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244 Cards in this Set
- Front
- Back
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Units of length
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distance = cm,ft,mm
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Units of area
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cm2,ft2,mm2
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Units of volume
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cm3,ft3,cc(cubic cm)
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Units of time
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sec,min,years
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What is sound?
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A mechanical longirudinal wave that travels in a straight line
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What are the 4 acoustic variables that affect sound?
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pressure,density,temperature,distance
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What is a transverse wave?
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Particles of medium move in direction perpendicular of the wave
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What is a longitudinal wave?
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Particles of medium move in same direction as wave travels
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What are sound waves composed of?
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Compressions and Rare-Fractions
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Can period or frequency be changed by you?
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No
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Can amplitude, power, or intensity by changed by you?
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Yes
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What is period?
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Length of time it takes to complete a single cycle
Start of one cysle to start of next |
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What is frquency?
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Number of certain events that occur in a specific duration of time
cycles per second |
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What is frequency for ultrasound?
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Above 20,000 hz or 20 k
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What is audible sound?
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20Hz - 20,000Hz
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What is infrasound?
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So low can not be heard less than 20Hz
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If frequency increases what happens to the period?
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As frequency increases your period decreases and vice versa
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What are the 3 parameters related to size of sound wave?
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Amplitude, Power, Intensity
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Does amplitude increase or decrease as sound propagates thru the body?
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It decreases
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Does power decrease or increase as it travels thru the body?
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It decreases
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How is power related to amplitude & intensity?
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It is directly related if one goes up so does the other
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What is the formula for intensity?
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watts/cm2
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What is a wavelength?
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The distance or length that one complete cycle ocupies
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Can wavelegth by changed by you?
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No ~ It is determined by both the source and the medium
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How is wavelength and frequency related?
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Inversley if one goes up other comes down - if you increase your frequency you will have a shorter wavelength
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What does a shorter wavelength generally produce?
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Higher quality images
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What is propagation speed?
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It is the speed at which sound moves through the medium
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What determines the spped?
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Density and Stiffness
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T/F All sound regardless of freqency travels at same speed thru the same medium.
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True
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Does bone or a cotton ball have a higher speed?
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A bone is stiffer so it's speed is faster than a cotton ball.
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What is average speed of sound in soft tissue?
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1.54 Km/s
1540 m/s 1.54 mm/us |
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Is speed of sound faster in Air or Soft Tissue?
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Air - 3.30 m/s
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What is a pulse?
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A collection of cycles that travel together.
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What is pulse duration?
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Time of start of pulse to the end - only the on time
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What is pulse repetition period?
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The time from start of one pulse to start of the next pulse. This includes both the on and off time. AKA Period Analogous
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What is pulse repetition frequency?
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The number of pulses that occur in a single second.
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What is the duty factor?
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On time - the % or fractino of time that the u/s machine is producing a pulse or transmitting sound
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What is the units of duty factor?
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It is unitless
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How is the duty factor determined?
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It is determined by the sound source/us system
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What is the spatial pulse length?
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The length or distance the pulse occupies in space - The distance from start of pulse to the end
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What determines the Spatial Pulse Length?
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It is determined by the souce and the medium
Can NOT be changed by you |
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What is the equation for SPL?
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SPL=#cycles in pulse X wavelength
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What is the Piezoelectric Effect?
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The process of changing mechanical energy to electrical
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What are the units of intensity?
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watts per cm2
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Name four ways to report intensity
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Spatial, Temporal, Peak, Average
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What is spatial?
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Refers to distance or space
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What is temporal?
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Refers to time
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What is Peak?
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Max value (sp or tp)
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What is average?
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Mean value (sa,ta)
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What is the Beam Uniformity Coeefficient?
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Unitless ratio that describes the distribution of u/s beam in space
AKA SP/SA Factor |
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What are units for Duty Factor and Beam Uniformity Coefficient?
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It is unitless
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What is logarithms?
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An alternative way to rank numbers
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What is decibels?
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A unit to express a relative difference between 2 acoustic signals.
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In ultrasound with dB be positive or negative?
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They will always be negative.
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What is attenuation?
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The weakening of a sound wave as it travels.
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What 3 factors cause attenuation?
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Absorption, Reflection and Scattering
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What is absorption?
