1.ULTRASOUND PHYSICS ELEMENTARY PRINCIPLES

Question 1

What is Sound?

Answer 1

Answer: Sound is a mechanical wave that propagates in a longitudinal direction and carries energy from one place to other through an elastic media. Sound waves propagate by oscillatory motion of the particles in the medium, creating alternating regions of compressions and rarefactions.

Question 2

What is audible sound?

Answer 2

Answer: Audible sound refers to sound waves that can be heard by humans. The frequency range of audible sound is between 20 Hz to 20,000Hz

Question 3

What is Ultrasound?

Answer 3

Answer: Ultrasound is defined as a sound wave with a frequency greater than 20,000 Hertz or 0.02 MHz.

Ultrasound is inaudible to humans. Its frequency is higher than human hearing range which is 20 to 20,000 Hertz.

Question 4

What is Infrasound?

Answer 4

Answer: Infrasound is defined as a sound wave with a frequency lower than 20 Hertz.

Infrasound is inaudible to humans. Its frequency is lower than human (hearing range which is 20 to 20,000 Hertz.

Infrasound waves travel at the same speed as waves with higher frequencies. Infrasound waves attenuate at a lesser rate compared to higher frequency sound waves.

Question 5

Is there any difference between the behavior of ultrasound waves and audible sound waves?

Answer 5

Answer: There is no difference in the fundamental behavior of ultrasound waves and audible sound waves. Both follow the same physical principles.
All sound waves, whether audible or ultrasound, travel at the same speed in a given medium.

Question 6

What is a longitudinal wave?

Answer 6

Answer: A longitudinal wave is a wave in which particles vibrate back and forth in the same direction that the wave is propagating or travelling.
For example, a wave is traveling from North towards the South at a speed of 5 miles per hour. The direction of motion of particles within the wave will be from North to South and then from South to North back and forth.

Question 7

What is a transverse wave?

Answer 7

Answer: A transverse wave is a wave in which particles vibrate in a direction that is perpendicular to the direction in which wave travels itself.
A water wave is a transverse wave. The wave travels along the surface of the water, whereas a boat floating on top of the water moves up and down as the wave passes.
A transverse wave is a wave in which the direction of propagation of wave is perpendicular to the direction of particles motion in the wave.

Question 8

Sound is what kind of wave?

Answer 8

Answer: Sound is a mechanical wave and a longitudinal wave. The molecules of the medium vibrate and transfer sound energy from one place to another. Sound needs a medium to travel it cannot travel in the vacuum.

Question 9

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

Answer 9

Answer: The average velocity 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 You must memorize these different variations of speed of sound in soft tissue.
You must memorize these different variations of speed of sound in soft tissue.

Question 10

What are Acoustic Variables?

Answer 10

Answer: Acoustic variables are properties that change as a sound wave propagates through a medium. They help identify sound waves.
The key acoustic variables are:
- Pressure
- Density
- Particle motion (distance)

Question 11

What are the units of Acoustic Variables?

Answer 11

Answer: The units of acoustic variables are same as units of pressure, temperature, density and distance.

Pressure = Pascals, or Ib/in

Density = Ib/in3, or kg/m

Temperature = Fahrenheit degrees, or Centigrade degrees

Distance = mm, or cm, or miles

Question 12

What are acoustic parameters?

Answer 12

Answer: Acoustic Parameters are the characteristics that describe a sound
Following are the parameters of a sound wave:
a) Frequency
b) Period
c) Wavelength
d) Propagation Speed
e) Amplitude
f) Power
g) Intensity

Question 13

What is Frequency?

Answer 13

Answer: Frequency is described as the number of cycles that occur per second.
Frequency is described as the number of times per second that the particles in a medium oscillate back and forth as a sound wave propagates through a medium.
The unit of frequency is Hertz. The frequencies most used in diagnostic ultrasound imaging range from 1 to 10 megahertz (MHZ).

Question 14

Can a sonographer change the frequency of a transducer?

Answer 14

Answer: The sonographer cannot change the frequency de a transducer.

To change the frequency, the sonographer has to select a different transducer.Modern ultrasound transducers contain multiple piezoelectric crystals.
The frequency is changed by selecting the different piezoelectric crystal in a transducer.

Question 15

What happens to the frequency when ultrasound wave passes through a medium?

Answer 15

Answer: The frequency of a sound wave remains the same when it passes through a medium.
The frequency is determined by the sound source and the medium has no effect on the frequency of the sound wave.

Question 16

Ultrasound is defined as a sound with a frequency greater than
0.02 MHz.

