Contrast-enhanced ultrasound (CEUS) — focal liver lesion characterisation

The target lesion held in a single acoustic window, imaged continuously through arterial, portal venous and late phases, followed by a survey of the remaining liver.

Typical, not policy

Timings, volumes and delays here are representative values drawn from published guidance. Scanner generation, injector, cardiac output and local preference all move them. Confirm against your department's own protocol before you rely on a number.

When to use it

Characterisation of a focal liver lesion found incidentally on ultrasound, where the alternative is a multiphase CT or MRI in a patient who does not otherwise need one.
Characterisation where iodinated contrast and gadolinium are both undesirable — significant renal impairment, or a prior severe reaction to both agent classes.
Problem-solving an indeterminate lesion on CT or MRI, where real-time observation of wash-in and wash-out adds information that discrete acquired phases cannot.
Confirming that an incidental lesion is a haemangioma, where peripheral nodular fill-in is seen dynamically rather than inferred between two timepoints.
Characterisation of an indeterminate renal cyst where septal and nodular enhancement is the question and cross-sectional contrast cannot be given.

Technique

A low mechanical index contrast-specific mode is essential; imaging at diagnostic mechanical index destroys the microbubbles and the study fails.
The great advantage over CT and MRI is temporal resolution: the arterial phase is watched in real time from about 10-20 s, so the pattern of fill-in — peripheral nodular, centripetal, spoke-wheel, chaotic — is observed rather than sampled.
The late phase extends to several minutes and is where wash-out is judged; the timing and degree of wash-out is what separates a malignant lesion from a benign hypervascular one.
The clock starts at injection and the lesion must be found before the agent is given, because there is no second chance within that bolus.

Where it goes wrong

Only one lesion can be interrogated per bolus and only within one acoustic window — this is a targeted characterisation study, not a staging study, and it cannot survey the liver for additional lesions during the arterial phase.
A deep lesion, a steatotic or cirrhotic liver, or a large body habitus attenuates the signal and can make the study non-diagnostic; the same limitations that made the greyscale study difficult apply.
Wash-out kinetics differ from CT and MRI: microbubbles remain intravascular, so late-phase wash-out is a different observation and CT/MRI thresholds must not be transposed onto it.
Serious hypersensitivity reactions are rare but described, so the study is performed where resuscitation facilities are available; it is not a "contrast-free" examination in the safety sense even though it carries no renal risk.

Clinical questions that reach this study

Suspected intra-abdominal abscess or collection Major trauma — whole-body (pan-scan) versus selective CT Suspected acute diverticulitis Acute pancreatitis — severity and complication assessment Suspected acute cholecystitis Obstructive jaundice and suspected biliary obstruction Suspected hepatocellular carcinoma in cirrhosis Characterisation of an incidental liver lesion (non-cirrhotic liver)Suspected pancreatic mass or painless obstructive jaundice Aortic aneurysm surveillance and post-repair follow-up

Contrast

Microbubble, intravenous

A typical sulphur hexafluoride or perflutren microbubble agent given as a small intravenous bolus of a few millilitres through a cannula of at least 20G, followed by a saline flush, with the sweep started at the moment of injection. A second bolus can be given for a repeat or a second lesion within the same appointment.

Microbubbles are a pure blood-pool agent: they do not diffuse into the interstitium and are not excreted by the kidney, so there is no nephrotoxicity and no requirement for an eGFR before administration.
They are cleared by exhalation and by the reticuloendothelial system, which is why the enhancement pattern differs from iodinated and gadolinium agents rather than merely being an ultrasound version of them.

Acquisition

Breathing: Quiet breathing with the lesion kept in the imaging plane; a breath-hold is used only for the arterial sweep if the patient can manage it.
Preparation: Fasting 4-6 h improves gallbladder distension and reduces bowel gas.