Optical techniques for 3D surface reconstruction in computer-assisted laparoscopic surgery

One of the main challenges for computer-assisted surgery (CAS) is to determine the intra-opera- tive morphology and motion of soft-tissues. This information is prerequisite to the registration of multi-modal patient-specific data for enhancing the surgeon’s navigation capabilites by observ- ing beyond exposed tissue surfaces and for providing intelligent control of robotic-assisted in- struments. In minimally invasive surgery (MIS), optical techniques are an increasingly attractive approach for in vivo 3D reconstruction of the soft-tissue surface geometry. This paper reviews the state-of-the-art methods for optical intra-operative 3D reconstruction in laparoscopic surgery and discusses the technical challenges and future perspectives towards clinical translation. With the recent paradigm shift of surgical practice towards MIS and new developments in 3D opti- cal imaging, this is a timely discussion about technologies that could facilitate complex CAS procedures in dynamic and deformable anatomical regions

EndoSLAM Dataset and An Unsupervised Monocular Visual Odometry and Depth Estimation Approach for Endoscopic Videos: Endo-SfMLearner

Deep learning techniques hold promise to develop dense topography reconstruction and pose estimation methods for endoscopic videos. However, currently available datasets do not support effective quantitative benchmarking. In this paper, we introduce a comprehensive endoscopic SLAM dataset consisting of 3D point cloud data for six porcine organs, capsule and standard endoscopy recordings as well as synthetically generated data. A Panda robotic arm, two commercially available capsule endoscopes, two conventional endoscopes with different camera properties, and two high precision 3D scanners were employed to collect data from 8 ex-vivo porcine gastrointestinal (GI)-tract organs. In total, 35 sub-datasets are provided with 6D pose ground truth for the ex-vivo part: 18 sub-dataset for colon, 12 sub-datasets for stomach and 5 sub-datasets for small intestine, while four of these contain polyp-mimicking elevations carried out by an expert gastroenterologist. Synthetic capsule endoscopy frames from GI-tract with both depth and pose annotations are included to facilitate the study of simulation-to-real transfer learning algorithms. Additionally, we propound Endo-SfMLearner, an unsupervised monocular depth and pose estimation method that combines residual networks with spatial attention module in order to dictate the network to focus on distinguishable and highly textured tissue regions. The proposed approach makes use of a brightness-aware photometric loss to improve the robustness under fast frame-to-frame illumination changes. To exemplify the use-case of the EndoSLAM dataset, the performance of Endo-SfMLearner is extensively compared with the state-of-the-art. The codes and the link for the dataset are publicly available at https://github.com/CapsuleEndoscope/EndoSLAM. A video demonstrating the experimental setup and procedure is accessible through https://www.youtube.com/watch?v=G_LCe0aWWdQ.Comment: 27 pages, 16 figure

THULIUM FIBER LASER LITHOTRIPSY

The Thulium Fiber Laser (TFL) has been studied as a potential alternative to the conventional Holmium:YAG laser (Ho:YAG) for the treatment of kidney stones. The TFL is more ideally suited for laser lithotripsy because of the higher absorption coefficient of the emitted wavelength in water, the superior Gaussian profile of the laser beam, and the ability to operate at arbitrary temporal pulse profiles. The higher absorption of the TFL by water helps translate into higher ablation of urinary stones using less energy. The Gaussian spatial beam profile allows the TFL to couple into fibers much smaller than those currently being used for Ho:YAG lithotripsy. Lastly, the ability of arbitrary pulse operation by the TFL allows energy to be delivered to the stone efficiently so as to avoid negative effects (such as burning or bouncing of the stone) while maximizing ablation. Along with these improvements, the unique properties of the TFL have led to more novel techniques that have currently not been used in the clinic, such as the ability to control the movement of stones based on the manner in which the laser energy is delivered. Lastly, the TFL has led to the development of novel fibers, such as the tapered fiber and removable tip fiber, to be used for lithotripsy which can lead to safer and less expensive treatment of urinary stones. Overall, the TFL has been demonstrated as a viable alternative to the conventional Ho:YAG laser and has the potential to advance methods and tools for treatment of kidney stones

