Steering and Harvesting Technology for Minimally Invasive Biopsy

Abstract

Contemporary medical imaging technologies, such as computed tomography or magnetic resonance imaging, play a pivotal role in medical diagnosis, allowing for a relatively fast and non-invasive examination of the human body. In the field of cancer surgery they allow for preoperative detection of tumorous tissue and aid the surgical planning. However, only recent developments in the imaging field have introduced the possibility for a real-time non-invasive intraoperative detection of tumorous tissue with sufficient margins for radical tumour resection. These imaging technologies are collectively called optical biopsy and besides providing the real-time visualisation of the tumorous tissue on a large scale, e.g. near-infrared fluorescence, they allow for an instant tumour detection and analysis on a small scale, e.g. differential pathlength spectroscopy, ultimately without the need for any pathological analysis. While the optical biopsy provides an answer to the tumour detection, its subsequent accurate resection, or mechanical biopsy, remains a challenge. This challenge is further aggravated with more demanding applications, such as minimally invasive surgery, as compared to open surgery, and accurate resection of organ exterior as compared to organ interior. Yet, as challenges are here to be solved, the aim of this work is to provide an answer to combining the optical and the mechanical biopsies in an accurate manner with the aim to perform safe minimally invasive resection of small tumours at organ and tissue surfaces. Furthermore, as minimally invasive surgical applications pose various spatial restrictions on tissue manipulation, the second objective of this work is to present a reliable joint construction for the envisioned tissue resection instrument, allowing it to attain a proper orientation to the tissue of interest. As the focus of this thesis is twofold, its chapters are grouped into two parts. The first part of this thesis treats the combination of the optical and the mechanical biopsies in a reliable and an effective manner, showing the development of a resection tip, the opto-mechanical biopsy harvester, for a minimally invasive surgical instrument (Chapters 2-4). The second part of this thesis addresses the issue of steerable joint constructions in the minimally invasive surgical instruments and their reliable controllability in order to provide both flexibility and stability for the accurate tumour detection and resection (Chapters 5-8). With the vision to devise the design of the opto-mechanical biopsy harvester, a review of the state-of-the-art minimally invasive surgical instruments capable of performing the optical and the mechanical biopsies successively and accurately was performed and it is presented in Chapter 2. In addition, the review outlines any and all the minimally invasive surgical devices housing an accessory channel, thus mechanically capable of integrating a fibre optic cable for optical biopsy. As the findings of the aforementioned literature review were rather limited, this gave an opportunity to conceive and develop a novel bio-inspired design of a frontally-acting opto-mechanical biopsy harvester. Its experimental design and prototype are presented in Chapter 3 together with feasibility tests proving the concept. While the instrument steerability was not yet incorporated, the experimental design was created with a great consideration of its ultimate functionality. Chapter 4 concludes the first part of this thesis with a follow-up optimisation of the biopsy harvester’s collapsible resection device, the crown-cutter, bio-inspired by the sea urchin’s chewing organ Aristotle’s lantern and shaped as a crown of numerous pointy teeth. The study researches the impact of tooth quantity and type of their bevel on the induced tissue deformation, penetration forces and proper tooth collapsibility. Similarly to the first part of this thesis, the second part begins with a review article in Chapter 5 of all the mechanical joint constructions used in the state-of-the-art steerable minimally invasive surgical instruments. By clear categorisation, the aim of this review is to help identify a reliably controllable steerable joint ensuring accurate operation of the envisioned instrument’s tip. The fundamental joint classification can also serve as a design aid for other developments in this field. With the vision to develop a stiff and reliably controllable joint for the envisioned biopsy instrument, a novel steerable laparoscopic instrument prototype DragonFlex was developed. As discussed in Chapter 6, its simple, repetitive and symmetrical design incorporates a rolling joint with a special tight cable guidance. Together they maximise the driving cable lifespan, equalise the forces in both cables and enable control of seven instrument degrees of freedom by only seven structural components. Not only is DragonFlex the world’s first almost entirely additive manufactured steerable laparoscopic instrument prototype, but it also sheds new light on the potential of additive manufacturing in the surgical field. The promisingly high bending stiffness of DragonFlex’s rolling joint is evaluated in Chapter 7, which provides an empirical evidence that this joint construction is indeed superior to the state of the art in this respect. As clarified, the insight into achieving high bending stiffness of cable-driven joint constructions lies in the principle of full actuation of each degree of freedom, as opposed to underactuation. In order to perfect DragonFlex’s already stiff rolling joint Chapter 8 illustrates a way to minimise the small degree of remaining cable slack in the original design. As opposed to the common design practice attempting to eliminate the cable slack by a cable tensioning mechanism, this chapter introduces a more fundamental solution applicable to rolling joints in general. On top of minimising the cable slack, this solution removes the need for a cable tensioning mechanism, hence simplifying the overall design and assembly even further. The thesis is concluded with a discussion section in Chapter 9 outlining the combination of the reliable steering and the accurate harvesting technology developed for the purpose of minimally invasive biopsy. This last chapter presents the envisioned design and the real-scale fully functional prototype of the steerable minimally invasive opto-mechanical biopsy harvester composed of a permanent and a disposable section. The fusion of all the presented insights and designs is addressed in a practical manner, especially with regard to the manufacturability and the proposed usage of the final envisioned instrument.