Ultrasound Flashcards
Mechanical energy that propagates thru a continuous, elastic medium by the compression and rarefaction of particles that comprise it
Sound
Generated by a mechanical displacement in compressible medium, which is modeled as an elastic spring
Ultrasound energy
Shown as a function of time, resulting in areas of compression and rarefaction with corresponding variations in positive and negative pressure amplitude
Energy propagation
Distance between compressions or rarefactions or between any two points that repeat on the sinusoidal wave of pressure amplitude
Wavelength
Number of times the wave oscillates thru one cycle each second
Frequency
Sound waves with frequencies less than 15 cycles per second are called
Infrasound
Frequency range of 15 and 20 kHz comprises the
Audible acoustic spectrum
Frequency range above 20 kHz are
Ultrasound
Medical ultrasound is at what frequency range
2-10 MHz
Specialized medical ultrasound applications are up to what frequency range
50 MHz
Time duration of one wave cycle an is equal to 1/f
Period
Distance travelled by wave per unit time and is equal to the wavelength divided by the period
Speed of sound
A highly compressible medium such as air, has a high or low speed of sound?
Low speed of sound
A less compressible medium such as bone, has a higher or lower speed of sound?
Higher speed of sound
True or false: ultrasound frequency is unaffected by changes in sound speed as the acoustic beam propagates thru different media
True
True or false: ultrasound wavelength affects the spatial resolution achievable along the direction of the beam
True
Provides better resolution and image detail than a low frequency beam
High frequency ultrasound beam
Interaction of 2 or more separate ultrasound beams in a medium can result in
Constructive and/or destructive wave interference
Position of the periodic wave with respect to a reference point
Phase
Amount of constructive or destructive interference depends on several factors, but the most are the
Phase and amplitude of interacting beams
Defined as the peak maximum or peak minimum value from the average pressure on the medium in the absence of soundwave
Pressure amplitude
In diagnostic ultrasound applications, the compressional amplitude significantly _______ the rarefactional amplitude
Exceeds
SI unit for pressure is the
Pascal (Pa) defined as 1 newton per square meter
Relative intensity and pressure levels are described as a logarithmic ratio, the
Decibel