Early detection of life-threatening diseases often relies on high-quality and timely biomedical imaging for doctors to make an accurate diagnosis. To expedite and improve the process, UCLA bioengineering associate professor Liang Gao is leading a team of engineers, scientists and doctors to develop a promising new technique that can provide microscopic imaging in detail while cutting unnecessary wait time.
Fluorescence lifetime imaging microscopy, or FLIM, is a commonly used biomedical imaging technique that looks for the telltale light signatures of specific molecules. That information can illuminate what’s happening in and around a cell by showing whether certain molecules are present. Tissue samples are prepared with dyes containing fluorophores — essentially little glowsticks that switch on for a few nanoseconds (the duration of their lifetime) before decaying. The method can also pinpoint target molecules by their light signature alone without the need for dyes or stains.
FLIM technology has been in existence since the late ’80s. However, it is a relatively slow process, sometimes taking several minutes to scan just one prepared slide pixel by pixel, or line by line. For 3D imaging, it takes even longer.
The UCLA-led team has adapted FLIM to produce highly detailed real-time 3D images of tissue sections in little more than 30 seconds compared to the 10-plus minutes required using conventional technology.
Detailed in the Proceedings of the National Academy of Science, the combined light-field tomographic FLIM (LIFT-FLIM) approach could open a range of new avenues in basic scientific research as well as biomedical applications where rapid biological sample mapping is needed.
In designing the new technique, Gao’s research group Intelligent Optics Laboratory at the UCLA Samueli School of Engineering leveraged its previously developed ultrafast 3D camera LIFT technology, which can take 3D images at 100-billion-frames per second. The LIFT-outfitted camera uses an array of lenses focused on one focal point, with each different orientation of the lenses offering a unique perspective. Following computer processing, the resulting 3D images present an ultrafine resolution. This enables video capturing of transient light events, such as fluorescence decay in FLIM, to process and combine a set of scans that makes up a final image at lightning speed.
With LIFT-FLIM, the researchers use a single camera that has a steerable mirror designed to capture a sample’s different viewing angles. Once the sample is imaged, the scanning and computational processing take just a few to tens of seconds to produce fully realized 3D fluorescence lifetime images that provide critical quantitative readouts of biomedical microenvironments. These images show what happens inside tissues cell by cell.
The researchers tested the new technique on a mouse kidney section slide using fluorophore-filled dyes. They also tested human lung cancer pathology slides where the presence of particular molecules is picked up by the camera without the use of fluorescence.
“With the LIFT-FLIM technique, we can distinguish tumors from normal tissues just by looking for differences in their natural metabolic activity without the need to add external contrasting stains,” Gao said. “This capability makes it a promising tool for cancer imaging, both for the ultraclear resolution it provides and the much shorter time it takes compared to other technologies.”
The team also demonstrated the technique’s versatility using lung organoids, which are miniature 3D tissue structures created from stem cells that mimic the structure and function of human lungs. The researchers used four different fluorophores, each one lit up to detect whether target molecules are active by scanning multiple parts of the light spectrum at once.
In addition to using LIFT-FLIM to help doctors detect tumor cells and decipher their margins, the researchers say the technique can also apply to metabolism studies and help speed up screening of potential drugs for personalized medicine at assembly-line speeds and volumes.
The research was supported by grants from the National Institutes of Health. The study’s co-first authors are Yayao Ma, a former UCLA doctoral student advised by Gao; and Jongchan Park, a research scientist with Gao’s lab.
Aydogan Ozcan, UCLA’s Volgenau Chair for Engineering Innovation and a professor of electrical and computer engineering and bioengineering, is a senior author. Other senior authors are from UCLA Health — Dr. Robert Cameron, a thoracic surgeon; Dr. Brigitte Gomperts, a pulmonary medicine specialist and co-director for cancer stem cell biology at the Jonsson Comprehensive Cancer Center; and Dr. Gregory Fishbein, an anatomic pathologist.
UCLA Samueli doctoral student Xilin Yang, as well as Luzhe Huang and Qi Cui, who both graduated with a Ph.D. from UCLA this year, are also authors on the paper. Other authors on the paper include Edoardo Charbon, Samuel Burri and Claudio Bruschini — all from the Ecole Polytechnique Federale de Lausanne in Switzerland.
The UCLA Technology Development Group has filed for U.S. patents on the new technology.