The scanner could help detect tumours

This would mean women would not have to undergo unnecessary biopsies to get the all-clear, they say.

Mammograms, which are simple X-rays that show up denser tissue in the breast, are used to check women over 35 for breast cancer.

But critics say they often detect harmless lumps.

Something non-invasive that was able to ... reduce the numbers of women called back for further invasive checks, would be welcome Professor Stephen Duffy, Cancer Research UK

Experts estimate that in the UK, between 70 and 90% of lumps detected by mammograms prove not to be cancerous.

These can be worrying and painful procedures for women, and can prove a significant cost to health services.

The new scanning technique could be used to double-check mammogram results, say its makers.

Blood supply

Dobi Medical Systems, based in New York, US, is developing the scanner.

The company says it looks for the network of blood vessels present to feed tumours with oxygen and nutrients.

The faster the tumour is growing, the denser the network of capillaries.

The check squeezes the breast between a camera and bright red LEDs, using less pressure than potentially painful mammograms.

The Dobi scanner squeezes the blood out of most of the breast, but some remains trapped in tumour capillaries which are particularly convoluted.

Philip Thomas, of Dobi, said: "They are very tortuous, intertwined like a bird's nest."

Blood absorbs red light, so if there is a tumour, the area will show up as a darker patch.

The company says its scanner would be cheaper than magnetic resonance imaging (MRI) scans which can produce similar images.

If the Dobi scan and the mammogram indicate problems in the same area, that would be a strong indication it is cancer, it says.

Younger women

Preliminary tests in 200 women showed using both checks cut the number of "false positive" results by 70%.

However, Martin Yaffe, a breast-imaging specialist from the University of Toronto, said the development of some types of aggressive cancers were not associated with the development of new blood vessels.

And he warned that, until the scan was proved to be reliable, it was better to do a biopsy than risk a woman's life.

Dr Yaffe said it could also be difficult to distinguish between the capillary clusters around cancerous and benign tumours, and that there was a risk of "false negative" results.

However Richard Davies of the Hackensack University Medical Center in New Jersey, who has been supervising trials of the Dobi scanner, said the check could be useful in assessing the breast tissue of younger women.

They are not suitable for mammograms because their breast tissue is denser than that of older women.

It may also be possible for the scanner to provide even speck-sized tumours which are too small to show up on mammograms.

The research will be presented to a US conference next week and is published in New Scientist magazine.

Clinical trials are due to take place later this year.

Sensitivity

Professor Stephen Duffy, an expert in cancer screening from Cancer Research UK, told BBC News Online: "Something non-invasive that was able to be done at the same time as a mammogram, and therefore reduce the numbers of women called back for further invasive checks, would be welcome."

But he added: "I'd want this to be researched thoroughly to ensure that increased specificity was not paid for by a drop in sensitivity."

He said a scanner which could be used to check younger women's breasts would be extremely useful.