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Medikal uygulamalar için tulyum laser sistemi tasarimi ve geliştirilmesi
The Thulium (Tm:YAP) laser is suitable for medical applications due to strongabsorption in water. In this thesis, a computer controlled Tm:YAP laser system witha power output up to 1 W and emission wavelength of 1980 nm were established.Once the laser system was stabilized, its output power, spot size, and light intensitymeasurements were performed. The thermal effects of the laser system on brain, liver,heart, and kidney tissues were macroscopically analyzed. The ablation efficiency ofthe laser system was experimentally tested on ex-vivo brain tissue. The maximumablation efficiency was obtained at a power level of 200 mW with a duration of 10seconds (69 W/cm2). The fluence effect for skin ablation was analyzed by histology onWistar rat skin tissues during a 4-day healing period. Temperature measurements bythermal camera and thermocouples were investigated to see the temperature effect ofCW and modulated mode of the Tm:YAP laser under skin and on skin surface. Thetemperature increase was faster and the temperature decrease was found slower in CWmode. The main aim of the study is to explore the welding capabilities of Tm:YAPlaser in modulated and CW modes of operation on Wistar rat skin during 21-dayhealing period. Full-thickness incisions were welded at 100 mW and 5 s (34.6 W/cm2).The results were compared to conventional suture techniques by both histology andtensile strength measurements. After day 4, full closure was obtained for both lasermodes, whereas, full closure was not observed till day 4 in suture group. In tensilestrength analysis, tensile forces found for both modulated and CW modes of operationwere significantly higher than the tensile force values found for conventional suturetechnique. Tm:YAP laser tissue welding possessed significantly stronger closure thanconventional suture technique.
Gözü bağlı ve doğuştan görmeyen deneklerde dokunsal zihinde döndürme
Mental rotation is the process of imagining an object rotated into a different orientation in space. This well-known visual phenomenon may be used to understand the cognitive processing by applying it to the tactile modality. Linear correlation between response times and angular orientations of the explored objects shows the mental rotation effect.Twelve sighted, 12 congenitally blind subjects participated in this study. All subjects were right handed. Gender and age were balanced. The sighted were blindfolded through the experiments. Two tactile L-shaped objects were glued on cardboards as pairs rotated at ve orientations (0°, 45°, 90°, 135°, 180°). A passive touch method was developed, subjects' hands were steady on a platform and objects were placed andlifted with a lever. Subjects used their palms to passively touch the objects. The subjects were instructed to explore the objects tactually and decide if the pairs weresame or different, different meaning mirror as known to the experimenter. Response times and accuracies were recorded. Correlation analysis and ANOVA were performed using Matlab. Results showed that both the blindfolded and congenitally blind subjects used mental rotation process during tactile exploration of the stimuli.The results support the idea that an analog representation is used in the cortex which totally lacked visual input. The data presented in this study, combined with the literature further supports the hypothesis that spatial properties of the objects are encoded similarly for touch and vision.
Tomosentezin diş x-ray görüntülerine uygulanmasi
Digital tomosynthesis is a method of reconstructing any number oftomographic planes, by using a set of limited angle projections,acquired as the X-ray source moves in an arc around the object.In some cases the quality of the reconstructed planes is affectedby structured noise, due to blur from planes other than thefulcrum plane. The purpose of this project is to implement theMultiple Projection Algorithm along with the out-of-plane blurremoval method that could remove the noise from the reconstructedplanes and improve their quality.For this purpose, one software phantom was used to evaluate theparameters that affect the image quality. Different groups werecreated with varying arc lenghts and projection counts . Theseimages were reconstructed with the Multiple ProjectionsReconstruction Algorithm (MPA) written in MATLAB.Blur removal method was implemented to increase image quality.Image quality was assessed by evaluation of the reconstructedplanes in terms of both visual assessment and SSIM analysis. TheMPA followed by the proposed noise removal algorithm resulted inless noisy tomosynthesis images.The algorithm was also tested with dental phantom data set. Theresults showed that the tomosynthesis image reconstruction is apromising and a low cost method to evaluate digital dental x-rayswithout excess radiation to the patient.
Development of an acqusition and image enhancement platform for digital dental imaging
With technologıcal developments in X-ray imaging, digital systems started to replace analog systems. Principle advantages of digital X-ray imaging are; it has lower cost (in the long run), is ready to be processed with a computer, could acquire 3D images and has better imaging quality even at low radiation doses. Usage of digital technology in dental imaging is also increasing rapidly. Although, dental dose levels are significantly less than other X-ray imaging techniques, its cumulative effects could be harmful in the long term. Main aim of this thesis is to set up a digital dental imaging system and to implement its image processing software. A digital dental Xray system consists of three of the shelf components; a digital intraoral X-ray sensor, a portable X-ray tube and a computer. The new digital system and its acqusition software are tested on phantom and cadaver tests. Furthermore, effects of several image enhancement techniques on low dose dental radiographic images are examined.
