Capsule optoacoustic endoscopy for esophageal imaging

Abstract

Detection and monitoring of esophageal cancer severity require an imaging technique sensitive enough to detect early pathological changes in the esophagus and capable of analyzing the esophagus over 360 °in a non‐invasive manner. Optoacoustic endoscopy (COE) has been shown to resolve superficial vascular structure of the esophageal lumen in rats and rabbits using catheter‐type probes. Although these systems can work well in small animals, they are unsuitable for larger lumens with thicker walls as required for human esophageal screening, due to their lack of position stability along the full organ circumference, sub‐optimal acoustic coupling and limited signal‐to‐noise ratio (SNR). In this work, we introduce a novel capsule COE system that provides high‐quality 360° images of the entire lumen, specifically designed for typical dimensions of human esophagus. The pill‐shaped encapsulated probe consists of a novel and highly sensitive ultrasound transducer fitted with an integrated miniature pre‐amplifier, which increases SNR of 10 dB by minimizing artifacts during signal transmission compared to the configuration without the preamplifier. The scanner rotates helically around the central axis of the probe to capture three‐dimensional images with uniform quality. We demonstrate for the first time ex vivo volumetric vascular network images to a depth of 2 mm in swine esophageal lining using COE. Vascular information can be resolved within the mucosa and submucosa layers as confirmed by histology of samples stained with hematoxylin and eosin and with antibody against vascular marker CD31. COE creates new opportunities for optoacoustic screening of esophageal cancer in humans.

Ultra-broadband axicon transducer for optoacoustic endoscopy

“…3 ), while reducing the overall ultrasound sensitivity proportional to the area of the hole. A central aperture is advantageous for coaxial illumination, which is desirable for endoscopic applications 17 . For this reason, we designed two transducers with central apertures: an axicon transducer and a spherical transducer for comparison.…”

“…The high frequency broadband axicon transducer presented here could enable high-resolution optoacoustic imaging at greater depths than commonly used spherical detectors. This is particularly relevant for endoscopic applications, where tomographic reconstruction views are limited and real-time image processing is required 17 . Axicon performance is achieved solely by forming a lens in a conical rather than spherical shape in a lens-based focused transducer.…”

“…Three broadband single element optoacoustic detectors were manufactured, including a standard RSOM transducer 2 and two endoscopic transducers with dimensions suitable for capsule endoscopy 17 . The frequency bandwidths were designed to detect signals from a few MHz up to a 100 MHz to resolve the vascular layers in the esophagus wall with sufficient sensitivity 8 .…”

“…Optical ultrasound detectors operating at 20 MHz have also been employed for endoscopic applications; however, only for forward looking configurations 16 . Recently, our group implemented a 20 mm diameter stand-alone capsule optoacoustic endoscope, which featured a 30 MHz side-looking focused transducer with an opening for central illumination 17 . This endoscope could be oriented directly toward the organ wall to avoid indirect signal detection through reflective elements and reduce the propagation distance to improve acoustic sensitivity.…”

In vivo optical endomicroscopy: two decades of translational research towards next generation diagnosis of eosinophilic esophagitis

“…laser marking [110]). The TCE community is growing; other leading research groups in the field of endoscopic OCT [111][112][113][114][115] and photoacoustic imaging [116] have already integrated TCE into their scientific portfolios.…”