Passively scanned, single-fiber optical coherence tomography probes for gastrointestinal devices

Abstract

Background/objectives: Optical coherence tomography (OCT) uses low coherence interferometry to obtain depth-resolved tissue reflectivity profiles (M-mode) and transverse beam scanning to create images of two-dimensional tissue morphology (B-mode). Endoscopic OCT imaging probes typically employ proximal or distal mechanical beam scanning mechanisms that increase cost, complexity, and size. Here, we demonstrate in the gastrointestinal (GI) tracts of unsedated human patients, that a passive, single-fiber probe can be used to guide device placement, conduct device-tissue physical contact sensing, and obtain two-dimensional OCT images via M-to-B-mode conversion.

Materials and methods: We designed and developed ultrasmall, manually scannable, side- and forward-viewing single fiber-optic probes that can capture M-mode OCT data. Side-viewing M-mode OCT probes were incorporated into brush biopsy devices designed to harvest the microbiome and forward-viewing M-mode OCT probes were integrated into devices that measure intestinal potential difference (IPD). The M-mode OCT probe-coupled devices were utilized in the GI tract in six unsedated patients in vivo. M-mode data were converted into B-mode images using an M-to-B-mode conversion algorithm. The effectiveness of physical contact sensing by the M-mode OCT probes was assessed by comparing the variances of the IPD values when the probe was in physical contact with the tissue versus when it was not. The capacity of forward- and side-viewing M-mode OCT probes to produce high-quality B-mode images was compared by computing the percentages of the M-to-B-mode images that showed close contact between the probe and the luminal surface. Passively scanned M-to-B-mode images were qualitatively compared to B-mode images obtained by mechanical scanning OCT tethered capsule endomicroscopy (TCE) imaging devices.

Results: The incorporation of M-mode OCT probes in these nonendoscopic GI devices safely and effectively enabled M-mode OCT imaging, facilitating real-time device placement guidance and contact sensing in vivo. Results showed that M-mode OCT contact sensing improved the variance of IPD measurements threefold and side-viewing probes increased M-to-B-mode image visibility by 10%. Images of the esophagus, stomach, and duodenum generated by the passively scanned probes and M-to-B-mode conversion were qualitatively superior to B-mode images obtained by mechanically scanning OCT TCE devices.

Conclusion: These results show that passive, single optical fiber OCT probes can be effectively utilized for nonendoscopic device placement guidance, device contact sensing, and two-dimensional morphologic imaging in the human GI tract in vivo. Due to their small size, lower cost, and reduced complexity, these M-mode OCT probes may provide an easier avenue for the incorporation of OCT functionality into endoscopic/nonendoscopic devices.

Keywords: B-mode OCT; M-mode OCT; endoscopic probe.

Figure 1

(A) M‐mode OCT probe embedded in an intestinal potential difference (IPD) device. The forward‐viewing probe contains a single‐mode fiber (250 µm diameter) terminated by a distal ball lens. (B) Side‐viewing M‐mode OCT probe, comprising only an angle‐polished fiber (80 mm diameter), attached to an endoscopic sampling brush device. OCT, optical coherence tomography.

Figure 2

Schematic for acquiring M‐mode OCT frames and converting them to an M‐to‐B‐mode OCT image. (A) M‐mode OCT frames were grabbed as the M‐mode OCT probe was translated over the tissue. The M‐mode OCT frames (B) were concatenated to create one M‐mode OCT image (C). (D) Sequential uncorrelated A‐lines were identified in the M‐mode OCT image. (E) Correlated A‐lines between successive uncorrelated A‐lines were averaged to create one unique A‐line. (F) These averaged A‐lines were placed side‐by‐side to create an M‐to‐B‐mode image. OCT, Optical coherence tomography. Figure created with BioRender. com

Figure 3

(A) M‐mode OCT image using an IPD probe that was not in contact with the mucosa. (B) M‐mode OCT image obtained with the IPD probe in contact with mucosa as evidenced by the increased tissue light scattering adjacent to the ball lens’ surface. IPD, intestinal potential difference; OCT, optical coherence tomography.

Figure 4

(A) M‐mode OCT images obtained from a patient's duodenum in vivo. When the brush was inside the TNIT, the image showed reflectance coming from the TNIT's wall. (B) When the brush was outside the TNIT, bile/mucus and tissue were visualized, but no such reflectance from the TNIT was seen. OCT, optical coherence tomography; TNIT, transnasal introduction tube.

Figure 5

(A) IPD values measured using a forward‐viewing IPD probe in a patient's small intestine with regions of no contact, determined by M‐mode OCT imaging, indicated by the dashed rectangles. (B) Graph showing that the variance in IPD values was greater when the IPD probe was not in contact with the intestinal mucosal surface, as determined by M‐mode OCT imaging. Error bars denote standard deviation. IPD, intestinal potential difference; OCT, optical coherence tomography.

Figure 6

Representative M‐to‐B‐mode images of the esophagus obtained in vivo with the side‐viewing M‐mode imaging brush (A) and the forward‐viewing M‐mode imaging IPD probe (B). Dotted lines represent the depth locations where OCT signal values were measured to ascertain % contact for good M‐to‐B‐mode imaging for both probe configurations. (C) Plot showing that the side‐viewing brush probe was in contact with the mucosal surface for a greater percentage of M‐to‐B‐mode images (*p < 0.05). Error bars denote standard deviation. IPD, intestinal potential difference; OCT, optical coherence tomography.

Figure 7

OCT images acquired from the upper gastrointestinal tracts of unsedated subjects, in vivo. (A) An M‐to‐B‐mode images acquired from the esophagus using the side‐viewing M‐mode imaging brush and a B‐mode OCT image of the esophagus acquired using the mechanically scanning tethered capsule endomicroscopy (TCE) device. The epithelium (EP), lamina propria (LP), submucosa (SM), muscularis mucosa (MM), inner muscle (IM), and outer muscular layers can be visualized in the M‐to‐B‐mode OCT image, consistent with the layers observed when using the TCE device. (B) M‐to‐B‐mode OCT image of the stomach obtained with the side‐viewing M‐mode imaging brush and a B‐mode OCT image of the stomach acquired using the mechanically scanning TCE device. Gastric pits (red arrows) were readily visible in the M‐to‐B‐mode frame and in the B‐mode image obtained via the TCE device. (C) M‐to‐B‐mode OCT image of the duodenum captured using the side‐viewing M‐mode imaging brush and the mechanically scanning TCE device. Duodenal villi (green arrows) seen in the M‐to‐B‐mode OCT image were similar to those visualized with the TCE device. OCT, optical coherence tomography.