Frequency, Penetration and Attenuation

Absorption and scattering are both highly frequency dependent.

High frequency sound produces better image resolution, but is attenuated by a smaller depth of tissue. This means that penetration to deeper tissues is limited when using a high frequency transducer.

There is always a compromise between resolution and penetration.

In practice, use the highest frequency that allows adequate penetration to the depth of interest.

As sound travels through tissue, it will lose energy. A number of interactions contribute to this process of attenuation including reflection, scattering and absorption. This results in an exponential decrease in the energy of the pulse, therefore producing weaker echo signals, the deeper it travels into the patient.

This graph shows the exponential decrease in pulse intensity with depth.