Factors like, (i) noise and (ii) artifacts, that occur depending on acoustical properties of tissues, (iii) wrong selection of
system variables, like (a) wrong operation frequency, (b) poor calibration, and (c) improper location of focal points, may
cause high amount of image degradation during ultrasound imaging. This, in return, may lead to misdiagnoses, making
correct diagnosis of uncommon cases impossible. These misdiagnoses may be avoided by enhanced training of
physicians. Commercially available phantoms are limited in content and relatively expensive, which makes the
simulation of ultrasound imaging a mandatory component in diagnostic ultrasound training. The aim of this study was to
investigate the feasibility of the simulation of ultrasound imaging. Under the scope of this work, ultrasound imaging was
simulated by using FIELD II program set developed by J.A. Jensen by for various settings. In order to compare the
results a selected cyst phantom was used and the effects of simulation frequency and sampling frequency on visibility
and simulation times were observed. The quality of generated images was evaluated by measuring the visibility of the
cyst phantom. Identification of cysts was accomplished by detection of the cysts with an algorithm to perform a series of
image processing operations. Located objects were classified manually and errors (with respect to size and position of
cysts) were calculated. Our observations indicated that to obtain a good image quality, interdependent simulation and
sampling frequencies should be selected carefully, which in return requires longer simulation times at higher frequencies.
Optical properties of tissues and tissue components are important parameters in biomedical optics. We report measurements of tissue refractive index n and the attenuation coefficient µt using optical coherence tomography (OCT) of individual vascular wall layers and plaque components. Moreover, since the temperature dependence of optical properties is widely known, we compare measurements at room and body temperatures. A decrease of n and µt is observed in all samples, with the most profound effect on samples with high lipid content. The sample temperature is of influence on the quantitative measurements within OCT images. For extrapolation of ex-vivo experimental results, especially for structures with high lipid content, this effect should be taken into account.
Optical properties of tissues and tissue components are important parameters in biomedical optics. We report measurements of tissue refractive index n, and the attenuation coefficient μt using optical coherence tomography of individual vascular wall layers and plaque components. Moreover, since the temperature dependence of optical properties is widely known, we compared measurements at room and body temperatures. A decrease of n and μt was observed in all samples, with most profound effect on samples with high lipid content. The sample temperature is of influence on the quantitative measurements within OCT images. For extrapolation of ex vivo experimental results, especially for structures with high lipid content, this effect should be taken into account.
Early diagnosis with esophageal cancer limited to the mucosa will allow for local endoscopic treatment and improve prognosis. We compared with histology OCT images of healthy human esophageal tissue from two systems operating at 800 and 1275 nm to investigate which wavelength was best suited for detailed OCT imaging of the esophageal wall, and to localize the muscularis mucosae. Within an hour of surgical resection, an esophageal specimen was cleaned of excess blood and soaked in formalin for a minimum of 48 hours. In order to precisely localize the different layers of the esophageal wall on an OCT image, well-defined structures within the esophageal wall were sought. Following OCT imaging the specimen was prepared for routine histology. We observed that our 1275 nm system with 12 micrometers resolution was superior in terms of penetration. As compared to histology, the 4 micrometers resolution of our 800 nm system made fine details more visible. Using either system, a minimally trained eye could recognize the muscularis mucosae as a hypo-reflective layer. Although different conditions may apply in vivo, our ex vivo study paves the path to precise interpretation of OCT images of the esophageal wall.
The use of 980 nm diode laser irradiation within cortical tissue was investigated by the author's previous work. In the present study the lesions created in cortical and subcortical tissues and lesioning effects of diode laser applied in continuous and pulsed regimes were compared. In vivo stereotaxic neurosurgical procedure was performed on female Wistar rats' cortical and subcortical tissues. 980 nm diode laser was applied in two different regimes, cw and pulsed wave respectively. Lesion dimensions were measured and compared. The lasing parameters were found suitable for both brain regions. No significant difference was found between tissues. Lesions diameters varied in the range of 1.0-9.0 mm. Histological examination revealed data for a limited thermal damage in the surrounding tissue for all lesions. Cortical and subcortical tissues did not show significant differences due to same amount of energy delivered. The lasing regime did not influence the dimensions of lesions. Applied energy was found the key element determining the amount of lesion. Results were consistent with the findings found in the previous dosimetry studies.
