Gallstone lithotripsy with the pulsed dye laser: in vitro studies

The use of a pulsed dye laser to fragment human gallstones is reported. Laser energy was delivered by a 320 microns quartz fibre at wavelengths of 440, 480, 504, 560, 590, and 635 nm, in 1 microsecond pulses at energies of 5-60 mJ per pulse, producing peak powers of the order of 10(5) W. Cholesterol, pigment and mixed stones were fragmented. The shorter wavelengths were most efficient, using significantly less energy at 440 and 480 nm than at the longer wavelengths. Pigment stones were fragmented with significantly less energy than those in which cholesterol predominated. Thermal imaging during laser treatment showed no significant rise in temperature in the bulk of the stone. Absorption spectroscopy of bile revealed a peak at 450 nm, coinciding with the known absorption characteristic of bilirubin. Bile strongly attenuated light at shorter wavelengths, even at dilutions as great as 1:20 and protected samples of biliary epithelium from laser damage except when the optical fibre was in direct contact. The pulsed dye laser may offer significant advantages over current methods of biliary stone fragmentation.     

Laser lithotripsy with a 504 nm pulsed dye laser: in vitro fragmentation related to stone weight and pulse energy

Biliary, urinary and salivary stones were fragmented in vitro with a flashlamp-pumped dye laser operating at 504 nm. A clinical fragmentation criterion was formulated; fragmentation was continued until all fragments had passed through a sieve with holes of 1.5×1.5 mm². The number of shots of 50 mJ necessary for total fragmentation appeared to be proportional to the stone mass. The three types of stones showed statistically significant differences in the number of shots per unit mass, necessary for fragmentation. On biliary calculi we investigated the influence of the energy per laser pulse. For pulse energies of 32 mJ and larger, the energy necessary for fragmentation appeared to be proportional to the initial stone mass, but did not depend on the energy per pulse.     

Measurement of the optical and thermal properties of biliary calculi using pulsed photothermal radiometry

The optical absorption coefficients for biliary calculi are important in understanding the mechanism of laser-induced stone fragmentation. However, the heterogeneous composition of calculi and difficulties in producing optically thin samples prevent conventional spectrophotometric measurement techniques from being used. To overcome these limitations, we used a pulsed photothermal radiometry system to measure the optical absorption coefficients and thermal diffusivities of various biliary calculi. In the wavelength range examined (350-1,060 nm), there was strong optical absorption which was greater for pigment stones than for cholesterol stones. The data support the theory that the initiation of the plasma accompanying laser fragmentation of calculi is a thermal process.     

Biliary lithotripsy as an adjunct to laparoscopic common bile duct stone extraction

Summary We investigated various energy sources and delivery systems suitable for fragmentation of common duct calculi by a laparoscopic technique. We evaluated electrohydraulic lithotripsy (EHL) using 1.9-Fr probe delivering 80 W and laser lithotripsy using a 200-m fiber delivering 30–70 mJ/pulse at 5–20 Hz. In vitro biliary stone fragmentation analysis suggested that the laser lithotripsy produced a more controllable fragmentation than EHL. Initial attempts to employ EHL techniques in animal models resulted in common bile duct injury or inadequate fragmentation of stones. In contrast, biliary lithotripsy was accomplished in pigs using the pulsed-dye laser at 10 Hz and 60 mJ/pulse. Histologic evaluation revealed no evidence of ductal injury related to laser stone fragmentation. Subsequently, laser common duct lithotripsy was used in two human subjects. One patient had a 1.8-cm impacted ampullary stone and one patient had a 3-cm intrahepatic stone. In both cases, the stones were removed laparoscopically after laser fragmentation. Our experience suggests that the laser lithotripsy may facilitate laparoscopic common duct stone extraction procedures.     

