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physics 1
first physics test for Jodie b4 registry
| Question | Answer |
|---|---|
| Pressure | concentration of force within an area (Pa) Pascal’s |
| Density | concentration of mass within a volume (kg/cm^3) |
| Distance – | measure of particle motion (cm. feet.) |
| Acoustic variable (3) | Pretty Dang dumb Pressure, Density, distance |
| Mechanical energy | sound is a |
| Mechanical energy is comprised of – | rarefactions and compressions |
| Sound waves have to have molecules to travel, therefore they cannot travel in a – | vacuum |
| Rarefaction | area of low pressure and density |
| Compression | area of high pressure and density |
| Biological effects | effects of sound waves on tissue |
| Acoustic propagation properties | effects of tissue on the sound wave |
| Frequency and period are – | reciprocals |
| Formula for period | P=1/f |
| Formula for frequency | f=1/p |
| Period is _____ related to frequency | inversely (^P vf) |
| If the frequency is 8Hz/sec then the period is – | 1/8 |
| If the frequency is 4Hz/s then period is – | ¼ |
| Ultrasound – | frequency greater than 20,000 hertz (20 KHz) |
| Audible sound | Frequency below 20 Hz and 20,000 hertz (20 kHz) |
| Infrasound | frequency below 20 Hz |
| Transverse waves | Particles move in a direction that is perpendicular to the direction of the sound wave |
| Longitudinal waves | particles moving in the same direction as the wave |
| Sound is a __________________ and _____________________ wave | mechanical, longitudinal |
| Sound source consists of ___________ ultrasound machine with one _____________ | one , tranducer |
| Every transducer that made now can change __________________ from 2.5 MHz to 5MHz | frequency |
| Units of period | seconds, ms, hours |
| Period is determined by | the sound source |
| Can the period be changed by the sonographer | no |
| Period is the – | period of time it takes for a wave to vibrate a single cycle or from the start of one cycle to the end of the cycle |
| Units of frequency are | per second, 1/sec, Hz |
| Frequency is determined by the – | sound source |
| Can the frequency be changed by the sonographer | no |
| Frequency | the number of cycles that occur in one second |
| If the period is .005 sec, what is the frequency | .0002 MHz Final answer must be in Hz because question is sec F=1/p |
| What is the frequency of a wave with a 1 msec period | 1 kHz 1msec=.001 s f=1/p 1000 hz = |
| Which is an infrasonic wave? 4 MHz, 400kHz, 20 HZ or 2 Hz | 2 Hz |
| Identify the wave that is ultrasonic? 400 MHz(4Hz), 4MHz(4000000Hz) 28 Hz, or 2Hz | 4MHz (ultrasound uses between 2 |
| Amplitude can be expressed in – | dB (can be any of the acoustic variables pressure, distance, or density) |
| What is amplitude determined by | the sound source initially |
| Can amplitude be changed by the sonographer | yes |
| Amplitude decreases as – | sound propagates through the body |
| Amplitude | the difference between maximum value and the average or undisturbed value of the acoustic variable |
| What is the average range of amplitude | 1 |
| Bigness factors of a wave | amplitude, power, intensity |
| The bigger the wave the ____________ energy it has | more |
| Peak to peak amplitude | amplitude is half of the peak to peak amplitude |
| Solve: Max 100 Min 50 Amplitude? | 100 |
| Units of power | watts |
| Is power changeable by the sonographer? | yes |
| Power is proportional to the waves | amplitude squared |
| Power | rate of energy transfer or rate at which work is performed |
| If amplitude in halved the power? | goes down by a quarter (x^2)2) |
| ______________ is determined by the sound source and decreases as it travels | Power |
| Intensity | the concentration of energy in a sound beam |
| Formula for intensity | the power in the beam divided by the beams cross sectional area I (W/cm^2)=Power(Watts)/beam area (cm^2) |
| What is intensity determined by? | the sound source |
| Can intensity be changed by the sonographer? | yes |
| Intensity is proportional to – | (or directly related to ) power |
| If power doubles what else doubles? | intensity (^I^P) |
| This is what you remember about intensity and amplitude – | amplitude squared |
| Intensity is _______________ to the waves amplitude squared | proportional |
| If amplitude goes up by 6, the intensity | goes up by 36 |
| If amplitude goes down by ¼, intensity – | goes down by 1/16 |
| If the intensity of a sound beam remains unchanged while the beam area is reduced in half, what has happened to the power? | halved |
| Wavelength is determined by | both the source and the medium (remember 2 things!) |
| Can the wavelength be changed by the sonographer? | no |
| Formula for wavelength | λ(mm)=propagation speed(mm/us)/frequency(MHz) |
| Wavelength | the distance or length from one complete cycle. |
| In any medium, the lower the frequency | the longer the wavelength |
| In any medium, the higher the frequency | the shorter the wavelength (better image) |
| When traveling through the same medium, if the frequency is doubled, the wavelength is | halved |
| Wavelength and frequency are ______________ related. | inversely (remember: nobody likes frequency) |
| Propagation speed aka | speed of sound |
| Units for propagation speed | meters per sec, mm/us |
