SPIE Photonics West 2017

In an interview with SPIE last fall, Rafael Yuste, professor of neuroscience at Columbia University (USA) and the “brains” behind the US BRAIN Initiative, stated, “One of the big challenges I see (in advancing the study of the human brain) is the need to image in 3D, and that calls for the reinvention of the microscope.”

If the presentations at the Hot Topics and the neurophotonics plenary sessions at SPIE Photonics West are any indication, the biophotonics research community is well on its way to meeting the challenge.

Advances in microscopy dominated the rapid-fire Hot Topics presentations at BiOS, where technologies that could dramatically influence molecular research, drug development, and clinical diagnostics were detailed. And the neurophotonics plenary session was just as strongly focused on technologies being developed by neuroscientists, engineers, physicists, and clinical researchers to measure tens of thousands of neurons simultaneously.

“SPIE recognized the need to bring together all the different groups in this field to get an overview of the many neurophotonics activities going on,” said Neurophotonics editor-in-chief and SPIE Fellow David Boas, who moderated the neurophotonics plenary session, the first at Photonics West.

The neurophotonics plenary presentations highlighted the diversity of these research efforts, from genetically encoded indicators of neuronal activity to 3-photon microscopy for deep brain imaging, chemical sectioning for high throughput brain imaging, and mapping functional connections in the brain.

“We need to step back and think about all of these important methods and the larger picture,” said Yuste, a pioneer in the development of optical methods for brain research. His presentation covered novel neurotechnologies and their impact on science, medicine, and society.

“Why don’t we already understand the brain?” Yuste asked. “People say it’s just too complicated, but I believe the reason … is that we don’t have the right method yet. We do have methods that allow us to see the entire activity of the brain, but not enough resolution of a single neuron.

“We need to be able to record from inside the neuron and capture every single spike in every neuron in brain circuits,” he said.

Here are highlights from other neurophotonics plenary talks, which were among 4700 presentations at Photonics West this year:

SPIE Fellow Peter So, professor of mechanical and biological engineering at Massachusetts Institute of Technology (USA), described his group’s work using 3D holographic excitation for targeted scanning as a way to study and map synaptic locations in the brain. “Neurons generate responses from many synaptic inputs,” he said, “and we found that there are over 10,000 synaptic locations we would like to look at in parallel and map using synaptic coordinates to map activity,”

Three-photon microscopy “has vastly improved the signal-to-background ratio for deep imaging in a non-sparsely labeled brain,” said Chris Xu of Cornell University (USA). By combining a long wavelength (1300-1700 nm, the optimum spectral windows for deep imaging) with high excitation, Xu said researchers are making new inroads into deep imaging of brain tissue. Three-photon microscopy is also valuable for structural imaging and for imaging brain activity “in an entire mouse cortical column,” Xu added.

The wiring diagram of a human brain, measured in a healthy individual, where the movement of water molecules is measured by diffuse tensor magnetic resonance imaging, revealing the connections. This is an example of the type of work being done by the Human Connectome Project.

Mapping brain function is typically performed using task-based approaches to relate brain topography to function, noted Adam Bauer of Washington University School of Medicine (USA). “But we want to … help patients who are incapable of performing tasks, such as infants and those with impairments,” he said. For this reason, Bauer’s lab has developed the functional connectivity optical intrinsic signal (fcOIS) imaging system to study mouse models of Alzheimer’s, functional connectivity following focal ischemia, and to map cell-specific connectivity in awake mice.

Edmund Talley of the US National Institutes of Health shared his experiences with the US BRAIN Initiative, slated to receive more than $430 million in the 2017 federal budget, plus $1.6 billion in dedicated funds through 2026 via the 21st Century Cures Act passed in December 2016. “There is some very serious investment in neurotechnologies to understand how the mind works, and there is bipartisan political support,” Talley said. “Multiple federal agencies are funding this.”

Taking a cue from Nobel Laureate Roger Tsien, a pioneer in the field of engineering proteins for neuroscience, Canadian researchers at the University of Alberta are working to develop new kinds of protein indicators to study neuronal activity, noted the university’s Robert Campbell. While early calcium indicators were synthetic tools, the Campbell Lab is working on genetically encoded proteins, taking a fluorescent protein and turning it into a calcium indicator, “a proxy for neuronal activity,” Campbell said. Most recently, they have developed FlicR1, a new type of red fluorescent voltage indicator that can be used to image spontaneous activity in neurons. “We are very optimistic about this new indicator,” he said.

Optical detection of spatial-temporal correlations in whole brain activity is “very important because morphology and functionality in the brain are tightly correlated to each other,” said SPIE Fellow Francesco Pavone of Università degli Studi di Firenze in Italy. Pavone’s group is taking a multimodal approach in mouse models to study brain rehabilitation following a stroke. Techniques include using light-sheet microscopy to look at vasculature remodeling, two-photon imaging to study structural plastics, and wide-field meso-scale imaging to evaluate functional plasticity.