Experimental study of application of excimer laser to laser angioplasty

The possible application of excimer laser to laser angioplasty was studied. In the first experiment, the ablative effects of excimer laser at wavelengths of 248 nm and 308 nm on the pig myocardium were examined in vitro at an air-tissue interface. Crater depth increased with total delivered energy and energy per pulse. Very clear cuts could be observed by histological examination. There was no evidence of thermal damage at a wavelength of 248 nm, at 10 pps. Above 10 pps, a thin bordering zone of suspicious thermal damage was noted with the wavelengths of 248 nm and 308 nm. Thermal damage increased with pulse repetition rate. In the second experiment, the effects of excimer laser irradiation on blood were examined. Five vials, each of which contained 3 ml of blood, were exposed to 37.5 mJ laser beam at 10 pps in repetition rate for 10, 20, 30, 40, 50 seconds. One vial was left untreated as a control. No change in hematocrit value was observed after excimer laser irradiation. In contrast, the level of plasma free hemoglobin rose progressively with each increased duration of exposure. This result indicates that the lysis of erythrocytes does not occur in the laser-exposed cells. However, the damage to erythrocyte membrane took place as it was evidenced by progressive hemoglobin leakage into plasma. In the third experiment, the excimer laser was coupled to a 400 microns quartz optical fiber and the laser energy transmitted through the fiber was measured. At a wavelength of 308 nm, pulse energies up to 9 mJ were noted at the tip of the fiber. At a wavelength of 248 nm, the fiber tip was destroyed. In the fourth experiment, acute and chronic healing responses of normal canine arteries to excimer laser irradiation were studied in 4 mongrel dogs. The artery healed completely at the 18th day after the excimer laser irradiation. There was no evidence of thrombus formation and intimal hyperplasia in these arteries. The results suggest the applicability of excimer laser to laser angioplasty.     

An Er:YAG laser endoscopic fiber delivery system for lithotripsy of salivary stones

BACKGROUND AND OBJECTIVES: Endoscopic applications of Erbium:YAG lasers are still very limited due to lack of appropriate fiber delivery capabilities. Recent reports on potential advantages of this laser for lithotripsy of ureteral stones prompted us to develop an Er:YAG fiber delivery system for endoscopic lithotripsy of salivary stones. We report on the development of this system and its clinical use on 17 patients. STUDY DESIGN/MATERIALS AND METHODS: Ho:YAG and Er:YAG laser fragmentation performances were initially compared. Optimal laser parameters for lithotripsy of salivary stones were then established ex vivo using a commercial dental Er:YAG laser (Lumenis Opusdent 20). Metal hollow waveguides optimized for Er:YAG laser transmission were end sealed with a polished sapphire rod of 0.63 mm diameter and designed to adapt to the Opusdent laser and to a Storz sialoendoscope. The system was tested ex vivo for durability and clinical compatibility at input energies up to 700 mJ, 10-20 Hz. Following Helsinki approval the system was clinically tested on 17 patients with sialolithiasis. RESULTS: Lithotripsy threshold was around 80 mJ/pulse (26 J/cm2) while efficient fragmentation, with microscopic fragments, was observed at an output energy range of 150-300 mJ/pulse. At 10 Hz, fragmentation rates of about 1.8 mm3/second were achieved enabling lithotripsy of a 6 mm stone in about 2 minutes. Front surface damage to the sapphire rod occurred but did not contribute to significant loss in fragmentation efficiency. Of the 21 stones treated clinically, 5 were fully fragmented, 7 were prepared for extraction by mini forceps, and 9 were released from surrounding soft tissues for subsequent removal. Fifteen of the 18 treated glands returned to normal function without any symptoms. CONCLUSIONS: The Er:YAG endoscopic delivery system described is a clinically viable and cost-effective device for a range of hard and soft tissue wet field applications accessible through rigid or semi-rigid endoscopes. Further improvements in the waveguide may allow access also through fully flexible endoscopes.     

Biliary laser lithotripsy.

