Impact of Pulse Mode on Dusting Effect for Holmium Laser Lithotripsy: In Vitro Evaluation With Calcium Oxalate Monohydrate Stones.

OBJECTIVE: To assess the distribution of stone fragments (<0.25->2 mm) after in vitro dusting laser lithotripsy with varying pulse modes using canine calcium oxalate monohydrate (COM) stones. Recent work demonstrates that fragments <0.25 mm are ideal for dusting, and we hypothesized advanced pulse modes might improve this outcome. METHODS: A 3D-printed bulb was used as a calyceal model containing a single COM stone. A 230-core fiber (Lumenis) was passed through a ureteroscope (LithoVue, Boston Scientific). Contact laser lithotripsy by a single operator was performed with dusting settings (0.5J x 30Hz; Moses Pulse120H) to deliver 1kJ of energy for each trial. Short pulse (SP), long pulse (LP), Moses Distance (MD) and Moses Contact (MC) modes were tested with 5 trials for each parameter. Primary outcome was mass of fragments <0.25, <0.5, <1, and <2 mm. Laser fiber tip degradation was measured using a digital caliper. RESULTS: Mass of stone fragments <0.25 mm varied from 34.6%-43.0% depending on the pulse mode, with no statistically significant differences between modes. MC (98.5%) produced a greater mass of fragments <2 mm compared to LP (86.1%; P = .046) but not SP (92.0%). Significantly less fiber tip burnback occurred with MC (0.29 mm) and MD (0.28 mm), compared to SP (0.83 mm; P < .0005). CONCLUSION: Regardless of pulse mode, greater than one-third of the mass of COM stone was reduced to fragments <0.25 mm following contact laser lithotripsy. MC produced a greater mass of fragments <2 mm compared to LP and demonstrated less fiber tip burnback compared to SP.

Burnback: the role of pulse duration and energy on fiber-tip degradation during high-power laser lithotripsy.

High-power holmium lasers have become popular for ureteroscopic laser lithotripsy and dusting. Our aim was to investigate the effect of pulse duration and pulse energy on fiber-tip degradation when using high-power settings for popcorn lithotripsy. BegoStones were fragmented in a glass bulb to simulate renal calyx, using a 120 W Ho:YAG laser. A 242 µm fiber was placed via the ureteroscope 2 mm distance from stones (popcorn model). To assess the effect of pulse duration on fiber-tip degradation, long pulse (LP) and short pulse (SP) settings were compared at settings of 1.0Jx20Hz (20 W), 0.5Jx70Hz (35 W), and 1.0Jx40Hz (40 W). To assess the effect of pulse energy on tip degradation, 40 W SP settings (0.5Jx80Hz, 0.8Jx50Hz, and 1.0Jx40Hz) were tested. Pulse duration was measured using a photodetector and peak power was then calculated using the pulse duration and pulse energy. Experiments were conducted for 4 min. Fiber-tip length was measured before and after using a digital caliper. Fiber-tip degradation was least when using LP for all settings tested (p < 0.01). For 40 W settings, tip degradation was significantly lower when using a pulse energy of 0.5 J compared to 0.8 J or 1.0 J (p < 0.004). LP mode results in less fiber burnback for all power settings tested. Total power is more important than frequency in the development of burnback. However, high-power 40 W settings can be utilized with less burnback if lower pulse energies are used. Understanding these parameters can improve the longevity of the laser fiber and improve procedural efficiency.

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.

Frequency Threshold for Ablation During Holmium Laser Lithotripsy: How High Can You Go?

Purpose: We performed in vitro studies to assess the relationship of pulse frequency on stone ablation during contact laser lithotripsy and determine if there is a threshold after which its effect on lithotripsy is limited. Methods: BegoStones were fragmented using a Ho:YAG laser (P120 Moses) and a 230 µm fiber at 0.5 J on long pulse (LP) and Moses distance (MD) modes in contact with the stone. The relationship between the number of pulses (1-40 Hz) on stone crater volume was assessed using three-dimensional confocal microscopy and nonlinear-segmented regression. To simulate a painting technique, we assessed fragmentation (mg/second) at 20, 40, and 60 Hz, with the fiber moving at a speed of 1 and 3 mm/second, respectively. High-speed imaging was used to record ablation. Results: When the laser fiber was fixed, after 13.0 (LP) and 15.4 (MD) pulses, greater pulse frequency did not lead to a significant increase in stone crater volume. Fragmentation was greatest at higher frequencies and faster fiber speed. Increasing the frequency from 20 to 60 Hz at 3 mm/second increased fragmentation by 82% and 61% for LP and MD modes, respectively. Using high-speed data, if the laser fiber is moving at 1 mm/second, a hypothetical frequency threshold for ablation was calculated to be 52 and 61.6 Hz for LP and MD modes, respectively. Conclusion: Increasing the fiber speed increases stone ablation when using high frequency settings. When the fiber is fixed there is a threshold after which increasing the pulse frequency leads to minimal gain in ablation. The exact value for threshold when the fiber is moving needs further study. Our study serves to provide insight for parameter selection and safety of laser lithotripsy for dusting technique.

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.

