# Shared Flashcard Set

## Details

Ultrasound Physics--Chapter 4 and 5
Pulsed Sound and Intensity
35
Physics
Professional
01/25/2021

Term
 What is a pulsed wave?
Definition
 In diagnostic imaging, short pulses of acoustic energy are used to create anatomic images. It is also known as "pulse-echo technique." A pulse is a collection of cycles that travel together. A pulse must have a beginning and an end., otherwise the sound is continuous wave. Two components of pulsed ultrasound are the cycles of pulsed sound called the "transmit" time or "on" time, and the dead time or "received" time or "listening" time or "off" time.
Term
 Define:   Pulse Duration (PD) Units?   Determined by?   Changed by sonographer?   Typical values?   Equation?
Definition
 The time from the start of a pulse to the end of that pulse, the actual time that the pulse is on. μsec or any unit of time   Determined by the sound source   The sonographer cannot change (A pulse is a pulse is a pulse)   0.3 μs - 3 μs   PD = # cycles in pulse x period
Term
 Define: Spatial Pulse Length   Units?   Determined by?   Changed by sonographer?   Typical values?   Equation?
Definition
 The length or distance that an entire pulse occupies in space. The distance from the start to the end of one pulse.   mm or any unit of distance   Determined by BOTH the sound source & the medium. Since λ is determined by source & medium, so too is the SPL   No, cannot be changed by the sonographer   0.1 mm to 1 mm   SPL (mm) = # of cycles x wavelength (mm)
Term
 Define: Pulse Repetition Period (PRP)   Units?   Determined by?   Changed by sonographer?   Typical values?   Equation?
Definition
 Pulse repetition period is the time from the start of one pulse to the start of the next pulse. It includes one PD and one "listening" time.   ms or any unit of time   Determined by sound source   Yes, by changing the depth of view, the sonographer can change PRP. Only the "listening" time is changed.   100 μs to 1 ms   PRP (μs) = imaging depth (cm) x 13 μs/cm
Term
 What happens to PRP with a shallow image?
Definition
 The PRP is short
Term
 What happens to PRP when an image is deep?
Definition
 PRP is long
Term
 Define: Pulse Repetition Frequency (PRF)   Units?   Determined by?   Changed by sonographer?   Typical values?   Equation?
Definition
 PRF is the number of pulses that occur in one second.   Hertz, Hz, per second   Determined by the sound source   Yes, by changing the depth of view, the sonographer can change the PRF   1 - 10 kHz   PRF in soft tissue (Hz) = 77,000 cm/s ÷ imaging depth
Term
 What is the relationship between imaging depth and PRP?
Definition
 Directly related
Term
 What is the relationship between PRF and imaging depth?
Definition
 Inversely related
Term
 What is the relationship between PRP and PRF?
Definition
 Reciprocal relationship   PRP x PRF = 1   PRP = 1/PRF   PRF = 1/PRP
Term
 Define: Duty Factor (DF)   Units?   Determined by?   Changed by the sonographer?   Typical values?   Equation?
Definition
 The percentage or fraction of time that the system transmits sound.   No units! %   Determined by the sound source   Yes, by changing the depth of view, the sonographer can change DF   PW: 0.1% - 1%   DF (%) = PD (ms) / PRP (ms) x 100
Term
 What happens to DF with a shallow image?
Definition
 Higher DF
Term
 What happens to DF with deeper image?
Definition
 lower DF
Term
 What is the relationship between DF and PRP?
Definition
 Directly proportional
Term
 Define:     Intensity   What is equation   What are the units?
Definition
 Intensity is the concentration of the power in a beam.   Intensity (w/cm2) = power/beam area   W/cm2   *
Term
 True or False?       Intensity is not uniform across a sound beam?
Definition
 True
Term
 True or False?   With pulsed ultrasound, intensity is not uniform throughout time.
Definition
 True
Term
 Name 2 Intensity key words that has to do with LEVEL
Definition
 Peak and Average
Term
 Name 3 Intensity key words that has to do with LOCATION
Definition
 Spacial, Temporal, Pulsed
Term
 True or False       Intensity is described with space and time
Definition
 True
Term
 How is Spatial Intensity described?
Definition
 Peak and Average
Term
 How is Temporal Intensity described?
Definition
 Peak, Most intense half-cycle, Pulse Avg, and Temporal Avg
Term
 Name the six resulting intensity descriptions from highest to lowest
Definition
 SPTP   SATP   SPTA   SATA   SPPA   SAPA
Term
 Which intensity description is most important in regards to bioeffects?
Definition
 SPTA
Term
 Define:   Beam Uniformity Coefficient (BUC)   Units?   Typical value?   Equation?
Definition
 a value which represents how equal the INTENSITY distribution is across a sound beam.   Unitless! %   Value is always greater than 1 if pulsed wave. 1 if CW.   SP/SA
Term
 Define:       Decibels   Units?
Definition
 A logarithmic scale. A relative scale--ratio of the final to the initial strengths. A comparison, therefor, two intensities are need to calculate decibels.     dB
Term
 What does positive decibels signify?
Definition
 Intensity is increasing
Term
 What does negative decibels signify?
Definition
 Intensity is decreasing
Term
 The final intensity is 2 times bigger than the original intensity, how many decibels?
Definition
 3dB
Term
 The final intensity is 4 times bigger than the original intensity, how many decibels?
Definition
 6dB
Term
 The final intensity is 8 times bigger than the original intensity, how many decibels?
Definition
 9db
Term
 The final intensity is 10 times bigger than the original intensity, how many decibels?
Definition
 10db
Term
 The final intensity is 100 times bigger than the original intensity, how many decibels?
Definition
 20db
Term
 What are the decibels if the final intensity is 10,000 times greater than the original intensity?
Definition
 40dB
Term
 What are the decibels if the final intensity is 1/8 the original intensity?
Definition
 -9dB
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