An imaging direction, backwards relative to a short axis of the human body from the back to the front.

If available, some graphic aids can be helpful to show image orientations.
1) A graphic icon of the labeled primary axes (A, L, H) with relative lengths given by direction sines and orientation as if viewed from the normal to the image plane can help orient the viewer, both to identify image plane orientation and to indicate possible in plane rotation.
2) Ingraphic prescription of obliques from other images, a sample original image with an overlaid line or set of lines indicating the intersection of the original and oblique image planes can help orient the viewer.


In all cases the scanning surface is assigned to the top of the image. The orientation of single oblique slices can be specified by rotating a slice in one of the basic orientations toward one of the other two basic orthogonal planes about an axis defined by the intersection of the 2 planes.

See also Histogram.

Anatomic structures respond with characteristic features on ultrasound scanning.
There are some ultrasound terms, referring to the echo appearance, that describes tissue appearance in a uniform manner:

Tendons characteristically are hyperechoic on ultrasound because of the fibrillar pattern. Ligaments appear hyperechoic when the beam is perpendicular to the tissue. Peripheral nerves are hyperechoic relative to muscle.
Muscle appears relatively hypoechoic to tendon fibers. Close observation reveals hypoechoic muscle fibers separated by hyperechoic septae that converge on a hyperechoic aponeurosis. Articular hyaline cartilage appears hypoechoic. The presence of fluid within the joint outlining the cartilage produces a thin bright echo at this interface.
Sound beams do not penetrate the bone cortex. The very bright echo produced at the interface allows both recognition of the bone cortex but also can demonstrate fracture, spurring and bone callus bridging. Abnormal soft tissue calcification and ossification also produces bright reflective echoes.
Cysts or fluid filled areas are without internal echoes and are called echo free or anechoic and may demonstrate enhanced soft tissue echoes posterior to the fluid collection. Inflamed metatarsal bursae and calcaneal bursae clearly depict fluid swelling.

See also Beam Pattern and Zero Offset.

The transforaminal or sub-occipital acoustic window is found in the space between the atlas and the base of the skull (through the foramen magnum insonated from the top of the neck below the occiput). Practiced in the prone position (or sitting).
This acoustic window allows the insonation of the vertebral arteries, basilar artery and some of the other branches of the posterior circulation (e.g. posterior inferior cerebellar artery).

See also Transcranial Doppler.

The temporal area is the thinnest portion of the skull and the squamous component with less cancellous bone provides ultrasound permeability. The transtemporal window is found between the angle of the eye and the pinna of the ear above the zygomatic ridge. Finding this window can be difficult because size and location vary with each patient (more difficult in elderly and females) and from one side to the other.
This window allows the insonation of the middle, anterior and posterior cerebral arteries, the anterior and posterior communicating, and the terminal internal carotid.

See also Transcranial Doppler.