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Over the past two weeks, doctors at the Toronto General Hospital have been quietly running tests on the most sophisticated CT scanner in the world.

The $2.5-million machine - called Aquilion One - represents the next big leap in medical imaging of the heart. The Toronto General's Peter Munk Cardiac Centre is one of the first medical institutions to purchase the device from Toshiba, the Japanese-based manufacturer.

Hospitals in only four other cities - Baltimore, Boston, Berlin and Nagoya, Japan, - can boast of such advanced CT equipment.

The machine looks like a giant white glazed doughnut that stands more than two metres high. A patient is placed in the "hole" of this high-tech doughnut, and within a matter of seconds, the machine can collect enough data to produce three-dimensional images of the heart on a computer screen.

That means doctors can immediately see if the patient has any narrowed or obstructed coronary arteries that could be an early warning sign of an impending heart attack.

So far, the Toronto doctors have been impressed by the scans they've done on volunteers willing to test the new technology.

"The potential for this machine is huge," said Narinder Paul, section chief of cardiothoracic imaging at the University Health Network, which includes the Toronto General.

For one thing, the scanner is a lot less invasive than the current "gold standard" test for detecting clogged coronary arteries - cardiac catheterization. This procedure involves inserting a flexible tube, or catheter, in a blood vessel in the groin and threading it all the way to the heart.

Once in position, the tube releases a special dye that allow X-rays to "see" the vessels supplying blood to the heart muscle. The images are known as angiograms.

Cardiac catheterization is highly effective at pinpointing obstructed arteries, but it also carries risks, said Catherine Zahn, executive vice-president, clinical programs and professional practice at the University Health Network.

The tube can dislodge unstable plaque and cholesterol along blood vessel walls. Those little bits of debris could form a clot that triggers a heart attack or stroke.

The chances of something going wrong are relatively small - about one in 1,000 - but when it happens "it can be devastating," said Dr. Zahn.

So, doctors have been looking at alternatives and, in recent years, they have turned their attention to advances in CT imaging, or Computed Tomography.

The technology - which used to be called a "CAT" scan - works by placing the patient in between a spinning source of X-rays and rows of special receptors. It produces cross-sectional images, or slices, which can be stacked up to created three-dimensional pictures of the internal organs.

"It's like cutting up a salami ... you can look inside every slice," said Patrice Bret, chief of medical imaging at the University Health Network.

When CT scanning was first introduced in the mid-1970s, the machines were slow and could only produce a few slices at a time. The patient had to hold still so the image didn't blur. Capturing a clear picture of a beating heart was simply beyond the scope of the equipment.

As a result, the first scanners were used for studying body parts that can remain motionless - such as the brain of a stroke patient.

Over the years, CTs have become increasingly faster and the number of X-ray slices has jumped from four to eight to 16 to 32 and then to 64 at one time.

One recent study found that a 64-slice CT scanner can "freeze" parts of the heart in motion and reveal telltale signs of narrowed blood vessels. Patients just have to be able to hold their breath for six to eight seconds so the chest doesn't move. The speedy scanner does the rest.

But the 64-slice scanner still can't capture the entire heart in one go - only 3.2 centimetres of it. So multiple sweeps are needed to create a full image of the vital organ. The additional shots, which require some overlapping sections to "stitch" together a complete 3-D picture, mean the patient is exposed to higher levels of radiation.

According to some estimates, a patient gets between three to four times more radiation from a 64-slice CT scan of the heart, compared with the X-rays involved in a cardiac catheterization procedure.

And that's why Toshiba's Aquilion One, with 320 slices, holds out so much promise. "You can get the whole heart at once," Dr. Paul said, noting the image extends 16 centimetres, which is more than enough to cover an adult heart. "And because it is such a quick scan, the radiation dose will be less." Indeed, patients only have to hold their breath for a second or two.

Dr. Paul said there are lots of people who have cardiac risk factors - such as a family history of heart disease or they suffer from diabetes or elevated cholesterol levels - but they show no outward symptoms of a compromised heart.

"You can't justify putting them through cardiac catheterization - it's invasive, it's risky," said Dr. Paul. If the 320-CT scanner lives up to expectations, it could provide a relatively safe, fast and efficient way to spot heart disease in its earliest stages. Patients found at risk could then be singled out for treatment including lifestyle changes, medications or even surgery.

Still, a lot of research will be needed to prove that the latest innovation in CT scanning can make a real difference in the lives of patients.

"We don't just want another gadget that can make a pretty picture," said Dr. Bret. "We want to show that what we are doing is actually resulting in ... fewer people dying [prematurely]."

In many respects, the new scanner is part of a much larger trend towards less invasive treatments for cardiovascular disease, noted John Parker, medical director of the Peter Munk Cardiac Centre. For instance, rather than cutting through the chest to operate, obstructed arteries can now be propped open with "stents," fished into place through tiny incisions.

This approach has fuelled the need for new imaging equipment that can peer inside the body and it has also sparked turf wars over who will control the technology - the imaging specialists, radiologists; or the heart doctors, cardiologists.

But at Toronto General - which got a $37-million cash infusion from gold mining executive Peter Munk last year - doctors from all the different medical disciplines involved in heart care are "working together" to get the new 320-slice CT scanner up and running, said Dr. Parker.

"We are trying to dissolve the traditional silos" that have led to the turf wars within the medical profession, said Dr. Parker, adding that patient care should benefit.

As Dr. Zahn put it, the new scanner "looks like one of the most, if not the most, powerful tools for low-risk imaging ... of the blood vessels of the heart."

A PERSONAL ODYSSEY

It was an opportunity I couldn't let pass. When I heard volunteers were needed, I leapt at the chance to be one of the first people in Canada to have my heart checked out by Toshiba's new 320-slice CT scanner at the Toronto General Hospital.

My scan would be part of a study assessing the lowest level of radiation needed to produce a clear CT image. Yet it would also reveal if the arteries supplying blood to my heart were in good shape - or clogged by plaque and cholesterol.

My father died of a heart attack at the age of 61 and my sister succumbed to the same fate at 52.

Now I'm 52 - and I wanted to know what the future might hold for me.

The test is as simple as it gets. An hour before the procedure, I was given a beta blocker, a tablet to slow my heart to fewer than 60 beats a minute. (The typical adult has a heart rate in the mid-70 range.) An intravenous needle was also inserted into my arm so a special X-ray-sensitive dye could be injected into my veins while I was scanned.

I was then escorted to the pristine CT scanner room. I lay down on a narrow motorized table, which eased me, feet first, through the "hole" of the scanner until the doughnut-shaped machine surrounded my chest.

It then began to make a great whirring noise, like a jet engine preparing for takeoff, as the X-ray and sensor equipment started spinning inside the "doughnut."

The CT's robotic female voice instructed me to hold my breath as the machine took some initial readings. (If it detected a build-up of calcium lining my blood vessels, the test might have been stopped because the deposits can make it hard to interpret the images.) I was now a "go" for scanning. To open wide my blood vessels, a tiny nitroglycerin tablet was popped under my tongue, resulting in a sudden, though mild, headache. A moment later, the IV needle released the X-ray-enhancing dye into my veins, producing a gush of warmth throughout my body and an odd metallic taste in my mouth.

The robotic voice once again instructed me to hold my breath. I did so, and in a few seconds, it was all over. The scanner had gathered all the data it needed.

With a bit of trepidation, I got up and walked into the adjacent room, where hospital and Toshiba staff were transfixed by the images of my heart on a computer screen.

"It looks good," said study leader Narinder Paul, as he explained I had no signs of heart disease.

Paul Taylor