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Contrast-enhanced ultrasound for the evaluation of liver lesions

Author
Christoph F Dietrich, MD, MBA
Section Editor
Jonathan B Kruskal, MD, PhD
Deputy Editor
Anne C Travis, MD, MSc, FACG, AGAF

INTRODUCTION

Contrast-enhanced ultrasound (CEUS) is a well-established technique for imaging the liver and other organs [1-6]. It is used in most of Europe and Asia, as well as in many other countries worldwide. However, the contrast agents used for CEUS of the liver have not been approved by the US Food and Drug Administration, so its use in the United States is limited to research settings [1,2,7]. It is most often used for imaging the liver.

This topic will review the role of CEUS in evaluating liver lesions, including the indications for the procedure and findings associated with various lesions. The general evaluation of liver lesions is discussed in detail elsewhere. (See "Solid liver lesions: Differential diagnosis and evaluation" and "Diagnosis and management of cystic lesions of the liver".)

GENERAL PRINCIPLES

Standard CEUS — Contrast-enhanced ultrasound (CEUS) uses ultrasound contrast agents to improve visualization and characterization of anatomic structures and lesions. It is most often performed transcutaneously, though it can also be used intraoperatively. There are several contrast agents available for CEUS. Currently used ultrasound contrast agents are microbubbles consisting of gas bubbles stabilized by a shell. The most commonly used include sulfur hexafluoride with a phospholipid shell (SonoVue), octafluoropropane (perflutren with a lipid shell; Definity/Luminity), and perfluorobutane with a phospholipid shell (Sonazoid). Other ultrasound contrast agents are available, but they are not licensed for liver imaging or, in some cases (eg, Levovist), are no longer produced. (See "Contrast echocardiography: Contrast agents, safety, and imaging technique", section on 'Second generation contrast agents'.)

Ultrasound contrast agents are 1 to 10 microns in size (equal to or smaller than red blood cells) and permit visualization of both the macrovasculature and the microvasculature. The minute bubbles survive transpulmonary passage and recirculate, producing systemic ultrasound enhancement. This is an advantage over larger molecules that are retained in vascular beds [1,2,8]. Most ultrasound contrast agents are confined to the vascular space. By contrast, most of the contrast agents used for computed tomography or magnetic resonance imaging (MRI) are rapidly cleared from the blood pool into the extravascular space [2]. Because ultrasound contrast agents remain within the vascular space, only a small amount of contrast agent is required (typically 1 to 2 mL).

CEUS permits real-time visualization of contrast-enhancement patterns during all vascular phases (arterial, portal-venous, and late) [9]. This results in higher temporal resolution than can be achieved with other imaging modalities. The arterial phase provides information on the extent and pattern of the vascular supply. The arterial phase starts 10 to 20 seconds after contrast injection and lasts approximately 25 to 35 seconds. The portal-venous phase starts a few seconds after the arterial phase. It typically lasts until two minutes after contrast injection. The portal-venous phase is followed by the late phase, which lasts until the ultrasound contrast agents are cleared from the circulation (typically four to six minutes). In the case of the contrast agent Sonazoid, it is taken up by Kupffer cells, so there is an additional postvascular (or Kupffer) phase that starts 10 minutes after injection and lasts for an hour or more [1,2,10-13]. The images are analogous to those obtained with gadolinium-ethoxybenzyl-diethylenetriamine-enhanced MRI [9].

                   

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Literature review current through: Nov 2016. | This topic last updated: Fri Sep 26 00:00:00 GMT 2014.
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