Sunday, July 5, 2009

A new face of nuclear medicine

Six thousand people each year pass through the glass doors off Ruskin Avenue in Ottawa, walk past the turkey burgers and beef Stroganoff at Tickers cafeteria, and go upstairs to have radioactive dye injected into their arms.

At the University of Ottawa Heart Institute, they will wait as the dye - actually a colourless liquid - circulates and reaches their hearts.

There, in the muscles of the heart, it will give off radiation in patterns that tell a doctor whether the heart is able to pump properly. It's a picture, painted in gamma rays shooting out from the heart cells.

Rob de Kemp points at one dull area in an otherwise bright image. He's the chief physicist in the department making these images.

``This one might be a little bit of disease. You see there's a lower intensity (of colour) there at the top? So there's been a little less rubidium trapped in the heart muscle.''

Rubidium is a radioactive ``dye.'' If it's not reaching some of the heart muscle, then blood isn't, either. Starved for oxygen and nutrients, that muscle can't pump well.

``That's what they're looking for in the scans - regions where there's less blood flow,'' de Kemp explains.

The shutdown of the aging NRU reactor at Chalk River has cut off the supply of the main radioactive material the Heart Institute uses, called technetium-99.

But as one supply is squeezed, other materials, including this rubidium dye, can sometimes take its place.

In the institute's basement, there's a machine with a name like a carnival ride - the cyclotron - that produces medical isotopes (radioactive atoms) without a nuclear reactor.

To anyone who has toured a nuclear reactor building, the contrast is startling. Reactors are huge machines in earthquake-proof buildings running 24 hours a day, surrounded by layer upon layer of security and shutdown systems, and with radioactive waste that will last for millennia.

The cyclotron at the Heart Institute is a big metal box in a room that measures about eight by 10 metres. You can walk right up to it safely while it's running.

At night, the staff just turn it off and go home.

``The isotopes emit radiation. They emit in this case gamma rays, which the camera can detect. Some cameras get a three-dimensional view of the heart showing where there is normal blood flow and where there is reduced blood flow due to a blockage or a narrowing in the coronary arteries,'' de Kemp says.

The ``dye'' itself is a liquid - radioactive material dissolved in salt water. The dye is injected through a needle, and after a few minutes of travel through the body it arrives at the heart.

This test is far easier than the alternative - sticking a catheter in through a thigh artery, sliding it up to the heart, and releasing material that can produce X-rays of the heart.

About 80 per cent of what the Heart Institute uses, traditionally, is technetium-99, made from radioactive material from Chalk River. That supply is shut down for now, though there are reduced amounts available from other parts of the world.

There's a great deal of current research into better ways to produce technetium, says Dr. Terrence Ruddy, chief of cardiology at the institute.

``On the other hand, say it doesn't work out (because of shortages), there's a lot of work going into alternatives,'' such as iodine, which comes from a cyclotron.

Rubidium is a major alternative to technetium, and it needs no nuclear reactor. The Heart Institute buys radioactive strontium from a cyclotron in Vancouver, and converts it to rubidium. The ``generator'' that does this is a bedside box the size of a photocopier.

Indium is used fairly rarely, mostly to make images of infected or inflamed areas. For thyroid images, and some other parts of the body, there's radioactive iodine. And the Heart Institute now uses a lot of thallium for heart images.

And as well as the isotopes - which are radioactive atoms - comes a radioactive molecule made at the Heart Institute called sodium fluoride. That's sodium bonded with a radioactive fluorine atom.

``The sodium fluoride test is also one that we will probably make available to patients soon, either here or at the Ottawa Hospital, which also has a PET scanner,'' de Kemp says. It's used for bone scans to detect suspected cancer.

They can make four types of radioactive isotopes in Ottawa, of which fluorine is the most useful for medical images.

And if Ottawa heart patients didn't have these radioactive dyes?

``The alternative would be more invasive tests - more of these procedures where we put catheters up into your leg and injected X-ray dye,'' de Kemp says.

``Puncturing an artery is not a minor surgery. The costs of that are also much, much higher than nuclear medicine where they might be here for an hour - in and out, and they have their diagnosis.''

© Copyright (c) Canwest News Service

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