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Ultrasound Physics Review

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Define bandwith.
The range of frequencies contained within a pulse
What is better Narrow or broad bandwidth?
Broad due to the larger spectrum of frequencies
What is the main pulse that is emitted from the transducer termed?
Operating/Resonance
What is the process that increases the range of frequencies called?
Damping
Define Velocity.
Speed with direction of motion specified
What is velocity determined by?
Density and stiffness
What is the formula for propagation speed?
C=wavelength X Freq
What 2 variables determine the mediums properties?
Stiffness-resistance of a material to compression, and Density-concentration of mass per unit of volume
What is the rule of thumb regarding propagation speed?
Prop speed increase=Stiffness increase=Density decrease
What are the ranges for PRF?
1000-10,000Hz
Define PRF.
Number of electrical pulses per second
What is the typical range for pulse duration?
.5-3 microseconds
What are the units for duty factor and pulsed ultrasound?
Unitless
What happens to duty factor when PRP increases?
DF decreases
What happens to duty factor when Imaging depth increases?
DF decreases
What happens to duty factor when Pulse duration increases?
DF increases
What happens to duty factor when PRF increases?
DF increases
What are the 2 types of detail resolution?
Axial and Lateral
Define Axial resolution.
The minimum reflector separation necessary to resolve reflectors ALONG a scan line
Define Lateral resolution.
The minimum reflector separation necessary to resolve reflectors ACROSS a scan line
What are the 3 modes of focusing for a mechanical transducer?
Lens, Curved element, Mirrors
Define wavelength.
The length of space over which one cycle occurs
What is the formula for wavelength?
wavelenght=c/f
What 2 things determine a wavelength?
Frequency and propagation speed
What does wavelength influence?
Axial/longitudinal resolution
If frequencyy is doubled what happens to the wavelength?
It is halved
What are the effects of ultrasound on tissue termed?
Bioeffects
What are the 2 types of bioeffects to mammalian tissue?
Heating and Mechanical
What are the units for wavelength?
mm
The level at which signals are not transmitted through an ultrasound receiver is termed what?
Rejection
How long is the typical pulsed duration?
.5-3 microseconds
What is spacial pulse length analogus to?
wavelength
Define beam steering.
Movement of the transducer over the area of interest
What does lateral resolution equal?
Beam diameter
Axial resolution = what?
spl/2
Is the following operator adjustable: compensation and rejection?
Yes
Is the following operator adjustable: amplification and compensation?
yes
Is the following operator adjustable: demodulation and compression
no
Is the following operator adjustable: rejection and amplification?
yes
Define pixel.
Unit which imaging information is divided for storage and display in a digital instrument
Define dead zone.
Distance between the transducer face and the 1st rod, no image, area very close to the transducer
Define M mode.
B mode presentation of changing reflector position, time, motion, and amplitude
Define B mode
Information displayed as brightness
Define matching layer.
Material attached to the front of a transducer to reduce the reflections at the transducer element
Define damping material.
Material attached to the rear of the transducer to reduce the pulse duration
Define Q factor.
Recriprical of fractional bandwidth
Define Linear array.
Array made of rectangular elements arranged in a line
Define Sequential array.
Array of elements which are activated one at a time
Define Annular array.
Array of crystals arragned in a circular symmetry.
What is the equation for: Prop speed?
C=1540m/s
What is the equation for: Intensity formula?
I(mw/cm2)=P(mw)/A(cm2)
What is the equation for: spatial pulse length?
spl=number of cycles X wavelength
What is the equation for: Impedance formula?
Z(rayls)=density X prop speed
What is the equation for: Wavelength?
Wavelength=prop.speed / frequency
What is the equation for: Pulse Duration?
pd=number of cycles X period
Define: Grating lobes?
Additional, weaker beams of sound traveling in directions different from the primary beam
Define: Slice thickness.
Also called sectional thickness, Echoes from adjacent tissues filling what should be anechoic
Define: refraction.
Change of sound direction on passing from one medium to another
What is a type of imaging that relates to the height of the vertical defection?
A-mode
What is a type of imaging that relates to time and motion?
M-mode
What is a type of imaging that relates to the brightness of the returning echo?
B-mode
Define duty factor?
The fraction of time the pulsed ultrasound is on
What is the typical duty factor in pulsed echo?
.1-1.0
What is the typical duty factor in continuous wave?
100%
Define: Attenuation.
Reductin of power or intensity as sound travels through a medium
What are the units of attenuation?
dB/cm/MHz
What is attenuation coefficient?
