Darren’s sight saving cryosurgery
At Nu Perspectives we design, manufacture and test cryoprobes and one such probe is a device we worked with Keeler to design and develop. Recently a member of the Nu Perspectives team, Darren, whose role is to test the probes, underwent eye surgery for a detached retina and by strange coincidence the surgeon was using one of our Keeler probes to reattach the retina by using cryosurgery.
Just days before his cryosurgery, Darren had started complaining about flashing lights in his eye. He knew the flashing lights in his eye were a sign of a retinal tear as he had suffered with one in the past.
At the hospital Darren had a retinal examination which revealed that he had torn his retina again and the fluid inside his eye had leaked through the tear. The retina had been pushed away from the eye by the build-up of fluid between the eye and the retina.
The surgeon warned that although retinal tears do not usually cause vision loss, retinal detachments almost always do. It was critical that Darren underwent surgery immediately to prevent the possibility of losing his sight
Pneumatic Retinopexy, involves an injection of air, or a gas bubble, into the back of the eye. The gas bubble expands and seals the tear to prevent more fluid from leaking through it. The unwanted fluid under the retina is eventually pumped out by cells in the retina, allowing the retina to reattach. Over time, the gas bubble is replaced by a natural fluid created by the eye, until fully healed.
In his follow up appointment, Darren was told that his cryosurgery had worked brilliantly, and that the retina was now fully re-attached.
The surgeon explained that, by using both cryosurgery and laser treatment, he had been able to irritate the tissue causing it to grow and form a strong seal along the tear. After examining Darren’s eye, he commented that the cryo had done a much neater job than the laser.
The surgeon shook Darren’s hand at the end of the consultation and thanked him for doing a great job with the cryoprobes. Cryosurgery, using Keeler probes, is now common practice for detached retina and many procedures every week to help save people’s sight, using this technique.
At Nu Perspectives we are very proud of the part we play in this amazing process.
The treatment of liver cancer by cryoablation
Some twenty years ago a surgeon called Tim Allen-Mersh, was pioneering a method of freezing cancerous tumours with liquid nitrogen. The method involved inserting a probe into a tumour, via a needle and freezing the tip to create an ice ball. The ice ball would then be used to freeze the tumour. Tim’s aim was to find a method that could not only delay symptoms resulting from the growth of the disease, and in turn sustain the patient's quality of life, but could also prolong life by controlling the disease within the liver.
In this pursuit, Tim focused his attention on finding a way to treat liver cancer by cryoablation. He was working with a liquid nitrogen system that he had used many times before, but the freeze performance was not sufficient for this particular procedure.
The system he had been using came from Spembly Medical, a company Nu Perspectives Director, Louise Cuff, was working at as a design engineer. She was asked to redesign the probe and enhance its performance. Tim wanted the probe’s diameter to decrease but the ice ball size to increase.
Louise incorporated a heat exchanger in the tip of the probe, enabling her to extract as much cold energy from the liquid nitrogen as possible. She continued to optimise the probe until she produced larger ice balls yet decreased the tip of the probe’s size from around 10mm to 5mm.
Once satisfied with the results, Louise took the probes to the Chelsea and Westminster hospital for Tim to use in surgery. Under general anaesthetic in the CAT scan suite, the patient was scanned to locate the tumour’s position. Tim then inserted a needle through the abdomen into the tumour, whilst continuing to re-scan the patient and re-position the needle until he was satisfied it was in the most effective position. He then inserted the probe percutaneously. With the needle acting as a guide he began a freeze cycle of 15 minutes. Louise's role was to advise Tim on expected ice ball size and temperature.
Louise also worked with Tim to develop a second probe to work alongside the original one. Both probes, used together, produced a bigger ice ball. This enabled Tim to treat much larger tumours, using the same method.
Working directly with the surgeon and participating in the surgical procedure, enabled Louise to match the design of the probe to his requirements. It also gave her a better understanding of how to achieve the best freezing performance possible by getting the maximum amount of cold gas and liquid in the tip of the probe.
At Nu Perspectives, we design, engineer and build prototypes, using the knowledge gained from every professional experience, to continually develop the most efficient probes and stems for our clients.
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.