ARDMS Ultrasound Physics & Instrumentation Practice Exam

What happens to absorption as frequency increases?

1. Absorption decreases

2. Absorption increases

3. Absorption remains constant

4. Absorption varies

The correct answer is: Absorption increases

As frequency increases, absorption increases due to a number of factors intrinsic to ultrasound physics and the properties of tissue. Higher frequency sound waves tend to have shorter wavelengths, which leads to greater interaction of the sound waves with the medium through which they are passing, such as human tissue. In biological tissues, the molecular interaction mechanisms, such as vibrations at a cellular level, become more pronounced with increased frequency. This results in more energy being converted to heat as the sound waves penetrate the tissue, thereby enhancing the rate of absorption. Consequently, with higher frequencies, the sound waves do not travel as deeply into the tissue, as much of the ultrasonic energy is absorbed near the surface, leading to the phenomenon where the overall absorption of the ultrasound increases with frequency.