What results in a thicker half-value layer thickness?

The half-value layer thickness (HVL) refers to the thickness of material needed to reduce the intensity of the ultrasound beam by half and is influenced by both frequency and the attenuation properties of the medium. A thicker HVL indicates that ultrasound can penetrate more deeply without losing as much intensity.

When considering the impact of frequency and attenuation rate, a low frequency leads to less scattering and absorption as sound waves travel through a medium. Furthermore, a medium with a low attenuation rate inherently enables the sound waves to preserve their strength over greater distances. This combination means that less material is required to reduce the intensity of the sound waves by half, resulting in a thicker HVL.

In contrast, high frequency is associated with greater attenuation (loss of intensity), meaning higher frequencies are absorbed and scattered more quickly, resulting in a thinner HVL. Therefore, the correct choice reflects the combination of low frequency and low attenuation rate as factors that contribute to a thicker HVL.