170
5 Acoustics in Biology and Medicine
dissolve after a few minutes. During resonance, they emit harmonic signals which
can be selectively detected.
The imaging of focal liver lesions is an important application of ‘contrastenhanced ultrasonics’ (CEUS).
Acoustical Holography
Appendix C describes the principles underlying holography.
An acoustical hologram of organs in the body can be generated by immersion
of the body in water. A US emitter sends sound waves toward the body, and
also toward an array of two-dimensional piezoelectric transducers. The interference
pattern of the direct versus the reflected waves is recorded. That record can be used
to reconstruct the reflecting tissue and organs in the body, as a three-dimensional
image. This is best done on a computer and screen.
5.22.2 Doppler Rheology
As we have described, the Doppler effect is the shift in the frequency of sound
because of the relative motion between the source and the observer.
When ultrasound projected into our body reaches a moving material, such as
a heart valve or the blood in an artery, that material responds by vibrating at
the ultrasound frequency f shifted by the Doppler factor. In addition, because
the material is in motion, the sound wave it emits in response to the ultrasound
will be detected at a different frequency f than from the material emitting the
pulse. The frequency detected, f , will be related to the US probe frequency by:
f = 2f/(1 + u · r/v), where u is the speed of the echoing material, r is the
direction from the source of the ultrasound to the location of the echoing material,
and v is the speed of sound in the body tissue.
The fastest moving internal material in the body is blood moving through the
aorta, which travels at a maximum speed of about a meter per second. The maximum
Doppler shift for a 1 MHz US in-coming wave is therefore f ≤ 2 f u/v = 2 ·
1 MHz(1 m/s 1500 m/s) = 1.2 kHz. (The echo from flowing blood will be audible)
(Fig. 5.22).
5.22.3 Physiotherapy
Some medical applications of ultrasonics in therapy include:
• Ultrasonic Diathermy (Producing tissue heating with ultrasonics)
• Ultrasonic breakup of calculi (such as kidney stones and gallstones)
5 Acoustics in Biology and Medicine
dissolve after a few minutes. During resonance, they emit harmonic signals which
can be selectively detected.
The imaging of focal liver lesions is an important application of ‘contrastenhanced ultrasonics’ (CEUS).
Acoustical Holography
Appendix C describes the principles underlying holography.
An acoustical hologram of organs in the body can be generated by immersion
of the body in water. A US emitter sends sound waves toward the body, and
also toward an array of two-dimensional piezoelectric transducers. The interference
pattern of the direct versus the reflected waves is recorded. That record can be used
to reconstruct the reflecting tissue and organs in the body, as a three-dimensional
image. This is best done on a computer and screen.
5.22.2 Doppler Rheology
As we have described, the Doppler effect is the shift in the frequency of sound
because of the relative motion between the source and the observer.
When ultrasound projected into our body reaches a moving material, such as
a heart valve or the blood in an artery, that material responds by vibrating at
the ultrasound frequency f shifted by the Doppler factor. In addition, because
the material is in motion, the sound wave it emits in response to the ultrasound
will be detected at a different frequency f than from the material emitting the
pulse. The frequency detected, f , will be related to the US probe frequency by:
f = 2f/(1 + u · r/v), where u is the speed of the echoing material, r is the
direction from the source of the ultrasound to the location of the echoing material,
and v is the speed of sound in the body tissue.
The fastest moving internal material in the body is blood moving through the
aorta, which travels at a maximum speed of about a meter per second. The maximum
Doppler shift for a 1 MHz US in-coming wave is therefore f ≤ 2 f u/v = 2 ·
1 MHz(1 m/s 1500 m/s) = 1.2 kHz. (The echo from flowing blood will be audible)
(Fig. 5.22).
5.22.3 Physiotherapy
Some medical applications of ultrasonics in therapy include:
• Ultrasonic Diathermy (Producing tissue heating with ultrasonics)
• Ultrasonic breakup of calculi (such as kidney stones and gallstones)