Lecture Notes: The Five Parameters of Pulsed Sound

Introduction

• Sound discussed in abstract; now focus on pulsed sound.
• Continuous vs. Pulsed Wave:
  • Continuous Wave: Ongoing without interruption.
  • Pulsed Wave: Has a transmit (on) and receive (off) time.
• Importance in Ultrasound:
  • Pulse waves are essential for creating images.
  • Allows processing time for echoes to create images.

Continuous vs. Pulsed Wave Comparison

• Continuous Wave:
  • Like writing in cursive, continuous without breaks.
  • Difficult to parse without breaks.
• Pulsed Wave:
  • Like words separated by spaces.
  • Easier to understand due to clear start and end.

Parameters of Sound

• Previous parameters applicable to both wave types:
  • Frequency, period, propagation speed, wavelength, amplitude, power, intensity.
• Focus on Pulsed Waves in this Lecture:
  • New parameters: Pulse Duration, Spatial Pulse Length, Pulse Repetition Period, Pulse Repetition Frequency, Duty Factor.

Understanding Pulsed Waves

• Essential for image creation in ultrasound.
• Receive time processes echo information to form images.
• Shorter pulses create more accurate images.
• B-Mode Imaging:
  • Uses 2-4 cycles per pulse for accuracy.
• Doppler Ultrasound:
  • Requires more cycles for accurate data.

Key Parameters of Pulsed Waves

1. Pulse Duration
   • Time to complete one pulse.
   • Measured in microseconds.
   • Not adjustable by sonographers.
   • Formula: Pulse Duration = Number of Cycles / Frequency.
2. Spatial Pulse Length
   • Distance a pulse occupies in space.
   • Related to wavelength; affects axial resolution.
   • Shorter SPL improves resolution.
   • Formula: SPL = Number of Cycles x Wavelength.
3. Pulse Repetition Period (PRP)
   • Time from start of one pulse to the next.
   • Includes on and off time.
   • Adjustable by changing imaging depth.
   • Formula: PRP x PRF = 1.
4. Pulse Repetition Frequency (PRF)
   • Number of pulses per second.
   • Inversely related to PRP.
   • Affected by depth.
   • Formula: PRF = 1 / PRP.
5. Duty Factor
   • Percentage of time machine is transmitting.
   • Pulse Duration / PRP.
   • Increases with more "talking" time (more pulses).

Depth and Imaging

• Depth adjustments affect PRP, PRF, and Duty Factor.
• Shallow Depth:
  • Shorter PRP, higher PRF, higher Duty Factor.
• Deep Depth:
  • Longer PRP, lower PRF, lower Duty Factor.

Practical Applications

• Use of high-frequency transducers for better detail.
• Shorter receive time is crucial for imaging moving objects (e.g., heart).
• Adjust depth to optimize image quality and frame rate.

Conclusion

• Understanding the parameters helps in making informed decisions as a sonographer.
• Importance of consistently revising concepts for practical application in medical ultrasound.

• Practice and Review:
  • Engage with practice problems to reinforce understanding.
  • Use workbook activities to organize and digest information.