Browsing by Subject "Laser ablation."

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Open Access
Imitation of radiofrequency ablation with fiber delivered laser system for magnetic resonance guided treatment of atrial fibrillation
(2010) Kerse, M. Can
Atrial Fibrillation (AF) is among the most common cardiac arrhythmias with a high risk of mortality and morbidity. As a cure several minimally invasive catheter approaches are performed under imaging guidance. These treatments imitate linear and transmural cuts and sutures along the atrial walls similar to the widely accepted surgical Cox Maze procedure to block undesired currents. Catheter delivery of RF energy to the cardiac chamber is widely used and approved as safe and successful. The operation is commonly performed under X-Ray which is deprived of soft tissue contrast. Besides, combination of the image with ECG (electrocardiogram) data makes the operation technically difficult and time consuming. Due to the long exposure times, X-Ray burns may be seen on the patient. MR images can be taken during RF ablation with proper matching and tuning circuits, however, during the operation RF and ECG catheters may cause artifacts in the image for some orientations. On the other hand, fiber delivery of laser energy has no significant MR compatibility issues and can be used under MR guidance. Nevertheless, MR guided laser ablation is not in clinical practice as a minimally invasive technique for curing AF possibly because of the risk of perforating the myocardial wall. Excess light intensity at the end of the fiber tip causes rapid changes in the temperature gradients which may cause charring. This is an undesired effect and especially in cardiac ablations, light intensity should be diffused. There are several diffusing tip designs to emit light in cylindrical symmetry, but, due to their orientation with respect to the cardiac chamber, common RF delivery methods cannot be applied directly. In this thesis, we propose a novel multiple fiber laser energy delivery with catheter approach and a system that imitates the scars created with RF probes under MR guidance. The system closely imitates the ablation pattern of RF delivery and therefore is expected to have quick adaptation by physicians. As a proof of principle, we used 3 fibers oriented in different directions and obtained real time MR thermometry maps of the ex-vivo and in-vitro ablation zones during laser delivery. In addition, various light diffusion methods are considered for single fiber power delivery. We believe the combination of these methods will be the solution for the MR compatible RF laser ablation system.
Open Access
Laser synthesized gold nanoparticles for high sensitive strain gauges
(2013) Burzhuev, Salamat
Recently, the conduction properties of nanoparticle films have received great deal of attention due to their unique properties attributed to quantum tunneling effect. Quantum tunneling effect, highly dependent on quantum barrier height and width, is very attractive for sensor applications. Resistive strain gauges based on gold nanoparticle (Au-NP) films show high strain sensitivity. These strain gauges are applicable for miniature applications because of its size. In addition, this nanoparticle films could be also used for various applications such as pressure and vapor sensors. Clean surfaces of laser generated Au-NPs provide high tunneling decay constant. Therefore, these films are promising for high sensitive sensor applications. In our study, the Au-NPs were directly synthesized in deionized water by nanosecond laser ablation method. The clean surface, size and aggregate clusters of Au-NPs offer advantages for high sensitivity strain sensor. We prepared Au-NPs films on flexible PDMS substrate by using hands-on drop-cast method. To obtain high gauge factor, we also investigated the nanoparticle concentration on the thin films. Laser-generated AuNPs films demonstrated gauge factor of ∼300 for higher than 0.22% strain and ∼80 for the strain lower than 0.22%, which is favorably comparable to reported sensitivities for strain sensors based on Au-NPs. Mechanical characterizations for the prolonged working durations suggest long term stability of these strain sensors. We discuss several models describing conductance of Au-NP films in low and high strain regimes. To the best of our knowledge, the conduction of laser generated Au-NP films has not been studied up to date, and it is the first study that shows high strain sensitivity of these films. Au-NP films may be promising for sensor applications.
Open Access
Synthesization of noble metal nanoparticles by pulsed laser ablation method in liquids and thin film applications
(2012) Vural, Hüseyin Avni
Pulsed Laser Ablation in Liquid (PLAL) is promising, alternative, easy, fast and free of agent method for synthesization of nanoparticles (NPs). Various kinds of NPs can be synthesized easily by PLAL, such as base metals, noble metals, semiconductors, nanoalloys, magnetic and core–shell nanostructures. Additionally, crystallized NPs can be easily obtained in one-step procedure by PLAL without subsequent heat-treatments. Synthesization of gold (Au), silver (Ag) and platinum (Pt) NPs with PLAL using Nd: YLF laser (Q-Switched Laser, 527 nm wavelength, 16 W average power, 110 ns pulse duration, and 16 mJ pulse energy for 1 kHz) in different liquid environments is reported. Firstly, Ag, Au and Pt NPs have been synthesized with pulsed Nd: YLF laser in deionized water. Secondly, these NPs have been synthesized in methanol under similar conditions. Colloidal NP solutions are then characterized with Transmission Electron Microscopy, Scanning Electron Microscopy, X-Ray Photoelectron Spectrophotometer, X-Ray Diffractometer and UV-Vis Photospectrometer analysis techniques.In the second part, applications of noble metal nanoparticles have been investigated. Firstly, Au and Ag NPs have been synthesized in Polyvinylpyrolidone solution in order to prepare nanofibrous composites. The Au and Ag NPs embedded in nanofibrous composites then characterized with UV-Vis Photospectrometer and Transmission Electron Microscopy. In addition, AuNPs have been synthesized with varying energies of laser (9,2 mJ, 12 mJ and 16 mJ for 1kHz) in order to understand the role of laser energy on PLAL. Finally, thin-film applications also presented: Pulsed Laser Deposition by PLAL and simple spin-coating deposition with AuNPs synthesized in methanol.