77. ULTRASOUNDS: FOCUSED TRANSDUCERS

Question 1

1. Which 2 mechanisms help to focus all Diagnostic Transducers?

Answer 1

1. Curved Piezo Electric Crystals
2. Acoustic Lenses

Question 2

2. What do transducers use an array of Piezoelectric elements for?

Answer 2

• they use them to transmit and receive sound and
  echoes

Question 3

3. What is Phased Array?

Answer 3

THIS IS WHEN:
- transmitting and receiving signals
- can be individually delayed in time

Question 4

4. What does Phased Array do?

Answer 4

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

Question 5

5. What does Beam Forming produce?

Answer 5

• it produces a 2D or 3D map
• of the scattered echoes on the display

Question 6

6. What does the Frequency of the ultrasound beam affect?

Answer 6

• it affects the quality of the resulting image
• it does this to a great degree

Question 7

7. What kind of near field and divergence do Higher Frequency ultrasound waves have?

Answer 7

HIGHER FREQUENCY ULTRASOUND WAVES:
- have a longer near field
- they have less divergence in the far field

Question 8

8. What effect does the frequency of the ultrasound wave have on the resolution?

Answer 8

A HIGHER FREQUENCY ULTRASOUND WAVE:
- permits better resolution of the small structures

Question 9

9. What characteristics does a smaller diameter Transducer have?

Answer 9

• it has a shorter and smaller near field
• it has more divergence in the far field

Question 10

10. What characteristics does a larger diameter Transducer have?

Answer 10

• it has a longer near field
• it has less divergence in the far field

Question 11

11. What kind of focus does a Higher frequency sound wave create?

Answer 11

• it creates a deeper focus
• this is used to image superficial structures

Question 12

12. How did Transducer manufacturers overcome the deep focus create by High Frequency sound waves?

Answer 12

• they made the diameter very small
• thy used high frequency crystals
• these crystals are very small

Question 13

13. What effect does a smaller diameter have on a High Frequency sound wave?

Answer 13

• it displaces the focus
• it makes it shallower
• this makes the Transducer clinically useful

Question 14

14. What is the mathematical relationship between diameter, frequency and focal depth?

Answer 14

NB:
- the diameter affects the focal depth more than the
frequency

Question 15

15. What does this image show?

Answer 15

• an Ultrasonic beam that is being emitted by an
  unfocused Transducer

NB:
- this is an example of Mechanical focus

Question 16

16. What does this image show?

Answer 16

• an Ultrasonic beam that is being emitted by a focused
  Transducer

NB:
- this is an example of Mechanical Focus

Question 17

17. What is this image an example of?

Answer 17

ELECTRONIC FOCUS

THE DIAGRAM SHOWS HOW A PHASED ARRAY TRANSDUCER:
- can focus the ultrasonic beam

Question 18

18. What can we see in this image?

Answer 18

• there are waves coming from each element
• each wave is focused on a different beam of the
  Transducer

Question 19

19. What causes Electronic Focus?

Answer 19

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

Question 20

20. Does this diagram make sense?

Answer 20

• yes
• the sound waves will begin at different times