Lesson 4 (Part 1) Flashcards
If frequency increases, what happens to the wavelength? How does this effect the image?
- Wavelength decreases
2. Leads to a better quality in photos
If frequency decreases, what happens to the wavelength? How does this effect the image?
- Wavelength increases
2. Leads to a poorer quality in photos
What do different transducers have?
Different frequencies
What is the frequency that you choose called?
Fundamental frequency
What are 2 other names for fundamental frequency?
- Operating frequency
2. Transmit frequency
Why do we have listening time?
The ultrasound needs to receive all of the echoes back
What happens to pulse duration if frequency increases?
It decreases
What happens to spatial pulse length if frequency decreases?
It increases
When do you use higher frequencies?
When you are scanning superficially
- less penetration
What do high frequencies produce?
Better quality image
When do you use lower frequencies?
When you are scanning deeper in the body
- better penetration
What do low frequencies produce?
Worse quality images
What is one way to achieve high frequency waves in order to get better quality images?
The use of harmonics
What is a basic sound wave an example of?
Sinusoidal waveform
Sinusoidal waveform
Continuous smooth periodic oscillations
Does sound change shape when it travels through tissues?
Yes
- sinusoidal to non-sinusoidal
Non linear propagation
Changing the wave shape
Do more dense areas move faster or slower?
Faster
Do less dense areas move faster or slower?
Slower
What do nonsinusoidal waves contain?
Additional frequencies
- even and odd multiples of fundamental frequencies
What does it mean when you have less sinusoidal shape?
Stronger harmonics
Harmonics
Send out one frequency, get back several higher frequencies
Pulse
A few cycles of ultrasound
What are pulses separated by in pulse waves?
Separated in time by gaps of no ultrasound
Pulsed wave
A pulse that is followed by a gap
- listening time and downtime
Why do we have a gap in pulsed waves?
So we can listen
