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109 Cards in this Set
- Front
- Back
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Sound is a _________, ___________ wave. |
Mechanical, longitudinal |
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Sound requires a ________ to travel |
Medium |
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Waves carry? |
Energy |
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Sound travels in a series of ______ an _______ |
Compressions and refractions |
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What are the acoustic variables |
Pressure, density, distance, and temperature |
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What are the units for Pressure Density Distance |
Pascals (Pa) Kg/cm^3 cm, mm |
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Frequency |
cycles per second |
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Range of frequency for ultrasound |
>20 kHz |
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How will an increase in frequency affect Period Wavelength Penetration depth Pulse duration Spatial pulse length Resolution |
Decrease Decrease Decrease Decreases Decrease Increase |
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Sound waves are described by (parameters) |
Period Frequency Propagation speed Wavelength Amplitude Power Intensity |
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10^9 10^-9 |
Giga, G, billion Nano, n, billionth |
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10^6 10^-6 |
Mega, M, million Micro, u, millionth |
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10^3 10^-3 |
Kilo, k, thousand Milli, m, thousandth |
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10^2 10^-2 |
Hecto, h, hundred Centi, c, hundredth |
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10^1 10^-1 |
Deca, da, ten Deci, d, tenth |
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What is the period for 10MHz and 7MHZ |
10MHz = .1 us 7MHz = .14 us |
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Define wavelength |
Length of one cycle |
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Formula of wavelength in soft tissue |
Wavelength (mm) = 1.54 (mm/us) / frequency (MHz) |
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Units for the following terms Wavelength Frequency Intensity Propagation speed Period Power |
millimeters Hertz W/cm^2 m/sec or mm/usec seconds W |
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How will an increase in wavelength affect Frequency Period Penetration Depth Pulse duration Spatial pulse length Resolution |
Decrease Increase Increase Increase Increase Decrease |
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What is the propagation speed in soft tissue and how does it change when the frequency is increased? |
1.54 (mm/us) It doesn't change |
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What determines the following parameters? Wavelength Frequency Intensity Propagation speed Period Power |
Both Sound source Sound source medium sound source sound source |
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What happens to speed when density increases? |
Speed will decrease |
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Which of the following can or cannot be changed by the operator? Wavelength Amplitude Intensity Propagation speed Period Power |
Cannot Can Can Cannot Cannot Can |
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Put mediums in order from fastest to slowest propagation speed: Muscle, air, soft tissue, fat, bone |
Bone - 3500m/s Muscle - 1600 m/s Soft tissue - 1540 m/s Fat - 1450 m/s Air - 330 m/s |
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Period |
Time to complete one cycle -milliseconds usually -determined by the sound source not medium -Cannot be changed by sonographer |
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What is the relationship between Period and frequency |
Period = 1/frequency inversely proportional as period increases frequency decreased reciprocals |
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Frequency |
Number of cycles per second -measured in Hz, MHz, KHz -not adjustable |
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Infrasonic |
Below hearing range < 20 Hz |
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Audible Sound |
20 Hz to 20,000 Hz |
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Ultrasound |
>20,000 Hz (20kHz) |
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Propagation Speed (c) |
Speed sound travels through a medium |
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Determinants of Propagation speed |
Stiffness (hardness, elasticity) Density |
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How fast the wave travels in a medium is determined by a medium's? |
Stiffness and density |
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What frequency wave will have the longest wavelength |
Low frequency |
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Wavelength |
Distance in space a wave occupies -the distance of the length of one complete cycle -measured in the unit of length -Determined by both sound source and medium -cannot be changed by the sonographer |
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As frequency increases, wavelength |
Decreases |
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Wave equation |
Speed = frequency x wavelength |
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What wavelength produces higher quality images with greater detail |
Shorter wavelength, higher frequency |
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Amplitude is the difference between the ____ value and the ____ value of an acoustic variable. |
Mean, average |
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Amplitude |