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Eneregy is lost by its conversion to another form of energy
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What percentage of total attenuation of soft tissue is caused by absorption?
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80%
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What is reflection?
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It occurs when some of the sound waves is redirected and returned back to the transducer
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What is rayleigh scattering?
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it is when the reflector is much smaller than sounds wavelength and the sound wave is deverted in all directions
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What is attenuation coefficient?
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The amount of attenuation per cm of tissue
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What is impedance?
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It is the accoustic resistance to sound traveling thru a medium
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What is the units of impedence?
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Rayls
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What is meant by back scattering?
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AKA diffuse scattering the scattering returning in general direction of transducer
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What is specular reflections?
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They are produced when sound waves strike a smooth surface.
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When imaging in 2d the sonographer ideally should be at what degrees to organ or vessal?
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90 degrees
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What is normal incidence?
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Normal incidence occurs when sound beam strikes the boundary between different tissue at exactly 90 degrees. AKA right angles, perpindular or orthogonal
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What is oblique incidence?
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It occurs when sound beam strikes a boundary between tissue at an angle other than 90 degrees.
AKA acute and obtuse angles are oblique |
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In clinical imaging what percent of instensity is reflected back towards the transducer at a boundary between soft tissue?
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Less than 1%
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What is Intensity Reflection Coefficient (IRC)?
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The percentage of sounds intensity bounced back when sound passes from one tissue to anothe. 20%
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What is Intensity Transmission Coefficient (ITC)?
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The percentage of sounds intensity that is allowed to pass through. 80%
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What is Normal Incidence?
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It is when a wave strikes a boundary between two medias at 90 degrees.
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Reflection only occurs when?
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It only occurs if there are different acoustic impedences bewtween the two medias.
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How do you determine Impedence?
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IRC is reflected intensity/incident intensity
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What happens when 2 medias have teh identical impedence?
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All the intensity is transmitted - non is relfected.
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What is considered a relfected angle?
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An angle between reflected sound and interferance. AKA Angle of Incident
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What is refraction?
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A change in direction or bending away from a straight line. Path of wave traveling from one medium to another.
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Refraction only occurs when?
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When both propagational speeds and oblique incidents occur. Refraction if through the medium.
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What describes refraction?
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Snell's Law
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What is Snells Law?
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When propagational speed 2 is greater than propafational speed 1 then transmission angle is greater than incident image.
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What does ultrasound system use to measure distance?
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A ruler is not used instead they use time of flight of u/s pulse to calculate depth of a reflector.
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What is the Time of Flight?
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iIt is the lapsed time between pulse production and echo reception by th etransducer.
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If you have a Time of Flight of 26 us and depth of reflector is 2 what is your distance traveled?
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4 cm
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What is a transducer?
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Any device that converts one form of energy to another. They conduct electrical energy into acoustic energy during transmission.
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What are most crystals made up of?
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Lead Zirconate Titanate (PZT)
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If you heat pizioelectric material above this temperature the material is depolarized and loses its pizioelectricity.
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Curie Temperature
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Can you heat a steralized transducer?
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No
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What is the damping element?
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The damping element is on back of active element and acts to limit ringing of crystal.
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Does the dampening material improve picture quality?
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Yes
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What decreases the Q factor and decreases the transducers sensibility to reflected echo?
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Dampening material
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What increases the bandwidth?
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Dampening material
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Does the dampening material shorten SPL and Pulse Duration?
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Yes
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What is matching layer?
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It has an impendence between the skin and active element so that more sound energy is transmitted between crystal and skin.
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Does the matching layer help propegate sound?
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Yes
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What prevents electrical noise from interferring, protects fragile compnents of transducers and portects patients from electrical shock?
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Case and Insulator
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What determines the frequency on a continuous wave?
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The voltage
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The frequency of sound is determined by what?
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The characteristics of PZT Crystal
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The frequency of sound by pulsed wave transducer is determined by a combination of what 2 factors?
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Thickness of crystal and the propergational speed of sound in crystal.
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The thicker the crystal, will the frequency be lower or higher?
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Lower
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How is frequency related to the speed of sound in a crystal?
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It is directly related - The higher the speed the igher the frequency
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What is the bandwidth?
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The range of frequencies above and below the main frequency. Example: highest to lowest frequency
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What is the Q factor?
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It is the ability of transducer to admit a clean pulse with a narrow band width.
