Physics - Ch. 4: Describing Pulsed Waves

What are the 5 Parameters for Pulsed Sound?

• Pulse duration

• Pulse repetition period 

• Pulse repetition frequency 

• Duty factor 

• Spatial pulse length 

Pulse Duration:

• Definition 

• Units

• Determined By

• Adjustable 

• Actual time from start of a pulse to the end of that pulse

• Time; microseconds

• Sound source

• No

Pulse Duration:

• Characteristics of Long Duration

• Characteristics of Short Duration

• Which one is more desirable in diagnostic imaging, and why?

• Long Duration = many cycles in pulse or individual cycles with long periods

• Short Duration = few cycles in pulse or individual cycles with short periods

• Short durtaiton because they create a more accurate images

Spatial Pulse Length:

• Definition 

• Units  

• Determined By

• Adjustable 

• Distance that a pulse occupies in a space from the start to the end of a pulse 

• Distance; mm

• Both; sound source and medium 

• No

Spatial Pulse Length Relationships (list 3)

• Directly proportional to number of cycles in the pulse 

• Directly proportional to wavelength 

• Inversely proportional to frequency 

What is the Difference Between Pulse Duration & Spatial Pulse Length?

• Pulse duration = time & pulse is “on”

• Spatial Pulse = distance of the pulse end to end

Pulse Repetition Period:

• Definition 

• Units 

• Determined By 

• Adjustable

• Time from start of one pulse to the start of the next pulse 

• Time

• Sound source + imaging depth

• Yes

What is Depth of View?

• Maximum distance into body that an ultrasound system is imaging

How are Pulse Repetition Period and Depth of View Related?

• Directly related; pulsed repetition period increases, depth of view increases

What are the Two Components of Pulse Repetition Period? Which One Can the Sonographer Change?

• Transmit time or on time & receive time or off time 

• Receive or “listening time” 

Pulse Repetition Frequency:

• Definition

• Units

• Determined By

• Adjustable 

• Number of pulses that an ultrasound system transmits into body each second; only interested in number of pulses created each second

• Hz or per second 

• Sound Source 

• Yes

How are Pulse Repetition Frequency & Depth of View Related?

• Inversely related; pulse repetition frequency increases, depth of view decreases

An Ultrasound Machine is Imaging to a Depth of 2 cm. Would the Pulse Repetition Frequency be Described as High or Low?

• High, because the machine is sending many pulses in a short time to image a shallow depth

An Ultrasound Machine is Imaging to a Depth of 20 cm. Would the Pulse Repetition Frequency be Described as High or Low?

• Low, because the machine sends fewer pulses over a longer time to image a greater depth

Relationship Between Pulse Repetition Period and Pulse Repetition Frequency?

• Inversely related; pulse repetition period increases, pulse repetition frequency decreases

• Reciprocal relationship

Duty Factor:

• Definition

• Unit

• Determined By

• Adjustable

• Percentage or fraction of time that the system transmit a pulse

• None

• Sound source

• Yes

How is Duty Factor Calculated? (formula)

• Duty factor (%) = pulse duration / pulse repetition period x 100

What are the Maximum and Minimum Values for Duty Factor?

• Maximum value = 1 or 100%

• Minimum value = 0%

How Does the Sonographer Change Duty Factor?

• Duty factor changes when the sonographer alters imaging depth

• Imaging depth increases, duty factor increases with shallower imaging

Shallow Imaging (list 4)

• Less listening

• Shorter PRP

• Higher PRF

• Higher duty factor 

Deep Imaging (list 4)

• More listening

• Longer PRP

• Lower PRF

• Lower duty factor

Parameters that Describes Both Pulsed and Continuous Waves

• Period

• Frequency 

• Wavelength 

• Propagation speed