Answer 16

Answer: True
Ultrasound is defined as a sound with a frequency above 20,000 Hz or 2KHZ, Or 0.02 MHZ

Question 17

An Ultrasound wave is traveling in the body. What determines the Frequency of ultrasound wave?

Answer 17

Answer: The frequency of ultrasound wave is determined by two factors.

• thickness of the piezoelectric element.
• propagation speed of the piezoelectric element.

The frequency is higher when the crystal is thin, and its propagation speed is high

The frequency is lower when the crystal is thicker, and its propagation speed is low.

• The diameter of the Crystal does not affect the frequency of the ultrasound wave.

Question 18

If we increase the frequency, the near zone length will increase?

Answer 18

Answer: True
If we increase the frequency, the near zone length will increase.
Near zone length is the distance from the transducer to the focus. The near zone length is determined by the transducer diameter and frequency of the ultrasound.

Question 19

If the frequency is decreased, the numerical value of the radial resolution will decrease?

Answer 19

Answer: True
If the frequency is increased, the numerical value of the radial resolution will decrease.
For soft tissue:

Axial Resolution =0.77 x # cycles in pulse/Frequency (MHz)

As frequency increases, the numerical value of the LARRD resolution decreases. Axial resolution is best in transducers with the highest frequency and the fewest numbers of cycles per pulse. Axial resolution is worst in transducers with the lowest frequency and the largest number of cycles per pulse.

Question 20

What is the period of a wave?

Answer 20

Answer: The period of a wave is the time from the start of a cycle to the end of that cycle. Period is the time it takes for one cycle to occur
In diagnostic ultrasound imaging the waves have period in the range of 0.1 to 1.0 usec.

Question 21

If the frequency of an US wave is doubled, what happens to the period?

Answer 21

Answer: If the frequency of a US wave is doubled, the period is halved.
Frequency and period have inverse relationship. As frequency increases, period decreases.

period = 1/ frequency

Question 22

What happens to the period of a wave as it propagates?

Answer 22

Answer: The period of a wave remains unchanged as it propagates through a medium.

Question 23

Does the sonographer have the ability to change the period of an ultrasound wave?

Answer 23

Answer: The period of an ultrasound wave is determined by the sound source which produces the acoustic signal. The sonographer cannot change the period of a wave in a particular ultrasound system.

The sonographer must select a different transducer with different frequency to change the period of a wave.

Question 24

What is the effect of medium on the period of a wave?

Answer 24

Answer: The medium does not affect the period of a wave. The period of a wave will not change as it propagates through one medium to another medium.

Question 25

Two ultrasound transducers are used during an exam. The frequencies of transducers are 5 MHz and 2.5 MHz. The imaging depth remains the same. Will the period of 2.5 MHz frequency sound wave will be greater than the period of 5 MHz frequency sound wave?

Answer 25

Answer: True. The period of 2.5 MHz frequency sound wave will be greater than the period of 5 MHz frequency sound wave. Period is the amount of time it takes from the start of a cycle to the end of that cycle of sound wave. Period and Frequency are inversely proportional to each other. If the frequency is lower the period of the sound wave will be higher. If the frequency is higher the period will be lower.

Question 26

Compare two sound waves A and B. The frequency of a wave A is one third that of wave B. How does the period of wave A compare to the period of wave B?

Answer 26

Answer: The period of wave A is three times as long as the period of wave B. The period is inversely proportional to the frequency. period =1/frequency (f) As the frequency decreases, the period increases.

Question 27

Two waves, a 5 MHz wave and a 1 MHz wave travel through soft tissue. The period of 5 Mhz wave is greater than the period of 1 MHz wave?

Answer 27

Answer: False The period and frequency of a wave are inversely proportional. Higher the frequency of a wave, the shorter the period of that wave will be. In this case, the 5 MHz wave has a higher frequency than 1 MHz wave and therefore will have a shorter period.

Question 28

What is Wavelength?

Answer 28

Answer: Wavelength is the distance from the beginning of a cycle to the end of that cycle. Wavelength is the distance covered by one cycle. Wavelength is equal to the propagation speed of sound in the medium divided by the frequency.

Question 29

What is the relationship between frequency and wavelength?

Answer 29

Answer: Frequency and wavelength are inversely proportional. When traveling through a particular medium, the lower frequency sound waves have longer wavelengths and the higher frequency sound waves have shorter wavelengths. For example, a 2 MHz frequency sound wave will have longer wavelength than a 5 MHz frequency sound wave.

Question 30

Which sound wave will have the shortest wavelengths?

Answer 30

Answer: Sound wave with high frequency and traveling in a slow medium will have the shortest wavelengths.

Question 32

What is the relationship between frequency and wavelength for sound traveling in soft tissue?

