Anisotropic is an area or structure with varying acoustic properties according to the direction in which they are imaged. For example, the characteristic ultrasound appearances of tendons are hyperechoic, but they appear hypoechoic when the sound beam is not at right angles to the tendon fibers.

An image artifact is any image attribute, which is not present in the original imaged object. An image artifact is sometime the result of an improper operation of the imager, and in other times a consequence of natural processes or properties of the human body.
Artifacts in diagnostic ultrasound are a reflection or an echo, which appears on the display and represents the real anatomical structure not correctly. An artifact can be a false, multiple or misleading information introduced by the imaging system or by interaction of ultrasound with the adjacent tissue.

Artifacts in ultrasound can be classified as to their source like e.g.:
Image artifacts can occur in each medical ultrasound. Then an interpretation of the image is complicated and can eliminate the structural information of objects looking for.

See also Ultrasound Imaging Procedures.

The beam vessel angle is between the axis of the ultrasound beam and the axis of a vessel lumen. This angle is equal to the Doppler angle when flow is parallel to the vessel axis.
Also called angle of attack.

For the flowprobe a vessel is positioned between transducers which generate wide beams of ultrasound to fully illuminate the vessel. The ultrasound beams alternately intersect the flowing blood in upstream and downstream directions. The flowmeter derives an accurate measure of the changes in transit time influenced by the motion of the blood.

See also Bi-directional Flow.

(TIB) The bone thermal index is an exposure model for the case that the ultrasound beam passes through soft tissue and a focal region is in the immediate vicinity of bone.
The longitudinal waves of ultrasound are reflected and transformed into transverse waves, creating a heating effect. Muscle and bone absorb more energy at interfaces with other heterogeneous tissues.

See also Sheer Wave.