Radiology/Imaging Flashcards
How are x-rays produced in a generator?
by the interaction of an electron beam with a Tungsten target
Why do spaces on x-rays appear black?
This is where the x-ray beam was not absorbed
What determines how much of the x-ray beam will be absorbed?
The density of the object being imaged
Dense structures _____ more of the x-ray beam than less dense structures and appear _____ on film.
Absorb / white
radioopaque
material that does not allow x-rays to pass, or attenuates them
radiolucent
material that allows x-rays to pass (such as air)
4 Basic radiographic densities
- air - black
- fat - dark gray
- soft tissues/organs - gray
- metal/calcium/bone - white
Water density
term referring to the shades of gray seen on x-ray
How is a CT different from an x-ray?
the gantry moves around the supine patient in CT, as opposed to the stationary, uni directional radiograph
How are CT axial images obtained?
the patient slides through the gantry as it circles the patient, so each “slice” is viewed by the scanner at 90 degrees to the transverse axis
Main factors affecting CT appearance
- density of a structure
- display of the image
- the use of contrast enhancement agents/not
Which imaging modality allows structures of differing densities to be seen in varying shades of gray?
CT - because of it’s spatial resolution capabilities, superior to x-ray
How does IV dye enhance structures on CT?
IV dye is injected; the more dye a structure absorbs, the lighter gray it appears, the more it is said to be enhanced
In the brain, the white matter tracts appear _____ than the gray matter.
darker
Regions well-observed on CT
chest
abdomen
brain
also useful for intraarticular join evaluation
