incidence of complications.

RESULTS

Operation time in the FURL with 365 μm laser was significantly shortened and no significance was observed in the complication rate. Stone size and location were identified as two major confounding factors for the operation time and SFR. Moreover, the FURL using 365 μm laser showed less operation time for renal stones with the diameter between 1 and 2 cm, stones located in lower calyx and multiple calculi; stones larger than 2 cm and/or located in lower pole inclined to present better SFR using the FURL with 365 μm laser.

CONCLUSIONS

The FURL combined with 365 μm holmium laser is safer and highly efficacious for the management of nephrolithiasis when compared to conventional FURL procedures, especially for those located in lower pole and larger than 2 cm.

Fragments and dust after Holmium laser lithotripsy with or without "Moses technology": How are they different?

Urinary stones can be readily disintegrated by Holmium:YAG laser (Holmium laser lithotripsy), resulting in a mixture of small stone dust particles, which will spontaneously evacuate with urine and larger residual fragments (RF) requiring mechanical retrieval. Differences between fragments and dust have not been well characterized. Also, it remains unknown how the recently introduced "Moses technology" may alter stone disintegration products. Three complementary analytical techniques have been used in this study to offer an in-depth characterization of disintegration products after in vitro Holmium laser lithotripsy: stereoscopic microscopy, scanning electron microscopy and Fourier-transform infrared spectroscopy. Dust was separated from fragments based on its floating ability in saline irrigation. Depending on initial crystalline constituents, stone dust either conserved attributes found in larger RFs or showed changes in crystalline organization. These included conversion of calcium oxalate dihydrate towards calcium oxalate monohydrate, changes in carbapatite spectra towards an amorphous phase, changes of magnesium ammonium phosphate towards a differing amorphous and crystalline phase and the appearance of hydroxyapatite on brushite fragments. Comparatively, "Moses technology" produced more pronounced changes. These findings provide new insights suggesting a photothermal effect occurring in Holmium laser lithotripsy. Figure: Appearance of hydroxyapatite hexagons on stone dust collected after Holmium laser lithotripsy of a brushite stone using "Moses technology."

Role of lasers in urology

Laser technology has long been a standard treatment for many diseases. In particular, laser treatment is considered the standard of care in various urological diseases. While originally primarily restricted to stone treatment, lasers have since evolved to play an important role even in the treatment of malignant diseases. In this review, we take a closer look at the history of lasers in urology and some implications for treatments today.

Ho:YAG laser lithotripsy in non-contact mode: optimization of fiber to stone working distance to improve ablation efficiency

PURPOSE

To evaluate how variable working distances between the laser fiber and the stone influence ablation volume.

METHODS

A laser fiber was fixed on a robotic arm perpendicular to an artificial stone. A single laser pulse was triggered at different working distances (0-2.0 mm in 0.2 mm increments) between the distal fiber tip and the stone. To achieve a measurable impact, pulse energy was set to 2 and 3 J, with either short or long pulse duration. Ablation volume was calculated with an optical microscope. Experiments were repeated five times for each setting.

RESULTS

Highest ablation volume was observed with a long pulse of 3 J at a working distance of 0.4 mm between the laser fiber and the stone surface (p value < 0.05). At 2 J, the highest ablation volume was noticed with a short pulse in contact mode. However, ablation volume of the latter was not significantly greater than with a long pulse of 2 J at a working distance of 0.4 mm (p value > 0.05). Compared to lithotripsy in contact mode, triggering a single long pulse at 0.4 mm increased ablation volume by 81% (p value = 0.016) at 2 J and by 89% (p value = 0.034) at 3 J.

CONCLUSIONS

For Ho:YAG laser lithotripsy, ablation volume may be higher in non-contact mode using long pulses, rather than in direct contact to the stone. Findings of the current study support the need of further studies of lithotripsy in non-contact mode.

Understanding the Popcorn Effect During Holmium Laser Lithotripsy for Dusting

OBJECTIVE

To assess low and high power settings for the popcorn technique, and relationship of laser fiber-to-stone distance and calyceal size on submillimeter fragmentation. Our in vitro findings may help guide strategies to improve a dusting technique for ureteroscopy.

