Modelling and Analysis of a new Integrated Radiofrequency Ablation and Division Device

Master'sMASTER OF ENGINEERIN

Noninvasive laser vasectomy

Development of a noninvasive vasectomy technique may eliminate male fear of complications (incision, bleeding, infection, and scrotal pain) and result in a more popular procedure. These studies build off previous studies that report the ability to thermally target tissue substructures with near infrared laser radiation while maintaining a healthy superficial layer of tissue through active surface cooling. Initial studies showed the ability to increase the working depth compared to that of common dermatological procedures and the translation into an ex vivo canine model targeting the vas deferens in a noninvasive laser vasectomy. Laser and cooling parameter optimization was required to determine the best possible wavelength for a safe transition to an in vivo canine model. Optical clearing agents were investigated as a mechanism to decrease tissue scattering during in vivo procedures to increase optical penetration depth and reduce the overall power required. Optical and thermal computer models were developed to determine the efficacy for a successful transition into a human model. Common clinical imaging modalities (ultrasound, high frequency ultrasound, and optical coherence tomography) were tested as possible candidates for real-time imaging feedback to determine surgical success. Finally, a noninvasive laser vasectomy prototype clamp incorporating laser, cooling, and control in a single package was designed and tested in vivo. Occlusion of the canine vas deferens able to withstand physiological burst pressures measured postoperative was shown during acute and chronic studies. This procedure is ready for azoospermia and recanalization studies in a clinical setting

Investigation of Heat Therapies using Multi-Scale Models and Statistical Methods

Ph.DDOCTOR OF PHILOSOPH

Models for force control in telesurgical robot systems

Surgical robotics is one of the most rapidly developing fields within robotics. Besides general motion control issues, control engineers often find it challenging to design robotic telesurgery systems, as these have to deal with complex environmental constrains. The unique behavior of soft tissues requires special approaches in both robot control and system modeling in the case of robotic tissue manipulation. Precise control depends on the appropriate modeling of the interaction between the manipulated tissues and the instruments held by the robotic arm, frequently referred to as the tool–tissue interaction. Due to the nature of the physiological environment, the mechatronics of the systems and the time delays, it is difficult to introduce a universal model or a general modeling approach. This paper gives an overview of the emerging problems in the design and modeling of telesurgical systems, analyzing each component, and introducing the most widely employed models. The arising control problems are reviewed in the frames of master–slave type teleoperation, proposing a novel oft tissue model and providing an overview of the possible control approaches

Computational Models and Experimentation for Radiofrequency-based Ablative Techniques

