Design and Simulation of a Ring-Shaped Linear Array for Microultrasound Capsule Endoscopy

Video capsule endoscopy (VCE) has significantly advanced visualization of the gastrointestinal tract (GI tract) since its introduction in the last 20 years. Work is now under way to combine VCE with microultrasound imaging. However, small maximum capsule dimensions, coupled with the electronics required to integrate ultrasound imaging capabilities, pose significant design challenges. This paper describes a simulation process for testing transducer geometries and imaging methodologies to achieve satisfactory imaging performance within the physical limitations of the capsule size and outlines many of the trade-offs needed in the design of this new class of ultrasound capsule endoscopy (USCE) device. A hybrid MATLAB model is described, incorporating KLM circuit elements and digitizing and beamforming elements to render a grey-scale B-mode. This model is combined with a model of acoustic propagation to generate images of point scatterers. The models are used to demonstrate the performance of a USCE transducer configuration comprising a single, unfocused transmit ring of radius 5 mm separated into eight segments for electrical impedance control and a 512-element receive linear array, also formed into a ring. The MATLAB model includes an ultrasonic pulser circuit connected to a piezocrystal composite transmit transducer with a center frequency of 25 MHz. B-scan images are simulated for wire target phantoms, multilayered phantoms, and a gut wall model. To demonstrate the USCE system’s ability to image tissue, a digital phantom was created from single-element ultrasonic transducer scans of porcine small bowel ex vivo obtained at a frequency of 45 MHz

Integrated Front End Circuitry for Microultrasound Capsule Endoscopy

Video capsule endoscopy (VCE) was originally developed to address the limitation of conventional endoscopy in accessing the small bowel as a remote part of the gastrointestinal tract. To further enhance the diagnostic ability of VCE, microultrasound capsule endoscopy is under development for identification of disease at an earlier stage and visualisation of subsurface tissue features. This paper presents an evaluation of two approaches to improve signal to noise ratio (SNR) in rapid prototyped capsule endoscopes. First, noise reduction techniques are applied to the integrated front-end circuits in the prototype capsules. Secondly, multiple types of coded excitation transmission are tested and benchmarked with respect to non-coded transmission. Results are presented for both bench top phantom imaging and in vivo translational trial imaging

Translational trial outcomes for capsule endoscopy test devices

Current clinical standards in the endoscopic diagnosis of gastrointestinal diseases are primarily based on the use of optical systems. Ultrasound has established diagnostic credibility in the form of endoscopic ultrasound (EUS), however it is limited to examination of the upper gastrointestinal tract (oesophagus, stomach and upper (proximal) small bowel). Access to the remainder of the small bowel is currently limited to optical capsule endoscopes and a limited number of other modalities as these capsules are restricted to visual examination of the surface or mucosa of the gut wall. Ultrasound capsule endoscopy has been proposed to integrate microultrasound imaging capabilities into the existing capsule format and extend examination capabilities beyond the mucosa. To establish the ability of high frequency ultrasound to resolve the histological structure of the gastrointestinal tract, ex vivo scans of pig and human tissue were performed. This was done using 25 and 34 MHz single element, physically focused composite transducers mechanically scanned along the tissue. Tethered prototype devices were then developed with 30 MHz physically focused polyvinylidene fluoride (PVDF) single element transducers embedded for use in initial translational trials in the small bowel of porcine subjects. B-scan images from the ex vivo model validation and the in vivo trials are presented

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

In Vivo Characterization of a Wireless Telemetry Module for a Capsule Endoscopy System Utilizing a Conformal Antenna

This paper describes the design, fabrication, packaging, and performance characterization of a conformal helix antenna created on the outside of a 10 mm ×30 mm capsule endoscope designed to operate at a carrier frequency of 433 MHz within human tissue. Wireless data transfer was established between the integrated capsule system and an external receiver. The telemetry system was tested within a tissue phantom and in vivo porcine models. Two different types of transmission modes were tested. The first mode, replicating normal operating conditions, used data packets at a steady power level of 0 dBm, while the capsule was being withdrawn at a steady rate from the small intestine. The second mode, replicating the worst-case clinical scenario of capsule retention within the small bowel, sent data with stepwise increasing power levels of –10, 0, 6, and 10 dBm, with the capsule fixed in position. The temperature of the tissue surrounding the external antenna was monitored at all times using thermistors embedded within the capsule shell to observe potential safety issues. The recorded data showed, for both modes of operation, a low error transmission of 10−3 packet error rate and 10−5 bit error rate and no temperature increase of the tissue according to IEEE standards

Design and simulation of a high-frequency ring-shaped linear array for capsule ultrasound endoscopy

