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188 Cards in this Set
- Front
- Back
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Rttt |
Round trip travel time = 13 ųsec/cm
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PD
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Pulse duration
Pd=n*T =n/f |
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PRP
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Pulse repetition period
Listening time + pulse (infinitely small) |
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PRF
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Pulse repetition frequency
1/PRP |
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Time
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d/v
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PRP min
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2d/v
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PRF max
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v/2d
1/rttt*d |
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DF
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Duty factor
PD/PRP *100 |
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SPL
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Spatial pulse length
n*wavelength v*PD |
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Matching layer thickness
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1/4 wavelength
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Crystal converts what?
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Electrical impulse to mechanical wave
Echos back into electrical impulses |
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Why is matching layer 1/4 wavelength?
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To create constructive interference
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Types of piezoelectric crystals?
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Natural: quartz, Rochelle salt, tourmaline
Manmade: PZT lead-zirconate-titanite |
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How are crystals created?
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Crystal heated above curie temperature, magnetic field causes dipoles to line up, cooled below curie temp to keep in place
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Can you sterilze probe?
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NO it will release dipoles at high temp
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What is the piezoelectric effect?
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Convergence of mechanical wave into electrical wave
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Converse piezoelectric effect
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Electrical energy into mechanical wave
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Thickness of crystal
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1/2 wavelength
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Frequency of crystal depends on
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Thickness of the crystal
Speed sound in crystal Voltage applied to crystal |
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Frequency of the crystal is called
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Natural f
Resonance f Central f |
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What is the range of frequencies of crystal called
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Band width
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10 kHZ is equal to? (Hz)
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10,000 Hz
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What is .004 m in mm?
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4mm
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What type of wave is sound?
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Mechanical Longitudinal wave
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Equation for simple harmonic motion
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SHM=ACos(wt+0)
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Equation for angular frequency?
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w=2 pi f
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What are the acoustic variables?
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Pressure, temperature, density, and displacement
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What is the audible frequency range?
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20-20,000 Hz
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What frequency is considered ultrasound?
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>20,000 Hz
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What is the frequency range for diagnostic US?
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2-20 MHz
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What is the frequency range for therapeutic US?
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.5-3 MHz
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What is the frequency range for high frequency US?
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.5-10 MHz
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What is the frequency range for intravascular ultrasound
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30-40 MHz
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Bulk modulus equation
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Stress/Strain
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What properties of the medium determine v?
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Compressability, elasticity, density
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Velocity in the medium equation
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V=Square root (Bulk Modulus/density)
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y=logx converted
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x=10^y
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3dB deceased the value by how much?
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1/2
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Is decibel a true value or a ration of values?
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Ratio
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Decibel equation
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10log Ifinal/Iinitial
Amplitude 20log If/Ii |
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Attenuation due to absorption
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=u(mew)df
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Attenuation coefficient
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.5 db/cm MHz
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What accounts for most of the attenuation?
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Absorption 80%
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What is diffraction?
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The sound beam will bend around objects
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What is HVL?
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Half value layer is the distance that intensity will reduce to half of the original.
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What type of refection is responsible for imaging?
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Specular imaging
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What is the law of reflection?
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Angle of reflection = angle of incidence
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What is normal incidence?
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Normal incidence is perpendicular to the medium. All angles are measured from normal incidence
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Impedance equation
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z=p(density)v
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What is impedance units?
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Rayl
or Kg/m^2 sec |
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Reflection coefficient equation
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[(Z2-Z1)/(Z2+Z1)]^2
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Transmission coefficient equation
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(4*Z1*Z2)/(Z2+Z1)^2
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What is Rayleigh scatter?
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Reflection from very small reflectors such as RBCs
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Attenuation due to reflection equation
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10 log 100/%R
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What is diffuse reflection?
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Reflection from a bumpy surface scatters
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Snells law
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(Sin Angle T/Sin Angle I) = (v T/V I)
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Does refraction contribute to attenuation?
