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Question 1

_____ is a wave that travels through a medium and carries energy from one place to another.

Answer 1

Sound

Question 2

What is ultrasound?

Answer 2

Ultrasound is defined as a sound wave with frequency above 20,000 cycles per second or hertz. One hertz means one event per second. The frequency of an ultrasonic wave is so high that it is inaudible to humans.

Question 3

What is audible sound?

Answer 3

Audible sound is defined as a sound wave that can be heard by man. The frequency range of audible sound is from 20Hz-20,000 Hz

Question 4

What is infrasound?

Answer 4

Infrasound is defined as a sound wave with a frequency less than 20hertz. The frequency of infrasound is so low that is is inaudible to the human ear.

Question 5

Two sound waves are traveling through an open house. One wave was produced by a soprano, while a baritone produced the other. Which sound wave travels faster?

Answer 5

Both waves travel at exactly the same speed. Only the characteristics of the medium through which sound travels determines the speed of sound. The speed of sound is not affected by the characteristics of the wave. Since both waves are traveling through the same medium they must have identical speeds.

Question 6

At what speed does sound travel thought the body?

Answer 6

It’s is important to know that the speed of sound in soft tissue is 1,540meters per sound. That is, all sound waves travel nearly one mile per second through the body.

Question 7

While traveling through the body, ultrasound waves encounter many different media, including bone, fat, lung, and soft tissue. Rank these four media according to their propagation speed, in increasing order.

Answer 7

1-lung
2-fat
3-soft tissue
4-bone
The propagation speed of the sound is slowest in air filled lungs,then fat, soft tissue and fastest in bone

Question 8

What is the frequency of a sound wave?

Answer 8

Frequency refers to the number of times per second that the particles in a medium oscillate back and forth as a sound wave propagates through the medium

Question 9

What units are used to report frequency?

Answer 9

Frequency is reported in the following units: per second, or hertz (Hz)

Question 10

What is the frequency range of the ultrasound waves used in diagnostic imaging?

Answer 10

The sound waves used in diagnostic imaging have a frequency range of 2 million to 10 million cycles per second (2-10Hz)

Question 11

What is the definition of wavelength?

Answer 11

Wavelength is the distance occupied by a single cycle in a wave, wavelength is measured in units of distance, most commonly in millimeters.

Question 12

________ is determined both by the frequency of the sound and the medium through which the sound travels

Answer 12

Wavelength

Question 13

What is the importance of wavelength in diagnostic imaging?

Answer 13

Wavelength is important because it helps to determine image quality. Shorter wavelengths produce higher quality images. The wavelengths of ultrasound traveling through soft tissue range from 0.2-0.8mm. There is a inverse relationship between frequency and wavelength, while lower frequency waves have longer wavelengths.

Question 14

What is the wavelength of 1MHz sound in soft tissue?

Answer 14

The wavelength of 1 MHz sound in soft tissue is 1.54mm

Question 15

________ is defined as the concentration of force within a particular area and is reported in units called ______.

Answer 15

Pressure
Pascals

Question 16

_____ is the amount of energy per second that is delivered by an ultrasound beam, it is measured in _____.

Answer 16

Power
Watts

Question 17

What is the meaning of the term intensity? Which units are used to measure intensity?

Answer 17

Intensity is the concentration of power within a particular area of the sound beam, intensity is measured in watts per square centimeter (watts/cm^2)

Question 18

What is a decibel?

Answer 18

A decibel(dB) is a unit that is used to measure the relative change in the intensity or power of a sound beam. A relative change compares the current intensity of the sound beam with its original intensity. For example of a sound beam’s power has increased by 50%, compared with its original power, this is relative change

Question 19

What is the meaning of 3 dB? What is the meaning of -3dB?

Answer 19

3dB means that the beam’s intensity has doubled, -3dB means the beams intensity is only half the original intensity.

Question 20

What is the meaning of 10dB? What is the meaning of -10dB?

Answer 20

10dB means that the beam’s intensity is 10 times greater. -10dB means that the beam’s intensity is only 1/10th of the original intensity.