Untersuchungen zur laserinduzierten Lithotripsie

Die laserinduzierte Lithotripsie ist eine endoskopische Methode zur Behandlung von Harnsteinleiden. Sie steht in direkter Konkurrenz zur extrakorporalen Stoßwellenlithotripsie (ESWL) und der perkutanen Nephrolitholapaxie (PCNL). Bei der laserinduzierten Lithotripsie wird gepulstes Laserlicht über einen Lichtwellenleiter im Arbeitskanal eines Endoskops direkt auf den Harnstein geleitet und sorgt dort aufgrund photothermischer und mechanischer Effekte für die Zerkleinerung des Steines. Der Ho:YAG Laser (λ: 2.1 μm) gilt aufgrund der hohen Absorption dieser Wellenlänge in Wasser (α: 2.78 mm-1) und der guten Transmission der mittleren-Infrarotstrahlung in Low-OH Glasfasern als Goldstandard für diese Vorgehensweise in der Steintherapie. Die eingebrachte Laserenergie bewirkt aber auch eine Krafteinwirkung auf den Stein und umliegende Fragmente was zu einer Steinbewegung führt (Propulsion). Durch die Propulsion können zurückgestoßene Fragmente schwer auffindbar sein oder die Operation aufgrund zeitintensiven Nachführens des Endoskops erschweren. Dies kann einerseits zu einer erhöhten Rezidivrate durch Fragmentreste oder zu insgesamt längeren Operationszeit führen. Daher wurde ein modellhafter Aufbau zur Quantifizierung von Fragmentierungsraten und Propulsionseinflüssen durch Variation der Laserparameter (Energie pro Puls, Repetitionsrate und optische Pulslänge) bei der Ho:YAG laserinduzierten Lithotripsie entwickelt. Des Weiteren wurden die Fluoreszenzeigenschaften von humanen Nierensteinen mittels spektraler Fluoreszenzmikroskopie bei unterschiedlichen Anregungswellenlängen betrachtet, mit dem Ziel das Auffinden von Steinen und Fragmenten technisch zu vereinfachen. Zur Quantifizierung der Abtragsraten wurde ein Messaufbau konstruiert und im Rahmen von Untersuchungen systematisch verschiedene Laserparameter (Energie (E): 0.5 J/Puls - 2.5 J/Puls, Repetitionsraten (f): 10 Hz - 80 Hz, optische Pulsdauer (t) 0.3 ms - 4 ms an künstlichen Steinen (Bego, Mischverhältnis 15:4, Kantenlänge 5 mm) bewertet. Bei der Fragmentierung (Ablation) wurde insbesondere das sogenannte “Dusting” untersucht. Hierbei ist das Ziel den Stein aufgrund geschickt gewählter Laserparameter zu zerstäuben (Fragmente < 1 mm) und direkt mit den Spülstrom auszuwaschen. Die Untersuchung der Propulsion erfolgte mit einem Messaufbau, bestehend aus einem Plexiglasröhrchen mit einer konisch zulaufenden Innenbohrung (Ø: 8 mm), welches als Führung für den durch bodenseitige Laserapplikation nach oben beschleunigten künstlichen Stein dient. Aufgrund von Hydrodynamik und Schwerkraft wird der Stein in seine Ausgangsposition zurückgebracht. Diese Steinbewegung wird mit einer High-Speed-Kamera (1000 Bilder/s) aufgenommen und per Software in ein Bewegungsprofil umgewandelt. Durch Bestimmung der Steigung für jede der aufsteigenden Flanken, respektive der mittleren Geschwindigkeit in diesem Zeitintervall, kann eine Quantifizierung der Propulsion erreicht werden. Von Patienten stammende Harnsteine wurden mit einem Fluoreszenzmikroskop in vitro für die Anregungswellenlängen (400±5) nm, (450±10) nm und (550±5) nm auf ihre Fluoreszenz untersucht. Das remittierte Fluoreszenzlicht durchlief vor der spektralen Detektion je nach Anregungslicht verschiedene Langpassfilter (λ > 470 nm, λ > 520 nm, λ > 590 nm). Zusätzlich wurde in vivo die Fluoreszenzantwort zweier Nierensteine während einer OP bei grüner Anregung (λ = 500- 570 nm) im Spektralbereich oberhalb 610 nm mit einem Endoskopkamerasystem beobachtet. Die optischen Gewebeeigenschaften, Absorption und reduzierte Streuung, wurden am Schweinemodell (Leber, Lunge, Gehirn, Muskel) über ortsaufgelöste Remissions- und Ulbrichtkugelmessungen bestimmt. Die Bestimmung der optischen Eigenschaften von sezierten und homogenisierten Gewebeproben am Schweinemodell fokussierte sich auf die Vergleichbarkeit und Reproduzierbarkeit der Messergebnisse für diese beiden Präparationsmethoden. Neue Ho:YAG Lasersysteme mit vier Laserkavitäten bieten eine große Variation an Laserparametern: Repetitionsraten bis zu 100 Hz, Pulsenergien bis 6 J und Pulslängen von bis zu 4 ms. Durch die hohen eingebrachten mittleren optischen Leistungen (bis zu 120 W) können Kollateralschäden an umliegenden Geweben entweder durch direkten Laserbeschuss oder durch die Erhitzung des Gemisches aus Harn und Spülflüssigkeit kommen. Die durchgeführten Experimente zur Bestimmung der optischen Eigenschaften sind auch für Laserlicht den mittleren Infrarotbereich anwendbar, bilden die Basis für Untersuchungen zu möglichen Kollateralschäden bei medizinischen Laseranwendungen und können somit wichtige Anhaltspunkte für zukünftige technische Entwicklung von medizinischen Lasergeräten mit sich bringen

