High-frequency ultrasonographic imaging of the gastrointestinal wall

Quantitative characterization of duodenal gastrinoma autofluorescence using multiphoton microscopy

BACKGROUND

Duodenal gastrinomas (DGASTs) are neuroendocrine tumors that develop in the submucosa of the duodenum and produce the hormone gastrin. Surgical resection of DGASTs is complicated by the small size of these tumors and the tendency for them to develop diffusely in the duodenum. Endoscopic mucosal resection of DGASTs is an increasingly popular method for treating this disease due to its low complication rate but suffers from poor rates of pathologically negative margins. Multiphoton microscopy can capture high-resolution images of biological tissue with contrast generated from endogenous fluorescence (autofluorescence [AF]) through two-photon excited fluorescence (2PEF). Second harmonic generation is another popular method of generating image contrast with multiphoton microscopy (MPM) and is a light-scattering phenomenon that occurs predominantly from structures such as collagen in biological samples. Some molecules that contribute to AF change in abundance from processes related to the cancer disease process (e.g., metabolic changes, oxidative stress, and angiogenesis).

STUDY DESIGN/MATERIALS AND METHODS

MPM was used to image 12 separate patient samples of formalin-fixed and paraffin-embedded duodenal gastrinoma slides with a second-harmonic generation (SHG) channel and four 2PEF channels. The excitation and emission profiles of each 2PEF channel were tuned to capture signal dominated by distinct fluorophores with well-characterized fluorescent spectra and known connections to the physiologic changes that arise in cancerous tissue.

RESULTS

We found that there was a significant difference in the relative abundance of signal generated in the 2PEF channels for regions of DGASTs in comparison to the neighboring tissues of the duodenum. Data generated from texture feature extraction of the MPM images were used in linear discriminant analysis models to create classifiers for tumor versus all other tissue types before and after principal component analysis (PCA). PCA improved the classifier accuracy and reduced the number of features required to achieve maximum accuracy. The linear discriminant classifier after PCA distinguished between tumor and other tissue types with an accuracy of 90.6%-93.8%.

CONCLUSIONS

These results suggest that multiphoton microscopy 2PEF and SHG imaging is a promising label-free method for discriminating between DGASTs and normal duodenal tissue which has implications for future applications of in vivo assessment of resection margins with endoscopic MPM.

Ex vivo ultrasonographic and histological morphometry of small intestinal wall layers in horses

Ultrasonographic morphometry of wall layers is commonly used in veterinary patients with suspected small intestinal disease, however published studies comparing this method with histopathology in horses are limited. This prospective, methods comparison study compared the qualitative and quantitative characteristics of small intestinal wall layers using ex vivo high‐frequency ultrasound versus histopathology in a sample of 16 horses. Transverse section images of duodenum, distal jejunum, and ileum were acquired with a high‐frequency linear transducer (7–15 MHz). Transverse histological cryosections were obtained at the same level. Appearance and measurements of the intestinal wall layers were assessed on the ultrasonographic and histological images. High‐frequency scanning with the probe in close contact with the serosal surface of the equine intestinal wall allowed a clear and detailed definition of wall layers. A hyperechoic line was consistently detected within the tunica muscularis in all the intestinal tracts, corresponding histologically to the interface between its longitudinal and circular muscle layers. The overall trend of the values for wall layers thickness was comparable between ex vivo ultrasonography and histology. However, a poor agreement was found between the two methods for all layers. The ultrasonographic measurements were thicker compared to histological measurements, with the exception of the total wall and the muscular layer thicknesses. These layers were thinner on ultrasonography in the duodenum and in all the intestinal segments, respectively. Findings from the current study can be used as background for future ultrasonographic investigations of small intestinal diseases in horses.

A Learning-Based Microultrasound System for the Detection of Inflammation of the Gastrointestinal Tract

Inflammation of the gastrointestinal (GI) tract accompanies several diseases, including Crohn's disease. Currently, video capsule endoscopy and deep bowel enteroscopy are the main means for direct visualisation of the bowel surface. However, the use of optical imaging limits visualisation to the luminal surface only, which makes early-stage diagnosis difficult. In this study, we propose a learning enabled microultrasound ( μ US) system that aims to classify inflamed and non-inflamed bowel tissues. μ US images of the caecum, small bowel and colon were obtained from mice treated with agents to induce inflammation. Those images were then used to train three deep learning networks and to provide a ground truth of inflammation status. The classification accuracy was evaluated using 10-fold evaluation and additional B-scan images. Our deep learning approach allowed robust differentiation between healthy tissue and tissue with early signs of inflammation that is not detectable by current endoscopic methods or by human inspection of the μ US images. The methods may be a foundation for future early GI disease diagnosis and enhanced management with computer-aided imaging.

