Treatment of Gunpowder Traumatic Tattoo by Q-Switched Nd:YAG Laser: An Unusual Adverse Effect

BACKGROUND: The Q-switched Nd:YAG laser can completely eliminate traumatic tattoos. OBJECTIVE: We report the results of the unsuccessful removal of traumatic tattoos among three patients with dermal inclusions of gunpowder who were shot at close range. METHODS: Treatment was tried in each patient with a Q-switched Nd:YAG laser at a medium fluence (4-6 J/cm2). RESULTS: During treatment of our patients, each pulse provoked sparks and the immediate formation of bleeding trans- epidermal pits. After the healing process was completed, we observed poxlike scars and the spreading of pigments in the skin around the initial points of the tattoo. CONCLUSION: We hypothesize that the rapid transfer of high-energy pulses to powder particles creates microexplosions of these fragments resulting in cavitation and provoking transepidermal holes and subsequent scars. This adverse effect was only produced if the tattoo resulted from gun powder being shot at a short distance from the skin.     

Femtosecond laser-assisted selective reduction of neovascularization in rat cornea

Nonlinear multiphoton absorption induced by focusing near infrared (NIR) femtosecond (fs) laser pulses into a transparent cornea allows surgery on neovascular structures with minimal collateral damage. In this report, we introduce an fs laser-based microsurgery for selective treatment of rat corneal neovascularizations (in vivo). Contiguous tissue effects are achieved by scanning a focused laser pulse below the corneal surface with a fluence range of 2.2–8.6 J/cm². The minimal visible laser lesion (MVL) threshold determined over the corneal neovascular structures was found to be 4.3 J/cm². Histological and optical coherence tomography examinations of the anterior segment after laser irradiations show localized degeneration of neovascular structures without any unexpected change in adjacent tissues. Furthermore, an approximately 30 % reduction in corneal neovascularizations was observed after 5 days of fs laser exposure. The femtosecond laser is thus a promising tool for minimally invasive intrastromal surgery with the aid of a significantly smaller and more deterministic photodisruptive energy threshold for the interaction between the fs laser pulse and corneal neovascular structures.     

Amplification of pressure waves in laser-assisted endodontics with synchronized delivery of Er:YAG laser pulses

When attempting to clean surfaces of dental root canals with laser-induced cavitation bubbles, the resulting cavitation oscillations are significantly prolonged due to friction on the cavity walls and other factors. Consequently, the collapses are less intense and the shock waves that are usually emitted following a bubble’s collapse are diminished or not present at all. A new technique of synchronized laser-pulse delivery intended to enhance the emission of shock waves from collapsed bubbles in fluid-filled endodontic canals is reported. A laser beam deflection probe, a high-speed camera, and shadow photography were used to characterize the induced photoacoustic phenomena during synchronized delivery of Er:YAG laser pulses in a confined volume of water. A shock wave enhancing technique was employed which consists of delivering a second laser pulse at a delay with regard to the first cavitation bubble-forming laser pulse. Influence of the delay between the first and second laser pulses on the generation of pressure and shock waves during the first bubble’s collapse was measured for different laser pulse energies and cavity volumes. Results show that the optimal delay between the two laser pulses is strongly correlated with the cavitation bubble’s oscillation period. Under optimal synchronization conditions, the growth of the second cavitation bubble was observed to accelerate the collapse of the first cavitation bubble, leading to a violent collapse, during which shock waves are emitted. Additionally, shock waves created by the accelerated collapse of the primary cavitation bubble and as well of the accompanying smaller secondary bubbles near the cavity walls were observed. The reported phenomena may have applications in improved laser cleaning of surfaces during laser-assisted dental root canal treatments.     

In vivo study of intradermal focusing for tattoo removal

. Delivery of intradermally focused nanosecond laser pulses with small energy as an alternate technique applicable to clinical procedures in dermatological and plastic surgery is an area of relatively new interest with multiple potential applications. We assessed this approach on common tattoo pigments in dermis in an in vivo study using a wavelength of 1064 nm. Paired micropigs were tattooed with standard blue, black, green and red pigments. The tattoos were allowed to mature and then treated by 12 ns pulses in a focused beam of 11.4° cone angle. Visual observation and histological analysis of biopsies were performed to evaluate results. Significant reduction in pulse energy and collateral damage was achieved with pulse energy ranging between 38 to 63 mJ. Blue and black tattoos were found to respond well from a clinical standpoint. The depth dependence of tissue response and pigment redistributions at 1 hour, 1 week and 1 month after laser treatment was quantitatively analysed through biopsies and a strong relationship was demonstrated between tattoo response and laser-induced dermal vacuolation. The optical absorption coefficients of the four tattoo pigments were measured to be approximately the same and the laser-induced plasma is suggested to be responsible for the pigment redistribution. As we hypothesised, intradermal focusing of nanosecond pulses significantly reduced required pulse energy for tattoo ablation to about 60 mJ or less. These results stimulate a number of additional questions relevant not only to clinical applications but also to the understanding of the fundamental process of laser–pigment interaction in the dermis as it relates to tattoo removal. Paper received 1 November 2001; accepted after revision 14 December 2001     

