A minor tweak to a major workhorse eye-scanning technology, described in a Nature Communications study, could lead to “virtual biopsies:" visualizing tissue in 3D at microscope-quality resolution, without having to carve it out of the patient.
You may not have heard of optical coherence tomography, or OCT. But if you’ve visited an ophthalmologist recently, chances are your eye came within an inch or two of a scanning device employing the technology. Tens of thousands of these devices are in place in doctors’ offices, where they’re widely used to check for eye diseases. OCT is a billion-dollar business. Every year, more than 10 million OCT scans are performed to diagnose or monitor conditions from age-related macular degeneration to melanoma. The technology has been adapted for endoscopic use in pulmonary, gastrointestinal and cardiovascular medicine.
OCT can optically penetrate a couple of millimeters or so into tissue, which in principle could allow physicians to perform some biopsies via a strictly visual scan.
But because of the way it works (for details, see my release), OCT has been bedeviled since its invention in 1991 by a form of noise that, unlike the random noise all sensing systems generate, is constant and stationary: There it is, right in the same place, every time you look. So it can’t be “washed away” simply by repeatedly imaging the item of interest and then averaging the results of all those scans with a computer program. Trying to do that is like covering up freckles with a coat of makeup: You get a smoother appearance, at the cost of lost detail.
De la Zerda's team modified a couple of commercially available OCT systems with a pair of lenses and some software tweaks. The resulting fix let them create a second, virtual image — a holograph-like exact lookalike of the viewed item that materialized in free space between the added lenses and the item. The scientists now found a way to reach in there as if they had a magic molecular tweezers (they did it optically, using a piece of ground glass) and "move" the microscopic elements composing the virtual image just a tiny bit, again and again.
Each time they did that, the noise pattern shifted ever so slightly. Now the noise could be removed by obtaining several successive images of the serially rearranged "virtual" object, and averaging them.
The resulting much-improved resolution revealed cell-scale features in intact tissues. For example, an incision-free look at the fingertip of one of the study’s co-authors let them see an anatomical feature never before glimpsed with OCT: Meissner’s corpuscle, a nerve bundle responsible for tactile sensations.
“We showed that you can take effectively any OCT system out there and, with minimal changes, boost its resolution to the point where it can detect anatomical features smaller than the size of a typical cell,” de la Zerda told me.
Previously: Gold particles light the way for brain surgeons: Adam de la Zerda presents at TEDxStanford, Seeing under the skin, The "sky's the limit" for young Stanford structural biologist and Stanford structural biologist named one of Forbes Magazine's 30 under 30 rising stars
Photo by andrea-prieto