Question:
Which one of the following options represents the correct order of the speed of ultrasound wave propagation in bone, air, and soft tissue?
Which one of the following options represents the correct order of the speed of ultrasound wave propagation in bone, air, and soft tissue?
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Speed of sound rises with the stiffness and density of the medium: solids fastest, water-rich soft tissue next, gas (air) slowest.
Updated On: Aug 7, 2026
- bone > air > soft tissue
- bone > soft tissue > air
- air > bone > soft tissue
- soft tissue > bone > air
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The Correct Option is B
Solution and Explanation
Step 1: Understanding the Question:
We need to rank three body materials, bone, soft tissue, and air, by how fast an ultrasound wave travels through each of them.
Step 2: Key Formula or Approach:
The speed of a sound wave in a medium depends on how stiff (incompressible) and how dense the medium is. In a solid, \(c = \sqrt{E/\rho}\), where \(E\) is the elastic modulus and \(\rho\) is the density. A stiffer, more tightly packed medium carries sound faster than a loose, compressible one.
Step 3: Detailed Explanation:
Bone is a dense, rigid, mineralised tissue. Its high stiffness lets an ultrasound wave travel through it at roughly 3500 to 4000 m/s, the fastest of the three.
Soft tissue (muscle, fat, organ tissue) is mostly water. Its stiffness is much lower than bone but it is still a packed, nearly incompressible medium, so sound moves through it at about 1540 m/s, the value used as the standard reference speed in diagnostic ultrasound machines.
Air is a gas. Its molecules are far apart and it is highly compressible, so it barely resists the passing wave. Sound in air travels at only about 340 m/s, far slower than in bone or soft tissue. This is also why an air gap between the probe and the skin ruins an ultrasound scan, so gel is used to remove any trapped air.
Putting the three speeds in decreasing order: bone (about 3500 to 4000 m/s) is greater than soft tissue (about 1540 m/s), which is greater than air (about 340 m/s).
Step 4: Final Answer:
The order is bone > soft tissue > air, so option (B) is correct.
We need to rank three body materials, bone, soft tissue, and air, by how fast an ultrasound wave travels through each of them.
Step 2: Key Formula or Approach:
The speed of a sound wave in a medium depends on how stiff (incompressible) and how dense the medium is. In a solid, \(c = \sqrt{E/\rho}\), where \(E\) is the elastic modulus and \(\rho\) is the density. A stiffer, more tightly packed medium carries sound faster than a loose, compressible one.
Step 3: Detailed Explanation:
Bone is a dense, rigid, mineralised tissue. Its high stiffness lets an ultrasound wave travel through it at roughly 3500 to 4000 m/s, the fastest of the three.
Soft tissue (muscle, fat, organ tissue) is mostly water. Its stiffness is much lower than bone but it is still a packed, nearly incompressible medium, so sound moves through it at about 1540 m/s, the value used as the standard reference speed in diagnostic ultrasound machines.
Air is a gas. Its molecules are far apart and it is highly compressible, so it barely resists the passing wave. Sound in air travels at only about 340 m/s, far slower than in bone or soft tissue. This is also why an air gap between the probe and the skin ruins an ultrasound scan, so gel is used to remove any trapped air.
Putting the three speeds in decreasing order: bone (about 3500 to 4000 m/s) is greater than soft tissue (about 1540 m/s), which is greater than air (about 340 m/s).
Step 4: Final Answer:
The order is bone > soft tissue > air, so option (B) is correct.
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