In this pilot study, comprehensive esophageal microscopy in vivo has been demonstrated for the first time by using a prototype OFDI system. High-resolution images were obtained from the distal esophagus and the gastroesophageal junction, which permitted clear visualization of the anatomic layers of the esophagus and of the vascular network of the muscularis mucosa. Procedure times were less than 6 minutes, but the image acquisition speed of the prototype system was limited entirely by the rate at which data could be continuously archived via a standard computer bus to a hard drive. This limitation will be addressed in future systems by implementing hardware-based digital signal processing and, as a result, we anticipate that imaging speed will be increased an additional 10-fold. Comprehensive microscopic imaging of the distal esophagus would be a valuable tool for disease screening and surveillance, particularly in the management of Barrett's esophagus. OCT was previously demonstrated for “optical biopsy” at discrete locations, but fundamental technologic limitations prevented imaging of large tissue areas. In this study, a prototype OFDI system was used to overcome this limitation. The animal studies demonstrated that OFDI operates at a significantly increased image acquisition rate and detection sensitivity and, when coupled with a balloon-centering catheter, can be used for comprehensive imaging with a resolution and image quality identical to OCT.
Although the inflated diameter and the length of the imaging segment of the balloon catheter were appropriate for OFDI, the core diameter (1.5 mm) was significantly larger than required for the drive shaft and the optical fiber. The integration of a centering balloon onto a flexible catheter with a diameter similar to those used for intracoronary OCT imaging17
may permit comprehensive esophageal imaging to be performed less invasively and in a standalone mode, thus significantly reducing the cost of screening and opening the possibility of epidemiologic studies of Barrett's esophagus across a broader segment of the population. In the role of surveillance, comprehensive microscopic imaging may reduce the sampling artifact inherent to random biopsy sampling and could improve the sensitivity of detecting dysplasia and epithelial cancer.
Previous studies identified and prospectively tested OCT criteria for the diagnosis of specialized intestinal metaplasia, dysplasia, and intramucosal cancer of the esophagus.6-8,18
These criteria were specific to imaging with a catheter that did not compress the esophageal wall. It is unclear whether tissue compression arising from the balloon will adversely affect the accuracy of OCT diagnostic criteria; additional studies will be required. From our preliminary results, the balloon catheter appeared to affect imaging in 2 ways. First, it smoothed the tissue surface and thus made epithelial topology difficult to identify. Second, the expansion of the balloon compressed the anatomical layers and increased the OFDI signal. These effects were also noted in prior OCT studies.19
The increased OFDI signal may be advantageous, because compression appears to increase the contrast and the visibility of the architecture of the esophageal wall and permits imaging depths extending to the outer muscularis propria.
Although clinical studies are required to further evaluate the utility of OFDI, the ability to comprehensively image the distal esophagus with the resolution and contrast of OCT may provide a powerful tool for diagnostic screening and surveillance in patients with Barrett's esophagus.
What is already known on this topic
• The diagnostic potential of endoscopic OCT has been demonstrated, but the systems have functioned effectively only in a “point-sampling” mode, unable to survey large areas of the GI tract.
What this study adds to our knowledge
• An OFDI system used in a swine model provided high-resolution images from the distal esophagus and gastroesophageal junction, permitting clear visualization of the anatomic layers of the esophagus and of the vascular network of the muscularis mucosa.