Incorporating robotics into endoscopic optical coherence tomography

Modern endoscopes enable doctors to visualize various regions inside the body in real time during minimally invasive procedures, making early diagnosis of diseases such as cancer much easier. However, more sophisticated imaging modalities besides standard light-based ones are sometimes needed to detect elusive lesions. That is why, in recent years, a technique called optical coherence tomography (OCT), originally developed for imaging the retina, has been adapted for endoscopic systems, primarily those used for exploring the digestive tract. 

Endoscopic OCT systems generally consist of a small flexible catheter containing the necessary optical components at the tip. The catheter is attached at the end of the endoscope alongside the standard cameras. Since miniature OCT probes have a very small field of view, doctors must position them close to a suspected lesion guided by standard images and then manually scan the target area little by little. Robotized flexible OCT probes make this process easier. Using them, a doctor does not need to move the entire endoscope tip and can instead reposition the probe alone. However, currently available robotic probes have limited degrees of freedom and must be controlled manually, making the scanning procedure complex and error prone.

Against this backdrop, a research team from the University of Strasbourg, France, recently developed an innovative endoscopic OCT system capable of automatic volumetric (3D) scanning. Their findings, published recently in the Journal of Optical Microsystems, demonstrate how concepts from the field of robotics can be leveraged for the design of OCT catheters for endoscopy.

The proposed system uses a steerable catheter with a low-profile OCT probe attached to a custom endoscope. Notably, the catheter can move with three degrees of freedom. The probe tip can fully rotate at its base and also bend to the sides at angles ranging from 0 to 90 degrees by using 11 links vaguely resembling the vertebrae of the spine. Moreover, the tip assembly can be extended and retracted to alter its length.

By combining these independent movements, the steerable catheter can scan a large 3D region with a volume of 255 cm³. The researchers confirmed this by developing a model of their device and analyzing the geometry of the possible catheter motions by attaching an electromagnetic positional sensor to the catheter.

To demonstrate the advantages of automatic scanning, the team ran a series of experiments in which various endoscopic OCT systems were used to scan a printed target using a predefined scanning path. When the proposed system was used in automatic scanning mode, the motion of the probe was smooth, which is essential to minimize errors when processing the acquired images. In contrast, the probe movements were relatively less smooth when teleoperated (operated remotely) or when the endoscope itself was moved manually.

Furthermore, automatic scanning was about twice as fast as teleoperated scanning and followed the predefined path much more precisely, with 1.54 mm spacing between 15 sweep trajectories, each of which took an average of 3.11 seconds. This mode had spectral arc length of –3.18, maximum translation of 27.99 mm, and covered area of 10.11 cm².    

Implementing automatic scanning would enable doctors to focus more on the potential lesions and less on the operation of the endoscopic OCT probe, which could improve the accuracy of diagnostic procedures. The proposed device could also increase the quality of reconstructed OCT images thanks to its smooth motion, large field of view, and compliance with predefined scanning motions. Moreover, additional sensing mechanisms and control techniques could be incorporated into the proposed design to facilitate automatic scanning of lesions with complex shapes, such as polyps.

Overall, this study provides strong evidence that concepts borrowed from robotics can be very valuable in the context of medical imaging. Future interdisciplinary research may pave the way to better endoscopic systems for diagnosing digestive tract conditions.   

Read the Gold Open Access paper by Caravaca-Mora et al., “Automatic intraluminal scanning with a steerable endoscopic optical coherence tomography catheter for gastroenterology applications,” J. Opt. Microsys., 3(1) 011005 (2023) doi 10.1117/1.JOM.3.1.011005.