1. Why is the low MHz range used in ultrasound imaging? 2. Do you expect sound t

Question

1.         Why is the low MHz range used in ultrasound imaging?

2.         Do you expect sound to travel faster in soft tissue or bone? Why?

3.         How much energy is reflected back when an ultrasound pulse passes from muscle to bone? How much is transmitted? (Use values for Z from Table 4.1).

4. An ultrasound pulse passes through soft tissue and reflects off an interface, producing an echo 0.07 ms later. How deep is the reflecting interface?

5.         If the delay between successive ultrasound pulses is 0.3 ms, what is the maximum range over which the system can successfully produce images, assuming the speed of the pulses in soft tissue is 1540 ms-1. Note: The echo from one pulse should be received before the transmission of the next.

6.         The intensity of an ultrasound beam falls by a factor of 67 in passing through a material. Express this drop in dB.

Explanation / Answer

Answer :

1. The frequencies used for medical imaging are generally in the range of 1 to 18MHz. Higher frequencies have a correspondingly smaller wavelength, and can be used to make sonograms wth smaller details. However, the attenuation of the sound wave is increased at higher frequencies, so in order to have better penetration of deeper tissues, a lower frequency (3-5MHz) is used.

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