A new scanning test developed in the UK could help doctors pinpoint dangerous cancers before they spread around the body.
The technique uses magnetic resonance imaging (MRI) to map regions of oxygen deprivation within tumours.
Lack of oxygen, or hypoxia, is often a sign that a cancer is growing aggressively. It also stimulates the growth of blood vessels linked to tumours that promote cancer spread.
The new scan could guide the targeting of dangerous tumours with high-dose radiotherapy, and track the effectiveness of cancer treatments by monitoring oxygen.
Study co-leader Dr Simon Robinson, from The Institute of Cancer Research in London, said: "Our technique uses MRI technology to detect tumours with areas of oxygen depletion, which tend to be more aggressive and more resistant to radiotherapy and chemotherapy.
"Our study provides strong pre-clinical evidence to validate the use of oxygen-enhanced MRI to identify, quantify and map tumour hypoxia."
The results of tests of the new scan on mice are reported in the journal Cancer Research.
Oxygen-enhanced MRI works by monitoring changes to image intensity caused by concentrations of dissolved oxygen altering in blood plasma and tissue fluid. It is carried out while the patient inhales pure oxygen.
Some tissues take up the extra oxygen more rapidly than others. The scientists predicted that the image alterations would be much less marked in hypoxic tumour regions.
The technology is now being further developed with clinical studies of cancer patients.
Dr James O'Connor, from the University of Manchester, who also led the research, said: "There is currently no validated, affordable and widely available clinical imaging technique that can rapidly assess the distribution of tumour hypoxia.
"Our findings from studies in mice are already being translated for use on conventional clinical MRI scanners.
"Ultimately we hope that oxygen-enhanced MRI will not only help to identify the most dangerous tumours, but to assist radiotherapy treatment planning and for monitoring treatment response."
Nell Barrie, senior science information manager at Cancer Research UK, said: "When cancer cells run out of oxygen, they're more likely to spread from the original tumour, making the disease much harder to treat.
"Spotting this process in action could help improve treatment, especially for more aggressive tumours."