Answer 32

Answer: Inverse Frequency and wavelength are inversely proportional to each other. If frequency increases, the wavelength decreases. If frequency decreases, the wavelength increases. wavelength = propagation speed/frequency

Question 33

Two waves, a 5 MHz wave and a 1 Muz wave travel through soft tissue. The wavelength of 5 MHz/wave is greater than the wavelength of 1 MHz wave.

Answer 33

Answer: False When sound waves travel through a medium, the higher frequency wave has a shorter wavelength and lower frequency wave has longer wavelength. In this case the 5 MHz wave has a higher frequency than 1 MHz wave. Therefore, the wavelength of 5 MHz wave will be shorter than the wavelength of 1 MHz wave.

Question 34

Two ultrasound transducers are used during an exam. The frequencies of transducers are 5 MHz and 2.5 MHz. The imaging depth remains the same. Will the wavelength of 2.5 MHZ frequency sound wave be greater than the wavelength of 5 MHz/frequency sound wave?

Answer 34

Answer: True. The wavelength of 2.5 MHz frequency sound wave will be greater than the wavelength of 5 MHz frequency sound wave. Wavelength is the distance of a cycle of a sound wave that it occupies. The wavelength of a sound wave is determined by the particular medium through which it travels. The sound waves with lower frequencies have longer wavelengths and sound waves with higher frequencies have shorter wavelength when they travel through a particular medium.

Question 35

If the frequency of ultrasound is increased from 0.77 MHz to 1.54 MHz, what happens to the wavelength?

Answer 35

Answer: The wavelength is halved. Frequency and wavelength are inversely proportional to each other. If frequency increases, the wavelength decreases. If frequency decreases, the wavelength increases. wavelength = propagation speed/frequency

Question 36

What is Amplitude?

Answer 36

Answer: Amplitude is the maximum variation that occurs in an acoustic variable pressure, density, or particle motion. **Amplitude is the strength of a sound wave**. The initial strength or amplitude of a wave is determined by the power applied to the piezoelectric crystal. **The amplitude of a wave will increase if the amount of power applied increased**. The sonographer can change the amplitude of the sound wave by increasing or decreasing the output power.

Question 37

What happens to the Amplitude of a wave when it travels through the body?

Answer 37

Answer: The Amplitude of a wave decreases when it travels through the body. This process is called attenuation. The farther the sound wave travels the weaker it becomes.

Question 38

What are the units of Amplitude?

Answer 38

Answer: The units of Amplitude are same as the units of acoustic variables. The units of acoustic variables are same as units of pressure, temperature, density and distance. Pressure = Pascals, Ib/in Density = Ib/in3, kg/m3 Temperature = Fahrenheit degrees, Centigrade degrees Distance = mm, cm, miles Amplitude can also be **expressed as decibels, db**.

Question 39

With standard diagnostic imaging instrumentation, the sonographer has the ability to vary the amplitude of a sound wave produced by the transducer.

Answer 39

Answer: True The sonographer has the ability to vary the amplitude of a sound wave produced by the transducer by increasing or decreasing the output power.

Question 40

What is Power and what happens to the power of sound wave when it travels through the body?

Answer 40

Answer: Power is the rate at which energy is transferred or the rate at which work is performed. As the sound wave travels in the body, the power diminishes. This process is called attenuation. Power and amplitude are both measures of strength of ultrasound wave. Power is proportional to the amplitude squared Power = (Amplitude) 2 Power decreases as the sound propagates through the body.

Question 41

What is Intensity of an ultrasound beam?

Answer 41

Answer: The Intensity of an ultrasound beam is defined as the concentration of power in the beam area. Intensity represents the strength of the sound beam. Intensity is calculated by dividing the power in a beam by its cross sectional area. intesity = power/beam area **The unit of intensity is watts per centimeter squared**.

Question 42

What happens to the intensity of the sound wave when it travels through the body?

Answer 42

Answer: The intensity of the sound wave decreases as it travels through the body due to the process of attenuation. The sound wave can be reflected, refracted and absorbed when it travels through the body.

Question 43

If the amplitude of a wave is doubled, what happens to the power?

Answer 43

Answer: If a wave's amplitude is doubled, the power is quadrupled. Power = (Amplitude) 2 If the amplitude of a wave is doubled, the power is quadrupled.

Question 44

If the amplitude is doubled, what happens to the intensity?

Answer 44

Answer: If the amplitude is doubled the intensity is increased 4 times. Power = (Amplitude) If the amplitude of a wave is doubled, the power is quadrupled. Intensity is directly proportional to power. When the power goes up, the intensity goes up. If the power is quadrupled, the intensity is also quadrupled.

