Lectures

Harmonic Imaging: tissues and microbubbles

Most metastases are hypovascular and they may show a peripheral marginal arterial supply with no apparent internal supply; in the sinusoidal phase they appear as defects as the liver increases in signal intensity, exactly as with the high MI late phase technique such as ADI.

Vascularity of Liver Masses

These approaches are helpful in the characterisation and detection of focal liver lesions but they are also important in the control of interstitial therapy which is often conducted under ultrasound guidance. Determining whether complete oblation has been achieved with RF maybe difficult with B-mode or Doppler ultrasound but the microvascular perfusion data contributed by microbubble specific ultrasound methods not only improves the differentiation between viable and ablated tissue but allows this distinction to be made during the ultrasound-controlled ablation session, thus avoiding anaesthetised patients having to be moved to CT and then back again to ultrasound.

Another important application of this technique is in solid abdominal trauma: haematomas and fractures in the liver, kidneys and spleen can be delineated and these studies can be performed within the A&E department with agents that are not nephrotoxic and do not impose an osmotic load.

An additional application of microbubbles is as haemodynamic tracers with which the function of organs can be tracked. The most important application of this to date has been the interrogation of arterialisation of the liver’s blood supply: normally the liver is predominantly supplied by the portal vein but in cirrhosis and in metastatic disease there is arterialisation of the supply and this results in a fast transit between the time of injection and the arrival of the contrast in the hepatic veins. This is simple to measure and could stage liver involvement in malignancy or the cirrhotic status of hepatitis patients completely non-invasively. Both these diagnoses have major clinical implications.