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ARDSM SPI EXAM Q&R review (MANSOOR KAHAN BOOK0 > Unit 3 > Flashcards

Unit 3 Flashcards

1
Q

What is propagation of sound?

A

The propagation of sound is the process by which sound waves travel through mediums such as air, water and soft tissue etc.

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2
Q

What the effects of soft tissue on ultrasound are called?

A

The effects of soft tissue on ultrasound are called acoustic propagation properties.

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3
Q

The propagation speed of sound in a medium is determined by what factors?

A

density and stiffness of the medium
The propagation speed of sound in a particular medium is determined by density and stiffness of that medium, for example density and stiffness of gas, liquids and solids is different therefore the speed of sound will be different in these three mediums.

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4
Q

What is density and what is the relationship between the density and the propagation speed of sound?

A

Answer: Density is the relative weight of a material. When equal volumes of different materials are compared the dense material will weigh the most.
Density and propagation speed of sound are inversely related. As density of a medium increases, the propagation speed of sound in that medium decreases.

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5
Q

As a result of decreasing compressibility and decreasing density the propagation speed increases?

A

Answer: True
Density and Stiffness of a particular medium determines the speed of sound in that particular medium. The propagation speed of sound increases in a medium with decreased compressibility and decreased density.
Compressibility and stiffness are opposite of each other. As compressibility decreases the stiffness increases. As stiffness of a medium increases, the propagation speed of ultrasound in that medium increases.
Density and propagation speed are inversely related to each other. As the medium becomes denser, the propagation speed of ultrasound in that medium decreases.

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6
Q

What is the average propagation speed of ultrasound in soft tissue at 5 MHz?

A

Answer: The average propagation speed of ultrasound in soft tissue is 1540 meters per second, 1.54 mm/us or 154,000 cm/sec or 1.54 km/s.
The sound waves, regardless of the frequency travel at the same speed through any specific medium. For example sound with frequency of 7 MHz and sound with frequency of 2.5 MHz will travel at the same speed through the same medium.

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7
Q

The propagation speed of continuous wave ultrasound is 1.54 km/sec. The wave is then pulsed with duty factor of 25%. What is the new propagation speed?

A

1.54 km/sec
There is no difference in the propagation speed of sound whether the wave is pulsed or continuous wave. The propagation speed of sound is determined by the properties of medium which are stiffness and density.
So the propagation speed of sound will be same 1.54 km/sec with pulsed ultrasound.

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8
Q

Which of the following has a propagation speed closest to soft tissue? air, bone, fat, muscle

A

Answer: muscle
The propagation speed of sound in muscle is closest to soft tissue.

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9
Q

Put in decreasing order of propagation speed gas, liquid and solid?

A

Answer: solid, liquid and gas
The propagation speed of sound is higher in solids such as steel and slower in gases such as air.

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10
Q

Put in increasing order of propagation speed bone, water, and air?

A

Answer: air, water, bone
The propagation speed of sound is slower in air and faster in bone.

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11
Q

Which artifact is created by sound moving through a medium with a propagation speed less than soft tissue?

A

Answer: vertical misregistration
If the sound beam passes from a medium of higher propagation speed into a medium of a lesser propagation speed, then the distance will be calculated more than the actual distance and the reflectors will be placed too deep which is also called vertical misregistration.
Propagation speed error artifacts are also called range error artifacts, and range ambiguity artifacts.

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12
Q

Propagation speed of sound can be recorded with which of the following units?

a) mph
b) mm/usec
c) km/sec
d) all of the above

A

Answer: d. all of the above
Propagation speed of sound can be recorded in mph, mm/usec, and km/sec as each is a valid unit of speed.

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13
Q

What is the propagation speed of a 3 MHz sound wave in soft
tissue?

a) 1,450 km/sec
b) 1,450 m/s
c) 1.54 mm/us
d) 1.54 m/s

A

Answer: c. 1.54 mm/us
The propagation speed of sound is determined by the medium. The frequency does not affect the speed of sound.
The average propagation speed of ultrasound in soft tissue is 1540 meters per second, or 1.54 mm/us or 154,000 cm/sec or 1.54 km/s.