| Propagation speed is determined by the | medium only (density and stiffness) |
| Can a sonographer change propagation speed? | no |
| Prop speed (m/s)= | frequency (Hz)/ λ (wavelength) |
| Propogation speed definition | rate at which sound travels through a medium |
| What is the only way to change propagation speed? | removing one medium and putting another one down |
| Propogation speed is sometimes written as | c (λ (wavelength) =sp©/f or f= c/λ (wavelength) |
| Name the average speed of sound in soft tissue different ways | 1,540 m/s, 154,000 cm/s, 1.54 mm/us, and 1.54 km/s |
| Sound always travels | 1 mile per second |
| What are two characteristics of medium that affect the speed of sound? | stiffness and density |
| Stiffness and density are | inversely related |
| Stiffness definition | the ability of an object to resist compression |
| Density definition | the relative weight of a material |
| What is the mnemonic to remember when looking at the speed of sound in biologic media? | All little fat soft livers Kan build many tough bones. |
| Rules of thumb for Stiffness and Density | ^stiffness, speed increases |
| Stiffness and speed are _____________ related | directly |
| Density and speed are _______________ related | inversely |
| These are inversely related and recipricols(2 things) | period and frequency |
| These can be changed by the sonographer (3 things) | amplitude, power, intensity: they have knobs |
| All of these are determined by the sound source(5 things) | period, frequency, amplitude, power, intensity |
| The degree of stiffness may also be described with the terms | elasticity or compressibility |
| Elastic and compressible are the _____________ of stiff | opposite |
| Non stiff media are described as | elastic or compressible |
| CDE | Compressibility, Density, and elasticity (have same effect on speed: all inversely related to speed |
| Compressibility | describes its ability to reduce its volume when force is applied. Ex. Marshmallow gets smaller when squeezed |
| Elasticity | same meaning as compressibility. |
| Wavelength is determined by what – | (2 things) the medium and the sound source |
| Speed is determined by what | the medium |
| Does propagation speed increase as frequency increases? | no because frequency and speed have no relationship the only way to change speed is to change the medium and sound source for frequency |
| If intensity remains the same while the power is doubled, what happens to the beam area? | it doubles I=Power (watts)/BA (cm^2) |
| T or F a wave with the frequency of 15, 000 MHz is ultrasonic | true ultra >20,000 Hz audible 20 Hz to 20,000 Hz and infra < 20 Hz |
| Particle motion is the same as | distance so it is an acoustic variable |
| This is the fastest characteristics to create the fasted speed of sound | low density and high stiffness |
| Interference | when 2 waves overlap at the same location and at the same time, they combine with each other. The result is the creation of a single, new wave. This is the summation. |
| Construction interference | in phase |
| Destructive interference | out of phase |
| This is what construction interference does | When peaks and troughs come together at exactly the same time and when they do their waves overlap and we end up with a bigger wave that the initial wave. They come in contact at just the right time and their peaks and trough align. |
| This is what destructive interference does | out of phase where two waves don’t hit at the right time and the result is cancelling each other out and a making smaller wave |
| This is when the amplitude is less than one of the original two waves | Out of phase destruction interface |
| The logarithm of any number represents the number of ________ that are multiplied together to create the original number | 10’s |
| What is the log of 100? | 2 |
| Relative scale | it is a ration the actual level is divided by the starting level intensity levels (dB) |
| How many intensities are required for a relative scale | two intensities? |
| Decibel notation is | 1. A relative measurement (not absolute number) 2. A comparison of the beginning to the end 3. A ratio actual level is divided by the starting level |
| Positive dB means | getting bigger (increasing) |
| 3 dB means | times 2 (the final intensity is twice as big as the original intensity) |
| 6 dB means | two times two the final intensity is 4 times the original |
| 9 dB means | 2 times2time2times. The final is 8 times the original |
| 10 dB means – | times 10. The final intensity is 10 times bigger than the original intensity |
| 20 dB | Minus10 times 10 times. The final intensity is 100 times bigger than the original |
| Negative decibels means – | getting smaller (decreasing) |
| Neg 3 means | ½ We have fallen to ½ the original value. |
| Neg 6 means | we have fallen to ¼ (1/2of ½) of the original value |
| Neg 9 means | we have fallen to 1/8 (1/2 of1/2of1/2) of the original value |
| Neg 10 means | we 1/10th we have fallen to 1/10 of the original value. |
| Neg 20 dB means | we have fallen to 1/100 (1/10of1/10) of the original value |
| A signals power increases from 1 watt to 100 watts. How is this expressed in dB’s | 20 dB |
| The power of a system is at 100 percent and this is 0 dB. What is the change in dB’s when the system is at 50 percent? | neg 3 dB |