Question 21

What is the pulse repetition frequency?

Answer 21

The pulse repetition frequency is defined as the number of sound pulses emitted by a transducer in one second.

Question 22

What units are used to measure the pulse repetition frequency?

Answer 22

The units used to measure PRF are persons or hertz.

Question 23

What determines the PRF of a diagnostic imaging system?

Answer 23

The PRF is determined by the maximum imaging depth or “depth-of-view” of the image. By selecting the maximum depth from which the ultrasound system will provide images, the sonographer in effect determines the PRF of the ultrasound system

Question 24

I hat is the pulse repetition period?

Answer 24

The pulse repetition period is the time span extending from the start of one sound pulse to the start of the next pulse. The pulse repetition period is composed of two durations: the duration of the pulse (the “on” “talking” or transmitting time) and the duration of the silence (the “off” “listening” or receiving time)

Question 25

What are the units of the PRP?

Answer 25

The units of the PRP are any measurements of time, such as milliseconds

Question 26

What determines the PRP of a diagnostic imaging system?

Answer 26

The PRP is determined by the sum of the talking and listening durations. The transmitting time is determined only by the ultrasound system and cannot be adjusted by the sonographer.

Question 27

What is the duty factor?

Answer 27

The duty factor is the fraction or percentage of time during which an ultrasound machine is transmitting sound or “talking”. A continuous-wave ultrasound system is always transmitting sound, and it’s duty factor is 1 or 100%. When a system is not in operation, and this not transmitting sound, it’s duty factor is zero or 0%

Question 28

What is the importance of the duty factor?

Answer 28

Duty factor is very important in the study of biological effects of the US

Question 29

What are the units of the duty factor?

Answer 29

The duty factor has no units and is expressed merely by percentage ranging from 0% to 100%

Question 30

Does the sonographer have the ability to alter the duty factor of an ultrasound?

Answer 30

The sonographer doe have ability to alter the duty factor by changing the depth-of-view or maximum imaging depth. When maximum imaging depth is shallow, the system is listening less, and therefore is transmitting a greater percentage of time(high duty factor) when the maximum imaging depth is deep, the system is listening more, and therefore has a low duty factor the greater the imaging depth, the lesser the duty factor.

Question 31

What is meant by reflection of an ultrasound wave?

Answer 31

Reflection is the redirection or turning back of an ultrasound wave toward the transducer.

Question 32

What causes reflection of a sound wave in the body?

Answer 32

Reflection occurs when a sound wave traveling through the body reaches a boundary between two media that have dissimilar characteristics, referred to the acoustic impedances. The degree of differences in the acoustic impedance between the two media at the boundary determines how much ultrasonic energy is reflected back toward the transducer. As a rule, when sound strikes a boundary between two types of soft tissue in the body, only a very small percentage of energy is reflected.

Question 33

Approximately how much of the energy contained in a sound wave is reflected at the boundary between muscle and blood?

Answer 33

When a sound wave strikes a boundary between muscle and blood, less than 1/10th of 1% of the energy is reflected. The remaining 99.9% continues to propagate in the forward direction. This is called transmission. This is small reflection indicates that the impedance of blood and muscle are only slightly different.

Question 34

Approximately how much of the energy contained in a sound wave is reflected at the boundary between muscle and bone?

Answer 34

When a sound wave strikes the boundary between muscle and bone, approximately 50% of the energy is reflected. The remaining 50% continues to transmit in the forward direction. This large reflection Indicated that the impedances of muscle and bone are significantly different.

Question 35

What is specular reflection?

Answer 35

Specular reflection refers to reflection that occurs when a wave strikes very smooth boundary. Speculation reflections are organized, regular, and predictable. One example of a specular reflection is that of a light wave being reflected off of a mirror.

Question 36

What is scattering?

Answer 36

Scattering is the reflection of a wave in many different directions after striking a boundary between two different media. Scattering is chaotic, disorganized, and random.

Question 37

What two factors affect the degree of scattering?

