The formation of kidney stones is the third most common urological disease worldwide. In Italy, every year 100.000 new patients are affected by kidney stones. The most common surgical procedures performed to remove the stones are Extracorporeal Shock Wave Lithotripsy (EWSL), Percutaneous Nephrolithotomy (PCNL), and Flexible Ureteroscopy (fURS). EWSL is a minimally invasive surgery (MIS) technique that uses ultrasound waves to break up the stones into small pieces that can be then expelled in the urine. PCNL consists of the removal of stones using a scope inserted through a small incision performed in the back of the patient. It is efficient for large stones, but it is more invasive. fURS, differently, consist of the passage of a flexible endoscope, called ureteroscope, through the urethra and the bladder up to the ureter to collect and remove the stones. Compared to the first two interventions, fURS has some advantages. First, as it is minimally invasive, the risks of infection are minimized, and patient recovery is faster. Compared to EWSL, also a MIS, it has the advantage of being independent of the stone composition. In fact, some stone components (i.e. calcium oxalate monohydrate, brushite, or cystine) are not reactive to ultrasounds, thus leading to the failure of this technique. Moreover, fURS has been proven as the optimal choice for patients considered more fragile (i.e. pregnant women, patients affected by renal anomalies, and patients under anticoagulant treatment). For those reasons, fURS is the first choice procedure in presence of intermediate size stones. The main drawback of fURS is that finding the ureter orifice (UO) is challenging even for the most experienced surgeons. That is why they always perform a cystoscopy before fURS. A cystoscopy is an intervention where an endoscope is inserted in the bladder of the patient (passing through the urethra) to inspect the bladder. Surgeons, looking at the images reported by the endoscope camera, aim in trying to orient themselves in the bladder, to localize and cannulate the orifice. However, this can lead to two unfortunate consequences. The first is that, even with cystoscopy, sometimes the UO isn’t found, and so the intervention fails. The second is that trying to enter and cannulate the UO can result in unwanted trauma to the orifice or intramural mucosa, making any subsequent ureteroscopy difficult. Moreover, many surgeons report orthopedic complaints, due to the suboptimal posture they’re keeping while performing the interventions. Trying to overcome the limits of fURS, this thesis proposes a design of a ureteroscope prototype and a path planning strategy specifically for it. The idea is to help the surgeon finding the orifice with the visual support of a pre-planned path, while he controls remotely the ureteroscope prototype. Having a pre-operative path, in fact, could reduce the surgeon’s burden and cystoscopy could be avoided. Easing the task of finding the orifice, its cannulation wouldn’t be necessary. Designing a flexible robot comes with some challenges determined by its future environment and use. In this case, the prototype is required to have a small diameter, to have high axial stiffness to allow reliable control, and low bending stiffness to allow flexibility. It needs to have bidirectional maneuverability and its control needs to be user-friendly. The prototype is composed of two independent steerable segments and a rigid shaft. Each segment is steerable in two directions. The device is 3D printed in one step (no need of post-assembly) and is tendon-driven. Each segment is controlled by 4 tendons. Each tendon is controlled by a stepper motor. Motor control relies on joysticks. At this stage of research, the prototype is manually-driven. Next version of it will investigate automatic control. The path planning strategy aims in helping the surgeon guide the ureteroscope in the urethra and the bladder of the patient, and in finding the UO. The working space of the robot is composed of the urethra and the bladder. Those organs are made of soft tissue, which easily undergoes deformation due to gravity and other factors. Therefore, an innovative path planning strategy was needed. The strategy is created by extracting information from a rendered bladder model, created using the average male urethra diameter and bladder height, length, and width. The model is customizable, in fact its morphological parameters can be adapted to each patient taking data from CT scans. CT scans are, in fact, commonly taken before such an intervention. The algorithm is made of two different phases that were adopted to adapt the algorithm to the anatomic structure involved in that part of the path. When the device is inserted in the urethra, being the diameter of the lumen small and the structure delicate, the path is created to make the device proceed along the axis of the lumen. This will prevent the device from hitting the walls of the urethra. When the device enters the