Ultrasound Safety and Harm Overview

A measure of the potential for tissue temperature rise due to ultrasound energy.

A measure of the risk of non-thermal damage from ultrasound, like cavitation.

The principle of keeping exposure to ultrasound as low as reasonably achievable.

The amount of ultrasound power emitted by the transducer divided by the power required to raise the temperature by 1°C.

The peak negative pressure divided by the square root of the ultrasound frequency.

The use of sound waves to create images of internal organs and tissues.

The primary source of harm from ultrasound is the generation of heat due to the absorption of sound waves by tissue.

Cavitation is the formation of bubbles in tissue due to the rapid pressure changes caused by ultrasound waves.

Microstreaming arises from the movement of fluids around a vibrating sound wave source, possibly causing local changes in fluid flow.

This refers to any potential harm from ultrasound that is not caused by heating, like cavitation or microstreaming.

This is frequently used for medical imaging and other applications. It is a valuable tool in diagnostics, but its proper use with adequate safety measures is crucial.

These indices help determine the safety of an ultrasound procedure. They measure the intensity of the sound waves and their potential for causing harm.

The energy transfer process where ultrasound waves interact with tissue, causing an increase in tissue temperature.

The potential for heating in ultrasound depends on the imaging mode used, primarily influenced by the intensity and power of ultrasound waves.

The maximum distance a particle in a medium moves due to a sound wave's pressure, determining the strength of the wave.

The rate at which a sound source produces energy. Higher power means quicker energy production.

The power of a sound wave flowing through a specific area, presented perpendicular to its direction of propagation.

Cavitation is the formation, growth, and collapse of gas bubbles in a liquid due to the pressure variations associated with ultrasound waves.

Ultrasound imaging uses high-frequency sound waves to create images of internal structures. These sound waves can be absorbed, reflected, or transmitted depending on the tissue they encounter. The intensity of the sound waves can cause heating or cavitation, potentially harming the tissues.

The thermal index (TI) measures the potential for tissue heating due to ultrasound absorption. It's calculated by dividing the actual acoustic power by the power required to raise tissue temperature by 1 degree Celsius. It's important to keep the TI below certain thresholds to prevent tissue damage. The mechanical index (MI) indicates the potential for cavitation, the formation of bubbles in tissue due to ultrasound pressure. It's calculated by dividing the peak rarefactional pressure by the square root of the ultrasound frequency.

Different tissues have different acoustic properties, leading to varying degrees of sound wave absorption, reflection, and transmission. The density of the tissue determines how much the sound wave is reflected. The higher the density, the greater the reflection. The stiffness of the tissue determines how much the sound wave is transmitted. The stiffer the tissue, the less transmission. This is why different tissues appear differently on an ultrasound image.

The ALARA principle stands for "As Low As Reasonably Achievable." It applies to all forms of radiation and emphasizes the importance of minimizing exposure to potentially harmful levels. In ultrasound, this means using the lowest possible intensity and shortest scan duration to obtain the necessary information, while still maintaining image quality.

Ultrasound imaging relies on the transmission and reflection of sound waves through tissues. The pulse-echo principle describes how short pulses of sound are emitted, and the returning echoes are used to create images. The time it takes for the echoes to return is directly related to the depth of the tissue. Reflected sound waves are converted into electrical signals that are then processed to form an image on the screen.