SPIE member Valentina Emiliani, director of the Neurophotonics Laboratory at Université Paris Descartes (France), discussed her lab’s work on multicell, multiplane optogenetics with millisecond temporal resolution and single cell precision. Researchers are working with computer-generated holography, spatial light modulators (SLMs), and endoscopy to control the activity of a single neuronal cell. “We have been able to achieve very robust photostimulation of a cell while the mice were freely moving, with nice spatial resolution,” she said.

SPIE member Maria Angela Franceschini of the Athinoula A. Martinos Center for Biomedical Imaging (USA) described her group’s work developing MetaOX, a tissue oxygen consumption monitor. The instrument has been tested in neonatal intensive care units to monitor hypoxic ischemic injury and therapeutic hypothermia. It uses frequency-domain near IR spectroscopy (NIRS) to acquire quantitative measurements of hemoglobin concentration and oxygenation and diffuse correlation spectroscopy (DCS) to create an index of blood flow. The device is also being evaluated in Africa to study the effects of malnutrition on brain development and hydrocephalus outcomes in newborns.

Shaoqun Zeng of the Wuhan National Lab for Optoelectronics in China outlined his group’s work using chemical sectioning for high-throughput fluorescence imaging of a whole mouse brain at synaptic resolution. The goal is to systematically and automatically obtain a complete morphology of individual neurons.

The Hot Topics session began with a talk by SPIE Fellow Christopher Contag of Michigan State University (USA), recipient of the 2017 SPIE Britton Chance Biomedical Optics Award. Contag, a pioneer of in vivo optical imaging using bioluminescent reporters, described advances in imaging and microscopy technologies, including a tiny snap-together microscope.

Microscopy was certainly a running theme throughout the Hot Topics session, with talks on noninvasive optical biopsies, cardiac optogenetics, next-generation optical coherence tomography (OCT), and optical topography.

SPIE Fellow Alberto Diaspro of the Istituto Italiano di Tecnologia (Italy) celebrated the evolution of the microscope in his talk, “The Extra Microscope.” From the “microscopiums” and “telescopiums” of the 1600s to the nanoscale optical microscopes (“nanoscopy”) of today, “with the microscope we can make visible what is invisible,” Diaspro noted. “We are interested not only in the cell, but what is in the cell, the cell interactions. And this is what we can address with the microscope.”

Toward this end, SPIE member Richard Levenson, a medical doctor and professor at the University of California, Davis Medical Center (USA), described a novel technique that uses ultraviolet surface excitation for slide-free tissue microscopy. Dubbed “MUSE,” it could have profound implications for global health, Levenson said.

“Pathology is still the gold standard for diagnosis and therapy guidance, and we still use ‘state of the art’ equipment: a microscope and a slide,” he said. “But the pathologist has to go through multiple steps, and it takes hours to go from a ‘lump’ to a slide. With MUSE, we are proposing to get rid of all those steps and make it a three-minute process.”

Based on intellectual property jointly developed at Lawrence Livermore National Lab and UC Davis, the MUSE microscope uses short-wavelength UV light that penetrates only microns-deep into tissue, eliminating the need for precision-cut, thin specimens. The physical setup is simple (the light source, for example, is a single UV LED) — so simple, in fact, that some people are adapting MUSE for use with cell phones. In addition, the single-wavelength, 280-nm LED can excite many fluorescent dyes simultaneously.

“We can also look at very large fields of view, such as a whole brain slice, because we don’t have to make thin slices,” Levenson said. “So it makes it a very convenient tool for neurophotonics, for looking at very large areas of the brain.”

“With MUSE, we see surfaces, not just cut sections,” he said. “So we can see what things actually look like. We can see the structure and ‘color’ (false color) of things more or less in their native format, vs. arbitrarily in sections. With MUSE you get a combination of electron microscopy and fluorescence.”

In his talk on “Biomedical Imaging and Spectroscopy with Scattered Light,” Lev Perelman of Harvard University Beth Israel Deaconess Medical Center (USA) shared his group’s research involving confocal light absorption and scattering spectroscopic (CLASS) microscopy. This unique type of microscopy provide new insights into cell structures using the innate light-scattering spectra within each cell as the source of the contrast.

“There are approximately 1000 different types of cells in the human body, but they are all built from the same set of building blocks: organelles, or membrane-bounded compartments inside the cells,” Perelman said. “And different wavelengths of light can be used to look at how light is scattered by these organelles, without the need for any external markers.”

