Ultrasound Physics: Interactions of Sound With Tissue

Front

What is attenuation in the context of ultrasound?

Back

Attenuation is a decrease in the amplitude, power, and intensity of the sound beam as sound travels through tissue.

Front

What are the four mechanisms of attenuation?

Back

1. Absorption 2. Reflection 3. Scattering 4. Transmission

Front

How is the attenuation coefficient defined in soft tissue?

Back

The attenuation coefficient (in dB/cm) is equal to one half of the frequency (f/2) in soft tissue.

Front

What is the average rate of attenuation in soft tissue?

Back

0.7 dB/cm/MHz.

Front

What is a specular reflector?

Back

A specular reflector is a large, smooth reflector that reflects sound at a 90-degree angle, and its size is larger than the wavelength of the incident beam.

Front

Give examples of specular reflectors.

Back

1. The diaphragm 2. The capsules of organs 3. The wall of the aorta.

Front

What are non-specular reflectors?

Back

Non-specular reflectors are smaller than the wavelength of the incident beam and scatter sound in many different directions.

Front

How does backscatter intensity compare between specular and non-specular reflectors?

Back

The intensity of backscatter from non-specular reflectors is much lower than that from specular reflectors.

Front

What is the significance of 'speckle' in ultrasound imaging?

Back

Speckle is a result of scattering of ultrasound energy, producing texture within tissues, and can affect the appearance of images.

Front

What conditions must be met for a reflection to occur?

Back

1. There must be normal incidence (90 degrees). 2. The two media must have different impedances.