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160 Cards in this Set
- Front
- Back
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Lung
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500m/s
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Fat
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1450m/s
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Soft Tissue (average)
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1540m/s
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Liver and Blood
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1560m/s
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Muscle
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1600m/s
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Tendon
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1700m/s
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Bone
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3500m/s
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Air
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330m/s
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Water
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1480m/s
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Metals
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2000-7000m/s
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What are the acoustic variables?
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pressure, density, and distance
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pressure
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concentration of force in an area, Pascals (Pa)
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density
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concentration of mass in a volume, kg/cm3
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distance
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measure of particle motion, cm, mm
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Parameters to describe a sound wave:
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period, frequency, amplitude, power, intensity, wavelength, propagation speed
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Period
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time it takes a wave to vibrate a single cycle; units of time; determined by sound source
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Frequency
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number of particular events that occurs in a specific duration of time; units of per sec (Hz); determined by sound source
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3 parameters that describe the "bigness" of wave:
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amplitude, power, and intensity
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amplitude
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bigness of a wave; units of pressure, density, particle motion; determined by sound source (US system)
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power
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rate of energy transfer or rate of work; units of watts; determined by sound source
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intensity
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concentration of energy in a sound beam; units are watts/cm2; determined by sound source
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wavelength
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distance of one cycle; units of length; determined by source and medium
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propagation speed
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distance that sound travels in a medium in one sec; units of m/s,mm/microsec,or distance/time; determined by medium
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2 characteristics of a medium affect the speed of sound
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stiffness, and density
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stiffness
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the ability of an object to resist compression
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density
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the relative weight of a material
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Stiffness and Speed
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Increase, Increase
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Density and Speed
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Increase, Decrease
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Duty Factor
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the percentage or fraction of time that they system is transmitting a pulse; determined by sound source; max value = 1 or 100%
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What affects duty factor?
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imaging depth; as imaging depth increases, duty factor increases (shorter listening time)
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3dB
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double
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10dB
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ten times larger
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-3dB
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half
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-10
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one-tenth
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Decibels
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dB; a logarithmic and relative scale
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attenuation
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weakening of a sound wave as it propagates through a medium
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2 factors that determine attenuation
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path length, and frequency of sound
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more attenuation:
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longer distances, higher frequencies
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less attenuation:
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shorter distances, lower frequencies
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3 processes contribute to attenuation
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reflection, scattering, absorption
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reflection
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as sound strikes a boundary a portion of waves energy is reflected back to sound source
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Two forms of reflection
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specular and diffuse
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specular reflection
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boundary is smooth sound is reflected in one direction in organized maner
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diffuse reflection
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reflections in more than one direction, or backscatter
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scattering
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reflected in many directions, no organized maner
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rayleigh scattering
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occurs when structures are much smaller than the beams wavelength, equal in all directions
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total attenuation(dB):
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=attenuation coeff x dist
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attenuation coeff (dB/cm):
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=frequency (MHz) / 2
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Impedance
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acoustic resistance to sound traveling in a medium; Rayls
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Impedance (Z)=
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=density x prop speed
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oblique incidence
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sound beam strikes boundary at any angle other than 90
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normal incidence
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sound beam strikes boundary at 90 degrees
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refraction
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oblique incidence and diff propagation speeds
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Snells Law
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refraction
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13 micro sec rule
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for every 13 micro sec of go return time, the distance traveled is 1cm
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axial resolution
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measures the ability of the system to measure two structures parallel to the sound beam
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axial resolution is determined by
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spatial pulse length
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axial resolution =
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SPL/2
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axial resolution is improved by
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shorter pulses
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Axial resolution-LARRD
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Longitudinal, axial, radial, range, depth
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To improve axial resolution
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shorter spatial pulse length, shorter pulse duration, higher frequencies, lower numerical values,fewer cycles per pulse
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bandwidth
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range or difference between highest and lowest frequencies in the pulse
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imaging probes create ____ range of frequencies
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wide
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CW probes create ____ range of frequencies
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narrow
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quality factor
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unitless number related to bandwidth
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quality factor =
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main frequency/bandwidth
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wide bandwidth probes have ____ Q factor
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low
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narrow bandwidth probes have ____ Q factor
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high
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Imaging Transducers
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pulses with short duration in length, uses backing material, reduced sensitivity, wide bandwidth, low Q factor, improved axial resolution
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Non imaging transducers
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CW or pulses with long duration in length, no backing material, increased sensivity, narrow bandwidth, high Q factor, no image
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Curie temperature or Curie Point
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temperature at which PZT becomes polarized
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which resolution is best?
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axial resolution
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CW transducer frequency
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continous; determined by the frequency of the electrical signal created by the ultrasound system
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PW transducer frequency
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creates short duration; determined by speed of sound in PZT and thickness of PZT
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Speed of sound in PZT affect frequency?
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PW; speed of sound and freq are directly related; When speed of sound in PZT is faster, the frequency is higher
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Thickness of PZT crystal affect frequency?