Multispectral image analysis in laparoscopy – A machine learning approach to live perfusion monitoring

Modern visceral surgery is often performed through small incisions. Compared to open surgery, these minimally invasive interventions result in smaller scars, fewer complications and a quicker recovery. While to the patients benefit, it has the drawback of limiting the physician’s perception largely to that of visual feedback through a camera mounted on a rod lens: the laparoscope. Conventional laparoscopes are limited by “imitating” the human eye. Multispectral cameras remove this arbitrary restriction of recording only red, green and blue colors. Instead, they capture many specific bands of light. Although these could help characterize important indications such as ischemia and early stage adenoma, the lack of powerful digital image processing prevents realizing the technique’s full potential. The primary objective of this thesis was to pioneer fluent functional multispectral imaging (MSI) in laparoscopy. The main technical obstacles were: (1) The lack of image analysis concepts that provide both high accuracy and speed. (2) Multispectral image recording is slow, typically ranging from seconds to minutes. (3) Obtaining a quantitative ground truth for the measurements is hard or even impossible. To overcome these hurdles and enable functional laparoscopy, for the first time in this field physical models are combined with powerful machine learning techniques. The physical model is employed to create highly accurate simulations, which in turn teach the algorithm to rapidly relate multispectral pixels to underlying functional changes. To reduce the domain shift introduced by learning from simulations, a novel transfer learning approach automatically adapts generic simulations to match almost arbitrary recordings of visceral tissue. In combination with the only available video-rate capable multispectral sensor, the method pioneers fluent perfusion monitoring with MSI. This system was carefully tested in a multistage process, involving in silico quantitative evaluations, tissue phantoms and a porcine study. Clinical applicability was ensured through in-patient recordings in the context of partial nephrectomy; in these, the novel system characterized ischemia live during the intervention. Verified against a fluorescence reference, the results indicate that fluent, non-invasive ischemia detection and monitoring is now possible. In conclusion, this thesis presents the first multispectral laparoscope capable of videorate functional analysis. The system was successfully evaluated in in-patient trials, and future work should be directed towards evaluation of the system in a larger study. Due to the broad applicability and the large potential clinical benefit of the presented functional estimation approach, I am confident the descendants of this system are an integral part of the next generation OR

