A material's half-value layer, or half-value thickness, is the thickness of the material at which the intensity of radiation entering it is reduced by one half.

How do you calculate half value thickness?

HVL is measured in millimeters of aluminum. After filtration by one HVL, the subsequent HVL will be higher as the filtered photons have higher energy (thicker material is required to attenuate half of the penetrating beams). It is related to linear attenuation coefficient (μ) with following formula: HVL = 0.693 / μ

What is half value layer in ultrasound?

Half value layer thickness. The depth of tissue that results in 3 dB of attenuation to the intensity. The distance sound travels in a tissue that reduces the intensity of sound to one half its original value.