Duty Factor

The duty factor is a significant parameter in ultrasound imaging, particularly concerning the characteristics of the emitted pulse and patient safety.

Here's what you need to know about duty factor:

• Definition: The duty factor represents the proportion or percentage of time that an ultrasound pulse is actively propagating. It can be expressed as a percentage or a fraction ranging from 0% to 100%.
• Continuous Wave vs. Pulsed Operation: A 100% continuous duty cycle corresponds to continuous wave emission, while 0% defines a quiescent system. However, imaging inherently utilizes pulsed ultrasound with fractional duty factors below 100%, typically around 0.01 or less clinically.
• Typical Clinical Values: Clinical duty factors typically range from 0.001 to 0.01. This means that the system is listening for echoes for most of the time, allowing for echo reception from depths up to 30 cm.
• Determinants and Adjustability: The duty factor depends on adjustable timing circuit parameters and is determined by the sound source. While it's primarily source-dependent, the sonographer's adjustments to imaging depth can indirectly change the duty factor, influencing image quality and depth.
• Relationship to Safety: Low duty cycles, combined with short pulse lengths, are crucial for safety. This pulsing approach ensures that only one pulse traverses the imaging plane at a time, localizing energy deposition spatially and temporally, thereby improving safety. Understanding duty factor principles helps in evaluating potential bioeffects.
• Impact on Intensity: The duty factor is important for quantifying intensities.