Ultrasound, used to scan babies in the womb, could also help doctors work out the best way to treat cancer patients.

Scientists at the Hammersmith Hospital in London have found the non-invasive and painless technique can help spot which patients are likely to be resistant to a particular drug.

In those cases, doctors could use two or three chemotherapy drugs to tackle the cancer.

Trials have been conducted on women with a particular form of cancer associated with pregnancy.

The discovery ... will hopefully mean better treatment and cure rates for patients with this common disease Dr Michael Seckl, Hammersmith Hospital

But the research team, led by Dr Michael Seckl, say it could also be applied to the care of patients suffering from "organ" cancers such as ovarian, womb, renal and testicular.

He said: "The discovery that such a common technique - ultrasound - can help in the fight against cancer will hopefully mean better treatment and cure rates for patients with this common disease.

"We believe that the same principle will apply to other 'organ' cancers and we are now taking this finding on to investigate whether ultrasound can also help in the diagnosis and treatment of these diseases."

Biopsy technique

At the moment, doctors trying to find out if patient's cancers are drug resistant have to analyse a biopsy of the tumour.

They then measure the blood circulating in the cancer.

The more blood vessels, the more likely the cancer is to resist chemotherapy.

But Dr Seckl said these biopsies were not always accurate, because the samples were so small.

The new technique uses ultrasound, to look at the blood supply in the major artery that supplies the tumour.

He told BBC News Online: "The ultrasound lights up the blood vessels. You can tell how much blood is going to the tumour."

The technique will, he said, be useful in cancers where there is one main blood supply, such as gynaecological cancers.

Lord Winston, director of research and development at the Hammersmith Hospital, said: "Dr Seckl's new finding is a real advance in the struggle to understand the progression of cancer and its response to treatment.

"As ultrasound already exists in most hospitals and is continually being improved, this new technique could help many patients across the UK - especially if the technique provides similar results in other common tumours."

A spokesman for the Cancer Research Campaign, said: "The effectiveness of current cancer therapies is severely hampered by the development of resistance by tumours to some drugs, and the majority of cancer deaths are due to drug resistance.

"Therefore Dr Seckl's work on improving the assessment of drug resistance is important and welcome."

The findings are to be revealed at a meeting of the American Association for Cancer Research in New Orleans on Monday.