| The power of a system is at 100 percent and this is 0dB. The system is adjusted to neg 6 dB. What is the systems power at this setting – | 25percent |
| The decrease in intensity, power, and amplitude as sound travels | attenuation |
| What happens when attenuation occurs? | sound energy is extracted from the wave |
| As sound travels what happens to it waves? | they get smaller |
| Attenuation is determined by – | frequency and path length ^freq ^ attenuation ^path length ^attenuation |
| More attenuation | higher frequency, longer path length (distance) |
| Less attenuation | lower frequency , shorter path length (distance) |
| A 3 MHz sound beam travels 10 cm, 6 cm in medium a and 4 cm in medium b. the total attenuation is 14 dB. If the sound beam attenuated is 4 dB in medium A, then how much attenuation occurred in medium B? | 10 dB |
| A 3 MHz sound beam travels through 2 media. It attenuates 5 dB in medium A and 6 dB in medium B. what is the total attenuation that sound beam undergoes as it travels through both media? – | 11 dB |
| A 3 MHz beams travels 7 cm in a medium. The total attenuation is 5 dB. How much attenuation will 6 MHz sound beam undergo when traveling 3.5 cm in the same medium? | 5 dB (even though frequency doubled, distance halved. So attenuation remains the same. |
| Two things affect attenuation | frequency and path length |
| Medium will effect attenuation but not ________________ to it | contribute |
| 3 processes that contribute to attenuation | reflection, scattering, and absorption |
| Two types of reflection | specular and diffuse |
| AKA scattering | Rayleigh scattering |
| What is absorption | sound dissipated in heat |
| Reflection explanation | boundary bigger wavelength smaller . Comes in specular and back scatter / diffuse |
| Scaλλering explanation | (remember to use the wavelength sign for the t’s) λ bigger, boundary smaller: Raleigh scattering. |
| Absorption explanation | turns to heat |
| Reflection definition | as sound waves strike a boundary, a portion of the waves energy may be redirected, or reflected, back to the sound source. |
| There are two types of reflection and they are | specular and diffuse (backscatter) |
| A specular reflection happens when | the boundary is smooth the sound source is reflected in only one direction in an organized manner |
| When does specular reflection occur | when the λ is much smaller than the irregularities in the boundary |
| When are specular reflectors well seen? | When the sound wave strikes the reflector at 90 degrees (if not at 90 degrees they will bounce off to a different angle) |
| Examples of specular reflectors? | Diaphragm, big long vessels |
| Diffuse reflection aka | back scatter |
| When a wave reflects off an_____________, it radiates in more than one direction this is called diffuse reflection | irregular surface |
| Diffuse reflection occurs when the boundary has irregularities that are | approximately the same size as the sounds wavelength. (Boundary is about the same size or a little bigger) |
| Only good thing about diffuse scattering is because – stransducer | o many are bouncing back in different directions that more goes back into the |
| Example of diffuse relection | broken glass, wet pavement at night |
| Scattering of ultrasound is the – | random redirection of sound into many directions |
| Sound scatters when the tissue interface is – | small, that is, equal to or less than the wavelength of the incident beam |
| ___________ Frequency sound beams scaλλer more than _______ frequencies | higher, low |
| Raleigh scaλλering – | is a reflector is much smaller than the pulse wavelength this occurs. Redirection of the sound wave equally redirected in all directions. It is organized(omnidirectional) |
| This is proportional to frequency^4 and it very dependent on the transducer frequency | Rayleigh^4 scattering |
| Red blood cells are | R^4 scatters |
| If transducer doubles | Rayleigh scattering would be to the 16th |
| Why do we care about attenuation? | b/c it determines what transducer frequency we need to use high or low |
| What is the significance of attenuation in diagnostic imaging? | attenuation limits the maximum depth form which images are obtained |
| Attenuation is ____________ in both bone and in lung compared to soft tissue | higher |
| Bone is a good ___________ and ______________ | absorber and reflector |
| Lung is a great______________ | scatterer |
| Attenuation of sound in blood is approximately equal to that in – | soft tissue |
| BAR | blood is a absorber and reflector |
| Ultrasonic energy is converted into another energy | heat |
| High frequency waves attenuate more than ______ frequency | lower |
| Absorption is ___________ related to frequency | directly |
| Attenuation coefficient | the amount of attenuation per centimeter |
| Units of attenuation – | dB/cm |
| Formula for total attenuation (dB) | path length (cm) X atten. Coefficient (dB/cm) |
| Definition of attenuation coefficient | number of dB of attenuation that occur when a sound travels one centimeter |
| Remember this about Abe Lincoln | Abraham Lincoln was an attenuator: Abe Lincoln sold water. (air bone lungs soft tissue water) |
| If we do not know the attenuation coefficient | we should know that its half our frequency |
