Most ultrasound devices put the transducer (which makes the sound waves) and the
ID: 85940 • Letter: M
Question
Most ultrasound devices put the transducer (which makes the sound waves) and the detector on the same probe. Thus reflected sound waves are what is detected. Determine the fractional sound intensity that is detected by tracking a 1 MHz beam transmitted through material X, reflected at normal incidence at the interface with material Y, and again transmitted through material X when (Assume all sound from the transducer enters X and all reflected sound enters the detector): (a) X is 2 cm of muscle and Y is bone. (b) X is 4 cm of fat and Y is muscle. (c) A generous dab of gel is put on the probe head before it is placed on the skin. Why? What are the desired properties of this gel? (gamma_sound in s/m is 7 times 10^-6 for fat, 2 times 10^-5 for muscle, and 2 times 10^-4 for bone) Reflected sound is 1.08% for fat/muscle interface and 41.23% for muscle/bone.Explanation / Answer
They have given the values of reflected sound as 1.08% for fat/muscle interface and 41.23% for muscle/bone interface.
a) 1 MHz beam is transmitted through muscle and reflected by bone
41.23% of these 1 MHz beam is reflected
Therefore, the fraction of sound intensity that reaches back the detector is 41.23% of 1 MHz which comes to 0.4123 MHz and transmitted to the bone is 0.5877 MHz.
b) 1.08% of sound is reflected at fat/muscle interface
Therefore, the fraction of sound that reaches the detector back is 1.08% of 1 MHz or 0.108 MHz and transmitted to muscle is 0.9892 MHz.
c) A generous dab of gel is applied on the ultrasound probe head. This gel acts as a conducting medium that enables a tight bond between the skin and the probe. The gel enables ultrasound waves to be transmitted directly to the tissues reducing reflection. This maximizes the transmission of acoustic energy to the tissue.
The desired properties of gel used in ultrasound probe are,
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