Inci F. Cilesiz

Controlled temperature tissue fusion: argon laser welding of rat intestine in vivo. Part one.

Thermal denaturation of proteins is recognized as a rate process governed by the local temperature‐time response. Since rate processes are exponential with temperature, laser‐assisted tissue welding was performed with and without temperature feedback control (TFC) to investigate the efficacy of temperature feedback in enhancing the photothermal welding process in vivo.

Comparative optical coherence tomography imaging of human esophagus: How accurate is localization of the muscularis mucosae?

BACKGROUND Early diagnosis of esophageal cancer limited to the mucosa allows local endoscopic treatment and thereby improves prognosis. Optical coherence tomography images of normal human esophageal tissue obtained with 2 systems with light sources that provide different wavelengths (800 nm and 1275 nm) were compared with histology to determine which wavelength is best suited for detailed optical coherence tomography imaging of the esophageal wall, and to precisely localize the muscularis mucosae. METHODS Within 1 hour of surgical resection, an esophageal specimen was cleaned of excess blood with saline solution and soaked in formalin for a minimum of 48 hours. After optical coherence tomography imaging, the specimen was prepared for routine histologic assessment. To precisely localize the different layers of the esophageal wall on an optical coherence tomography image, well-defined structures within the esophageal wall were sought. RESULTS The 1275 nm system with 12 mm resolution was superior in terms of imaging depth. As compared with histology, the 4 microm resolution of the 800 nm system made fine detail more visible. With minimal experience, the muscularis mucosae could be recognized with either system as a hyporeflective layer with a diameter of around 180 microm. CONCLUSIONS Based on appearance and location of morphologic landmarks, layers of normal esophageal wall, specifically, the location and extent of the muscularis mucosae, could be recognized by using both the 800 nm and 1275 nm optical coherence tomography system. Although different conditions may be operative in vivo, the present ex vivo study further verifies by precise interpretation that optical coherence tomography provides precise images of the esophageal wall.

Controlled temperature tissue fusion: Ho:YAG laser welding of rat intestine in vivo, Part Two

Temperature feedback control (TFC) during laser‐assisted tissue welding was implemented to eliminate exponential increases in the rate of denaturation associated with rapidly increasing temperatures. This study was undertaken to investigate and compare the weld strengths and healing responses of laser welded enterotomies with and without TFC using a cw Ho:YAG laser and to examine the effects of wavelength on weld strength and histology. The Ho:YAG experimental results were compared with a similar study using cw argon ion laser irradiation.

Application of the 980-nm diode laser in stereotaxic surgery

With recent developments in laser technology, diode laser and optical delivery systems have become highly promising surgical devices with advantages of lower cost and higher precision. The aim of the study was to test the 980-nm diode laser for its potential use in stereotaxic surgery. In our dosimetric study, the response of cortical tissue to different energy levels of laser irradiation was investigated with different exposure durations. In vivo stereotaxic neurosurgical procedure was performed on female Wistar rats weighing 180 to 220 gr. In order to investigate the lesioning effects of the 980-nm diode laser as a function of pulse duration, laser power was adjusted to 2.0 and 3.0 W with exposure times ranging from 1.3 to 3.0 s resulting in an irradiance of 5.97 to 17.91 J/mm/sup 2/. Histologic investigation of brain specimens indicated that the 980-nm diode laser has the potential to create lesions in stereotaxic surgery. With proper selection of power level and exposure duration, target tissues could be evaporated and/or coagulated. We found the 980-nm diode laser a promising tool for neurosurgical applications.

CONTROLLED TEMPERATURE PHOTOTHERMAL TISSUE WELDING

Photothermal tissue welding has been investigated as an alternative surgical tool to improve bonding of a variety of severed tissues. Yet, after almost two decades of research, inconsistencies in interpretation of experimental reports and, consequently, mechanism of this photothermal process as well as control of dosimetry remain an enigma. Widespread clinical use may greatly depend on full automation of light dosimetry to perform durable and reproducible welds with minimal thermal damage to surrounding and/or underlying tissues. Recognizing photothermal damage as a rate process, radiometrically measured tissue surface temperature has been studied as an indirect marker of tissue status during laser irradiation. Dosimetry control systems and surgical devices were developed to perform controlled temperature tissue welding using surface temperature feedback from the site of laser impact. Nevertheless, end points that mark the completion of a durable and stable weld have not been precisely identified, and subsequently, not incorporated into dosimetry control algorithms. This manuscript reviews thermal dosimetry control systems of the 1990s in an attempt to systematically indicate the difficulties encountered so far and to elaborate on major issues for photothermal tissue welding to become a clinical reality in the new millennium.

