1. Ultrasound
Physics

2. Characteristics of Sound
• Requires medium for its transmission.
• Compression and rarefaction.
• Propagation.

3. Ultrasound waves
• Range
• Longitudinal waves
• Length of wave
• Wave once generated continue in original
direction until it is either reflected, refracted or
absorbed

4. Velocity of Sound
• Independent of frequency
• medium
How velocity is related to:
• Compressibility
• Density
• Intensity

6. Transducers
• Converts an electrical signals into ultrasonic
energy that can be transmitted to tissues & vice
versa
• Constituents :-
1. Piezoelectrical crystals
2. Two electrodes
3. Backing block
4. Acoustic insulator(rubber )
5. Plastic housing

8. • Two basic modes of transducers
1. Continuous mode – doppler studies
2. Pulse mode

9. Curie temperature
Resonant frequency
Transducer Q factor
•Two characteristics-
purity of sound & length of sound
•High Q transducer
•Low Q transducer

10. Advantage of High frequency over low frequency
Depth resolution is superior & near zone is long
Dis-advantage
Tissue absorption increases with increased
frequency

11. Interaction between ultrasound & matter
1. Reflection
2. Refraction
3. Absorption

12. Reflection
• Reflected wave sound produces image
• It depends on
1. Acoustic impedance
2 Angle of incidence

13. Acoustic impedance
• Impedance is product of tissue density with
velocity of sound in the material.
Angle of incidence
Higher the amount of angle less is the amount
of sound reflected
Specular interface Examples
diaphragm,walls of the vessels
boundaries of many organs

14. Refraction
• Bending of waves as they pass from one medium
to another is called refraction
• Interfaces that are either smaller than the
wavelength or not smooth are nonspecular
interface
• Example
Rbc,liver parenchyma

16. Absorption
• It means conversion of ultrasonic to thermal
energy
• It depend on
1. Frequency of sound
2. Viscosity of medium
3. Relaxation time

17. Ultrasonic display
• A Mode– displayed as spikes projecting from baseline. Spike
height is proportional to echo intensity. It is static one-
dimensional mode.
• TM Mode– echoes produced by moving structures as dots.
• B Mode– produces a picture of a slice of tissue. Echoes
displayed as dots.
• Gray scale Imaging– It’s a B mode type displaying large
amplitude of echoes arising from tissues as varying shades of
gray

18. • Real time imaging–
produces multiple images in a very short period
• Two types
1. Mechanical– Oscillating & Rotating wheel
2. Electronic array– Linear array & phased or
steered array

19. PRINCIPLES
OF
DOPPLER
ULTRASOUND

20. BASIC PRINCIPLE
• Doppler ultrasound is a technique for making
non-invasive velocity measurements of blood
flow.
• Christian Doppler was the first to describe the
frequency shift that occurs when sound or
light is emitted from a moving source.
• Ultrasound is transmitted into a vessel and
the sound that is reflected from the blood is
detected. Because the blood is moving, the
sound undergoes a frequency (Doppler) shift.

23. Uses of doppler
• Determination of anatomy.
• Determination of small vessel flow distribution.
• Detection of vascular dilatation, obstruction.
• Evaluation of intravascular disease and
evaluation.
• Detection of extra vascular flow.

24. 1) Continuous wave doppler
• Without B MODE imaging
2) Pulsed wave doppler
• Pulsed Doppler ultrasound is a technique for measuring
the velocity of blood in a small sample volume
• Used in general & obstetric ultrasound & also used to
provide data for doppler sonograms & colour flow images.
Disadvantage – “Aliasing”
3) Color Doppler

26. DOPPLER INDICES