Dr Ka-Wai Kwok, Assistant Professor in the Department of Mechanical Engineering, has been working with two teams on different projects. His innovative work for cardiac catheterisation involved designing versatile actuators capable of operating in an MRI (Magnetic Resonance Imaging) environment, without adversely affecting the MRI quality.
“Since MRI is a diagnostic technique that uses strong magnetic fields and radio waves, the actuators cannot have any ferromagnetic materials in them, nor can they have a conventional motor,” said
What the team has come up with is an MR-safe robot for use in cardiac catheterisation. It is driven by a new form of actuator, which is capable of moving or controlling the mechanism precisely, and is operated by a source of energy – in this case hydraulic fluid pressure.
“In simple terms, an actuator is a mover,” said Dr Kwok. “We have invented a motor that uses water – that is, hydraulics – which gives you very good control. Actuators act as a key component of any robotic device. In MRI environments, electromagnetic (EM) and electrically conductive components that induce EM interference have to be handled with caution. Our research focussed on intrinsically MR-safe actuators driven by other energy sources, such as pressurised fluid flow commonly available in clinical settings. Motors in the control room, outside the actual MRI facility, drive the robot in the MRI room via several 10-metre long hydraulic tubes.”
Dr Kwok’s team awarded the Best Live Demonstration Prize at the Surgical Robot Challenge 2016 in London.
This is the first robot in the world that is capable of controlling a cardiac catheter while under the MRI environment. HKU’s Technology Transfer Office has registered the patent on the invention.
“Usually, for cardiac catheter procedures, surgeons have to look at many screens,” said Dr Kwok. “They use a catheter tip to burn on the inner surface of the left ventricle, but they tend to make conservative burns as they can’t see what they are doing and if they burn too much it could result in perforation, and that would be disastrous.
“One plausible way to see what you are doing in real-time is with MRI, which tells you how tissue has changed, and provides good intra-operative feedback. But you can’t have screens to display the information in the MRI facility unless you have EM shields over them, which cost US$30,000–40,000 each. This is one of the main reasons why we need the catheter robot, and why we must be able to tele-operate it outside the MRI room.
“Intra-operative MRI provides fast and high contrast soft tissue images without emitting radiation. During ablation any physiological changes in tissue can be easily distinguished and physicians can therefore monitor the ablation progress and reduce the chances of arrhythmias recurrence.”
When developing the MRI robot, they made several factors priorities. “We wanted it to have good actuation – so we used hydraulics; good sensing, so the robot has a kind of GPS inside the scanner via real-time MR-based positional tracking units; and good interfacing in the form of visual feedback. We were able to put tracking units on the catheter tips, by which the surgeon can trace where the tip is and at the same time monitor if the burn is good.”
In London last year, his team showed the robot at the Surgical Robot Challenge 2016 and won the Best Live Demonstration Prize.
Dr Ka-Wai Kwok
Intra-operative MRI [Magnetic Resonance Imaging] provides fast and high contrast soft tissue images without emitting radiation. During ablation any
physiological changes in tissue can be
easily distinguished and physicians can therefore monitor the ablation progress
and reduce the chances of arrhythmias recurrence.
3D printing to aid surgery
A second project, which introduces three-dimensional (3D) printing to aid cardiac surgery, is also gaining attention. ”For this research we are the end-users, prototyping for rehearsal prior to surgery,” said Dr Kwok. “The Cardiology Division in the Department of Medicine and Therapeutics, at the Chinese University of Hong Kong (CUHK) approached us about introducing 3D printing technology as a means to practise complex cardiac procedures before carrying out the real operation.”
This involved using a 3D printer, capable of producing soft materials to form models of parts of the heart which can be used in cardiovascular surgery planning. By making silicone-based 3D models of the heart structures the cardiologists can personalise the planning for a cardiovascular implantation for each patient. The models were made using echocardiographic data of the patient’s heart.
The teams from CUHK and HKU used the technique last year on a complex case of a 78-year-old woman who needed Left Atrial Appendage (LAA) occlusion. Transesophageal echocardiography had shown that the patient had a double-lobed LAA that would make the occluder implantation more difficult as it would be necessary to occlude the ostia of both lobes with a single device.
They simulated the whole procedure using a 3D silicone LAA model which was made to measure using data from the patient’s transesophageal echocardiography. This enabled the cardiologists to work out the ideal position to implant the LAA closure device, thereby reducing the risk of procedural complications or failure. The procedure was successful and the patient is in good condition.
“We hope that using advanced geometric modelling and 3D printing in this way will add to the cardiologist’s confidence in performing safer, more accurate and effective cardiovascular intervention procedures,” said Dr Kwok.
The Heart of the Matter
Research teams from the Mechanical Engineering Department have made innovative advances that will aid two different medical procedures for heart patients – cardiac catheterisation and complex cardiac surgery.
The team at HKU’s Department of Surgery.