Introduction
This topic covers the imaging of diffuse (non-focal) liver disease: which modality to use, and how hepatic steatosis, liver fibrosis and cirrhosis appear on ultrasound, CT and MRI, with the main differential diagnoses and the imaging signs of portal hypertension. Focal lesions and tumours belong to the next topic and are only mentioned where they affect the differential.
Imaging modalities for the liver
Ultrasound (US) is the first-line examination for the liver because it is cheap, fast, radiation-free and widely available. Colour and spectral Doppler assess portal, hepatic venous and arterial flow. Ultrasound elastography estimates liver stiffness. Its weaknesses are operator dependence and poor penetration in obese patients or those with ascites.
- Computed tomography (CT): unenhanced scans quantify liver attenuation; contrast-enhanced multiphase scans show morphology, vessels and collaterals.
- Magnetic resonance imaging (MRI): the most accurate non-invasive tool for fat quantification and iron assessment; MR elastography is the most accurate non-invasive method for fibrosis staging.
- Transient elastography (FibroScan) and shear-wave elastography: measure stiffness in kPa; quick, inexpensive and used for screening and follow-up.
- Nuclear medicine (Tc-99m sulfur colloid SPECT): reflects Kupffer cell function; in cirrhosis uptake is reduced in the liver with increased uptake in the spleen and bone marrow. It is rarely used now.