Understanding Ultrasound Physics - Exam Review - PULSED ULTRASOUND

A sonographer adjusts the maximum imaging depth of an ultrasound system. Which of the following also changes? (More than one answer may be correct.) A. PRP B. Wavelength C. PRF D. frequency

A and C. PRP and PRF as imaging depth is altered, the PRF and PRP change. the wavelength and frequency remain constant, as these terms describe the attributes of a single cycle within the pulse, and are not affected by alterations in imaging depth.

Two ultrasound systems, one producing sound with a frequency of 3 MHz and the other at 6 MHz, are used to image a patient. The maximum imaging depth of both exams is 8 cm. True or False? The pulses produced by both systems travel at the same speed in the patient.

True. All sound waves travel in the same medium at identical speeds. Frequency and speed are unrelated.

The maximum imaging depth during an exam is unchanged. A new transducer with a longer pulse duration is used. True or False? The duty factor is increased.

True. Duty cycle is calculated by dividing the pulse duration by the pulse repetition period (PRP). In this example, the PRP is unchanged. By changing to a transducer with a longer pulse duration while the PRP stays constant, the duty factor increases.

True or False? The pulse repetition frequency and the frequency are unrelated.

True. PRF and frequency are unrelated. the PRF is determined only by the depth of view. The frequency is determined by the characteristics of the transducer.

Two ultrasound systems, one producing sound with a frequency of 3 MHz and the other at 6 MHz, are used to image a patient. The maximum imaging depth of both exams is 8 cm. True or False? The period of the 3 MHz sound is greater than the period of the 6 MHz sound.

True. The period of a wave is the time that is required to complete one single cycle. A sound signal's period and frequency are reciprocals; therefore, the lower the frequency, the higher the period. In this case, the 3 MHz wave has a period twice as long as the 6 MHz wave.

True or False? The sonographer cannot change the duration of a sound pulse unless the transducers are switched.

True. the pulse duration depends upon the interaction of the pulser electronics of the machine and the transducer. The pulse duration may change when the sonographer changes transducers.

True or False? The sonographer alters the duty cycle when adjusting the maximum imaging depth of a scan.

True. The duty cycle is the percentage of time that an ultrasound system is creating an acoustic wave. Duty factor is inversely related to depth of view. Duty factor decreases when depth of view increases.

True or False? While imaging soft tissue, the spatial pulse length does not change as long as the components of the ultrasound system are the same.

True. The overall length of a pulse is equal to the wavelength multiplied by the number of cycles in the pulse. Using a particular ultrasound system and transducer, the pulse length cannot change.

true or false? the pulse duration of an US and transducer system does not change significantly as long as the system components remain unchanged.

True. The pulse duration is the timespan that a pulse exists. it is determined by the ultrasound system and the transducer. Generally, it remains constant for a particular transducer.

Two ultrasound systems, one producing sound with a frequency of 3 MHz and the other at 6 MHz, are used to image a patient. The maximum imaging depth of both exams is 8 cm. True or False? The wavelength of the 3 MHz sound is greater than the period of the 6 MHz sound.

True. Wavelength is the distance that a single cycle of a pulse occupies in space. When traveling through a particular medium, cycles from waves with lower frequencies have longer wavelengths. Thus, cycles from a 3 MHz wave have longer wavelengths than those from a 6 MHz wave.

While using the same ultrasound machine and transducer, which of the following can a sonographer alter? (more than one answer may be correct.) A. pulse repetition period B. PRF C. frequency D. duty cycle E. pulse duration

A, B, and D. While adjusting the desired maximum imaging depth in an exam, the sonographer adjusts the pulse repetition period and the PRF. The duty factor is also altered. Unlike choices A, B, and D, the frequency of the ultrasound and the pulse duration are fixed once a transducer is selected. These parameters cannot be altered.

The pulse repetition frequency of ultrasound produced by a transducer typical of diagnostic imaging systems _______. A. can be changed by the sonographer B. depends on the medium through which the sound travels. C. Is unchanged as long as the same ultrasound system is used D. has nothing to do with clinical imaging

A. can be changed by the sonographer. the pulse repetition frequency (PRF) is inversely related to the maximum imaging depth that is achieved during an exam. As the sonographer increases the maximum imaging depth, the PRF must decrease. This occurs because the transducer must wait a longer time for echoes to return from deeper depths. Sonographers, therefore, alter the PRF when they adjust the maximum imaging depth.

the pulse duration is expressed in the same units as the _____. A. period. B. PRF C. wavelength D. density

A. period. the pulse duration and the period are measured in units of time, such as seconds, minutes, or hours. PRF has units of hertz. Wavelength has units of distance. Density has units of mass per volume.

what determines the pulse duration? A. the source of the wave B. the medium in which the pulse travels C. both A and B D. neither A nor B

A. the source of the wave the pulse duration is the actual time that a transducer is creating one sound pulse and is determined by the ultrasound system. pulse duration does not include the listening time.

