Through diffraction and refraction on intersections edge acoustic shadowing can be created. The acoustic shadowing artifact is the loss of information below a dense object because the majority of the sound energy was reflected back by the object.
Shadowing artifacts occur if decreasing of the echo amplitude is not exponential with penetration depth caused by inhomogeneous tissue layers and fluid or air-filled regions. Bone, air, foreign bodies and calcification stop the transmission of sound waves producing a 'sonic shadow' which is a dark region distal to the echogenic obstructing region. This artifact occurs also in objects like e.g. prosthetic valves.

See also Boundary Layer, and Half-Value Layer.

The amplitude is the signal height. The amplitude of the ultrasound echo is proportional to the difference of the acoustical impedance caused by different tissue layers. The amplitude decreases with increasing penetration depth of a homogeneous tissue.

See also Color Amplitude Imaging.

Increasing the frequency of the transmitted power improves the image quality of ultrasound, but the improvement in resolution results in a decreased signal to noise ratio (SNR). Higher acoustic power levels can prevent the loss in SNR, but among other reasons, ultrasound regulations limit this to avoid heating or cavitation.
Coded excitation increase the signal to noise ratio without the loss of resolution by using coded waveforms. Coded excitation allows transmitting a long wide-band pulse with more acoustic power and high penetration of the sound beam.

To calculate the echo position, a constant sound speed of 1538.5 m/sec is assumed. Tissue penetration is frequency depended, if the frequency increases, the imaging depth decreases. The range resolution defines the depth. Ultrasound propagating in tissue is attenuated due to scattering and absorption. The attenuation is proportional to depth and frequency and is typically in the range from 0.5 to 1 dB/(MHz cm).

See also Attenuation Coefficient, Proximity Sensor, and Echo Ranging.

Enhancement artifacts occur if decreasing of the echo amplitude is not equal with penetration depth caused by inhomogeneous tissue layers and fluids like cysts or air-filled regions. The enhancement artifact appears as a hyperintense (hyperechoic) signal. The attenuation of the ultrasound wave in fluids is much lower as the attenuation in other tissues, therefore tissues distal to fluid are enhanced. Artificial enhancement may also be found distal to a homogeneous solid tumor surrounded by adipose tissue, due to the comparatively high attenuation in fat.

See also Boundary Layer, and Half-Value Layer.