Ultrasound Flashcards
With what frequencies do diagnostic ultrasound work?
1-20MHz
What is the relationship of velocity (speed) of sound and frequency?
They are independent of each other.
What is the velocity of sound dependent on?
Inversely proportional to the square root of the compressibility of individual tissues (eg. bone has low compressibility and therefore, high sound velocity).
What tissue material has higher sound velocity? Soft tissue or bone?
Bone –> less compressible, therefore higher velocity
They travel even slower in air!
What is the acoustic impedance unit called?
Rayl
Which two subject tissues have a lack of transmission (ie. do not allow to image past them)?
Air and bone (b/c they mostly reflect the US beam)
What does hyperechoic mean?
Higher scatter amplitude relative to the background
signal (ie. the internal structures of the tissue cause the beam to scatter)
What does hypoechoic mean?
There is not scatter of the US beam b/c there are no internal structures to the tissue (eg. fluid-filled cysts)
What is the function of a pizoelectric transducer?
Converts electrical energy to ultrasonic energy
Can sound waves travel through a vacuum?
NO!
Which is faster - sound waves or electromagnetic waves?
EM waves
Wavelengths of high frequency will penetrate superficially or deeply?
High frequency (low wavelength) will penetrate shallowly BUT give better resolution!
What will present as hyperechoic on US?
Bones & stones (Ca2+)
What will present as anechoic on US?
Fluid - blood, bile, water, urine etc.
