April 2014

Seeing the blood flow that helps us see

By Ken Tichauer | Posted: 30 April 2014

The quality of the posters at the the OSA biomedical optics conference this year has been exceptionally high and over the last three days I came across a number of projects that warranted highlighting in the blog. Some of these include the work of Jessica Kishimoto and Prof. Keith St. Lawrence at Western University on the application of diffuse correlation spectroscopy and ultrasound imaging to monitor blood flow changes in preterm infants with post-hemorrhagic hydrocephalus,1 and the work of William Rice and Prof. Anand Kumar at Massachusetts General Hospital on separating fluorescence from multiple similar fluorescent proteins and autofluorescence based on some elegant lifetime analysis.2 However, some of the work that stuck with me the most were some developments in the use of optical coherence microscopy to measure mean blood flow.

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Optical Tomographers Beware!

By Ken Tichauer | Posted: 30 April 2014

To all of you optical tomography researchers reading this: admit it, you’re a bit of a gadget geek. The last thing you want is to let your expensive, fancy equipment come into contact with your imaging subjects, especially animals. That’s the real reason why you keep building all of your systems in “non-contact” geometries. Well, according to Shelley Taylor from Prof. Hamid Dehghani’s lab at the University of Birmingham your OCD may finally be coming back to bite you in the a...*cough*…back.

It turns out that if you have your system in a non-contact geometry and you aren’t carrying out the appropriate free-space modeling (incorporating the orientation of the surface of the imaging subject at each detection position into your reconstruction model), you could be opening yourself up to errors in approximately 25%. Don’t take my word for it; Dr. James Guggenheim has recently published a very nice demonstration of this effect in his recent manuscript published in JOSA A.1

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The integration of optical technologies to manipulate and monitor biological samples

By Kyle Quinn | Posted: 29 April 2014

This morning at the BIOMED meeting, there were back-to-back talks in the Optical Molecular Biophysics / Neurophotonics session that highlighted the unique insights that can be obtained by integrating different optical technologies. Anna-Karin Gustavsson from Dr. Caroline Adiels group gave an interesting talk that integrated multifluidics, optical trapping, and NADH autofluorescence measurements to monitor glycolytic oscillations in individual yeast cells. Optical trapping was used to maintain and calibrate specific cell-cell distances, while a microfluidic flow chamber provided the influx of different concentrations of glucose, cyanide, and acetaldehyde to the cells. Glycolytic oscillations could then be monitored through NADH autofluorescence fluctuations measured by an EM-CCD. Using this controlled environment, fundamental studies to understand cell-cell communication and cell coupling are being explored.

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Speeding up multi-photon microscopy

By Kyle Quinn | Posted: 29 April 2014

As someone with strong research interests in multiphoton microscopy (MPM), I was excited to hear Dr. Peter So’s plenary talk on Day 3 of the BIOMED meeting. Dr. So provided an overview of the development of his multiphoton tissue cytometry equipment over the years, and its applications in neurobiology. MPM has emerged as key tool in neuroscience to non-invasively image deeper within the brain. Although multiphoton microscopy is well-positioned to provide high content information throughout the cortex of rodents and other smaller species, his work has primarily been motivated by efforts to maximize the throughput of this technology. By imaging faster and over a wider field of view, important questions regarding the functional and structural plasticity of neurons can be addressed.

Traditionally MPM involves raster scanning to produce an image one pixel at a time, but Dr. So’s work has involved the development of wide-field MPM techniques that utilize a CCD or multi-anode PMTs for the simultaneous collection of points. There are a number of technical challenges associated with the different approaches to wide-field MPM imaging, and Dr. So provided insight into the different solutions to these problems (e.g. temporal focusing, eliminating issues of dead space between PMTs, non-descanned detection) and the many iterations of his microscopes. In addition to imaging faster through these wide-field techniques, his group can take advantage of the inherent high content of microscopy techniques to acquire spectral data, such as fluorescence lifetime and phosphorescence lifetime imaging. Phosphorescence lifetime imaging is typically challenging because it requires very long image acquisition times, but his temporal-focusing wide-field MPM approaches can substantially reduce imaging times to enable relatively fast, high resolution imaging of oxygen distributions in the brain.

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The OSA BIOMED Meeting Day 1: Things are heating up in Miami

By Kyle Quinn | Posted: 28 April 2014

Greetings from Miami! BIOMED has gotten off to great start with a pair of plenary talks by Dr. Xingde Li and Dr. Adam Wax. As I mentioned in a previous post, Dr. Li has been developing and refining endomicroscopic probes to facilitate non-linear optical microscopy in hard to reach places such as the kidney, intestine, and cervix. Dr. Wax, on the other hand, has taken a different approach to delivering and detecting photons from deeper within the body through the use of low coherence interferometry (LCI).

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The Binding Finding of a Fluorescence Lifetime

By Ken Tichauer | Posted: 27 April 2014

In this afternoon’s session on Luminescence and Absorption on Cellular and Tissue Levels, Prof. Victor Chernomordik gave an overview of the extensive work he and his colleagues have been undertaking to make fluorescence molecular imaging more quantitative. Much of their work has focused specifically on how to quantify human epidermal growth factor receptor 2 (HER2) concentrations (a key receptor of interest in breast cancer) using kinetic models, and they have a number of publications in this area that I urge you to check out;1-5 however, what I was most intrigued by was there recent results demonstrating a dependence of fluorescence lifetime on the binding state of a targeted fluorescent tracer. In simpler terms, what they found was that the timing characteristics of fluorescence emission was significantly different depending on whether their fluorescent tracer was bound to the target of interest or not.6,7