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14
Q

The propagation speed of sound traveling through bone is———— soft tissue.
a) lower than
b) higher than
c) equalto
d) cannot be determined

A

Answer: b. higher than
The propagation speed of sound is affected by two key properties of the medium it travels through: density and stiffness (bulk modulus or compressibility).
The reason the propagation speed of ultrasound is higher in bone than in soft tissue is due to to the stiffness of the bone.
The high stiffness of bone compared to soft tissue is the primary reason why the propagation speed of ultrasound is significantly higher in bone.
The propagation speed of sound in bone is about 3,000-4,000 m/s

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15
Q

The propagation speed of sound traveling through a mass is ———— soft tissue.
a) lower than
b) higher than
c) equalto
d) cannot be determined

A

Answer: a. lower than
The propagation speed of sound traveling through a mass is generally lower than soft tissue.
This is because a mass or abnormal tissue often has different characteristics, such as increased density or altered elasticity (stiffness), which can affect how sound waves travel through it. In most cases, the higher density and possibly lower stiffness of a mass slow down the propagation speed of sound compared to normal soft tissue.
The exact propagation speed can vary depending on the type and composition of the mass.

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16
Q

The propagation speed of an ultrasound wave through lung tissue is ———— soft tissue.

a) slower than
b) faster than
c) equal
d) cannot be determined

A

Answer: a. slower than
The propagation speed of an ultrasound wave through lung tissue is slower than in soft tissue. Lung tissue contains a large amount of air, and sound waves travel much more slowly through air compared to soft tissue. Air has a very low density and stiffness compared to other biological tissues, which causes the ultrasound waves to slow down. The average speed of sound in air is about 330 m/s.

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17
Q

What is the speed of sound in tendon?
a) 1,200 m/s
b) 1,540 m/s
c) 5,450 m/s
d) 1,754 m/s

A

Answer: d. 1,754 m/s
The speed of sound in tendon is higher than in soft tissue because tendons are more stiff (less compressible) and somewhat denser compared to regular soft tissues like muscles or organs. The higher speed of sound in tendons is primarily due to their greater stiffness.
The speed of sound in tendon is around 1,700-1,850 meters per second (m/s).

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18
Q

List in increasing order of propagation speeds.
a) solid, liquid, gas
b) gas, liquid, solid
c) gas, solid, liquid
d) liquid, solid, gas

A

Answer: b. gas, liquid, solid
This is because the stiffness (ability to resist compression) increases from gases to liquids to solids, which directly affects how fast sound waves can travel through each medium. Sound travels slowest in gases (due to low density and stiffness), faster in liquids, and fastest in solids (due to high stiffness).

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19
Q

What is the speed of sound in air?
a) 2,710 m/s
b) 330 m/s
c) 230 m/s
d) 1,540 m/s

A

Answer: b. 330 m/s
The speed of sound in air is 330 m/s.

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20
Q

The speed at which a sound wave travels through a medium is determined by:
a) the properties of sound waves only
b) properties of both sound waves and medium
c) properties of medium only
d) all of the above

A

Answer: c. properties of medium only
The speed at which a sound wave travels through a medium is determined by properties of medium only.
The speed at which a sound wave travels through a medium is determined by two key properties:
Stiffness (or Bulk Modulus) and Density

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21
Q

What are the two properties of medium which determine propagation speed of sound in a given medium?
a) viscosity and density
b) density and stiffness
c) elasticity and stiffness
d) stiffness and impedance

A

Answer: b. density and stiffness
Density and stiffness are the two properties of medium which determine propagation speed of sound in a given medium.
Sound travels faster in materials that are stiffer and less dense (such as solids) and slower in materials that are less stiff and more dense (like gases). The combination of stiffness and density determines the overall speed of sound in any medium.

