Chap 4 Lvl 1 Flashcards
What is a continuous wave
A continuously transmitted wave where the pulse is simultaneously transmitted and received
Negatives of a continuous wave
- A lack of range specificity (range ambiguity)
- overlapping waves that make it impossible to determine the distance of the source you’re targeting
Is it easier to distinguish space between structures that are farther apart or closer together?
It is easier to distinguish between structures that are farther apart
Shorter vs longer pulse
A shorter pulse will give you a better axial resolution due to less attenuation
Why do we use pw for ultrasound
Cw is unable to provide a range resolution to understand depth so we need to use a pulse wave to allow receiving waves to not overlap
What is Pulse duration
The amount of time a transmitted pulse last.
What is the pulse repetition period
Refers to the time a pulse starts and the following pulse begins
What is the reciprocal to pulse repetition period
PRP=1/Pulse Repetion Frequency
What is the Pulse Repetition Frequency
The number of pulses that occur per time
What is the duty factor
The time the source is transmitting energy divided by the time until the process is repeated
Equation for duty factor
DF=Pd/PRP x 100
What is the duty factor for a continuous wave?
1, because a continuous wave is always transmitting and receiving
If a Pulse duration is longer than ____ is greater
Duty factor
What does the duty factor represent
The % of time the system is actively transmitting energy into the patient.
What happens if the duty factor is too large
A greater build up of heat and in turn could cause a greater risk of bio effects
What is range resolution
the ability of pulsed ultrasound to precisely locate a returning echo.
Range resolution equation
Range resolution=spatial pulse length/2
What are the pulse wave parameters
Define the duration of the pulse, how often the pulse is repeated, and the spatial length the pulse occupies in the medium
How are the frequency and period determined in echo
Both are determined by the vibration of the crystal
Equation for pulse duration
PD = period x # of cycles
How to determine how often a transmit will be repeated
The time it will take for the sound wave to travel the required round trip distance
What is the Spatial pulse length
The entire physical distance the pulse occupies in the medium
Equation for spatial pulse length
SPL = wavelength x # of cycles
How does spatial pulse length affect axial resolution
Fewer cycles and shorter wavelength will improve axial resolution. Vice versa for poor resolution
In terms of pulse waves. What are factors of time
- pulse duration
- Pulse repetion period
- duty factor
In terms of pulse waves, what are factors of distance
- spatial pulse length
- wavelength
