Ultrasound uses high frequency sound waves to create images. The image is generated as the waves reflect off objects, with the reflection's amplitude determining brightness. Image resolution depends on factors like wavelength, line density, and frame rate. Artifacts appear due to attenuation or reflections, but can provide useful information. Doppler ultrasound detects movement by measuring frequency shifts from reflections, and settings like pulse repetition frequency impact its accuracy for measuring velocities.

2. OVERVIEW
What are waves-sound vs ultrasound waves
How image is created by USG
Factors affecting image resolution
Artefacts
Doppler effect
Pulse/continuous and color doppler

5. USG waves

6. Characteristics
of a wave
• Velocity=frequency x wavelength
• Wavelength=1/frequency if velocity assumed 1540 m/s

7. USG PULSES

8. USG WAVES IN BODY
ATTENUATION

9. IMAGE
GENERATION
• Amplitude =brightness value on grayscale
• Time taken to reflect=distance of the
object
• Multiple one-dimensional beams fan out
• Multiple beams and averaging process
=2D or B mode
• Number of images in a second =Frame
rate

10. M mode

11. AXIAL RESOLUTION
• discern two objects longitudinally adjacent to each other
• depends on wavelength /Frequency

12. Lateral resolution
• discern two separate objects that
are adjacent to each other
• depends on –line density and
number of focal points
• More lines =better lateral
resolution

13. TEMPORAL RESOLUTION
• distinguish changes between successive image frames over time
• Higher frame rate =higher temporal resolution
Temporal
vs Lateral
Frame
rate
sector
size
line
density

14. Settings to
optimize
view
• Sector size
• frame rate vs lateral resolution
• Focus-beams converge with acoustic lens–
maximal overlap in area chosen
• Gain –degree of amplification of returning signal
• Time gain compensation-software adjusts
degree of amplification

16. Artefacts

17. Doppler Principal

18. Doppler
Principal

20. PULSE WAVE
• sample volume
• Aliasing above 2 m/sec
• Nyquist limit=PRF/2
• LVOT ,DIASTOLOGY,CO

21. PUSE vs PRP vs PRF
Nyquist limit=PRF/2
• Use high frequency
• Sample shallow
• Use continuous wave
• Change baseline
Spatial pulse length

22. Continuous wave
• Range ambiguity -not site
specific
• Useful for high velocities -AS

23. Color doppler
• BART
• AVERAGES SEVERAL GATES
• USE HIGH FRAME RATE
• CHECK COLOUR SCALE
• DON’T OVERGAIN
• DON’T USE FOR
QUANTIFICAITION

24. SUMMARY
USG WAVES-high frequency ,longitudinal mechanical waves
Pulse , Pulse length , PRP,PRF, Frame rate
Depth vs axial
Frame rate vs line density vs sector size
Artefacts can be useful
Pulse wave-Nyquist limit=PRF/2
Limitations of color doppler