Sonography of the gallbladder is a reliable technique for diagnosing e.g., gallstones, cholecystitis, tumors, polyps, or ductal obstruction. Patient should be examined with empty stomach and on a low fat diet the night before. Barium studies, endoscopy, ERCP, colonoscopy, and abdominal CT should be performed after this examination.
Gallbladder ultrasound is best performed with a 5 MHz curved array or a linear array transducer in cases of a very superficial gallbladder. In obese patients or in patients with difficult sonographic access, a 3.5 MHz sector or curved linear transducer is advantageous.
Gallbladder and biliary tree are usually imaged in supine and posterior oblique (LPO) positions. Sometimes very small gallstones are better visible in upright and prone position.

Regulations governing the output of diagnostic ultrasound have been largely set by the USA's Food and Drug Administration (FDA), although the International Electrotechnical Commission (IEC) is currently in the process of setting internationally agreed standards.
The relevant national societies for ultrasound users (e.g. American Institute of Ultrasound in Medicine (AIUM), British Medical Ultrasound Society (BMUS)) usually have safety committees who offer advice on the safe use of ultrasound. In 1992, the AIUM, in conjunction with the National Electrical Manufacturers Association (NEMA) developed the Output Display Standard (ODS), including the thermal index and mechanical index which have been incorporated in the FDA's new regulations.
Within Europe, the Federation of Societies of Ultrasound in Medicine and Biology (EFSUMB) also addresses safety and has produced safety guidelines (through the European Committee for Ultrasound Radiation Safety). The World Federation (WFUMB) held safety symposia in 1991 (on thermal issues) and 1996 (thermal and non-thermal issues), at which recommendations were proffered.
The FDA ultrasound safety regulations from 1993 combine an overall limit of spatial peak time averaged intensity (I-SPTA) of 720 mW/cm2 for all equipment. A system of output displays allows users to employ effective and judicious levels of ultrasound appropriate to the examination. The output display is based on two indices, the mechanical index (MI) and the thermal index (TI).

See also ALARA Principle, and Radiological Society of North America.

(LUS) Diagnostic laparoscopy combined with laparoscopic ultrasound is used for staging tumors and to monitor surgical interventions like for example radiofrequency ablation or cryotherapy. Laparoscopic ultrasound provides direct contact imaging of organs with high frequency ultrasound. Laparoscopic ultrasound identifies and characterizes the tumor, guides the probe, and monitors the progression of the freezing or the thermal destruction. This procedure avoid unnecessary open surgery and improves selection of patients for tumor resection e.g., in liver and pancreas.
Challenges of LUS are limitations of the intraoperative acoustic windows and the possible movement of the probe and that standard orientation techniques are difficult to apply with laparoscopic instruments, resulting in images from oblique planes. 3D ultrasound or special navigation systems may be helpful.

See also Ultrasound Therapy.

Ultrasound elastography is a specialized imaging technique that provides information about tissue elasticity or stiffness. It is used to assess the mechanical properties of tissues, helping to differentiate between normal and abnormal tissue conditions.
The basic principle behind ultrasound elastography involves the application of mechanical stress to the tissue and measuring its resulting deformation. This is typically achieved by using either external compression or shear waves generated by the ultrasound transducer.
There are two main types of ultrasound elastography:
Both strain elastography and shear wave elastography offer valuable insights into tissue characteristics and can assist in the diagnosis and characterization of various conditions. In clinical practice, ultrasound elastography is particularly useful for evaluating liver fibrosis, breast lesions, thyroid nodules, prostate abnormalities, and musculoskeletal conditions. By providing additional information about tissue stiffness, ultrasound elastography enhances the diagnostic capabilities of traditional ultrasound imaging. It allows for non-invasive assessment, improves the accuracy of tissue characterization, and aids in treatment planning and monitoring of various medical conditions.
See also Ultrasound Accessories and Supplies, Sonographer and Ultrasound Technology.

(IVUS) For intravascular ultrasound a small IVUS catheter with a probe is introduced into the artery. The transducer transmits and receives acoustic energy through this catheter. The reflected acoustic energy is used to build a picture of the inside of the vessel. A IVUS image consists of three layers around the lumen, the intima, media and adventitia.
In addition, elastography or palpography could be used to evaluate the local mechanical properties of tissues (e.g. lipid pools in high-risk vulnerable atherosclerotic plaques). These techniques use the deformation caused by the intraluminal pressure generated by the probe.
A high strain region at the lumen vessel wall boundary has 88% sensitivity and 89% specificity for identifying vulnerable plaques. There are high strain values of 1% in soft plaques with increased strain up to 2% at the shoulders of the plaque, while calcified material shows low strain values (0-0.2%). The radial strain in the tissue is obtained by cross-correlation techniques on the radio frequency signal. The strain is color-coded and plotted as a complimentary image to the intravascular ultrasound echogram.

See also Interventional Ultrasound, Vascular Ultrasound.