You are imaging the phantom with a conventional linear array. Why does the tube labeled "B" contain echoes, whereas the tube labeled "A" does not?

You are imaging the phantom with a conventional linear array. Why does the tube labeled "B" contain echoes, whereas the tube labeled "A" does not?

• A. Since axial resolution decreases with depth, artifactual echoes are displayed from above and below the tube
• B. The frame rate was too slow to display the deeper tube accurately
• C. The slice thickness at the level of tube B was wider than at tube A
• D. The electronic focusing at the level of tube A is more powerful than at the level of tube B

Answer: (C)

Slice thickness (section thickness) artifact is the key idea. An ultrasound beam has a finite thickness, and the image reflects echoes coming from within that slice, not just from a perfectly flat plane. If a structure lies within a thicker portion of the beam at a given depth, echoes from it are included in the image; if the slice is thinner at another location, those echoes may not be present. Here, tube B sits where the slice thickness is relatively wide, so echoes from the tube are detected and displayed. Tube A lies where the slice is thinner, so the tube may not contribute detectable echoes. That difference in slice thickness at the two locations explains why one tube shows echoes while the other does not.

Slice thickness (section thickness) artifact is the key idea. An ultrasound beam has a finite thickness, and the image reflects echoes coming from within that slice, not just from a perfectly flat plane. If a structure lies within a thicker portion of the beam at a given depth, echoes from it are included in the image; if the slice is thinner at another location, those echoes may not be present.

Here, tube B sits where the slice thickness is relatively wide, so echoes from the tube are detected and displayed. Tube A lies where the slice is thinner, so the tube may not contribute detectable echoes. That difference in slice thickness at the two locations explains why one tube shows echoes while the other does not.