Ex vivo comparison of ultrasonographic intestinal wall layering with histology in horses: A feasibilty study

Ultrasonography is increasingly being used as a clinical and research method for evaluating the gastrointestinal tract in horses, however published studies comparing ultrasonographic and histologic characteristics of equine intestinal wall layers are currently lacking. Objectives of this prospective, observational, methods comparison, case series study were to compare the layering pattern and thickness of the intestinal wall layers determined using ex vivo and in vivo ultrasonography with those determined using histology. For the ex vivo study, twelve horses were euthanized for reasons unrelated to gastrointestinal disease, and samples of the duodenum, jejunum, ileum, cecum, right dorsal colon, and small colon were collected and imaged sonographically ex vivo in an isotonic bath within 1 hour of euthanasia. For the in vivo study, ultrasonography was performed in four clinical cases, and findings were compared with histopathology. A 5-layer pattern of alternating echogenicity was observed in 70 of 72 ex vivo samples. Agreement between histologic and sonographic measurements was deemed good for all segments except the ileum. Formalin fixation did not alter the sonographic appearance or wall measurements. Findings from the four clinical cases illustrated the feasibility of also obtaining ultrasonographic images with sufficient sonographic detail in vivo to recognize wall layering and obtain comparable results to pathologic lesions. Findings from the current study can serve as background for future studies comparing ultrasonographic characteristics of the intestinal wall in horses with different gastrointestinal diseases.

Intelligent magnetic manipulation for gastrointestinal ultrasound

Diagnostic endoscopy in the gastrointestinal tract has remained largely unchanged for decades and is limited to the visualization of the tissue surface, the collection of biopsy samples for diagnoses, and minor interventions such as clipping or tissue removal. In this work, we present the autonomous servoing of a magnetic capsule robot for in-situ, subsurface diagnostics of microanatomy. We investigated and showed the feasibility of closed-loop magnetic control using digitized microultrasound (μUS) feedback; this is crucial for obtaining robust imaging in an unknown and unconstrained environment. We demonstrated the functionality of an autonomous servoing algorithm that uses μUS feedback, both on benchtop trials as well as in-vivo in a porcine model. We have validated this magnetic-μUS servoing in instances of autonomous linear probe motion and were able to locate markers in an agar phantom with 1.0 ± 0.9 mm position accuracy using a fusion of robot localization and μUS image information. This work demonstrates the feasibility of closed-loop robotic μUS imaging in the bowel without the need for either a rigid physical link between the transducer and extracorporeal tools or complex manual manipulation.

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 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 tradeoffs needed in the design of this new class of ultrasound capsule endoscopy (USCE) device. A hybrid MATLAB model is described, incorporating Krimholtz-Leedom-Matthaei circuit elements and digitizing and beamforming elements to render a gray-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.

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.

Acoustic Sensing and Ultrasonic Drug Delivery in Multimodal Theranostic Capsule Endoscopy

Video capsule endoscopy (VCE) is now a clinically accepted diagnostic modality in which miniaturized technology, an on-board power supply and wireless telemetry stand as technological foundations for other capsule endoscopy (CE) devices. However, VCE does not provide therapeutic functionality, and research towards therapeutic CE (TCE) has been limited. In this paper, a route towards viable TCE is proposed, based on multiple CE devices including important acoustic sensing and drug delivery components. In this approach, an initial multimodal diagnostic device with high-frequency quantitative microultrasound that complements video imaging allows surface and subsurface visualization and computer-assisted diagnosis. Using focused ultrasound (US) to mark sites of pathology with exogenous fluorescent agents permits follow-up with another device to provide therapy. This is based on an US-mediated targeted drug delivery system with fluorescence imaging guidance. An additional device may then be utilized for treatment verification and monitoring, exploiting the minimally invasive nature of CE. While such a theranostic patient pathway for gastrointestinal treatment is presently incomplete, the description in this paper of previous research and work under way to realize further components for the proposed pathway suggests it is feasible and provides a framework around which to structure further work.

Ultrasound capsule endoscopy: sounding out the future

Video capsule endoscopy (VCE) has been of immense benefit in the diagnosis and management of gastrointestinal (GI) disorders since its introduction in 2001. However, it suffers from a number of well recognized deficiencies. Amongst these is the limited capability of white light imaging, which is restricted to analysis of the mucosal surface. Current capsule endoscopes are dependent on visual manifestation of disease and limited in regards to transmural imaging and detection of deeper pathology. Ultrasound capsule endoscopy (USCE) has the potential to overcome surface only imaging and provide transmural scans of the GI tract. The integration of high frequency microultrasound (µUS) into capsule endoscopy would allow high resolution transmural images and provide a means of both qualitative and quantitative assessment of the bowel wall. Quantitative ultrasound (QUS) can provide data in an objective and measurable manner, potentially reducing lengthy interpretation times by incorporation into an automated diagnostic process. The research described here is focused on the development of USCE and other complementary diagnostic and therapeutic modalities. Presently investigations have entered a preclinical phase with laboratory investigations running concurrently.

