Describing Pulsed Waves class notes

Describing Pulsed Waves

Pulsed Sound Waves

• Characterized by cycles and pauses.

• Involve both transmitting and receiving.

Pulsed Wave Parameters

• Pulse Duration

• Pulse Repetition Frequency

• Pulse Repetition Period

• Duty Factor

• Spatial Pulse Length

Pulse Duration

• Definition: Actual time from the beginning of a pulse to the end of the pulse (Transmit Time).

• Units: Time (microseconds).

• Range: 0.3-2.0 microseconds.

• Determined by: Sound source only.

• Calculation:

  • Equal to the number of cycles multiplied by the period of cycles.

  • Equal to the number of cycles divided by the frequency.

• Relationship: Directly proportional to the number of cycles in the pulse.

Spatial Pulse Length

• Definition: Distance in space occupied by a pulse from beginning to end.

• Units: Distance (mm).

• Range: 0.1 to 1 mm.

• Determined by: Sound source and medium.

• Calculation: Number of cycles in pulse multiplied by the wavelength of each cycle.

• Relationship:

  • Directly proportional to the number of cycles in the pulse.

  • Directly proportional to wavelength.

Pulse Repetition Period (PRP)

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

• Units: Time (microseconds to milliseconds).

• Range: 100 microseconds to one millisecond.

• Determined by: Sound source.

• Adjusted by: Imaging depth controls.

• Relationship: Unrelated to period.

• Note: Depth of view is the maximum distance into the body.

Pulse Repetition Frequency (PRF)

• Definition: Number of pulses transmitted into the body per second.

• Adjusted via: Imaging depth.

• Range: 1000 to 10,000 Hz.

• Relationship:

  • PRF is unrelated to frequency.

  • Shallow depth = higher PRF.

  • Deeper depth = lower PRF.

Relationship Between PRP and PRF

• Inverse relationship.

• Reciprocal relationship.

• Formulas:

  • PRF = \frac{1}{PRP}

  • PRP = \frac{1}{PRF}

  • PRF * PRP = 1

Duty Factor (DF)

• Definition: Percentage of time the system is transmitting a pulse.

• Units: Percentage (%).

• Range: 0.25-0.5%.

• Continuous wave: Has a DF of 100%.

• Determined by: Sound Source only, Depth Control

• Inversely Related to imaging depth.

Shallow vs. Deep Imaging

Intensity

• Definition: Beam’s power divided by its area.

• Different ways of describing beam intensity:

  • Spatial

  • Temporal

  • Peak

  • Average

  • Pulsed

Spatial Intensity

• Refers to: Distance or space.

• Characteristics: Intensity of the beam changes at different locations within the beam.

• Types:

  • Spatial Peak Intensity

  • Spatial Average Intensity

Temporal Intensity

• Refers to: Time.

• Characteristics: Sound wave intensities vary over time.

• Types:

  • Temporal Peak Intensity: Maximum Intensity-Average intensity during most intense half cycle

  • Pulse Average Intensity: Average Intensity during pulse duration

  • Temporal Average Intensity: Average intensity during pulse repetition period

Measuring Intensities

• Intensity Measurement Methods:

  • SPTP: spatial peak, temporal peak

  • SATP: spatial average, temporal peak

  • SPTA: spatial peak, temporal average

  • SATA: spatial average, temporal average

  • SPPA: spatial peak, pulse average

  • SAPA: spatial average, pulse average