His group has used this approach to study cancer progression in live esophageal cells and also to image organs, such as Barrett’s esophagus, often a precursor to oral and pharyngeal cancers. “Using endoscopic multispectral scanning light-scattering imaging, it takes only one minute to scan the entire esophagus,” he said.

Richard Levenson	Emilia Entcheva	Robert Alfano
Lev Perelman	Zhongping Chen	Hideaki Koizumi
Alberto Diaspro	Enrico Gratton	Rafael Yuste

Robert Alfano from the City College of New York/City University of New York (USA), a pioneer in the development of optical biopsy techniques, provided an update on recent advances in this field. Among the notable findings from his lab: that tryptophan is a key marker for aggressive cancer. “Cancer cells like to eat tryptophan,” he said.

In addition, his research team has demonstrated three short-wave IR optical windows that appear to offer advantages for optical biopsies: 1100-1350 nm, 1600-1870 nm, and 2100-2300 nm. “Over the years, the 650-950 nm was mainly used to go into tissues via silicon detectors,” Alfano said. “But with the advent of InGaAs and InSb CCD/CMOS detectors, we can now go into the infrared. In particular, 1700 nm allows you to go deep into tissue without scattering and with good absorption. So as long as you’re not photon starved, you will get good images.”

Emilia Entcheva, professor of biomedical engineering at George Washington University (USA), walked the audience through her group’s work in cardiac optogenetics, a new framework for the study of cardiac electrophysiology and arrhythmias. Their goal is to use optogenetic sensors and actuators to achieve high throughput, all-optical cardiac electrophysiology for applications in drug development (cardiotoxicity screen), drug discovery, and patient-specific therapies via the functional characterization of stem-cell derived heart microtissues.

Her group has developed OptoDyCE, a fully automated system for all-optical cardiac electrophysiology. The device is the first high-throughput cardiac optogenetic system that can do this, according to Entcheva, and it has the potential to process 600 independent multicellular tissue samples per hour and more than 10,000 compounds per day.

SPIE Fellow Zhongping Chen of the University of California, Irvine (USA) discussed advances in functional OCT, noting that 2016 was the 25th anniversary of OCT and 2017 is the 20th anniversary of Doppler OCT and OCT angiography. Chen’s talk focused primarily on OCT angiography and Doppler OCT. In addition to clinical applications, Doppler OCT is important for vascular mapping, neuron detection, and for studying neurovascular disease and respiratory cilia function, Chen noted.

“OCT has made a tremendous impact in clinical medicine, particularly ophthalmology,” he said. “What is most exciting is that this technology has been translated to the clinic, where it has become the standard of care for studying microvasculature.”

Speakers also included Enrico Gratton, also of UC-Irvine, and Hideaki Koizumi of Hitachi (Japan). Gratton’s work centers on new forms of fluctuation correlation spectroscopy and fluorescence diffusion tensor image analysis to map the diffusion of molecules. Koizumi discussed instrumentation and applications for optical topography (functional NIRS) and said his dream is to develop a “mindscope” that could be used for diagnosing brain diseases such as depression and schizophrenia.

Plenary talks on quantum dot technologies for secure telecommunications, EUV light sources for high-volume manufacturing lithography, and nanorobots for in vivo imaging and drug delivery mesmerized audiences at the LASE, OPTO, and nano/ biophotonics plenary sessions at Photonics West this year.

Some of the world’s most respected scientists also made plenary presentations on the Laser Interferometer Gravitational-wave Observatory (LIGO) and its potential for exploring dark matter in the cosmos; additive manufacturing techniques combined with laser-based direct-write (LDW) methods to print hybrid electronics; thermal metaphotonics for controlling light and heat; and LiFi, wireless communication using visible light.

The speakers were:

• Dieter Bimberg, founder of the Center of Nanophotonics at Technische Universität Berlin (Germany)
• Karsten Danzmann, director of the Max Planck Institute for Gravitational Physics and the Institute for Gravitational Physics at Leibniz Universität Hannover and a member of the LIGO Scientific Collaboration (Germany)
• Shanhui Fan, professor of electrical engineering at Stanford University (USA)
• Harald Haas of pureLiFi Ltd., chair of mobile communications and director of the LiFi Research and Development Center at University of Edinburgh (UK)
• SPIE member Hakaru Mizoguchi, CTO and vice president of Gigaphoton (Japan)
• SPIE Fellow Alberto Piqué, acting head of the Materials and Sensor Branch of the Materials Science Division at the Naval Research Lab (USA)
• Michael Sailor, Distinguished Professor of Chemistry and Biochemistry at University of California, San Diego (USA)

The SPIE Newsroom has audio and slides from several of these presentations and from speakers from other plenary sessions.

Summaries of plenary and keynote talks, as well as information on other activities at Photonics West 2017, are also available.

–Kathy Kincade is a freelance science and technology writer based in California (USA).

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