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22
Q

Which of the media has the slowest propagation speed?
a) low stiffness and low density
b) low compressibility and low stiffness
c) high density and high elasticity
d) low density and high stiffness

A

Answer: c. high density and high elasticity

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23
Q

Which two terms describe the same property as compressibility?
a) stiffness and elasticity
b) elasticity and impedance
c) density and stiffness
d) density and viscosity

A

Answer: a. stiffness and elasticity
Stiffness and elasticity are the two terms that describe the same property as compressibility.

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24
Q

When the elasticity of a medium is high, the medium is high?
of the
a) viscosity
b) compressibility
c) propagation speed
d) stiffness

A

b. compressibility
Elasticity refers to the ability of a medium to return to its original shape after being deformed, which is closely related to how compressible the medium is.

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25
Two sound waves with frequencies of 5 MHz and 2.5 Mhz, travel to a depth of 10 cm in a medium and then reflect back to the surface of the body. Which sound wave arrives first at the surface of the body? a) 2.5 MHz wave b) 5 MHz wave c) neither d) cannot be determined
Answer: c. neither The frequency of sound does not affect the propagation speed in a given medium. The propagation speed of sound is determined by the properties of the medium (such as stiffness and density), not by the frequency of the sound wave.
26
Q123. If the sound travels at **exactly 1,540 m/sec** in a particular medium, then the medium————? a) must be soft tissue b) may be soft tissue c) cannot be soft tissue
Answer: b. may be soft tissue This speed is the average propagation speed of sound in human soft tissues, commonly used as a standard reference in medical ultrasound.
27
If the sound does not travel at 1,540 m/sec in a medium, then the medium————? a) must be soft tissue b) may be soft tissue c) cannot be soft tissue
Answer: c. cannot be soft tissue If sound does not travel at 1,540 m/sec in a medium, then the medium is not soft tissue or differs in density and stiffness from typical soft tissue. Other tissues or materials, like bone, air, or fluids, have distinct propagation speeds that are either higher or lower than 1,540 m/sec due to variations in their physical properties.
28
The propagation speeds of ultrasound waves in liver, kidney, muscle, and blood are —————? a) exactly the same b) very similar to each other c) vastly different
Answer: b. very similar to each other The propagation speeds of ultrasound waves in different biological tissues are fairly similar but can vary slightly depending on the specific properties of each tissue. Here are the approximate propagation speeds for the different tissues: Liver: ~ 1,540 m/s Kidney: ~ 1,560 m/s Muscle: ~ 1,580 m/s Blood: ~ 1,570 m/s These values are close to the average speed of sound in soft tissue, which is typically 1,540 m/s. The small differences are due to variations in tissue density and stiffness.
29
Two ultrasound waves travel through the same medium. Frequency of one ultrasound wave is 2 MHz and the frequency of other wave is 5 MHz. Which ultrasound pulse has a longer wavelength? a) 5 MHz pulse b) 2 MHz pulse c) cannot be determined d) neither pulse
b. 2 MHz pulse The ultrasound wave with the lower frequency has the longer wavelength. The wave with a frequency of 2 MHz will have a longer wavelength compared to the wave with a frequency of 5 MHz. This is because wavelength and frequency (f) are inversely related in a given medium.
30
Two ultrasound pulses travel through the same medium. Frequency of one ultrasound wave is 3 MHz and the frequency of other wave is 5 MHz. Which ultrasound pulse has a lower propagation speed? a) 5 MHz pulse b) 3 MHz pulse c) cannot be determined d) neither pulse
d. neither pulse The speed at which a sound wave travels through a medium is determined by properties of medium only. The sound waves with different frequencies travel at the same speed through a particular medium.
31
Two ultrasound pulses travel through the same medium. Frequency of one ultrasound wave is 2 MHz and the frequency of other wave is 5 MHz. Which ultrasound pulse has a longer period? a) 5 MHz pulse b) 2 MHz pulse c) cannot be determined d) neither pulse
Answer: b. 2 MHz pulse The ultrasound wave with the lower frequency has a longer period. The period is inversely related to frequency, the lower frequency wave (2 MHz) will have a longer period compared to the higher frequency wave (5 MHz). Thus, the 2 MHz ultrasound wave will have a longer period.
