Experimental application of pulsed Ho:YAG laser-induced liquid jet as a novel rigid neuroendoscopic dissection device

BACKGROUND AND OBJECTIVES: Although water jet technology has been considered as a feasible neuroendoscopic dissection methodology because of its ability to perform selective tissue dissection without thermal damage, problems associated with continuous use of water and the ensuing fountain-effect-with catapulting of the tissue-could make water jets unsuitable for endoscopic use, in terms of safety and ease of handling. Therefore, the authors experimented with minimization of water usage during the application of a pulsed holmium:yttrium-aluminum-garnet (Ho:YAG) laser-induced liquid jet (LILJ), while assuring the dissection quality and the controllability of a conventional water jet dissection device. We have developed the LILJ generator for use as a rigid neuroendoscope, discerned its mechanical behavior, and evaluated its dissection ability using the cadaveric rabbit ventricular wall. STUDY DESIGN/MATERIALS AND METHODS: The LILJ generator is incorporated into the tip of a stainless steel tube (length: 22 cm; internal diameter: 1.0 mm; external diameter: 1.4 mm), so that the device can be inserted into a commercial, rigid neuroendoscope. Briefly, the LILJ is generated by irradiating an internally supplied water column within the stainless steel tube using the pulsed Ho:YAG laser (wave length: 2.1 microm, pulse duration time: 350 microseconds) and is then ejected through the metal nozzle (internal diameter: 100 microm). The Ho:YAG laser pulse energy is conveyed through optical quartz fiber (core diameter: 400 microm), while cold water (5 degrees C) is internally supplied at a rate of 40 ml/hour. The relationship between laser energy (range: 40-433 mJ/pulse), standoff distance (defined as the distance between the tip of the optical fiber and the nozzle end; range: 10-30 mm), and the velocity, shape, pressure, and average volume of the ejected jet were analyzed by means of high-speed camera, PVDF needle hydrophone, and digital scale. The quality of the dissection plane, the preservation of blood vessels, and the penetration depth were evaluated using five fresh cadaveric rabbit ventricular walls, under neuroendoscopic vision. RESULTS: Jet velocity (7.0-19.6 m/second) and pressure (0.07-0.28 MPa) could be controlled by varying the laser energy, which determined the penetration depth in the cadaveric rabbit ventricular wall (0.07-1.30 mm/shot). The latter could be cut into desirable shapes-without thermal effects-under clear neuroendoscopic vision. The average volume of a single ejected jet could be confined to 0.42-1.52 microl/shot, and there was no accompanying generation of shock waves. Histological specimens revealed a sharp dissection plane and demonstrated that blood vessels of diameter over 100 microm could be preserved, without thermal damage. CONCLUSIONS: The present pulsed LILJ system holds promise as a safe and reliable dissection device for deployment in a rigid neuroendoscope.     

Holmium: YAG laser-induced liquid jet knife: possible novel method for dissection

BACKGROUND AND OBJECTIVES: Making surgical incisions in vessel-rich organs without causing bleeding is difficult. Thus, it is necessary to develop new devices for this purpose, especially for surgery involving small vessels as in neurosurgery, where damage against even small cerebral vessels result in severe neurological deficits. STUDY DESIGN/MATERIALS AND METHODS: A laser-induced liquid jet was generated by irradiating pulsed Holmium Yttrium-Aluminum-Garnet (Ho: YAG) laser (beams of 350 microseconds pulse width) within a copper tube (internal diameter, 1 mm) with pure water (150 ml /hour). Ho: YAG laser beams were irradiated through an optical fiber (core diameter, 0.4 mm). The influence of the input of laser energy, structure of the nozzle, and the stand-off distance between the optical fiber tip and nozzle exit on the jet velocity was measured by a high-speed video camera to evaluate controllability of jet. The effect on artificial organs made of 10 and 30%(w/v) gelatin, each of which represent features of soft tissue and blood vessels. RESULTS: Jet velocity increased in proportion to gain in laser energy input, and maximum penetration depth into 10%(w/v) gelatin was 35 mm by single exposure at 350 mJ/pulse without impairing a vessel model. Shapes of nozzle also modified jet velocity with optimal nozzle/tube area ratio of 0.25. CONCLUSIONS: The laser-induced liquid jet has excellent potential as a new tool for removing soft tissue without damaging vital structures.     

