Diagnostic Imaging Flashcards
Radiodensity:
- amount of radiation a material absorbs
Radio-opaque =
ABSORBS MORE RADIATION
Radiolucent =
ABSORBS LESS RADIATION
List of materials found in the human body from most radiodense to least radiodense:
- foreign heavy metal (absorbs most radiation)
- enamel
- bone
- water density (muscle, cartilage, blood, etc.)
- fat
- air (absorbs least radiation)
The more radiodense an object is, what color does it appear on XR and CT?
- Lighter/whiter
What happens to the film as the thickness of the material that the x-ray passes through increases?
- more radiation absorbed
- less radiation reaches film
- object appears lighter/whiter
How can you determine if an object is in the front or the back of another object in an XR/CT?
- Cannot tell from a single image.
- Need to take multiple projections.
- Perpendicular projections will give you 3D.
Anterior projection acronym and description:
- PA
- Anterior side faces film.
- Posterior side faces XR source.
Posterior projection acronym and description:
- AP
- Posterior side faces film.
- Anterior side faces XR source.
Left lateral projection description:
- Patients left side faces film.
Right lateral projection:
- Patients right side faces film.
The four oblique projections:
BASED ON BODY PART CLOSEST TO FILM.
TYPICALLY AT 45°.
- Left anterior oblique (LAO)
- Right anterior oblique (RAO)
- Left posterior oblique (LPO)
- Right posterior oblique (RPO)
How are diagnostic images always read?
- always as if the patient is facing/looking at you.
If you are interested in a particular structure, how should the patient be oriented relative to the film?
- With the structure of interest closest to the film.
- Increases resolution of the structure.
- e.g. if you want image of spine, order posterior projection since patients posterior side will be closest to the film.
The closer a structure is to a film:
- the higher the resolution.
Penumbra effect:
- further an object is from the film, the more blurry the edge will be.
Magnification of an object/structure on a film increases:
- the further that object is from the film.
How do you minimize the superimposition of structures on a XR/CT film?
- Use oblique projections.
How to read a computed tomography (CT) and MRI scans:
- as if you are looking up into a supine patient from the patient’s feet.
- top film = anterior
- bottom film = posterior
- left film = right
- right film = left
Label this image:
What kind of images do CT and MRI scans take?
- Axial (cross-sectional) images
Colors on CT scans (white and black):
- white = radiodense (bone, metal)
- black = radiolucent (fat, air)
Colors on MRI scans (white and black):
- white = radiolucent (air, fat)
- black = radiodense (bone, metal)
What do MRIs measure?
- Very strong magnet aligns hydrogen atoms.
- Radiofrequency pulse (RF pulse) causes hydrogen atoms to bend.
- RF pulse turned off, hydrogen atoms return to alignment and release energy.
- Amount of energy released is measured.
What is ultrasonography good at imaging?
- interfaces between solids and fluids (i.e. embryo in amniotic sac)
- cheap and portable