Er:YAG Laser Ablation of Cerebellar and Cerebral Tissue

Abstract. With the availability of suitable fibres, the Er:YAG laser has become an indispensable tool for invasive neurosurgical applications as a source of precise ablation. The aim of this study was to investigate the ablative effects of the Er:YAG laser on brain tissue. The response of neuronal tissue to 2.94 µm Er:YAG laser irradiation was investigated on excised rat brain specimens. Ablation craters were created in cerebral and cerebellar tissues using 0.3, 0.5 and 1.0 J single pulses of 150 µs duration. The corresponding average irradiances were 37.7 J/cm2, 62.9 J/cm2 and 125.8 J/cm2, respectively. Craters were checked qualitatively, crater dimensions were measured and compared, and volume of ablated tissue was estimated. Laser-induced crater dimensions were found to be significantly different at different energy levels applied. Moreover, dimensions of craters on cerebral and cerebellar tissues were significantly different in terms of dimensions. We observed that with the Er:YAG laser ablation craters were created with practically no thermal damage to adjacent tissues. The differences observed in the response of cerebral and cerebellar cortical tissues were dependent on the anatomical and chemical differences.

980-nm-wavelength diode laser application in stereotaxic neurosurgery in the rat

With recent developments in laser technology, high power diode laser and optical delivery systems have become highly promising surgical devices with advantages of lower cost and higher precision. The aim of the present study was to test the 980 nm wavelength laser (Opto Power OPC-D010-980-FCPS) for its potential use in neurosurgery. Response of neural tissue to different energy levels of laser irradiation was investigated with different exposure durations in a dosimetric study using Wistar rats. Laser-induced lesions were placed stereotactically in anesthetized Wistar rats both cortically and subcortically. In order to investigate the lesioning effects of the 980 nm diode laser as a function of pulse duration, laser power was varied between 0.5 to 3.0 Watts with 0.5 to 3.0 sec exposures. Histologic investigation of brain specimens indicated that the 980 nm wavelength high power diode laser has the potential to be used for coagulation/ablation with proper selection of energy level and exposure duration.

Thermal-feedback-controlled coagulation of egg white by the CO 2 laser

Temperature feedback control during laser-assisted tissue coagulation was investigated and demonstrated with the egg-white model. We observed the dynamics of photothermal denaturation during CO2 laser irradiation by simultaneously controlling surface temperature and monitoring He-Ne laser transmission of egg-white samples. Once a quasi-constant surface temperature was established, transmission of egg white tended to decrease linearly with time. Analysis of experimental data strongly suggested a first-order rate process. Since transmission was primarily affected by heat-induced increase in the scattering coefficient and depth of coagulation, we speculated that changes in transmission were reliable indicators of accumulating photothermal damage. Our experiments demonstrated that thermal feedback can effectively control or limit photothermal damage.

An experimental study on photothermal damage to tissue: the role of irradiance and wavelength

Laser exposure time and irradiance are crucial parameters governing the process of thermal damage. The goal of our in vitro study was to study and determine optimal parameters for the onset of coagulation and carbonization at three different wavelengths (980, 1070 and 1940 nm). We also compared photothermal effects at these three wavelengths by varying laser exposure time and irradiance. Fresh bovine liver specimens were used for experimentation. The onset of thermal damage at different irradiances and for different exposure time was studied macroscopically and histologically. Photothermal damage or lesion volume generally decreased with irradiance and increasing exposure time. We observed an exponential and linear relationship between irradiance and exposure time for specific thermal endpoints. These specific endpoints were the onset of (i) coagulation, and (ii) carbonization. The time interval or difference between these specific endpoints termed as Δt (t carbonization − t coagulation) (s) was also determined. This relation between irradiance and exposure time will make possible the pre-estimation of thermal tissue lesion volume before operation, and photothermal therapy may thus be performed with minimum side effects on liver tissue.

PROPAGATION OF DIFFRACTION-FREE AND ACCELERATING LASER BEAMS IN TURBID MEDIA

We experimentally investigate propagation of laser beams with Gaussian, Bessel and Airy transverse profiles in turbid media. We evaluate and compare the self- healing properties of these beams.