71. ULTRASOUNDS: SPECULAR REFLECTION

Question 1

1. What happens when we have an acoustic interface that is large and smooth?

Answer 1

• it reflects sound
• as much as a mirror reflects light

Question 2

2. What is another term for Sound Interfaces?

Answer 2

• Specular Reflectors

Question 3

3. What are 2 examples of Specular Reflectors in the human body?

Answer 3

• Diaphragm
• Urine-filled bladder

Question 4

4. What source do Specular Echoes originate from?

Answer 4

THEY ORIGINATE FROM OBJECTS THAT ARE:
- relatively large
- strongly reflective
- regularly shaped
- that have smooth surfaces

Question 5

5. What are some characteristics of Specular Echoes?

Answer 5

THEY ARE:
- relatively intense
- angle dependent

Question 6

6. Are most interfaces in the body smooth?

Answer 6

• no
• they have irregularities

Question 7

7. What happens when a wave reflects off of an irregular surface?

Answer 7

• the wave radiates in more than one direction
• this is called Diffuse Reflection
• this is also known as Back Scatter

Question 8

8. What is the advantage of Diffuse Reflections?

Answer 8

INTERFACES THAT ARE AT SUBOPTIMAL ANGLES
TO THE SOUND BEAM:
- will still produce reflections
- these can be imaged

Question 9

9. What is the disadvantage of Diffuse Reflections?

Answer 9

DIFFUSE REFLECTIONS:
- have lower signals than specular reflections

Question 10

10. Define Acoustic Impedance?

Answer 10

• this is property that tissues have
• it allows for the propagation of Sound Waves
• it is represented by the symbol: z

Question 11

11. How do we calculate the Acoustic Impedance?

Answer 11

p = density of the medium
v = speed of sound in the medium

Question 12

12. What does Higher AcousticImpedance of the tissue result in?

Answer 12

• it results in less propagation of the sound wave

NB:
- sound waves cannot propagate through materials with
High Impedance

Question 13

13. What can be said about the amount of sound energy that is reflected back to the Transducer?

Answer 13

• this amount is directly proportional to the
  difference in Acoustic Impedance
  between tissues

Question 14

14. What are the 3 kinds of Acoustic Impedance that we can have?

Answer 14

1. Hyperechoic
2. Hypoechoic
3. Anechoic

Question 15

15. What is Hyperechoic Acoustic Impedance?

Answer 15

• the medium is the Bone
• it appears as white on the Ultrasound
• this is because it has very high density

Question 16

16. What is Hypoechoic Acoustic Impedance?

Answer 16

• the medium is Muscle or Liver
• they appear as grey on the Ultrasound image
• this is because they have a medium density

Question 17

17. What is Anechoic Acoustic Impedance?

Answer 17

• the medium is fluid
• this can be blood, ascites or pleural effusions
• they appear as Black on the Ultrasound image
• this is because they have a low density

Question 18

18. What kind of images do High-Frequency sound waves provide?

Answer 18

• they provide higher resolution images
• these images are of relatively superficial structures

Question 19

19. What kind of images do Low-Frequency sound waves provide?

Answer 19

• they provide images of deeper tissues
• this is because they have better penetration

Question 20

20. How should we position the sound waves in relation to the tissue?

Answer 20

• they should be positioned as close to perpendicular as
  possible to the tissue under evaluation

THIS ALLOWS SOUND WAVES:
- to return back to the Transducer
- this produces the best visualisation

Question 21

21. What kind of reflections produce the brightest and most hyperechoic signals?

Answer 21

• the reflection of sound wavs back from specific tissues
• these tissues have the largest differences in
  Impedance