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PW; thinner elements create higher frequency pulses, PZT thickness and frequency are inversely related. Thicker elements create lower frequency pulses
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thickness of PZT crystal in PW =
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wavelength of PZT sound/2
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Focal Depth also called
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focal length, or near zone length
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Focal depth
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distance from transducer to narrowest part of the beam, also known as the focus
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2 factors combine that determine focal depth
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transducer diameter, frequency of the sound
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transducer diameter affects focal depth
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increasing diameter results in deeper focus, decreased diameter results in shallower focus
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frequency affects focal depth
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higher frequency results in deeper focus, lower frequency results in shallower focus
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shallow focus
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smaller diameter of PZT,
lower frequency |
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deep focus
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larger diameter of PZT,
higher frequency |
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2 factors combine to determine beam divergence
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transducer diameter,
frequency of sound |
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Smaller diameter crystals produce beams that spread out or diverge ____ in the far field
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more
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larger diameter crystals produce beams that diverge ___ in the far field
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less
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larger diameter crystals improve _____ resoultion in the far field
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lateral
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Frequency affect beam divergence?
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lower frequency sound beams diverge more in the deep far zone; high frequency diverge less
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higher frequency sound improves ______ resolution in the far field
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lateral
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lateral resolution
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identify two structures that are side by side, or perpendicular to sound beam
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lateral resolution is determined by
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width of sound beam
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Lateral resolution: narrow width
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better resolution
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beam diamter varies with ?
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depth
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Lateral Resolution: LATA
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lateral, angular, transverse, azimuthal
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Lateral resolution is best
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at focus where beam is narrowest
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Which type of resolution is superior in the clinical setting?
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axial
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Adv's of using high frequency transducer?
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improves axial and lateral resolution
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temporal resolution is determined by
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frame rate
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temporal resolution
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"accuracy in time" ; precisely position moving structures from instant to instant
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temporal resolution is improved by
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higher frame rate
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temporal resolution is degraded by
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lower frame rate
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frame rate is determined by
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sounds speed in a medium,
the depth of imaging; Hz or "per second" |
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imaging depth and frame rate
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shallow-higher frame rate, better temp res; deeper-lower frame rate, degrades temp res
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number or pulses in image affect temp resolution
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fewer pulses-higher frame rate, better temporal resolution; more pulses-vice versa
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Multi focus_____ frame rate and ______ temp resolution
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decreases; degrades
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Advantage of multi focus?
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increases lateral resolution
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sector size affects temp resolution
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increased sector size- decreased temp resolution; decreased sector size- vice versa
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line density affects temp resolution
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increased line density-decreased temp resolution; decreased line density-increased temp resolution
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adv of increased line density
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improved spatial resolution
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6 ultrasound system components
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transducer, pulser and beam former, receiver, display, storage and master synchronizer
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5 Receiver operations
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amplification, compensation, compression, demodulation and reject
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amplification
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entire image is made brighter or darker; does not improve signal-to-noise ratio
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amplification (units)
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dB
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amplification is also called
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receiver gain
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compensation
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creates an image that is uniformly bright from top to bottom: treats echoes diff depending on depth
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compensation effect on image
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near zone-stronger sound beam
far zone-weaker sound beam |
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compensation also known as
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TGC, depth gain compensation, swept gain
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TGC curve- superficial depth
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near gain
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TGC curve- deep depth
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far gain
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compression
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keeps images grayscale content within the range of detection of the human eye, 20 shades; dB
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compression effect on image
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changes grayscale
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compression synonyms
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dynamic range, log compression
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demodulation
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changes electrical signals to a form more suitable for display
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rectification
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converts all neg voltages into positive voltages
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smoothing or enveloping
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places smooth line around bumps to even them out
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demodulation effect on image
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NONE
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reject
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controlled by sonographer; displays low level echoes, does not affect bright echoes
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reject is also called
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threshold or suppression
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reject effect on image
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affects all low level echoes regardless of location
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dynamic range
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dB; ratio of smallest and largest signals
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Narrow dynamic range
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fewer gray shades; high contrast images display few shades of gray
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wide dynamic range
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many shades of gray; low contrast images display many shades of gray
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Harmonic imaging
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equals twice the frequency of transmitted sound
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transmitted freq is called
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fundamental freq
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harmonic frequency waves are
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non-linear
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fundamental freq
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sound created by the transducer and transmitted into the body
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2 forms of harmonics
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tissue and contrast
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tissue harmonics
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miniscule amount of energy is converted from fundamental freq to harmonic freq
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tissue harmonics are created
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deeper in tissues, created during transmission, more likely to be created along beams main axis
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3 forms of flow
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pulsatile, phasic, steady
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pulsatile flow
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blood moves with variable velocity; arterial flow
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phasic flow
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blood moves with variable velocity; venous
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steady flow
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constant speed or velocity
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plug flow
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all levels of blood travel at same velocity
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parabolic
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velocity of blood is highest at center of lumen and gradually decreases to minimum at vessel wall
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pressure gradient=
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flow x resistance
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Nyquist limit
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1/2 PRF
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aliasing exists only with ____ doppler
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PW
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Less aliasing
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slower blood velocity, low freq transducer, high PRF
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More aliasing
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faster blood velocity, high freq transducer, low PRF
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To eliminate aliasing
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use lower freq transducer, higher PRF, shallow sample gate, use CW doppler and use baseline shift
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aliasing on color map
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colors wrap around
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flow reversal
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colors seperated by black line (no doppler shift)
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Power =
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Intensity x area
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annular array uses what kind of steering?
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mechanical
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linear phased array has a ?
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small
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spatial pulse length can be improved by
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using greatly damped transducers
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curved fireing pattern means what kind of beam?
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focused
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which transducers can be electronically steered?
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sector phased array and linear phased array
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