Understanding stroke
Just down the hall from Dr. Thompson, AHFMR Senior Scholar Dr. Christian Beaulieu is developing MRI technology to better understand the brain. One of his interests is developing sodium imaging. Conventional MRI measures the hydrogen atoms in water. "But water is everywhere in the body—inside and outside of cells—so it's not very specific," explains Dr. Beaulieu. "Sodium is more specifically involved in cell function. But because there is much less of it and the physics is different, sodium is much more difficult to detect." After seven years of work led by Dr. Beaulieu's Ph.D. student Rob Stobbe, the team has developed the hardware, software, and expertise required for sodium imaging by magnetic resonance. "Now we have some of the best sodium images in the world. Very few labs have this capability," says Dr. Beaulieu.
Sodium imaging may be particularly useful for determining exactly when a person has had a stroke. Stroke is the number three cause of death and the number one cause of adult disability in Canada. There is only one approved drug for acute stroke—tissue plasminogen activator (tPA) also known as the "clot-buster drug". TPA has to be given within 4.5 hours of a stroke, after that the risk of hemorrhage (internal bleeding) outweighs the benefits. But about 30% of patients have a stroke in their sleep, making it impossible to determine when they had their stroke. In these cases, physicians use "time last seen well," which is usually before bed and therefore makes tPA therapy unavailable to these patients.
But what if the stroke is what woke these patients up? They may in fact be good candidates for tPA, reasons Dr. Beaulieu. His team has shown that, after a stroke, there is more sodium at the site of the stroke. Until recently, his team had performed sodium imaging on people whose time of stroke was known. Now they are scanning patients who woke up with a stroke. The goal is to understand exactly how sodium levels change, which may make it possible to estimate how much time has passed since the stroke occurred, even if it happened during sleep.
Sodium imaging might also help to diagnose and monitor damage to cartilage, the rubbery tissue that cushions bones at the joints. Because sodium levels decrease when cartilage is damaged, sodium imaging may be an ideal non-invasive way to test whether new drugs that have been developed to restore cartilage are effective. "The cartilage project illustrates a key point about my research," notes Dr. Beaulieu. "Once we develop a technology for a specific purpose, like brain imaging, we ask ourselves: What else can we use this for? New applications are part of the excitement around this research."