Video work creates lifelike heart simulation
Anaesthetists from London's Heart Hospital teamed up with film animators and model makers to create the most visually realistic computer simulation of a human heart available that will be used to train doctors on using ultrasound scans.
The doctors – Bruce Martin, Andrew Smith and Sue Wright – were frustrated by the poor tools they had to use when training student doctors in the art of interpreting ultrasound images of the heart. Ultrasound imaging has swept into surgical theatres around the world. Originally used just for heart surgery, letting anaesthetists get an early warning of problems, the technique is rapidly becoming routine for monitoring patients.
“As anaesthetists, we are interested in how the heart wall contracts. That can help us understand when we should give the patient fluids and help maintain blood pressure as the surgery proceeds,” said Wright.
With transoesophageal echocardiography, the anaesthetist passes a tube down the throat of the patient so that an ultrasound probe at the end nestles behind the heart. With careful steering, the anaesthetist can zoom in on different parts of the heart and see whether it is beating normally. But the grainy ultrasound images are hard for novices to interpret. Even getting the instrument to the right place is tricky. Trainee anaesthetists have to do at least 125 supervised examinations of patients’ ultrasound scans and pass an exam to be able to wield the instrument in surgery.
“For someone learning the technique, there is a long, steep learning curve,” said Wright. “Traditionally, people have to look at the anatomy of the heart through textbooks like Gray’s Anatomy. And it is hard to imagine the 3D structure of the heart through the 2D images you see in the ultrasound.”
The Heart Hospital team started by customising plastic models of the heart, showing how the plane of ultrasound reflections slices through it. From those physical models, trainees eventually work out how to mentally convert what they see in 2D into what it actually happening in three dimensions inside the organ itself. “For some people, that never comes,” said Wright.
“We reached the point where we decided we wanted something better. And we decided we wanted to make our own model of the heart and our own teaching tools,” Wright explained. “Interactivity was important to us, so people can focus on any part of the heart. Surgeons might focus on the heart valves; anaesthetists might focus on the structure and pumping action. And we thought it would be ideal to have some kind of ultrasound simulation.”
A chance conversation with a friend of Wright’s led not to a specialist medical software developer but the world of advertising and film animation. The advert and film animator Glassworks played the anaesthetists a show reel that included the Björk video. “The tissue was very close to the level of detail we wanted.”
Adam Cubitt, software developer at Glassworks, was not so sure. Each frame in the video took hours to render on a server farm. The doctors wanted a heart beating realistically in real time. But, having worked on a number of animation projects that needed custom software work, they took it on, to the point that the developers and animators filmed heart surgery to get a better grasp of the subtleties of the way in which the organ moves.
Although the techniques demand a lot of compute power, the Glassworks team found that much of the animation could be performed on a gamer’s graphics card.
“We were getting low frame rates, just 16 to 17 frames per second. At those rates, you break the illusion of movement. But then nVidia came to our rescue and released the Quadra 5600. It was nearly an overnight solution,” Cubitt claimed.
The film world also came up with a dummy that students could use to try out their ultrasound probing skills. Looking like half a tailor’s dummy on the outside, the ‘throat’ of the model put together by effects company Asylum, simulates the feel of a real patient. As the student moves the probe around, a 3D model of a beating heart changes perspective and generates a companion image of what the ultrasound scan would look like.
The charity that funded the work has now created a company, Inventive Medical, to sell the model and simulation software. Two systems have gone on trial in New York, according to Smith. The US potentially provides a large market for the system.
“In the US, they are having to give all of their residents training in transoesophageal echocardiography,” Smith claimed.