SAN JOSE, CA - Judging by the number of presentations, discussions, and devices devoted to optical imaging at last month’s Biomedical Optics meeting (BiOS) at Photonics West, it is clear that the optical coherence tomography (OCT), fluorescence and Raman spectroscopy, and confocal microscopy are making huge strides toward the Holy Grail of real-time in vivo optical biopsies. As noted during the BiOS meeting-especially the Saturday night Hot Topics sessions-and repeatedly in the pages of this newsletter, one technique receiving a significant amount of attention these days is near-infrared imaging, involving lasers and LEDs in the 800-1300 nm range (a nice optical window in tissue), particularly for the early diagnosis of cancer.
And near infrared imaging is by no means the only technique being developed for the study of cancer, Alzheimer’s, Parkinson’s, and other diseases and biological processes. At the BiOS Hot Topics session, for example, leading researchers from around the world discussed the latest advances in spectroscopy, confocal imaging, endoscopic microscopy, and high-resolution OCT. Daniel Farkas, head of the Minimally Invasive Surgical Technology Institute at Cedar-Sinai (Los Angeles, CA), discussed the evolution of translational imaging and microscopy, noting that while the goal of moving this technology from benchtop to bedside is a good idea, it has to be done with “relevance”-that is, the development of in vivo diagnostic tools should be focused on the goal of yielding better clinical outcomes. He also took imaging technology developers to task, saying that “today we can image dust on Mars (with the rover) better than we can image inside the human body.”
At present, OCT-which typically involves laser and light sources in the 980-1300 nm range-remains the most well-established optical diagostic technique. Some analysts estimate that the OEM market for optical sources in OCT equipment is more than $100 million/year worldwide. At this point, ophthalmology remains the primary market for OCT systems. Carl Zeiss, which holds about 80% of the ophthalmic OCT market, reportedly sells 400-500 units/month, at a cost of about US$50,000 per system. Looking ahead, because OCT methods lend themselves to fiberoptic delivery of imaging light to and from tissue, and because OCT can be used with many types of endoscopes to access tissue inside the body as well, OCT should be able to compete with, or at least complement, ultrasonic imaging methods in virtually all applications.
During the BiOS Hot Topics, Wolfgang Drexler (University of Vienna) said in his talk on trends in ultra-high-resolution OCT that since the first published studies involving OCT (in Science in 1995), the technology has come a long way. Noting that the current emphasis in OCT studies is on achieving in vivo optical biopsies, Drexler rattled off descriptions of 10 different types of OCT that are currently under clinical development, from 3D OCT with less than 5 µm resolution to cellular resolution OCT (.5 µm resolution), adaptive optics OCT imaging, in vitro ultra-high-resolution full field OCT, polarization-sensitive OCT, molecular contrast OCT, magnetomotive OCT, and second-harmonic generation OCT.
In another Hot Topics presentation Chi-Kuang Sun of National University Taiwan focused on his group’s work with optical harmonic-generation microscopy, in the study of organized protein structures in tissue, axons in nerves, and skeletal and cardiac muscle fibers. He believes their second-harmonic generation (SHG) imaging approach (which uses a Cr4:fosterite laser) offers a better alternative to other near-infrared imaging techniques (especially those using femtosecond lasers) for these applications because, among other things, it does not require any dye markers and the energy deposition is zero. In addition, he noted that their SHG technology is highly penetrative (1.4 µm) and offers spatial resolution down to 500 nm and below.
- Kathy Kincade