A liver sonography is a diagnostic tool to image the liver and adjoining upper abdominal organs such as the gallbladder, spleen, and pancreas. Deeper structures such as liver and pancreas are imaged at a lower frequency 1-6 MHz with lower axial and lateral resolution but greater penetration. The diagnostic capabilities in this area can be limited by gas in the bowel scattering the sound waves.
The application of microbubbles may be useful for detection of liver lesions and for lesion characterization. Some microbubbles have a liver-specific post vascular phase where they appear to be taken up by the reticuloendothelial system (RES). Dynamic contrast enhanced scans in a similar way as with CT or MRI can be used to studying the arterial, venous and tissue phase.
After a bolus injection, early vascular enhancement is seen at around 30sec in arterialized lesions (e.g., hepatocellular carcinomas (HCC), focal nodular hyperplasia (FNH)). Later enhancement is typical of hemangiomas with gradually filling towards the center. In the late phase at around 90sec, HCCs appear as defects against the liver background. Most metastases are relatively hypovascular and so do not show much enhancement and are seen as signal voids in the different phases.
Either with an intermittent imaging technique or by continuous scanning in a nondestructive, low power mode, characteristic time patterns can be used to differentiate lesions.

See also Medical Imaging, B-Mode, High Intensity Focused Ultrasound, Ultrasound Safety and Contrast Medium.

(TCCS) Transcranial color coded sonography is a combination of B-mode and pulsed wave Doppler. TCCS is used to study morphological and functional assessment of the circle of Willis, intracranial hemodynamics caused by extracranial artery stenosis, collateral flow and the vascular supply of intracranial lesion. Color imaging of the intracranial vessels allows placing the spectral Doppler volume correctly. This modality has encouraged the widespread use.
Contrast enhanced TCCS analysis of cerebral arteriovenous transit time (cTT) is used as a measure of cerebral microcirculation.
The windows that are used for transcranial Doppler examinations include regions where the skull bones are relatively thin or where naturally occurring gaps allow proper penetration of the sound beam.

See also A-Mode, Cranial Bone Thermal Index, Transcranial Doppler and Transcranial Window.

The transorbital window allow to insonate ophthalmic artery and ipsilateral carotid siphon through the eye. It is also possible to use the transorbital entrance to scan the middle and anterior cerebral arteries, if it is impossible through the transtemporal window.
The patient is asked to remove any contact lenses prior to examination and is instructed to close the eyes. The power output of the Doppler instrument has to be decreased to 10-20% to reduce the ultrasonic exposure of the eye.

See also Transcranial Doppler, Ultrasound Safety.

A phantom is used to control the imaging performance of ultrasound transducers. The spatial resolution, dead zone, linear fidelity, depth of penetration and image uniformity is important for the image quality. For the axial and lateral resolution, the standard definition is the resolution of objects parallel and perpendicular to the path of the sound beam. Ultrasound pictures created by scans of specially designed ultrasound phantoms can quantify the imaging quality and transducer performance.
Phantoms contain one or more materials that simulate a tissue in its interaction with ultrasound. Several phantoms are available specifically for quality control. Transducer characterization consists of a standard pulse echo analysis and insertion loss measurement for each probe. The quality variation from the baseline should be tracked over a period.