The aim of the present study was to test the feasibility of the 980 nm diode laser for LEP (Laser Evoked Potentials) studies. Human subjects were exposed to laser stimulation. After the pain thresholds of the subjects were determined with respect to laser power level, 1.5 times the threshold value was applied and laser evoked potentials were recorded using standard EEG techniques. LEPs were obtained due to right hand stimulation. Latency and amplitude values of LEPs were found in accordance with those reported in the literature. Statistical evaluation showed differences in the LEPs at C3 and C4 locations as a function of the sex of the subjects. The power levels used in the present study was three times less than the levels applied for Nd: YAG laser in the literature. The evoked potential parameters measured were in consistence with the data reported by earlier researchers. Moreover, it was found that, LEPs due to 980 nm wavelength irradiation can be recorded by applying less energy when compared to Nd:YAG laser. This result indicated the potential of diode laser for LEP studies.
Background and objectives: Laser soldering of tissues is based on the application of a biological solder on the approximated edges of a cut. Our goal was to use laser soldering for sealing cuts in skin under temperature feedback control and compare the results with ones obtained using standard sutures. Materials and methods: Albumin solder was applied onto the approximated edges of cuts created in rat skin. A fiberoptic system was used to deliver the radiation of a CO2 laser, to heat a spot near the cut edges, and to control the temperature. Laser soldering was carried out, spot by spot, where the temperature at each spot was kept at 65-70 degree(s)C for 10 seconds. Results: The tensile strength of laser-soldered cuts was measured after 3-28 days postoperatively and was found comparable to that of sutured cuts. Histopathological studies showed no thermal damage and less inflammatory reaction than that caused by standard sutures. Conclusions: Temperature controlled laser soldering of cuts in rat skin gave strong bonding. The cosmetic and histological results were very good, in comparison to those of standard sutures.
Temperature feedback control during laser-assisted tissue coagulation was investigated and demonstrated using the egg white model. Dynamics of photothermal denaturation during CO2 laser irradiation was observed by simultaneously controlling surface temperature and monitoring HeNe laser transmission of egg white samples. Once a quasi-constant surface temperature was established, transmission of egg white tended to decrease linearly with time. A first order rate process was observed. Our experiments demonstrated that thermal feedback can effectively control/limit photothermal damage.
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.
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.
Temperature feedback control (TFC) of cw argon ion and cw Ho:YAG laser-assisted anastomoses of severed rat intestines increased wound stability during the first 72 hours after surgery when compared to laser anastomosies formed without temperature control. Comparisons of in vitro bursting pressures measurements and qualitative and quantitative histopathology observations of wound healing were performed to discover the factors associated with this increased stability. Close apposition of the wound edges and decreased abscess formation were found to be associated with good wound healing. No differences in bursting pressure measurements and wound healing patterns were associated with the laser (wavelength) used or between the TFC and non-TFC groups.
The results of a closed loop thermal feedback controlled laser-assisted tissue welding study in vivo are reported. A series of experiments was carried out to study and compare the weld strength and healing response of sutured and laser welded rat enterotomies with and without temperature feedback control (TFC) using a cryogenically cooled Ho:YAG laser. Although assignment of animals to three groups (control sutured, laser welded with and without TFC) and four observation periods (1, 3, 7, and 21 days) was randomized, several laser welded enterotomies without TFC had complications resulting in death of the animals. Those experiments were repeated. From the failure rates encountered, it is shown that TFC improves the quality of laser-assisted enterotomy closures.
Laser tissue welding has been applied successfully to several tissues using microscopic and macroscopic surgical techniques. The advantages of laser tissue welding include the formation of fluid tight bonds, decreased foreign body (suture) reaction scar formation, decreased anastomotic time and growth of the bond. The disadvantages compared to conventional suture and stapling techniques include decreased initial mechanical strengths, poor reproducibility and inadequate control of bond formation. These disadvantages have prevented general acceptance of laser-welding techniques by the general and specialty surgeon. Recently, several laboratories have introduced modified techniques to improve laser tissue welding. These include the use of exogenous dyes and bonding materials to make stronger bonds and computer driven temperature and optical feed-back systems to control bond formation. The advantages provided by the no-touch, fiberoptic delivery of precisely controlled laser light energy to limited endoscopic surgical fields are added reasons to reconsider the usefulness of laser tissue welding.
Numerical modeling and experimental verification studies were conducted to compare continuous wave Ar, Tm:YAG, and Ho:YAG fusion characteristics in rat intestinal tissues. Spot sizes, powers, and activation times were varied according to laser characteristics. Exposed transected bowel wall was apposed and irradiated to obtain fusion in vivo. Tissue surface temperature distributions were measured with a thermal camera in the 8 to 12 micrometers band for calibration of the numerical models. The lasers were operated at fixed power, duration, and spot size. Experimental results were analyzed histologically to determine the extent of changes in submucosal collagen as indicated by birefringence loss. Modeling studies based on damage kinetics were conducted for the Tm:YAG and Ho:YAG experiments to study the microscale thermal and damage accumulation phenomena. Comparisons between predicted and measured damage boundaries showed favorable agreement.
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