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All sound beams lose energy, or become attenuated, during transmission through tissues; therefore, the returning sound wave is weaker than when it started. Different frequencies (MHz) are attenuated to different degrees. Because higher frequency probes send more waves per second, there is greater tissue interaction with the sound waves. This provides improved resolution but undergoes more attenuation. Low‐frequency sound waves are less attenuated because of less tissue interaction, and therefore allow deeper tissue penetration. Strategies that include lowering the MHz for better penetration (depth) come at the expense of detail. Conversely, using higher frequency for more detail comes at the cost of less penetration (depth). Furthermore, high‐density tissues attenuate the sound waves more than low‐density tissues (Figure 2.3).

Pearl: The analogy of hearing a boom box from a distance can help you remember which MHz penetrates more. The bass dominates (low MHz) over higher frequencies (high MHz); thus, low MHz penetrates deeply at the expense of detail, and high MHz give better detail at the expense of penetration.