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No
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What is critical angle?
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Angle of incidence that creates a beam parallel to the interface (90 degrees)
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What is the range equation?
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round trip travel time 13microsec/cm
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What of the following can the tech adjust?
frequency, wavelength, period, power, PRP, PRF, Duty Factor, SPL |
frequency, PRP, PRF, and Duty factor
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Matching layer equation
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1/4 wavelength
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Does the transducer use piezoelectric effect or converse piezoelectric?
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Both. Converse to transmit and piezo to receive.
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Frequency equation for pulse wave?
Continuous wave? |
Vcrystal / 2 thickness
CW f determined by voltage applied to crystal |
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Q value equation
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central f/bandwidth
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are high or low Q transducers used for imaging?
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Low Q
High Q is used for doppler |
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What are the characteristics of low Q transducers?
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Wide bandwidth
short pulse 1-5 cycles Good sensitivity |
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What are the characteristics of high Q transducers?
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narrow bandwidth
long pulse 5-10 cycles Poor sensitivity, good for doppler |
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What is frequency fusion?
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The ability to select a certain frequency in bandwidth to "hear"
Not changing the frequency |
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More damping material =
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shorter pulse
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LARRD stands for
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Longitudinal
Axial Radial, Range Depth |
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LATA stands for
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Lateral
Angular Transverse Azimuthal |
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LARD equation
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1/2 SPL
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LATA near field
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R^2 f/v
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LATA Focal point
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1/3 width crystal
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LATA far field
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Sin Angle = .61v/Rf
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Define LARD
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Min distance between two objects that is distinguishable
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Define LATA
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Ability to distinguish two objects perpendicular to the beam
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What are the external and internal ways to fixed focus?
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external- acoustic mirror and lens
internal curved crystal |
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Types of steering?
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Mechanical, manual, electric
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Frame rate equation
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FR=v/2dl
PRF max/ l |
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Units of Frame Rate
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Hz, fps
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Can 10.5 be a unit of frame rate
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No, must be a whole number
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What is temporal resolution?
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Shows changes in time
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Types of focusing
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fixed: internal, external
adjustable: aperature, electronic, transmit, dynamic |
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What is sequential (switched) technology?
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Crystals fired one at a time in sequence
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What is segmental technology?
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Group of crystal fired at same time
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What is step down technology?
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Group of crystal fired, but some overlap
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What is phased technology?
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Crystal fired with a small time delay that can allow steering
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What is Huygen's principle?
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Every point of the wavefront acts as a source creating tiny wavelets
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What is dynamic focusing?
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adjusting # of listening crystals
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What image shape does a single element transducer have?
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sector
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What image shape does a linear transducer have?
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Rectangle
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What image shape does a curvolinear transducer have?
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Pie with bite out
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What image shape does a linear phased array transducer have?
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Sector
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What image shape does a annular transducer have?
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Sector
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What image shape does a vector element transducer have?
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Trapezoid
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What type of steering does single element transducer have?
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Mechanical
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What type of steering does a sequential or segmental transducer have?
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No steering
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What type of steering does a phased transducer have?
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Electronic
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What type of steering does a vector transducer have?
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electronic along sides
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What type of steering does annular transducer have?
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Mechanical
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What type of focus does a single element transducer have?
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fixed
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What type of focus does a sequential transducer have?
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fixed
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What type of focus does a segmental transducer have?
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Aperature
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What type of focus does a phased transducer have?
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Electronic
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What type of focus does a vector transducer have?
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Electronic
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What type of focus does an annular transducer have?
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electronic
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How does a multidimensional transducer work?
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There are multiple rows of crystals that each take a 2D slice
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What does the beam former use?
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Apodization
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What is Apodization?
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Controls which elements are active or not
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What does the pulser control?
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Steering, focus, focal points, image shape and size, and line density
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How is steering achieved?
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Delay of crystals
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What is the equation for mechanical index
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peak rarefactional pressure/ square root f
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What is the receiver responsible for?