32
Two ultrasound pulses travel through the same medium. Frequency of one ultrasound wave is 2 MHz and the frequency of other wave is 5 MHz. Which ultrasound pulse has the lowest power? a) 5 MHz pulse b) 2 MHz pulse c) cannot be determined d) neither pulse
Answer: c. cannot be determined The frequency of an ultrasound wave does not directly determine its power. Power depends on the intensity of the ultrasound pulse, which is influenced by the amplitude of the wave and the settings of the ultrasound machine, not the frequency. Thus, without additional information about the amplitudes or intensities of the waves, we cannot definitively say which pulse has the lower power based on frequency alone. The relationship between power and frequency is not direct.
33
Two ultrasound pulses travel through the same medium. Frequency of one ultrasound wave is 2 MHz and the frequency of other wave is 5 MHz. Which ultrasound pulse has a longer spatial pulse length? a) 5 MHz pulse b) 2 MHz pulse c) cannot be determined d) neither pulse
Answer: b. 2 MHz pulse The ultrasound pulse with the lower frequency will have the longer spatial pulse length (SPL), Spatial Pulse Length (SPL) is the physical length of a pulse in space and is given by the formula: SPL = wavelength x number of cycles in the pulse Since the wavelength is inversely related to the frequency (i.e., lower frequency waves have longer wavelengths), and both pulses travel through the same medium (so the speed of sound is constant), the pulse with the lower frequency (2 MHZ) will have a longer wavelength and, consequently, a longer SPL.
34
What is attenuation?
Answer: **Attenuation is the decrease in amplitude, intensity, and power of ultrasound wave as it travels through a medium**. As ultrasound wave travels through the body, it continuously loses energy. As a result of attenuation, the returning echoes from deeper structures become weaker than echoes returning from superficial structures. The factors that contribute to attenuation are reflection, scattering, and absorption.
35
What are the factors which determine attenuation?
Answer: Attenuation refers to the gradual loss of energy or weakening of the sound wave as it travels through a medium. Several factors determine the amount of attenuation in ultrasound. The primary factors that determine attenuation are the **frequency of the sound wave,** the **distance traveled,** the properties of the medium, and interactions like absorption, scattering, and reflection.
36
What is the effect of frequency and distance on attenuation?
Answer: Frequency and distance are directly related to the attenuation. Attenuation of sound increases when frequency increases or path length increases. Higher frequency sound waves attenuate more compared to lower frequency ultrasound waves. The sound wave will also attenuate more if it has to travel deeper in the body.
37
The role of sound attenuation in tissue is expressed in terms of.
Answer: The role of sound attenuation in tissue is typically expressed in terms of the **attenuation coefficient**. The attenuation coefficient quantifies how much a sound wave's intensity decreases as it travels through a medium, and it is usually measured in decibels per centimeter (dB/cm). **This represents the amount of attenuation (loss of sound intensity) per centimeter of travel in the medium**. It depends on the frequency of the sound wave and the type of tissue it passes through. **Higher frequencies have larger attenuation coefficients.**
38
Which has the greatest amount of attenuation? muscle, water, fat, bone?
Answer: bone Bone has the greatest amount of attenuation compared to muscle, water and fat. Bone attenuates sound the most, while water attenuates it the least.
39
An ultrasound wave travels through two media and has attenuation of 3dB in the first and 5 dB in the second. What is the total attenuation?
Answer: 8dB Total attenuation = 3 dB + 5 dB Total attenuation = 8 dB
40
What is the attenuation coefficient?
Answer: **Attenuation coefficient is the amount of attenuation per centimeter that a sound wave undergoes while traveling through a medium**. Attenuation coefficient remains constant, regardless of the actual path length. The attenuation coefficient helps determine how quickly sound energy is lost as it travels through different tissues or materials and is an important factor in ultrasound imaging. For soft tissue, the attenuation coefficient is roughly 0.5 dB/cm/MHz. So, for a 2 MHz wave, the attenuation would be approximately 1 dB/cm, while for a 5 MHz wave, it would be around 2.5 dB/cm.
41
What is the approximate attenuation coefficient of 1MHz ultrasound in soft tissue?
