10 Ultrasound Flashcards
Sound waves
Pressure disturbance that propagates through a material
The amplitude of a wave
The size of pressure difference from the equilibrium value.
Wavelength (λ)
The distance between successive wave crests.
Frequency (f)
- The number of oscillations in each second.
* The number of wavelengths that pass a given point each second.
Longitudinal waves in ultrasound
Have vibrations along their travel direction.
Transverse waves in ultrasound
Have vibrations perpendicular to the travel direction.
The period
The time between successive oscillations.
Diagnostic ultrasound uses transducers with frequencies ranging
1 to 20 MHz.
velocity (v).
v = f ×λ (m/s).
The ultrasound intensity
Measuring the energy flowing through a given cross-sectional area each second.
Relative sound intensity
Measured on a logarithmic scale and may be expressed in decibel (dB).
Negative decibel values
Correspond to signal attenuation.
Positive decibel values
Correspond to signal amplification.
The acoustic impedance
- Describes how much resistance an ultrasound beam encounters as it passes through a tissue.
- The acoustic impedance (Z) of a material is the product of the density (ρ) and the sound velocity (v) in the material.
- Z = ρ × v
- The acoustic impedance unit is called the Rayl.
Reflections in ultrasound
A portion of the ultrasound beam is reflected at tissue interfaces.
[(Z2 − Z1)/(Z2 + Z1)]^2.
Nonspecular reflections in ultrasound
Diffuse scatter from rough surfaces where the irregular contours are bigger than the ultrasound wavelength.
Specular reflections in ultrasound
Occur from large smooth surfaces. Specular reflection intensity is independent of frequency.