Current research into endoscopy and colonoscopy has significantly advanced visualization of the gastrointestinal tract (GIT). The Sonopill project seeks to combine the imaging capabilities of endoscopic ultrasound with the full GIT transit of capsule endoscopy through the development of a capsule capable of ultrasonic imaging of the GIT, focusing on the small intestine. However, due to the small volume of the proposed capsule and the need to transmit received data wirelessly, the Sonopill system is limited both in data bandwidth and power. This paper presents a MATLAB-based simulation to allow testing of transducer topologies and imaging methodologies to achieve optimum results within the physical limitations of the system. To allow rapid evaluation of possible transducer configurations and circuit elements, a hybrid MATLAB simulation was created, incorporating both KLM circuit elements for analog analysis and digitizing and beamforming elements to render a final grey-scale image for imaging quality analysis. This was used in conjunction with a theoretical acoustic propagation model to image ideal point scatterers. The proposed transducers consist of a single, unfocused transmit ring of radius 5 mm separated into eight segments for impedance control, and a 512-element receive linear array curved into a matching ring. Because of the high element count and pad limitations on the intended electronics, the design requires the use of 32 integrated 16:1 multiplexers which will be bonded directly to the connecting flex circuit before the ASIC. Simulating the loading effects of these multiplexers as well as the proposed transducer configuration was critical to the analysis of the design. The MATLAB model was used to simulate a standard pulser transmitting over a 2.5 m cable to a 0.25 mm × 8 mm × 85 μm PMN-PT piezocrystal transmit transducer with a centre frequency of 25 MHz. B-scan images were then modelled for three imaging phantoms, one containing three point target resolution phantoms, a resolution phantom containing two virtual walls, and a tissue mimicking phantom containing particles with two levels of reflectivity to represent a three layer gut phantom with a high-reflectivity front surface

Development of a Hybrid Custom / Commercial Multi-Channel, High-Frequency Transmit Pulser and Beamformer System

The progressive development of a custom series of microultrasound transmit circuits is presented, with bipolar operation in both single-pulse and extended pulse operation. We have developed a series of low-cost, expandable channel-count circuits to drive microultrasound transducer arrays at frequencies up to 50 MHz and voltages up to 80 Vpp. This includes both bench-top supply and electrical mains powered system development with expandable channel count and also includes integration with the multi-channel FI Toolbox commercial product (Diagnostic Sonar, Livingston, UK). A series of discrete focusing delay chips with variable delay steps allows them to be programmed either serially or in parallel. In turn, this allows the system to be operated in isolation or in conjunction with commercial generic hardware platforms

Ultrasound Capsule Endoscopy Components for in vivo and ex vivo Microultrasound Near-Field Imaging

Ultrasound capsule endoscopy (USCE) has attracted increased interest recently. In order to image the walls of the gastrointestinal (GI) tract with USCE efficiently, both high-frequency ultrasound (i.e. microultrasound) imaging and good acoustic coupling are needed. Tissue to be scanned is expected close to the transducer surface, but the near-field tissue echoes may be easily lost in the acoustic ring-down. Here, we present experimental ex vivo and in vivo porcine small bowel imaging results from an USCE prototype. The preliminary results show that the near-field image can be recovered after post-processing. Although some limitations in imaging the GI tract are inherent in the use of focused single element transducers, solving the problem of near-field imaging is relevant to all USCE implementations

High Resolution Microultrasound (μUS) Investigation of the Gastrointestinal (GI) Tract

High resolution, microultrasound (μUS) scanning of the gastrointestinal (GI) tract has potential as an important transmural imaging modality to aid in diagnosis. Operating at higher frequencies than conventional clinical ultrasound instruments, μUS is capable of providing scanned images of the GI tract with higher resolution. To investigate the use of μUS for this application, a phantom which is cost effective, within ethical guidelines and, most importantly, similar in histology to the human GI tract is necessary. Therefore, a phantom utilizing porcine small bowel tissue has been developed for custom assembled μUS scanning systems. Two such systems, a stepping scanner and a continuous sweep scanner were utilized to repeatedly scan regions of prepared samples of porcine small bowel tissue. The porcine small bowel tissue phantom was perfused with degassed phosphate buffer saline (dPBS) solution through a cannula inserted in its mesenteric vessel to simulate in vivo conditions and achieve better μUS mucosal characterization. The μUS system scans a transducer across the tissue phantom to acquire RF echo data, which is then processed using MATLAB. A B-scan reconstruction produces 2D images with relative echo strength mapped to a color map of the user's choice. The phantom developed also allows for modifications such as the insertion of fiducial markers to detect tissue change over time and simultaneous perfusion and scanning, providing a platform for more detailed research and investigation into μUS scanning of the GI tract