Ultrasound Flashcards
properties of sound waves ,piezoelectric affect, acoustic impedance
What are the properties of sound waves
and what equation expresses them
Velocity = frequency x wavelength V= f x y
Define amplitude, wavelength, frequency and cycle in terms of soundwaves.
Amplitude is the measurement of a wave from its equilibrium
Wavelength= the distance between the corresponding points of two waves
Frequency= the number of cycles per a second
Cycle = one complete oscillation
How is ultrasound attenuated?
it can be absorbed, reflected, refracted or scattered
What is the medical ultrasound frequency range
2mhz - 20mhz
How does tissue type affect the speed of sound?
The density of a material affects the speed of sound. speed travels faster in more dense materials that resist compression such as fat and bone whereas in materials that are easily compressible such as fluid and gas speed travels slow.
What is the piezoelectric effect?
the process of converting kinetic energy into electrical energy through crystal deformation. Piezoelectric crystals are attached to the front of the transducer and connected to the machine via electrodes. When an electric current is applied to the crystals it causes them to vibrate and these vibrations generate ultrasound waves.
What is Acoustic Impedance ?
how much resistance the ultrasound wave encounters as it passes through a tissue , this is determined by the density of the tissue and the speed of the sound wave
What is the equation for acoustic impedance ?
Z = D x C
Acoustic impedance= tissue density x speed of sound
Why is acoustic impedance important in ultrasound ?
The ability of an ultrasound wave to transfer from one tissue to another depends on the differences in impedance of the two tissues. The reflection is biggest between materials differing in density if the difference is big the soundwave will be reflected and not penetrate deeper. Therefore smaller acoustic impedance differences in tissues are more useful for echo imaging