Why stones break better at slow shockwave rates than at fast rates: in vitro study with a research electrohydraulic lithotripter

BACKGROUND AND PURPOSE: Stones break better when the rate of shockwave (SW) delivery is slowed. It has been hypothesized that the greater cavitation accompanying a fast rate shields pulse propagation, thus interfering with the delivery of SW energy to the stone. We tested this idea by correlating waveforms measured at the SW focus with cavitation viewed using high-speed imaging. MATERIALS AND METHODS: A series of U30 gypsum stones held in a 2-mm mesh basket were exposed to 200 SWs at 30 or 120 SW/min from a research electrohydraulic lithotripter (HM3 clone). Waveforms were collected using a fiberoptic probe hydrophone. High-speed imaging was used to observe cavitation bubbles in the water and at the stone surface. Results: Stone breakage was significantly better at 30 SW/min than at 120 SW/min. The rate had little effect on SW parameters in the water free field. In the presence of particulates released from stones, the positive pressure of the SW remained unaffected, but the trailing tensile phase of the pulse was significantly reduced at 120 SW/min. CONCLUSIONS: Cavitation bubbles do not persist between SWs. Thus, mature bubbles from one pulse do not interfere with the next pulse, even at 120 SW/min. However, cavitation nuclei carried by fine particles released from stones can persist between pulses. These nuclei have little effect on the compressive wave but seed cavitation under the influence of the tensile wave. Bubble growth draws energy from the negative-pressure phase of the SW, reducing its amplitude. This likely affects the dynamics of cavitation bubble clusters at the stone surface, reducing the effectiveness of bubble action in stone comminution.     

Ultrafast imaging of tissue ablation by a XeCl excimer laser in saline.

To determine the temporal evolution of laser induced tissue ablation, arterial wall specimens with either hard calcified or fatty plaques and normal tissue were irradiated in a 0.9% saline solution using a XeCl excimer laser (wavelength 308 nm, energy fluence 7 J/cm2, pulse width 30 ns) through a 600 microns fused silica fiber pointing perpendicular either at a 0.5 mm distance or in direct contact to the vascular surface. Radiation of a pulsed dye laser (wavelength 580 nm) was used to illuminate the tissue surface. The ablation process and the arising bubble above the tissue surface were recorded with a CCD camera attached to a computer based image-processing system. Spherical cavitation bubbles and small tissue particles emerging from the irradiated area have been recorded. The volume of this bubble increased faster for calcified plaques than for normal tissue.     

The effect of frequency doubled double pulse Nd:YAG laser fiber proximity to the target stone on transient cavitation and acoustic emission

PURPOSE: Scant information has been published describing the effect of laser fiber distance from the stone target on the mechanism of calculus fragmentation. Using high speed photography and acoustic emission measurements we characterized the impact of laser fiber proximity on stone comminution. We evaluated the effect of laser fiber distance from the stone target on resultant cavitation bubble formation and shock wave generation. MATERIALS AND METHODS: Stone fragmentation was assessed using a FREDDY (frequency doubled double pulse Nd:YAG) (World of Medicine, Orlando, Florida) laser and a holmium laser. The FREDDY laser was operated using a 420 microm fiber at an output energy of 120 and 160 mJ in single and double pulse settings, and a pulse repetition rate of 1 Hz. The holmium laser was operated using a 200 microm fiber at an output energy of 1 to 3 J and a pulse repetition rate of 1 Hz. The surface of a 1 cm square BegoStone (Bego, Bremen, Germany) attached to an X-Y-Z translational stage was aligned perpendicular to the laser fiber, which was immersed in a Lucite tank filled with water at room temperature. An Imacon 200 high speed camera was used to capture transient cavitation bubbles at a framing rate of up to 1,000,000 frames per second. Acoustic emission signals associated with shock waves generated during the rapid expansion and collapse of the cavitation bubble were measured using a 1 MHz focused ultrasound transducer. RESULTS: At laser fiber distances of 3.0 mm or less cavitation bubbles and shock waves were observed with the FREDDY laser. In contrast to the holmium laser, the bubble size and shock wave intensity of the FREDDY laser was inversely related to the fiber-to-stone distance over the range tested (0.5 to 3.0 mm). CONCLUSIONS: While bubble size was noted to increase with a larger stone-to-fiber distance using the holmium laser, to consistently generate cavitation bubbles and shock waves using the FREDDY laser the laser fiber should be operated within 3.0 mm of the target stone. These findings have significant implications during clinical laser stone fragmentation.     

