Elastography and strain rate imaging of the gastrointestinal tract

https://doi.org/10.1016/j.ejrad.2013.05.018Get rights and content

Abstract

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.

Introduction

Ultrasonography of the wall of the GI tract shows a layered structure of 3–9 layers, depending on the frequency of the transducer used [1]. Usually 5 layers are observed representing from inside-out, the interface between mucosa and lumen, the mucosa, the submucosa and two layers of muscularis propria [1]. When examining the intestines, it is sufficient to use frequencies of around 5 MHz, but preferably between 10 and 15 MHz, to enable optimal visualisation of wall layers, thickened bowel walls and target lesions. This also applies for strain imaging and, fortunately, the linear high-frequency external probes or endoluminal probes are usually well suited for elasticity imaging.

Section snippets

Methods of strain imaging

Several methods for elasticity imaging have developed over the last years. Basically these methods can be divided into strain elastography [2] and shear-wave elastography [3], [4]. Strain elastography methods map the shape change of the tissue over a time interval by tracking the echogenic spots in the B-mode image as the tissue is being exposed to a stretching or contracting force. When this is done manually the method is referred to as quasi-static elastography [2]. Induction of the

Gastrointestinal wall pathology

Because the bowel wall is a long and thin organ largely surrounded by the serosa on the outside and with a luminal inside frequently containing gas and food undergoing digestion, it is not an ideal organ to visualise with US elastography with the current methods. Both the serosa and the luminal side allow substantial movement, which may appear in elastography images as very soft tissue or even no-signal areas. One of the advantages of B-mode ultrasonography is the detailed visualisation of wall

Gastrointestinal motility

The trans-abdominal application has been used for Strain rate imaging (SRI), which use tracking of tissue Doppler and preserving the sign of recorded strain in order to map contractions (negative strain) and relaxation/stretch (positive strain) [12]. Strain rate imaging is the temporal derivative of strain, i.e. it images the amount of strain per time unit. SRI is capable of differentiating between actively contracting muscle and passively following tissue. SRI enables separation of the

Limitations of methods

It is not possible to obtain a complete overview of all bowel segments using transabdominal ultrasound. Therefore, only selective segments of the intestines can be scanned. A major challenge to strain imaging of the bowel is peristaltic movements that introduce error in strain imaging. Also the thin structure of a normal bowel wall and the serosa and luminal surface that allows relatively large movements along these planes impairs at least strain based imaging. For endoscopic application, only

Summary

Imaging of the elastic properties in the GI tract may be technically demanding and not all of the current methods may be useful. Pathological lesions often represent areas of bowel wall thickening with reduced peristalsis, which enhance the applicability of elasticity imaging. Both neoplastic and inflammatory lesions may increase the bowel wall hardness. Weather ultrasound elastography may be used for differentiation between predominantly fibrotic or predominantly inflammatory lesions in IBD

Conflicts of interest

No conflicts of interests.

References (15)

There are more references available in the full text version of this article.

Cited by (27)

  • Ultrasound elastography and contrast-enhanced ultrasound in infants, children and adolescents

    2014, European Journal of Radiology
    Citation Excerpt :

    Malignant nodes were stiffer (median 25 kPa; range 6.9–278.9 kPa) than benign nodes (median 21.4 kPa; range 8.9–30.2 kPa); but there was a large overlap [21]. And potentially elastography could be helpful to differentiate between acute inflammation with a decrease in bowel wall stiffness and chronic, fibrotic alterations of the thickened bowel wall which should be associated with increased stiffness [22,23]. Fig. 2 shows focal thyroid inflammation in strain imaging, Fig. 3 shows shear-wave elastography of the liver.

  • Gastrointestinal ultrasound in neonates, infants and children

    2014, European Journal of Radiology
    Citation Excerpt :

    Recently extended applications have also been explored, including the GI tract particularly in IBD. In the GI tract, specific challenges rise from the anatomy and physiology of the bowel with thin wall, non-constant boundary conditions and intrinsic contractility, although pathological conditions are often related with increased bowel wall thickness and decreased bowel peristalsis [11,12]. Endoscopic US is another emerging field in adult GI tract imaging, although with limited experience and applicability in the pediatric population, partially due to lack of dedicated pediatric transducers [13].

View all citing articles on Scopus
View full text