| Example of attien coeff | 2 dB/cm for every cm we are losing 2 dB off sound wave |
| What is the total attenuation of 2 dB at 4 cm – | 8 dB lost |
| Half value layer thickness | penetration depth or half boundry level |
| This is the distance that sound travels in a tissue that reduces the intensity of the sound to one half its original value | ½ value layer thickness |
| Units for half value thickness | cm(length) |
| 2 things that affect HVL | frequency and attenuation |
| HVL aka | penetration depth and half value level |
| Acoustic impedance | strength or amplitude and amount of reflected echoes |
| Air or air filled structure (lung) has a very ______ acoustic imperdance compared to tissue. – | low |
| Acoustic imped resistance to sound traveling in a ________. | medium |
| This is a characteristic of the medium through which sound travels. | acoustic impedance |
| Unit for Acc impedance | rayls |
| Formula for acoustic impedance | (rayls)=density(kg/m^3 X prop. Speed(m/s) or Z (impedance)=pc |
| Acoustic impedance increases when | the density increases and when the propagation speed increases. |
| Imperdance is ____, not measured. – | calculated |
| The reflection of an ultrasound wave depends upon a difference in the ________ ________ at the boundary between the two media. – | acoustic impedances |
| Two media, A and B, have the same prop. Speed. Medium A’s density is 10 percent higher than medium B’s. which medium has the highest impedance (resistance)? | Medium A |
| Normal incidence | PORNN |
| Pornn stands for – | perpendicular, orthogonal, right, normal, ninety (just means its hitting something at 90 degrees) |
| Oblique incidence | not at rt. Angles can be acute < 90 degrees or obtuse > 90 degrees |
| Intensity (W/cm^2) 3 kinds | incident int, reflected int., and transmitted intensity. |
| Incident intensity | the intensity that the sound wave possess at the instant prior to striking the boundary |
| Reflected intensity | the intensity that, after striking the boundary, changes direction and returns back in the direction it came from |
| Transmitted intensity | the intensity that, after striking a boundary, continues on in the same general direction that it was traveling |
| Incident (starting) intensity= | reflected intensity plus transmitted intensity (not energy lost or gained) |
| In clinical imaging, very little of the US intensity is reflected back to the transducer at the boundary between _____________________. – | Soft tissues the remainder is transmitted and continues to propagate in the forward direction. |
| Intensity reflection coefficient (IRC) is a – | percentage |
| Intensity transmission coeffiencent (ITC) is a – | percentage |
| Formula for IRC and ITC | IRC (percentage) + ITC (percentage)= 100 percent |
| _______ or more of a sound waves intensity is transmitted at a boundary between 2 soft tissues. | 99 percent |
| A greater percentage of the wave is reflected, approx. 50 percent, when sound is reflected off of a ______ /_______ interface | bone/soft tissue |
| Even more sound is reflected, approx. 99 percent, when sound is reflected off an _____/_______ interface | air/soft tissue |
| IRC percent + | (z1 |
| Refliection (spelled like this because) | reflection deals with impedance different impedances and Pornn |
| Refliection occurs only when | there are different impedances at the boundary between two media. |
| Transmission with normal incidence | when all intensity is transmitted ITC= transmitted intensity/incident intensity X 100 percent then 100 percent – intensity reflection coefficient |
| Reflection and transmission with oblique incidence | transmission and reflection may or may not occur with oblique incidence |
| 2 physical principles always apply to reflection with oblique incidences | conservation of energy and reflection angle (incident angle) |
| 100 percent = | reflected coefficient + transmission coefficient |
| Incident intensity formula (W/cm^2) = | reflected intensity + transmitted intensity |
| Reflection angle = | incident angle |
| Refraction | a change in direction of wave propagation when traveling from one medium to another. Associated with transmission (transmission with a bend) Oblique incidence |
| Refraction can only occur when what 2 things are present | 1. Different propagation speeds and 2. Oblique incidence (can’t occur with normal incidence or with identical speeds) |
| Snell’s law | refraction is described by this (sine transmission angle = prop speed 2/sine incident angle prop speed 1 |
| If propagation speed 2 is < than prop speed 1 then | transmission angle is < than the incident angle |
| If propagation speed 2 is >er than prop speed 1, then the transmission angle is | >er than the incident angle |
| Remember that refraction requires | two different prop speeds |
| No refraction, transmission angle = incident angle | speed 2=speed 1 |
| Transmission angle greater than incident angle | speed 2 is greater than speed 1 |
| Transmission angle less that incident angle – | speed 2 less than speed 1 |
| Reflection with normal incidence | different impedances required |
| Reflection with oblique incidence | we do not know! |
| Transmission | derive this from reflection information, use law of conservation |
| Refraction | oblique incidence and different speeds required |
