ultrasound physics

1. Introduction to Ultrasound physics

2. objectives
• Explain the pulse-echo principle used in
sonographic imaging.
• Describe the image formats used in
sonography.
• Explain how the Doppler effect is applied in
sonography.
• List the ways in which Doppler information is
presented

3. OUTLINE
• Sonography
• Doppler Ultrasound

4. Ultrasound
• Sound is a traveling variation of acoustic
variables
• Ultrasound is a sound waves of frequencies
exceeding the range of human hearing and
their propagation in a medium.

5. Sonography
Medical imaging with ultrasound
Medical 2D and 3D anatomic and flow imaging
with the use of ultrasound.
Medical diagnostic ultrasound is a modality that
uses ultrasound energy and the acoustic
properties of the body to produce an image.
Sonography is accomplished with a pulse-echo
technique

6. pulse-echo technique
• The echoes from one pulse appear as one scan
line
• Sonographic images are composed of many scan
lines.
• Pulse echoes scan lines
• The US transducer converts electrical energy to a
brief pulse of high-frequency sound energy that is
transmitted into patient tissues
• The US transducer then becomes a receiver,
detecting echoes of sound energy reflected from
tissue.

7. pulse-echo technique

8. linear image
• The rectangular display resulting from Pulses
that travel in the same direction from different
points and yield vertical parallel scan line is
called a linear scan.
• referring to the linear-array transducer that is
used to produce it.

9. sector image
• each pulse originates from the same starting
point, but subsequent pulses go out in slightly
different directions.
• This approach results in a sector scan, or
sector image,
• a shape similar to a slice of pie

10. sector image

11. Modified form of a sector scan
• different starting points but each pulse (and
scan line) travels in a slightly different
direction as in a sector image
• 2D images are presented in linear and sector
forms.

12. DOPPLER ULTRASOUND
• Moving objects have frequencies that are
different from the pulses sent into the body
• The Doppler effect is a change in frequency
caused by moving objects.
• The Doppler effect is a shift in the frequency of
returning echoes, compared with the
transmitted pulse, caused by reflection of the
sound wave from a moving object.

13. Doppler effect
• In medical imaging, the moving objects of
interest are red blood cells in flowing blood.
• If blood flow is relatively away from the face
of the transducer, the echo frequency is
shifted lower and vice versa.
• The amount of frequency shift is proportional
to the relative velocity of the red blood cells.

14. Doppler US
• Doppler US can detect not only the presence
of blood flow but can also determine its
direction and velocity.
• The Doppler frequency shift is in the audible
range, producing a sound of blood flow that
has additional diagnostic value

15. Doppler information
presentation
• Doppler information is presented in audible,
color doppler, and spectral-Doppler forms

17. Reference