1940-nm tulyum fiber lazeri ile seramik braketlerin çikarilmasi
The aim of the study was to determine the proper laser paramaters for 1940-nm Thulium Fiber Laser for ceramic bracket removing. In order to assess the effectiveness of 1940-nm Thulium Fiber Laser in orthodontic ceramic bracket debonding , polycrystalline ceramic brackets were bonded to mandibular bovine teeth with adhesive agent . The samples were divided into 9 different groups , 11 in each , due to applied laser power and laser duration, debonding method used . In addition, there was a control group that had no laser application . The debonding process was performed by 1940-nm Thulium Fiber Laser in CW (continous mode ) . The efficency of the laser was investigated together with the required debonding forces and intrapulpal temperature changes . In this study, keeping intrapulpal temperature changes below the threshold value that is accepted 5.5 °C must be accepted as a must. In most of the lasing groups , the increase in intrapulpal temperature changes were observed almost below the threshold value 5.5 °C . The findings revealed that 1940-nm Thulium Fiber Laser irradiation could reduce the needed debonding force or SBS (shear bond strength ) values significantly compared to control group . Irradiation of the specimens by 1940-nm Thulium Fiber Laser caused almost more than 50 % reduction in the needed debonding force when compared to the control group. Different application methods : non-scanning and scanning were studied to assess the effects of the distinct configurations. Scanning method was tried to reduce the intrapulpal temperature rise during laser irradiation but in this study side effects of this method were faced . Different application methods did not create any remarkable differences. In the lasing groups with the energies 25 J and more , adhesive remnant has not been observed on the enamel surfaces.
Laser etching of enamel for bonding orthodontic bracket
The aim of this study is to determine the optimum laser parameters to provide the maximum bonding strength with reference to conventional bonding technique for orthodontic braces. 1940 nm Thulium Fiber Laser was used in pulse mode and in two different parameters for enamel etching procedure. In addition, there is a control group which had conventional acid etching technique.Laser etching procedure was carried out by two different approaches: Lasing without cooling and with cooling. For the first approach, according to the whitening of the enamel initiation, application time of laser irradiation was defined for each laser parameters.For the second approach, in order to prevent damage on alive tissue, water spray and air pressure cooling was applied during lasing to limit pulp temperature to maximum 5,5 °C which is the critical temperature.After the bonding of ceramic braces, they were debonded from the enamel surface using mechanical test machine. When the bonding strength of the braces were analyzed, it was observed that the mean bonding strength of both the etching without cooling group and etching with cooling group are significantly different from acid etched group (p<0.05, student t-test). SEM evaluations of etched surface with laser showed that surface morphologies were not similar with acid etching group.
Neuroimaging of brain activity using spatio-temporal signal modelling
Functional neuroimaging enables us to obtain information about how the brain responds to cognitive and/or emotional tasks.Neuroimaging of brain activity requires spatio-temporal modelling of measured electrical and/or hemodynamic data and integration of the measurements obtained at different spatial and or temporal scales. In this thesis, new techniques are employed for the investigation of spatio-temporal dynamics of different functional data as the EEG-ERP, the invasive/non-nonivasive recordings of epileptic EEG, and simultaneously recorded steady state EEG-fMRI. Spatio-temporal wavelet decompositions using realistic head models are applied in order to produce simple stationary input subtopographies for the source localization. Besides, a spatial decomposition method based on radial basis functions is used. The usage of the subtopographies facilitate the inverse solution and it is shown that even the temporally correlated EEG sources can be localized by this approach.Integration of the data obtained from different spatial scales is an important problem in epileptic EEG. To assess their reliability, the spatial performance of the scalp EEG based inverse solutions are compared with deep or cortical measurements and their simultaneously measured datasets. The multimodal functional information integration is proposed to compare the dynamics deduced by the simultaneously recorded SSVEP and fMRI. The temporal correlation between the time series of EEG and fMRI is calculated via the GLM. It is observed that the SSVEP source maps are the spatial subsets of the fMRI activity.The study demonstrates the applicability and potential of new spatio-temporal methods in EEG research which can be used to study cognition, attention, memory, and perception. Proposed methods can also be used as tools in more practical areas like brain computer interfacing, neurosurgical planning and neuro-psychological assessment of certain disorders.