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What is the units of a Q factor?
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It is a unitless #
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What is the shape of sound beam?
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A sound beam is shaped like an hour glass.
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As sound travels does teh width of the beam change or does it stay the same?
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It changes
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What is the focus?
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It is the location where the diameter of the u/s beam is at its minimum.
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What is focal length?
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It is the distance from the transducer face to the location where beam reaches smallest diamter.
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What is another name for the near zone?
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Fresnel Zone
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What is another name for the Far Zone?
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Fraunhofer ZOne
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What is your focal zone?
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It is the region surrounding focus generally has a narrow beam.
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What determines the focal length?
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The diamter of PZT crystal and the omitted frequency.
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Higher frequency probes are used for what type of scanning?
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Superficial
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What is diffraction?
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It is the spreading out of a sound beam, caused by a small sound source.
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What is Huygen's Principle?
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The central beam has a shape of hour glass - imaging transducers do not defract because they obey Huygens Principle.
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Most high frquency transducers have a smaller beam divergence in the far field due to what?
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The small diameter of the crystal.
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What does focusing do?
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Causes the middle of sound beam to get narrower.
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What are four methods of focusing?
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Lens
Curved PZT Crystal Focusing Mirror Electronic Focusing |
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What type of focusing is it when you focus with a lens, curved crystal, or a mirror?
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Conventional focusing
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What type of focusing is used in phased array technology?
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Electronic
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Describe resolution.
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The ability to accurately image structures
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Two characteristics of a pulse that improve image quality are:
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Shorter pulses and Narrower pulses
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What is longitudinal resolution:
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Ability to distinguish two structures that are close to each other from front to back.
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What is another name for longitudinal resolution?
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LARD
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What does LARD stand for?
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Longitudinal
Axil Range or Radial Depth |
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What is the equation for LARD?
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LARD=spl/2
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Wht determines longitudinal resolution?
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The sound source and the medium
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Does higher frequency create better LARD Resolution?
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Yes and higher quality images
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What is a type of artifact known as?
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Reverberation
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What is meant by Lateral Resolution?
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It is the minimum distance that 2 side by side structures can be seperated and still produce 2 distinct echos.
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What is another name for Lateral Resolution?
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LATA
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What is meant by LATA?
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Lateral
Angular Transverse Azimuthall |
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What is temporal resolution?
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Accurately locate position of moving structure at a particular instant in time. (time and motion)
Higher frame rate equals better temporal resolution |
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What is frame rate?
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The number of frames or images created each sec
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What type of image does a mechanical transducer produce?
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A sector shaped image
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What is one advantage of a mechanical transducer?
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Small acoustic footprint
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How many disc shaped elements does a mechanical transducer contain?
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Single
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What type of focus does a mechanical transducer have?
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A conventional fixed focus
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What happens when a PZT goes out on a mechanical transducer?
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You lose the entire image
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What is transducer arrays?
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A collection of active elements within a single transducer housing layer
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Name two types of transducer arrays
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Linear Array
Annular Array |
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What is a linear array?
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Collection of elements arranged in a straight line
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What is meant by annular array?
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A collection of ring shaped elements with a common center
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What type of image shape does a linear switched array have?
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A rectangular image shape
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What tyoe if focusing does a linear switched array have?
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Conventional
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What type of footprint is a linear switched array?
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A large acoustic footprint
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What a crystal goes out on a linear switcher array what happens?
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A single ine of data extending downward drops out due to the broken crystal.
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How are elements arranged in a convex switched array?
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Elements are arranged in an arch
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What type of image doe a convex array have?
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The image is blunted or fan shaped
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When is the convex switched array difficult when you have a large acoustic footprint?
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When you have a small acoustic window
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If a crystal goes out on a convex switched array what happens to the image?
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You will have a line extending down from broken crystal that is lost
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What type of beam steering do you have with a linear phased array transducer?
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Beam steering is electronic
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How are elements arranged in a linear phased array?
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Elements are arranged in a straight line, but array is very small.
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What type of image do you get with a linear phased array transducer?
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The image is fan or sector shaped
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What type of focusing do you have with linear phased array?
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Focusing is electronic, which means that sonographer can change the focal depth
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Electronic Curvature =
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beam focusing
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Electronic slope =
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beam stearing
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What is annular phased arrays?
