Another way to peer inside the body

Optical coherence tomography combines interferometry and high-tech light sources to capture images of living tissue. This schematic illustrates OCT imaging based on a low-coherence Michelson interferometer. The detector sweeps out an interferogram as the reference arm scans through path length matches with reflections from the sample. A profile of tissue reflectivity is measured as a function of depth while the reference path length is swept and the probe beam held stationary. Many reflectivity profiles are measured as the probe beam scans the sample. The bottom panel shows a representative OCT image (approximately 7 x 15 mm) of the anterior segment of the eye. These are real-time endoscopic OCT images of normal human A) esophagus, B) stomach, C) small intestine, and D) colon. Images are 600 600 pixels reconstructed from 1,000 depth scans and were recorded, transformed, and displayed at four frames/sec. Tick-marks on the axes represent 1 mm. This real-time OCT image of a human fingernail fold measures approximately 2.5 x 6 mm. The fingernail can be seen emerging from beneath the cuticle. The stratum corneum, or outer layer of skin, is translucent compared to the living layers of skin underneath. Doctors and medical researchers have a long list of imaging technologies they use to explore the human body. But none are perfect. Microscopes, for example, are fine for cells and small tissue samples, but aren't well suited for examining them inside the body. Ultrasound, CT, and MRI can peer inside the body but don't have the resolution to capture cellular detail. And although electron microscopy picks up extremely fine detail, it doesn't work with living samples. Optical coherence tomography (OCT), a relatively new imaging technique, lets physicians and medical researchers capture small features and textures in living tissue and when combined with catheters, is small enough to fit inside the