Washington, Apr 1 : A team of researchers from Stanford University School of Medicine, led by an Indian-origin scientist, has developed a new type of imaging system, called Raman spectroscopy, that can illuminate details of tumours and tissues with a precision 1,000 times sharper than existing techniques.
Raman spectroscopy can depict tumours in living subjects within a precision of nearly one-trillionth of a meter and has already been used to image both normal tissues and tumours in mice.
"This is an entirely new way of imaging living subjects, not based on anything previously used," said Gambhir.
He added that Raman spectroscopy emits signals that are stronger and longer-lived than other available methods, and the type of particles used in this method can transmit information about multiple types of molecular targets simultaneously.
"Usually we can measure one or two things at a time. With this, we can now likely see 10, 20, 30 things at once," he said.
In Gambhir's opinion, this is the first time Raman spectroscopy has been used to image deep within the body, using tiny nanoparticles injected into the body as markers. When laser light is beamed from a source outside the body, these specialized particles emit signals that can be measured and converted into a visible indicator of their location in the body.
Gambhir said that none of the usual methods can accomplish all the desired qualities of an imaging tool, which include being able to finely detect small biochemical details, being able to detect more than one target at a time and being cheap and easy to use.
Thus, the researchers made good use of the Raman Effect, the physical phenomenon that occurs when light from a source such as a laser is shined on an object. This leads to a spectral fingerprint, which is unique to each type of molecule and can be measured. The researchers used two types of engineered Raman nanoparticles: gold nanoparticles and single-wall carbon nanotubes.
First, they injected mice with some of the Raman nanoparticles with different "tags" - peptides or antibodies. To see the nanoparticles, they used a special microscope that the group had adapted to view anesthetized mice exposed to laser light. This enabled them to see the nanoparticles migrated to the liver, where they were processed for excretion.
As part of a proof-of-principle work, i.e. the gold nanoparticles were tagged with different pieces of proteins that homed in on different tumor molecules, thus making it easy for the detection of the molecular structures.
"We could attach pretty much anything," said Gambhir.
The Raman effect also lasts indefinitely, so the particles don't lose effectiveness as indicators as long as they stay in the body. The researchers could see targets on a scale 1,000 times smaller than what is now obtainable by the most precise fluorescence imaging using quantum dots.
The researchers said that when adapted for human use, the technique has the potential to be useful during surgery, for example, in the removal of cancerous tissue. The extreme sensitivity of the imager could enable detection of even the tiniest of malignant tissues.
The study is published in the latest advance online issue of the Proceedings of the National Academy of Sciences.