Ten years in the making

May 1, 2020

EDEN2020 team publish paper on the steerable needle simulation; embodying ten years of work.

Paper: An adaptive finite element model for steerable needles in Biomechanics and Modeling in Mechanobiology (2020) by Michele Terzano, Daniele Dini, Ferdinando Rodriguez y Baena, Andrea Spagnoli &  Matthew Oldfield.

 

If we go directly to the abstract, the paper is about the development of “an adaptive finite element algorithm to simulate the penetration of a steerable needle in brain-like gelatine material, where the penetration path is not predetermined”. To help us unpack what exactly this means, we talk to one of the engineers behind this monumental work, Dr Matthew Oldfield. Now located at the University of Surrey in the Centre for Biomedical Engineering, Dr Oldfield worked at Imperial College London for eight years in the Mechatronics in Medicine Laboratory with EDEN2020 coordinator, Prof Ferdinando Y Baena Rodriguez.

This paper represents ten years of insurmountable hard work and dedication from the group investigating the interactions between a soft, surgical catheter and bodily tissue, namely brain tissue. Dr Oldfield tells us about the work leading to this paper, the challenges faced and a bit of what can always be expected in scientific investigations; the unexpected.

Right off the bat, Dr Oldfield, what does this publication mean for you and the EDEN2020 team?

Dr Oldfield: The work building towards this publication began when I joined Imperial College. Understanding the mechanics of needle insertions into tissue and relating these mechanics to the STING device was my particular responsibility. It began with understanding how stiff needles cut through tissue and progressed to soft, steerable needles like the STING proof of concept.

Over time, difficulties of the simulation task were addressed, solved and then new ones presented themselves! Finally having a publication that captures the end-product is tremendously satisfying and provides a tool against which all of the empirical findings about needle steering can be justified and put into context. This is important for the EDEN2020 team and for the wider biomedical engineering community.

More information on the STING project available on the Imperial College webpage

If you were to explain the paper to someone with no scientific background, what would you say?

Dr Oldfield: The body of research was associated with trying to understand the interactions between a needle and body tissue, e.g., brain tissue that cause the needle to bend and follow a curved path during insertion. There are many experiments that show this behaviour and the factors that influence the path – needle shape, needle flexibility and the stiffness of the tissue – but few that are able to show, in detail, how and why these factors are important.

By building simulations of the needle passing through tissue, important factors can be controlled very carefully. The simulations also allow features that can’t be measured in physical experiments to be analysed. These features include how the tissue is deformed around the needle and why the tissue breaks in a particular way allowing the needle to pass.

Understanding the impact of, for example, needle stiffness and seeing the influence this has on the deformation and separation of the tissue allows design decisions to be made. These decisions will influence the material from which the STING is produced, the shape of the needle tip and how the needle steering is controlled.

This video formed as supplementary material to the published article:

Terzano, M., Dini, D., Rodriguez y Baena, F. et al. An adaptive finite element model for steerable needles. Biomech Model Mechanobiol (2020). https://doi.org/10.1007/s10237-020-01310-x
This article is open access and licensed under a Creative Commons Attribution 4.0 International License. No changes were made to the video. 

In simple terms, so what?

Dr Oldfield: The research was needed to provide scientific rigour in the explanation of the STING’s observed behaviour. Having that information could then improve the design of the STING as it evolved into its current embodiment.

What did you find the most challenging?

Dr Oldfield: The biggest challenges with the research were always technical. The approach used provides very detailed information about all of the areas that influence the needle’s behaviour. However, with that detail came a multitude of small technical refinements that had to be made. These took a considerable amount of time and often it felt like two steps forward, one step back! Nonetheless, as the approach in the paper evolved, there were big enough increments in the state of the art for several publications. One of the biggest difficulties with the approach is that it takes a long time to get results. A simulation that represents something taking about a minute in real life could easily take more than a day on the computer.

Any unexpected learnings/findings?

Dr Oldfield: The simulations also provided a background for the development of a novel experimental technique for studying the deformation around the needle tip in gelatine tissue substitutes. Parallels between simulation and experiment could then be used to show how accurate the simulations were. The experimental technique, known as digital image correlation, was also the subject of several research publications and substantially improved the state of the art in its area.

All of the technical challenges that were overcome meant that I learned a lot. Subsequently, I have used that specialist knowledge in a wide variety of areas including modelling of composites with military and automotive applications. The wider area of modelling soft biological material is something in which I have an active research interest and, in particular, I am seeking to apply that in meeting the challenge of understanding the complex muscles of the pelvis and how they interact with each other.

Where to now from this research?

Dr Oldfield: As with all research papers, there is a section concerning ‘future work’. This would include making the tissue even more realistic in its response and capturing the changes in the needle as it has evolved from the STING to its current embodiment in the EDEN2020 project. Two major areas of research and innovation remain for the simulation of the EDEN2020 needle insertion. The first is to be able to simulate the full 3D steering capabilities of the needle – the current paper looks at steering in 2D only. The second area is to create simulations that give the same richness of information but using an approach that runs more quickly. This would allow simulations to be used in planning surgery and evaluating new controllers without costly physical prototyping.

Who were involved?

As with most scientific publications, there are many contributing authors. It was a pleasure to collaborate with colleagues both at Imperial College and wider afield. In particular, the person who gave the final and substantial push that got the work published, Michele Terzano, from the University of Parma deserves an enormous amount of credit!

More about Dr. Oldfield

My research focus is structural mechanics as it is applied in biomedical engineering. Often this research is in the form of creating realistic, informative computer simulations that can either reveal something about biomedical behaviour or improve the design of a piece of equipment. Since I started working at the University of Surrey, I have become more involved with the mechanics of human (and animal) movement.

Dr Matthew Oldfield’s research profile is located on the University of Surrey website