77. ULTRASOUNDS: FOCUSED TRANSDUCERS Flashcards
- Which 2 mechanisms help to focus all Diagnostic Transducers?
- Curved Piezo Electric Crystals
- Acoustic Lenses
- What do transducers use an array of Piezoelectric elements for?
- they use them to transmit and receive sound and
echoes
- What is Phased Array?
THIS IS WHEN:
- transmitting and receiving signals
- can be individually delayed in time
- What does Phased Array do?
THIS ARRANGEMENT ELECTRONICALLY:
- steers and focuses each sequence of acoustic pulses
- through the volume of the object that is being imaged
- this is known as Beam Forming
- What does Beam Forming produce?
- it produces a 2D or 3D map
- of the scattered echoes on the display
- What does the Frequency of the ultrasound beam affect?
- it affects the quality of the resulting image
- it does this to a great degree
- What kind of near field and divergence do Higher Frequency ultrasound waves have?
HIGHER FREQUENCY ULTRASOUND WAVES:
- have a longer near field
- they have less divergence in the far field
- What effect does the frequency of the ultrasound wave have on the resolution?
A HIGHER FREQUENCY ULTRASOUND WAVE:
- permits better resolution of the small structures
- What characteristics does a smaller diameter Transducer have?
- it has a shorter and smaller near field
- it has more divergence in the far field
- What characteristics does a larger diameter Transducer have?
- it has a longer near field
- it has less divergence in the far field
- What kind of focus does a Higher frequency sound wave create?
- it creates a deeper focus
- this is used to image superficial structures
- How did Transducer manufacturers overcome the deep focus create by High Frequency sound waves?
- they made the diameter very small
- thy used high frequency crystals
- these crystals are very small
- What effect does a smaller diameter have on a High Frequency sound wave?
- it displaces the focus
- it makes it shallower
- this makes the Transducer clinically useful
- What is the mathematical relationship between diameter, frequency and focal depth?
NB:
- the diameter affects the focal depth more than the
frequency
- What does this image show?
- an Ultrasonic beam that is being emitted by an
unfocused Transducer
NB:
- this is an example of Mechanical focus
- What does this image show?
- an Ultrasonic beam that is being emitted by a focused
Transducer
NB:
- this is an example of Mechanical Focus
- What is this image an example of?
ELECTRONIC FOCUS
THE DIAGRAM SHOWS HOW A PHASED ARRAY TRANSDUCER:
- can focus the ultrasonic beam
- What can we see in this image?
- there are waves coming from each element
- each wave is focused on a different beam of the
Transducer
- What causes Electronic Focus?
BY THE APPROPRIATE TIMING OF THE INDIVIDUAL ELEMENTS:
- the leading edges of the wavelets can produce a
concentrically curved wave front
THE RESULTANT ULTRASONIC BEAM:
- focuses on a given point from the Transducer
- Does this diagram make sense?
- yes
- the sound waves will begin at different times