Equals the difference between average and maximum -"Bigness" -determined by the sound source -can be changed by the sonographer -pascals, g/cm^3, dB |
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Term is described as the rate of doing work |
Power |
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Power |
Proportional to amplitude squared Measured in watts determined by the sound source decreases as sound propagates through a medium can be changed |
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If the sonographer increases amplitude by a factor of 8. What happens to power? |
64 times bigger |
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Intensity |
Amount of power in a given area - Intensity = power (W) / beam area (cm^2) - determined by the sound source -can be changed by the sonographer |
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If the cross-sectional area of sound beam doubles and everything else stays the same, what happens to intensity |
Intensity is halved |
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What intensity is most important when determining bioeffects? |
SPTA (spatial peak temporal average) |
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Pulse Duration |
"On" time -seconds, msec -determined by the sound source -cannot be changed |
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What type of pulses create higher quality images |
Shorter |
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Pulse Duration equations |
PD= # cycles in pulse x period (msec) PD= # cycles in pulse/frequency (Hz) |
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Pulse Repetition Period |
Includes the on time and dead time - any unit of time -determined by the sound source -can be changed by sonographer (depth) |
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How are depth and PRP related? |
Directly As depth increases, PRP increases |
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Pulse repetition frequency |
Number of pulses that occur in a single second -determined by the sound source -Hz (per second) - Can be changed by the sonographer |
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How are depth and PRF related |
Inversely |
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How are PRF and PRP related? |
Reciprocals and inversely |
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Duty Factor |
Percentage or fraction of time that ultrasound is producing a pulse -can be determined by the sound source -can be changed by the sonographer |
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Duty factor formula |
DF= Pulse duration/ pulse repition period |
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Spatial Pulse Length (SPL) |
Length or distance a pulse occupies in space or distance from the start of a pulse to the end of the same pulse -determined by sound source and medium -mm -determines longitudinal resolution (image quality) |
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Formula for Spatial pulse length |
SPL (mm) = # of cycles in pulse x wavelength (mm) |
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How is Spatial pulse length related to frequency |
Inversely proportional |
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How is Spatial pulse length related to wavelength |
Directly proportional |
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How is Spatial pulse length related to # of cycles in the pulse |
Directly proportional |
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An ultrasound beam does not have the same intensity at different locations within the beam. This is referred to as _____ intensity. |
Spatial (space) |
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A pulsed ultrasound beam does not have the same intensity at different times. This refers to ______ intensity |
Temporal (time) |
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Highest intensity\Lowest intensity |
SPTP/SATA |
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Beam uniformity coefficient (BUC) |
Describes the distribution of ultrasound beam in space - SP/SA factor -unitless ratio |
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What are the 3 components of attenuation |
Absorption (attenuates sound the most) Reflection Scattering |
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Equation for attenuation coefficient in soft tissue |
Frequency (MHz)/2 |
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Equation for total attenuation |
Total attenuation (dB) = path length x attenuation coefficient |
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If the attenuation coefficient of a tissue is 0.3 dB/cm at 1MHz, how much will a 5 MHz beam be attenuated over 5cm distance? |
7.5 dB - 5 x 0.3 = 1.5 dB @ 1MHz - 1.5 x 5 = 7.5 dB @ 5MHz |
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Attenuation coefficient |
Amount of attenuation per centimeter -dB/cm -Used as a way to report attenuation without dealing with distance -does not change when the path length changes |
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As the path length increases, attenuation of US in soft tissue _____ |
Increases |
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In soft tissue, attenuation coefficient is directly related to _______ |
Frequency |
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Attenuation |
Sound energy decreases as it propagates |
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Attenuation is due to |
Reflection Scatter Absorption Refraction Beam divergence |
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What is the relationship between attenuation and depth and frequency |
Varies directly |
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Reflections from a smooth reflector such as a mirror. They return in one direction and are referred to as _______ reflection. |