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Concentric rings cut from same circular slab of PZT
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What type of steering does annular phased arrays have?
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Mechanical
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What type of shape does annular phased arrays have?
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Sector shaped
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If element malfunctions on an annular phased array transducer what happens to the image?
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There is a band of image dropout at a particular depth on the image.
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What is the best transducer?
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One that provides optimal images quality while meeting challenges of specific clinical settings.
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What is a water path scanner?
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A standoff pad, puts more distance between transducer and scanning, sometimes it is built into the probe.
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When would a water path scanner be best used?
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In superficial images only to see them more clearly
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How is frequency related to crystal thickness?
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Inversley
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What is temporal resolution?
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The ability to accurately determine position of anatomic structure at a particular time
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What 2 factors does temporal resolution depend on?
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The extent at which structures move
Frame Rate=#frames/sec+#images/sec |
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What are 4 factors that change temporal reoslution:
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Imaging depth
multiple focal zones line density frame rate |
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What is the doppler effect?
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Doppler is used to determine speed and direction of blood
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What is a doppler shift?
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A doppler shift is a change in frquency of sounth that results from motion.
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What is the range of a doppler shift?
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A doppler shift ranges from a -10KHZ to +10KHZ
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If you have flow coming towards the transducer the is equal to what type of frequency and what type of wavelength?
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Higher frequency and shorter wavelength
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Velocity is equal to what?
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To speed and direction of flow
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Speed is equal to what?
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How fast the object is moving
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The doppler shift depends upon what?
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The cosign of the angle between sound beam and direction of the motion
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When is the most accurate measurement of velocity?
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It is obtained when red blood cells are traveling in direction parellel to u/s beam directly towards or away from the transducer
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What is the cosign of 45 degree?
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.70
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What is cosign of 60 degree ?
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.50
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If angle is 90 degrees what is the cosign?
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Cosign is 0 NO doppler shift
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Angle of 0 degrees or 180 degrees velocity is equal to waht?
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It is equal to true velocity
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CW Dopler contains two crystals. What are they?
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One transmits all the time - 100% Duty Factor
One recieves all the time - 0 |
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Can CW be used for imaging?
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NO
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What is advantage and disadvantage of CW?
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It can measure very high velosities.
Disadvantage is range ambiguity and you do not get a specific velocity it is a range of velocities. |
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What is PW?
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It is a single crystal that alternates between sending and recieving.
PW uses a sample gate that analyzes only the area being investigated |
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What is one advantage and disadvantage of PW?
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Advantage is knowing the location of blood cell that creates the doppler shift and the disadvantage is inability to correctly measure high velocities - the high velocities appear negative
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What is the most common observed artifact in pulsed wave imaging?
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Aliasing
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What is aliasing?
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when high velocities appear negative
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What is Nyquilst Frequency?
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It is the highest frequency at which aliasing occurs=to half PRF
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What can you do to help elminate aliasing?
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Select lower frequency transducer and select new imaging depth
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What are two types of color maps?
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Velocity Mode and Variance Mode
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What is velocity mode map?
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Gives you a mean the measured velocity for each gate is averaged and info is consolidated into a single #
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What is variance mode color map?
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It is an average velocity plus variability between individual velocities
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What do the two sides on a variance mode color map mean?
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Left side means laminer flow and right side means turbulant flow
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What is power doppler?
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It is not angle dependant and can not get a velocity tells rather or not something moves
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What are three limitations of color flow mapping?
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Reduces frame rate (temporal resolution)
Aliasing Tomographic |
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What are four characteristics that reduce frame rate?
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Pkt Size
Depth of region where color box is placed Width of color box Line density |
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What is tomographic?
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Images are in a single slice of targer - sections you get no direect knowledge of flow
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What is an ultrasound system?
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It is comprised of all the components necessary to produce a sound beam, retrieve echos and produce video and audio signals.
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What 4 types of information does the ultrasound system process?
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time of flight
strength direction frequency |
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What is a master sycronizer?
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It cordinates all components of the ultrasound system.
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What is the pulser - transmitter component of the ultrasound system?
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Controls electrical signal sent to the transducer
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What does reciever and image processor do?
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Accepts small voltage produced by transducer as it responds to reflected echos.
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What are five functions of a receiver?
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Amplification
Compensation Compression Demodulation Reject |
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What is amplification?
