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Imaging technique reveals tumors in mice


Scientists have developed a new imaging technique that may eventually allow doctors to view the changes taking place inside a patient's cell during the earliest stages of disease. In a demonstration, the researchers determined the shape of brain tumors in living mice and measured the levels of a key enzyme.

Mouse head with tumor fluoresced: MR image slice super-imposed on FMT image.

The technique, called fluorescence molecular tomography, offers the potential for identifying disease-related changes in cells earlier than is typically possible using other techniques, such as an X-ray CAT scan and molecular resonance imaging (MRI). These provide snapshots of the physiology of disease after it has already taken shape in the body.

"Molecular imaging can tell you not only that the disease is there, but what this disease is made of and the information to best cure it," says Vasilis Ntziachristos, who led the study at the Center for Molecular Imaging Research at Massachusetts General Hospital and Harvard Medical School in Charlestown, Massachusetts.

As a test case, the researchers implanted tumor cells into the brains of living mice. These cells grew into tumors that expressed the enzyme cathepsin-B. The team then injected 'probes' that attached to the enzyme. The fluorescent probes lit up when exposed to light, indicating the presence of the enzyme and revealing the shape of the tumor.

The researchers also measured changes in the amount of enzyme in tumors. They were able to detect tumors that had five times the amount of enzyme compared to other tumors, according to the findings published in Nature Medicine.

The number of known targets for detecting disease is "increasing at a tremendous rate as a consequence of genome-sequencing projects," the researchers write in their paper.

Left: Image of tumor in white light. Right: Same tumor with fluorescent probe activation after FMT.

Fluorescence molecular tomography is one of several imaging techniques being used to study individual molecules or cells. The Center for Molecular Imaging Research is investigating technologies for monitoring how drugs are delivered to cells, the effects of gene therapy, and the spread of viruses in the body.

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Ntziachristos, V. et al. Fluorescence molecular tomography resolves protease activity in vivo. Nat Med 8, 757-760 (July 2002).

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