| Pressure | concentration of force within an area (Pa) Pascal’s |
| Density | concentration of mass within a volume (kg/cm^3) |
| Distance | measure of particle motion (cm. feet) |
| Acoustic variable (3) | Pretty Dang dumb Pressure, Density, distance |
| Mechanical energy | sound is a |
| Mechanical energy is comprised of – | rarefactions and compressions |
| Sound waves have to have molecules to travel, therefore they cannot travel in a – | vacuum |
| Rarefaction | area of low pressure and density |
| Compression | area of high pressure and density |
| Biological effects | effects of sound waves on tissue |
| Acoustic propagation properties | effects of tissue on the sound wave |
| Frequency and period are – | reciprocals |
| Formula for period | P=1/f |
| Formula for frequency | f=1/p |
| Period is _____ related to frequency | inversely (^P vf) |
| If the frequency is 8Hz/sec then the period is – | 1/8 |
| If the frequency is 4Hz/s then period is – | ¼ |
| Ultrasound – | frequency greater than 20,000 hertz (20 KHz) |
| Audible sound | Frequency below 20 Hz and 20,000 hertz (20 kHz) |
| Infrasound | frequency below 20 Hz |
| Transverse waves | Particles move in a direction that is perpendicular to the direction of the sound wave |
| Longitudinal waves | particles moving in the same direction as the wave |
| Sound is a __________________ and _____________________ wave | mechanical, longitudinal |
| Sound source consists of ___________ ultrasound machine with one _____________ | one , tranducer |
| Every transducer that made now can change __________________ from 2.5 MHz to 5MHz | frequency |
| Units of period | seconds, ms, hours |
| Period is determined by | the sound source |
| Can the period be changed by the sonographer | no |
| Period is the – | period of time it takes for a wave to vibrate a single cycle or from the start of one cycle to the end of the cycle |
| Units of frequency are | per second, 1/sec, Hz |
| Frequency is determined by the – | sound source |
| Can the frequency be changed by the sonographer | no |
| Frequency | the number of cycles that occur in one second |
| If the period is .005 sec, what is the frequency | .0002 MHz Final answer must be in Hz because question is sec F=1/p |
| What is the frequency of a wave with a 1 msec period | 1 kHz 1msec=.001 s f=1/p 1000 hz = |
| Which is an infrasonic wave? 4 MHz, 400kHz, 20 HZ or 2 Hz | 2 Hz |
| Identify the wave that is ultrasonic? 400 MHz(4Hz), 4MHz(4000000Hz) 28 Hz, or 2Hz | 4MHz (ultrasound uses between 2 |
| Amplitude can be expressed in – | dB (can be any of the acoustic variables pressure, distance, or density) |
| What is amplitude determined by | the sound source initially |
| Can amplitude be changed by the sonographer | yes |
| Amplitude decreases as – | sound propagates through the body |
| Amplitude | the difference between maximum value and the average or undisturbed value of the acoustic variable |
| What is the average range of amplitude | 1 |
| Bigness factors of a wave | amplitude, power, intensity |
| The bigger the wave the ____________ energy it has | more |
| Peak to peak amplitude | amplitude is half of the peak to peak amplitude |
| Solve: Max 100 Min 50 Amplitude? | 100 |
| Units of power | watts |
| Is power changeable by the sonographer? | yes |
| Power is proportional to the waves | amplitude squared |
| Power | rate of energy transfer or rate at which work is performed |
| If amplitude in halved the power? | goes down by a quarter (x^2)2) |
| ______________ is determined by the sound source and decreases as it travels | Power |
| Intensity | the concentration of energy in a sound beam |
| Formula for intensity | the power in the beam divided by the beams cross sectional area I (W/cm^2)=Power(Watts)/beam area (cm^2) |
| What is intensity determined by? | the sound source |
| Can intensity be changed by the sonographer? | yes |
| Intensity is proportional to – | (or directly related to ) power |
| If power doubles what else doubles? | intensity (^I^P) |
| This is what you remember about intensity and amplitude – | amplitude squared |
| Intensity is _______________ to the waves amplitude squared | proportional |
| If amplitude goes up by 6, the intensity | goes up by 36 |
| If amplitude goes down by ¼, intensity – | goes down by 1/16 |
| If the intensity of a sound beam remains unchanged while the beam area is reduced in half, what has happened to the power? | halved |
| Wavelength is determined by | both the source and the medium (remember 2 things!) |
| Can the wavelength be changed by the sonographer? | no |
| Formula for wavelength | λ(mm)=propagation speed(mm/us)/frequency(MHz) |
| Wavelength | the distance or length from one complete cycle. |
| In any medium, the lower the frequency | the longer the wavelength |
| In any medium, the higher the frequency | the shorter the wavelength (better image) |
| When traveling through the same medium, if the frequency is doubled, the wavelength is | halved |
| Wavelength and frequency are ______________ related. | inversely (remember: nobody likes frequency) |
| Propagation speed aka | speed of sound |
| Units for propagation speed | meters per sec, mm/us |
| Propagation speed is determined by the – | medium only (density and stiffness) |
| Can a sonographer change propagation speed? | no |