Dynamics of shock waves and cavitation bubbles generated by picosecond laser pulses in corneal tissue and water

Time-resolved flash photography was used to investigate the dynamics of shock waves and cavitation bubbles generated by picosecond optical breakdown in bovine corneal tissue and water. A picosecond Nd:YLF laser was employed. A rapid decay of the shock waves was observed in both materials, with similar temporal characteristics, indicating that water serves as a good model for shock wave studies. In contrast, differences in the cavitation bubble dynamics were found between cornea and water, which are related to differences in the mechanical and thermal properties of the two media, suggesting that water should not be used to model cavitation dynamics in cornea. The experimental results also suggest that the efficiency of intrastromal ablation may be increased by using short pulses and moderate pulse energies in order to avoid the creation of large cavitation bubbles. The experiment indicates that the optimum laser repetition rate for intrastromal ablation is between 1 and 5 kHz. © 1994 Wiley-Liss, Inc.     

Reduction of collateral thermal impact of diode laser irradiation on soft tissue due to modified application parameters

The aim of this study was to investigate the effect of different working modes (pulsed and micropulsed) and power settings of a standardized 980-nm diode laser on collateral thermal soft-tissue damage. A total of 108 bovine liver samples were cut with a diode laser at various settings in pulsed and micropulsed mode and histologically assessed to determine the area and depth of carbonization, necrosis and reversible tissue damage, as well as incision depth and width. Incision depth and width and the area and depth of carbonization, necrosis and reversible damage were correlated strongly with cutting speed. The area and depth of reversible damage were correlated with average power. The micropulsed mode produced a smaller zone of carbonization and necrosis and a smaller incision width. Setting the laser parameters in accordance with the absorption characteristics of the tissue reduced collateral thermal tissue damage while maintaining an acceptable cutting ability. Reducing collateral thermal damage from diode laser incisions is clinically relevant for promoting wound healing.     

Effects of pulse width on erbium: YAG laser photothermal trabecular ablation (LTA)

An erbium (Er):YAG laser can remove trabecular meshwork (TM) by photothermal ablation with minimal contiguous thermal damage. A variable pulse width Er:YAG laser was used to investigate the effect of varying pulse width on ablation of human TM. Trabecular photothermal ablation was performed on tissue obtained from eye bank eyes at pulse widths of 50, 150, and 250μs, with energy held constant at 4 mJ. At this energy, a single laser pulse was sufficient for full-thickness ablation of TM. Laser energy was delivered through a 200-μm diameter optical fiber held in apposition to the tissue sample, which was immersed in physiologic saline. High-speed photography of the resultant steam bubbles also was performed. Light microscopy and scanning electron microscopy of TM ablated at 50 μs revealed the greatest variability in size (0–140 μm) of the full-thickness ablated areas and demonstrated blast effects, tissue shredding and ?10 μm thermal damage. At 150 μs, the full-thickness ablated areas were more consistent in size (115–120 μm), showed no blast effects and 10 to 20 μm thermal damage. At 250 μs, the largest ablations were found (180–220 μm) and showed no blast damage; however, a significant amount of thermal damage (?50 μm) was evident. The steam bubbles produced by the laser energy were largest at 50 μs and did not begin to collapse until well over twice the original pulse interval. At 150 and 250 μs, the steam bubbles were successively smaller and dissipated at the end of the laser pulse. In single pulse Er:YAG photothermal laser trabecular ablation, a pulse width (total energy of 4 mJ) around 150 μs appears to be optimal. The resultant acoustic shock wave from steam bubble formation is smaller, its duration does not exceed the laser pulse width and tissue thermal damage is minimal. © 1993 Wiley-Liss, Inc.     

