Pulsed Waves

Ch4: Pulsed Waves

Pulsed Echo Technique

• Ultrasound Information Collection:

  • Primarily utilizes pulsing.

Pulse

• Definition: A pulse is a collection of cycles that travel together as a single unit.

Pulse-Echo Technique

• Process of Image Formation:

  1. A pulse of sound is sent into the body.

  2. The pulse reflects off structures within the body.

  3. The reflected sound returns to the transducer.

  4. Collected information is processed for display.

Pulsed Wave Parameters

• These parameters define the features of pulsed sound and must possess all five characteristics to function properly.

• Determined by either the source or the medium:

1. Pulse Duration

• Definition: The time duration of one pulse.

• Units: Microseconds (µs).

• Alternate Name: Known as "Talking Time."

• Determination:

  • By the source of the ultrasound.

• Adjustability: No, it is not adjustable.

• Formula:
  PD = ext{#Cycles} imes ext{Period}

2. Spatial Pulse Length (SPL)

• Definition: The distance of one pulse.

• Units: Millimeters (mm).

• Determination:

  • By the source and the medium.

• Adjustability: No, it is not adjustable.

• Formula:
  SPL = ext{#Cycles} imes ext{Wavelength}

3. Pulse Repetition Period (PRP)

• Definition: The time from the start of one pulse to the start of the next pulse.

• Units: Time measured in milliseconds (ms).

• Alternate Names: Known as both "Talking Time" and "Listening Time."

• Determination:

  • By the source of the ultrasound.

• Adjustability: Yes, adjustable via depth.

• Formula:

  • Adjusts listening time:
    $PRP = rac{1}{ ext{PRF}}$

  • Or measured in seconds per pulse:
    $PRP = ext{Seconds/Pulse}$

• Comparison: PRP is 100-1000 times longer than Pulse Duration.

4. Pulse Repetition Frequency (PRF)

• Definition: The number of pulses emitted per second.

• Units: Measured in MegaHertz (MHz).

• Determination:

  • Primarily determined by the source.

• Adjustability: Yes, indirectly adjustable via depth.

• Formula:

  • Adjusts listening time:
    $PRF = ext{Pulses/Second}$

  • Or relation to PRP:
    $PRF = rac{1}{ ext{PRP}}$

5. Duty Factor

• Definition: Represents the amount of talking time relative to the overall time.

• Units: Dimensionless (no units).

• Typical Values: Ranges from 0.1% to 0.5% for pulsed waves.

• Determination:

  • Determined by the source of the ultrasound.

• Adjustability: Yes, adjustable via depth.

• Formula:the
  $DF = rac{PD}{PRP}$

• Notes:

  • Duty Factor is always 100% for Continuous Waves.

  • Duty Factor for Pulsed Waves is always <100%.