Ch. 4: Describing Pulsed Waves

Question 1

• The five following additional parameters are needed to completely describe pulsed sound:

Answer 1

• Pulse duration
  • Pulse repetition period
  • Pulse repetition frequency
  • Duty factor
  • Spatial pulse length

Question 2

Pulsed Ultrasound

• In diagnostic ultrasound, ____ wave sound cannot create atomic images
• Rather, imaging systems produce short bursts, or ____ of acoustic energy to create every picture of anatomy

Answer 2

Pulsed Ultrasound

• In diagnostic ultrasound, continuous wave sound cannot create a atomic images
• Rather, imaging systems produce short bursts, or pulses, of acoustic energy to create every picture of anatomy

Question 3

What is pulsed sound?

• A pulse of ultrasound is a collection of ____ that ____ together
• A pulse must have a ____ and an ____
• Although a pulse is made up of ____ cycles, the entire pulse moves as a single unit
• A pulse is similar to a train
• A train consist of individual cars, but travels as a single entity
• Similarly, a pulse consists of individual cycles, but propagates as a single unit

Answer 3

What is pulsed sound?

• A pulse of ultrasound is a collection of that travel together
• A pulse must have a beginning and an end
• Although a pulse is made up of individual cycles, the entire pulse moves as a single unit
• A pulse is similar to a train
• A train consist of individual cars, but travels as a single entity
• Similarly, a pulse consists of individual cycles, but propagates as a single unit

Question 4

Pulsed ultrasound has two components:

• ____– ____, talking, or “____” time
• ____– ____, listening, or “____” time

Answer 4

Pulsed ultrasound has two components:

• Pulse– Transmit, talking, or “on” time
• Echo– Receive, listening, or “off” time

Question 5

Pulsed Duration

• Each particular ultrasound transducer emits a pulse with a ____ duration
• The pulse duration ____ change for that transducer
• Definition— Pulse duration is the *____ ____ from the ____ of a ____ to the ____ of that ____
  
  • Pulse duration is a single____, talking, or “____” time
• Units— Pulse duration is reported in units of ____, such as microseconds (µs)
• Typical values— The typical value of pulse duration in diagnostic ultrasound is ____ to ____ ____ (µs)
  
  • Microseconds, or millionths of a second
• Determined by— Pulse duration is determined by the ____only, not by the ____ through which the sound travels
• Adjustable— ____. The sonographer ____ alter pulse duration while using a particular ultrasound system and transducer
• Formula— Pulse duration is equal to the number of ____ in each ____, ____ by the ____ of each cycle
  
  • Pulse duration (µs) = #
  • PD = n x p

Answer 5

Pulsed Duration

• Each particular ultrasound transducer emits a pulse with a fixed duration
• The pulse duration cannot change for that transducer
• Definition— Pulse duration is the *actual time from the start of a pulse to the end of that pulse
  
  • Pulse duration is a single transmit, talking, or “on” time
• Units— Pulse duration is reported in units of time, such as microseconds (µs)
• Typical values— The typical value of pulse duration in diagnostic ultrasound is 0.3 to 2.0 microseconds (µs)
  
  • Microseconds, or millionths of a second
• Determined by— Pulse duration is determined by the sound sourceonly, not by the medium through which the sound travels
• Adjustable— No. The sonographer cannot alter pulse duration while using a particular ultrasound system and transducer
• Formula— Pulse duration is equal to the number of cycles in each pulse, multiplied by the period of each cycle
  
  • Pulse duration (µs) = # cycles x period (µs)
  • PD = n x p

Question 6

Pulse duration is:
- Directly proportional to the number of ____ in the ____
- Directly proportional to ____
- Inversely proportional to ____
- Pulse duration (µs) = # cycles / frequency (MHz)
- Where # cycle = n
- PD = n x p
- P = 1/f
- PD = n x (1/f)
- PD = n/f

Answer 6

Pulse duration is:
- Directly proportional to the number of cycles in the pulse
- Directly proportional to period
- Inversely proportional to frequency
- Pulse duration (µs) = # cycles / frequency (MHz)
- Where # cycle = n
- PD = n x p
- P = 1/f
- PD = n x (1/f)
- PD = n/f

Question 7

What characteristics distinguish pulses with long duration from those with short duration?

• Two characteristics create pulse of long duration:
  
  • ____ cycles in the pulse, or
  • ____ cycles with ____ periods
• Two characteristics create pulse of short duration:
  
  • ____ cycles in the pulse, or
  • ____ cycles with ____ periods
• In clinical imaging, a pulse typically contains ____ to ____ cycles

Answer 7

What characteristics distinguish pulses with long duration from those with short duration?

• Two characteristics create pulse of long duration:
  
  • Many cycles in the pulse, or
  • Individual cycles with long periods
• Two characteristics create pulse of short duration:
  
  • Few cycles in the pulse, or
  • Individual cycles with short periods
• In clinical imaging, a pulse typically contains 2 to 4 cycles

Question 8

Which type of pulse is more desirable in diagnostic imaging, and why?

• ____ duration pulses are desirable for imaging because they create images of ____ accuracy/ ____ ____

Answer 8

Which type of pulse is more desirable in diagnostic imaging, and why?

• Shorter duration pulses are desirable for imaging because they create images of greater accuracy

Question 9

Spatial Pulse Length

• Spatial pulse length is the ____ from the front tip of out imaginary “train” to the end of the “caboose”
• Definition— Spatial pulse length is the ____ that a ____ occupies in space from the ____ to the ____ of a pulse
  
  • [Spacial— ____]
  • [SPL— ____ of a pulse]
• Units— Spatial pulse length has units of ____, such as ____ - Typical values— In clinical imaging, spatial pulse length in soft tissue ranged from ____ to ____ ____
• Determined by— Pulse length is determined by ____
  
  • It equals the number of ____ in each pulse times the ____ of each cycle
  • Since ____ is determined by both the source and the medium, so is the spatial pulse length
• Adjustable— No. The sonographer cannot alter pulse length
  
  • In a particular medium, a transducer’s pulse has a fixed length that cannot change
• Formula— Spacial pulse length (mm) = # of cycles x wavelength (mm)
  
  • SPL = ____ x λ
  • SPL = (n x c)/____

Answer 9

Spatial Pulse Length

• Spatial pulse length is the distance from the front tip of out imaginary “train” to the end of the “caboose”
• Definition— Spatial pulse length is the distance that a pulse occupies in space from the start to the end of a pulse
  
  • [Spacial— Space]
  • [SPL— Length of a pulse]
• Units— Spatial pulse length has units of distance, such as mm
• Typical values— In clinical imaging, spatial pulse length in soft tissue ranged from 0.1 to 1.0 mm
• Determined by— Pulse length is determined by both the source and the medium
  
  • It equals the number of cycles in each pulse times the wavelength of each cycle
  • Since wavelength is determined by both the source and the medium, so is the spatial pulse length
• Adjustable— No. The sonographer cannot alter pulse length
  
  • In a particular medium, a transducer’s pulse has a fixed length that cannot change
• Formula— Spacial pulse length (mm) = # of cycles x wavelength (mm)
  
  • SPL = n x λ
  • SPL = (n x c)/f