Our initial experience with balloon catheter–based OFDI indicates that comprehensive imaging of the microscopic architecture of the distal esophagus is feasible and safe. Furthermore, our results suggest that comprehensive OFDI may enable the visualization of disease that cannot be seen by endoscopy and subsequent biopsy. By screening the distal esophagus to identify suspect regions that contain disease that cannot be recognized by videoendoscopy, this technology may be used to guide biopsy and minimize sampling error associated with the random biopsy technique.
However, to realize the potential of this technology, additional research must be conducted to improve our understanding of the images. In this article, we have attempted to interpret our OFDI images by using criteria developed from OCT images obtained with a noncontact linearly scanning probe.9
When in contact with the esophageal wall, the balloon catheter necessarily compressed the mucosa, making it difficult to visualize surface topology, which is one feature that has been used to diagnose SIM.15
Furthermore, studies conducted to investigate the effects of compression on OCT images have shown that the images change significantly with increasing pressure.26
The degree to which mucosal compression by the balloon affects the accuracy of previously developed OCT diagnostic criteria applied to OFDI images is unknown. Finally, we currently do not understand the intraobserver or interobserver diagnostic variability for balloon-OFDI imaging, and we do not have information on the reproducibility of the findings.
A study to compare balloon-based OFDI and histopathologic diagnoses would be valuable for answering these questions. In our current study, we were not able to obtain a one-to-one correlation of OFDI data with histopathologic diagnoses because we could not register the 3-dimensional data set with the biopsy location. A possible solution to this problem would be to reimage the esophagus after biopsy. After coregistration of the two OFDI volumes, the biopsy locations seen on the second data set could then be used to identify the image regions in the first data set that correspond to the biopsy sites. Difficulties with this approach include the presence of blood, which could attenuate the optical signal and the additional time required for the experimental procedure. Another possibility is some form of esophageal marking applied when images of interest are identified after the OFDI scan and while the balloon is still in place. Biopsy specimens could then be acquired at the marked location after withdrawal of the balloon. Adequate targeting can be evaluated by performing OFDI of the biopsy specimen to ensure that it contains the same images that were obtained in vivo. Development of such a technique would also be beneficial clinically because it would provide the foundation for a guided biopsy platform.
Other artifacts such as poor balloon contact with the esophagus and peristalsis affected image quality. In some individuals, especially those with large hiatal hernias, tissue contact with the balloon surface was not maintained throughout the full 360-degree, ~6-cm imaging window. Although OFDI does not require a transducing medium, mucus and blood between the balloon surface and the esophageal wall sometimes decreased the OFDI signal, reducing the clarity of the images. Future development of a catheter with a variable inflation diameter could provide adequate tissue contact while minimizing excessive tissue compression. Peristalsis made it difficult to reconstruct longitudinal data sets with fidelity because the balloon typically oscillated along the longitudinal extent of the esophagus. Increased imaging speed27
and proper contact between the balloon and the esophageal wall could minimize this artifact.
Although comprehensive evaluation of the entire distal esophagus with the OFDI balloon-catheter holds the promise of reducing the sampling error associated with BE screening and surveillance, it introduces challenges associated with the manipulation, assessment, and storage of very large digital data files. In our study, storage requirements approached 40 GB for a single volumetric pullback. Additionally, because a single 6-cm pullback contains approximately 1200 cross-sectional images, where each un-compressed image spanned a dimension of 7168 × 7168 pixels (49 MB per image), rigorous assessment and interpretation of the acquired data were time consuming and laborious. The development of automated or semiautomated computer-aided detection and diagnostic algorithms will therefore be a high priority for future research. One possibility is that the entire volume will be scanned with OFDI, and through the use of pattern recognition algorithms, the computer will automatically select subsets of the volume data set that are most likely to contain the severest disease. These subsets will then be presented to the physician in 2- or 3-dimensional image format. Such algorithms would significantly decrease the time required to evaluate the OFDI data sets, facilitating diagnosis in the endoscopy suite at the time of the procedure.