Researchers at Stanford University (Stanford, CA) have figured out how to retrofit optical coherence tomography (OCT) systems with off-the-shelf components, increasing OCT's resolution several-fold and promising earlier detection of retinal and corneal damage, incipient tumors, and more.
The researchers' components fix entails a pair of lenses, a piece of ground glass, and some software tweaks to eliminate the noise issues obtained via OCT. The improvement, combined with OCT technology's ability to optically penetrate up to 2 mm into tissue, could enable physicians to perform "virtual biopsies," visualizing tissue in three dimensions at microscope-quality resolution without excising any tissue from patients.
The researchers tested the enhancement in two different commercially available OCT devices. They were able to view cell-scale features in intact tissues, including in a living mouse's ear and a human fingertip, says Adam de la Zerda, Ph.D., assistant professor of structural biology and the study's senior author. The study’s lead author is electrical-engineering graduate student Orly Liba.
Somewhat analogous to ultrasound, OCT penetrates tissues optically instead of with sound waves. The device aims beams of laser light at an object—such as a tissue sample or a patient's eye—and records what comes back when light bounces off reflective elements within the sample or eyeball. Adjusting the depth of penetration, a user can scan layer upon layer of a tissue and, piling virtual slices of tissue atop one another, assemble them to generate a volumetric image.
However, OCT continues to be plagued by a form of noise that, unlike the random noise generated by any sensing system, cannot be eliminated by repeatedly imaging the object of interest and averaging the results with a computer program. The noise generated by OCT, called speckle, is an inherent feature of the architecture of the object being viewed and the unique properties of laser light.
By positioning a couple of additional lenses in the OCT device's line of sight, the researchers were able to create a second image—a holograph-like exact lookalike of the viewed sample that appeared elsewhere along the line of sight, between the added lenses and the sample. By inserting what they call a diffuser—a plate of glass they'd had roughened by randomly etching tiny grooves into it—at just the right point in the line of sight and methodically moving it between each round of repeated scans, they achieved the optical equivalent of shifting the geographical relationship of the sample's components just a tiny bit each time they scanned it.
Now, averaging the successive images removed the speckles. The research team used the resulting enhanced capability to acquire detailed, essentially noise-free images of a living, anesthetized mouse's ear, including sebaceous glands, hair follicles, blood vessels, and lymph vessels, Liba says.
They also obtained high-resolution images of a mouse retina and cornea. Finally, an incision-free look at the fingertip of one of the study's co-authors let them see an anatomical feature called Meissner's corpuscle, a nerve bundle responsible for tactile sensations.
Stanford's Office of Technology Licensing has applied for patents on intellectual property associated with the findings in the study.
Full details of the work appear in the journal Nature Communications; for more information, please visit http://dx.doi.org/10.1038/ncomms15845.