Researchers have created a non-invasive imaging technique that allows laser light to penetrate deeper into living tissues, producing clearer images of cells. This advancement could assist clinical biologists in monitoring disease progression and developing new treatments.
Metabolic imaging is a non-invasive approach that allows scientists and clinicians to observe living cells using laser light, enabling them to evaluate how diseases progress and how treatments respond.
Light scatters when it enters biological tissues, which restricts its penetration depth and reduces the quality of the images produced.
Recently, MIT researchers have introduced a novel technique that significantly increases the depth limitation of metabolic imaging. Their innovation also enhances imaging speed, resulting in more detailed and enriched images.
This method does not require any prior preparation of the tissue, such as cutting or staining. Instead, a specialized laser is used to shine deep into the tissue, prompting specific intrinsic molecules within the cells and tissues to emit light. This ensures that the tissue remains unaltered, allowing for a more authentic and accurate depiction of its structure and functioning.
The researchers accomplished this by adaptively refining the laser light for deep tissue applications. By utilizing a newly designed fiber shaper, which they can manipulate by bending it, they can adjust the color and pulses of light to reduce scattering and enhance the signal as it penetrates deeper into the tissue. This technique allows them to visualize much deeper into living tissues and capture clearer images.
The improved depth penetration, increased speed, and enhanced resolution make this method especially suitable for complex imaging needs, such as cancer research, tissue engineering, drug discovery, and examining immune responses.
“This work highlights a significant leap in depth penetration for label-free metabolic imaging and opens new pathways for investigating metabolic dynamics deep within living biological systems,” states Sixian You, an assistant professor in the Department of Electrical Engineering and Computer Science (EECS), who is a key author of the study on this imaging method.
She is joined in this research by lead author Kunzan Liu, an EECS graduate student; Tong Qiu, a postdoc at MIT; Honghao Cao, an EECS graduate student; Fan Wang, a professor of brain and cognitive sciences; Roger Kamm, the Cecil and Ida Green Distinguished Professor of Biological and Mechanical Engineering; Linda Griffith, a Teaching Innovation Professor at the Department of Biological Engineering; and other MIT collaborators. The findings will be published in Science Advances.
Laser-focused
This innovative technique is categorized under label-free imaging, meaning that the tissue does not require staining beforehand. Staining can create contrast that enhances a clinical biologist’s ability to observe cell nuclei and proteins. However, staining often necessitates slicing the sample, which can damage the tissue and prevents the observation of dynamic processes in living cells.
In label-free imaging methods, researchers use lasers to illuminate specific molecules in cells, causing them to emit light in various colors that reveal differing molecular constituents and cellular structures. Nevertheless, producing optimal laser light with specific wavelengths and high-quality pulses for deep tissue imaging has proven challenging.
To address this problem, the researchers devised a new strategy. They utilized a multimode fiber—an optical fiber capable of transmitting significant power—and paired it with a compact apparatus called a “fiber shaper.” This shaper enables them to precisely adjust the propagation of light by modifying the fiber’s shape. Bending the fiber alters the color and intensity of the laser light.
Building on previous research, the team adapted the original version of the fiber shaper for enhanced multimodal metabolic imaging.
“Our goal is to concentrate all this energy into the desired colors with specified pulse properties. This approach enhances generation efficiency and yields a clearer image, even deep within tissues,” says Cao.
Once they developed the controllable mechanism, they created an imaging platform that harnesses the powerful laser source to produce longer wavelengths of light, which are vital for better penetration into biological tissues.
“We believe this technology can significantly propel biological research forward. By making it affordable and more accessible to biology laboratories, we aim to provide scientists with a powerful tool for discovery,” Liu explains.
Dynamic applications
When the researchers tested their imaging device, they discovered that the light could penetrate more than 700 micrometers into a biological sample, while the best previous techniques only reached about 200 micrometers.
“With this innovative deep imaging method, we aim to explore biological samples and observe phenomena we’ve never seen before,” adds Liu.
This deep imaging capability has enabled researchers to visualize cells at various levels within a living system, which can facilitate the examination of metabolic changes occurring at different depths. Additionally, the increased imaging speed allows for the collection of more detailed information about how a cell’s metabolism influences its movement speed and direction.
This new imaging technique could significantly enhance the research on organoids—engineered cellular structures that mimic the architecture and function of actual organs. Researchers in the labs of Kamm and Griffith are leading efforts in developing brain and endometrial organoids capable of growing like organs for the assessment of diseases and treatments.
However, accurately observing the internal activities without slicing or staining the tissue remains a challenge, as those processes often destroy the sample.
This new method enables scientists to monitor the metabolic states inside living organoids as they continue to grow without invasive interference.
With these and other biomedical applications on the horizon, the researchers aim to produce even higher-resolution images. They are also working on creating lower-noise laser sources that could further extend imaging capabilities while minimizing light dosage.
Additionally, they are developing algorithms that can respond to the images captured and reconstruct high-resolution, full 3D structures of biological samples.
Ultimately, they aspire to implement this technique in real-world scenarios to aid biologists in tracking drug responses in real-time, contributing to the development of new medicinal therapies.
“By facilitating multimodal metabolic imaging that penetrates deeply into tissues, we are offering researchers an exceptional opportunity to observe opaque biological systems in their natural state. We are eager to collaborate with clinicians, biologists, and bioengineers to further advance this technology and transform these insights into tangible medical breakthroughs,” remarks You.
This research has been supported in part by MIT startup funds, a U.S. National Science Foundation CAREER Award, an MIT Irwin Jacobs and Joan Klein Presidential Fellowship, and an MIT Kailath Fellowship.
