Tumour cells can be found in the bloodstream in the early stages of cancer. However, their low concentration -- around one in a million -- means that detecting these "rare cells" is very difficult. The best technique available today, automated digital microscopy, is too slow for practical diagnosis because it can take up to 32 hours to scan a typical sample, which contains around 50 million blood cells. In contrast, the new FAST scanner -- which relies on various techniques developed for laser printing -- can scan a similar sample in only two minutes.

The technique works by first tagging cancer cells with a fluorescent label, as in conventional imaging methods. This is done with a special antibody reaction that is specific to the cancer cells. A laser is then used to excite the sample and any fluorescence is collected in an array of optical fibres. The field of view in the FAST approach is 50 millimetres, compared with around 1 millimetre for digital microscopy, and this translates into an increase of 500 for the speed with which samples can be scanned.

Initially, the FAST scanner will be used as a pre-screening device to identify candidate tumour cells that would then be examined in more detail with digital microscopy. The device could also be used to detect other rare cells, such as foetal cells in the mother's bloodstream and viral-infected cells.

"Our goal is to enable identification of rare cells in the clinic," says team leader Richard Bruce. "Because the FAST cytometer uses simple, robust technology and enables cost-effective operation, we believe it could make screening for cancer and other rare cells as routine as an annual blood test".