Laser-Assisted Hair Transplantation: Histologic Comparison Between CO2 and Ho:YAG Lasers

BACKGROUND: Various laser wavelengths and devices have been advocated for use in the creation of recipient channels during hair transplant surgery, including flash-scanned CO2, Ho:YAG (lambda = 2.12 microm), and Er:YAG (lambda = 2.94 microm). OBJECTIVE: To determine the tissue injury caused by flash-scanned CO2 and pulsed Ho:YAG lasers during the creation of hair transplant recipient channels and to assess the efficacy of the Ho:YAG laser. METHODS: Recipient channels were created in vivo in human scalp tissue using both lasers, and were excised and prepared for histologic examination. Optical micrometry of tissue sections was used to assess thermal injury. RESULTS: The Ho:YAG laser created jagged, irregular-shaped channels with larger zones of thermal injury (superficial deepithelialization, thermal necrosis, and thermal damage). In contrast, the CO2 laser produced well-defined cylindrically shaped channels free of cellular debris with minimal epithelial disruption and significantly less lateral thermal injury. CONCLUSION: Given that the Ho:YAG produced larger regions of thermal injury and recipient channels that were unacceptable for graft, the CO2 laser remains the better choice for the creation of recipient channels during hair transplant surgery. However, ongoing research will be necessary to determine the optimal laser wavelength and/or devices for this procedure.     

Acute response of the arterial wall to pulsed laser irradiation

This study was designed to examine the acute response of normal arterial wall to pulsed laser irradiation. Irradiation with an Excimer or a Holmium YAG laser was performed in 15 normal iliac sites of 8 male New Zealand white rabbits. The excimer laser was operated at 308 nm, 25 Hz, 50 mj/mm²/pulse, and 135 nsec/pulse and the Ho:YAG laser was operated at 2.1 μm, 3.5 Hz, 400 mj/ pulse, 250 μsec/pulse. The excimer and Ho:YAG laser were coupled into a multifiber wire-guided catheter of 1.4 and 1.5 mm diameter, respectively. The mean luminal diameter increased similarly from 2.01 ± 0.29 to 2.46 ± 0.27 mm (P < 0.0005) and from 2.09 ± 0.53 to 2.45 ± 0.30 mm (P < 0.005) after excimer and Ho:YAG laser irradiation, respectively. Perforation occurred in 3 of 15 Ho:YAG irradiated sites and 0 of 15 excimer laser irradiated sites. The sites irradiated with excimer or Ho:YAG laser had similar histologic features, consisting of shedding of the endothelium, disorganization of internal elastic lamina, localized necrosis of vascular smooth muscle cells, and fissures in the medial layer. However, the sites irradiated with excimer laser had lower grading scores than those irradiated with the Ho:YAG laser (P<0.05). Irradiation with excimer or Ho:YAG laser of normal arteries results in: (1) vasodilation of the irradiated artery; (2) localized mechanical vascular injury, and (3) Ho:YAG laser induces more severe damage to the arterial wall than excimer. © 1993 Wiley-Liss, Inc.     

Pulsed liquid jet dissector using holmium:YAG laser--a novel neurosurgical device for brain incision without impairing vessels

BACKGROUND: Neurosurgery has long required a method for dissecting brain tissue without damaging principal vessels and adjacent tissue, so as to prevent neurological complications after operation. In this study we constructed a prototype of such a device and used it in an attempt to resect beagle brain cortex. METHOD: The prototype device consisted of an optical fibre, a Y adaptor, and a nozzle whose internal exit diameter was 100 microm. Cold physiological saline (4 degrees C) was supplied to it at a rate of 40 ml/h. Pulsed liquid jets were ejected from the nozzle by a pulsed Holmium:YAG) (Ho:YAG) laser at an irradiation energy of 300 mJ/pulse. The profile of the liquid jet was observed with a high-speed camera while changing the distance between the optical fibre end and nozzle exit (equivalent to the standoff distance). With this device (3 Hz operation), brain dissection of anaesthetized beagles was attempted while measuring the local temperature of the target. A histological study of the incised parts was also performed. FINDINGS: When the standoff distance was 24 mm, the liquid jet was emitted straight from the nozzle at a maximum initial velocity of 50 m/s. The brain parenchyma was cut with this device while preserving vessels larger than 200 microm in diameter and keeping the operative field clear. The local temperature rose to no more than 41 degrees C, below the functional heat damage threshold of brain tissue. Histological findings showed no signs of thermal tissue damage around the dissected margin. INTERPRETATION: The Ho:YAG laser-induced liquid jet dissector can be applied to neurosurgery after incorporating some minor improvements.     

