Ultrasound capsule endoscopy with a mechanically scanning micro-ultrasound: a porcine study

Wireless capsule endoscopy has been used for the clinical examination of the gastrointestinal (GI) tract for two decades. However, most commercially available devices only utilise optical imaging to examine the GI wall surface. Using this sensing modality, pathology within the GI wall cannot be detected. Micro-ultrasound (μUS) using high-frequency (>20 MHz) ultrasound can provide a means of transmural or cross-sectional image of the GI tract. Depth of imaging is approximately 10 mm with a resolution of between 40–120 μm that is sufficient to differentiate between subsurface histologic layers of the various regions of the GI tract. Ultrasound capsule endoscopy (USCE) uses a capsule equipped with μUS transducers that are capable of imaging below the GI wall surface, offering thereby a complementary sensing technique to optical imaging capsule endoscopy. In this work, a USCE device integrated with a ∼30 MHz ultrasonic transducer was developed to capture a full 360° image of the lumen. The performance of the device was initially evaluated using a wire phantom, indicating an axial resolution of 69.0 μm and lateral resolution of 262.5 μm. Later, in vivo imaging performance was characterised in the oesophagus and small intestine of anaesthetized pigs. The reconstructed images demonstrate clear layer differentiation of the lumen wall. The tissue thicknesses measured from the B-scan images show good agreement with ex vivo images from the literature. The high-resolution ultrasound images in the in vivo porcine model achieved with this device is an encouraging preliminary step in the translation of these devices toward future clinical use.