The Hindu : Front Page : Tale of high-tech heart scans

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Wednesday, Nov 07, 2007
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Tale of high-tech heart scans

‘Super X-rays’ show promise for finding disease but produce high radiation dose

Uses 64 detectors to produce, combine images
Nine out of 10 with blockages identified by scan

ORLANDO: A type of “super X-ray” has shown promise in its first big test as a potentially cheaper, faster and painless way to find out whether certain people with signs of heart disease actually have it and need treatment.

The scans might eliminate the need for some of the millions of cardiac catheterisation procedures done each year to check for clogged arteries, said Julie Miller of Johns Hopkins University.

But the newer scans are controversial, partly because they supply a big dose of radiation. That raises the risk of cancer and might spur thousands of additional cases if the scans were widely used in the population, said Michael Lauer of the National Heart, Lung and Blood Institute.

Speaking at an American Heart Association conference where study results were presented on Monday, Dr. Lauer called on doctors not to use the scans until research proves they save lives.

The imaging technique, called 64-slice computed tomography angiography, is already used by many hospitals across the world.

Its name comes from the fact that it uses 64 detectors to produce and combine images.

In the new study, the scans were tested against the current gold standard method of checking a patient for heart disease: angiograms done in a cardiac catheterisation lab. A tube is placed in a blood vessel in the groin and manoeuvred near the heart, and a special dye is infused that makes the arteries show up on X-rays. These can reveal who has blockages and needs treatment with bypass surgery or the artery-opening balloon angioplasty.

The new scans deliver 10 times more radiation to the patient than a standard angiogram. Dr. Miller’s international study was the first direct comparison. It was funded by scanner maker Toshiba Medical Systems, and Dr. Miller has had research grants from the company.

Researchers started with 405 people suspected of having heart disease and eliminated about one-fourth because they had high amounts of calcium in their artery walls. This is common as people age and the arteries harden, and doctors worried that such findings could look like blockages and introduce an element of bias in the results. The remaining 291 people were given the new CT scans, then standard angiograms.

Nine out of 10 patients with blockages were identified by the scans, as were 83 per cent of those without blockages. The scans ruled out heart disease in half the patients — people who could have been spared the pain, expense and risk of catheterisation, Dr. Miller said.

The new scans cost in the U.S. under $1,000 (about Rs. 4,000); angiograms from catheterisation cost $2,500 (about Rs. 10,000) or more. Advanced scanners offering 128- and even 256-slice images are coming into use, so the issue will grow as images become more detailed. — AP

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