Specular |
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What is the type of reflection when a boundary is rough and the reflected sound is disorganized and random |
Diffuse or backscatter |
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Scattering that occurs when a structure's dimension is much smaller than the sound's wavelength. Scattering redirects the sound wave equally in all directions. This refers to ______scattering |
Rayleigh |
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dB is a mathematical representation with a ____scale |
Logarithmic |
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Every 3 dB change means that intensity will |
DOuble |
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Every 10 dB change means that the intensity will ______ |
Increase ten times |
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Positive decibels |
Report signals that are increasing in strength -- getting larger |
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-10 dB means that the intensity is reduced to _____of its original value |
One-tenth |
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A drop in intensity to one-quarter of its original value is ______dB |
-6 |
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Negative Decibels |
Describes signals that are decreasing in strength |
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________ refers to the depth of tissue that results in 3dB of attenuation |
Half-value layer thickness |
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________ refers to acoustic resistance to sound traveling in medium |
Impedance |
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Impedance |
important in reflections at boundaries - rayls represented by "Z" - transmission is critical to ultrasound ability to image structures located deep in the body -characteristic of the medium -calculated |
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For normal incidence, a larger difference in acoustic impedance means there will be a ____________ reflection. |
Larger |
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For oblique incidence, a large difference in acoustic impedance means there will be a ________ reflection. |
Uncertain |
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At an interface between fat and muscle there is only a small difference in acoustic impedance. 99% of the sound energy will be transmitted. What is the intensity Reflection Coefficient? |
1% |
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Specular reflectors are ______, ________, and highly ____________ |
Larger, Smooth, angle dependent |
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Sound scatters when reflectors are _____, or _____. Scatter reflectors are not __________ |
Small, rough, angle dependent |
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The formula (z1 -z2 / z2 + z1)^2 applies to what type of incidence and predicts what |
Normal incidence -The percent of the incident beam that is reflected |
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When would each incident occur -no reflection -small reflection -large reflection |
-identical impedances -slightly different -substantially different |
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If the incidence angle is 40 degrees. What will the angle of reflection be? |
40 degrees - reflected angle always equals incidence angle |
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What does Snell's Law predict |
Whether refraction will occur |
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Name 2 situations where refraction will not occur |
When there is perpendicular incidence Oblique incidence but propagation speeds of the two media are equal |
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Write the number 35800 using scientific notation |
3.58 x 10^5 |
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Write the number 0.0001540 using scientific notation |
1.54 x 10^-4 |
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What is the log of 10,000 |
4 - 10x10x10x10 = 10000 |
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3 dB of attenuation represents ____% increase or decrease in the sound wave's intensity |
Every 3 dB of attenuation represents a 50% decrease |
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A sound wave traveling in soft tissue has an initial intensity of 100mW/cm^2. If the intensity attenuates by 6 dB what is the final intensity? |
25mW/cm^2 |
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For soft tissue, what is the attenuation coefficient for a 10 MHz probe |
5dB/cm -10MHz/2 |
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For soft tissue, what is the attenuation coefficient for a 10 MHz probe. Given this information what is the total attenuation for a sound wave traveling 3 cm? |
5dB x 3 = 15 dB |
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For soft tissue, what is the attenuation coefficient for a 10 MHz probe. Given this information what is the Half Value Layer?
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5dB/1cm x 3dB/? 3/5 = .6 cm |
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A sonographer is scanning superficially in soft tissue using a 3 cycle 10MHz transducer. The image depth is set at 5cm. The sound wave strikes a reflector with normal incidence. The time of flight is 26us. Wavelength Period Pulse duration Spatial pulse length Reflector Attenuation coefficient Total attenuation |
Wavelength .154 mm = 1.54/10 Period .1us = 1/10 Pulse duration .3us = .1 x 3 SPL .462mm = 1.53 x 3 Reflector 2cm = 26/13 Attenuation coefficient 5dB/cm = 10/2 Total attenuation 25dB = 5 x 5 |
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If the sonographer wants to image a structure located much deeper, what should they do? |
Select a lower frequency transducer |