Laser lithotripsy is an excellent method of fragmenting those biliary stones that cannot be removed easily by less technically advanced methods such as basket extraction. The energy can be delivered through fine flexible fibers, around 200 to 320 microns in diameter, that can be passed through the channels of a variety of small endoscopes. Currently, the optimal laser seems to a pulsed system because of the conversion of light to acoustic energy with minimal heating of the surrounding tissues, thus avoiding the chance of tissue injury and perforation. The best wavelength seems to be 504 nm, because at this wavelength, there is maximum absorption of laser energy by pigment stones, resulting in fragmentation using low-energy pulses. With further research, optimal wavelengths and pulse durations may emerge.     

Comparison of holmium and flashlamp pumped dye lasers for use in lithotripsy of biliary calculi.

The characteristics of laser lithotripsy of biliary calculi are compared for a flashlamp pumped dye laser (lambda = 640 nm) and a Cr:Tm:Ho-YAG laser (lambda = 2.1 microns). Data on fragmentation efficiency with respect to laser power and pulse repetition rate are presented for different types of stones. It is shown that both lasers can produce effective stone fragmentation. The laser power required for efficient fragmentation characteristics is significantly less for the visible wavelength laser. However, the problems associated with damage to the fiber tips of the delivery system during operation were found to be less with the near infrared wavelength. The laser power for efficient fragmentation with the dye laser varies significantly for different types of stones while the power for efficient fragmentation with the holmium laser is the same for all stones.     

In vitro analysis of stone fragmentation ability of the FREDDY laser

BACKGROUND AND PURPOSE: The Frequency-Doubled Double-Pulse Nd:Yag) (FREDDY) laser (World of Medicine, Berlin Germany) is a short-pulsed, double-frequency solid-state laser with wavelengths of 532 and 1064 nm. This low-power, low-cost laser was developed for intracorporeal lithotripsy. We designed an experimental set-up to test its fragmentation efficiency at different energy and frequency settings. MATERIALS AND METHODS: Forty previously weighed plaster-of-Paris stone phantoms were divided into four groups in order to test fragmentation at 5 and 10 Hz for 2 and 4 minutes. A hands-off underwater laboratory set-up including a holder to keep the stone phantom in contact with the quartz laser fiber was utilized. The 280-microm laser fiber was cleaved and stripped between runs to ensure optimal energy delivery. After fragmentation was completed, all of the stone fragments remaining within the holder were allowed to desiccate for 48 hours and reweighed. Fragmentation was measured as the percentage weight loss. RESULTS: Stone phantoms fragmented at 5 Hz for 2 minutes sustained a mean 24% loss of weight, whereas the 4-minute treatment at 5 Hz reduced stone weight by 54%. Treatment at 10 Hz for 2 minutes demonstrated results similar to those of stones treated for 4 minutes at 5 Hz, reducing stone weight by 51%. Fragmentation at 10 Hz for 4 minutes revealed a 64% loss of mass, less than expected for these power settings. Fiber deterioration observed at the higher energy settings may be the cause of the reduced stone-fragmentation efficiency. CONCLUSIONS: Fragmentation with the FREDDY laser in the 5 Hz, 4 minutes and 10 Hz, 2 minutes protocols is comparable, suggesting that stone fragmentation correlates well with the total energy delivered to the stone. The slight drop in fragmentation efficiency at 10 Hz, 4 minutes is most likely explained by fiber damage occurring consistently at these higher energy settings. The safety profile and low investment and running costs of this laser are advantages that suggest the laser warrants further clinical trials.     

Painless lithotripsy by flashlamp-excited dye laser for impacted biliary stones: an experimental and clinical study.

