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Ultrasound Parameters Overview

Sep 4, 2025

Overview

This lecture covers the five key parameters of pulsed ultrasound waves, distinguishing them from continuous waves, and explains how each parameter affects image quality and is influenced by machine settings and imaging depth.

Continuous vs. Pulsed Ultrasound

  • Continuous waves are ongoing and do not create images; pulsed waves have on (transmit) and off (receive) time, allowing image creation.
  • Pulsed wave ultrasound groups cycles into pulses, separated by breaks for echo processing.
  • Shorter pulses (fewer cycles, higher frequency) result in more accurate B-mode images; Doppler imaging uses longer pulses.

The Five Parameters of Pulsed Sound

  • Five unique parameters for pulse waves: Pulse Duration, Spatial Pulse Length (SPL), Pulse Repetition Period (PRP), Pulse Repetition Frequency (PRF), and Duty Factor.

1. Pulse Duration

  • Definition: Time to complete one pulse (on/transmit time).
  • Formula: Pulse Duration = Number of Cycles × Period or = Number of Cycles / Frequency.
  • Units: Microseconds (Ξs).
  • Not adjustable by sonographer; set by machine/frequency.

2. Spatial Pulse Length (SPL)

  • Definition: Distance a pulse occupies in space.
  • Formula: SPL = Number of Cycles × Wavelength.
  • Units: Millimeters (mm).
  • Shorter SPL improves axial resolution; determined by machine and medium.

3. Pulse Repetition Period (PRP)

  • Definition: Time from start of one pulse to start of next (on + off time).
  • Formula: PRP × PRF = 1; PRP ∝ imaging depth.
  • Units: Microseconds (Ξs), milliseconds (ms).
  • Adjustable by changing imaging depth; deeper depth increases PRP.

4. Pulse Repetition Frequency (PRF)

  • Definition: Number of pulses emitted per second.
  • Formula: PRF = 1 / PRP; PRF ∝ 1/depth.
  • Units: Kilohertz (kHz).
  • Adjustable by changing depth; shallow depth increases PRF.

5. Duty Factor

  • Definition: Fraction or percent of time the machine is transmitting (on time / total cycle).
  • Formula: Duty Factor = (Pulse Duration / PRP) × 100%.
  • Units: Unitless or percent.
  • Adjustable via depth (by changing PRP); B-mode <1%, Doppler 1–10%, continuous wave 100%.

Relationships and Exam Takeaways

  • Short pulses (short pulse duration/SPL) yield better image detail.
  • Only PRF, PRP, and Duty Factor change with imaging depth; others are constant for a given transducer and medium.
  • PRF and PRP are reciprocals; increasing one decreases the other.
  • Duty Factor increases with shorter PRP or longer pulse duration.
  • Decreasing depth increases PRF and duty factor, decreases PRP.

Key Terms & Definitions

  • Pulse Duration (PD) — Time it takes for one pulse to occur.
  • Spatial Pulse Length (SPL) — Physical length a pulse occupies in space.
  • Pulse Repetition Period (PRP) — Time from start of one pulse to the next.
  • Pulse Repetition Frequency (PRF) — Number of pulses sent per second.
  • Duty Factor (DF) — Percentage of time the system transmits a pulse.

Action Items / Next Steps

  • Complete practice problems calculating PD, SPL, PRP, PRF, and DF.
  • Review and memorize key formulas and parameter relationships.
  • Read workbook charts and summaries on parameter definitions, units, symbols, and adjustability.
  • Take the unit quiz to check understanding of parameter effects and adjustments.

Full transcript