Las técnicas ablativas basadas en energía por radiofrecuencia (RF) se emplean con el fin de lograr un calentamiento seguro y localizado en el tejido biológico. En los últimos años ha habido un rápido crecimiento en el número de nuevos procedimientos médicos que hacen uso de dichas técnicas, lo cual ha ido acompañado de la aparición de nuevos diseños de electrodos y protocolos de aplicación de energía. Sin embargo, existen todavía muchas incógnitas sobre el verdadero comportamiento electro-térmico de los aplicadores de energía, así como de la interacción energía-tejido en aplicaciones concretas. El principal propósito de esta Tesis Doctoral es adquirir un mejor conocimiento de los fenómenos eléctricos y térmicos involucrados en los procesos de calentamiento de tejidos biológicos mediante corrientes de RF. Esto permitirá, por un lado, mejorar la eficacia y seguridad de las técnicas actualmente empleadas en la clínica en campos tan diferentes como la cirugía cardiaca, oncológica o dermatológica; y por otro, sugerir mejoras tecnológicas para el diseño de nuevos aplicadores. La Tesis Doctoral combina dos metodologías ampliamente utilizadas en el campo de la Ingeniería Biomédica, como son el modelado computacional (matemático) y la experimentación (ex vivo e in vivo). En cuanto al área cardiaca, la investigación se ha centrado, por una parte, en mejorar la ablación intraoperatoria de la fibrilación auricular por aproximación epicárdica, es decir, susceptible de ser realizada de forma mínimamente invasiva. Para ello, se ha estudiado mediante modelos matemáticos un sistema de medida de la impedancia epicárdica como método de valoración de la cantidad de grasa previo a la ablación. Por otra parte, se ha estudiado cómo mejorar la ablación de la pared ventricular por aproximación endocárdica-endocárdica (septo interventricular) y endocárdica-epicárdica (pared libre del ventrículo). Con este objetivo, se han comparado mediante modelado por computador la eficacia de los modos de ablación bipolar y unipolar en términos de la transmuralidad de la lesión en la pared ventricular. En lo que respecta al área de cirugía oncológica, la investigación se ha centrado en la resección hepática asistida por RF. Las técnicas de calentamiento por RF deberían ser capaces de minimizar el sangrado intraoperatorio y sellar vasos y ductos mediante la creación de una necrosis coagulativa por calentamiento. Si este calentamiento se produce en las cercanías de grandes vasos, existe un problema potencial de daño a la pared de dicho vaso. En este sentido, se ha evaluado con modelos matemáticos y experimentación in vivo si el efecto del flujo de sangre dentro de un gran vaso es capaz de proteger térmicamente su pared cuando se realiza una resección asistida por RF en sus cercanías. Además, se ha realizado un estudio computacional y experimental ex vivo e in vivo del comportamiento electro-térmico de aplicadores de RF bipolares internamente refrigerados, puesto que representan una opción más segura frente a los monopolares en la medida en que las corrientes de RF fluyen casi exclusivamente por el tejido biológico situado entre ambos electrodos. Respecto al área dermatológica, la investigación se ha centrado en mejorar el tratamiento de enfermedades o desórdenes del tejido subcutáneo (tales como lipomatosis, lipedema, enfermedad de Madelung y celulitis) mediante el estudio teórico de la dosimetría correcta en cada caso. Para ello, se han evaluado los efectos eléctricos, térmicos y termo-elásticos de dos estructuras diferentes de tejido subcutáneo durante el calentamiento por RF, y se ha cuantificado el daño térmico producido en ambas estructuras tras dicho calentamientoGonzález Suárez, A. (2014). Computational Models and Experimentation for Radiofrequency-based Ablative Techniques [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/36502TESI

Smart knives: controlled cutting schemes to enable advanced endoscopic surgery

With the backdrop of the rapidly developing research in Natural Orifice Transluminal Endoscopic Surgery (NOTES), analysis of the literature supported the view that inventing new, controlled tissue dissection methods for flexible endoscopic surgery may be necessary. The literature also confirmed that white space exists for research into and the development of new cutting tools. The strategy of “deconstructing dissection” proposed in this thesis may provide dissection control benefits, which may help address the unique manoeuvring challenges for tissue dissection at flexible endoscopy. This assertion was supported by investigating six embodiments of the strategy which provided varying degrees of enhanced tissue dissection control. Seven additional concepts employing the strategy which were not prototyped also were offered as potential solutions that eventually might contribute evidence in defence of the strategy. One concept for selective ablation — dye-mediated laser ablation — was explored in-depth by theoretical analysis, experimentation and computation. The ablation process was found to behave relatively similar to unmediated laser ablation, but also to depend on cyclic carbonisation for sustained ablation once the dye had disappeared. An Arrhenius model of carbonisation based on the pyrolysis and combustion of wood cellulose was used in a tissue ablation model, which produced reasonable results. Qualitative results from four methods for dye application and speculation on three methods for dye removal complete the framework by which dye-mediated laser ablation might deliver on the promise offered by “deconstructing dissection”. Overall, this work provided the “deconstructing dissection” strategic framework for controlled cutting schemes and offered plausible evidence that the strategy could work by investigating embodiments of the scheme. In particular, dye-mediated laser ablation can provide selective ablation of tissue, and a theoretical model for the method of operation was offered. However, some practical hurdles need to be overcome before it can be useful in a clinical setting