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Enlarges returning echo
If too much amplification is aplied all eaches will appear super bright and this is called saturation |
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What is compensation and what does it do?
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It is directly related to pathlength so echo returning from greater depth has lower amplitude - compensation makes all echos arising from similiar structure appear at the same brightness
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What is another name for compensation?
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TGC (Time Game Compensation)
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What is compression?
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It reduces the total range of signals from smallest to largest
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What is demodulation?
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It changes the shape of electrical signal into a format that matches requirement of input signal into monitor
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What is rectification?
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Changes negative into positive
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What is reject?
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It elminates all signals below minimum removing some of the useless noise
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What does a scan converter do?
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It makes grey scale display possible by storing image and then deisplays on screen
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When does processing take place in a scan converter?
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It is manipulating or altering the image while stored in the scan converter
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When does preprocessing take place in a scan converter?
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Before it is stored in the scan converter
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When does postprocessing take place in a scan converter?
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After it is stored in the scan converter
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Give details of an analog scan converter?
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It is the earliest form of converter and the disadvantages are image fade, image flicker, inconsistent piture and deteriation
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What are the details of a digital scan converter?
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It uses computer and computer memory to digitize it is uniform, stability, durable, fast and error free
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What is a pixel?
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Smallest amount of digital picture. The more pixels the more detail
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What is a bit?
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Binary Digit - Smallest amount of computer memory. AKA Ram
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What is a byte?
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A byte is a colletion of 8 bits...
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How do you find out how many bits are assigned to each pixel?
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Multiply 2 by itself the same # of times
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What is a tv that has alternating odd and even lines called?
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interlaced display
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What are different types of artifacts?
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Axil resolution, lateral resolution, acoustic speckle, slice thickness, refraction, reverb,etc.
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What is an acoustic speckle?
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Appears on image as bright tissue texture close to the transducer
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What is meant by refracton?
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Assumes sound travels in a straight line Reflection created after refraction appears on the screen as an improper location
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What is meant by reverberation?
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It appears as multiple equally spaced reflections - the sound ping pongs back and forth bettween 2 strong reflectors and it places too many echos on the image
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What is Comet Tail?
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Form of reverberation - 2 or more strong reflectors in medium with very high propergational speeds
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What is another name for Comet Tail?
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Ring Down Artifact
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What is mirror Image?
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Strong reflector acts a mirror and redirects pulse - duplication of real anatomy and the duplicate always appears deeper
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What is side lobes?
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Produced by a single crystal transducer - not hourglass shape sound beam
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What is grating lobes?
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array transducers produce off axis acoustic waves as result of regular systematic spacing of active elements - energy in direction other than that of beams main axis
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What are two causes of shadowing?
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Abnormally high attenuation and refraction
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What is shadowing?
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Absence or reduction in brightness of reflectors on image caused by weakening of sound beam
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What is another name for enhancement?
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Thru Transmission
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What are two causes of enhancement?
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Abnormally low attenuation and focusing
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What is enhancement?
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Overly bright reflectors appear on image
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What is QA or Quality Assurance?
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A routine periodic evaluation of u/s system to optimize image quality
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What are 4 requirements for a QA program?
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Variety of tests to evaluate system
Repairs Preventative Maintenance Record Keeping |
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Name 3 Different Test Objects?
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AIUM 100 milimeters test object
Tissue Equivelent Phantom Doppler Phantom |
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What is Tissue Equivelent Phantom?
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Evaluates gray scale by viewing hollow and solid cysts withing the phantom. Evaluates characteristics in modern systems. contains medium that mimics softt issue
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What is the Doppler Phantom?
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Used to check aquaracy of all doppler systems. contains simulated vessels poistioned at variety of angles to imaging surfaces
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How does AIUM test object evaluate lateral resolution?
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Meausred by measuring the size of the pins located perpendicular to the sound beam
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How does AIUM test object measure axial resolution?
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Axial resolution is evaluated when the pins are parallel to the sounds main beam axis ahnd the smallest distance in which 2 pins parallet to the primary beam are displayed as seperate objects.
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What is the first commandment regarding u/s?
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Benefit must outweigh the risks.
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What are two mechanisms of bioeffects?
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Thermal and Cavitation
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What are two foms of cavitation?
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Stable and Transiant
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