Pulsed Sound Chapter 3 Flashcards
In diagnostic imaging, what is required to create an anatomic images?
Short pulses of acoustic energy
What is a pulse?
A collection of cycles that travel together
What are the two components of pulsed ultrasound?
on/transmit time and dead/off time
What are the 5 additional parameters that describe pulsed sound?
Pulse duration, pulse repetition period, PRF, duty factor, spatial pulse length
What is pulse duration? Units? Sound source? Can it be changed? Typical values? Equation?
The actual time form the start to end of a pulse aka the talking time. Time (sec). Sound source. No, characteristic of each transducer. 0.5 to 0.3 microsecs. Pulse duration (us) = # cycles in pulse x period (us).
What is spatial pulse length? Units? Determined by? Can it be changed? Typical values? Equation? How does this affect the image?
The distance or length from the start to end of one pulse. Distance (mm). Both the source and the medium, bc wavelength is also determined by both the source and medium. No. 0.1 to 1 mm. =# of cycles x wavelength (mm). Affects image quality (axial resolution) - shorter pulses=higher quality images.
What is pulse repetition period? Units? Determined by? Can it be changed? Typical values? How does it affect the image?
PRP is the time from the start of one pulse to the start of the next, included one pulse duration + one dead time. Time (sec). Sound source. Yes, PRP is determined by imaging depth. 100us to 1 ms. As PR increases, imaging depth increases.
What is PRF? Units? What is it determined by? Can it be changed? Typical values? What does it have a relationship with? Formula?
Number of pulses created by the system per second. Hz/sec. Sound source. Yes (imaging depth). 1-10kHz. Pulse repetition period and PRF are reciprocals= both of these depend on depth. Pulse repetition period (sec) x PRF (Hz)= 1
How does a shallow image affect PRF? Deep image? Why is this? What does PRF stand for? Is it related to frequency?
Shallow image = higher PRF. Deeper image = lower PRF. PRF is determined by imaging depth only. Pulse repetition frequency. PRF is not related to frequency.
What is duty factor? Units? What is it determined by? Can it be changed but the sonographer? Typical values?
The percentage or fraction of time that the system transmits sound. Unitless. Sound source. Yes, when imaging depth is changed. From 0.1% to 1% (little talking, lots of listening)
How does a shallow image affect duty factor? Deep image? What is always true about this value? Why is this?
Shallow image = higher duty factor. Deep image = lower duty factor. Duty factor is always a small value, typically less than 1%, with deeper imaging it’s even smaller. An imaging system must use pulsed ultrasound, so the duty factor is always less than 100%. This is because continuous waves (100% DF) cannot create anatomical images.
How are PRF PRP and duty factor affected by shallow imaging? What about deep imaging?
Shallow= high PRF, short pulse repetition period, high duty factor. Deep = low PRF, long pulse repetition period, low duty factor.
Can pulsed sound be used to create an atomic images? Why or why not?
Yes, never continuous waves
What parameters describe both pulsed and continuous waves? Why is this?
Period, frequency, wavelength, propagation speed. Continuous and pulsed sound are both comprised of cycles therefore any parameter that describes a cycle describes both PW and CW sound.
What changes when adjusting the imaging depth?
Changes the pulse repetition period, PRF, and duty factor.
