Tissue Ablation and Laser Surgery

Due to its undisputed advantages, the laser is still of great interest as a tool for surgical applications. A quick analysis of the number of publications on the topic “laser surgery“ over time by using the analysis tool of the Web of Science reveals that there has been a steady increase in the number of publications since the Seventies. Sorting these publications by publication date returns as a first result an article on ophthalmology. Also, the Web of Science category for the topic “laser surgery“ showing the most articles is ophthalmology, roughly one third. These numbers are in accordance with what one would probably get as an answer if one asked people on the street what comes to their mind if they hear the topic “laser surgery“: using the laser for correcting refractive errors of the eye so patients can get rid of their glasses. This is also what one gets when searching for “laser surgery“ on Google: most of the hits on the first page are related to refractive cornea surgery. So without any doubt, refractive cornea surgery is one of the success stories of laser surgery. At a first glance, this is surprising considering the facts that 1) for example in Germany, this surgical procedure is normally not covered by the health care insurance system but people have to pay for it from their own pockets, and that 2) systems for this procedure are very expensive and complex. These are normally reasons which guarantee the economic flop of a medical treatment. But in this case the advantage for the patients is undisputed: they can get rid of their glasses. And the laser is the only tool which is reasonably usable for this treatment: it provides the necessary precision, it is highly automatable, it hardly affects the surrounding tissue by heat and it requires no mechanical contact. The advantages of using a laser as a tool are not limited to medical applications but the advantages apply also to its industrial use. Demonstrating how to make use of the unique advantages of the laser for surgery is also the goal of the articles in this issue. The first article of Hardy et al. [p. 1240] investigates the use of a thulium fiber laser as an alternative light source for the well-established Ho:YAG laser for laser lithotripsy. They point out that the thulium fiber laser has several advantages – for example its wavelength (λ=1908 nm) is closer to an absorption maximum of water than the wavelength of the Ho:YAG laser (λ=2100 nm). By using high-speed videos of phantom experiments with a saline bath serving as phantom, Hardy et al. investigate the formation of laser-induced bubbles and their characteristics. Their experiments show that the thulium fiber laser causes lower pressures so they can confirm the empirical results of less stone retropulsion. M. Rohde, the first author of the second article [p. 1250] is one of my colleagues (I am one of the co-authors). In this article it is demonstrated how laser induced breakdown spectroscopy (LIBS) can be used to differentiate oral soft and hard tissue for the use in a smart laser scalpel: a scalpel which tells the doctor which tissue he is currently cutting. The experiments are carried out using ex vivo porcine tissue. For almost all tissue combinations high differentiation accuracy can be achieved. The third article by Herzog et al. [p. 1262] shows how the geometry of the fiber tip influences the tissue ablation of porcine aorta tissue. The emphasis of the work is on the photomechanical effects. For their experiments they use a pulsed frequency tripled Nd:YAG laser (λ=355 nm). Based on numerical simulations and experiments they show that the usage of a ferrule at the fiber tip has a positive effect on pressure transients so that the disruptive effects of the laser ablation are reduced. The fourth article is also from Herzog, but different co-authors are involved [p. 1271]. While the other article concentrates on a single detail of using a pulsed, frequency tripled Nd:YAG laser for tissue ablation, the authors demonstrate in this article how such a light source can be used for laser atherectomy. They show the results of a cadaveric study, an in vivo animal model study (pig) and the results of two clinical cases. They conclude that the laser is suitable for this procedure, so the XeCl excimer laser used so far could be replaced in the future by a more modern light source. In the article by Singh et al. [p. 1279] multispectral fluorescence imaging is employed for the diagnostics of dental diseases (caries and calculus). The authors used human ex vivo teeth for their experiments. An LED illumination was used to get fluorescence; the fluorescence was recorded by an LCFT camera. The results are compelling with a high statistical significance (p<0.0001). Abusalah et al. [p. 1287] investigate in their article if photobiomodulation (PBM) therapy can improve the wound healing process after tattoo removal by a Q-switched Nd:YAG laser. The PBM is carried out by a diode laser (λ=808 nm; F=5 J/cm2; I=0.1 W/cm2). They used two groups of rats to investigate the advantages of PBM. Their results point out that PBM might improve the clearing of the ink fragments as well as wound healing. This special topic of the Journal of Biophotonics closes with an article from de Menezes et al. [p. 1292]. The article concentrates on two topics: First, the thermal effects of an fs-laser when used for caries removal. Second, the use of fsLIBS to characterize and differentiate the ablated material with the same idea as Rohde et al. do in their article: to apply it in a smart laser scalpel. They used different samples: human ex vivo teeth as well as bovine bones. They found a parameter window which shows minimal thermal damage but is still suitable for fsLIBS. The seven articles of this issue present interesting new approaches mainly for laser surgery or related methods, but they also show the long journey of a new idea from its first appearance to its application in hospitals. The articles range from simulation or phantom studies to clinical cases while the majority of the contributions concentrate on non-clinical cases. Furthermore, all articles in this special topic are about non-ophthalmological applications. This is only a limited view on current research in laser surgery but it shows that in non-ophthalmological laser surgery there is still a lot of research going on. So in some years, “laser surgery” might no longer be exclusively connected to refractive cornea surgery in the common understanding. Florian Klämpfl Friedrich-Alexander-Universität Erlangen-Nürnberg Lehrstuhl für Photonische Technologien Erlangen, Germany