Dependence of the XeCl laser cut rate of plaque on the degree of calcification, laser fluence, and optical pulse duration

A XeCl laser with an optical pulse duration of 35 ns was used to determine the cut depth per laser pulse of postmortem human aorta as a function of laser fluence for four main categories of plaque development. The data indicate that the cut depth per pulse progressively decreases as the degree of calcification increases even at very high (100 mJ/mm2) laser fluences. A comparison was made between the XeCl laser cut rate data obtained using the 35-ns duration laser pulses to data obtained using 200-ns duration pulses for each of the four plaque types. As the degree of tissue calcification increased higher XeCl laser fluences were required for the long pulse case to achieve the same cut depth per pulse as that observed using the shorter pulse duration.     

Treatment of an Amalgam Tattoo with a Q-Switched Alexandrite (755 nm) Laser

BACKGROUND: Amalgam tattoos result from deposition of metallic particles (eg, silver, mercury, copper, zinc, and tin) into the oral mucosa. Their clinical and histologic appearance is similar to that of decorative tattoos. OBJECTIVE: To describe the successful use of a Q-switched alexandrite laser for removal of an amalgam tattoo. MATERIALS AND METHODS: An amalgam tattoo on the buccal mucosa and gingiva was treated with a QS 755 nm alexandrite laser. Three treatments were delivered at 8-week time intervals (average fluence = 6.8 J/cm2). RESULTS: Significant lightening of the tattoo was achieved after each of the three treatments without adverse sequelae. CONCLUSION: Q-switched alexandrite laser irradiation can safely and effectively eradicate amalgam tattoos.     

Analysis of fibre tip damage risk during pulsed holmium laser application under water

Breaking of optical fibre tips during medical holmium laser applications involving endoscopic irradiation in a liquid environment, such as arthroscopy, has been reported. This represents a risk of complications due to foreign body reactions induced by quartz fragments remaining at the operation site. Fibre breakage has been analysed under controlled conditions at clinically used laser energies of 20–1000 mJ. The generation of pressure transients at the collapse of laser-induced vapour bubbles is identified as the mechanism of fibre tip destruction. Fibre damage is observed only in a confining liquid envivronment. The highest fibre damage occurrence is observed for laser fluences of 70–250 J cm^-25 at the bare fibre tip, at pulse durations of 200–350 Μs. The fibre damage occurrence and extent increase with the fibre diameter. Avoiding the identified dangerous fluence range or use of fibres smaller than 400Μm diameter is recommended to perform endoscopic holmium laser application with minimal fibre damage risk.     

The influence of water/air cooling on collateral tissue damage using a diode laser with an innovative pulse design (micropulsed mode)—an in vitro study

Since the diode laser is a good compromise for the daily use in dental offices, finding usage in numerous dental indications (e.g., surgery, periodontics, and endodontics), the minimization of the collateral damage in laser surgery is important to improve the therapeutical outcome. The aim of this study was to investigate the effect of water/air cooling on the collateral thermal soft tissue damage of 980-nm diode laser incisions. A total of 36 mechanically executed laser cuts in pork liver were made with a 980-nm diode laser in micropulsed mode with three different settings of water/air cooling and examined by histological assessment to determine the area and size of carbonization, necrosis, and reversible tissue damage as well as incision depth and width. In our study, clearly the incision depth increased significantly under water/air cooling (270.9 versus 502.3 μm—test group 3) without significant changes of incision width. In test group 2, the total area of damage was significantly smaller than in the control group (in this group, the incision depth increases by 65 %). In test group 3, the total area of damage was significantly higher (incision depth increased by 85 %), but the bigger part of it represented a reversible tissue alteration leaving the amount of irreversible damage almost the same as in the control group. This first pilot study clearly shows that water/air cooling in vitro has an effect on collateral tissue damage. Further studies will have to verify, if the reduced collateral damage we have proved in this study can lead to accelerated wound healing. Reduction of collateral thermal damage after diode laser incisions is clinically relevant for promoted wound healing.     

Ultrashort pulsed laser ablation and stripping of freeze-dried dermis

Plasma-mediated laser ablation and dissection of freeze-dried human dermis using an ultrashort pulsed laser of pulse width 900 fs and wavelength 1,552 nm were investigated. The surface ablation line width and depth in relation to irradiation fluence and pulse overlap rate were characterized and measured by scanning electron microscopy. The ablation threshold fluence for freeze-dried dermis was determined as 8.32 J/cm² and the incubation factor subject to pulse train irradiation was found to be 0.54. Histological examination showed no thermal damage with single line ablation. Even with multiline ablation, thermal damage was insignificant and the lateral damage zone was generally within 10 μm with 100 continuously repeated line scans. Ultrashort pulsed laser ablation of the interior of dry dermal tissue was shown to strip thin dermal slices with different thicknesses ranging from 20 to 40 μm.     

