Attenuation

Formulas & Definitions

Impedance Formula

P x C

Intensity Reflection Coefficient (IRC)

(Z2-Z1/Z2+Z1)²

Intensity Transmission Coefficient (ITC)

100% - IRC

Momentum

Mass x Acceleration

Rayleigh Scatter

Frequency^4

Snells Law

Ci/Ct = Sin(degree i)/ Sin(degree t)

Critical Angle Snells Law

Sin (degree t) will be 90 degrees, which equals 1

Percent Change

(new-old/old)x100

Attenuation Rate for Soft Tissue

0.5 dB

Attenuation Rate for Muscle

1.0 dB

Attenuation Rate for Blood

0.125 dB

Attenuation Coefficient

AR x F or Decibels of Attenuation/ Path length

Total Attenuation in dB one way

AC x Path Length

Total Attenuation in dB Round Trip

AC x Path length x 2

Half Value Layer

3dB/AC

Maximum Imaging Depth

AR x (2xMID) x F or AC(2xMID)

Diagnostic Range for HVL

0.3-1.0cm

Attenuation

A decrease in wave amplitude.

3 Types of Attenuation

Absorption, Refraction, Reflection

Leading cause of attenuation

absorption

Specular Reflection

Strongest type, occurs when interface is large and smooth in relation to the sound wave. Most occur at 90 degrees

Diffuse Scatter

Occurs when the surface is rough, reflections are received at slightly different times.

Rayleigh Scatter

Happens when structure is small in comparison to sound wave. This is RBCs

Viscosity

Viscous media cause increase loss of energy due to molecules being difficult to move.

2 Key Ideas about Absorption

The dominant form of attenuation in ST and it increases exponentially with frequency