What are the units of pulse repetition frequency (PRF) ? A. seconds B. 1/seconds C. mm/microseconds D. second ^ -2

B. 1/seconds Pulse repetition frequency is the number of pulses that are produced by the ultrasound system in one second. PRF has the same units as frequency, and these units are hertz, Hz, or per second.

Two transducers send ultrasound pulses into soft tissue. One transducer emits sound with a 4 MHz frequency, and the other produces sound at a 6 MHz frequency. Each pulse contains 4 cycles. Which has a greater spatial pulse length? A. 6 MHz pulse B. 4 MHz pulse C. they are the same D. cannot be determined

B. 4 MHz pulse. Since both pulses have the same number of cycles, the pulse whose individual cycles have a longer wavelength will have the greater overall length. In a given medium, waves with lower frequencies have longer wavelengths. The 4 MHz wave has a longer wavelength than the 6 MHz wave and therefore will have a longer spatial pulse length.

What happens to the pulse repetition period if the sonographer decreases the maximum imaging depth achieved in an ultrasound scan? A. increases B. decreases C. remains the same D. cannot be determined

B. decreases As the maximum imaging depth, or depth of view, is decreased, the interval of time during which the ultrasound machine listens for returning echoes is diminished. As a result of this shorter listening time, the pulse repetition period is shortened. Simply stated, pulse repetition period and depth of view are directly related.

While using a particular imaging system, what happens to the duty factor when the depth of view increases? A. increases B. decreases C. unchanged

B. decreases Duty factor is inversely related to depth of view. As the system images to a greater depth, the system requires more time to listen for reflections, and the duty factor decreases. The duty factor is the fraction or percentage of time that an imaging system is transmitting. It is equal to the pulse duration divided by the pulse repetition period. Never changes. However, as depth of view increases, the pulse repetition period increases.

Which of the following terms does not belong with the others? A. increased depth of view B. increased duty factor C. increased pulse repetition period D. decreased pulse repetition frequency

B. increased duty factor increased duty factors are related to shallower imaging. The other three selections are consistent with deeper imaging.

What is the importance of describing sound beam intensities in a variety of ways with regard to space and time? A. it allows better transducer design B. it's important when studying bioeffects C. it optimizes image quality D. harmonics can be measured

B. it's important when studying bioeffects Describing the intensity of sound beams as they vary in time and in space is important in the study of bioeffects.

In diagnostic imaging, what determines the spatial pulse length? A. the ultrasound system B. the medium through which the pulse travels C. both A and B D. neither A nor B

C. Both A and B The spatial pulse length is the distance, or length, of a pulse. It depends, in part, upon the wavelength of each cycle in the pulse. Wavelength depends upon both the source of the sound and the medium through which the sound travels. The length of the entire pulse also depends upon both the source and the medium.

Which intensity is most closely correlated to tissue heating? A. SPTP B. SATP C. SPTA D. SATA

C. SPTA The SPTA intensity relates most closely to tissue temperature elevation.

In the case of pulsed ultrasound, what is the maximum value of the duty factor? A. 100 B. 1 C. less than 100% D. none of the above.

C. less than 100% This question is a bit tricky. When dealing with a pulsed ultrasound system, at least a tiny bit of time must be spent listening rather than transmitting. Therefore, the percentage of time transmitting must be less than 1 or 100%. If the percentage equals 100%, the system is continuous wave. The correct choice, C, distinguishes between pulsed and continuous wave by stating that the maximum value of the duty cycle must be less than 100% for a pulsed system.

what happens to the pulse duration when a sonographer decreases the maximum imaging depth in an ultrasound scan? A. increases B. decreases C. remains the same D. cannot be determined

C. remains the same The time that a transducer is "pulsing" does not change with alterations in depth of view.

Which of the following correctly describes pulse repetition period? A. the product of wavelength and propagation speed B. the reciprocal of the frequency C. the sum of the pulse's "on" time and the listening "off" time D. the time that the transducer is pulsing

C. the sum of the pulse's "on" time and the listening "off" time The pulse repetition period is the actual time from the start of one pulse to the start of the next pulse. It is equal to the time that the transducer is pulsing (the pulse duration) plus the time that the ultrasound system is listening for reflected echoes.

What are the units of pulse duration? A. units of frequency (Hz, etc.) B. msec only C. units of time (sec, years, etc.) D. units of distance (feet, etc.)

C. units of time the pulse duration is the actual time that a transducer is creating one pulse. hence, it has units of time.