bladder, the robot will proceed towards the UO. The orifice is located thanks to information extracted from the customized urinary system model. The code was written using Python. Some validation experiments have been conducted. Three participants have been asked to perform the trials. Experiments were done to test if human control could easily move the prototype, if this one could properly steer inside a phantom model and if the path designed could guide participants in steering the prototype towards the orifice. Two different experiments were performed. The experiments consist of participants steering the prototype tip towards the orifice of a silicon bladder and urethra phantom model using two different strategies. During the first modality of the experiments, the participant is moving the prototype towards the target (= UO of a phantom bladder) while he/she is given directions from another user looking at the scene. During the second modality of the experiments, the participant has to reach the target (same as the one in the first modality) steering the prototype tip while looking at the computer screen. This displays the path designed and, superimposed to it, the real-time position of the tip. The segments of the prototype are controlled remotely by joysticks controlled by the participants. Both left and right orifices of the phantom model have been used as targets. For each orifice, three trials have been performed in each mode. The tip position in space was recorded in all trials, exploiting electromagnetic tracking. The path made by the tip in each trial has been plotted, together with the path designed. The lengths of each path have been calculated, and a Student’s T-Test has been performed to see if any statistically significant difference was present between the paths lengths of the two experiments. Moreover, the time needed in each trial to complete the task has been recorded. The experiments and the analysis of the collected data enhance both promising and improvable aspects of this research. The prototype can steer easily in the phantom model and proves to be axially and torsionally stiff but flexible at the same time. The path designed guides the users correctly into the bladder and towards the proximity of the target. The length of the paths recorded during the second experiment is lower, as the participants tend to be more focused and to not err when having to reach the target following the displayed path. However, the differences are not statistically significant. The results not only appeared to be promising but they also threw light into future improvements and additions in the setup. For example, the integration of an endoscope camera and of a force sensor to alert risks of damage during the device insertion in the urethra could be of benefit and should be implemented in a future prototype.
L’urolitiasi, ovvero la formazione di calcoli renali nel sistema urinario, è la terza patologia urologica più diffusa al mondo. Solamente in Italia, ad esempio, ogni anno vengono diagnosticati 100.000 nuovi pazienti. Quando i calcoli raggiungono una dimensione maggiore di 5 mm in diametro possono causare complicazioni, quali il blocco dell’uretere e dolore addominale, ed è pertanto necessario un intervento chirurgico per la loro rimozione. Attualmente, i calcoli vengono trattati con maggiore frequenza tramite le seguenti tecniche: litotrissia extracorporea a onde d’urto, nefrolitotomia e ureteroscopia flessibile (detta anche fURS). La prima è una tecnica di chirurgia mininvasiva che sfrutta le onde d’urto per rompere i nefroliti in pezzi di dimensione minore, in modo tale che riescano poi ad essere espulsi tramite il tratto urinario. È una terapia efficace ma, talvolta, alcuni componenti chimici dei calcoli, come ad esempio monoidrato di calcio, brushite o cistina, sono resistenti alle onde, rendendo quindi inefficace il trattamento. La nefrolitotomia, invece, è una tecnica che prevede la rimozione dei calcoli tramite un endoscopio inserito in un’incisione che viene praticata nella schiena del paziente. Con questo intervento si riescono a rimuovere nefroliti anche di dimensioni maggiori; tuttavia, la tecnica risulta essere meno invasiva rispetto alle altre due. L’ureteroscopia flessibile, invece, consiste nel passaggio di un endoscopio flessibile che inserito nell’uretra del paziente e attraverso la vescica, raggiunge l’uretere, fino ad arrivare ai nefroliti. Rispetto ai due precedenti trattamenti, la fURS ha il vantaggio di essere una tecnica mininvasiva, dato che sfrutta i lumi anatomici per il passaggio dell’endoscopio, riducendo quindi i rischi legati a possibili infezioni e i tempi di recupero del paziente. Questo metodo è inoltre sicuro e preferito per quelle categorie di pazienti considerati a rischio, quali donne in gravidanza, pazienti affetti da anomalie renali o in trattamento di anticoagulanti. Per queste ragioni, è la tecnica preferita in casi di calcoli di dimensioni intermedie. La difficoltà