METHODS

BegoStones were fragmented in small (127 mm³) and large (411 mm³) sized bulbs to simulate calyces, using a 120 W Ho:YAG laser. A 242 μm fiber was introduced through a ureteroscope mounted to a 3D positioner with its tip located at 0 or 2 mm distance from the stones. 20 W [1 J × 20 Hz, 0.5 J × 40 Hz] and 40 W [1 J × 40 Hz, 0.5 J × 80 Hz] settings were assessed, including short pulse and long pulse modes. Total energy delivered was constant at 7.2 kJ. Primary outcome was percentage of stone mass converted to fragments <1 mm. High-speed imaging was performed to study stone movement and/or fragmentation.

RESULTS

For all settings, popcorn lithotripsy yielded more submillimeter fragments when performed with the fiber positioned on the stone compared to 2 mm from the stone (P <.05). Distribution of submillimeter fragments was higher when utilizing high frequencies regardless of pulse energy. At 2 mm distance, popcorning was more effective in the small model (P <.05). At 2 mm distance, short pulse was superior to long pulse. Video analysis showed fragmentation did not occur when stones collided with each other. At 80 Hz/2 mm distance, only 17.5% of pulses impacted fragments.

CONCLUSION

Popcorn technique is more effective when the fiber is directly in contact with stone, and when performed in a small calyceal model. Utilizing settings with higher frequencies may improve dusting outcomes.

Numerical Response Surfaces of Volume of Ablation and Retropulsion Amplitude by Settings of Ho:YAG Laser Lithotripter

Objectives

Although laser lithotripsy is now the preferred treatment option for urolithiasis due to shorter operation time and a better stone-free rate, the optimal laser settings for URS (ureteroscopic lithotripsy) for less operation time remain unclear. The aim of this study was to look for quantitative responses of calculus ablation and retropulsion by performing operator-independent experiments to determine the best fit versus the pulse energy, pulse width, and the number of pulses.

Methods

A lab-built Ho:YAG laser was used as the laser pulse source, with a pulse energy from 0.2 J up to 3.0 J and a pulse width of 150 μs up to 1000 μs. The retropulsion was monitored using a high-speed camera, and the laser-induced craters were evaluated with a 3-D digital microscope. The best fit to the experimental data is done by a design of experiment software.

Results

The numerical formulas for the response surfaces of ablation speed and retropulsion amplitude are generated.

Conclusions

The longer the pulse, the less the ablation or retropulsion, while the longer pulse makes the ablation decrease faster than the retropulsion. The best quadratic fit of the response surface for the volume of ablation varied nonlinearly with pulse duration and pulse number.

Evaluation of 200 Mm, 365 Mm and 500 Mm Fibers of Ho:YAG Laser in Transurethral Lithotripsy of Ureteral: A Randomize Control Trial

Introduction: Presently, different holmium: yttrium aluminum garnet (Ho:YAG) laser calibers are used for endoscopic stone treatment, which include 200, 365, 500 and 1000 Mm fibers. Currently, there are not enough studies to compare the performance of these fibers. In this retrospective investigation, we compared the outcome of 200, 365 and 500 Mm fibers of Ho:YAG laser in transurethral lithotripsy of ureteral stone. Methods: From January 2016 to June 2017, 74 subjects with mean age of 35.3 ± 5.6 were randomly allocated to 3 groups according to the caliber of laser, 200, 365 and 500 Mm for transurethral lithotripsy. The main purpose of this investigation was to evaluate mean operation time (MOT), stone free rate (SFR) and complications. Results: MOT and SFR were significantly different in 500 Mm laser caliber (P=0.046, P=0.029, respectively). There was no remarkable difference between the 3 groups in this regard. Conclusion: Based upon our data, the clinical potency of the Ho: YAG laser was great in all 3 fiber calibers. The most important results of this comparison were the significantly higher SFR with increased laser caliber.

Jackets Off: The Impact of Laser Fiber Stripping on Power Output and Stone Degradation

PURPOSE

To investigate the effect of laser fiber stripping on stone fragmentation and laser fiber power output.

MATERIALS AND METHODS

In a benchtop simulation of laser lithotripsy, 20 BegoStone phantoms were positioned within a ureteral model and irradiated for 10 minutes at 8 Hz and 0.8 J. A freshly cleaved 365 μm laser fiber was used for all trials, with half of the fibers also undergoing stripping. Power output was measured at 1-minute intervals, beginning with an initial prelithotripsy recording at 0 minutes. Fiber tips were imaged with scanning electron microscopy. In a single-blinded manner, final masses of residual stone fragments were measured and used to quantify stone breakdown. Independent-sample Mann-Whitney U tests were performed with significance set at p < 0.05, comparing stripped and unstripped fiber tips with respect to power output and fraction of stone fragmentation.