Question 45

What happens to the intensity of an ultrasound beam when the cross-sectional area of the beam remains unchanged while the amplitude of the wave triples?

Answer 45

Answer: Intensity of ultrasound beam increases by nine-fold. When amplitude is tripled, the power increases by nine-fold. Power = (Amplitude) 2 Power = (3)2 Power = (3 × 3) Power = (9) Intensity is directly proportional to power. intesity = power/beam area When power increases by nine-fold, the intensity increases by nine-fold.

Question 46

What happens to the intensity of the sound beam when the power in the beam increases by 25% while the cross-sectional area of the beam remains the same?

Answer 46

Answer: The intensity also increases by 25% Intensity is directly proportional to power. If intensity increases, the power also increases if the beam area is not changed. intesity = power/beam area

Question 47

If the power in an ultrasound beam is unchanged, while at the same time, the beam area doubles. What happens to the intensity of the beam?

Answer 47

Answer: The intensity of the beam is halved. The beam area and intensity are inversely proportional. If the beam area is increased, the intensity of the beam will decrease if the power remains the same. intesity =power/beam area

Question 48

What determines the intensity of an ultrasound beam after it enters the body?

Answer 48

Answer: After the sound wave enters a medium, **the frequency of the sound wave and the characteristics of the medium determine the amplitude**, power and intensity of the sound wave. The higher frequency sound waves attenuate more. The bone and lung have a greater attenuation rate than soft tissue. The blood or fluid has a lower attenuation rate than soft tissue.

Question 49

What is decibel?

Answer 49

Answer: **The dB is defined as the ratio of two intensities**. A ratio of two intensities, powers, or amplitudes will have unit of db.

Question 50

If the SPTA intensities are equal, the continuous wave will have the lowest SPPA.

Answer 50

Answer: True If the SPTA intensities are equal, the continuous wave will have the lowest SPPA.

Question 51

Which pair of intensities has the same value for continuous wave ultrasound?

Answer 51

Answer: **Pulse average** and **temporal average** intensities have the same value for **continuous wave ultrasound.**

Question 52

What is the minimum value of the SP/SA factor?

Answer 52

Answer: The minimum value of the SP/SA factor is 1.0 Beam uniformity coefficient also called SP/SA factor describes the spread of a beam in space. It is a unitless number.

Question 53

Put these intensities in decreasing order SPTP, SATA, SATP.

Answer 53

Answer: SPTP, SATP, SATA SPTA intensity has the highest value. SATA intensity has the lowest value.

Question 54

The reflected intensity of the sound beam determines the reflected signal amplitude in the transducers of an ultrasound system.

Answer 54

Answer: True **The reflected intensity of the sound beam** determines **the reflected signal amplitude in the transducers of an ultrasound system**.

Question 55

If the output of a US machine is calibrated in B and the output is increased by 20 dB, the beam intensity is increased by?

Answer 55

Answer: If the output of an US machine is calibrated in dB and the output is increased by 20 dB, the beam intensity is increased by 100 times.

Question 56

The relative output of a US instrument is calibrated in dB and the operator increases the output by 60 dB, The beam intensity is increased by?

Answer 56

Question 57

If the power of a sound wave is increased by a factor of 8 how many decibels is this?

Answer 57

Question 58

Sound intensity decreased by 75%. How many decibels of attenuation is this?

Answer 58

Answer: 6 decibels Sound intensity is decreased by 75% means that the intensity has fallen to ¼th the original value.

Question 59

How many decibels is related to 90% decrease in imaging power?

Answer 59

Answer: -10db 90% decrease in imaging power means the power has fallen to 1/10th of the original value.

Question 60

An ultrasound system is set at 0 dB and is transmitting at full intensity. What is the output power when the system is transmitting at 10% of full intensity?

Answer 60

Answer: -10 dB The intensity has fallen to 1/10th of the original value

Question 61

The fundamental frequency of a transducer is 3 MHz. What is the second harmonic frequency?

Answer 61

Answer: The second harmonic frequency is 6 MHz. **Fundamental frequency is the frequency of the transmitted sound.** Harmonic frequency is twice the fundamental or transmitted frequency. Transmitted sound has a particular frequency which is called fundamental frequency, but the image is created from the sound reflected at twice the fundamental frequency also called the harmonic or second harmonic frequency.

Question 62

What is decibel?

Answer 62

Answer: Decibel is a unit. It is used to measure the relative change in power or intensity of the ultrasound beam. The relative change in intensity compares the current intensity of the ultrasound beam with its original intensity. For example, the current intensity of the ultrasound beam has decreased 50% after traveling in the body, compared with its original intensity.