Yacov Domankevitz

Effects of CO2 laser pulse duration in ablation and residual thermal damage: Implications for skin resurfacing

Resurfacing with the CO2 laser is rapidly gaining acceptance for skin rejuvenation. Advances in CO2 laser and scanning technology allow for precise tissue removal with minimal thermal damage. High energy CO2 laser pulses have been widely used effectively to smooth the surface of facial skin; however, pulse duration effects on ablation and thermal damage have not been systematically studied over the millisecond region (0.25–10 ms).

Ablation of Rabbit Liver, Stomach, and Colon With a Pulsed Holmium Laser

A pulsed holmium laser (wavelength 2.1 microns, pulse duration 250 microseconds) was used to ablate rabbit liver, stomach, and colon in vivo. Microscopic examination of the tissues revealed zones of thermal damage extending 0.5-1.0 mm from ablation sites. In addition, ablation rates were measured using a mass loss technique and found to increase linearly with delivered radiant exposure. The threshold radiant exposure for ablation was calculated to be 50 J/cm2 with a heat of ablation of 7000 J/cm3. Because the holmium laser produces less thermal necrosis than current endoscopic laser systems, such as the continuous-wave neodymium:YAG laser, and because the ablation rate can be precisely controlled, the holmium laser shows promise as an alternative method for endoscopic removal of tissue.

Comparison of tissue ablation with pulsed holmium and thulium lasers

The ablation rates and tissue effects produced by a pulsed holmium laser (wavelength 2.12 mu m, pulse duration 250 mu s) and a pulsed thulium laser (wavelength 2.01 mu m, pulse duration 250 mu s) were compared. Because the absorption coefficient of water is almost three times greater at the shorter wavelength (65 versus 24 cm/sup -1/), the thulium laser should have a significantly lower threshold of ablation and produce significantly less residual thermal injury. These hypotheses were tested in vitro. Ablation rates were measured using fresh liver and a mass loss technique were found to increase linearly with delivered radiant exposure. The threshold radiant exposure for ablation was derived from the mass loss measurements and found to be 36 J/cm/sup 2/ for the holmium laser and 29 J/cm/sup 2/ for the thulium laser. The corresponding heats of ablation were 10 kJ/cm/sup 3/ for the holmium laser and 9.7 kJ/cm/sup 3/ for the thulium laser. >

Variable-pulse Nd:YAG laser in the treatment of facial telangiectasias.

BACKGROUND Variable-pulse 1,064 nm wavelength lasers have been used with good effectiveness on leg telangiectasias and reticular veins and have shown promising results on facial telangiectasias as well. OBJECTIVE To investigate the effectiveness of a variable-pulse neodymium:yttrium-aluminum-garnet (Nd:YAG) laser using a small spot size in the treatment of facial telangiectasias. METHODS Eight male patients (mean age 75 years) underwent a single treatment session using a variable-pulse 1.5 mm spot size Nd:YAG laser with epidermal cooling. Telangiectasia diameters were 0.3 to 2.0 mm. Test sites were performed using three pulse widths (3, 20, and 60 ms), with fluences varying depending on vessel size and response. Full treatments were performed using test parameters giving the best response. Thirteen weeks later, the patients returned for final evaluation and satisfaction rating. RESULTS Fluences ranged from 226 to 425 J/cm2, with smaller vessels requiring larger energies. Pulse duration was equally divided between the 20 and 60 ms settings. The shortest pulse width (3 ms) was inferior in all patients. Longer pulse durations achieved superior vessel elimination with minimal immediate purpura and no postinflammatory hyperpigmentation. The average mean vessel clearance was 26 to 50% in half of the patients and 51 to 75% in the other half as evaluated by three unbiased dermatologists with extensive laser experience. CONCLUSION A small-spot size Nd:YAG laser using a pulse width of 20 ms or higher appears to be effective in clearing a significant percentage of facial telangectasias with a single pass. The side effects were minimal.

Optimal pulse durations for the treatment of leg telangiectasias with an alexandrite laser.

Determine optimal settings using a long pulse 755 nm alexandrite laser in the treatment of superficial leg veins.

Laser leg vein treatment: a brief overview

Laser treatment of leg veins has been associated with a number of disadvantages, but the introduction of new devices has increased the role of lasers in the treatment of leg veins. This paper reviews the role of laser devices applied from the surface in the treatment of reticular and spider veins. Success is determined by the proper selection of wavelength, fluence, pulse duration, spot size, and number and frequency of treatments.

Effects of heterogeneous absorption of laser radiation in biotissue ablation: characterization of ablation of fat with a pulsed CO2 laser.

Physicians encounter several clinical situations in which fat must be removed. In this study, the characterization of fat ablation produced by a pulsed CO2 laser is reported.

Measurement of laser ablation threshold with a high-speed framing camera

A method for measuring laser ablation threshold energy with a high-speed framing camera is presented. To demonstrate the utility of the technique, the threshold energy for pulsed holmium laser ablation of liver was measured. The measured threshold radiant exposure of 30+or-3 J/cm/sup 2/ is in good agreement with values previously determined by alternate techniques. In addition to providing a rapid and reproducible measurement of laser ablation threshold, this technique also provides insight into the physical mechanisms of ablation. >

Use of a Variable Long‐Pulse Alexandrite Laser in the Treatment of Facial Telangiectasia

BACKGROUND The alexandrite laser selectively targets melanin and hemoglobin. We used the alexandrite laser with variable pulse widths to treat facial telangiectasia. METHODS Nineteen patients were enrolled in this study, which consisted of two parts: a series of test spots over a range of pulse durations (3–80 ms) and treatment over a larger area based on the pulse width–specific outcomes from the test spots. The final follow‐up visit was 12 weeks after irradiation. RESULTS The 40‐ms pulse width achieved the optimal balance of pain tolerance, epidermal tolerance, and vessel reduction. Mean fluence was 88 J/cm2, with a 6‐mm spot. Overall, a 48% reduction in vessels was noted after one treatment. Side effects were minimal. CONCLUSIONS In fair‐skinned patients with large telangiectasia, the alexandrite laser is a good option for vessel reduction. The equipment used in this study was loaned by Candela. Dr. Ross is on the medical advisory board for Candela and is a consultant to Palomar, Cutera, Sciton, and Lumenis. Y. Domankevitz is an employee of the Candela Corp.

Precise, controlled laser delivery with evanescent optical waves

Precise laser surgery is possible with laser pulses at wavelengths that are strongly absorbed at the surface of tissue. However, pulses at these wavelengths (far UV, far infrared) are not compatible with fiber-optic transmission, making endoscopic surgical procedures inside the body difficult. We use evanescent optical waves to demonstrate an alternative for confining energy near the tissue surface. Precise, superficial tissue ablation is achieved with evanescent waves generated at a sapphire-tissue interface by a free-electron laser, where the ablation depth may be varied. A new class of precise, controlled laser surgical tools may be achieved in this novel approach for use in endoscopic procedures. Electromagnetic theory governing evanescent-wave tissue ablation is presented.