This offers their group a window into separating non-specific uptake of a tracer, a major problem in conventional molecular imaging of tumors, from the more interesting bound fraction of the targeted tracer. Moreover, for reversible binding tracers (tracers that can dissociate from there targeted molecule), the ratio of the bound fraction of a tracer to the unbound fraction of tracer is directly proportional to the concentration of the targeted biomolecule.8 Therefore, as Prof. Chernomordik and his colleagues unearth the exact relationship between bound fraction and fluorescence lifetime, there is a clear pathway forward to using this approach to directly quantify HER2 concentration, something that is impossible to do with other conventional single tracer approaches in tumors.9

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The Early Photon Gets the Worm

By Ken Tichauer | Posted: 25 April 2014

One of the biggest problems with using light to analyze biological tissue is that photons in the visible and near-visible spectrum have a very high probability of scattering multiple times as they propagate through the tissue. This is a well-known problem that restricts high-resolution optical microscopy to tissue thicknesses of only a few microns. It has also led researchers to develop complicated iterative reconstruction algorithms that incorporate models of scattering light propagation as a means of achieving usable image resolution in thicker tissue samples or in small animals. Even so, the ultimate resolution of these reconstruction algorithms is on the order of millimeters, far from the impressive micron and sub-micron scale resolution achievable by microscopy.

So the question is, what if we could tell the difference between photons that took a direct route through the tissue (non-scattering photons) and photons that took a more roundabout route (scattering photons)?

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Are You Being Heard in the Optics and Photonics Community?

By Arti Agrawal | Posted: 21 April 2014

In case you missed it - International Women’s Day comes about in March every year, and much like many years there was bit of hype around it. The occasion is used by various women’s organisations, policymakers and governments to raise awareness of issues connected to women. The media is an important component in this ever-growing to-do. And commerce is never far behind in exploiting every possible opportunity (behold the offers to women in shops: shop for more than x amount and get 10% discount)!

For the scientific community, does this day have relevance?

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Incubator meeting, Honest meeting

By Miaochan Zhi | Posted: 11 April 2014

The essence of this Incubator, as one host Mark Neifeld put it, is: honest effort to solve practical problems. The hosts repeatedly called on all attendees to have honest and candid discussions. The purpose of this meeting was truly to look for opportunities within CS and was cleverly structured to give pro and con views of those opportunities.  This lead to open and frank discussions which the attendees really took advantage of those discussion opportunities.

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Collaboration is the Key

By Miaochan Zhi | Posted: 11 April 2014

A major part of the meeting are the breakout group discussions. Participants were assigned to one of five potential application areas: Commercial Security Cameras for use in Homes, Businesses, Stadiums or Airports; UAV Surveillance Imaging; Near IR Imaging for Intra-cranial Bleeding Detection and Localization; Soldier-scale Situational Awareness; and Astronomical Imaging Applications.

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OSA Incubator: Implications of Compressive Sensing Concepts to Imaging Systems

By Miaochan Zhi | Posted: 10 April 2014

While the hot topic of DC in general might be the Cherry Blossom Festival, here at OSA headquarters we’re focusing on compressive processing.

First, what is an Incubator?  The OSA Incubator Program began in 2011 and this week’s OSA Incubator Implications of Compressive Sensing Concepts to Imaging Systems is the 13th Incubator to date. Each Incubator differs not only in topic but in program design and outcome. The hosts work with OSA to design a program that will best achieve their goals for the Incubator. Similarly, there are a variety of outcomes, these Incubators have been covered in OPN, have fueled authorship of a whitepaper (Scaling Terabit Networks) and one meeting – Freeform Optics – has already become an OSA Topical Meeting.

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The Role of Chance in Biomedical Imaging

By Kyle Quinn | Posted: 7 April 2014

Much of my work as a postdoctoral trainee at Tufts University has focused on utilizing endogenous sources of optical contrast to assess tissue development and disease. To this end, our lab has utilized non-linear optical microscopy to non-destructively characterize tissue organization and metabolic function with an emphasis on understanding and detecting stem cell differentiation and precancerous transformations. As I think about all the researchers, past and present, that have provided fundamental contributions to my area of research, no one looms larger than Dr. Britton Chance. (Article continues below.)

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OSA Topological Order with Photons Incubator: Facilitating Discussion of this Nascent Field

By Sean Kelley | Posted: 4 April 2014

Greetings from the 12th installment of OSA Incubator meetings, the OSA Topological Order with Photons Incubator! Hosted by Steven Girvin, Yale University, United States; Mohammad Hafezi, Joint Quantum Institute, United States; Karyn Le Hur, Ecole Polytechnique, France; Jacob Taylor, National Institute of Standards & Technology, United States; the meeting will span two days, involving formal talks, informal discussion, and impressive coffee consumption. Sponsors include the Air Force Office of Scientific Research, the Army Research Office, Joint Quantum Institute and the Physics Frontier Center.

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How do you make a topologically interesting system with light?

By Sean Kelley | Posted: 4 April 2014

Quantum superposition states are immensely delicate things - any interaction with the environment can cause them to decohere. This poses a significant problem for quantum computing, where information would need to be stored within quantum states for relatively long periods of time. A promising way to isolate a system exploits the topology of the system, known as 'topological protection'. A state that is topologically isolated from its environment would be perfectly shielded from the sort of noise and environmental imperfections that creep into quantum systems now.

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What lies ahead for topological photonic systems?

By Sean Kelley | Posted: 4 April 2014

The final day of the Topological Order with Photons Incubator saw several more proposals for systems that could support topological edge states. Metamaterials are a promising environment, and talks were given by Alex Kanikaev and Gennady Shvets on fabricating bianistropic metamaterials to emulate electron spins and topological insulators. Na Young Kim and Alberto Ano laid different schemes for creating lattices of exiton-polariton microcavities, as well as roadmaps for potentially seeing topological effects in these systems.

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