鈥淥K, let鈥檚 do it,鈥� says a tall man in pale green surgical scrubs. 鈥淟ights please.鈥� As the lights fade, Stefan Brew stands silhouetted by the glow from a bank of X-ray monitors. In front of him a child鈥檚 hair peeps from under a blue drape that gently rises and falls as the young patient breathes.
All eyes focus on a pair of X-ray monitors showing the tree-like arrangement of arteries and veins in the boy鈥檚 brain. Suddenly, a handful of clumpy vessels turn white as a glue-like substance streams into them and seals them off. A few minutes pass before Brew announces to his team: 鈥淒one, thanks. It looks all right. He鈥檚 in pretty good shape.鈥�
James, the 8-year-old patient, suffered a stroke in February and required emergency surgery to drain a brain haemorrhage. Then last month, at London鈥檚 Great Ormond Street Hospital for Children, Brew鈥檚 team found the cause: James had a dangerous arteriovenous malformation (AVM), an abnormal cluster of potentially leaky connections between veins and arteries. During the procedure described above 鈥� called an embolisation 鈥� Brew sealed off the AVM by injecting a hard-setting plastic liquid through a catheter. The liquid is either an agent called onyx or else the superglue chemical cyanoacrylate, both of which set rapidly on contact with blood and block the abnormal vessels.
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It sounds simple, but the brain鈥檚 vasculature is complex and varies between patients. Doctors admit that working out which vessels to seal off is often a matter of trial and error, and around 1 in 10 patients suffer haemorrhages as a result of embolisation procedures.
鈥淎t the moment we do AVMs more or less blind,鈥� says Brew, an interventional neuroradiologist at the National Hospital for Neurology and Neurosurgery in London. 鈥淲e eliminate as much of it as we can, but it鈥檚 basically a blunderbuss approach.鈥�
Now that promises to change. A new imaging system aims to give surgeons a detailed, near real-time picture of the vasculature 鈥� and its abnormalities 鈥� and so remove much of the guesswork.
Called 鈥淕rid-enabled neurosurgical imaging simulation鈥�, or Genius, the system fires off brain scans to a network of supercomputers. These then use their collective processing might to generate an accurate 3D model of the unique blood flow patterns in a patient鈥檚 brain, showing the surgeon visual representations of critical parameters such as blood pressure and flow rate.
These models, created just prior to each operation and updated in near real-time, will also let doctors test the effect of a particular intervention before they actually do it. Within a year the system is expected to be part of the world鈥檚 first brain procedure guided by a real-time computer simulation.
The imaging side of Genius is being made possible by a brain scanning technique called rotational 3D angiography. This builds up a 3D image of the vasculature from large numbers of 2D X-ray slices shot from different angles around a 180-degree arc. The resulting model can be viewed from different angles, making it easier to spot vascular problems.
However, the shape of the blood vessels does not reveal the key pressures and flow velocities that may indicate where ruptures are likely. So Marco Mazzeo and Peter Coveney of University College London have written software that calculates these critical parameters, as well as stresses on artery and vein walls, based on a handful of pressure measurements made by the surgeon using a special catheter. That data can then be turned into colour-coded images so surgeons can see stress points.
Surgeons working on a patient also need such images to be bang up to date 鈥� not an old snapshot that may not reflect changes due to disease or physical injury, say. That means processing vast amounts of data to constantly update the model 鈥� around a trillion calculations per second.
To do this, Genius will access 20 supercomputers across the US鈥檚 TeraGrid and the UK鈥檚 National Grid Service, which offer a dedicated processing infrastructure for scientists. Special software will let surgeons make advance reservations for this processing time, or give them immediate access in emergencies.
鈥淭hese procedures involve life and death decision-making,鈥� says Coveney. 鈥淭he goal is to enhance the ability of clinicians to make these decisions through information technology and high-performance computing.鈥�
According to its developers, who also include teams at the Universities of Manchester and Edinburgh, UK, Genius will help surgeons deal with the three most common problems affecting neurovasculature: aneurysms, atherosclerosis and AVMs. Aneurysms are balloon-like swellings of vessels in the brain. If they rupture, blood pours into the fluid around the brain, depriving cells and tissue of oxygen and nutrients, and potentially triggering strokes.
Computing the risk
Experts believe that more than one in 100 people have a brain aneurysm. Most suffer no ill effects, but of those whose aneuryms rupture, around half will die as a result. Because doctors can鈥檛 easily tell whether an aneurysm is likely to rupture, this leaves them in an unenviable position: should they intervene or not? 鈥淚f you tried to treat the millions of aneurysms around the country, you would do more harm than good,鈥� says Brew. Supercomputer modelling will tell surgeons whether an aneurysm is likely to bleed, and if there is more than one aneurysm, which poses most risk.
Atherosclerosis, the hardening and narrowing of arteries, also causes strokes. Normal procedure now is to insert a stent to expand the vessel and restore blood flow, but in many cases the narrowing occurs at more than one location. This and the pulsed flow and variable viscosity of blood make predicting the outcomes of such procedures highly complex. Here again, Genius will help doctors customise their interventions.
Brew believes the system鈥檚 greatest potential is in the treatment of AVMs. 鈥淢odelling could allow us to identify the problem and deal with it in a safer, more focused way,鈥� he says.
Nor is Genius alone. It鈥檚 part of a wider effort to model organs or body systems under the umbrella of the Virtual Physiological Human (VPH) project. Other VPH efforts include a simulation of the musculoskeletal system by Marco Viceconti of the Rizzoli Orthopaedic Institute in Bologna, Italy; the Giome project to model the gut, coordinated by Danish researchers; the Renal Physiome Project to develop a virtual kidney, which is being spearheaded by French scientists; and an attempt in New Zealand to model the workings of the heart.
Last October the European Union allocated 卢72 million to VPH projects to help turn these efforts into clinical applications and establish a common framework that will one day allow them to be stitched together into a virtual human. The full price tag of the VPH vision has been estimated at 卢500 million.
Brew sees this approach as a major way to reduce risk and take fewer gambles, likening it to playing an intelligence-based game like chess instead of more chance-based poker.
鈥淚n chess the greater application of logic will always win out,鈥� he says. 鈥淲hile poker is also a game of skill, there is also a significant element of uncertainty and chance. Modelling has the potential to make these procedures more like chess and less like poker.鈥�
The Human Brain 鈥� With one hundred billion nerve cells, the complexity is mind-boggling. Learn more in our cutting edge special report.