RESULTS

Mean power output after 1 minute of lasing was significantly greater in unstripped laser fibers (p = 0.015), while fibers, whether stripped or not, demonstrated no significant output differences prelithotripsy or at any time from 2 to 10 minutes. However, stripped laser fibers achieved significantly increased stone breakdown compared to unstripped fibers (p = 0.004), fragmenting 63 mg (25%) more of the initial stone mass per trial.

CONCLUSIONS

Although unstripped laser fibers provided superior power output at 1 minute, output at all other time points was similar between stripped and unstripped fibers. However, despite similar optical output, stripped laser fibers achieved greater stone fragmentation, possibly due to improved contact between stone and fiber tip.

Optimal Settings for the Noncontact Holmium:YAG Stone Fragmentation Popcorn Technique

PURPOSE

The purpose of this study was to evaluate the popcorn technique using a wide range of holmium laser settings and fiber sizes in a systematic in vitro assessment.

MATERIALS AND METHODS

Evaluations were done with 4 artificial stones in a collection tube. A fixed ureteroscope was inserted through a ureteral access sheath to provide constant irrigation flow and the laser was placed 1 mm from the bottom. Combinations of 0.5 to 1.5 J, 10 to 20 and 40 Hz, and long and short pulses were tested for 2 and 4 minutes. We used 273 and 365 μm laser fibers. All tests were repeated 3 times. The stones were weighed before and after the experiments to evaluate the setting efficiency. Significant predictors of a highly efficient technique were assessed.

RESULTS

A total of 144 tests were performed. Mean starting weight of the stones was 0.23 gm, which was consistent among the groups. After the experiment the median weight difference was 0.07 gm (range 0.01 to 0.24). When designating a 50% reduction in stone volume as the threshold indicating high efficiency, the significant predictors of an efficient popcorn technique were a long pulse (OR 2.7, 95% CI 1.05-7.15), a longer duration (OR 11.4, 95% CI 3.88-33.29), a small (273 μm) laser fiber (OR 0.23, 95% CI 0.08-0.70) and higher power (W) (OR 1.14, 95% CI 1.09-1.20).

CONCLUSIONS

Higher energy, a longer pulse, frequencies higher than 10 Hz, a longer duration and a smaller laser fiber predict a popcorn technique that is more efficient at reducing stone volume.

Comparing the efficacy and safety of 365- and 550-μm laser fibers in semirigid ureteroscopic Ho:YAG lithotripsy

PURPOSE

To compare the efficacy and safety of 365- and 550-μm Ho:YAG laser fiber in semirigid ureteroscopic lithotripsy and to identify parameters that may affect laser energy and time during the procedure.

METHODS

A database of 111 patients who undergone a semirigid ureteroscopy (SRURS) for ureteral stone lithotripsy was analyzed. A 365-μm core fiber was used in 56 cases, and a multiple-uses 550-μm laser fiber was used in 55 cases. A standard 6.4 W protocol (8 Hz, 0.8 J/pulse) was used in all cases. The association between laser fiber diameter and several preoperative, intraoperative and postoperative parameters was evaluated.

RESULTS

Mean stone burden was 54.1 ± 39.1 mm(2), and postoperative stone-free and complication rate was 100.0 and 16.2 %, respectively. The 550-μm laser fiber diameter was significantly associated with lower laser energy (p = 0.01), energy/mm(3) (p = 0.031), number of pulses (p = 0.012), laser time (p = 0.012) and laser time/mm(3) (p = 0.043), while it did not affect postoperative outcomes. The multivariate analysis showed that shorter procedure duration, smaller stone burden and the 550-μm laser fiber were all significant independent predictors for decreased laser energy consumption.

CONCLUSION

The 550-μm laser fiber may decrease laser energy and time during SRURS lithotripsy with Ho:YAG laser compared to the 365 μm. Given its lower cost, it may represent the optimal choice for semirigid procedures.

Influence of saline on temperature profile of laser lithotripsy activation

PURPOSE

We established an ex vivo model to evaluate the temperature profile of the ureter during laser lithotripsy, the influence of irrigation on temperature, and thermal spread during lithotripsy with the holmium:yttrium-aluminum-garnet (Ho:YAG) laser.

