The Treatment of Liver Cancer by Cryoablation
Recently someone asked me if I could tell them about the most interesting project I had worked on within the field of cryogenics. For me the answer was simple.Some twenty years ago I had the privilege of working alongside a surgeon called Tim Allen-Mersh. He was pioneering a method of treating cancers by freezing tumours with liquid nitrogen. Tim believed that the procedure of inserting a probe via a needle and freezing the tip, creating an ice ball which would then freeze the tumour, could delay symptoms resulting from the disease's growth and sustain the patient's quality of life. His hope was that the procedure would also prolong life by controlling the disease within the liver.
His focus at that time was to find a way to treat liver cancer by cryoablation. Tim and his team were using a liquid nitrogen system that had been acquired by the company I worked for and the freeze performance wasn’t good enough for what they were trying to achieve. As one of Spembly Medical’s design engineers, I was asked if I could redesign the probe and enhance its performance so that the probe’s diameter decreased and the ice ball size increased.
By incorporating a heat exchanger in the tip, I was able extract as much cold energy from the liquid nitrogen as possible. Further optimisations of the probe allowed me to produce larger ice balls with smaller diameter probes, decreasing the tip from around 10mm to 5mm.
I manufactured and tested some prototypes and once I was satisfied with the result, I took the probes to the Chelsea and Westminster hospital in London, for use in surgery. The procedure was carried out under general anaesthetic in the CAT scan suite. I set up the machine by filling with liquid nitrogen and pressurising the unit, whilst the patient was scanned to locate the tumour’s position. A needle was then inserted through the abdomen into the tumour. The surgeon re-scanned the patient and re-positioned the needle until he was satisfied with the result.
The probe was then inserted percutaneously using the needle as a guide and a freeze cycle of 15 minutes then started. My role was to observe and advise Tim on expected ice ball size and temperature. Tim was able to measure the ice growth using an ultrasound scanner, with images in real time.
I visited the hospital a few more times and on each occasion, I made improvements to the performance of the probe and reduced the probe’s size. During those visits, I worked with Tim to make an additional probe and both probes were then used at the same time to make a much bigger ice ball, which had a better clinical outcome for treating larger tumours.
I still become very animated when I talk about it today. I remember the tension and anticipation, coupled with the excitement and relief of the success of the procedure. It was an amazing experience to have been a part of and from a professional point of view, it gave me a real sense of accomplishment.
Seeing the probes used in clinical use and discussing performance with the surgeon directly, allowed me to match the design of the probe perfectly with his needs and requirements. I gained a much better understanding of how to get the most out of cold gas and liquid in the tip of the probe, so that we could achieve the best freezing performance possible.
This is still our focus at Nu Perspectives today. We use the knowledge gained from such experiences and design, engineer and build prototypes which enable us to continue developing the most efficient probes and stems for our clients. We work closely with our clients at every stage of development to ensure that their expectations are met.
Dealing with the challenge of coupling design for cryogenics
All engineers working in cryogenics struggle with the challenge of coupling design. It’s important not to waste liquid nitrogen while keeping the liquid cold enough to work quickly. That’s why Nu Perspectives set about creating a brand new coupling design.
The team is developing a liquid nitrogen surgical system for cancer treatment which needs the ice ball at the end of the probe to be generated effectively. One of the issues is the coupling to connect the probe to the liquid nitrogen supply. The system is also a low flow system.
Here are the results we have achieved so far in this project:
The problem as soon as liquid nitrogen comes into direct contact with the coupling it starts to boil, turns into gas and stops the cold liquid reaching the probe tip.
We needed to achieve nucleate boiling at the tip quickly, to create an effective ice ball. This is particularly important when designing cryogenic surgical instruments. Any increase in the time to get to optimal freezing reduces the effectiveness of the surgical probe.
With this problem in mind and the fact that it was a low flow system, we decided to design and test the coupling and to measure the effect on the probe.
Adding the extra thermal mass of the coupling increased the time it took to get 100% liquid to the tip as the liquid boiled in the coupling. Adding the coupling also increased the time to achieve nucleate boiling in the tip of the probe, meaning it wasn’t working efficiently.
At Nu Perspectives we are able to create and test working prototypes on the premises, making it much easier and cheaper for us to carry out very precise tests and changes on instruments, until they are working effectively.
Firstly we looked to limit the length of the flow path of liquid nitrogen in direct contact with the coupling body material. This reduced the amount of liquid boil off in the coupling which had a positive effect. However, it meant the whole coupling body froze, so our next step was to take out as much of the coupling material as possible.
This had a positive impact on the results but not enough so we insulated the part of the coupling that was still in direct thermal contact with the liquid nitrogen, and this improved the performance further.
This is an ongoing project and while we have made significant progress we are still working to further reduce the time to nucleate boiling at the tip. Our approach has demonstrated that very small changes can make a big difference to the performance of an overall cryogenic system.
We are very lucky to have the in-house prototyping facility which really does make an enormous difference to this kind of precision engineering work. While this project is still ongoing we know that couplings are used in lots of cryogenics applications and that our findings could help others in the field.