First Assessment of a Carbon Monoxide Laser and a Thulium Fiber Laser for Fractional Ablation of Skin.

BACKGROUND AND OBJECTIVES: A recent generation of 5,500 nm wavelength carbon monoxide (CO) lasers could serve as a novel tool for applications in medicine and surgery. At this wavelength, the optical penetration depth is about three times higher than that of the 10,600 nm wavelength carbon dioxide (CO2 ) laser. As the amount of ablation and coagulation is strongly influenced by the wavelength, we anticipated that CO lasers would provide extended coagulation zones, which could be beneficial for several medical applications, such as tissue tightening effects after laser skin resurfacing. Until now, the 1,940 nm wavelength thulium fiber (Tm:fiber) laser is primarily known as a non-ablative laser with an optical penetration depth that is eight times higher than that of the CO2 laser. The advantage of lasers with shorter wavelengths is the ability to create smaller spot sizes, which has a determining influence on the ablation outcome. In this study, the ablation and coagulation characteristics of a novel CO laser and a high power Tm:fiber laser were investigated to evaluate their potential application for fractional ablation of the skin. STUDY DESIGN/MATERIALS AND METHODS: Laser-tissue exposures were performed using a novel CO laser, a modified, pulse-width-modulated CO2 laser, and a Tm:fiber laser. We used discarded ex vivo human skin obtained from abdominoplasty as tissue samples. Similar exposure parameters, such as spot size (108-120 µm), pulse duration (2 milliseconds), and pulse energy (~10-200 mJ) were adjusted for the different laser systems with comparable temporal pulse structures. Laser effects were quantified by histology. RESULTS: At radiant exposures 10-fold higher than the ablation threshold, the CO laser ablation depth was almost two times deeper than that of the CO2 laser. At 40-fold of the ablation threshold, the CO laser ablation was 47% deeper. The ablation craters produced by the CO laser exhibited about two times larger coagulation zones when compared with the CO2 laser. In contrast, the Tm:fiber laser exhibited superficial ablation craters with massive thermal damage. CONCLUSIONS: The tissue ablation using the Tm:fiber laser was very superficial in contrast to the CO laser and the CO2 laser. However, higher etch depths should be obtainable when the radiant exposure is increased by using higher pulse energies and/or smaller spot sizes. At radiant exposures normalized to the ablation threshold, the CO laser was capable of generating deeper ablation craters with extended coagulation zones compared with the CO2 laser, which is possibly desirable depending on the clinical goal. The effect of deep ablation combined with additional thermal damage on dermal remodeling needs to be further confirmed with in vivo studies. Lasers Surg. Med. © 2020 The Authors. Lasers in Surgery and Medicine Published by Wiley Periodicals, Inc.

Assessment of skin lesions produced by focused, tunable, mid-infrared chalcogenide laser radiation.

BACKGROUND: Traditionally, fractional laser treatments are performed with focused laser sources operating at a fixed wavelength. Using a tunable laser in the mid-infrared wavelength range, wavelength-dependent absorption properties on the ablation process and thermal damage formation were assessed with the goal to obtain customizable tissue ablations to provide guidance in finding optimized laser exposure parameters for clinical applications. METHODS: Laser tissue experiments were carried out on full thickness ex vivo human abdominal skin using a mid-infrared tunable chromium-doped zinc selenide/sulfide chalcogenide laser. The laser has two independent channels: a continuous wave (CW) output channel which covers a spectrum ranging from 2.4 µm to 3.0 µm with up to 9.2 W output power, and a pulsed output channel which ranges from 2.35 µm to 2.95 µm. The maximum pulse energy of the pulsed channel goes up to 2.8 mJ at 100 Hz to 1,000 Hz repetition rate with wavelength-dependent pulse durations of 4-7 ns. RESULTS: Total ablation depth, ablation efficiency, and coagulation zone thickness were highly correlated to wavelength, pulse width, and pulse energy. Using the same total radiant exposure at 2.85 µm wavelength resulted in 10-times smaller coagulation zones and 5-times deeper ablation craters for one hundred 6 ns pulses compared to one 100 ms pulse. For a fixed pulse duration of 6 ns and a total radiant exposure of 2.25 kJ/cm2 the ablation depth increased with longer wavelengths. CONCLUSION: The tunable laser system provides a useful research tool to investigate specific laser parameters such as wavelength on lesion shape, ablation depth and thermal tissue damage. It also allows for customization of the characteristics of laser lesions and therefore facilitates the selection of suitable laser parameters for optimized fractional laser treatments. Lasers Surg. Med. 50:961-972, 2018.© 2018 Wiley Periodicals, Inc.

Effects of deviation from focal plane on lesion geometry for ablative fractional photothermolysis.

BACKGROUND AND OBJECTIVE: Fractional Photothermolysis (FP) is a method of skin treatment that generates a thermal damage pattern consisting of multiple columns of thermal damage, also known as microscopic treatment zones (MTZs). They are very small in diameter and are generated by application of highly focused laser beams. In order to obtain the smallest spot size, the treatment should be performed in the focal plane. Any deviation from the focal plane (DFP) results in an increase of spot size. FP devices typically utilize distance holders in order to facilitate exposures at this specific location. In spite of the use of distance holders, DFP can occur. In particular, variations of contact pressure to the skin surface and anatomical treatment areas of high surface curvature may be prone to DFP during FP treatments. The impact of such distance variation on lesion geometry, such as depth and diameter of the thermal injury, has not previously been evaluated. The objective of this study was to investigate the relation between DFP and the resulting lesion geometry for a selected ablative fractional device. MATERIAL AND METHODS: A handpiece of an ablative fractional laser (DeepFX, UltraPulse Encore, Lumenis, Yokneam, Israel) was mounted to a rigid stand. Full thickness human skin obtained from abdominoplasty was mounted to a separate stand perpendicular to the handpiece. The tissue stand allowed the distance between the handpiece and the tissue to be adjusted to produce a variation up to ±3 mm from the focal plane. A 1 × 1 cm(2) scanning area of 169 MTZs, 50 mJ energy per MTZ, 120 µm nominal spot size, was applied at -3, -2, -1, 0, +1, +2, and +3 mm deviated from the focal plane. Minus (-) and plus (+) signs indicate decreasing and increasing distance between the handpiece and the tissue, respectively. Depth and diameter of the laser induced tissue lesions were assessed and quantified. RESULTS: DFPs produced a significant alteration of the lesion geometry. DFPs of -3, -2, -1, 0, +1, +2, +3 mm resulted in average lesion depths of 1,020 (-40%), 1,180 (-31%), 1,400 (-18%), 1,700 (0%), 1,620 (-5%), 780 (-55%), 680 (-60%) µm, and average lesion diameters of 314 (+26%), 311 (+25%), 273 (+10%), 248 (0%), 256 (+3%), 316 (+27%), 359 (+44%) µm, respectively. The underlined values represent the focal plane. The percentage changes relative to values at focal plane are in parentheses. CONCLUSIONS: A relatively minor DFP has a marked impact on the thermal injury profile, including lesion depth and diameter, of the laser-exposed tissue. Such marked changes of the thermal injury profile might affect the wound healing, safety, and efficacy of ablative fractional resurfacing procedures. Clinicians should carefully maintain the focal plane during ablative fractional treatment for reproducible results. The presented data are device specific and the clinical impact of such alteration of thermal injury profile warrants further investigation. Lasers Surg. Med. 48:555-561, 2016. © 2016 Wiley Periodicals, Inc.