MATERIALS AND METHODS

Two ex vivo models of Ovis aries urinary tract and human calcium oxalate calculi were used. The Open Ureteral Model was opened longitudinally to measure the thermal profile of the urothelium. On the Clinical Model, anterograde ureteroscopy was performed in an intact urinary system. Temperatures were measured on the external portion of the ureter and the urothelium during lithotripsy and intentional perforation. The lithotripsy group (n=20) was divided into irrigated (n=10) and nonirrigated (n=10), which were compared for thermal spread length and values during laser activation. The intentional perforation group (n=10) was evaluated under saline flow. The Ho:YAG laser with a 365 μm laser fiber and power at 10W was used (1J/Pulse at 10 Hz). Infrared Fluke Ti55 Thermal Imager was used for evaluation. Maximum temperature values were recorded and compared.

RESULTS

On the Clinical Model, the external ureteral wall obtained a temperature of 37.4°C±2.5° and 49.5°C±2.3° (P=0.003) and in the Open Ureteral Model, 49.7°C and 112.4°C with and without irrigation, respectively (P<0.05). The thermal spread along the external ureter wall was not statically significant with or without irrigation (P=0.065). During intentional perforation, differences in temperatures were found between groups (opened with and without irrigation): 81.8°±8.8° and 145.0°±15.0°, respectively (P<0.005).

CONCLUSION

There is an increase in the external ureteral temperature during laser activation, but ureteral thermal values decreased when saline flow was applied. Ureter thermal spread showed no difference between irrigated and nonirrigated subgroups. This is the first laser lithotripsy thermography study establishing the framework to evaluate the temperature profile in the future.

Systematic evaluation of a holmium:yttrium-aluminum-garnet laser lithotripsy device with variable pulse peak power and pulse duration

OBJECTIVE

The Holmium:yttrium-aluminum-garnet (Ho:YAG) laser is the standard lithotrite for ureteroscopy. This paper is to evaluate a Ho:YAG laser with a novel effect function in vitro, which allows a real-time variation of pulse duration and pulse peak power.

METHODS

Two types of phantom calculi with four degrees of hardness were made for fragmentation and retropulsion experiments. Fragmentation was analysed at 5 (0.5 J/10 Hz), 10 (1 J/10 Hz), and 20 (2 J/10 Hz) W in non-floating phantom calculi, retropulsion in an ureteral model at 10 (1 J/10 Hz) and 20 (2 J/10 Hz) W using floating phantom calculi. The effect function was set to 25%, 50%, 75%, and 100% of the maximum possible effect function at each power setting. Primary outcomes: fragmentation (mm3), the distance of retropulsion (cm); ≥5 measurements for each trial.

RESULTS

An increase of the effect feature (25% vs. 100%), i.e., an increase of pulse peak power and decrease of pulse duration, improved Ho:YAG laser fragmentation. This effect was remarkable in soft stone composition, while there was a trend for improved fragmentation with an increase of the effect feature in hard stone composition. Retropulsion increased with increasing effect function, independently of stone composition. The major limitations of the study are the use of artificial stones and the in vitro setup.

CONCLUSION

Changes in pulse duration and pulse peak power may lead to improved stone fragmentation, most prominently in soft stones, but also lead to increased retropulsion. This new effect function may enhance Ho:YAG laser fragmentation when maximum power output is limited or retropulsion is excluded.

Update on lasers in urology 2014: current assessment on holmium:yttrium-aluminum-garnet (Ho:YAG) laser lithotripter settings and laser fibers

PURPOSE

The purpose of the study was to review the existing literature on holmium:yttrium-aluminum-garnet laser lithotripsy regarding lithotripter settings and laser fibers.

METHODS

An online search of current and past peer-reviewed literature on holmium laser lithotripsy was performed on several databases, including PubMed, SciElo, and Google Scholar. Relevant studies and original articles about lithotripter settings and laser fibers were examined, and the most important information is summarized and presented here.

RESULTS

We examine how the choice of lithotripter settings and laser fibers influences the performance of holmium laser lithotripsy. Traditional laser lithotripter settings are analyzed, including pulse energy, pulse frequency, and power levels, as well as newly developed long-pulse modes. The impact of these settings on ablation volume, fragment size, and retropulsion is also examined. Advantages of small- and large-diameter laser fibers are discussed, and controversies are highlighted. Additionally, the influence of the laser fiber is examined, specifically the fiber tip preparation and the lithotripter settings' influence on tip degradation.