Endoscopic Optical Coherence Tomography: Design and Application

This thesis presents an investigation on endoscopic optical coherence tomography (OCT). As a noninvasive imaging modality, OCT emerges as an increasingly important diagnostic tool for many clinical applications. Despite of many of its merits, such as high resolution and depth resolvability, a major limitation is the relatively shallow penetration depth in tissue (about 2∼3 mm). This is mainly due to tissue scattering and absorption. To overcome this limitation, people have been developing many different endoscopic OCT systems. By utilizing a minimally invasive endoscope, the OCT probing beam can be brought to the close vicinity of the tissue of interest and bypass the scattering of intervening tissues so that it can collect the reflected light signal from desired depth and provide a clear image representing the physiological structure of the region, which can not be disclosed by traditional OCT. In this thesis, three endoscope designs have been studied. While they rely on vastly different principles, they all converge to solve this long-standing problem. A hand-held endoscope with manual scanning is first explored. When a user is holding a hand- held endoscope to examine samples, the movement of the device provides a natural scanning. We proposed and implemented an optical tracking system to estimate and record the trajectory of the device. By registering the OCT axial scan with the spatial information obtained from the tracking system, one can use this system to simply ‘paint’ a desired volume and get any arbitrary scanning pattern by manually waving the endoscope over the region of interest. The accuracy of the tracking system was measured to be about 10 microns, which is comparable to the lateral resolution of most OCT system. Targeted phantom sample and biological samples were manually scanned and the reconstructed images verified the method. Next, we investigated a mechanical way to steer the beam in an OCT endoscope, which is termed as Paired-angle-rotation scanning (PARS). This concept was proposed by my colleague and we further developed this technology by enhancing the longevity of the device, reducing the diameter of the probe, and shrinking down the form factor of the hand-piece. Several families of probes have been designed and fabricated with various optical performances. They have been applied to different applications, including the collector channel examination for glaucoma stent implantation, and vitreous remnant detection during live animal vitrectomy. Lastly a novel non-moving scanning method has been devised. This approach is based on the EO effect of a KTN crystal. With Ohmic contact of the electrodes, the KTN crystal can exhibit a special mode of EO effect, termed as space-charge-controlled electro-optic effect, where the carrier electron will be injected into the material via the Ohmic contact. By applying a high voltage across the material, a linear phase profile can be built under this mode, which in turn deflects the light beam passing through. We constructed a relay telescope to adapt the KTN deflector into a bench top OCT scanning system. One of major technical challenges for this system is the strong chromatic dispersion of KTN crystal within the wavelength band of OCT system. We investigated its impact on the acquired OCT images and proposed a new approach to estimate and compensate the actual dispersion. Comparing with traditional methods, the new method is more computational efficient and accurate. Some biological samples were scanned by this KTN based system. The acquired images justified the feasibility of the usage of this system into a endoscopy setting. My research above all aims to provide solutions to implement an OCT endoscope. As technology evolves from manual, to mechanical, and to electrical approaches, different solutions are presented. Since all have their own advantages and disadvantages, one has to determine the actual requirements and select the best fit for a specific application.</p