Potential applications of the erbium:YAG laser in endourology.

The holmium:YAG laser has become the laser of choice in endourology because of its multiple applications in the fragmentation of kidney stones, incision of strictures, and coagulation of tumors. This paper describes the potential use of a new laser, the erbium:YAG laser, for applications in endourology. Recent studies suggest that the Er:YAG laser may be superior to the Ho:YAG laser for precise ablation of strictures with minimal peripheral thermal damage and for more efficient laser lithotripsy. The Er:YAG laser cuts urethral and ureteral tissues more precisely than does the Ho:YAG laser, leaving a residual peripheral thermal damage zone of 30 +/- 10 microm compared with 290 +/- 30 microm for the Ho:YAG laser. This result may be important in the treatment of strictures, where residual thermal damage may induce scarring and result in stricture recurrence. The Er:YAG laser may represent an alternative to the cold knife and Ho:YAG laser in applications where minimal mechanical and thermal insult to tissue is required.     

Injury and adhesion formation following ovarian wedge resection with different thermal surgical modalities

The purpose of this study is to determine the role of bleeding, acute thermal damage, and charring in adhesion formation. Postoperative adhesions were compared following ovarian wedge resection in 48 rabbits using different lasers, electrosurgery, and scalpel. Twelve ovaries were sectioned per modality, in randomized pairs. Acute thermal injury as assessed by histology, bleeding, and charring differed amonge the modalities used. Adhesions were assessed 4 weeks later, by an investigator completely blinded of the treatment protocol. The adhesion scores were 11.6 ± 8.0 with pulsed Er:YAG laser; 11.9 ± 7.5 with scalpel; 8.3 ± 9.3 with electrocautery; 6.7 ± 8.8 with a continuous (c.w.) Nd:YAG laser; 5.3 ± 4.8 with c.w. CO₂ laser; 3.1 ± 2.7 with pulsed CO₂ laser; 1.7 ± 1.8 with pulsed Ho:YAG laser; and 0.8 ± 1.5 in the control (no resection) group. Ho:YAG, Nd:YAG, and electrocautery were completely hemostatic. Bleeding was minimal with the CO₂ lasers. Er:YAG and scalpel caused maximum bleeding, requiring hemostatic measures to prevent exanguination. Charring occurred with electrocautery, CO₂ laser, and Nd:YAG laser. Bleeding and charring correlated with adhesion formation, but the histological depth of thermal damage did not. The Ho:YAG laser is a hemostatic, fiber-optic compatible laser causing significantly fewer adhesions (P<0.04) than scalpel, electrocautery, Nd:YAG, Er:YAG, and c.w. CO₂ lasers. Clinical use of the Ho:YAG laser, and the role of carbonization in promoting adhesions, deserve further study. © 1993 Wiley-Liss, Inc.     

Preliminary observations of holmium:YAG laser tissue interaction using human uterus.

Preliminary observations of a pulsed Ho:YAG laser on human uterine tissue in-vitro are presented. The tissue effect on the uterine myometrium was demonstrated using fresh uteri which had been subjected to laser energy. The laser crater and surrounding zone of thermal necrosis (ZTN) was quantified. Measurements demonstrated a consistent narrow ZTN (0.8-1.8 mm) irrespective of power or pulse frequency used. The percentage forward transmission of laser energy through 1 mm of myometrium was investigated using a pyroelectric detector and found to be 0.41%. Finally, a visible and measureable photoacoustic component to the Ho:YAG laser was demonstrated using a water bath and needle hydrophone.     