CONCLUSIONS

Many technical factors influence the performance of holmium laser lithotripsy. Knowing and understanding these controllable parameters allows the urologist to perform a laser lithotripsy procedure safely, efficiently, and with few complications.

In vitro fragmentation efficiency of holmium: yttrium-aluminum-garnet (YAG) laser lithotripsy--a comprehensive study encompassing different frequencies, pulse energies, total power levels and laser fibre diameters

OBJECTIVE

To assess the fragmentation (ablation) efficiency of laser lithotripsy along a wide range of pulse energies, frequencies, power settings and different laser fibres, in particular to compare high- with low-frequency lithotripsy using a dynamic and innovative testing procedure free from any human interaction bias.

MATERIALS AND METHODS

An automated laser fragmentation testing system was developed. The unmoving laser fibres fired at the surface of an artificial stone while the stone was moved past at a constant velocity, thus creating a fissure. The lithotripter settings were 0.2-1.2 J pulse energies, 5-40 Hz frequencies, 4-20 W power levels, and 200 and 550 μm core laser fibres. Fissure width, depth, and volume were analysed and comparisons between laser settings, fibres and ablation rates were made.

RESULTS

Low frequency-high pulse energy (LoFr-HiPE) settings were (up to six times) more ablative than high frequency-low pulse energy (HiFr-LoPE) at the same power levels (P < 0.001), as they produced deeper (P < 0.01) and wider (P < 0.001) fissures. There were linear correlations between pulse energy and fragmentation volume, fissure width, and fissure depth (all P < 0.001). Total power did not correlate with fragmentation measurements. Laser fibre diameter did not affect fragmentation volume (P = 0.81), except at very low pulse energies (0.2 J), where the large fibre was less efficient (P = 0.015).

CONCLUSIONS

At the same total power level, LoFr-HiPE lithotripsy was most efficient. Pulse energy was the key variable that drove fragmentation efficiency. Attention must be paid to prevent the formation of time-consuming bulky debris and adapt the lithotripter settings to one's needs. As fibre diameter did not affect fragmentation efficiency, small fibres are preferable due to better scope irrigation and manoeuvrability.

Therapeutic applications of lasers in urology: an update

There has been renewed interest in the use of lasers for minimally invasive treatment of urologic diseases in recent years. The introduction of more compact, higher power, less expensive and more user-friendly solid-state lasers, such as the holmium:yttrium-aluminum-garnet (YAG), frequency-doubled neodymium:YAG and diode lasers has made the technology more attractive for clinical use. The availability of small, flexible, biocompatible, inexpensive and disposable silica optical fiber delivery systems for use in flexible endoscopes has also promoted the development of new laser procedures. The holmium:YAG laser is currently the workhorse laser in urology since it can be used for multiple soft- and hard-tissue applications, including laser lithotripsy, benign prostate hyperplasia, bladder tumors and strictures. More recently, higher power potassium-titanyl-phosphate lasers have been introduced and show promise for the treatment of benign prostatic hyperplasia. On the horizon, newer and more effective photosensitizing drugs are being tested for potential use in photodynamic therapy of bladder and prostate cancer. Additionally, new experimental lasers such as the erbium:YAG, Thulium and Thulium fiber lasers, may provide more precise incision of soft tissues, more efficient laser lithotripsy and more rapid prostate ablation. This review provides an update on the most important new clinical and experimental therapeutic applications of lasers in urology over the past 5 years.

Evaluation of a new 240-μm single-use holmium:YAG optical fiber for flexible ureteroscopy

BACKGROUND AND PURPOSE

Numerous holmium:yttrium-aluminum-garnet laser fibers are available for flexible ureteroscopy. Performance and durability of fibers can vary widely among different manufacturers and their product lines with differences within a single product line have been reported. We sought to evaluate a newly developed nontapered, single-use 240-μm fiber, Flexiva™ 200 (Boston Scientific, Natick, MA), during clinical use and in a bench-testing model.

MATERIALS AND METHODS

A total of 100 new fibers were tested after their use in 100 consecutive flexible ureteroscopic lithotripsy procedures by a single surgeon (B.K.). Prospectively recorded clinical parameters were laser pulse energy and frequency settings, total energy delivered and fibers failure. Subsequently, each fiber was bench-tested using an established protocol. Parameters evaluated for were fibers true diameter, flexibility, tip degradation, energy transmission in straight and 180° bend configuration and fibers failure threshold with stress testing.