Answer: 0.5 dB/cm Attenuation Coefficient is the attenuation per unit length of sound wave travels (amount of attenuation per centimeter). Attenuation Coefficient for soft tissue is approximately half of the operating frequency of the transducer. For every centimeter per megahertz there is approximately 0.5 dB of attenuation. ( 0.5 dB/ cm/ MHz
42
What is total attenuation?
Total attenuation is the total amount of sound that has been attenuated at a given path length. total attenuation = attenuation coefficient x path length This expresses how much the sound wave's intensity decreases after traveling a certain distance through tissue. It is typically expressed in decibels (dB) and represents the cumulative loss of sound energy due to absorption, scattering, and reflection over a specific distance.
43
What is half value layer?
Answer: **The half value layer is the thickness of tissue where sound intensity is reduced to half of its original value due to attenuation**. Half value layer measured in centimeters (cm), representing the thickness of the tissue or material required to achieve this reduction.
44
A sound beam travels 10 cm in soft tissue. The attenuation coefficient is 2 dB/cm. What is the **total attenuation** that the sound beam experiences?
45
A sound beam travels 10 cm in soft tissue. The attenuation coefficient is 2 dB/cm. What is the total attenuation that the sound beam experiences?
Answer: 20 dB
46
In soft tissue, attenuation coefficient is determined by ————?
Answer: Frequency In soft tissue, attenuation coefficient is determined by the frequency of sound only. In soft tissue, the attenuation coefficient (dB/cm) is approximately half of the frequency measured in MHz. Attenuation coefficient = frequency/2 If the operating frequency of a transducer is 5 MHz, then the attenuation coefficient will be approximately 2.5 dB/cm.
47
What is half value layer?
Answer: The half value layer is the thickness of tissue where sound intensity is reduced to half of its original value. The half value layer is the thickness of tissue where sound attenuates by 3dB. Half value layer depends upon medium and frequency.
48
What is Impedance?
Answer: Impedance (denoted as Z) is the resistance that a material offers to the propagation of sound. **It determines how easily a sound wave can travel through a medium.** Impedance is the acoustic resistance to sound traveling in a medium. **The impedance depends on the density and the propagation speed of the medium**. The impedance is calculated by multiplying the density of a material by the propagation speed of that material. **impedance = density x propagation speed** The unit of impedance is Rayls (Z).
49
What is the impedance of soft tissue?
Answer: The impedance of soft tissue is in the range of **1.5 - 2.5 million Rayls**. The impedance of soft tissue is approximately 1.54 million Rayls (or 1.54 x 10^6 Rayls). The impedance value of soft tissue is crucial for understanding how ultrasound waves behave when they encounter different types of tissues (such as muscle, fat, or bone). It affects the amount of reflection and transmission of the ultrasound waves, which in turn influences image quality. Comparing the impedance of soft tissue with that of other materials (like air, bone, or fat) helps in optimizing ultrasound imaging techniques and improving diagnostic accuracy.
50
What is Reflection of ultrasound wave?
Answer: Reflection is the redirection or turning back of the ultrasound wave. **Reflection occurs when sound wave strikes a boundary between two media and a portion of the ultrasound sound wave is reflected back to the transducer**. The reflection of an ultrasound pulse occurs at the interface, or boundary, between two media with different acoustic impedances. The degree of differences in the acoustic impedances between the two media at the boundary determines how much of the ultrasound wave will be reflected back to the transducer. Only a portion of the ultrasound pulse is reflected back, the rest of the ultrasound pulse is transmitted into the body.
51
The most likely amount of reflection at a boundary between soft tissues is 1%.
Answer: True 1% or less of the incident ultrasound intensity is reflected at a soft tissue boundary between different biologic media such as blood and muscle.
52
the impedances or acoustic resistance to sound traveling in a medium, becomes different at an interface, the reflection increases.
Answer: True If there is a difference in impedance at an interface, some of the sound will be reflected. The greater the difference in impedances at an interface, the greater the reflection of ultrasound waves will occur.
53