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amplification, compensation, compression, rejection, and demodulation
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What is amplification?
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Gain
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What is compenstation
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tgc
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What is compression
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compensates for large differences in high and low. Shrinks it
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What is rejection
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rejects noise of not moving objects
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What is demodulation
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changes signal to all positive and smoothes out waves and puts an "envelope" around
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What does the scan converter do?
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Stores and process info from reciever
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How does info go into the machine and then displayed? Which converters?
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First AD converter, then DA converter
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How many shades of gray can human eye see?
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32
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What are bits
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memory stored of negative or positive charge
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shades equation
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#=2^n
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What is zoom read
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zoom already stored
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what is zoom write
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zoom and more lines scanned
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What is persistance
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avg several frames
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what is edge enhance
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avg pixels
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What is compounding
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combining electrical signals
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what is harmonics
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fundamental f, harmonics is two, three, ...... times
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What is harmonic imaging
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tissues vibrate at their fundamental f
can also use contrast |
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Types of video display
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CRT - Cathode ray tube
LCD - liquid crystal display DLP - digital light processing tiny mirrors |
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How large should the gate be set?
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2/3 diameter of vessel
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Angle range appropriate for doppler
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45-60
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Scale equation
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(1540m/s)^2 / 8 fo d Cos
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Doppler equation
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2 v blood fo Cos / 1540
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velocity of blood equation
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(1540 m/s *f) / 2 fo Cos
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Continuity eq
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Q=va
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Poiseulles eq
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p/R
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Resistance eq
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8 nl / pi r^4
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Bernouilles eq
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P total = P dyn + P hyd + P static
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P dyn e
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p(density) v^2 / 2
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P hyd
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p(density) g h
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What is static pressure
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pressure measured by bp
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What pressure increases in stenosis
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hydrostatic
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What does a very low blood pressure indicate
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stenosis
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doppler f eq
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(v+-vr)/v-+vs) *f
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In order of v
fat, st, lung, bone, air |
air lung fat st bone
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What does a hydrophone measure
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Intensity
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What do you adjust first for 2D
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gain
tgc depth focus compress |
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What to adjust first doppler
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angle
gate gain scale filter |
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What to adjust first color
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Angle
steer box gain scale filter |
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If the size of the crystal decrease, the frequency...
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increases
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BUR
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SP/SA
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DF (intensity)
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TP/TA
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Intensity equation
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Power/ Area
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Total attenuation
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dB=1/2 f *d
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If aperature increases, near zone
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increases
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Intensity is measured
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W/cm2
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What is bistable
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black and white image
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If compression increases DR
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decreases
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Is water higher or lower v than st
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lower
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What are SPTP limit for focused
unfocused |
f 1000 mw/cm2
u 100 mw/cm2 |
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stable cavitation
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does not burst
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transient caviation
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bursts
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What does CW use to calc
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FFT
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What does color use to calc
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autocorrelation
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What is used to detect shift doppler
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demodulation or heterodyning
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what are the old techniques of detect shift doppler
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zero cross detector
time interval histogram |
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What is used to detect doppler direction
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quadrature detector
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what is old technique to detect flow direction
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singe sideband
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What type is filtered with wall filter
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slow
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What does FFT do
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converts signal into individualf. time to f domain
blood calc for each f |
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What is aliasing
how to fix |
insufficient scale
increase scale |
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what is nyquist limit
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must sample each cycle two times to get accurate
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What must the scale be above
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1/2 v/2d
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Enhancement
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increased speed, less attenuate
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Acoustic shadow
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decreased speed, more attenuate
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reverberation
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beam bounce back and forth
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comet tail
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distal to high reflect, tail down
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slice thickness artifact
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smaller than slice thickness and not shown
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side lobes
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side of beam single element
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cross talk
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also see on spectral
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grating lobes
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array probes
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edge shadow
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along sides whiskers
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How to get rid of side and grating lobes
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subdicing
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anechoic
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echo free
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multipath artifact
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and back
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