Answer 37

Scattering is more likely to occur when the boundary struck by the ultrasound wave is rough or irregular. The degree of scattering is likely to be especially significant when the size of the irregular structures is smaller than the wavelength of the ultrasound beam. This is referred to as Raleigh scattering
The second factor that determines the degree of scattering is the frequency of the sound wave. Scattering is more substantial when the frequency of a sound wave is high rather than low. therefore the degree of scattering would be greater than 8-MHz ultrasound beam than for a 3 MHz beam.

Question 38

Assume your have a sound wave travels through the body and strikes a boundary between two media.
What is the normal incidence? What other terms have a meaning similar to normal incidence?

Answer 38

Normal incidence refers to a sound wave, striking the boundary between two media and angle of exactly 90°. Similar terms used to describe normal incidence 1) perpendicular, 2) at right angles, 3) at 90°, or 4) orthogonal

Question 39

What is oblique incidence?

Answer 39

Oblique incident refers to a sound wave, striking the boundary between to media at an angle other than 90°. Any angle different from 90° (even and angle of 89.99°) Is oblique.

Question 40

What is attenuation?

Answer 40

Attenuation refers to the decrease in the strength of an ultrasound
wave as it travels through tissue.

Question 41

What three processes contribute to attenuation?

Answer 41

Three processes that contribute to attenuation are reflection,
scattering, and absorption. Absorption is the conversion of sound
energy into heat energy.

Question 42

How is attenuation related to the frequency of a sound wave?

Answer 42

Higher frequency sound is attenuated to a greater degree than low
frequency sound. This is why lower frequency transducers are more
successful at imaging structures that lie deep within the body than
higher frequency transducers.

Question 43

Compared with soft tissue, is ultrasound attenuated more or less
when it travels through air?

Answer 43

Compared with soft tissue, ultrasound experiences enormously more
attenuation when it travels through air.

Question 44

Compared with soft tissue, is ultrasound attenuated more or less
when it travels through bone?

Answer 44

Compared with soft tissue, ultrasound experiences much more
attenuation when it travels through bone because bone absorbs
ultrasonic energy. However, attenuation in bone is less than in air.

Question 45

Compare with soft tissue, is ultrasound attenuated more or less
when it travels through lung?

Answer 45

Compared with soft tissue, ultrasound experiences much more
attenuation when it travels through lung because lung scatters
ultrasonic energy. However, attenuation in lung is less than in air.

Question 46

Compared with soft tissue, is ultrasound attenuated more or less
when it travels through water?

Answer 46

Compared with soft tissue, ultrasound experiences substantially less
attenuation when it travels through water.

Question 47

Although low-frequency transducers are useful for obtaining images at substantial depths, what is their main disadvantage?

Answer 47

It is indeed true that low-frequency transducers are more successful at imaging structures at greater depths, compared with high-frequency transducers. However, higher frequency transducers generally provide images of a superior quality. This is due to higher frequency waves having shorter wavelengths.

Question 48

What is the role of the sonographer in relation to this tradeoff?

Answer 48

The role of the sonographer in relation to this tradeofl’ is to strike a balance between the depth that the ultrasound beam needs to travel to image the target area and the quality of the resultant image. As a rule, this is accomplished by using the highest frequency transducer that can successfully image the structure of clinical interest. However, when a higher frequency transducer is unsuccessful in imaging a structure located deep within the body, the only alternative may be to use a low frequency transducer at the expense of image quality

Question 49

What is a transducer?

Answer 49

A transducer is any device that converts one form of energy into another. Examples of transducers include a light bulb (converts electrical energy into heat and light), and a stereo speaker (converts electrical energy into sound).

Question 50

What is the piezoelectric effect?

Answer 50

The piezoelectric effect is the process by which pressure energy is converted into electrical energy. Ultrasound transducers use piezoelectric crystals to produce images. When a sound wave reflects off a structure in the body, the wave returns to the transducer and strikes piezoelectric crystals. The crystal vibrates, resulting in an electrical signal. The ultrasound system then processes the electrical signal into an image.
During transmission, electrical signals produced by the ultrasound system excite the piezoelectric material in the transducer and create a sound wave. This is sometimes called the reverse piezoelectric effect.

