This study identified specific OCT image characteristics that can distinguish intestinal metaplasia from benign, normal mucosa at the SCJ in a cohort of patients undergoing routine upper endoscopy. Although there is moderate variability in this distinction, a diagnostic sensitivity of 81% for SIM compares favorably with that of published endoscopic sensitivities (82%).17
Our results strengthen the growing body of literature that describes the ability of OCT to distinguish tissue types on a histologic scale.18,19
The diagnostic flow chart accurately identified SIM when retrospectively applied to the training set, but the accuracy declined when prospectively applied to the validation set. Potential explanations of this difference in accuracy are inadequate tissue representation with the training set, registration error, and architectural distortion. The histologic diagnosis of SIM requires the identification of goblet cells on routine H&E staining of esophageal biopsy specimens. Because current OCT systems cannot resolve individual goblet cells, the image characteristics of intestinal metaplasia based on tissue architecture needed to be determined. Gastric cardia and SIM comprised 17.5% and 50% of the training set, respectively. The analyzed validation set, however, contained 29% and 17% of gastric cardia and of SIM, respectively. It is possible that the training set did not provide an adequate representation of the variability of gastric cardia images, thereby reducing the overall OCT image accuracy. The accuracy of registration of biopsy sampling and image acquisition during the endoscopic procedure is difficult to estimate. Errors on the order of a few millimeters were likely and may have contributed to misdiagnosis by OCT. Histologic architectural changes, although sensitive for intestinal metaplasia, are not perfectly accurate; are seen in nonmetaplastic columnar mucosa; and when solely relied upon for a histologic diagnosis, could lead to significant errors in accuracy. Support for this hypothesis is shown in , which shows that gastric cardia (n = 31) and columnar epithelia (n = 24) tissue types accounted for the majority (70%) of false positives. Precision of SIM diagnosis between readers, however, was excellent. A discrepant diagnosis of SIM was rendered only twice, whereas columnar epithelia (cardia and columnar) for histologic diagnosis accounted for 7 and 12 discrepant diagnoses ().
The majority of images removed from the validation set were those that corresponded to a histologic diagnosis of the SCJ and the cardia (). Reasons for poor image acquisition of these areas are not completely understood but may be due to physical constraints of the OCT catheter within the working channel as torque is applied to the endoscope. Motion artifact from a moving esophagus is also a potential source of image distortion. Further study into OCT imaging of the SCJ is ongoing and may provide additional insights. Efforts to improve the OCT devices to minimize the percentage of poor quality images are also necessary.
There was good agreement between the observers' diagnoses of intestinal metaplasia (κ = 0.53), though there are no published data quantifying interobserver agreement of OCT image interpretation in the esophagus. For this study, we attempted to generate relatively simple diagnostic criteria to maintain reproducibility. It is possible that greater agreement between OCT and histopathology could arise from a more intricate scoring system. Future studies with more complex diagnostic criteria and larger data sets may be warranted to improve the accuracy of this technique.
A previous study examined OCT image features of SIM, squamous mucosa, and gastric mucosa.13
In contrast to this previous study, where tissue samples were taken randomly from the esophagus and the stomach, biopsy-correlated images in our study were performed only at the SCJ, thereby including a much higher proportion of image samples of gastric cardia and columnar epithelium. The proportional increase in columnar epithelium in this data set likely accounts for the differences in the determined sensitivities for SIM. Our study supports and confirms the ability of OCT to distinguish SIM by using a simple subjective visual assessment. This is a significant step in the application of OCT as a screening technique in the treatment and care of patients with GERD.
Before broad acceptance of OCT as a valid screening technique for detecting SIM in patients with GERD, further research in 3 areas will be needed. First, a system must be developed to deliver the OCT catheter to the esophageal lining in a simple manner that is comfortable to the patient and applicable to a large population. Second, dysplasia in BE will need to be easily and accurately identifiable. Third, computer-software-aided image processing and classification algorithms to allow easier interpretation of data by the practicing gastroenterologist will need to be generated. Finally, these applications and results must be reproducible on a large scale. Current OCT technology is rapidly advancing. High-resolution systems that produce better than 5-mm resolution are on the horizon.20,21
If these efforts are successful and if the criteria are sufficiently accurate, OCT may be used to comprehensively screen the SCJ without endoscopy, thus avoiding the costs of endoscopy, biopsy preparation, and pathology review. These technologic improvements may propel OCT to the forefront of optical biopsy technologies as a first-line screening technique in the management of GERD.
What is already known on this topic
•OCT produces high-resolution, cross-sectional images of the esophagus, but its accuracy for differentiating tissue types at the SCJ has not been established.
What this study adds to our knowledge
•In a blinded prospective study that used an algorithm for diagnosing SIM and a validation set of 123 biopsy-correlated OCT images, a diagnostic sensitivity of 81% for SIM indicated that OCT imaging can identify SIM at the SCJ with accuracy similar to that of endoscopy.
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