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110 Cards in this Set
- Front
- Back
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Sound wave definition:
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idk
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Sound waves move in a
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straight line/para to the sound source
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Sound wave is a ___________ vibration
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Mechanical
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Sound wave is a ________ variation
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pressure
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Four acoustic Variables of sound
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Pressure
Density Temp Particle motion |
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Regions of high density and particle concentration
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Compression
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Regions of low density and particle motion
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rarefraction
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Infrasound/Subsonic sound
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<20Hz
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Audible/Doppler sound
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20 Hz to 20 kHz
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Ultrasound
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20 kHz to 1Mhz
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Diagnostic Medical Ultrasound
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>1Mhz
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Frequency
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Number of cycles in one second
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Period
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Time required for a single cycle
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Wavelength
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Length or distance of a single cycle
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Prop Speed
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Speed at which sound travels through a medium
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Amplitude
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Max hight or varaible of a sound wave
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Power
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Rate at which energy is transfered
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Intensity
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Concentration of energy that passes a sound beam throu a unti area
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3Mhz =
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3 Million cycles per second
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If the period of a wave is 1/2 sec and the wavelength is 4mm what is the frequency and prop speed of the wave?
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Freq= 2Hz
C= 8mm/s |
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Mega =
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Micro
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Seconds=
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Hz
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Can ultrasound travel in vaccum?
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No
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All fat Women show more big butts
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air
fat water soft tissue blood bone |
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Density in medium 1=4 and in medium 2=7. Speed of sound will be greater in what medium?
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Medium 1
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Prop speed is determined by
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The medium ONLY
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Changing the freq _____ on the speed or transmission
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HAS no impact
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Density is realted to prop speed how?
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Inverse
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A Dense object will have a _____ prop speed
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LOW
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a low density object will have a ______ prop speed
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Higher
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a soft object will have a ______ prop speed
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slow
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Negative interference:
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when out of phase waves meet, their intensity and amplitude are subtracted from eachother
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Positive interference:
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When inphase waves meet, their intensity and amplitude are added to eachother
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Pulsed Ultrasound
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collection of pulses that travel together and are sent by the TX which are seperated by no pulse time (LT)
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PRP
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time from the beginning of one pulse to the beginning of the next pulse
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PRF
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number of pulses occuring in one second
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Pulse Duration (PD)
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time pulse is actually on
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SPL
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length of space a pulse takes up
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DF
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a fraction/percent of time pulse is actually on
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LT
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time pulse is off and echos are coming back
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what decreases with high frequency?
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Wavelength, Period, SPL, PD
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a small # of SPL leads to ______ resolution
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improved image
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Attenuation
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Loss of intensity, power, and amplitude as sound travels through a medium
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3 components of attenuation
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Absorption
Reflection Scattering |
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Absorption
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Conversion to heat
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Reflection
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occurs at boundries in normal incidence
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Scattering
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all directions
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AC
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amount of attenuation occuring in 1cm
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Frequency = 5Mhz, Ac=
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2.5dB/cm
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If freq increases,
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attenuation and Ac increase
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a 7 Mhz TX travels at 4 cm into the body. What is the total attenuation
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14dB
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Which one penetrates better?
which one has better resolution? 2MHz and 5MHz |
2MHz penetrates deeper
5MHz better resolution |
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Intensities in descending order
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SPTP
SATP SPPA SAPA SPTA SATA |
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IN a continuous wave which are =?
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TP=TA
SPTP=SPTA SATP=SATA |
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Highest intensity
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SPTP
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Lowest Intensity
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SATA
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If initial intensity is more then the recieved intensity then there is a ________ change in dB
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Negative
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Decibel
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measure of sound ration (log rhytmic scale) on a relative scale
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0dB
3dB 6dB 9dB |
0
50%=2 times 75%= 4times 87%= 8 Times |
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Logarithm base log is always
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10
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10
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1
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100
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2
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1000
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3
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Reflection occurs at the
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Impedance Mismatch
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Types of scattering
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Rayleigh
Non-specular |
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Ex of specular reflector
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Diaghram
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Ex of rayleigh scattering
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RBC's
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Incident intensity
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sound/intensity that comes from the TX to the medium (100%)
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reflected intensity
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sound leaves TX, goes to medium, and comes back to TX
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Trasmitted Intensity
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Sound leaves TX, hits medium, and continues to the next medium
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Types of modes
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A mode
B mode M mode |
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Bandwidth
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range of freqs w/in a pulsed ultrasound.
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In order for bandwidth to be useful it must have at least____ of the main intenstiy in the pulse
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50%
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Normal Incidence AKA
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Perpindicular
Orthogonal Right angle Ninety degrees Normal incidence |
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a sound beam strikes at normal incidence what occurs?
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Transmission and reflection but NOT refraction
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Acoustic Impedance
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The difference of a medium to sound prop
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Oblique Incidence is AKA
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Lateral
azmuital transverse angular |
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How does the different prop speeds affect the bending of the sound beam?
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idk
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C1>C2
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SMALLER TRANSMISSION (BIGGER INCIDENCE ANGLE)
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C2>C1
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GREATER TRANSMISSION (SMALLER INCIDENCE ANGLE)
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C1=C2
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NO REFRACTION
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Angle of incidence is always equal too
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angle of reflection
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When a sound beam passes at oblique incidence_____ occurs if theres a difference in prop speeds of two mediums
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REFRACTION
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Variable for range equation:
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Time
Depth Distance |
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A sound pulse hits a medium in 26 micro seconds. What is the depth of the medium?
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2CM
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Transducer converts
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one form of energy into another
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Piezoelectric effect
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Converts sound into electricity (echo)
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Reverse Piezoelectric Effect
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Converts electricty into sound (pulse)
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The material that expands and contracts when electrical field is applied is known as
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PZT (lead ziconate titante)
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curie point
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360 c
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Operating freq is determined by
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prop speed of crystals and thickness of crystals
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crystal thickness determines
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frequency
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effects of damping material
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Improve pic quality
increase bandwidth decrease tx sensitivity decrease q factor reduce PD and SPL |
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Purpose of matching layers
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improve sound transmission
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matching layers help reduce
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reflection as beam stikes the skin
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Reflection occurs due to
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impedance mismatch
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a short pulse creates a_____ bandwidth
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wider
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Types of TX's
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Mechanical
Linear switched Convex phased Linear phased array Convex seq Annular phased |
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Probes with electronic focusing
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Linear phased array
Convex phased Vector Annular |
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Lateral resolution AKA
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Longitudinal
Axial Radial Range Depth |
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Axial resolution is
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CONSTANT
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Axial resolution can only be changed by
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changing the freq of the TX
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Lateral resolution is AKA
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Lateral
Azimuthal Transverse Angular |
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Lateral resolution is
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NOT CONSTANT
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Lateral resolution is determined by
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Width of the beam
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Axial resolution can be imporoved by using
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higher freq TX
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intensity of ultrasound beam in
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strongest at focal point
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beam converges at
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near zone
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Beam diverges at
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Far zone
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Beam is most intense at
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Focal zone
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