Functional parcellation of memory related brain networks by spectral clustering of EEG data
The EEG signal and its oscillatory components may relate with temporal modulation of information processing of a sensory activation in a local electrical field and neural populations. In this study, we investigate the clustering information of alpha band brain networks during memory load task. For this purpose, short time memory experiment with a varying memory was designed. The functional coupling among EEG electrodes were quantified via mutual information in the time-frequency plane. A spectral clustering algorithm was used to parcellate memory related circuits in the brain in a load-dependent manner. The method is based on determining the eigenspectrum of the adjacency matrix of a graph and assigning nodes to clusters with respect to this spectrum. To be able to circumvent the problem of choosing the number of clusters beforehand a soft clustering approach was implemented. It is a novel method which offers to construct significant clusters without fixing a specified number of clusters and increases the inside cluster significance by normalized-cut value decomposition at each clustering level. In the N-cut clustering results, clustered nodes which are projected on occipital and bilateral regions increase with respect to the memory load. In the soft clustering results, inter-cluster connections between left lateral and occipital clusters are decreasing in the second (1250ms) time interval which can be linked to the enhancement of posterior region due to the increase in the memory demand.
The effects of skin-tissue morphometry on the mechanical impedance of rat glabrous skin
In this thesis, the mechanical impedance of rat glabrous skin was measured at two different locations: the digit and the sole in the hind paw, at two frequencies: 40 Hz and 250 Hz with amplitude of 61 µm. The force (F), the velocity (v) and the phase difference between them (?) were measured to calculate the mechanical impedance components. Skin samples were also studied histologically from the same locations where the impedance measurements were obtained. On the microscope images, morphometrical measurements of the skin layers were performed. All mechanical impedance and morphometrical measurements were done in two different conditions: the normal and the epidermis-peeled condition.In the normal condition, two-way ANOVA showed that the effect of the location on the resistance was marginally significant (p=0.056), whereas the frequency had no effect (p=0.376). The effect of the frequency on the modulus was found to be significant (p=0.018); however, the effect of the location on the modulus was not significant (p=0.684). In the normal condition, there was a significant correlation between the resistance and the stratum corneum thickness at 40 Hz in the sole and marginally in the digit (r=0.61, p=0.06 for the digit; r=0.94, p<0.0001 for the sole). In the peeled condition, at 40 Hz, the remaining epidermis thickness in the digit was significantly correlated with the resistance, the reactance and the modulus (r=0.91, p<0.001 for the resistance; r=0.80, p<0.01 for the reactance; r=0.90, p<0.001 for the modulus). No correlations were found at 250 Hz either on normal and peeled conditions.According to these results, the impedance was found to be largely governed by resistance. The resistance of the skin was affected by the location and it was highly correlated with the stratum corneum thickness at 40 Hz. This suggests that stratum corneum may determine the mechanical properties of the skin at 40 Hz.
Erken ve geç laser uygulamanin sinir yenilenmesine etkisi
Studies to understand the operating mechanism of the nervous system and to find new treatments for its diseases have been growing at an increased pace. To accelerate the rate of regeneration, the laser is used immediately after surgeryand the protocols in literature are generally adapted to this method. After crushing or transection of nerve, the mononuclear cells invade the injured segment and remove injured nerve structure. This degenerative event takes place at the first week after injury. These two critical points gave rise to the question of this study; are there any differences between early and delayed application? In this regard, three experimental groups underwent surgery (sciatic nerve was damaged by crushing for 10 minutes by applying a force of 50 N using dead-weight machine) and two of which were administrated 14-days of low dose laser irradiation. 650 nm, 25 mW laser irradiation in continuous mode was applied to the early group immediately after injury whereas the therapy started one week after in the delayed group. The healing process of the damaged sciatic nerve has been shown to be accelerated in the laser therapy groups by means of functional, electrophysiological and histological examinations. It was observed that the sciatic functional index (SFI) value of the laser groups approximately reached to the normal whereas the SFI of the control group did not in day 21. However, this finding was not significantly important (p>0.05). In addition, it was observed that the latency of the Compound Action Potential (CAP) decreased significantly (p<0.05) in the delayed group. Moreover, histological examinations showed that the number of mononuclear cells was lower (p<0.05) in the laser groups.Although further tests are needed to be more conclusive, these results indicate that the laser therapy accelerates the rate of recovery. Both laser groups had positive results. However, the delayed group showed better recovery. This result may be due to the degeneration during the first-week.Keywords: nerve regeneration, laser, sciatic functional index