Pulsed laser-induced liquid jet microcatheter system for rapid and reliable fibrinolysis in acute cerebral embolisms: experiments on safety and preliminary application in porcine cranial vessels.

OBJECTIVE: The authors have incorporated a holmium: YAG laser-induced liquid jet (LILJ) within a microcatheter for rapid, safe, and reliable fibrinolysis, and reported its effectiveness in vitro. The purpose of this study is to evaluate an appropriate operation mode to minimize debris size and to apply the system in in vivo experiments using a porcine cranial artery model. MATERIALS: Evaluation of debris size: The relationships between laser energy and the size of the debris have been evaluated in in vitro experiments. Pulsed LILJ (3 Hz for 60 seconds) were applied to the artificial thrombi (made out of human blood taken from healthy volunteers) in a teflon tube (internal diameter: 4 mm) in the following operation modes: firstly, the laser energy was set at 0.6, 0.8, 1.0, 1.2, 1.4 W, and urokinase (UK) solution (12000 IU/mL) was supplied at rate of 40 mL/hour. In the 0.8 W operation, the concentrations of UK were changed between 0, 1200, 6000, and 12000 lU/mL. Immediately after application of LILJ, the remnant debris were collected and fixed with formaldehyde, and the size and numbers of debris were evaluated under a light microscope. Application in a porcine cranial artery model: The acute embolic models were made using four pigs: the artificial thrombi were made of porcine blood and 1 mL of embolus was used to occlude the left lingual artery via a catheter. After occlusion of lingual artery for 30 minutes, the LILJ microcatheter system was brought to the occlusion site via a guiding catheter and with the assistance of guide-wire. After every 2.5 minutes application of LILJ, angiographies were performed to evaluate the recanalization of the occluded vessels. Cold UK (1200 IU/mL) solution (4 degrees C) was supplied at the rate of 40 mL/hour with laser operation (2 pigs) and without laser operation (2 pigs: control). The pigs were decapitated, and vessels at the laser irradiation sites were obtained to evaluate the damage to the vessel wall. RESULTS: Evaluation of debris size: After application of UK solution by the LILJ (12000 lU/mL), 48.7 (1.0 W) to 72.0% (0.8 W) of debris were under 200 microm in size, while 3.7 (0.8 W) to 17.0% (1.2 W) of them exceeded 600 microm, and the 0.8 W operation mode had a tendency to be the better operation mode. During the 0.8 W operation mode, 58 (without UK) to 72% (12000 lU/mi) of debris were under 200 microm in size, while 3.5 (12000 lU/mL) to 8.5% (without UK) of them exceeded 600 microm. Application in a porcine cranial artery model: Recanalization of the occluded vessels was obtained at 15 and 20 minutes in the treatment group. Histological specimens showed neither apparent mechanical nor thermal damage. CONCLUSION: Although an additional system to collect debris, which cannot be dealt with in the pharmacological effect of fibrinolytics in the short-term, should be developed, the present results show the possibility of the LILJ microcatheter system to become a useful assistant device for the mechanical fragmentation of embolus and the enhancement of fibrinolytics.     

Use of the holmium:YAG laser in urology.

The tissue effects of a holmium:YAG (Ho:YAG) laser operating at a wavelength of 2.1 mu with a maximum power of 15 watts (W) and 10 different energy-pulse settings was systematically evaluated on kidney, bladder, prostate, ureteral, and vasal tissue in the dog. In addition, various urologic surgical procedures (partial nephrectomy, transurethral laser incision of the prostate, and laser-assisted vasovasostomy) were performed in the dog, and a laparoscopic pelvic lymph node dissection was carried out in a pig. Although the Ho:YAG laser has a strong affinity for water, precise tissue ablation was achieved in both the contact and non-contact mode when used endoscopically in a fluid medium to ablate prostatic and vesical tissue. Using the usual parameters for tissue destruction (blanching without charring), the depth of thermal injury in the bladder and ureter was kept superficial. In performing partial nephrectomies, a 2-fold reduction in the zone of coagulative necrosis was demonstrated compared to the use of the continuous wave Neodymium:YAG laser (Nd:YAG). When used through the laparoscope, the Ho:YAG laser provided precise cutting and, combined with electrocautery, allowed the dissection to proceed quickly and smoothly. Hemostatic control was adequate in all surgical procedures. Although the results of these investigations are preliminary, our initial experience with the Ho:YAG laser has been favorable and warrants further investigations.     

