What is Optical Molecular Imaging?

Molecular imaging is a technique where the cellular and molecular process of living organisms can be tracked and visualized. Cellular or molecular behavior is tracked or imaged by the use of biomarkers, which are designed to attach and enhance the contrast of diseased tissue or indicate the various pathways in a physiological process.

Molecular imaging opens up the possibility of personalized medicine as now drugs can be designed by seeing the effect they have in a living being on a cellular or molecular level. Usually, changes on a molecular level occur far earlier before a disease (such as cancer) becomes serious. Thus, early detection of these changes through molecular imaging allows early treatment and a far greater chance of cure. Furthermore, although humans are very similar on a genetic level, there are tiny differences based on origin, environment and ancestry, which affect the uptake, metabolism and eventual efficiency of any drug. By tracking or analyzing how drugs work on a molecular level in different subjects, drugs can be made more aligned to particular people, reducing risk and increasing the chances of cure.

Techniques such as PET (Positron Emission Tomography) and MRI (Molecular Resonance Imaging) are typical examples, but they require very expensive specialist equipment and also the use of radioactive materials. Optical imaging, on the other hand, provides functional in vivo molecular imaging at a comparatively lower cost with high sensitivity and minimal toxicity.

Light propagation through tissue is the basis of the technique, where the scattering, absorption and or fluorescence offer biological information due to influences of drugs or other physiological administrations. As disease detection, process and treatment will be based on the detection and monitoring of abnormal molecular processes using biomarkers.  The specificity of detection of these biomarkers provides critical information not only for initial diagnosis but also to determine the most effective course of action. 

In vivo imaging - ventral view: fluorescence intensity map (top) and lifetime map (bottom)
from left : pre-injection, 2h, 6h and 24h after injection of fluorescent probe
Image: Niculae Mincu,  ART Advanced Research Technologies

In vivo imaging - side view: fluorescence intensity map (top) and lifetime map (bottom); from left : pre-injection, 2h, 6h and 24h after injection of fluorescent probe
Image: Niculae Mincu,  ART Advanced Research Technologies

How can I use a SuperK supercontinuum laser source for Optical Molecular Imaging?

The fact that ALL wavelengths are available using supercontinuum technology is an attractive and important aspect. In vivo imaging requires the use of the near-infrared wavelengths between 650 and 900 nm where tissue absorption is much lower than at visible wavelengths and as there are not many light sources available in this area of the spectrum, supercontinuum laser sources is an exciting tool for optimal molecular imaging.

Advanced Research Technologies (ART Montreal) has explored the use of supercontinuum lasers for pre-clinical applications. In this case, OMI is usually conducted on an animal model (typically mice) during the research phases of drug discovery, to obtain information before translation to human application (clinical). In their study, a supercontinuum source (SuperK EXTREME with a SuperK SELECT tunable filter) was integrated with the Optix MX3 imaging system from ART, to provide a tunable light source. One additional, but equally, important aspect in the use of supercontinuum, is the pulsed nature of the source. In this case, increased specificity was obtained by using the lifetime of fluorescence and also allowed additional information such as concentration of and depth location of the biomarker (aka affected tissue).

However, this probe is excited at a wavelength of 578nm, which is difficult to obtain with traditional laser sources. The use of the SuperK EXTREME witht the tunable SELECT filter allowed ideal optimization of fluorescence imaging. With this technology, the time evolution of the probe in the liver and the spleen was also recorded, giving further information about the way a drug becomes metabolized in the living species.