Model study to investigate the contribution of spallation to pulsed laser ablation of tissue

Background and Objective: Absorption of a short laser pulse produces high thermoelastic stress in the irradiated volume. The relaxation of this stress at a free (tissue–air) surface leads to tensile loading, resulting in mechanical spallation. Using model substances, we investigated the role of this effect in tissue ablation. Study Design/Materials and Methods: Stained water and gelatine were irradiated with short pulses (8 ns duration) from a Nd:YAG laser at 1,064 nm wavelength. The dynamics of the induced effects were observed with laser-flash photography and stress wave detection. Results: Spallation is indicated by the formation of cavitation bubbles below the irradiated surface and is strongly influenced by impurities serving as nucleation sites. Material ejection due to spallation was observed in the liquid sample at a fluence leading to a temperature below the boiling point but needed a temperature in excess of 100°C in gelatine, owing to the small mechanical energy available for this process, estimated to be <1%. Conclusion: The mechanical action of thermoelastic stress waves is characterized by high stress amplitudes but low energetic efficiency. A model combining spallation and vaporization is therefore proposed for efficient tissue ablation.     

Use of the Q-switched alexandrite laser (755 nm, 100 nsec) for eyebrow tattoo removal.

BACKGROUND AND OBJECTIVE: Permanent tattooing for cosmetic reasons has increased in recent years; as a consequence, there has been an increase of requests for pigment removal due to complications or undesired results. The Q-switched alexandrite laser has been found useful in removing black exogenous pigment, which is the most popular color in eyebrow enhancement. We report the case of a patient with black-pigment eyebrow cosmetic tattoo after treatment with the Q-switched alexandrite laser. STUDY DESIGN/MATERIALS AND METHODS: Treatment conditions included 755-nm wavelength, 100 +/- 10-nsec pulse width, and 3-mm spot size. Fluence threshold was determined, and a spot test was made at the first visit. Single impact technique with 10% overlapping was applied to the whole tattoo. Five treatments were performed with a mean fluence of 7 J/cm(2). RESULTS: Complete pigment removal was achieved after five sessions. Superficial bleeding and vesicle formation was observed. CONCLUSIONS: Eyebrow tattooing can be treated efficiently with the use of the Q-switched alexandrite laser when black pigment has been used for cosmetic reasons.     

Q开关Nd:YAG激光低能量祛除21例文身疗效观察

目的:探讨Q开关Nd:YAG激光多次低能量祛除文身的临床疗效观察。方法:临床选取21例文身患者,治疗采用自身对比:A区为试验区,使用Q开关1064nm波长激光,光斑直径4～6mm,能量密度为2.0～4.0J/cm2,平行均匀照射1遍,术后即刻反应皮损变白霜,无皮肤出血点,每天治疗1次,连续治疗3～4次;B区为对照区,使用Q开关1064nm波长激光,光斑直径3～4mm,能量密度为5.0～8.0J/cm2,均匀照射1遍,即刻反应皮损灰白或皮肤出血。两组病例均于术后6个月观察疗效。结果:术后6个月观察,试验区:治愈9例(42.8%),显效12例(57.2%),无瘢痕形成;对照区:治愈3例(14%),显效5例(24%),好转13例(62%),2例(9.5%)出现轻度增生性瘢痕。结论:采用Q开关Nd:YAG激光多次低能量治疗文身的方法可加快文身消退病程,减少文身治疗中能量密度过大形成瘢痕或色素脱失的风险,为文身治疗提供一种新的治疗方法。     

Effect of the ArF excimer laser on human enamel.

Human enamel surface was irradiated with ArF excimer laser and examined under light microscopy and scanning electron microscopy (SEM). Enamel surface was irradiated at three different areas with different energy fluences. It is demonstrated that the ArF excimer laser causes ablation of the calcified hard enamel tissue. Ablation curves were measured. There was no significant difference found in the etch depth between the three different areas of enamel surface. The morphology of the irradiated areas seen under the SEM was found to be dependent on energy fluence. It changed with increase in energy fluence from being etched to forming a smooth, fused, glaze-like surface and then at very high energy fluences producing a rough surface. The influence of the laser irradiation was confined to the irradiated area only, with no visible heat damage to the surroundings. These results suggest that excimer laser could be applied in a controlled and defined manner for tooth enamel treatments in dentistry.