Photodynamic Therapy (PDT)
Photodynamic therapy is a relatively new prospective therapeutic modality for the treatment of definite types of malicious neoplastic formations. The method is based on the combination of a photocytotoxic action of a drug (toxic effect produced on the cells upon the drug‘s interaction with light of the specific wavelength) with its predominant accumulation in neoplastic tissues. The projects in our lab are carried out using photosensitizers delivered mainly in nanocarriers and irradiated with the proper wavelength for the application of PDT on cancer cells or bacteria.
Laser Tissue Interactions
Lasers produce a sterile incision, and reduce bleeding and operating time. Following laser surgery healing is rapid; postoperative pain is reduced; swelling and scarring is less than compared to other techniques. In the photothermal mechanism as photons are absorbed and thermal energy is generated, tissue changes result from the degree and distribution temperature elevation in the tissue. Depending on the duration and peak value of the tissue temperature achieved, different effects like coagulation, carbonization or necrosis, vaporization and denaturization or hyperthermia “In vitro photothermal effects of 980-nm diode laser on different biological tissues” Project No: BAP01R101
Laser tissue welding is a non-contact method aiming to bond biological tissue with the laser energy delivery. Three types of tissues welding can be defined: Direct Welding, Laser Soldering, and Dye-enhanced Laser Soldering. In order to produce bonding, target tissue is heated up with laser application in direct welding method. Even though the welding process is not fully understood, it is supposed that tissue heating leads to coagulation of proteins, collagens and therefore to an anastomotic bond of the tissue structures. In the second type of welding, use of soldering materials like albumin can contribute tissue welding with the selective heating of target tissue. Thus, this procedure is called tissue soldering. Thirdly, with the use of highly absorptive dyes (like ICG for near infrared wavelengths), the temperature of target tissue can also be increased to welding limits.
Medical Laser System Design
Having higher absorption characteristics by water, 1.9-µm lasers are found succesful in biophotonics applications. A diode-pumped Thulium (Tm:YAP) laser system with a power output up to 1 W (pulsed and CW) at 1980 nm are developed to be used in tissue ablation, coagulation, and welding applications. The thermal effects and tissue ablation zones by Tm:YAP laser system are analyzed in vivo by histological studies under light microscopy. In addition, in vivo laser tissue welding studies by Tm:YAP laser system are performed and the results are compared to traditional suture techniques by both histology and tensile strength measurements. The 1.9-µm lasers in tissue welding are found eliminating the transmission difficulties of lasers at higher wavelengths and they do not require solders to increase the thermal effect as in tissue welding by lasers at smaller wavelengths.
Nowadays diode lasers radiating in the near IR region (800-980-nm) have become commercially available. Their lightweight, portable sizes, lower cost, longer operating life and better operating conditions make them attractive for medical applications. A microcontroller based 808-nm high power diode laser system will be designed for further photodynamic applications. “Development of a high power diode laser system for photodynamic therapy applications” Project No: 04X101.
Stereotaxic Laser Surgery
Tm:YAP diode laser (tunable 1.9-2 μm) is cost-effective and has a low pumping power consuming system. Mid-infrared systems emitting around 2 μm are also gaining importance due to a growing number of applications in medical surgery and since Tm:YAP diode laser is tunable to 1940-nm, one of the peaks in absorption spectra of water it is a good candidate for ablation studies in neurosurgery.
It has been previously shown by Özgür Tabakoğlu and Özgüncem Bozkulak that 980 nm diode laser can be used to induce brain lesions with less thermal damage than mono- or bipolar electrosurgery. In addition to that Tm:YAP diode laser has absorption coefficient is higher than 980 nm diode laser. Therefore Tm:YAP diode laser is expected to create more controllable brain lesions than 980 nm diode laser.
Endovenous Laser Applications
Endovenous laser treatment becomes more preferable treatment technique than surgical vein stripping for varicose veins. It is safe and effective. Most importantly, it is minimally invasive. Its working principle is to deliver laser energy to blood vessel lumen. The laser light is converted into heat. It destroys vein wall, causes shrinkage and closure of the vein. Various lasers can be used for endovenous laser treatment, such as 810 nm, 980 nm, 1064 nm and 1070 nm wavelengths. But the best treatment parameters are still under investigation to find the optimal energy and wavelength. The goal of the optimum parameters is to achieve sufficient occlusion and fibrosis while minimizing complications.
Laser Debonding Of Orthodontic Ceramic Brackets
During 1980s and early 1990s the use of lasers was introduced into dentistry as various types. Orthodontics is a specialized branch of dentistry concerned with the development and management of irregularities and abnormalities of the teeth, jaws and face. Brackets are one of the different types of appliances used in orthodontics. Since the early 1990s lasers have been used experimentally for debonding ceramic brackets. Although their superior esthetics, ceramic brackets have several complications like damaged enamel and broken bracket wings while debonding. Laser irradiation decreases the bonding strength while heating the bracket that reduces the risk of enamel damage. Aim of the study is determination of the suitable Laser parameters for debonding ceramic brackets, keeping that intrapulpal temperature changes below the threshold value.
Simulation Of Optical And Thermal Responses Of Laser Irradiated Tissue
Lasers have been widely used in medicine for treatment. Main problem in laser applications is to estimate the right dose specific to the target tissue. Choosing the wavelength, pulse width, pulse shape, beam profile, power density depend on the predosimetry estimations. For photochemical applications, modeling light distribution is crucial, on the other hand, for photothermal applications estimating temperature distribution is essential in order to determine the extent of thermal changes such as coagulation and hyperthermia.
Corneal Tissue Welding
Infrared lasers can be used to weld soft tissues. Water molecules and also protein molecules such as collagen absorb the infrared energy and a temperature gradient can be created at the application site. Corneal welding is rather a new application area in laser medicine, and few studies reported successful welding dose for different infrared wavelengths. Different laser wavelengths are studied comparatively. Diode lasers (809-nm and 980-nm), a fiber laser (1070-nm) and a Tm: YAP lasers (1940-nm) are used in a power range of 200mW-3W.
In many studies until today, it is observed that low level lasers have a biostimulatory effect on organisms in molecular level. Wound healing is a well organized process in which the proliferation of fibroblasts and formation of exrtacellular matrix in the dermis play an important role. It is supposed that LLLT support wound healing process by enhancing fibroblast proliferation and thus formation of extracellular matrix. “The biological effects of 632.8-nm low energy He-Ne laser on peripheral blood mono nuclear cells”, “In vitro effects of 670-nm and 632.8-nm laser on fibroblast cell growth”
The laser-tissue interaction mechanisms are determined by laser wavelength, laser power, the available laser waveform, the optical and thermal parameters of target tissue. Absorption coefficient (ma), scattering coefficient (ms), albedo (a), and optical depth (t) of a target tissue can be calculated. “Foundation of Tissue Characterization Laboratory for Laser-Tissue Interactions and Invastigation of Optical Properties of Brain Tissues ” Project No: BAP01R101