Untersuchungen zur laserinduzierten Lithotripsie

Die laserinduzierte Lithotripsie ist eine endoskopische Methode zur Behandlung von Harnsteinleiden. Sie steht in direkter Konkurrenz zur extrakorporalen Stoßwellenlithotripsie (ESWL) und der perkutanen Nephrolitholapaxie (PCNL). Bei der laserinduzierten Lithotripsie wird gepulstes Laserlicht über einen Lichtwellenleiter im Arbeitskanal eines Endoskops direkt auf den Harnstein geleitet und sorgt dort aufgrund photothermischer und mechanischer Effekte für die Zerkleinerung des Steines. Der Ho:YAG Laser (λ: 2.1 μm) gilt aufgrund der hohen Absorption dieser Wellenlänge in Wasser (α: 2.78 mm-1) und der guten Transmission der mittleren-Infrarotstrahlung in Low-OH Glasfasern als Goldstandard für diese Vorgehensweise in der Steintherapie. Die eingebrachte Laserenergie bewirkt aber auch eine Krafteinwirkung auf den Stein und umliegende Fragmente was zu einer Steinbewegung führt (Propulsion). Durch die Propulsion können zurückgestoßene Fragmente schwer auffindbar sein oder die Operation aufgrund zeitintensiven Nachführens des Endoskops erschweren. Dies kann einerseits zu einer erhöhten Rezidivrate durch Fragmentreste oder zu insgesamt längeren Operationszeit führen. Daher wurde ein modellhafter Aufbau zur Quantifizierung von Fragmentierungsraten und Propulsionseinflüssen durch Variation der Laserparameter (Energie pro Puls, Repetitionsrate und optische Pulslänge) bei der Ho:YAG laserinduzierten Lithotripsie entwickelt. Des Weiteren wurden die Fluoreszenzeigenschaften von humanen Nierensteinen mittels spektraler Fluoreszenzmikroskopie bei unterschiedlichen Anregungswellenlängen betrachtet, mit dem Ziel das Auffinden von Steinen und Fragmenten technisch zu vereinfachen. Zur Quantifizierung der Abtragsraten wurde ein Messaufbau konstruiert und im Rahmen von Untersuchungen systematisch verschiedene Laserparameter (Energie (E): 0.5 J/Puls - 2.5 J/Puls, Repetitionsraten (f): 10 Hz - 80 Hz, optische Pulsdauer (t) 0.3 ms - 4 ms an künstlichen Steinen (Bego, Mischverhältnis 15:4, Kantenlänge 5 mm) bewertet. Bei der Fragmentierung (Ablation) wurde insbesondere das sogenannte “Dusting” untersucht. Hierbei ist das Ziel den Stein aufgrund geschickt gewählter Laserparameter zu zerstäuben (Fragmente < 1 mm) und direkt mit den Spülstrom auszuwaschen. Die Untersuchung der Propulsion erfolgte mit einem Messaufbau, bestehend aus einem Plexiglasröhrchen mit einer konisch zulaufenden Innenbohrung (Ø: 8 mm), welches als Führung für den durch bodenseitige Laserapplikation nach oben beschleunigten künstlichen Stein dient. Aufgrund von Hydrodynamik und Schwerkraft wird der Stein in seine Ausgangsposition zurückgebracht. Diese Steinbewegung wird mit einer High-Speed-Kamera (1000 Bilder/s) aufgenommen und per Software in ein Bewegungsprofil umgewandelt. Durch Bestimmung der Steigung für jede der aufsteigenden Flanken, respektive der mittleren Geschwindigkeit in diesem Zeitintervall, kann eine Quantifizierung der Propulsion erreicht werden. Von Patienten stammende Harnsteine wurden mit einem Fluoreszenzmikroskop in vitro für die Anregungswellenlängen (400±5) nm, (450±10) nm und (550±5) nm auf ihre Fluoreszenz untersucht. Das remittierte Fluoreszenzlicht durchlief vor der spektralen Detektion je nach Anregungslicht verschiedene Langpassfilter (λ > 470 nm, λ > 520 nm, λ > 590 nm). Zusätzlich wurde in vivo die Fluoreszenzantwort zweier Nierensteine während einer OP bei grüner Anregung (λ = 500- 570 nm) im Spektralbereich oberhalb 610 nm mit einem Endoskopkamerasystem beobachtet. Die optischen Gewebeeigenschaften, Absorption und reduzierte Streuung, wurden am Schweinemodell (Leber, Lunge, Gehirn, Muskel) über ortsaufgelöste Remissions- und Ulbrichtkugelmessungen bestimmt. Die Bestimmung der optischen Eigenschaften von sezierten und homogenisierten Gewebeproben am Schweinemodell fokussierte sich auf die Vergleichbarkeit und Reproduzierbarkeit der Messergebnisse für diese beiden Präparationsmethoden. Neue Ho:YAG Lasersysteme mit vier Laserkavitäten bieten eine große Variation an Laserparametern: Repetitionsraten bis zu 100 Hz, Pulsenergien bis 6 J und Pulslängen von bis zu 4 ms. Durch die hohen eingebrachten mittleren optischen Leistungen (bis zu 120 W) können Kollateralschäden an umliegenden Geweben entweder durch direkten Laserbeschuss oder durch die Erhitzung des Gemisches aus Harn und Spülflüssigkeit kommen. Die durchgeführten Experimente zur Bestimmung der optischen Eigenschaften sind auch für Laserlicht den mittleren Infrarotbereich anwendbar, bilden die Basis für Untersuchungen zu möglichen Kollateralschäden bei medizinischen Laseranwendungen und können somit wichtige Anhaltspunkte für zukünftige technische Entwicklung von medizinischen Lasergeräten mit sich bringen