| Prop speed (m/s)= | frequency (Hz)/ λ (wavelength) |
| Propogation speed definition | rate at which sound travels through a medium |
| What is the only way to change propagation speed? | removing one medium and putting another one down |
| Propogation speed is sometimes written as | c (λ (wavelength) =sp©/f or f= c/λ (wavelength) |
| Name the average speed of sound in soft tissue different ways | 1,540 m/s, 154,000 cm/s, 1.54 mm/us, and 1.54 km/s |
| Sound always travels | 1 mile per second |
| What are two characteristics of medium that affect the speed of sound? | stiffness and density |
| Stiffness and density are | inversely related |
| Stiffness definition | the ability of an object to resist compression |
| Density definition | the relative weight of a material |
| What is the mnemonic to remember when looking at the speed of sound in biologic media? | All little fat soft livers Kan build many tough bones. |
| Rules of thumb for Stiffness and Density | ^stiffness, speed increases |
| Stiffness and speed are _____________ related | directly |
| Density and speed are _______________ related | inversely |
| These are inversely related and recipricols(2 things) | period and frequency |
| These can be changed by the sonographer (3 things) | amplitude, power, intensity: they have knobs |
| All of these are determined by the sound source(5 things) | period, frequency, amplitude, power, intensity |
| The degree of stiffness may also be described with the terms | elasticity or compressibility |
| Elastic and compressible are the _____________ of stiff | opposite |
| Non | stiff media are described as |
| CDE | Compressibility, Density, and elasticity (have same effect on speed: all inversely related to speed |
| Compressibility | describes its ability to reduce its volume when force is applied. Ex. Marshmallow gets smaller when squeezed |
| Elasticity | same meaning as compressibility. |
| Wavelength is determined by what – | (2 things) the medium and the sound source |
| Speed is determined by what | the medium |
| Does propagation speed increase as frequency increases? | no because frequency and speed have no relationship the only way to change speed is to change the medium and sound source for frequency |
| If intensity remains the same while the power is doubled, what happens to the beam area? | it doubles I=Power (watts)/BA (cm^2) |
| T or F a wave with the frequency of 15, 000 MHz is ultrasonic | true ultra >20,000 Hz audible 20 Hz to 20,000 Hz and infra < 20 Hz |
| Particle motion is the same as – | distance so it is an acoustic variable |
| This is the fastest characteristics to create the fasted speed of sound | low density and high stiffness |
| Interference | when 2 waves overlap at the same location and at the same time, they combine with each other. The result is the creation of a single, new wave. This is the summation. |
| Construction interference | in phase |
| Destructive interference | out of phase |
| This is what construction interference does | When peaks and troughs come together at exactly the same time and when they do their waves overlap and we end up with a bigger wave that the initial wave. They come in contact at just the right time and their peaks and trough align. |
| This is what destructive interference does | out of phase where two waves don’t hit at the right time and the result is cancelling each other out and a making smaller wave |
| This is when the amplitude is less than one of the original two waves | Out of phase destruction interface |
| The logarithm of any number represents the number of ________ that are multiplied together to create the original number | 10’s |
| What is the log of 100? | 2 |
| Relative scale | it is a ration the actual level is divided by the starting level intensity levels (dB) |
| How many intensities are required for a relative scale | two intensities? |
| Decibel notation is | 1. A relative measurement (not absolute number) 2. A comparison of the beginning to the end 3. A ratio actual level is divided by the starting level |
| Positive dB means | getting bigger (increasing) |
| 3 dB means | times 2 (the final intensity is twice as big as the original intensity) |
| 6 dB means | two times two the final intensity is 4 times the original |
| 9 dB means | 2 times2time2times. The final is 8 times the original |
| 10 dB means – | times 10. The final intensity is 10 times bigger than the original intensity |
| 20 dB | Minus10 times 10 times. The final intensity is 100 times bigger than the original |
| Negative decibels means – | getting smaller (decreasing) |
| Neg 3 means | ½ We have fallen to ½ the original value. |
| Neg 6 means | we have fallen to ¼ (1/2of ½) of the original value |
| Neg 9 means | we have fallen to 1/8 (1/2 of1/2of1/2) of the original value |
| Neg 10 means | we 1/10th we have fallen to 1/10 of the original value. |
| Neg 20 dB means | we have fallen to 1/100 (1/10of1/10) of the original value |
| A signals power increases from 1 watt to 100 watts. How is this expressed in dB’s | 20 dB |
| The power of a system is at 100 percent and this is 0 dB. What is the change in dB’s when the system is at 50 percent? | neg 3 dB |
| The power of a system is at 100 percent and this is 0dB. The system is adjusted to neg 6 dB. What is the systems power at this setting – | 25percent |