Acute and chronic effects of transmyocardial laser revascularization in the nonischemic pig myocardium by using three laser systems

BACKGROUND AND OBJECTIVE: Transmyocardial laser revascularization (TMLR) improves symptoms in patients with coronary heart disease. It is based on the hypothesis of direct perfusion of ischemic myocardium by means of laser-created channels. Three different lasers were used to study alternative effects on myocardium. STUDY DESIGN/MATERIALS AND METHODS: The present study was conducted to evaluate comprehensively and compare the short and long-term tissue effects and the basic interaction mechanisms of CO2, Ho:YAG, and Er:YAG laser radiation with myocardium. The dynamics of laser-induced impacts in gel used as tissue phantom was visualized by time-resolved flash photography. Pressure measurements performed during perforation of myocardium in vitro revealed the explosive character of the ablation process. Channels made into the left ventricle of normal pig hearts were examined immediately and 6 weeks after creation. RESULTS: Regardless of laser source, all channels became occluded within 6 weeks by scar. Minimal acute thermal damage by Er:YAG laser corresponded to smaller scars. Pulsed Ho:YAG caused stronger tissue tearing than continuous wave CO2 irradiation. An increased volume density of intramyocardial vessels was found about the scars 6 weeks after treatment with all lasers. CONCLUSION: The laser sources permitted to study outcome of pressure effects and thermal damage in vivo. There were only minor differences between the three laser systems used. Rapid channel occlusion suggests that rather than revascularization, subsidiary physiologic tissue effects elicited by the thermal, oxidative, or mechanical action of the laser impact may contribute to the beneficial clinical effects of TMLR.     

Intraoperative arrhythmias and tissue damage during transmyocardial laser revascularization

BACKGROUND: Transmyocardial laser revascularization creates transmural channels to improve myocardial perfusion. Different laser sources and ablation modalities have been proposed for transmyocardial laser revascularization. We investigated the incidence of cardiac arrhythmias and laser-tissue interactions during transmyocardial laser revascularization of normal porcine myocardium with three different lasers. METHODS: We used a continuous-wave, chopped CO2 laser (20 J/pulse, 15 ms/pulse) synchronized with the R wave; a holmium:yttrium aluminum garnet (Ho:YAG) laser (2 J/pulse, 250 micros/pulse, 5 Hz); and a xenon-chloride (excimer, Xe:Cl) laser (35 mJ/pulse, 20 ns/pulse, 30 Hz). Each laser was used 30 times as the sole modality in four consecutive pigs, yielding 120 channels. RESULTS: The average number of pulses needed to create a channel was 1, 11 +/- 4, and 37 +/- 8 for the CO2, Ho:YAG, and Xe:Cl lasers, respectively. All Ho:YAG and Xe:Cl channels had premature ventricular contractions. Ventricular tachycardia occurred in 70% of the Xe:Cl and 60% of the Ho:YAG channels. Only 36% of the CO2 channels had premature ventricular contractions, and only 3% of the CO2 channels had ventricular tachycardia (p < 0.001 versus Ho:YAG and Xe:Cl). Ho:YAG channels were highly irregular: each had a 0.6-mm-wide central zone surrounded by a ring of coagulation necrosis (diameter, 1.84 +/- 0.67 mm) with effaced cellular architecture in a thin hemorrhagic zone. The Xe:Cl sections exhibited the same patterns on a smaller scale (diameter, 0.74 +/- 0.18 mm). The CO2 channels were straight and well demarcated. The zone of structural and thermal damage extended over half the channel's diameter, measuring 0.52 +/- 0.25 mm. CONCLUSIONS: During transmyocardial laser revascularization, the CO2 laser synchronized with the R wave is significantly less arrhythmogenic than the Ho:YAG and Xe:Cl lasers not synchronized with the R wave. In addition, the interaction of the CO2 laser with porcine cardiac tissue is significantly less traumatic than that of the Ho:YAG and the Xe:Cl lasers.     

