Ultrasound instrumentation Flashcards
Describe the function of the transmitter
Generates the electrical transmit pulse that is applied to the transducer
Describe the function of the transmit beam former
Uses electronic delays to form an appropriately focussed and/or steered beam from the transducer
How does receive beam forming work
Electronic delays are used to create the receive beam and these are continuously adjusted so the beam is focussed at the correct depth
What is the function of the amplifier
Amplifies the weak echo signals from the transducer so they are able to processed
This also reduces the degrading effect of electronic noise
Gain can be used to adjust the level of amplification
Describe the function of the time gain compensation
Variable amplification of detected echo signals, dependent of the depth from which they are received, to account for attenuation, to give a consistent image
Define the formula for dynamic range
DR = 10 x log (I max / I min) dB
Describes the ratio of the strongest echo intensities to the weakest
How does the machine adjust dynamic range
Compression of the dynamic range of echoes so it matches that of that of the display (and our eyes)
Generally the strongest echoes are compressed so weaker echoes can be differentiated
What is the function of the scan converter
What are the pieces of information used by the scan converter?
Places each echo in its correct position in the scan memory
Takes into account:
- Echo arrival time
- Probe geometry
- Beam position
- Image depth
- Image zoom
What is the image memory?
Digital memory where the image is stored in a two dimensional array of pixels
Generally hundreds of images running back several seconds, forming a cineloop
What are the differences between read and write zoom
Write zoom:
- Occurs in real time, enlarging the region so it occupies the entire image memory
- Increases frame rate
- Maintains image clarity
Read zoom:
- Part of the stored image is increased in size
- Pixelation occurs
What is frame averaging?
When is it not appropriate?
Also known as persistence
Averages the image with the one prior
Reduces speckle by averaging the speckle across the two images
Reduced frame rate
Not appropriate when imaging fast moving tissues (e.g. heart)
What is compound imaging
Machine acquires several images, each with the beam steered in a different direction
The machine then averages these images
Reduced speckle
Images tissue interfaces better
Reduced frame rate
