ARCHIVED - Close to the heart
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October 01, 2008— Winnipeg, Manitoba
Tiny coils and wires that capture images inside coronary arteries could soon improve the way physicians diagnose whether a patient has heart disease or suffered a heart attack.
The technologies, developed by the NRC Institute for Biodiagnostics (NRC-IBD) in Winnipeg, are based on magnetic resonance imaging (MRI) and optical coherence tomography (OCT). They could soon be in use in hospitals across Canada.
IMRIS Inc., a Winnipeg-based company specializing in advanced surgical imaging systems, is evaluating the prototype of a phased array radio frequency (RF) coil for MRI use in cardiac medicine, as part of its goal to create the "catheterization lab of the future." Developed by a team led by Dr. Scott King of NRC-IBD, the flexible, flat coil would sit atop a patient's chest and help a cardiologist open a patient's blocked coronary artery.
|NRC is working with IMRIS to bring magnetic resonance imaging (MRI) into interventional cardiac surgery. (IMRISneuro installation at Abbott Northwestern Hospital in Minneapolis)|
X-rays are currently used in medicine to guide the placement of a stent through the femoral artery into a coronary artery plugged by stenosis or arteriosclerosis. "Our system generates a 3D image that is far more detailed than what we get from X-rays — without the harmful ionizing radiation," explains Dr. King.
Clinical techniques such as X-ray, ultrasonography and fluorescent imaging cannot provide information on tissue biochemistry, such as lipid content. A significant amount of fat present in arterial-hardening plaque makes the plaque more vulnerable to being ruptured and, thus increases the chance of a heart attack.
Dr. King's MRI system could fill that gap.
Here's how it works: gradient coils in the magnetic field of an MRI scanner send out currents that, in turn, make the hydrogen atoms of water molecules emit different frequencies. The full array of radio-frequency signals generates a 3D image — in this case, of the coronary artery. The challenge is to acquire this data without blurring the picture from movement caused by a beating heart and a breathing patient. But recent advances in MRI over the past five years have increased the speed by which the technology can capture clear images when the heart is stationary for about 200 milliseconds.
Now, Dr. King is working on a new MRI method to delve even deeper into a patient's cardiac region and generate images with far greater resolution. His goal is to attach a tiny MRI coil to a catheter used to unclog a coronary artery. The coil would track the movement of the catheter, to ensure it hits the target. It could also obtain images of the vessel wall in order to measure the amount and vulnerability of plaque.
Part of Dr. King's challenge is to increase the resolution of MRI images. Currently, MRI can obtain a resolution of 1 millimetre (mm), which is about the thickness of an arterial wall. But in order to capture the necessary detail, Dr. King hopes to reduce the spatial resolution to 0.2 mm. "The idea is to have the coil keep the same motion as the heart and the coronary artery," says Dr. King, who is collaborating with Dr. Jonathan Sharp, an NRC-IBD researcher based in Calgary.
Meanwhile, their colleague Dr. Mike Sowa is overseeing the development of a new cardiac imaging system based on OCT technology, which also produces 3D images. The idea is to thread a tiny fibre-optic wire, attached to a catheter, into coronary arteries to determine the size and location of plaque — or whether the stent used in angioplasty was properly deployed.
"It's like ultrasound, except we're using light," says Dr. Sowa, who leads NRC-IBD's medical photonics group.
He says a major study last year in the United States revealed that 34 percent of patients who underwent angioplasty still reported chest pains 12 months later. Either the stent didn't properly deploy or it ended up in the wrong position, which can lead to another arterial blockage. "We're trying to develop technologies to reduce the incidence of these complications," says Dr. Sowa.
He adds that MRI coils and OCT wires would bring different strengths to cardiac medicine. MRI is more sensitive to the biochemistry of a blood vessel, whereas OCT can measure the structure of a vessel — such as its thickness, the depth and length of plaque, and so on. Once an OCT probe is MR-compatible, the two technologies could work concurrently to produce two different reports and help cardiac clinicians make the best decisions, stresses Dr. Sowa.
Dr. John Saunders, Chief Scientific Officer and founder of IMRIS, says the NRC technology will help his company expand its expertise into medical matters of the heart. "Our plan is to bring to interventional cardiology the same technologies we brought to neurosurgeons, and NRC is helping us develop them."
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