A new hi-tech body scan could provide a more reliable method of monitoring slow-growing prostate cancer, according to scientists.
The new technique, called diffusion-weighted magnetic resonance imaging, is designed to help doctors decide more effectively when a patient needs treatment.
Currently, many patients undergo "active surveillance", whereby doctors monitor their cancer with biopsies and blood tests, and start treatment when the tumour starts to grow more quickly.
The scan is described as more patient friendly, removing the need for painful and invasive biopsies, while the standard PSA (prostate specific antigen) blood test can be inaccurate.
In the pilot study, 50 patients were scanned at the time of their initial diagnosis and given another examination two years later.
Each scan was used to calculate a figure called "apparent diffusion coefficient", a measurement of water movement within tissue.
Previously it had been shown that these measurements are significantly lower in men with high-risk prostate tumours.
By the time of their follow-up appointment, 17 of the men had received required treatment while 33 remained under active surveillance.
The team found the diffusion-weighted readings fell between the two scans in men who progressed to treatment, but remained constant in those who did not.
Study leader Professor Nandita deSouza, from the Institute of Cancer Research, based in Sutton, Surrey, and London, said: "Diffusion-weighted MRI has a lot of potential for monitoring patients under active surveillance, as the scans clearly showed which men's cancers were progressing.
"If the technique continues to show promise in larger-scale studies, it could one day save men under active surveillance from the discomfort and potential complications of regular biopsies."
The findings were published in the British Journal of Radiology.