CT scanning is sometimes used to diagnose coronary artery blockages. The study, published in the New England Journal of Medicine found that the expensive CT scans can detect narrowed blood vessels in people with suspected heart disease nearly as well as the conventional test in which doctors thread a catheter directly into the heart.

Researchers at Johns Hopkins University in Baltimore found that so-called 64-row Computed Tomography, or CT, scans were 93 per cent as precise as conventional cardiac catheterisation without subjecting a patient to an invasive procedure.

In a statement, Johns Hopkins cardiologist Dr Joao Lima, one of the researchers, said CT scans are “an alternative diagnostic tool” that doctors can use to rule in or rule out coronary blockages when other, more indirect tests for reduced blood flow, such as cardiac stress testing, are unclear or unsafe for a particular patient.

The study, sponsored in part by the company that makes one brand of scanners, Toshiba Medical Systems, concluded scanners “cannot replace conventional coronary angiography at present”.

The problem is not just that the scans are not yet as good as conventional angiography. The amount of radiation received with a CT heart scan is double, triple or quadruple the exposure in conventional angiography.

“We’re talking about 500 chest X-rays with one of these cardiac CTs, so it’s a lot of radiation,” said the study’s co-author, cardiologist Dr Rita Redberg of the University of California. That could increase the risk of breast or lung cancer, another issue that should be studied.

And even if a correctable problem is found in a CT scan of the heart, doctors must do further testing and possibly more procedures. With conventional angiography, if doctors find a blocked blood vessel, they can often open it on the spot.