OBJECTIVE: To find out the appropriate dye laser output and frequency for each kind of stone experimentally, and to use flashlamp-excited dye laser for impacted biliary stones. DESIGN: Prospective study. SETTING: University hospital, Japan. SUBJECTS: 12 patients undergoing lithotripsy for both intrahepatic and extrahepatic impacted biliary stones. MAIN OUTCOME MEASURES: Appropriate dye laser output and frequency, histological changes in the bile duct wall, and outcome. RESULTS: Stones were pulverised, and required a median 155 pulses (range 80-205) at 40 mJ for bilirubin stones and 355 pulses (range 205-405) at 50 mJ for cholesterol stones. At the standard energies used, the laser caused only superficial damage to the serosa of the common bile duct. It was successful in fragmenting 133/135 stones (99%), and in addition pulverised 125/135 stones (93%). No patients complained of pain during laser lithotripsy even under local anaesthesia. All patients were discharged from the hospital after an uneventful recovery, and no recurrent stones have been found at outpatient follow-up ranging between 2 and 85 months. CONCLUSION: Flashlamp-excited dye laser with a small choledochoscope seems to be safe and painless way of treating biliary stones, even if they are impacted in the peripheral biliary tree and patients are at high risk.     

Excimer ablation of human intervertebral disc at 308 nanometers

Excimer laser energy, which has been shown to photoablate tissue at a precisely controllable rate with minimal thermal damage, was applied to human intervertebral disc in an effort to develop a technique for percutaneous discectomy. Cadaveric samples of human disc were used. Excimer laser energy was produced by a XeCl, magnetically switched, long-pulse laser working at 308 nm, 20 Hz. Annulus tissue of approximately 1 mm thickness was placed in contact with the output tip of a 400 microns core diameter quartz fiber, and measurements of ablation rate were made at different radiant exposures. Ablation rates were found to vary linearly with radiant exposure, from 0.7 micron/pulse at 10 mJ/mm2 to 11.0 microns/pulse at 55 mJ/mm2, with a correlation coefficient of 0.984. Threshold radiant exposure, calculated by extrapolation, was found to be about 7 mJ/mm2. Histologic analysis showed a minimum of thermal damage in these specimens, and when ablated with modification to maintain constant fiber-tissue contact, thermal injury was nearly absent, as compared to samples ablated with Nd:YAG through a contact probe. Thermographic analysis, performed using the AGA 782 Digital Thermography system, showed increasing temperature with increasing radiant exposure, with a maximum temperature of 47.2 degrees C at 55 mJ/mm2. In that precise tissue ablation was demonstrated with minimal generated heat, and excimer energy at 308 nm is transmissible through fiber optics, excimer holds great promise for the development of a percutaneous discectomy technique.     

Erbium:YAG laser lithotripsy using hybrid germanium/silica optical fibers

BACKGROUND AND PURPOSE: Previous studies have demonstrated that the erbium:YAG laser is two to three times more efficient for laser lithotripsy than the holmium:YAG laser. However, the lack of a suitable optical fiber delivery system remains a major obstacle to clinical application of Er:YAG laser lithotripsy. This paper describes the initial testing of a hybrid germanium oxide/silica optical fiber for potential endoscopic use with the Er:YAG laser. MATERIALS AND METHODS: Er:YAG laser radiation with a wavelength of 2.94 microm, a pulse energy of 10 to 600 mJ, a pulse length of 220 microsec, and pulse-repetition rates of 3 to 10 Hz was focused into either 350- or 425- microm-core hybrid germanium/silica fibers in contact with human uric acid or calcium oxalate monohydrate stones. RESULTS: Average Er:YAG pulse energies of 157 +/- 46 mJ (66 J/cm(2)) (N = 8) were delivered at 10 Hz through the 425-microm hybrid fibers in contact with urinary stones before fiber damage was observed. A maximum pulse energy of 233 mJ (98 J/cm(2)) was also measured through the hybrid fiber in contact with the stones. These values are significantly greater than the stone ablation thresholds of 15 to 23 mJ (6-10 J/cm(2)) and the fiber damage thresholds measured for germanium oxide, 18 +/- 1 mJ (13 J/cm(2)), and sapphire, 73 mJ (51 J/cm(2)), optical fibers during Er:YAG laser lithotripsy (P < 0.05). CONCLUSIONS: A prototype hybrid germanium/silica optical fiber demonstrated better performance than both germanium oxide and sapphire fibers for transmission of Er:YAG laser radiation during in vitro lithotripsy.     

