Normal ultrasonographic anatomy of the liver

Hepatic US is performed with standard curvilinear and high-resolution linear probes.

The curvilinear probe (2–6 MHz) allows acoustic penetration of deeper parenchyma while a high-resolution probe (7–12 MHz) may be used to depict greater surface detail.

Optimization of the gain, time-gain compensation, and tissue harmonics by an experienced sonologist, and second-look sonography by informed radiologists are requisites for achieving diagnostic examinations.

Normal liver parenchyma has a homogeneous echotexture, the assessment is subjective but the liver should not appear granular or coarsened if speckle reduction and compound imaging parameters are optimized.

Hepatic echogenicity is subjectively compared with that of adjacent solid viscera such as the kidneys and spleen; normal hepatic echogenicity is marginally higher than that of the kidney but less than that of the spleen.

The spleen provides a more reliable comparison because numerous intrinsic kidney diseases can alter their echogenicity.

Normal hepatic vessels have smooth walls and anechoic lumens.

Intrahepatic arteries are difficult to resolve on gray scale alone, but parallel the portal veins.

Normal spectral Doppler interrogation shows a low-resistance waveform with continuously hepatopetal diastolic flow.

Normal portal veins have thin echogenic walls and monophasic waveforms with mild respiratory variation. 

Alterations of portal mural echogenicity should be considered abnormal.

Normal hepatic veins and the inferior vena cava (IVC) lack discernible walls.

The normal hepatic venous waveform is triphasic, owing to 2 hepatofugal peaks and 1 hepatopetal peak reflecting primarily right atrial pressure.

The normal common bile duct measures up to 6 mm in normal individuals, but radiology dogma suggest that the diameter of the duct can increase with age.

The central intrahepatic ducts should normally measure 3 mm or less.

The diameter of the common bile duct may vary following cholecystectomy.

The normal perihepatic spaces should contain a variable amount of homogeneous fat; any ascites, fluid collection, or soft-tissue lesion should be considered abnormal.

Does MRI Solve Liver Problems?

MR imaging is considered the most accurate modality to the image the liver for the detection and characterization of focal and diffuse liver diseases.The superiority of MR imaging compared with other imaging modalities for liver evaluation has become more even apparent because of substantial improvements in 1.5 T magnets with faster image acquisition and better quality. Advancements in MR imaging hardware ,software and contrast agents have made a major impact on imaging of the liver, phased array surface coil technology significantly improved SNR and conventional spin echo pulse sequences have been replaced by faster sequences .Gradients-echo (GRE) sequences generally are used for T1–weighted sequences and echo-train sequences are used for T2–weighted sequences. Introduction of parallel imaging techniques has enabled further reduction of acquisition time and improved spatial resolution.