Surgical Subtask Automation for Intraluminal Procedures using Deep Reinforcement Learning

Intraluminal procedures have opened up a new sub-field of minimally invasive surgery that use flexible instruments to navigate through complex luminal structures of the body, resulting in reduced invasiveness and improved patient benefits. One of the major challenges in this field is the accurate and precise control of the instrument inside the human body. Robotics has emerged as a promising solution to this problem. However, to achieve successful robotic intraluminal interventions, the control of the instrument needs to be automated to a large extent. The thesis first examines the state-of-the-art in intraluminal surgical robotics and identifies the key challenges in this field, which include the need for safe and effective tool manipulation, and the ability to adapt to unexpected changes in the luminal environment. To address these challenges, the thesis proposes several levels of autonomy that enable the robotic system to perform individual subtasks autonomously, while still allowing the surgeon to retain overall control of the procedure. The approach facilitates the development of specialized algorithms such as Deep Reinforcement Learning (DRL) for subtasks like navigation and tissue manipulation to produce robust surgical gestures. Additionally, the thesis proposes a safety framework that provides formal guarantees to prevent risky actions. The presented approaches are evaluated through a series of experiments using simulation and robotic platforms. The experiments demonstrate that subtask automation can improve the accuracy and efficiency of tool positioning and tissue manipulation, while also reducing the cognitive load on the surgeon. The results of this research have the potential to improve the reliability and safety of intraluminal surgical interventions, ultimately leading to better outcomes for patients and surgeons