RESULTS

The mean total energy delivered was 2.20 kJ (range 0-18.24 kJ) and most common laser settings used were 0.8 J at 8 Hz, 0.2 J at 50 Hz, and 1.0 J at 10 Hz, respectively. No fiber fractured during clinical procedures. The true fiber diameter was 450 μm. Fiber tips burnt back an average of 1.664 mm, but were highly variable. With laser setting of 400 mJ at 5 Hz, the mean energy transmitted was 451 and 441 mJ in straight and 180° bend configuration, respectively. Thirteen percent of fibers fractured at the bend radius of 0.5 cm with a positive correlation to the total energy transmitted during clinical use identified.

CONCLUSION

Fiber performance was consistent in terms of energy transmission and resistance to fracture when activated in bent configuration. Fiber failure during stress testing showed significant correlation with the total energy delivered during the clinical procedure. The lack of fiber fracture during clinical use may reduce the risk of flexible endoscope damage due to fiber failure.

Optimal power settings for Holmium:YAG lithotripsy

PURPOSE

We determined the optimal Ho:YAG lithotripsy power settings to achieve maximal fragmentation, minimal fragment size and minimal retropulsion.

MATERIALS AND METHODS

Stone phantoms were irradiated in water with a Ho:YAG laser using a 365 μm optical fiber. Six distinct power settings were tested, including 0.2 to 2.0 J and 10 to 40 Hz. For all cohorts 500 J total radiant energy were delivered. A seventh cohort (0.2 J 40 Hz) was tested post hoc to a total energy of 1,250 J. Two experimental conditions were tested, including with and without phantom stabilization. Total fragmentation, fragment size and retropulsion were characterized. In mechanism experiments using human calculi we measured crater volume by optical coherence tomography and pressure transients by needle hydrophone across similar power settings.

RESULTS

Without stabilization increased pulse energy settings produced increased total fragmentation and increased retropulsion (each p <0.0001). Fragment size was smallest for the 0.2 J cohorts (p <0.02). With stabilization increased pulse energy settings produced increased total fragmentation and increased retropulsion but also increased fragment size (each p <0.0001). Craters remained symmetrical and volume increased as pulse energy increased. Pressure transients remained modest at less than 30 bars even at 2.0 J pulse energy.

CONCLUSIONS

Holmium:YAG lithotripsy varies as pulse energy settings vary. At low pulse energy (0.2 J) less fragmentation and retropulsion occur and small fragments are produced. At high pulse energy (2.0 J) more fragmentation and retropulsion occur with larger fragments. Anti-retropulsion devices produce more efficient lithotripsy, particularly at high pulse energy. Optimal lithotripsy laser dosimetry depends on the desired outcome.

High- vs low-power holmium laser lithotripsy: a prospective, randomized study in patients undergoing multitract minipercutaneous nephrolithotomy

OBJECTIVE

To determine the efficacy and safety of high-power holmium: yttrium aluminum-garnet (Ho:YAG) laser lithotripsy for multitract modified minimally invasive percutaneous nephrolithotomy (MPCNL) in the treatment of patients with large staghorn renal calculi.

METHODS

A randomized, prospective study was conducted. Two-hundred seventy-three consecutive patients (291 renal units) with large staghorn renal calculi were randomized to undergo multitract MPCNL with 30-W low-power or 70-W high-power Ho:YAG laser lithotripsy. Both groups were compared in terms of perioperative findings and postoperative outcomes, including procedure time, stone-free rate, length of hospital stay, transfusion rates, renal function recovery, and other complications.

RESULTS

The average patient age was 49.2 years (range 22-73) and mean stone size was 5.54±0.7 cm. The 2 groups had some comparable perioperative findings and outcome, including tracts required per operated renal unit (n), blood loss, postoperative fever, postoperative hospital stay, stone-free rate, and improvement of operated renal function. The operation time in the high-power group was significantly shorter than that in the low-power group (129.20±17.2 vs 105.18±14.2, P<.01).

CONCLUSION

A combination of multitract MPCNL and high-power Ho:YAG laser lithotripsy can greatly decrease the operative time without increasing the intraoperative complications or delaying postoperative renal function recovery when compared with low-power Ho:YAG laser lithotripsy.