Laser Skin Resurfacing of the Face with a Combined CO2/Er:YAG Laser

BACKGROUND: A combined, dual-wavelength CO2/Er:YAG laser system having the ability to deliver both clean ablation of skin with the erbium wavelength and a simultaneous deeper penetrating subablative thermal pulse of CO2 was developed for full-face resurfacing. The CO2 component can be pulsed from 1 to 100 msec at a power of 1-10 W with the Er:YAG component pulsed at 350 microsec at 1.7 J/cm2 through either a computer pattern generator with 3 mm diameter spot size or through a noncollimated spot ranging from 0.2 to 8 mm in diameter. Our previous study using this laser on the neck using a 4-8 mm diameter spot with Er:YAG fluence at 1.7 J and the CO2 at 5 W with a 50 msec pulse at a frequency of 10 Hz showed a higher degree of overall patient satisfaction, as well as improvement in skin texture and skin color, compared to patients treated with an Er:YAG laser alone. OBJECTIVE: This study evaluated the CO2/Er:YAG laser treatment modality in facial resurfacing. METHODS: Ten patients were treated with four passes at 1.7 J with a 4 mm diameter spot and the CO2 at 5 W with a 50-msec pulse at a frequency of 10 Hz. Photoaging scores as well as thermal damage and new collagen formation were compared immediately before and after treatment as well as at 2 weeks and 3 months postoperatively. RESULTS: The average pretreatment periorbital score was 6.2 The average posttreatment periorbital scores were 4.2 (P =.0239) at 2 weeks postoperatively (32% improvement) and 3.8 (P =.0028) at 3 months postoperatively (38% improvement). The average pretreatment perioral score was 5.9. The average posttreatment perioral scores were 3.0 (P =.0001) at 2 weeks postoperatively (49% improvement) and 3.3 (P =.0009) at 3 months postoperatively (44% improvement). The average pretreatment cheek score was 4.7. The average posttreatment cheek scores were 2.7 (P =.0066) at 2 weeks postoperatively (43% improvement) and 3.8 (P =. 0152) at 3 months postoperatively (36% improvement). The average pretreatment forehead score was 4.7. The average posttreatment forehead scores were 3.8 (P =.0340) at 2 weeks postoperatively (33% improvement) and 3.6 (P =.0147) at 3 months postoperatively (37% improvement). The average depth of collagen measured in the dermis pretreatment was 29 microm. The average depth of collagen 3 months posttreatment was 54 microm. This is an average increase of 25 microm or an 86% increase in collagen (P =.006). The average thermal damage immediately after treatment was 20 microm. CONCLUSION: The CO2/Er:YAG laser utilized with four passes at the above-mentioned parameters results in a similar degree of improvement as other forms of laser resurfacing with high-energy, short-pulsed CO2 lasers.     

Intravasular ultrasound can be used to evaluate pulsed laser ablation of arterial tissue

Background and Objective: Intravascular ultrasound (IVUS) has been used successfully to detect intravascular lesions. This study evaluates the ability of IVUS to detect acoustic damage to the arterial wall following high power, pulsed laser ablation. Study Design/Materials and Methods: Arterial ablation and disruption were performed in necropsy bovine aorta with a Ho:YAG laser using energy ranging from 140–720 mJ/pulse at 5 Hz. Laser energy was delivered with 2 mm diameter, multifiber over-the-wire catheters. A 20-MHz IVUS catheter was used to image the arterial damage prior to tissue fixation and morphometry. Results: IVUS images revealed ablation craters surrounded by high acoustically backscattering zones. By histology, the arteries revealed ablation craters lined with thermal coagulation surrounded by a region of dissection and vacuolization. The depth and width of the highly backscattering zones on IVUS images correlated strongly with the corresponding morphometric measurements of tissue dissection (r = 0.92, P = 0.0001 and r = 0.80, P = 0.0001, respectively). Morphometric measurements of the ablation crater depth correlated strongly with laser energy (r = 0.90, P= 0.0001), whereas crater width was not correlated with laser energy (r = 0.27, P = 0.09). Conclusion: This study demonstrates that IVUS can detect and measure the extent of arterial damage following pulsed laser ablation. This may provide a means of detecting the extent of tissue disruption and help develop approaches to reduce or prevent extensive tissue damage. © 1995 Wiley-Liss, Inc.     