| The decrease in intensity, power, and amplitude as sound travels | attenuation |
| What happens when attenuation occurs? | sound energy is extracted from the wave |
| As sound travels what happens to it waves? | they get smaller |
| Attenuation is determined by – | frequency and path length ^freq ^ attenuation ^path length ^attenuation |
| More attenuation | higher frequency, longer path length (distance) |
| Less attenuation | lower frequency , shorter path length (distance) |
| A 3 MHz sound beam travels 10 cm, 6 cm in medium a and 4 cm in medium b. the total attenuation is 14 dB. If the sound beam attenuated is 4 dB in medium A, then how much attenuation occurred in medium B? | 10 dB |
| A 3 MHz sound beam travels through 2 media. It attenuates 5 dB in medium A and 6 dB in medium B. what is the total attenuation that sound beam undergoes as it travels through both media? – | 11 dB |
| A 3 MHz beams travels 7 cm in a medium. The total attenuation is 5 dB. How much attenuation will 6 MHz sound beam undergo when traveling 3.5 cm in the same medium? | 5 dB (even though frequency doubled, distance halved. So attenuation remains the same. |
| Two things affect attenuation | frequency and path length |
| Medium will effect attenuation but not ________________ to it | contribute |
| 3 processes that contribute to attenuation | reflection, scattering, and absorption |
| Two types of reflection | specular and diffuse |
| AKA scattering | Rayleigh scattering |
| What is absorption | sound dissipated in heat |
| Reflection explanation | boundary bigger wavelength smaller . Comes in specular and back scatter / diffuse |
| Scaλλering explanation | (remember to use the wavelength sign for the t’s) λ bigger, boundary smaller: Raleigh scattering. |
| Absorption explanation | turns to heat |
| Reflection definition | as sound waves strike a boundary, a portion of the waves energy may be redirected, or reflected, back to the sound source. |
| There are two types of reflection and they are | specular and diffuse (backscatter) |
| A specular reflection happens when | the boundary is smooth the sound source is reflected in only one direction in an organized manner |
| When does specular reflection occur | when the λ is much smaller than the irregularities in the boundary |
| When are specular reflectors well seen? | When the sound wave strikes the reflector at 90 degrees (if not at 90 degrees they will bounce off to a different angle) |
| Examples of specular reflectors? | Diaphragm, big long vessels |
| Diffuse reflection aka | back scatter |
| When a wave reflects off an_____________, it radiates in more than one direction this is called diffuse reflection | irregular surface |
| Diffuse reflection occurs when the boundary has irregularities that are | approximately the same size as the sounds wavelength. (Boundary is about the same size or a little bigger) |
| Only good thing about diffuse scattering is because – | so many are bouncing back in different directions that more goes back into the transducer |
| Example of diffuse relection | broken glass, wet pavement at night |
| Scattering of ultrasound is the – | random redirection of sound into many directions |
| Sound scatters when the tissue interface is – | small, that is, equal to or less than the wavelength of the incident beam |
| ___________ Frequency sound beams scaλλer more than _______ frequencies | higher, low |
| Raleigh scaλλering – | is a reflector is much smaller than the pulse wavelength this occurs. Redirection of the sound wave equally redirected in all directions. It is organized(omnidirectional) |
| This is proportional to frequency^4 and it very dependent on the transducer frequency | Rayleigh^4 scattering |
| Red blood cells are | R^4 scatters |
| If transducer doubles | Rayleigh scattering would be to the 16th |
| Why do we care about attenuation? | b/c it determines what transducer frequency we need to use high or low |
| What is the significance of attenuation in diagnostic imaging? | attenuation limits the maximum depth form which images are obtained |
| Attenuation is ____________ in both bone and in lung compared to soft tissue | higher |
| Bone is a good ___________ and ______________ | absorber and reflector |
| Lung is a great______________ | scatterer |
| Attenuation of sound in blood is approximately equal to that in – | soft tissue |
| BAR | blood is a absorber and reflector |
| Ultrasonic energy is converted into another energy | heat |
| High frequency waves attenuate more than ______ frequency | lower |
| Absorption is ___________ related to frequency | directly |
| Attenuation coefficient | the amount of attenuation per centimeter |
| Units of attenuation – | dB/cm |
| Formula for total attenuation (dB) | path length (cm) X atten. Coefficient (dB/cm) |
| Definition of attenuation coefficient | number of dB of attenuation that occur when a sound travels one centimeter |
| Remember this about Abe Lincoln | Abraham Lincoln was an attenuator: Abe Lincoln sold water. (air bone lungs soft tissue water) |
| If we do not know the attenuation coefficient | we should know that its half our frequency |
| Example of attien coeff | 2 dB/cm for every cm we are losing 2 dB off sound wave |
| What is the total attenuation of 2 dB at 4 cm – | 8 dB lost |