maggiore durante l’intervento, riscontrata anche dai chirurghi più esperti, è la localizzazione dell’orifizio ureterale (UO). Motivo per cui, prima della procedura, viene svolta una cistoscopia. Questo intervento viene svolto con un endoscopio inserito nella vescica del paziente, tramite l’uretra, per ispezionare la vescica con la camera dell’endoscopio, cercando di localizzare l’UO e incannularlo. Tuttavia, queste operazioni portare a due conseguenze. La prima è che, nonostante la cistoscopia, l’orifizio non venga localizzato, cosa che provoca il fallimento dell’intervento. La seconda è che, durante l’incannulamento, si danneggi l’orifizio o la mucosa intramurale, rendendo così ulteriormente difficile una successiva ureteroscopia. Per cercare di superare i limiti dell’ureteroscopia, obiettivo di questa tesi è proporre un prototipo di ureteroscopio e creare una strategia di path-planning specifica. L’idea di fondo è quella di aiutare il chirurgo nel raggiungere l’orifizio, grazie alla proiezione di un percorso da seguire (creato ad hoc per il paziente) sullo schermo. In questo modo si tenta di ridurre il carico mentale del chirurgo ed evitare la cistoscopia. Creare un robot flessibile pone delle richieste dipendenti dall’ambiente in cui andrà a muoversi e dal suo uso. In questo caso, il robot deve essere rigido assialmente in modo da avere un controllo affidabile ma allo stesso tempo deve essere flessibile e permettere curve in spazi tortuosi. Deve inoltre essere manovrabile nelle due direzioni (destra/sinistra e alto/basso) e il suo controllo deve essere user-friendly. Il prototipo è composto da due segmenti controllabili indipendentemente, ognuno dei quali possiede due gradi di libertà e da uno shaft rigido. È realizzato, in un solo step, tramite stampa 3D, ed è controllato tramite cavi. Questi sono collegati a motori stepper, comandati da joysticks. Poiché il progetto è ancora ad uno stadio iniziale, né fotocamere né altri sensori sono stati ancora integrati nel prototipo. Al momento, il prototipo viene direzionato manualmente. Suoi sviluppi futuri si focalizzeranno sul suo controllo automatico. La strategia di path-planning ha l’obiettivo di guidare il chirurgo all’interno della vescica fino al raggiungimento dell’orifizio ureterale, passando per l’uretra. Nello stadio finale del suo sviluppo, infatti, il robot sarà in grado di muoversi autonomamente, seguendo il percorso sviluppato, per raggiungere l’orifizio. Attualmente, il prototipo viene mosso manualmente. Poiché il working space è costituito da uretra e vescica, che sono tessuti molli e sono sottoposti a deformazione a causa della gravità e altri fattori, l’ambiente e possibili ostacoli non sono conoscibili a priori. Per sviluppare il path, per prima cosa è stato ricostruito un modello virtuale di sistema urinario, contenente vescica, ureteri e uretra maschili. I parametri morfologici del modello, come lunghezza e altezza della vescica, possono essere modificati e customizzati per il singolo paziente. Tali parametri, infatti, possono essere ricavati facilmente tramite l’analisi delle scansioni TAC del paziente. Tale esame diagnostico è infatti routine prima di un intervento di ureteroscopia. Il path viene creato poi basandosi su informazioni legate al modello. In particolare, l'algoritmo comprende due diverse fasi, una per ciascun organo che lo strumento deve attraversare (uretra e vescica). Durante la permanenza nell’uretra, la strategia considerata ottimale è quella di mantenere il robot lungo l’asse centrale del lume, in modo tale da avere il minor contatto possibile con la delicata parete dell’uretra. Una volta entrato in vescica, il device segue un arco di circonferenza per raggiungere l’orifizio. Questa curva è stata scelta considerando l’alta flessibilità del prototipo e la sua facile capacità di seguire percorsi tortuosi. Il codice è stato scritto in Python. Sono stati svolti alcuni esperimenti per testare se il controllo manuale potesse essere efficace nel muovere il prototipo, se questo potesse facilmente entrare nel modello di vescica in silicone, e se il path creato fosse in grado di far dirigere il prototipo verso l’orifizio. La validazione della strategia e delle capacità del prototipo è stata fatta utilizzando dei fantocci di vescica creati col silicone, materiale che può riprodurre la deformabilità dei tessuti molli. Per validare il prototipo e il percorso creato con la strategia di path-planning sono state svolte due tipologie di prove. In entrambe la finalità dei partecipanti era quella di dirigere il prototipo verso l’orifizio ureterico del modello in silicone. Le prove sono state svolte da tre persone diverse, in modo tale da avere un pool di partecipanti maggiore. La prima tipologia consiste nel direzionare il prototipo verso l’orifizio del fantoccio seguendo le indicazioni di un utente (esterno) che ha la possibilità di visualizzare la scena. La seconda consiste nel muovere il prototipo seguendo il path sullo schermo, ove chi controlla i