Which of the following best describes the spatial pulse length? A. frequency multiplied by wavelength B. PRF multiplied by wavelength C. wavelength multiplied by the number of cycles in the pulse D. duty factor multiplied by the wavelength

C. wavelength multiplied by the number of cycles in the pulse. The total length of a pulse equals the length of each cycle in the pulse multiplied by the number of cycles in the pulse. Imagine the pulse as a train made up of a number of boxcars. The train's length (the spatial pulse length) equals the length of each car (the wavelength) multiplied by the number of cars in the train (the number of cycles in the pulse).

What is a typical value for the duty factor (also called the duty cycle) of pulsed sound waves used in diagnostic imaging? A. 0.001 msec B. 0.001 kg/cm^3 C. 0.75 D. 0.001

D. 0.001 Duty factor, or duty cycle, is the percentage or fraction of time that an ultrasound system produces an acoustic signal, or is transmitting. Typically, ultrasound transducers spend the vast majority of time receiving, and only a small fraction of time transmitting an acoustic signal.

The pulse repetition frequency is the _________. A. product of the wavelength and propagation speed B. reciprocal of the period C. sum of pulse duration and listening time D. reciprocal of pulse repetition period

D. Reciprocal of pulse repetition period. The PRF and the pulse repetition period are reciprocals. For example, if the PRF is 100 per second, then the pulse repetition period is one-hundredth of a second. If the system creates five hundred pulses per second, then the pulse repetition period is 1/500 of a second.

Which of the following terms does not belong with the others? A. increased depth of view B. decreased duty factor C. increased pulse repetition period D. decreased spatial pulse length

D. decreased spatial pulse length spatial pulse length is unrelated to alteration in depth of view. The other three selections are all related to deeper imaging.

What is the value of the duty cycle for continuous wave ultrasound? A. 100 B. 1% C. 1000% D. none of the above

D. none of the above. The duty factor for continuous wave ultrasound is 1.0 or 100%. This means that the transducer is producing an acoustic signal at all times. None of the answers indicate this: 100 is not 100%, 1% mean one-hundredth and is incorrect, and 1000% means 10 times and is also false.

What is the pulse duration equal to? A. frequency multiplied by period B. period multiplied by wavelength C. the number of cycles in the pulse divided by the wavelength D. period multiplied by the number of cycles in the pulse

D. period multiplied by the number of cycles in the pulse. The pulse duration is the total time that the transducer is producing a pulse. The pulse duration is equal to the time to make a single cycle (the period) multiplied by the number of cycles that make up the pulse. For example, if there are 6 cycles in a pulse, each with a period of 0.2 microseconds, then the pulse duration is 6 x 0.2 = 1.2 microseconds.

True or False? The pulse duration cannot be changed under any circumstances or by any action of the sonographer.

False. A sonographer can alter the pulse duration by using a different imaging transducer or ultrasound system.

The maximum imaging depth during an exam is unchanged. A new transducer with a longer pulse duration is used. True or False? The frequency is increased.

False. After reading the information in the question, you will note that nothing is stated regarding the frequency of sound emitted by the transducer. Therefore, nothing can be concluded regarding frequency.

The maximum imaging depth during an exam is unchanged. A new transducer with a longer pulse duration is used. True or False? The pulse repetition frequency is increased.

False. Pulse repetition frequency and pulse repetition period are reciprocals. If the pulse repetition period is unchanged, then the PRF must also remain unchanged.

The maximum imaging depth during an exam is unchanged. A new transducer with a longer pulse duration is used. True or False? the pulse repetition period is increased.

False. Pulse repetition period is determined by the depth of view. In this case, the maximum depth is unchanged, so the pulse repetition period is also unchanged.

Two ultrasound systems, one producing sound with a frequency of 3 MHz and the other at 6 MHz, are used to image a patient. The maximum imaging depth of both exams is 8 cm. True or False? The PRF of the 6 MHz transducer is greater than the PRF of the 3 MHz transducer.

False. The PRF is derived from the maximum imaging depth as established by the sonographer. The PRF changes only when the imaging depth changes. Since the depth of view for both systems is the same, the PRFs are also the same.

True or False? The duty factor is a characteristic of an ultrasound and transducer system and does not change as long as the system components remain unchanged.

False. The duty cycle changes when the sonographer adjusts the maximum imaging depth during an exam.

True or False? A sonographer can adjust the duration of an acoustic pulse since it depends upon the maximum imaging depth.

False. A sonographer cannot change the pulse duration. It has a constant value, and is not dependent on imaging depth.

True or False? A sonographer can adjust the duration of an acoustic pulse since it depends upon the pulse's propagation speed.

False. A sonographer cannot change the pulse duration. It is a fixed feature of the transducer and ultrasound system. It does not depend upon propagation speed.