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SPIE Professional April 2013

BiOS Hot Topics

From optogenetics to tissue imaging

BiOS at SPIE Photonics WestSpeakers at this year’s BiOS Hot Topics session at SPIE Photonics West discussed the challenge of integrating optics and photonics technologies into clinical practice and provided updates on applications such as surgical robotics and tissue imaging for diagnosing and treating stroke, cancer, and other conditions.

Hundreds of people packed into a room at the Moscone Center in San Francisco to hear eight speakers in a session moderated by SPIE member Sergio Fantini of Tufts University.

Many of the speakers’ presentations from Hot Topics and Photonics West plenary sessions are available in multimedia format.

The next BiOS Hot Topics session will be held 1 February 2014 during SPIE Photonics West.

Bamberg on optogenetics

Ernst Bamberg of Max Planck Institute fur Biophysik (Germany) led off with a talk on optogenetics, a field that uses light to signal functional changes in the activity of individual neurons in living tissue. The cells of the neurons express a protein, channelrhodopsin, which acts to light gate ion channels.

The absence or presence of light (or light of specific wavelengths) can inhibit nerve cells from firing. This capability can be used to map the motor functionality of the brain or to control functionality of other cells. Bamberg showed how this technique can be used to activate cells in the optic nerve for those without sight or to stop and start a beating heart in a small animal.

Sorger on robotic surgery

Jonathan Sorger of Intuitive Surgical (USA) discussed the benefits and challenges of robotic surgery and the desire to combine diagnosis, tissue characterization, and treatment into the clinical workflow. Robotics are minimally invasive and reduce bleeding, chance of infection, and length of hospital stay.

Robotic systems also provide a stable platform for imaging modalities used by the surgeons during procedures, Sorger explained. However, the surgical environment presents many challenges to this instrumentation, such as motion of the subject and the need for high positional accuracy.

Choi on imaging hemodynamics

SPIE member Bernard Choi of the Beckman Laser Institute (USA) spoke of the need for a real-time image guidance technique that identifies blood-flow changes during procedures such as laser treatments to reduce port-wine stain of the skin. He discussed speckle imaging techniques for that procedure as well as in neurosurgery, where blood flow needs to be monitored during clamping, cutting, and re-sectioning of blood vessels.

Choi presented approaches using the speckle produced by structured illumination to map scattered and absorbed light in such a way as to produce a more absolute scale of blood flow and help reduce the uncertainty associated with current practice.

Flow cytometry and high-speed OCT

SPIE member Vladimir Zharov of University of Arkansas for Medical Sciences (USA) explored ways of monitoring the characteristics of a patient’s blood as it passes through the veins. His approach uses magnetic nanoparticles targeted to attach to specific cells in the blood.

A strong magnet near a surface vessel would attract these particles to the vessel edge where they could be sampled by non-invasive techniques using lasers and the spectral response of the plasmonic nanoparticles. This could provide diagnostics, destroy cancer stem cells and/or infected cells, and provide therapy for the disease.

Ben Potsaid of Massachusetts Institute of Technology (USA) noted that optical coherence tomography (OCT) is a powerful technique for volumetric scanning through material like living tissue and for mapping the layers of cells within that tissue. However, in order to produce an image, the laser source needs to be swept across the sample in 2D fashion, and the data must be gathered quickly to create an image.

Initial implementations of OCT used time-domain techniques that limited data collection to 400 samples/second. The next advancement came with spectral domain OCT and improved the rate to 26,000 samples/second. Potsaid discussed a swept-source technique using a MEMs tunable vertical cavity surface-emitting laser (VCSEL) which improves speed by a factor of 50. The MEMS element is modulated at 600kHz over a range of only 1 micron.

Oron on tissue photoactivation

Dan Oron of Weizmann Institute of Science (Israel) discussed how to overcome a broad area of response from laser illumination of tissue that scatters light in front of and beyond the focus region. Oron discussed using two-photon techniques where only the region of interest contains the two-photon response; diffuse light is too weak in other regions.

Temporal focusing uses multiple pulses and changes the duration of the individual pulses so that their overlap at a specific location is limited in time. This combination of spatial and temporal focusing provides improved sensitivity which facilitates much longer depths of penetration in tissue. This technique was used to photoactively stimulate a single neuron through 200 microns of nerve tissue.

Fink and Culver on imaging

Mathias Fink of ESPCI, CNRS (France) explained his multiwave approach to elasticity, or shear-wave, imaging for cancer detection.

Acoustic imaging uses a phased array of ultrasound sources to focus a compression wave through the tissue. Fink showed how a time-reversal analysis technique of data from an array of receivers produces a reconstruction of the transversed medium and an image of internal subject. The time-reversal analysis is made possible because the speed of sound in most soft medium is fairly uniform.

The technique allows for faster scan times and more detail, both of which lead to improved specificity for detection of tissue density changes from cancer.

Joe Culver of Washington University in St. Louis (USA) described how diffuse optical imaging of scattered light is being investigated to produce a more portable brain-monitoring system.

Functional magnetic resonance imaging (fMRI) is currently used to map brain activity by employing tasked-based testing while the subject is in the MRI instrument. But this is not transportable to the operating environment.

The new technique uses correlations among multiple detector signals to map regions of brain activity. Pilot studies are underway in operating rooms and prenatal care units where resolution, field of view, and wearability of the instrument are being investigated.

Read more highlights from BiOS and other symposia at Photonics West 2013 online at spie.org/pwnews.

Other topics at BiOS: Bio-inspired camera lens

A bio-inspired design for a simple digital camera system was the topic of one of the first talks presented at SPIE Photonics West in February.

In “Digital cameras in bio-inspired designs: from humans to flies,” SPIE member John Rogers of University of Illinois at Urbana-Champaign explored methods of producing curved optical detector arrays with a thin silicon substrate and a pre-stretched elastomer base.

Proceedings from SPIE Photonics West can be viewed in the SPIE Digital Library

SPIE Photonics West 2014
Abstracts are due 22 July for Photonics West 2014.

DOI: 10.1117/2.4201304.14

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