Excimer laser irradiation of non-calcified and calcified human atheroma (248 and 308nm wavelengths)

In order to develop a system of peripheral arterial angioplasty, we carried out an in vitro study to define the quantitative, thermal and morphological characteristics of human-atheroma ablation by excimer laser. A multigas ‘Sopra’ laser was used. The study was performed by using 248nm, krypton fluoride (KrF), then 308nm, xenon chloride (XeCl) wavelengths. The delivered energy was up to 150 mJ pulse⁻¹, pulse duration was 25ns, and the repetition rate could be adjusted to up to 20Hz. Irradiated tissue segments of the superficial femoral and external iliac arteries were obtained in man during surgical procedures and were both calcified and non-calcified atherosclerotic lesions. Quantitative measurements showed a linear increase of ablated tissue mass depending on the energy delivered. For the same energy, the loss of mass was greater with the 248nm wavelength than with the 308nm. The maximum temperature rise measured at the site of irradiation was 6°C at 248nm and 25°C at 308nm. Histological analysis of the irradiated segments revealed neat and precise ablation without thermal injury of adjacent tissue. At 248nm, this phenomenon was observed for calcified as well as non-calcified atheromas. It is concluded that quantitative, thermal and morphological characteristics of in vitro ablation of calcified and non-calcified human atheroma by excimer laser are compatible to clinical requirements. The results observed at 248nm were experimentally more satisfactory.     

Characteristics of 308 nm excimer laser activated arterial tissue photoemission under ablative and non-ablative conditions

The present study was designed to assess the characteristics of tissue photoemission obtained from normal and atherosclerotic segments of human postmortem femoral arteries by 308 nm excimer laser irradiation of 60 ns pulsewidth. Three ablative (20, 30, and 40 mJ/pulse) and three non-ablative (2.5, 5, and 10 mJ/pulse) energy fluences were employed. Both the activating laser pulses and the induced photoemission were guided simultaneously over one and the same 1,000 micron core optical fiber that was positioned in direct tissue contact perpendicular to the vascular surface. The spectral lineshape of normal arterial and noncalcified atherosclerotic structures was characterized by a broad-continuum, double-peak emission of relevant intensity between wavelengths of 360 and 500 nm, with the most prominent emission in the range of 400-415 (407 nm peak) and 430-445 nm (437 nm peak). Fibrous and lipid atherosclerotic lesions, however, exhibited a significantly reduced intensity at 437 nm compared to normal artery layers (P less than 0.001), expressed as a 407/437 nm ratio of 1.321 +/- 0.075 for fibrous and 1.392 +/- 0.104 for lipid lesions. Normal artery components presented with approximately equal intensity at both emission peaks (407/437 nm ratio: intima, 1.054 +/- 0.033; media, 1.024 +/- 0.019; adventitia, 0.976 +/- 0.021). Comparison of spectral lineshape obtained under various energy fluences within a group of noncalcified tissues disclosed no substantial difference using the 407/437 nm ratio (P greater than 0.05). In contrast, calcified lesions revealed high-intensity multiple-line (397, 442, 461, and 528 nm) emission spectra under ablative energy fluences, whereas a low-intensity broad-continuum, single-peak spectrum resulted from irradiation beyond the ablation threshold. Thus, these findings suggest fluorescence phenomena for broad-continuum spectra, and plasma emission for multiple-line spectra as an underlying photodynamic process. Regardless of the activating energy fluence, spectral analysis of 308 nm activated photoemission provides accurate information about the laser target under standardized in vitro conditions. It is demonstrated that direct contact ablation and simultaneous spectral imaging of the target tissue via the same optical fiber is feasible.(ABSTRACT TRUNCATED AT 400 WORDS)     

Laser induced fragmentation of salivary stones: an in vitro comparison of two different, clinically approved laser systems