The attenuation that occurs with each cm the sound wave travels
What is reduced with attenuation?
Power and intensity
Describe the piezoelectric effect?
When electricity is applied the PZT elements converts the electricity into ultrasound pulses
What is the typical man made crystal used in most transducers today?
Lead Zirconat Titante (PZT)
What is the frequency for ultrasound?
> 20,000Hz Greater than audible range
What is infrasound?
<20Hz Less than the audible range
What are the frequencies of audbile sound?
20Hz-20,000Hz
What is sound?
A mechanical longitudinal wave
What is sound made up of?
Compressions and rarerefractions
What are the 3 mechanisms of action for ultrasonid bioeffects?
Heat-Intensity, Radiation force-Exposure time, and Cavitation-mechanical effect to tissue
What type of intensity does heating depend on?
SPTP- Spatial peak Temporal peak
If frequency decreases what happens to the SPL?
It increases
What 2 factors would increase ine intensity of a sound beam?
Increase power, Decrease focusing
What is Q factor?
The recriprical of fractional power
What is optimal Q factor?
Low
Qvalue equals what?
Material prop speed X thickness of the element
WHat factor is the operating crystal dependant on?
Thickness of the element and the mediums prop speed
How long is the round trip time for each cm of distance traveled in soft tissue?
13 microseconds
Define: Huygen's principle.
Each surface of multiple transducer, diffract producing small waves that join together and form one main energy sound beam
Define: Rayleigh's principle.
Scattering caused by RBC
Refraction can only occur if you have what 2 factors?
Oblique incidence, and Different prop speeds
Define: Period.
Time per cycle
Define: PRP.
Time from the beginning of one pulse to the next
Define: PRF.
Number of pulses per second
What are the units for: Period
(ms)
What are the units for: PRP
(ms)
What are the units for: PRF
(KHz)
Why do we use coupling gel?
To provide a good sound path from the transducer to the skin, eliminating the thin layer of air that would reflect the sound
What type of format, beam steering, and beam focusing does the following have: Linear Array.
Rectangular image, Electronic focusing, Mechanical steering
What type of format, beam steering, and beam focusing does the following have: Curved Array.
Convex image, Electronic focusing, Mechanical steering
What type of format, beam steering, and beam focusing does the following have: Phased array.
Sector image, Electronic focusing and steering
What type of format, beam steering, and beam focusing does the following have: Annular array.
Sector image, Mechanical steering, Electronic focusing
What type of format, beam steering, and beam focusing does the following have: Single element.
Pie shape image, Mechanical focusing and steering; Lens mirror
All of the following may be used as units of amplitude except which: Millimeters, Degrees, Pascals, meters per second
m/s
How are the spatial pulse length and the number of cycles in the pulse related?
Directly related
What 2 conditions are necessary for refraction to occur at a boundary between two media?
Different prop speeds and oblique incidence
When red blood cells move away from a transducer, the frequency of the wave returned from the RBC is what?
Less than the emitted frequency
What are the units of impedance?
Rayls
What best describes an angle with a measurement of 133degrees?
Obtuse
The sonographer increases the depth. Which parameter is decreased?
PRF
What is enhancement caused by?
Weakly attenuating structures
Which of the following parameters is determined by the medium: Wavelength, Freq, Period?
Wavelength and Spatial pulse length depend on the sound source and medium
Which of the following contributes most to total attenuation in soft tissue: Absorption, Reflection, Scattering?
Absorption
What are the units of the transmitted intensity of a sound wave?
W/cm2
Which of the following statements is true regarding axial resolution artifiacts: Higher quality images are associated with higher numbers, Axial resolution is reported in units of cm3, Numerically axial resolution equals 1/4 the pulse length, or Too few reflectors appear on the image?
Too few reflectors appear on the image
Which of the following is considered an acoustic variable: Freq, Period, Power, or Pressure?
Pressure
What are the effects of medium upon the ultrasound wave called?
Acoustic propagation properties
What is the acoustic velocity in soft tissue?
1540m/s
What is the power intensity for the following: 0dB, -3dB, -6dB, -9dB?
0=100%, -3=1/2, -6=1/4, -9=1/8
What 3 factors contribute to attenuation?
Absorption, Scattering, and Reflection
What is the formula for impedance?
Density X Prop Speed
What is impedance important in?
Reflection at boundries
What are the general frequencies used in ultrasound imaging and name a type of exam used for the transducers.
2.0-Cardiac, 3.5-OB/Abdominal, 5.0-Vascular, 7.5-Superficial, 10.0-Small parts