A novel method of drug delivery for fibrinolysis with Ho:YAG laser-induced liquid jet

. Two of the problems inherent in the treatment of cerebral emboli are the narrow therapeutic time window and the severe side effects of fibrinolytic drugs. Thus, it is necessary to develop a new method of removing a cerebral thrombus more rapidly and with smaller quantities of fibrinolytics. The behaviour of a bubble formed by holmium (Ho):YAG laser irradiation in a capillary tube filled with pure water was observed at various stand-off distances (L; distance between the end of optical fibre and the capillary exit). Subsequently, a liquid-jet generator was created by insertion of an optical fibre (core diameter: 0.6 mm) into a catheter (6 Fr) filled with pure water, and a pulsed Ho:YAG laser (pulse duration time=350 μs, laser energy=230 mJ/pulse) was used to irradiate the optical fibre. The maximum penetration depth, into a gelatin artificial thrombus, of a liquid jet generated with this device was measured for various stand-off distances. Additionally, the phenomenon and the pressure around the catheter exit were captured via shadowgraph and PVDF needle hydrophone, respectively. The laser-induced bubble in the capillary tube grew rapidly in the direction of propagation and generated a liquid jet. The maximum penetration depth of this liquid jet into an artificial thrombus increased in proportion to L and reached a maximum value (9 mm) when L was around 13 mm. A shock wave whose overpressure at a point 4 mm away from the catheter exit exceeded 12 MPa was captured by shadowgraph. It was concluded that Ho:YAG laser irradiation within a water-filled catheter caused liquid jet formation, which could penetrate straight into an artificial thrombus. Hence, this jet is expected to promote fibrinolysis by means of injecting fibrinolytics deeply into the thrombus. After resolving some problems, this system will be applied to an endovascular therapy for cerebral embolisms in the near future. Paper received 6 August 2001; accepted after revision 14 December 2001.     

Dependence of calculus retropulsion on pulse duration during Ho: YAG laser lithotripsy

BACKGROUND AND OBJECTIVES: The purpose of this study was to investigate the effect of optical pulse duration on stone retropulsion during Ho:YAG (lambda = 2.12 microm) laser lithotripsy. STUDY DESIGN/MATERIALS AND METHODS: A clinical Ho:YAG laser with pulse durations was employed to fragment calculus phantoms and to evaluate stone phantom retropulsion. At a given pulse energy, optical pulse durations were divided into two discrete conditions: short pulse (tau(p): 120 to approximately 190 microseconds at FWHM) and long pulse (tau(p): 210 to approximately 350 microseconds at FWHM). Plaster of Paris calculus phantoms were ablated at different energy levels using optical fibers of varying diameters (273, 365, and 550 microm in core size). The dynamics of the recoil action of a calculus phantom was monitored using a high-speed camera; the laser-induced craters were evaluated with optical coherent tomography (OCT). Bubble formation and collapse were recorded with a fast flash photography setup, and acoustic transients were measured with a hydrophone. RESULTS: Shorter pulse durations produced more stone retropulsion than longer pulses at any given pulse energy. Regardless of pulse duration, higher pulse energy and larger fibers resulted in larger ablation volume and retropulsion (P<0.05). For shorter pulse durations, more rapid bubble expansion was observed and higher amplitudes of the collapse pressure wave were measured (P<0.05). CONCLUSION: Less retropulsion and equivalent fragmentation occurred when Ho:YAG pulse duration increased.     

Myocardial scarring after transmyocardial laser revascularization: A potential mechanism of clinical improvement?

BACKGROUND AND OBJECTIVE: The morphological evolution of transmyocardial laser channels was analyzed in a pig model. MATERIALS AND METHODS: Five channels were created in the lateral wall of the left ventricle of 12 animals, using a Ho:YAG laser. In half of the animals, an additional infarction was induced in the same area. Animals were sacrificed at one-week intervals until week 5 and the critical regions of the left ventricular wall were subjected to microscopic computed morphometrical analysis. RESULTS: There was no clearly patent lumen at any stage. Cross-sectional area of the channels fell from 8.5 +/- 1.2 mm(2) at day 0 to 2.1 +/- 0.1 mm(2) at day 35. From day 7 onward, the channel area was gradually replaced by granulation tissue and the proportion of the channel occupied by granulation scar tissue increased from 37 +/- 2% at day 7 to 100% at day 28. In the subgroup with concomitant infarction, granulation tissue of both channel and infarction became indistinguishable from day 14 onward. CONCLUSIONS: These results suggest strongly that channel patency is not the mechanism of angina relief after transmyocardial laser revascularization with Ho:YAG laser.     