BACKGROUND: Clinical laser lithotripsy in urology promises a good fragmentation combined with a minimal risk of soft tissue damage and low medical complications. This in vitro study investigates the fragmentation of salivary stones by means of two clinically used laser systems. MATERIALS AND METHODS: The effects induced by the FREDDY laser (WOM, Germany, lambda = 532 nm/1,064 nm, E(pulse) = 120-160 mJ/pulse) and the Ho:YAG (AURIGA, StarMedTec, Germany, lambda = 2,100 nm, E(pulse) = 300-800 mJ/pulse) on clinical salivary calculi (n = 15) and on salivary gland tissue were investigated using clinical laser parameter settings. All experiments were performed in an under water experimental set-up using flexible fibres (core diameter 230 microm) positioned in front of each specimen. In order to assess fragmentation efficacy, each stone was placed on a grating (rhombic mash-diameter 1-3 mm). The fragmentation rate was calculated with respect to the energy applied (mg/J), to the number of pulses (mg/pulse), and to the time needed (mg/minute). In addition the composition of the stones were analysed spectrographically. The soft tissue interaction on human salivary duct mucosa was examined histologically (HE-staining). RESULTS: Spectrographic composition of the salivary stones showed a two component ratio of protein/carbonate apatite varying between 5/95 and 25/75. Stones treated by the Ho:YAG were vaporised in a milling-like process, while using the FREDDY laser stones are cracked into pieces and fragmentation failed in two cases. The fragmentation rates achieved by the FREDDY laser were greater than those of the Ho:YAG laser, but fragments mainly bigger. A dependency on the composition of the stones could not be found. Laser pulse effects on soft tissue were found slightly beyond the mucosa. CONCLUSION: This study clearly demonstrated the different processes of destroying salivary stones using two different laser systems. While the Ho:YAG vaporises the calculi in a more milling and soft sense, the FREDDY shows a more cracking and explosive destruction. Although both laser systems showed little direct risk to the surrounding tissue, it has to be proven whether cracked and accelerated particles could cause harm to soft tissue. With respect to this, further in vitro studies and clinical treatments in selected cases are needed to proof these results.     

Quantitative and ultrastructural studies of excimer laser ablation of the cornea at 193 and 248 nanometers

Excimer laser radiation at 193 nm and 248 nm was used to create linear etch perforations of enucleated calf corneas. The etch depth per pulse was determined for various exposures, and specimens were examined by light and transmission electron microscopy. Compared to 248 nm, excimer laser ablation at 193 nm was found to have a lower threshold for onset of ablation, less increase in etch depth per pulse at increasing fluences, and less structural alteration in adjacent cornea. For 193 nm, structural alterations were minimal, confined to an area less than 0.3 micron wide, and did not increase with increasing fluence. These studies suggest that clinical strategies for excimer laser refractive surgery will employ the 193-nm wavelength, with fluence chosen depending on surgical strategy. Ablation exposures above 600 mJ/cm2 at 193 nm may give the most repeatable etch depth.     

Extracorporeal shock-wave lithotripsy (ESWL). I. In vitro results of blast path treatment of human gallstones

To evaluate the efficacy of extracorporeal shock-wave lithotripsy (ESWL) for human gallstone fragmentation, biliary calculi of different size and composition were evaluated to determine clinical applicability of this technique. Human biliary calculi composed primarily of cholesterol (Group I, N = 6) and calcium bilirubinate (Group II, N = 6) were shocked in vitro at varying positions along the ESWL blast path. All calculi subjected to lithotripsy were fragmented. Cumulative fragment size was less than or equal to 2, 3, 5, and 8 mm in 73, 86, 94, and 100% of all stones treated, respectively. No statistically significant differences were observed following stone fragmentation when the two groups were compared. Further, no statistically significant differences were evident when comparing the energy expended during fracture of stones in the two groups, or in comparison of fracture with old or new electrodes. However, when fragmentation for stone remnants less than or equal to 2 mm in size was compared at 6- and 10-cm positions on the blast path, a statistically significant difference was noted (P less than 0.001). Stone fragmentation was greatest at positions closest to F2. These data indicate that biliary calculi can be fragmented when subjected to lithotripsy and positioned on the ESWL blast path.     