| Half value layer thickness | penetration depth or half boundry level |
| This is the distance that sound travels in a tissue that reduces the intensity of the sound to one half its original value | ½ value layer thickness |
| Units for half value thickness | cm(length) |
| 2 things that affect HVL | frequency and attenuation |
| HVL aka | penetration depth and half value level |
| Acoustic impedance | strength or amplitude and amount of reflected echoes |
| Air or air filled structure (lung) has a very ______ acoustic imperdance compared to tissue. – | low |
| Acoustic imped resistance to sound traveling in a ________. | medium |
| This is a characteristic of the medium through which sound travels. | acoustic impedance |
| Unit for Acc impedance | rayls |
| Formula for acoustic impedance | (rayls)=density(kg/m^3 X prop. Speed(m/s) or Z (impedance)=pc |
| Acoustic impedance increases when | the density increases and when the propagation speed increases. |
| Imperdance is ____, not measured. – | calculated |
| The reflection of an ultrasound wave depends upon a difference in the ________ ________ at the boundary between the two media. – | acoustic impedances |
| Two media, A and B, have the same prop. Speed. Medium A’s density is 10 percent higher than medium B’s. which medium has the highest impedance (resistance)? | Medium A |
| Normal incidence | PORNN |
| Pornn stands for – | perpendicular, orthogonal, right, normal, ninety (just means its hitting something at 90 degrees) |
| Oblique incidence | not at rt. Angles can be acute < 90 degrees or obtuse > 90 degrees |
| Intensity (W/cm^2) 3 kinds | incident int, reflected int., and transmitted intensity. |
| Incident intensity | the intensity that the sound wave possess at the instant prior to striking the boundary |
| Reflected intensity | the intensity that, after striking the boundary, changes direction and returns back in the direction it came from |
| Transmitted intensity | the intensity that, after striking a boundary, continues on in the same general direction that it was traveling |
| Incident (starting) intensity= | reflected intensity plus transmitted intensity (not energy lost or gained) |
| In clinical imaging, very little of the US intensity is reflected back to the transducer at the boundary between _____________________. – | Soft tissues the remainder is transmitted and continues to propagate in the forward direction. |
| Intensity reflection coefficient (IRC) is a – | percentage |
| Intensity transmission coeffiencent (ITC) is a – | percentage |
| Formula for IRC and ITC | IRC (percentage) + ITC (percentage)= 100 percent |
| _______ or more of a sound waves intensity is transmitted at a boundary between 2 soft tissues. | 99 percent |
| A greater percentage of the wave is reflected, approx. 50 percent, when sound is reflected off of a ______ /_______ interface | bone/soft tissue |
| Even more sound is reflected, approx. 99 percent, when sound is reflected off an _____/_______ interface | air/soft tissue |
| IRC percent + | (z1 |
| Refliection (spelled like this because) | reflection deals with impedance different impedances and Pornn |
| Refliection occurs only when | there are different impedances at the boundary between two media. |
| Transmission with normal incidence | when all intensity is transmitted ITC= transmitted intensity/incident intensity X 100 percent then 100 percent – intensity reflection coefficient |
| Reflection and transmission with oblique incidence | transmission and reflection may or may not occur with oblique incidence |
| 2 physical principles always apply to reflection with oblique incidences | conservation of energy and reflection angle (incident angle) |
| 100 percent = | reflected coefficient + transmission coefficient |
| Incident intensity formula (W/cm^2) = | reflected intensity + transmitted intensity |
| Reflection angle = | incident angle |
| Refraction | a change in direction of wave propagation when traveling from one medium to another. Associated with transmission (transmission with a bend) Oblique incidence |
| Refraction can only occur when what 2 things are present | 1. Different propagation speeds and 2. Oblique incidence (can’t occur with normal incidence or with identical speeds) |
| Snell’s law | refraction is described by this (sine transmission angle = prop speed 2/sine incident angle prop speed 1 |
| If propagation speed 2 is < than prop speed 1 then | transmission angle is < than the incident angle |
| If propagation speed 2 is >er than prop speed 1, then the transmission angle is | >er than the incident angle |
| Remember that refraction requires | two different prop speeds |
| No refraction, transmission angle = incident angle | speed 2=speed 1 |
| Transmission angle greater than incident angle | speed 2 is greater than speed 1 |
| Transmission angle less that incident angle – | speed 2 less than speed 1 |
| Reflection with normal incidence | different impedances required |
| Reflection with oblique incidence | we do not know! |
| Transmission | derive this from reflection information, use law of conservation |
| Refraction | oblique incidence and different speeds required |
| Intensity equals | power divided by area. |
| intensity is inversely related to | the area |
| If the area decreases then the intensity | will go up |
Created by:
hseratt