Defining Thermally Safe Laser Lithotripsy Power and Irrigation Parameters: In Vitro Model.

Introduction: High-power laser settings are commonly employed for stone dusting techniques. Previous in vitro and in vivo studies have demonstrated that a toxic thermal dose can result from treatment within a renal calix without adequate irrigation. Hence, both laser power and irrigation rate must be considered together to determine safe laser lithotripsy parameters. The objective of this in vitro study was to map parameter safety boundaries and create guidelines for selection of safe laser and irrigation settings. Methods: The experimental system consisted of in vitro models simulating ureter, renal calix, and renal pelvis placed in a water bath maintained at 37°C. Temperature was recorded during ureteroscopy with laser activation for 60 seconds. Trials were conducted at strategically selected power levels and irrigation rates. Thermal dose for each trial was calculated based on Sapareto and Dewey t43 methodology with thermal dose >120 equivalent minutes considered to result in thermal tissue injury. A parameter safety boundary was established by plotting the maximal safe power level for each irrigation rate. Results: The parameter safety boundary was found to be linear for each scenario with the renal pelvis able to tolerate the highest laser power and the renal calix the least power without injury. Conclusion: This study describes the methodology to determine parameter safety boundaries that can be used to guide proper selection of thermally safe laser settings and irrigation rates during ureteroscopy with laser lithotripsy. This work provides a framework to assess the effectiveness of various strategies to control and mitigate thermal dose.

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.

Emerging Laser Techniques for the Management of Stones.

Next-generation holmium laser systems provide the user with a range of parameters that can help optimize fragmentation efficiency. Ureteroscopic strategies broadly consist of fragmentation with active retrieval, or dusting, which uses low pulse energy settings to break stones into fine fragments for spontaneous passage. Techniques for dusting include dancing, chipping, and popcorning. The Moses technology is a multipulse mode that may help reduce retropulsion and increase fragmentation. The thulium fiber laser is an emerging laser technology that provides an extensive parameter range for dusting. Future studies are needed to define the role of these technologies and techniques for laser lithotripsy.

Ambulatory Tubeless Mini-Percutaneous Nephrolithotomy Using Moses Technology and Dusting Technique.

OBJECTIVE: To demonstrate the use of the Moses technology for holmium laser lithotripsy in conjunction with mini-percutaneous nephrolithotomy (PCNL) to treat a lower pole stone. The Moses technology is a pulse modulation method that can reduce stone retropulsion, which may have advantages when used during mini-PCNL. METHODS: A 63-year-old patient with a right-sided 1.5 cm lower pole stone (1300 Hounsfield Unit) underwent mini-PCNL using a 120W holmium laser (MosesP120, Lumenis). Moses has 2 modes-"Contact" and "Distance"-optimized for operation at 0-1 and 2-3 mm from the stone surface, respectively. Percutaneous access was obtained into the lower pole while the patient was in prone position. Using the medium (17.5F) mini-PCNL set (Karl Storz), the stone was fragmented using dusting settings with a 230 µm Moses fiber (0.3 J × 20-30 Hz; Moses Contact and Distance modes). RESULTS: The video demonstrates the capabilities of treating a lower pole stone with a dusting technique using Moses modes. Dusting, to decrease the stone size so that it can fit within the sheath, in combination with fragment expulsion with the Venturi effect, as well as extraction with graspers/baskets resulted in complete stone removal. Following placement of an antegrade ureteral stent (tubeless technique) and sealing of the tract with FloSeal, the patient was discharged from the recovery unit. There were no adverse events. The stent was removed after 7 days, and follow-up KUB at 2 weeks showed no residual fragment. CONCLUSION: Due to the miniaturization of equipment, the holmium laser serves as an ideal energy source for fragmentation. In our early experience, the Moses technology with mini-PCNL allows a combination of dusting and stone extraction. As mini-PCNL offers smaller tract dilatation, for lower pole stones it can be performed in an ambulatory setting and is an alternative to ureteroscopy or shockwave lithotripsy with the potential for complete stone clearance.

Student Factors That Influence Clerkship Grades and Matching Into a Surgical Residency.

OBJECTIVE: Evaluate the relationship between medical school factors (including preclinical mentorship, order of clerkships, and clerkship grades) and matching into surgical specialties. DESIGN: Clerkship information, match data, and data on structured preclinical research obtained from 2010 to 2015 for a single institution was obtained and analyzed using multivariate analysis. SETTING: University of Michigan Medical School. PARTICIPANTS: Seven hundred and forty-six students who took both the Internal Medicine and Surgery clerkships between 2010 and 2015 and have since participated in the match. RESULTS: Among 740 students studied, 243 matched into a surgical field. Higher Shelf scores were associated with higher clerkship grades in Surgery and Internal Medicine. Honors or High Pass in Surgery were associated with matching into a surgical field. Structured preclinical research in Surgery and order of clerkship were not associated with matching into a surgical field. CONCLUSIONS: Students who went into surgery were more likely to receive Honors or High Pass. Preclinical choices geared toward a surgical specialty (e.g., order of clerkship and structured research) were not associated with matching into a surgical field. These data may help guide school specific advice for students.