The main purpose of a coupling medium in ultrasound is to:

The main purpose of a coupling medium in ultrasound is to reduce reflection at the skin. When ultrasound waves travel from the transducer into the body, they encounter different acoustic impedances at the skin-air interface. The large difference in acoustic impedance between air and soft tissue results in a significant reflection of ultrasound energy, which can hinder the quality of the ultrasound image.

A coupling medium, such as gel, is applied between the transducer and the skin to eliminate the air gap. By creating a direct path for the sound waves, the medium allows ultrasound energy to efficiently transfer into the tissue, thereby minimizing reflection and enhancing the transmission of sound waves into the patient's body. This improved transmission is crucial for obtaining clear and accurate diagnostic images.

Other options, while related to aspects of ultrasound, do not accurately capture the primary function of the coupling medium. For instance, the coupling medium does not primarily enhance image resolution (though reduction of reflection may indirectly contribute to clearer images). It also does not increase sound velocity; instead, its primary role is to facilitate better sound transmission by matching impedances. Lastly, while it’s important to consider thermal protection during procedures, this is not a function of the coupling medium itself.