Researchers report strides in developing endoscopic OCT

Optical coherence tomography (OCT)
allows 3-D imaging of sub-
surface features in microscopic 
detail. (Images courtesy of MIT)

Researchers report an important advance in developing an ultra-high speed, optical coherence tomography (OCT) system that one day may allow doctors to see just below the surface of some tissues with microscopic detail. The technology is aimed at detecting microscopic pre-cancerous changes in the esophagus or colon.

Led by Dr. James Fujimoto, a professor of electrical engineering and computer science at the Massachusetts Institute of Technology, the researchers published details of the advance in image capture speed and device development in the August issue of the journal Biomedical Optics Express.

"Ultrahigh-speed imaging is important because it enables the acquisition of large three-dimensional volumetric data sets with micron-scale resolution," Fujimoto said in a prepared statement. (Link to published site.)

Their endoscopic OCTimaging system is capable of capturing data at a rate of 980 frames per second, which is equivalent to 480,000 axial scans per second. This is 10 times faster than previous studies, which permits imaging microscopic features less than 8 millionths of a meter in size.

Such high speeds and super-fine resolution allows the system to produce 3-D microscopic imaging of precancerous changes in the esophagus or colon or provide imaging support for endoscopic therapies.

OCT imaging works by directing a beam of light at microscopic-scale structural and pathological features on a tissue and measuring the magnitude and echo time-delay of backscattered light. Because the amount of light that can be recaptured and analyzed decreases quickly with depth in tissue due to scattering, the technique can generally only used to visualize subsurface features to a depth of 1 to 2 millimeters.

"However these depths are comparable to those sampled by pinch biopsies and unlike biopsy, information is available in real time," Fujimoto says. "Excisional biopsy is one of the gold standards for the diagnosis of cancer, but it is a sampling procedure. If the biopsy is taken in a normal region of tissue and misses the cancer, the biopsy result is negative although the patient still has cancer," Fujimoto says.

The advance reported in the study involved development of smaller probe, called a piezoelectric-transducer-based miniature catheter with an outer diameter of 3.5 mm for ultra-high speed endoscopic OCT. The miniaturized PZT bender actuates a fiber and the beam is scanned through a gradient index lens and a microprism. This allows high-speed side viewing. The probe can be pulled back over a long distance to acquire 3-D data sets covering a large area of the colon or esophagus.

"This device development is one of the major technical challenges in endoscopic OCT," Fujimoto says. “Because probes must be small enough so that they can be introduced into the body, but still be able to scan an optical beam at high speeds. Increasing imaging speeds has also been an important research objective because high-resolution volumetric imaging requires very large amounts of data in order to cover appreciable regions of tissue, so rapid image acquisition rates are a powerful advantage."

Using miniature fiber optic scanning catheters or probes, either on their own or in combination with standard endoscopes, colonoscopes, or laparoscopes, the researchers are working with clinicians at the VA Boston Healthcare System and Harvard Medical School to investigate developing endoscopic OCT as a method for guiding excisional biopsy to reduce false negative rates and improve diagnostic sensitivity.