In ultrasound, the coupling medium is used to ...

In ultrasound, the coupling medium is used to ...

• A. Increase impedance at air-skin interface
• B. Decrease impedance at the air-skin interface
• C. Absorb ultrasound energy
• D. Reflect energy away from skin

Answer: (B)

The coupling medium works by bridging the interface between the transducer and the skin to provide an acoustic path with impedance similar to body tissues. Air has a huge impedance mismatch with skin and tissue, which causes most of the ultrasound energy to reflect back. Filling gaps with gel or paste removes that air, lowers the impedance mismatch at the boundary, and allows more energy to enter the body. This improves transmission and image quality. The medium isn’t meant to absorb or reflect energy away; doing so would degrade instead of improve transmission.

The coupling medium works by bridging the interface between the transducer and the skin to provide an acoustic path with impedance similar to body tissues. Air has a huge impedance mismatch with skin and tissue, which causes most of the ultrasound energy to reflect back. Filling gaps with gel or paste removes that air, lowers the impedance mismatch at the boundary, and allows more energy to enter the body. This improves transmission and image quality. The medium isn’t meant to absorb or reflect energy away; doing so would degrade instead of improve transmission.