Erbium: YAG versus holmium:YAG lithotripsy

PURPOSE: We test the hypothesis that erbium:YAG (Er:YAG) lithotripsy is more efficient than holmium:YAG (Ho:YAG) lithotripsy. MATERIALS AND METHODS: Human calculi composed of greater than 97% calcium oxalate monohydrate and cystine were studied. Calculi were irradiated in water using Er:YAG or Ho:YAG lasers. Er:YAG lithotripsy was done with a 425 microm sapphire optical fiber at a pulse energy of 50 mJ at 10 Hz. Ho:YAG lithotripsy was performed with a 365 microm low hydroxy optical fiber at a pulse energy of 500 mJ at 10 Hz or a 425 microm sapphire optical fiber at a pulse energy of 50 mJ at 10 Hz. Fragmentation was defined as the initial stone mass minus the final dominant fragment mass and normalized for incident laser fluence (energy per unit area of fiber tip). RESULTS: Mean fragmentation plus or minus standard deviation for calcium oxalate monohydrate was 38 +/- 27 mg for Er:YAG and 22 +/- 6 for Ho:YAG (low hydroxy silica fiber) versus 5 +/- 1 for Ho:YAG (sapphire fiber, p = 0.001). When fragmentation was normalized for incident laser fluence given different optical fiber sizes, mean fragmentation efficiency was 53.6 +/- 38.7 g-microm2/J for Er:YAG lithotripsy compared with 22.6 +/- 6.4 for Ho:YAG (low hydroxy silica fiber) lithotripsy (p = 0.04). Mean cystine fragmentation was 15 +/- 3 mg for Er:YAG versus 9 +/- 1 for Ho:YAG (sapphire fiber, p = 0.0005). CONCLUSIONS: Er:YAG lithotripsy is more efficient than Ho:YAG lithotripsy.     

In vitro tissue effects of a combined Ho:YAG/Nd:YAG laser: sprinkling of tissue fragments by Ho:YAG laser light may be problematic for oncological interventions

BACKGROUND AND OBJECTIVE: Surgery of soft tissue, for example, of the tongue or the liver, requires a cutting and coagulating device. Therefore, a combined Ho:YAG/Nd:YAG laser providing the laser beam of both systems together in one bare fiber seems to be useful. STUDY DESIGN/MATERIALS AND METHODS: We studied the effect of such a laser system in vitro on tongues of pigs. RESULTS: Combined application of both lasers results in vitro in a thicker coagulation zone in soft tissue (tongue). Tissue fragments possibly containing vital cells are sprinkled by the pulsed energy of the Ho:YAG laser up to a distance of 20 cm. CONCLUSION: Using the pulsed Ho:YAG laser for oncologic interventions seems to be problematic. Combined laser effect in vivo may result in better hemostasis.     

Transcanalicular THC:YAG dacryocystorhinostomy.

Chromium-sensitized and thulium- and holmium-doped YAG lasers (THC:YAG laser) were used to create a nasal bony ostium in the area of the lacrimal sac fossa in four fresh frozen bisected human cadaver heads. The lasers-long pulsed (300 milliseconds), compact, self-contained, and solid state--operate in the near infrared (2.1 microns). The opening was created by passing the 320-micrometer laser fiber across the canalicular system. Pulse energies of 250 to 900 mJ were used with a repetition rate of 5 to 15 pulses per second. Energy levels ranging from 1.25 to 9 W produced a full-thickness bony ostium approximately 3 to 4 mm in diameter. Silicone tubing was then threaded through the superior and inferior canaliculus system in the standard fashion. This technique may simplify conventional dacryocystorhinostomy as well as endonasal laser dacryocystorhinostomy procedures.