Due to the absorption of ultrasound, heating of tissue (including bone) can occur. For this reason, the sonographer should follow the ALARA principle to minimize the potential for ultrasonic heating of tissue during for example M-mode ultrasound. The thermal effect of Doppler ultrasound flow examinations is significantly greater.

See also Thermal Index and Ultrasonic Power.

Classification by the Food and Drug Administration of medical devices according to potential risks like e.g. ultrasonic heating. The US FDA 510k document provides guidance in the preparation of a regulatory submission to prevent hazards.

Diagnostic ultrasound imaging has no known risks or long-term side effects. Discomfort to the patient is very rare if the sonogram is accurately performed by using appropriate frequencies and intensity ranges. However, the application of the ALARA principle is always recommended.
There are reports of low birth weight of babies after applying more than the recommended ultrasound examinations during pregnancy. Women who think they might be pregnant should raise this issue with the doctor before undergoing an abdominal ultrasound, to avoid any harm to the fetus in the early stages of development.
Since ultrasound is energy, sensitive tissues like the reproductive organs could possibly sustain damage if vibrated to a high degree by too intense ultrasound waves. In diagnostic ultrasonic procedures, such damage would only result from improper use of the equipment.

Possible ultrasound bioeffects:
The thermal effect is controlled by the displayed thermal index and the mechanical index indicates the risk of cavitation.
An ultrasound gel is applied to obtain better contact between the transducer and the skin. This has the consistency of thick mineral oil and is not associated with skin irritation or allergy.
Specific conditions for which ultrasound may be selected as a treatment may be attached with higher risks.

See also Ultrasound Imaging Procedures, Fetal Ultrasound and Obstetric and Gynecologic Ultrasound.

The ultrasonic power is the total amount of sound energy emitted by the transducer per unit of time.

See also Ultrasonic Heating.

In physics, the absorbed dose is the ultrasonic power absorbed per unit of mass of an object, and is measured in watts per kilogram (W/kg). The absorption increases with ultrasound intensity and frequency.
The thermal index describes the potential for heating of the patient's tissue due to the application of energy.

See also Thermal Effect, Ultrasound Safety, Ultrasound Regulations.