Ultrasonography in gastroenterology

Ultrasonography (US) is a safe and available real-time, high-resolution imaging method, which during the last decades has been increasingly integrated as a clinical tool in gastroenterology. New US applications have emerged with enforced data software and new technical solutions, including strain evaluation, three-dimensional imaging and use of ultrasound contrast agents. Specific gastroenterologic applications have been developed by combining US with other diagnostic or therapeutic methods, such as endoscopy, manometry, puncture needles, diathermy and stents. US provides detailed structural information about visceral organs without hazard to the patients and can play an important clinical role by reducing the need for invasive procedures. This paper presents different aspects of US in gastroenterology, with a special emphasis on the contribution from Nordic scientists in developing clinical applications.

Bowel perfusion measured with dynamic contrast-enhanced ultrasound predicts treatment outcome in patients with Crohn's disease

BACKGROUND

To improve management of patients with Crohn's disease (CD), objective measurements of the degree of local inflammation in the gastrointestinal wall are needed. Increased microvessel density and perfusion are typical features of acute inflammation and can be estimated with contrast-enhanced ultrasound (CEUS). The aim of the study was to investigate whether CEUS can provide prognostic information about patients treated medically for an acute exacerbation of CD.

METHODS

Fourteen patients with CD who received medical treatment for acute exacerbation with systemic steroids or tumor necrosis factor-α inhibitors were prospectively recruited. The patients were examined with clinical scoring, blood tests, and CEUS at time 0, 1, 3, and 12 months after initiation of the treatment. Outcome was treatment efficacy or treatment failure defined as change in medical treatment after 1 month or later. The perfusion analysis was performed with a commercially available software program that analyzes the contrast intensity in a selected area, fits the data to a standardized time-intensity curve, and derives several relative perfusion parameters.

RESULTS

Six of the 14 patients had treatment failure during the study period. There was a significant difference between the groups for peak contrast enhancement (P = 0.013), rate of wash-in (P = 0.020) and wash-out (P = 0.008), and the area under the time-intensity curve in the wash-in phase (0.013) at the examination 1 month after the start of treatment.

CONCLUSIONS

Perfusion analysis of the intestinal wall with CEUS 1 month after starting treatment in patients with CD can provide prognostic information regarding treatment efficacy.

Gastrointestinal ultrasonography of normal Standardbred neonates and frequency of asymptomatic intussusceptions

Background

Ultrasonographic appearance of the gastrointestinal (GI) tract of equine neonates has not been completely described.

Objectives

To describe (1) sonographic characteristics of the GI segments in normal nonsedated equine neonates, (2) intra‐ and interobserver variation in wall thickness, and (3) the sonographic appearance of asymptomatic intussusceptions, and (4) to compare age and sonographic findings of foals with and without asymptomatic intussusceptions.

Animals

Eighteen healthy Standardbred foals ≤5 days of age.

Methods

Prospective, cross‐sectional blinded study. Gastrointestinal sonograms were performed stall‐side. Intraobserver variability in wall thickness measurements was determined by calculating the coefficient of variation (CV). The Bland–Altman method was used to assess interobserver bias. Student's t‐test and Fisher's exact test were used to test the association among presence of intussusceptions, age, and selected sonographic findings.

Results

The reference ranges (95% predictive interval) for wall thickness were 1.6–3.6 mm for the stomach, 1.9–3.2 mm for the duodenum, 1.9–3.1 mm for the jejunum, 1.3–2.2 mm for the colon, and 0.8–2.7 mm for the cecum. Intraobserver wall thickness CV ranged from 8 to 21% for the 2 observers for 5 gastrointestinal segments. The interobserver bias for wall thickness measurements was not significant except for the stomach (0.14 mm, P < .05) and duodenum (0.29 mm, P < .05). Diagnostic images of mural blood flow could not be obtained. Asymptomatic intussusceptions were found in 10/18 neonates. Associations between sonographic variables or age and the presence of intussusceptions were not found.

Conclusions and Clinical Importance

Sonographic characteristics of the GI tract of normal Standardbred neonates can be useful in evaluating ill foals. Asymptomatic small intestinal intussusceptions occur in normal Standardbred neonates.

Elastography and strain rate imaging of the gastrointestinal tract

Ultrasound based elastography of the gastrointestinal tract may be a useful approach to improved tissue characterisation. Distinguishing malignant lesions from benign may be one useful application. Monitoring of inflammatory bowel lesions for degree of inflammation or fibrosis would be another clinically useful tool. The anatomy of the bowel, however, raises many challenges for strain or shear wave imaging due to thin structures, non-constant boundary conditions and intrinsic contractility. Pathological lesions tend to increase bowel wall thickness and may ease elastography imaging. Very few studies have addressed issues of bowel wall elastography so far, and both inflammatory and neoplastic lesions seem to increase tissue hardness in the bowel wall.