Model surgery from Heartworks

Technology previously used to bring computer game characters to life is set to transform the way cardiac anaesthesiologists are trained.

Heartworks (pictured below) combines a computer model of the heart with ultrasound simulation and a haptic interface to provide a training tool with unprecedented levels of realism.

It is the brainchild of thee clinicians at the Heart Hospital in London who wanted a tool to support their course in peri-operative transoesophageal echocardiography (TOE).

TOE is a process used in cardiac surgery in which a miniaturised ultrasound scanner is inserted via the patient’s mouth and down the oesophagus to a position behind the heart to constantly monitor its condition during the operation. It requires a high degree of skill and training for anaesthesiologists to place the scanner, select the appropriate planes through which to view the heart and interpret what the monitor displays.

Using Heartworks, a trainee inserts a model probe into a specially designed dummy patient torso. A screen displays any combination of accurate simulated ultrasound images; a detailed model heart, which can be cut away as required to see its internal workings; and labels of 130 structures in the heart.

The probe can be moved up or down and rotated through different planes of viewing, as would occur during surgery. This allows the user to directly relate what they see in the ultrasound image to the heart structures so they will know everything is functioning correctly in a real operation. Throughout it all, the heart continues beating and its constituent parts (such as the valves and chamber walls) behave realistically.

Dr Sue Wright explained: ‘There is a training curve in correlating where the ultrasound plane is in relation to the heart and what is seen on the screen when TOE is taught in hospitals.We looked at other TOE modelling solutions but the models they used were very basic. We decided to make our own model that would be anatomically accurate, realistic, beating, interactive and involve an ultrasound simulation.’

A chance conversation introduced Wright to Glassworks, a commercial digital animation company.

Adam Cubitt, a software developer at Glassworks, said: ‘The request came straight through to the R&D department, which is designed to field unusual jobs outside our usual areas of expertise. We’re not a medical simulation company — they tend to build up models of organs from the cells up. Our approach is top-down — we look at the end results and find a way to fake it so well you can’t tell the difference.’

The team started with an anatomically accurate polygonal model, such as those used for animated figures in a game or animated advert. They then applied high-resolution textures to make it look realistic. After that they added the demarcation of the heart structure regions, high-quality surface shading, 2D processing of the ultrasound slice and a graphical user interface (GUI).

One of the modellers, James Mann, took an interior cast of a healthy heart by filling it with latex. Realistic textures were then added to the surface of the heart.

At this stage the team invited top surgeons, including renowned cardiac expert Sir Magdi Yacoub, to get involved in the refinement process, and even went to see open-heart surgery in progress to ensure the system was realistic.

A challenge faced by the team was that occlusion culling (broadly defined as the process of determining which portions of objects are hidden by other objects from a given viewpoint) could not be employed as nearly all the heart needed to be visible at any time.

‘To make the animation smooth, we needed a frame-rate of 30 frames/sec in real time. On some projects that could take all night to process,’ said Cubitt. ‘We had it up to 16 frames/sec, then NVIDIA came to our rescue with a new graphics card.’

The project used NVIDIA’s Quadra 5600 card, which offered several times the processing power of its predecessor. It allows deferred shading, by which the properties of the surfaces can be rendered into buffers to give the desired frame-rate.

The project originally only intended to produce the software, but the clinicians decided to add a mannequin to make it an end-to-end training tool. Asylum Models, a commercial model-making company, took on the task.

Cubitt then created a model probe, which would interact with the dummy and heart model in the same way the real thing would during an ultrasound scan.

The finished system is already in use at London’s Heart Hospital, and is now being beta tested in the US.

Berenice Baker