An ultrasound wave strikes a boundary between two media at a 90-degree angle. The propagation speeds of the media are identical. The densities of the two media are different. Will reflection occur?
Answer: The reflection will occur. Impedance is calculated by: Impedance = density x propagation speed Z = px c Two media have same propagation speeds but they have different densities. Impedances of both media will be different due to different densities. With different impedances of medium and 90-degree angle incidence, reflection will occur.
54
The propagation speed of sound in the two media is different. The impedances of the two media are identical. A sound pulse strikes the boundary between these two media with normal incidence. Will the reflection occur?
Answer: The reflection will not occur. **Reflection only occurs when the sound wave strikes the boundary between two media with different impedances**. Different propagation speeds of sound do not affect the reflection of sound. In this case no reflection will occur because both media have same impedances though they have different propagation speeds of sound.
55
What is specular reflection?
Answer: Specular reflections occur when a boundary between two media is smooth. A portion of the sound wave is reflected in one direction and in an organized manner. The diaphragm, liver capsule and gallbladder walls are examples of specular reflectors. **Specular reflection occurs when sound waves encounter a large, smooth surface, and the wave is reflected in an organized, single direction.**
56
What is scattering?
Answer: **Scattering is redirection of sound waves in many directions** after striking a **rough boundary** between the two media. **Scattering is disorganized and random.**
57
What is diffuse scattering?
Answer: Diffuse Scattering is the redirection of the sound beam in more than one direction after it **strikes a rough or small boundary between the two media**. The **wavelength of the striking ultrasound wave is larger than the reflecting surface.** Diffuse scattering is seen with liver parenchyma.
58
What is Rayleigh scattering?
Answer: **Rayleigh scattering is seen when the reflector is much smaller than the wavelength of the ultrasound wave**. The ultrasound beam is diverted in all directions. **Red blood cells are an example of a Rayleigh** scatterer. Rayleigh scattering is related to frequency. **Higher frequency sound waves undergo more Rayleigh scattering.**
59
What is refraction and what conditions are necessary for refraction to occur at a boundary between two media?
Answer: Refraction is the transmission of sound wave with oblique incidence, also called Snell's Law. Refraction only occurs when there is an **oblique incidence of sound wave at the boundary between the two medium and both medium have different propagation speeds.**
60
What is normal incidence?
Normal incidence occurs when ultrasound wave strikes the boundary between two media at 90° angle. The striking sound wave is directed back to the transducer. Normal Incidence is also known as perpendicular incidence, orthogonal, right angle and ninety degrees.
61
What is oblique Incidence?
Answer: Oblique incidence occurs when the sound beam strikes a boundary at an angle different than 90° Reflection occurs with oblique incidence, but the sound wave is directed away from the transducer. The angle of incidence is equal to the angle of reflection. angle of incidence = the angle of reflection
62
A sound wave is travelling from medium A into medium B and strikes the boundary at 35 degrees angle. The medium A has the propagation speed of 1420 m/sec. The medium B has the propagation speed of 1620 m/sec. What will be the angle of transmission, greater than angle of incidence which is 35 degrees or smaller than angle of incidence?
Answer: The angle of transmission will be greater than angle of incidence (more than 35 degrees). With refraction, when the propagation speed of the medium that the sound is entering is greater than the propagation speed of the medium that the sound is currently in, the angle of transmission will be greater than the incident angle.
63
A sound wave is travelling from medium A into medium B and strikes the boundary at 55 degrees angle. The medium A has the propagation speed of 1620 m/sec. The medium B has the propagation speed of 1420 m/sec. What will be the angle of transmission, greater than angle of incidence which is 55 degrees or smaller than angle of incidence?
Answer: The angle of transmission will be smaller than angle of incidence (less than 55 degrees). With refraction, when the propagation speed of the medium that the sound is entering is less than the propagation speed of the medium that the sound is currently in, the angle of transmission will be smaller than the incident angle.