Percutaneous stone clearance of the gallbladder through an access cholecystostomy

Summary A laparoscopic — guided technique of percutaneous gallstone fragmentation/removal has been developed in the pig. The procedure entails the creation of a percutaneous access cholecystostomy. The access tract can be safely dilated after 7 days to F16, thereby allowing the introduction of both the Olympus flexible and the Berci-Shore rigid choledochoscopes. Following endoscopic occlusion of the cystic duct by a biliary balloon catheter, stone fragmentation can be conducted under direct visual control. In this particular study, electrohydraulic lithotripsy was performed of human cholesterol and bile-pigment stones inserted into the gallbladder of 16 pigs. The gallstone debris resulting from lithotripsy was then washed out with saline. Larger residual fragments could easily be extracted with the Dormia basket under visual guidance. There was a significant positive correlation between stone size (r=0.98) and weight (r=0.96) and the number of pulses needed to achieve satisfactory stone fragmentation. The gross composition of the stones (predominantly cholesterol or pigment) did not influence the number of pulses required. Electrohydraulic lithotripsy caused an explosion effect (the fragments hit the gallbladder wall), causing submucosal haematoma formation. This, however, was not followed by any untoward effect until sacrifice of the animals 10–16 weeks later. Electrohydraulic shocks delivered to the gallbladder wall itself resulted in larger haematoma formation and breach of the gallbladder mucosa with active bleeding into the gallbladder lumen, but again no instance of gallbladder perforation was encountered. The technique described is applicable to the human and has the advantage of avoiding stone migration into the common bile duct, thereby obviating complications such as cystic duct obstruction, jaundice and acute pancreatitis. However, the present studies indicate that gallstone lithotripsy is, perhaps, more safely achieved by ultrasound or laser fragmentation.     

Laser lithotripsy for the management of retained stones.

The morbidity of reoperation for retained biliary stones is not significant. Many techniques have been developed to avoid reoperation. This study analyzes T-tube tract choledochoscopy and lithotripsy using a 504-nm pulsed dye laser for treatment of retained stones. A flexible choledochoscope is passed into the biliary tract and laser energy is delivered under endoscopic visualization after passing a 320-microns laser fiber through the instrument channel. Eight patients were treated in nine sessions. The mean number of pulses was 1512.33, delivered at 3 to 5 Hz with an energy of 100 to 120 mJ. In all patients, the biliary tract was cleared. A single patient's treatment was complicated by transient bacteremia. Mean follow-up was 10 months. Choledochoscopic laser lithotripsy is a safe, effective technique that may also play a major role in laparoscopic common duct surgery.     

Techniques in endoscopic lithotripsy using pulsed dye laser

The pulsed dye laser represents a new tool in the treatment of ureteral calculi. Laser energy channeled through a delicate optical fiber is used to disimpact and fragment calculi. Standard ureteroscopic instruments including graspers, baskets and dilatation balloons can be used with the laser system. Interchangeable optical fibers ranging from 200 to 400 micrometers deliver up to 120 mJ of energy to the stone's surface. For two weeks in 1989 an endourology clinic was held in upper Egypt. Eighty patients ranging in age from nine years to sixty-seven years old were evaluated and treated endoscopically. Endoscopes ranging from 6.9F to 12.5F were used to deliver the optical fiber. All stones visualized endoscopically were fragmented. Greater than 60 percent of the stones fragmented were composed of pure calcium oxalate monohydrate. Schistosoma hematobium was endemic among our study group. Bilharzial strictures of the distal ureter were noted in 30 percent of these patients. Treatment of these strictures using both balloon dilatation and graduated Teflon dilators is reviewed. Techniques in treating different types of ureteral calculi were explored. Large calcium oxalate dihydrate stones were treated most efficiently with the 3-point fragmentation technique. The shear off-center technique was used for the calcium oxalate monohydrate calculi. Variations in total energy delivered and frequency of pulsation allowed for prompt stone disimpaction as well as prevention of retrograde fragment migration. Concurrent use of stone baskets and graspers with the pulsed dye laser was explored.