Question 51

What is the Curie temperature or Curie point?

Answer 51

Materials that possess piezoelectric properties are sensitive to high temperatures. If piezoelectric material is heated to temperatures in excess of the Curie temperature or Curie point, it will permanently lose its piezoelectric properties. The Curie temperature is in the range of 300° to 400° C.
Note: Heat damage to a transducer may occur even when the transducer’s temperature is raised to levels far below that of the Curie point. Glues and other materials in the transducer other than piezoelectric material may be damaged when exposed to moderately high temperatures. Therefore, ultrasound transducers should never be sterilized using either moist heat (autoclaving) or dry heat.

Question 52

What are the functions of the active element of an ultrasound transducer?

Answer 52

The active element of an ultrasound transducer has two functions.
During the transmission phase, when the transducer is producing an acoustic pulse, an electrical signal from the ultrasound system travels down the wire and strikes the active element. Because of its piezoelectric properties, the crystal vibrates and creates an acoustic wave. During the reception phase, an ultrasound pulse that reflects off of a structure in the body returns to the transducer and strikes the active element. The active element is deformed, and an electrical signal is produced. The electrical signal travels down the wire (component D in previous question) and returns to the ultrasound system where the signal is processed, resulting in the display of an anatomic image.

Question 53

What material is most commonly used to construct the active element?

Answer 53

Most active elements are fabricated from a material known as lead zirconate titanate or PZT.

Question 54

What is the function of the matching layer of an ultrasound transducer?

Answer 54

If a sound pulse was allowed to travel from the active element of a transducer directly to the skin, a giant reflection called the “main bang” would occur at the boundary between the active element and the skin. Such a large reflection would occur because of the dramatic difference in the acoustic impedances of these two structures. (Remember that the difference in the acoustic impedances of two media at the boundary determines the degree of reflection.)
The function of the matching layer, which is located in front of the active element, is to minimize the main bang. This is accomplished by constructing the matching layer out of material that has an acoustic impedance in between that of the active element and the skin. Thus, the matching layer permits more sound energy to travel into the body during transmission and reflected out of the body during reception.
Note: The impedance of gel is between those of the matching layer and the skin. This will lessen the effects of the impedance difference between the matching layer and the skin, its use will further minimize the main bang.

Question 55

Example: The impedance of PZT (lead zirconate titanate) is approximately 30,000,000 rayls, and the impedance of skin is about 1,600,000 rayls. (A rayl is a unit used to measure impedance.) For the purpose of ultrasonic imaging, which of the following represents the optimal choice for the impedances of the matching layer and the ultrasound gel?
A. Matching layer, 14,000,000 rayls. Gel, 25,000,000 rayls.
B. Matching layer, 20,000,000 rayls. Gel, 15,000,000 rayls.
C. Matching layer, 14,000,000 rayls. Gel, 45,000,000 rayls.

Answer 55

The answer is “B”. In order for the maximum amount of sound energy to be transmitted from one medium to another, the acoustic impedances of adjacent media should be as similar as possible. In this example, maximum sound transmission will occur when the impedances of all the media, from the active element to the skin, are in decreasing order. “B” is the appropriate choice because the impedances from the active element to the matching layer to the gel and, finally, to the skin decrease sequentially.

Question 56

What is the function of the damping material of an ultrasound transducer?

Answer 56

The damping material or backing material prevents the active element from ringing, and absorbs much of the acoustic energy produced by the active element. Thus, the duration of the acoustic pulse produced by the PZT is shortened. Shortening the pulse improves the quality of the images produced by an ultrasound system.

Question 57

What material is used to fabricate the damping material?

Answer 57

Damping material is often made of tungsten fibers embedded into an epoxy mixture. The epoxy mixture adheres to the backside of the active element. The active element is sandwiched between the damping material and the matching layer.