7.PULSE ECHO PRINCIPLE Flashcards
What is an ultrasound pulse?
Answer: An ultrasound pulse is a group of ultrasound waves that travel together. Each ultrasound pulse has a beginning and an end and has certain characteristics.
In pulsed ultrasound the same piezoelectric crystal is used to send the ultrasound pulse and receive the returning echoes.
What are the components of a pulse?
Answer: There are two components of a pulse:
The transmit time is also called the on time. During this time the ultrasound machine is on and short bursts of ultrasound pulses are produced and transmitted.
The receive time which is also called the off time. During this time the returning echo signals are received by the transducer. No sound pulses are produced during this time.
What is Spatial Pulse Length?
Answer: The Spatial Pulse Length is the distance, or length of a pulse. It is the distance from the start of a pulse to the end of that pulse.
What determines the spatial pulse length?
Answer:
a) The spatial pulse length is determined by both the source and the medium through which it travels.
b) Spatial pulse length is determined by the wavelength and the number of cycles in the pulse.
What is the effect of spatial pulse length on image quality?
Answer: Spatial pulse length determines the longitudinal resolution which determines the image quality.
Shorter pulses create higher quality images.
The axial resolution is also known as Longitudinal Resolution, Range Resolution, Radial Resolution, Depth Resolution.
What is Pulse Duration?
Answer: Pulse Duration is the amount of time it takes from the start of a pulse to the end of that pulse. It is the time when the ultrasound system is on and transmitting the ultrasound pulse.
The unit of pulse duration is unit of time such as msec, usec. The typical range of pulse duration in diagnostic ultrasound is 0.4 - 4 usec.
What happens to the pulse duration when the imaging depth is
changed?
Answer: The pulse duration does not change when the imaging depth is changed.The pulse duration is determined by the source and remains the same whether the imaging depth is increased or decreased.
The pulse duration can only be changed when a different transducer is used with a different pulse duration time.
What type of ultrasound pulse is more helpful in diagnostic imaging?
Answer: Shorter duration and shorter length pulses are needed in diagnostic imaging. Ultrasound pulses with short duration and shorter length create images of superior quality.
What happens to the pulse duration when the imaging depth is
changed?
Answer: The pulse duration does not change when the imaging depth is
changed.The pulse duration is determined by the source and remains the same whether the imaging depth is increased or decreased.
*The pulse duration can only be changed when a different transducer is used with a different pulse duration time.
What is the difference between spatial pulse length and pulse duration?
Answer: Spatial Pulse Length (SPL) is the distance from the start to the end of the pulse
Pulse Duration (PD) is the time that the pulse is on.
A sound wave is transmitted into the body. The pulse repetition period is 900 sec, the listening time is 800 usec. What is the pulse duration?
Answer: 100 sec
pulse duration is the time when the ultrasound system is on and transmitting the sound waves.
pulse repetition period = pulse duration + listening time
** or
pulse duration = pulse repetition period - listening time
pulse duration = 900 sec - 800 usec
pulse duration = 100 usec
What is Pulse Repetition Period?
Answer: The Pulse Repetition Period is the time it takes from the start of a pulse to the start of the next pulse. The pulse repetition period consists of two parts. First part is the pulse duration which is when the ultrasound system is on and transmitting the sound waves. The second part is when ultrasound system is listening to the returned sound waves.
Can the sonographer change the pulse repetition period?
Answer: The sonographer can change the PRP indirectly.
The sonographer cannot change the PRP directly, but he can change the listening time indirectly by increasing or decreasing the imaging depth.
A sound wave is transmitted into the body. The pulse duration is 100 usec, the listening time is 800 usec. What is the pulse repetition period?
Answer: 900 sec
Explanation:
Pulse repetition period is equal to the sum of pulse duration and listening time.
pulse repetition period = pulse duration + listening time
pulse repetition period = 100 usec + 800 usec
pulse repetition period = 900 usec
What is the relationship between imaging depth and pulse repetition period?
Answer:There is a direct relationship between the imaging depth and the pulse repetition period.
As imaging depth increases, the PRP increases. - As imaging depth decreases, the PRP decreases
Or
Increasing the pulse repetition period (PRP) increases the maximum depth that can be imaged.
Decreasing the pulse repetition period (PRP) decreases the maximum depth that can be imaged.
What happens to the pulse repetition period when the imaging depth is change?
Answer: The pulse repetition period changes when the imaging depth is changed. When the imaging depth is increased the pulse repetition period increases and when the imaging depth is decreased the pulse repetition period decreases.
The maximum imaging depth is obtained during an exam. A new transducer with longer pulse duration is used. What will be the effect on pulse repetition period?
Answer: The pulse repetition period will remain unchanged.
The pulse repetition period is determined by the imaging depth. If the imaging depth remains unchanged the pulse repetition period will remain unchanged.
What is Pulse Repetition Frequency and how it is determined?
Answer: The number of ultrasound pulses emitted per second by an ultrasound transducer is called pulse repetition frequency.
Pulse Repetition Frequency is determined by the source. The medium through which the sound travels does not affect the pulse repetition frequency*
What is the effect of imaging depth on pulse repetition frequency?
Answer: The pulse repetition frequency can be changed indirectly by the sonographer by changing the imaging depth. The pulse repetition frequency will decrease when the imaging depth is increased, and the pulse repetition frequency will increase when the imaging depth is decreased.
The maximum imaging depth is not changed during an exam.
A new transducer with longer pulse duration is used. What will be the effect on pulse repetition frequency?
Answer: The pulse repetition frequency will remain unchanged.
Pulse repetition period and pulse repetition frequency are inversely proportional. If imaging depth is not changed, then pulse repetition period will remain unchanged. If pulse repletion period is unchanged then pulse repetition frequency will remain unchanged.
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 PRF of 5 MHz transducer will be greater than PRF of 2.5 MHz transducer?
The Pulse repetition Frequency will be the same for both transducers.
The pulse repetition frequency is determined by the imaging depth. If the imaging depth is increased the pulse repetition frequency decreases because the ultrasound system spends more time on listening. If the imaging depth is decreased the pulse repetition frequency increases because ultrasound system spends less time on listening.
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 pulses produced by both transducers travel at different speeds in the body?
False. The pulses produced by both transducers will travel at the same speed in the body.
The speed of sound is determined by the medium not by the frequencies of the transducers. By changing frequencies of sound waves produced does not change the speed of sound in a particular medium. By changing medium will change the speed of sound, for example, speed of sound will be different in water than in the air.
What is Duty Factor?
Duty Factor is the percentage of time that an ultrasound transducer is producing and transmitting ultrasound pulses. It is the ratio between pulse duration and pulse repetition period.
Duty factor is equal to the pulse duration divided by the pulse repetition period.
What is the minimum value of the duty factor?
The minimum value of duty factor is 0.0 or 0%.
When the duty factor is 0.0 or 0%, that means ultrasound machine is not producing any sound pulses.
