A new medical imaging technique can reveal the chemical make-up as well as the shape of structures inside the body. It provides a non-invasive way to get information about tumours or other disease sites normally only accessible by biopsy.

That information can be crucial to knowing the nature of disease, for example, the aggressiveness of a tumour.

Today's medical scans, such as computed tomography (CT) and positron emission tomography (PET), can yield exquisite detail of the structure of organs and tumours. But they come with the added risk of radiation exposure and reveal nothing about the chemistry of the parts being imaged.

However, a scanning technique called Raman spectroscopy can now be used to reveal such information about cancers near the skin's surface without invasive procedures.

The new method uses safe, low-power infrared lasers in combination with nanoparticles that tag areas of interest, and has been used by a US research group to give full body cancer scans to rats, revealing the location of tumours.

Light shift

Before the scan, nanoparticles are coated with antibodies that bind to molecules of interest, for example a marker found on tumour cells. Once the nanoparticles are administered into the animal, they will bind to any cells with those markers.

The location of the nanoparticles, and hence the tumour, can then be detected because they shift the colour of the laser light shone into the body.

Nanoparticles of different sizes shift the laser light's colour by different amounts, while using different antibodies can be used to target them to different disease markers. Using those options together makes it possible to reveal different chemical structures – for example different kinds of cancer cell – as different colours in a single scan.

Sanjiv Gambhir, and colleagues at Stanford University, California, US, used gold nanoparticles coated in silica, as well as carbon nanotubes to perform their full-body scans (see image, top right).

The scans can so far reveal only tumours just under the rats’ skin, to a depth of 2 mm. Gambhir thinks that can be increased with higher nanoparticle concentrations or higher laser power, but says it is unclear how far the method will ultimately reach.

'Exciting opportunities'

Shuming Nie at Emory University, Atlanta, Georgia, US, and colleagues used gold nanoparticles to image cancer in rats in January this year, but were only able to scan small parts of the body at one time.

"Taken together, the Stanford paper and our own work open exciting opportunities in using Raman spectroscopy for in-vivo molecular imaging and detection," says Nie.

Ihtesham Rehman of Queen Mary University, London, UK says the technique has particular potential for cancer screening.

"The advance here is that you get the chemical structure of the cancer," he told New Scientist. "That's useful because you can look at the cancer type and grade." That should help clinicians choose a course of treatment quickly, without any painful biopsies and lengthy analysis, he explains.

Revealing different disease markers in multiple colours could also speed up treatment by searching for many different kinds of cancer in a single scan, he adds.

Journal references: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.0710575105) and Nature Biotechnology (DOI: 10.1038/nbt1377)

Top of Page

BACK to STEP News