ORIGINAL ARTICLE Optoacoustic monitoring of cutting efficiency and thermal damage during laser ablation Erwin Bay & Alexandre Douplik & Daniel Razansky Received: 3 December 2012 /Accepted: 27 August 2013 # Springer-Verlag London 2013 Abstract Successful laser surgery is characterized by a pre- cise cut and effective hemostasis with minimal collateral thermal damage to the adjacent tissues. Consequently, the surgeon needs to control several parameters, such as power, pulse repetition rate, and velocity of movements. In this study we propose utilizing optoacoustics for providing the necessary real-time feedback of cutting efficiency and collateral thermal damage. Laser ablation was performed on a bovine meat slab using a Q-switched Nd-YAG laser (532 nm, 4 kHz, 18 W). Due to the short pulse duration of 7.6 ns, the same laser has also been used for generation of optoacoustic signals. Both the shockwaves, generated due to tissue removal, as well as the normal optoacoustic responses from the surrounding tissue were detected using a single broadband piezoelectric trans- ducer. It has been observed that the rapid reduction in the shockwave amplitude occurs as more material is being removed, indicating decrease in cutting efficiency, whereas gradual decrease in the optoacoustic signal likely corresponds to coagulation around the ablation crater. Further heating of the surrounding tissue leads to carbonization accompanied by a significant shift in the optoacoustic spectra. Our results hold promise for real-time monitoring of cutting efficiency and collateral thermal damage during laser surgery. In practice, this could eventually facilitate development of automatic cut- off mechanisms that will guarantee an optimal tradeoff be- tween cutting and heating while avoiding severe thermal damage to the surrounding tissues. Keywords Optoacoustics . Cutting efficiency . Thermal damage . Laser ablation . Laser surgery . Shockwaves . Photoacoustic imaging Introduction Laser ablation has been so far widely applied in various surgical applications, ranging from ophthalmology to derma- tology and oncology, owing to its several critical advantages over conventional scalpel-based surgery [1–3]. In soft tissue applications, the fundamental advantage resides in the hemo- static effect of laser light. Besides tissue removal in the focus of the laser beam, the absorption of optical energy also causes heating of surrounding tissues. As a consequence, neighbor- ing blood vessels are sealed during coagulation [1, 4–6]. In this way, excessive bleeding can be avoided, leading to a simplified treatment protocol, reduced operational trauma, and lower risk for malignant cells to be introduced into blood circulation [1]. Although some coagulation of the surrounding soft tissues might therefore be desirable in order to induce hemostasis, excessive coagulation or even carbonization may lead instead to extensive thermal damage to adjacent critical structures E. Bay : D. Razansky Institute for Biological and Medical Imaging (IBMI), Helmholtz Center Munich, Ingoldstädter Landstraße 1, 85764 Neuherberg, Germany E. Bay : D. Razansky (*) Faculty of Medicine, Technical University of Munich, Ismaninger Straße 22, 81675 Munich, Germany e-mail: dr@tum.de A. Douplik Department of Physics, Ryerson University, 350 Victoria Street, Toronto M5B 2K3, Canada A. Douplik Clinical Photonics Lab (CPL), School of Advanced Optical Technologies (SAOT), Friedrich-Alexander Erlangen-Nuremberg University, Erlangen, Germany A. Douplik Medical Photonics Engineering Group (MPEG), Chair of Photonics Technologies, Friedrich-Alexander Erlangen-Nuremberg University, Erlangen, Germany Lasers Med Sci DOI 10.1007/s10103-013-1434-y