joysticks può vedere contemporaneamente sia la posizione attuale del sensore che il path creato automaticamente. Per ogni tipologia di prova, sia l’orifizio destro che il sinistro sono stati utilizzati come target. Ogni persona ha dovuto raggiungere ciascun orifizio 6 volte, 3 per ciascuna tipologia di prova. Durante gli esperimenti, la posizione del primo segmento del prototipo è stata registrata tramite tracking elettromagnetico. Il percorso seguito dal prototipo durante le due tipologie di prove è stato tracciato e comparato con il path creato. Inoltre, è stata calcolata la lunghezza di ogni path ed è stato svolto un test t di Student per valutare se la differenza in lunghezza nelle due tipologie fosse significativa. È stato inoltre registrato il tempo che ogni partecipante ha impiegato per lo svolgimento di ogni prova. Dagli esperimenti fatti e dall’analisi dei dati acquisiti sono emersi sia aspetti positivi che possibili miglioramenti necessari. Il prototipo ha dimostrato essere facilmente controllabile, avere una corretta robustezza assiale e torsionale ma, allo stesso tempo, un’alta flessibilità. La strategia di path planning realizzata si è dimostrata essere un supporto visivo efficace per l’ingresso del prototipo nella vescica e per il raggiungimento della prossimità dell’orifizio ureterale. Nonostante sia emersa la necessità di alcuni possibili miglioramenti per il setup e la necessità dell’integrazione di alcuni sensori (es. sensori di forza per una possibile allerta quando superata la soglia oltre cui c’è un possibile rischio di danneggiamento alle pareti dell’uretra -necessari data la mancanza di un feedback tattile usando un controllo remoto-, una fotocamera endoscopica per l’aumento di visione), i risultati appaiono promettenti per proseguire la ricerca in questa direzione.
Design of a ureteroscope prototype and of its path panning strategy
Scarzanella, Linda
2019/2020
Abstract
The formation of kidney stones is the third most common urological disease worldwide. In Italy, every year 100.000 new patients are affected by kidney stones. The most common surgical procedures performed to remove the stones are Extracorporeal Shock Wave Lithotripsy (EWSL), Percutaneous Nephrolithotomy (PCNL), and Flexible Ureteroscopy (fURS). EWSL is a minimally invasive surgery (MIS) technique that uses ultrasound waves to break up the stones into small pieces that can be then expelled in the urine. PCNL consists of the removal of stones using a scope inserted through a small incision performed in the back of the patient. It is efficient for large stones, but it is more invasive. fURS, differently, consist of the passage of a flexible endoscope, called ureteroscope, through the urethra and the bladder up to the ureter to collect and remove the stones. Compared to the first two interventions, fURS has some advantages. First, as it is minimally invasive, the risks of infection are minimized, and patient recovery is faster. Compared to EWSL, also a MIS, it has the advantage of being independent of the stone composition. In fact, some stone components (i.e. calcium oxalate monohydrate, brushite, or cystine) are not reactive to ultrasounds, thus leading to the failure of this technique. Moreover, fURS has been proven as the optimal choice for patients considered more fragile (i.e. pregnant women, patients affected by renal anomalies, and patients under anticoagulant treatment). For those reasons, fURS is the first choice procedure in presence of intermediate size stones. The main drawback of fURS is that finding the ureter orifice (UO) is challenging even for the most experienced surgeons. That is why they always perform a cystoscopy before fURS. A cystoscopy is an intervention where an endoscope is inserted in the bladder of the patient (passing through the urethra) to inspect the bladder. Surgeons, looking at the images reported by the endoscope camera, aim in trying to orient themselves in the bladder, to localize and cannulate the orifice. However, this can lead to two unfortunate consequences. The first is that, even with cystoscopy, sometimes the UO isn’t found, and so the intervention fails. The second is that trying to enter and cannulate the UO can result in unwanted trauma to the orifice or intramural mucosa, making any subsequent ureteroscopy difficult. Moreover, many surgeons report orthopedic complaints, due to the suboptimal posture they’re keeping while performing the interventions. Trying to overcome the limits of fURS, this thesis proposes a design of a ureteroscope prototype and a path planning strategy specifically for it. The idea is to help the surgeon finding the orifice with the visual support of a pre-planned path, while he controls remotely the ureteroscope prototype. Having a pre-operative path, in fact, could reduce the surgeon’s burden and cystoscopy could be avoided. Easing the task of finding the orifice, its cannulation wouldn’t be necessary. Designing a flexible robot comes with some challenges determined