64
A sound wave is traveling from medium A to medium B. Medium A has a propagation speed of 1,620 m/sec and an impedance of 1.74 MRayls. Medium B has a propagation speed of 1,420 m/sec and an impedance of 1.47 MRayls. The angle of incidence is 45 degrees. What will be the angle of reflection?
Answer: The angle of reflection will be equal to angle of incidence that is 45 degrees. With oblique incidence, the angle of reflection is always equal to the angle of incidence. All other information regarding the propagation speeds and impedances are irrelevant for this question.
65
An ultrasound wave is leaving soft tissue and entering into fat with a 75-degree incident angle. What will be the angle of transmission?
Answer: The angle of transmission will be less than the incident angle that is less than 75 degrees. **The propagation speed of sound in fat is less than propagation speed** of sound in soft tissue. With refraction, when the propagation speed of the medium that the sound is entering is less than the propagation speed of the medium that the sound is currently in, the angle of transmission will be smaller than the incident angle. Therefore, the angle of transmission will be less than the angle of incidence because sound wave is travelling from soft tissue into fat.
66
What is Range Equation?
Answer: Range Equation describes **the time that it takes for an ultrasound pulse to travel from the transducer to the reflector and then return back to the transducer.** The range equation is used in the ultrasound system to determine the depth of the reflector.
67
What does range equation relate to?
Answer: The range equation relates reflector distance to time of flight and propagation speed. distance to reflector =1/2 x propagation speed x go return time There are three components in the range equation distance from the reflector time of flight propagation speed
68
How does the ultrasound machine calculate the depth of a reflector?
Answer: The ultrasound machine calculates the depth of a reflector by measuring the **go return time or time of flight **of an ultrasound pulse. When an ultrasound pulse is transmitted, a digital clock starts. Upon receiving the reflected echo, the ultrasound machine measures the elapsed time between the transmission of the ultrasound pulse and reception of the reflected echo and estimates the reflector depth. This calculation is performed based on range equation. The range equation is: reflector depth = 1/2 x propagation speed x pulse round trip time The ultrasound machine assumes that the propagation speed of sound in soft tissue is 1540 m/s.
69
What is 13 microsecond rule?
Answer: An ultrasound pulse travels 1 cm in the body from the transducer and returns back to the transducer in 13 usec. This is called 13 microsecond rule. It will take 26 usec for ultrasound pulse to travel 2 cm and return back to the transducer. Similarly, it will take 39 usec for ultrasound pulse to travel 3 cm and return back to the transducer. In soft tissue, every 13 usec of time means the reflector is 1cm deep. When the total time of flight is: 13 sec - the reflector is 1 cm deep in the body 26 usec - the reflector is 2 cm deep in the body 39 usec - the reflector is 3 cm deep in the body 52 usec - the reflector is 4 cm deep in the body
70
If a reflector is moved twice as far away from the transducer, how will this affect the time of flight of a sound pulse?
Answer: The time of flight of the sound pulse will also be doubled. If the distance to a target is doubled, the time of flight for a pulse to travel to the target and back is also doubled.
71
A pulse is emitted by a transducer and is traveling in soft tissue. The go-return time or time of flight, of a sound pulse is 130 microseconds. What is the reflector depth? a) 10 cm b) 10 mm c) 10 m d) 130 mm e) 13 cm
Answer: a. 10 cm Range Equation describes the time that it takes for an ultrasound pulse to travel from the transducer to the reflector (the body tissue), and return to the transducer (the go-return time). Remember the 13 microsecond rule: In soft tissue, every 13 usec of time means the reflector is 1cm deep.
72
A sound wave travels 39 sec to a reflector in soft tissue. How far is the reflector?
Answer: 3.0 cm Explanation: Remember the 13 microsecond rule: In soft tissue, every 13 sec of time means the reflector is 1cm deep.
73
A reflector is 4.0 cm away from the transducer. How long does it take for sound to get back to the transducer?
Answer: 52 sec Explanation: Remember the 13 microsecond rule: In soft tissue, every 13 usec of time means the reflector is 1cm deep.

ARDSM SPI EXAM Q&R review (MANSOOR KAHAN BOOK0 (12 decks)

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