Navigation system based in motion tracking sensor for percutaneous renal access

Tese de Doutoramento em Engenharia BiomédicaMinimally-invasive kidney interventions are daily performed to diagnose and treat several renal diseases. Percutaneous renal access (PRA) is an essential but challenging stage for most of these procedures, since its outcome is directly linked to the physician’s ability to precisely visualize and reach the anatomical target. Nowadays, PRA is always guided with medical imaging assistance, most frequently using X-ray based imaging (e.g. fluoroscopy). Thus, radiation on the surgical theater represents a major risk to the medical team, where its exclusion from PRA has a direct impact diminishing the dose exposure on both patients and physicians. To solve the referred problems this thesis aims to develop a new hardware/software framework to intuitively and safely guide the surgeon during PRA planning and puncturing. In terms of surgical planning, a set of methodologies were developed to increase the certainty of reaching a specific target inside the kidney. The most relevant abdominal structures for PRA were automatically clustered into different 3D volumes. For that, primitive volumes were merged as a local optimization problem using the minimum description length principle and image statistical properties. A multi-volume Ray Cast method was then used to highlight each segmented volume. Results show that it is possible to detect all abdominal structures surrounding the kidney, with the ability to correctly estimate a virtual trajectory. Concerning the percutaneous puncturing stage, either an electromagnetic or optical solution were developed and tested in multiple in vitro, in vivo and ex vivo trials. The optical tracking solution aids in establishing the desired puncture site and choosing the best virtual puncture trajectory. However, this system required a line of sight to different optical markers placed at the needle base, limiting the accuracy when tracking inside the human body. Results show that the needle tip can deflect from its initial straight line trajectory with an error higher than 3 mm. Moreover, a complex registration procedure and initial setup is needed. On the other hand, a real-time electromagnetic tracking was developed. Hereto, a catheter was inserted trans-urethrally towards the renal target. This catheter has a position and orientation electromagnetic sensor on its tip that function as a real-time target locator. Then, a needle integrating a similar sensor is used. From the data provided by both sensors, one computes a virtual puncture trajectory, which is displayed in a 3D visualization software. In vivo tests showed a median renal and ureteral puncture times of 19 and 51 seconds, respectively (range 14 to 45 and 45 to 67 seconds). Such results represent a puncture time improvement between 75% and 85% when comparing to state of the art methods. 3D sound and vibrotactile feedback were also developed to provide additional information about the needle orientation. By using these kind of feedback, it was verified that the surgeon tends to follow a virtual puncture trajectory with a reduced amount of deviations from the ideal trajectory, being able to anticipate any movement even without looking to a monitor. Best results show that 3D sound sources were correctly identified 79.2 ± 8.1% of times with an average angulation error of 10.4º degrees. Vibration sources were accurately identified 91.1 ± 3.6% of times with an average angulation error of 8.0º degrees. Additionally to the EMT framework, three circular ultrasound transducers were built with a needle working channel. One explored different manufacture fabrication setups in terms of the piezoelectric materials, transducer construction, single vs. multi array configurations, backing and matching material design. The A-scan signals retrieved from each transducer were filtered and processed to automatically detect reflected echoes and to alert the surgeon when undesirable anatomical structures are in between the puncture path. The transducers were mapped in a water tank and tested in a study involving 45 phantoms. Results showed that the beam cross-sectional area oscillates around the ceramics radius and it was possible to automatically detect echo signals in phantoms with length higher than 80 mm. Hereupon, it is expected that the introduction of the proposed system on the PRA procedure, will allow to guide the surgeon through the optimal path towards the precise kidney target, increasing surgeon’s confidence and reducing complications (e.g. organ perforation) during PRA. Moreover, the developed framework has the potential to make the PRA free of radiation for both patient and surgeon and to broad the use of PRA to less specialized surgeons.Intervenções renais minimamente invasivas são realizadas diariamente para o tratamento e diagnóstico