Pre-coagulation of solid organs

Coagulation has and continues to be one of the most important elements in medicine. Issues from a lack of hemostasis range from poorer clinical outcomes to sudden death. The evolution of treatments for hemostasis have evolved from the use of Tamponade with direct pressure and bandages, the use of materials such as cobwebs and dust, the use of heat with hot oil or heated irons, to the use of suture, glues, plasmas, staplers, and electricity. This evolution has continued to bring about the prophylactic use of technology in an effort to prevent blood loss. This change from reactive treatments to proactive continue to be on a localized or superficial basis. One of the largest opportunities to proactively reduce blood loss in surgical patients is during the resection of solid organs such as the liver, kidney, and spleen. Few options have existed to help improve hemostasis short of the complete occlusion of blood supplying the tissue such as in the Pringle Maneuver. Recent studies have begun to show that practices such as this may have a significant detrimental effect on morbidity. It has been found that by applying radio frequency electrical energy in a particular way that large amounts of tissue can be pre-coagulated prior to resection. A series of animal and human clinical work has been completed to help evolve and confirm the method and the device that was created and refined during this effort. During the course of this work fifty-three patients were treated at four institutions on three continents. Average blood loss for liver resections performed with this pre-coagulation technique using the developed device in a multicenter control trail was 3.35 ml/cm2 as compared to 6.09 ml/cm2 (p < 0.05) for resections performed using standard surgical techniques alone. Additionally, the transection time necessary was also reduced from mean value of 27 minutes (2 -- 219 minutes) to 35 minutes (5 -- 65 minutes). Patients treated included those suffering from liver cirrhosis, fatty liver disease, and post chemotherapy fibrosis. From this work the use of pre-coagulation with methods and device developed was shown to be safe and effective for reducing the amount of blood loss and transection time during liver resections

Development and characterisation of holmium and erbium lasers for the ablation of biological tissue

The development of pulsed laser systems operating in the infrared at 2.1 µm and 2.94µm, based on Cr:Tm:Ho:YAG and Er:YAG laser crystals, and the ability of these lasers to ablate biological tissue is reported. Thermal lensing in the laser crystals has been investigated and found to be the main factor restricting the operating ranges of these lasers. Additionally, increases in the threshold of holmium lasers due to thermal population of the lower laser level increases the amount of heat dissipated in the crystal lattice, leading to increased thermal lensing. Thus, the divergence properties of resonators containing these crystals depends, additionally, on the operating temperature. Modelling of the divergence behaviour of resonators based around Cr:Tm:Ho:YAG and Er:YAG laser crystals in simple resonator geometries is demonstrated using computer based ray tracing algorithms. The temporal behaviour of these lasers has been experimentally assessed and compared to a 'rectangular pump pulse' theory. Using this theory it is possible to predict the delay between the start of the excitation pulse and the start of the laser pulse but not the duration of the output pulse. The reasons for this are discussed. Pulses of 2.94µm radiation ablate soft tissue more efficiently than similar pulses of 2.1µm. Mass loss due to laser radiation is shown to be linear with dose for the 2.1µm radiation. However, at 2.94µm mass removal is impeded at high doses by the extension of a charred zone into the ablation crater. Operation at high fluences is required to overcome this problem. However, there is an increase in mechanical damage to surrounding tissue and a change in crater shape at fluences greater than 0.085 J mm-2 coinciding with a significant impulse being imparted to the tissue. The maximum mass loss per unit of delivered energy at 2.1µm and 2.94µm are approximately 48% and 60% of that expected for ablation of a pure water target. Routes for the energy loss are discussed. The energy lost in the form of kinetic energy is determined experimentally to be less than 1% of the total energy delivered. A linear model was found to best described the ablation performance at both wavelengths. The implications of these findings are discussed