A team of investigators at the MGH Martinos Center for Biomedical Imaging has developed a tool that will allow researchers to measure multiple biological components or processes at the same time, opening up a host of applications, especially related to the study of disease. They describe the tool in a paper published today in the journal Optica.
Simultaneous acquisition of different types of information is typically referred to as ‘multiplexing.’ Researchers have demonstrated multiplexing with optical imaging methods, in particular by exploiting a parameter called fluorescence lifetime: that is, the time it takes for a molecule to relax to its ground state after it has been excited by a laser pulse. Different fluorescent dyes often have distinct fluorescence lifetimes, so by using multiple dyes researchers have been able to label different parts of a disease in tissue samples and visualize these parts using microscopy techniques.
There is a notable impediment to this approach for imaging in living animals, though: tissue scattering timescales are in the same range as the fluorescence lifetimes, thus impairing the accuracy of recovering short lifetimes in tissue.
The new tool reported in the Optica paper helps to overcome this obstacle. The researchers—Anand Kumar, Steven Hou and William Rice—had previously shown that high spatial light frequency patterns can help to reveal short fluorescence lifetimes in tissue. Drawing on this finding, they developed an approach—the spatial frequency-asymptotic time domain (SF-ATD) approach—that enables localization and quantification of multiple dyes with subnanosecond lifetimes in highly scattering biological tissue. The tool was made possible, said Kumar, an assistant professor of radiology and principal investigator of the Optical Molecular Imaging Laboratory in the Martinos Center, by using a simple movie projector coupled with a pulsed laser (instead of the standard LEDs) to shine spatial patterns onto the subject.
The first technique to combine the benefits of lifetime multiplexing and spatial frequency domain measurements, the SF-ATD approach will provide a powerful tool for imaging disease processes in whole-animal disease models, thus contributing in important ways to accelerating drug discovery. Potentially, the approach could also be applied in humans, Kumar said. To this end, he and his team are now optimizing it for in vivo applications.