Chapters 6-8 Study Guide Flashcards
A logarithmic scale is associated with
Decibel notation
The decibel notation for an acoustic signal that has attenuated would be
Negative
A ____ change in a value intensity means that the value has doubled.
3 dB
Attenuation is determined by
Path length and the frequency of sound.
Rayleigh scattering is related to
Frequency to the 4th power
Rayleigh scattering defined
Uniform dispersion of a sound wave in many different directions after striking a very small particle.
A sound beam travels ___ in soft tissue.
7cm
The attenuation coefficient is __.
3 dB/cm
What is the total attenuation that the sound beam experienced?
7 x 3 = 21 dB
The attenuation traveling through bone is _____ than its attenuation through soft tissue.
Greater
Attenuation through lung tissue is ____ than soft tissue.
Greater
Sound traveling through blood attenuates
To a lesser extent than when traveling through soft tissue.
Impedance is a property of the medium and has units of ____.
Rayls
To calculate acoustic impedance
Multiply the density by the propagation speed.
___Angles are less than ___ degrees.
Acute,90
___Angles are greater than ____ degrees.
Obtuse,90
Angles with a measure other than 90 are called
Oblique angles
Intensity transmission coefficient + ________ = 1.
Intensity reflection coefficient
Does intensity reflection coefficient have any associated units?
No.
When will reflection occur
When a sound beam strikes a tissue boundary at 90 degrees & media on either side of the boundary will have different impedances.
For refraction to occur at a boundary between 2 media there must be
Dissimilar propagation speeds and oblique incidence.
Backscatter reflection occurs when
A sound wave reaches a rough or irregular border between 2 media.
Snell’s law governs ____
Refraction
The ultrasound systems electronics determine the
Frequency of the sound produced by the transducer of a continuous wave system.
What would cause a PZT crystal to lose its special properties?
Exposure to high temperatures
Order of impedance from highest to lowest
PZT, matching layer, gel, skin.
Dampening material of an ultrasound transducer is made from
A slab of epoxy embedded with tungsten particles.
The purpose of the backing material of an ultrasound transducer is to
Shorten the pulses, thereby creating images with better image quality.
The active element thickness is
1/2 the wavelength of the soundwave in the PZT
Decibel notation can be described as
The ratio between 2 numbers.
Attenuation coefficient is
The amount of attenuation per cm that a sound wave undergoes.