by its future environment and use. In this case, the prototype is required to have a small diameter, to have high axial stiffness to allow reliable control, and low bending stiffness to allow flexibility. It needs to have bidirectional maneuverability and its control needs to be user-friendly. The prototype is composed of two independent steerable segments and a rigid shaft. Each segment is steerable in two directions. The device is 3D printed in one step (no need of post-assembly) and is tendon-driven. Each segment is controlled by 4 tendons. Each tendon is controlled by a stepper motor. Motor control relies on joysticks. At this stage of research, the prototype is manually-driven. Next version of it will investigate automatic control. The path planning strategy aims in helping the surgeon guide the ureteroscope in the urethra and the bladder of the patient, and in finding the UO. The working space of the robot is composed of the urethra and the bladder. Those organs are made of soft tissue, which easily undergoes deformation due to gravity and other factors. Therefore, an innovative path planning strategy was needed. The strategy is created by extracting information from a rendered bladder model, created using the average male urethra diameter and bladder height, length, and width. The model is customizable, in fact its morphological parameters can be adapted to each patient taking data from CT scans. CT scans are, in fact, commonly taken before such an intervention. The algorithm is made of two different phases that were adopted to adapt the algorithm to the anatomic structure involved in that part of the path. When the device is inserted in the urethra, being the diameter of the lumen small and the structure delicate, the path is created to make the device proceed along the axis of the lumen. This will prevent the device from hitting the walls of the urethra. When the device enters the bladder, the robot will proceed towards the UO. The orifice is located thanks to information extracted from the customized urinary system model. The code was written using Python. Some validation experiments have been conducted. Three participants have been asked to perform the trials. Experiments were done to test if human control could easily move the prototype, if this one could properly steer inside a phantom model and if the path designed could guide participants in steering the prototype towards the orifice. Two different experiments were performed. The experiments consist of participants steering the prototype tip towards the orifice of a silicon bladder and urethra phantom model using two different strategies. During the first modality of the experiments, the participant is moving the prototype towards the target (= UO of a phantom bladder) while he/she is given directions from another user looking at the scene. During the second modality of the experiments, the participant has to reach the target (same as the one in the first modality) steering the prototype tip while looking at the computer screen. This displays the path designed and, superimposed to it, the real-time position of the tip. The segments of the prototype are controlled remotely by joysticks controlled by the participants. Both left and right orifices of the phantom model have been used as targets. For each orifice, three trials have been performed in each mode. The tip position in space was recorded in all trials, exploiting electromagnetic tracking. The path made by the tip in each trial has been plotted, together with the path designed. The lengths of each path have been calculated, and a Student’s T-Test has been performed to see if any statistically significant difference was present between the paths lengths of the two experiments. Moreover, the time needed in each trial to complete the task has been recorded. The experiments and the analysis of the collected data enhance both promising and improvable aspects of this research. The prototype can steer easily in the phantom model and proves to be axially and torsionally stiff but flexible at the same time. The path designed guides the users correctly into the bladder and towards the proximity of the target. The length of the paths recorded during the second experiment is lower, as the participants tend to be more focused and to not err when having to reach the target following the displayed path. However, the differences are not statistically significant. The results not only appeared to be promising but they also threw light into future improvements and additions in the setup. For example, the integration of an endoscope camera and of a force sensor to alert risks of damage during the device insertion in the urethra could be of benefit and should be implemented in a future prototype.| File | Dimensione | Formato | |
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2020_12_Scarzanella.pdf
Open Access dal 26/11/2021
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https://hdl.handle.net/10589/170569