Over the last few years the SPIE Biomedical Optics (BiOS) portion of Photonics West (Jan. 19–24, 2008, San Jose, CA) has grown dramatically, reflecting the continued growth of the industry. The two-day weekend commercial exhibit has gone from a few tabletops in a meeting room at the San Jose Convention Center to 150 exhibitors filling half the main hall ithis year. And the scientific sessions, with more than 1300 papers , now stretch throughout the entire week. Some of the most well-attended sessions were those featuring 3-D tomography, single-molecule counting, and optical coherence tomography.
For example, tomographic phase microscopy has been the focus of research by Wonshik Choi and Michael Feld (Massachusetts Institute of Technology; Cambridge, MA). Choi and Feld sought to build a quantitative phase microscope that could produce a real-time, 3-D map of the index of the material in a living cell and thus observe changes in the cell under varying conditions. They applied techniques used for x-ray computed tomography in the optical regime by analyzing the interference fringes at multiple angles using rotating mirrors to tilt the beam before it passes through the sample. They have been able to extend their technique to high speed and are now performing video-rate optical tomography on cellular samples to monitor the changes in a living cell as it is exposed to different chemicals.
As always, the Saturday night BiOS Hot Topics session was packed. Among the highlights was a presentation by Rox Anderson of the Wellman Center for Photomedicine, Massachusetts General Hospital and Harvard School of Medicine (Boston), who described how laser-guided fractional microbeam surgery is now being used in ophthalmology and dermatology provides a new paradigm for treatment of more deadly cancers, and the potential for low-light laser therapy in treating and preventing stroke damage.
Other Hot Topics presenters included:
- Bruce Tromberg, Beckman Laser Institute and Medical Clinic, University of California Irvine, and Lihong Wang, Washington University in St. Louis, who showed impressive positive impacts on the success of therapy as a result of enhanced data gathered during treatment by diffuse optical imaging at Beckman and by photoacoustic tomography and microscopy at Washington University.
- David Piston, Vanderbilt University, who described real-time quantitative microscopy at the nanometer scale that enables more focused therapies, and Mary-Ann Mycek, University of Michigan, who showed how tissue optical spectroscopy is used in earlier, more accurate diagnosis and treatment of pancreatic disease.
- Paul French, Imperial College, who talked about how fluorescence lifetime imaging has been revolutionized by supercontinuum source technology.
- W. E. Moerner of Stanford University, who described single-molecule superresolution imaging and trapping to control molecular activity, and Stefan Andersson-Engels, Lund University, who reported on fiber-optic treatments for prostate and other cancers with greater tissue penetration than current photodynamic therapies.
Cause and effect
Another trend evident at this year’s BiOS meeting was the resurgence of more targeted “cause and effect” uses of lasers and optics, on a much finer scale than traditional therapeutic procedures such as vision correction, hair removal, and skin resurfacing. In recent years the bulk of the scientific sessions at the BiOS conference have focused on optical imaging for diagnostic and biological applications. In fact, one of the hottest “hot topics” at the 2008 BiOS conference was nerve stimulation.
Neuroscientists use nerve stimulation to study the fundamental principles of the nervous system and to research causes and treatments of Parkinson’s, Alzheimer’s, and nerve regeneration, among other things. Medical professionals use nerve stimulation for everything from pain and depression management to brain mapping. These applications traditionally involve stimulating the nerves with electrical current, which has some limitations given the ability of electrical current to transmit in wet media.
Several groups are now looking at optical nerve-stimulation techniques as an alternative. Pioneered by researchers at Vanderbilt University (Nashville, TN) and currently being commercialized by Aculight (Bothell, WA), laser-based nerve stimulation has emerged as an active area of application development in the last 12 months. Aculight, which has licensed much of the key technology and techniques developed at Vanderbilt, is working with mid-infrared (1850 nm) diode-laser technology to deliver optical energy directly to the sciatic, vestibular, and cochlear nerves to address issues with gait, balance, and hearing (see www.bioopticsworld.com/articles/316643).
A growing number of research groups are pursuing IR-laser applications for additional nerve-stimulation applications, according to Bendett. At the BiOS conference, Nathaniel Fried of the University of North Carolina at Charlotte gave a presentation on the use of a thulium fiber laser (1873 nm) to stimulate the cavernous nerve in rat prostates, thus overcoming (among other things) erectile dysfunction. In lab-based experiments involving five male rats, Fried and colleagues from Johns Hopkins University applied pulse energies of 7.5 mJ, radiant exposure of 1 J/cm2, pulse duration of 2.5 ms, pulse rates of 10 Hz, and 1 mm spot diameter for 60 s. They concluded that optical nerve stimulation may be an alternative to electrical nerve stimulation for measuring erectile response and preserving the cavernous nerves during radical prostatectomy.
Other potential applications involve the vagus nerve, which governs parasympathetic nerve responses. Electrical stimulation of the vagus nerve is already used to answer fundamental questions about the function of the nervous system, research into diseases such as multiple sclerosis and Alzheimer’s, and in clinical applications such as pain and depression management and the reduction of Parkinson’s tremors. Researchers are now beginning to apply optical technologies to these and other parasympathetic nerve responses, including high blood pressure and weight loss. At the BiOS meeting, a team from the University of Maryland School of Medicine discussed their early experiments using a 1.85 µm diode laser to stimulate the vagus nerve in rats; among other things, they were able to determine the feasibility of using IR stimulation to probe neuronal circuit properties in intact neural tissue and compare IR stimulation with another photostimulation technique (focal photolytic release of “caged” molecules).