The researchers at the Massachusetts Institute of Technology (MIT) in the US used their imaging system, named “DOLPHIN,” which relies on near-infrared light, to track a 0.1-millimetre fluorescent probe through the digestive tract of a living mouse.
They also showed that they can detect a signal to a tissue depth of eight centimeters, far deeper than any existing biomedical optical imaging technique. The researchers, including Neelkanth Bardhan, a postdoctoral fellow at MIT, and one of the lead authors of the study, hope to adapt their imaging technology for early diagnosis of ovarian and other cancers that are currently difficult to detect until late stages.
“We want to be able to find cancer much earlier,” said Angela Belcher, a professor at MIT.
“Our goal is to find tiny tumours, and do so in a noninvasive way,” Belcher said in a statement.
Existing methods for imaging tumours all have limitations that prevent them from being useful for early cancer diagnosis, according to the study published in the journal Scientific Reports.
Most have a tradeoff between resolution and depth of imaging, and none of the optical imaging techniques can image deeper than about three centimeters into tissue. Commonly used scans such as X-ray computed tomography (CT) and magnetic resonance imaging (MRI) can image through the whole body.
However, they can not reliably identify tumours until they reach about one centimetre in size, said researchers, including MIT graduate student Swati Kataria. The researchers wanted to develop technology that could image very small groups of cells deep within tissue and do so without any kind of radioactive labelling.
Near-infrared light, which has wavelengths from 900 to 1700 nanometres, is well-suited to tissue imaging because light with longer wavelengths does not scatter as much as when it strikes objects, which allows the light to penetrate deeper into the tissue.
To take advantage of this, the researchers used an approach known as hyperspectral imaging, which enables simultaneous imaging in multiple wavelengths of light. They tested the system with a variety of near-infrared fluorescent light-emitting probes, mainly sodium yttrium fluoride nanoparticles that have rare earth elements such as erbium, holmium, or praseodymium added through a process called doping.
Depending on the choice of the doping element, each of these particles emits near-infrared fluorescent light of different wavelengths. Using algorithms that they developed, the researchers can analyse the data from the hyperspectral scan to identify the sources of fluorescent light of different wavelengths, which allows them to determine the location of a particular probe.
By further analysing light from narrower wavelength bands within the entire near-IR spectrum, the researchers can also determine the depth at which a probe is located.
To demonstrate the potential usefulness of this system, the researchers tracked a 0.1-millimetre-sized cluster of fluorescent nanoparticles that was swallowed and then travelled through the digestive tract of a living mouse.
These probes could be modified so that they target and fluorescently label specific cancer cells.
“In terms of practical applications, this technique would allow us to non-invasively track a 0.1-millimetre-sized fluorescently-labelled tumour, which is a cluster of about a few hundred cells,” said Bardhan.
“To our knowledge, no one has been able to do this previously using optical imaging techniques,” he said.
Mar 12, 2019 12:04 IST