object thickness + inherent opacity (air, fat, soft tissue/fluid, mineral, metal)
How can you achieve some depth perception when looking at 2D radiographs?
- at least 2 orthogonal projections
- mentally reconstruct depth using 2 views
What is magnifications, and what causes it?
- enlargement relative to actual size
- varies with object-film distance; increased distance leads to increased magnification
What is distortion?
for a magnified image, each bit of information is spread over a larger area, leading to decreased sharpness [therefore, we want the object being imaged as close to the plate as possible...except lungs]
What causes a summation sign?
- when parts of a patient are in different planes but are superimposed on each other on an image
- this causes the opacity of both to increase (summed)
What opacity causes a negative summation?
gas [makes whatever it is summated with have a decreased opacity]
What causes a silhouette sign?
- two structures of similar opacity touch each other (but do not overlap really) and create a new silhouette
- may result in the two structures being unrecognizable
How do you name radiographic projections?
point of entrance --> point of exit [ex. ventro-dorsal, animal in dorsal recumbency]
How do you hand the different projections (by convention)?
- Lateral: head to left, spine at top
- VD/ DV: head at top, patients right on left side of image
- Craniocaudal/ dorsopalmar: proximal at top, lateral on left side of image
What is radiographic TPR?
- phase of Respiration
What are the Rontgen signs? (6)