rads

Radiography • differerential absorption is necessary to create an image. the image represents a lack of absorption; darker areas are where x rays were not absorbed, in contrast to bright shadows cast by structures with great absorption. In order to be visualized, a stucture must be surrounded by a substance of differing radiopacity.

• radiographic opacities

• geometry of magnification

• distortion (object and receiver planes are not parallel)

• “the unfamiliar image concept”

• loss of depth perception

• superimposition opacities (small structures surrounded by air cast disproportionately opaque superimposition opacities)

• summation sign

• silhouette sign/border effacement

Sonography • differential reflection. B-mode images are a collection of dots that correspond to the amplitude of strength of the returning echo. These dots are displayed on a black background. Increasing the power (V) leads to a uniform increase in image echogenicity. Keeping the power low helps improve image resolution and prevent artifacts. “subtle parenchymal echotexture”

Artifacts have the potential to enhance evaluation of structures by providing insight to their composition. Sonographic imaging of a fluid-filled structure is characterized by enhancement of soft tissues distal to it, where a hypoechoic tissue mass looks similar but does not show distal enhancement.

• echogenicity (the ability to generate echoes)

• attenuation

• acoustic shadows (soft tissue-bone and soft tissue-gas interfaces; renal, cystic, or cholecystic calculi)

• spatial compounding?

• acoustic enhancement

• reverberation artifacts

• mirror-image artifacts (when the liver is imaged with the diaphragm/lung interface acting as a highly reflective structure)

• slice thickness artifact (in the urinary and gallbladder, mimic the presence of sludge or sediment)

• refraction (displays organs to the side of their actual location, appear wider than normal)

• edge-shadowing artifact (refraction artifact created by a curved surface, with anechoic regions distal to the curved surface; seen with kidneys, urinary and gall bladder)