de várias doenças renais. O acesso renal percutâneo (ARP) é uma etapa essencial e desafiante na maior parte destes procedimentos. O seu resultado encontra-se diretamente relacionado com a capacidade do cirurgião visualizar e atingir com precisão o alvo anatómico. Hoje em dia, o ARP é sempre guiado com recurso a sistemas imagiológicos, na maior parte das vezes baseados em raios-X (p.e. a fluoroscopia). A radiação destes sistemas nas salas cirúrgicas representa um grande risco para a equipa médica, aonde a sua remoção levará a um impacto direto na diminuição da dose exposta aos pacientes e cirurgiões. De modo a resolver os problemas existentes, esta tese tem como objetivo o desenvolvimento de uma framework de hardware/software que permita, de forma intuitiva e segura, guiar o cirurgião durante o planeamento e punção do ARP. Em termos de planeamento, foi desenvolvido um conjunto de metodologias de modo a aumentar a eficácia com que o alvo anatómico é alcançado. As estruturas abdominais mais relevantes para o procedimento de ARP, foram automaticamente agrupadas em volumes 3D, através de um problema de optimização global com base no princípio de “minimum description length” e propriedades estatísticas da imagem. Por fim, um procedimento de Ray Cast, com múltiplas funções de transferência, foi utilizado para enfatizar as estruturas segmentadas. Os resultados mostram que é possível detetar todas as estruturas abdominais envolventes ao rim, com a capacidade para estimar corretamente uma trajetória virtual. No que diz respeito à fase de punção percutânea, foram testadas duas soluções de deteção de movimento (ótica e eletromagnética) em múltiplos ensaios in vitro, in vivo e ex vivo. A solução baseada em sensores óticos ajudou no cálculo do melhor ponto de punção e na definição da melhor trajetória a seguir. Contudo, este sistema necessita de uma linha de visão com diferentes marcadores óticos acoplados à base da agulha, limitando a precisão com que a agulha é detetada no interior do corpo humano. Os resultados indicam que a agulha pode sofrer deflexões à medida que vai sendo inserida, com erros superiores a 3 mm. Por outro lado, foi desenvolvida e testada uma solução com base em sensores eletromagnéticos. Para tal, um cateter que integra um sensor de posição e orientação na sua ponta, foi colocado por via trans-uretral junto do alvo renal. De seguida, uma agulha, integrando um sensor semelhante, é utilizada para a punção percutânea. A partir da diferença espacial de ambos os sensores, é possível gerar uma trajetória de punção virtual. A mediana do tempo necessário para puncionar o rim e ureter, segundo esta trajetória, foi de 19 e 51 segundos, respetivamente (variações de 14 a 45 e 45 a 67 segundos). Estes resultados representam uma melhoria do tempo de punção entre 75% e 85%, quando comparados com o estado da arte dos métodos atuais. Além do feedback visual, som 3D e feedback vibratório foram explorados de modo a fornecer informações complementares da posição da agulha. Verificou-se que com este tipo de feedback, o cirurgião tende a seguir uma trajetória de punção com desvios mínimos, sendo igualmente capaz de antecipar qualquer movimento, mesmo sem olhar para o monitor. Fontes de som e vibração podem ser corretamente detetadas em 79,2 ± 8,1% e 91,1 ± 3,6%, com erros médios de angulação de 10.4º e 8.0 graus, respetivamente. Adicionalmente ao sistema de navegação, foram também produzidos três transdutores de ultrassom circulares com um canal de trabalho para a agulha. Para tal, foram exploradas diferentes configurações de fabricação em termos de materiais piezoelétricos, transdutores multi-array ou singulares e espessura/material de layers de suporte. Os sinais originados em cada transdutor foram filtrados e processados de modo a detetar de forma automática os ecos refletidos, e assim, alertar o cirurgião quando existem variações anatómicas ao longo do caminho de punção. Os transdutores foram mapeados num tanque de água e testados em 45 phantoms. Os resultados mostraram que o feixe de área em corte transversal oscila em torno do raio de cerâmica, e que os ecos refletidos são detetados em phantoms com comprimentos superiores a 80 mm. Desta forma, é expectável que a introdução deste novo sistema a nível do ARP permitirá conduzir o cirurgião ao longo do caminho de punção ideal, aumentado a confiança do cirurgião e reduzindo possíveis complicações (p.e. a perfuração dos órgãos). Além disso, de realçar que este sistema apresenta o potencial de tornar o ARP livre de radiação e alarga-lo a cirurgiões menos especializados.The present work was only possible thanks to the support by the Portuguese Science and Technology Foundation through the PhD grant with reference SFRH/BD/74276/2010 funded by FCT/MEC (PIDDAC) and by Fundo Europeu de Desenvolvimento Regional (FEDER), Programa COMPETE - Programa Operacional Factores de Competitividade (POFC) do QREN