Medical Imaging Flashcards
What do PTs look for?
- More comprehensive Eval
- Alignment
- Fracture configuration
Want to move into ordering X-rays
History
- form of electromagnetic radiation
- made without contrast enhancement
X-Ray Wavelength
- Shorter the wavelength, the higher the energy & greater penetration of dense substances
- Produces ionization of atoms and molecules (loss of electrons)
- Results in a gray image on the radiograph
Requirements to produce a radiograph
- An x-ray beam source
- A pt
- A x-ray film or image receptor
X-Ray Tube
- Cathode (negative) and anode (positive) enclosed in glass envelope which maintains a vacuum.
- High voltage current passes through a vacuum
- Electrons are driven from cathode & strike the anode- decelerate & creates x-rays via energy consumption
Making a Radiograph
- Current is beamed through a series of shutters and directed toward the body [At or near a 90° angle]
- X-ray beam passes through the body and undergoes a process of Attenuation
- Human body absorbs rays in various amounts depen. on tissue characteristics
- X-ray film sensitive to light & radiation, chemical reaction occurs causing an image to be produced in shades of gray on a black film- Film is coated in silver causing an ionization of molecules to occur
- Final image is a representation of the radiodensity of the anatomical structures the x-rays have passed through [shows density of structure]
Attenuation
Defined as the gradual loss of intensity as a result of passing through a medium
Radiodensity
- Refers to the amount of blackening on the radiograph
- Determines how much radiation will be absorbed
- Radiolucent
- Radiopaque
Radiolucent
- Doesn’t absorb much radiation
- Appears dark grey or black
- Air and Fat
Radiopaque
- Absorbs a lot of radiation
- Appears more white
- Metal and bone
- Teeth are the most radiopaque
Radiodensity determined by…
- Atomic weight or composition
- The greater the atomic weight the greater the radiodensity- Lead used as a shielding device (high atomic weight) to prevent radiation into body - Thickness of the object
The thicker the object, the more radiation absorbed = more radiodense
Densographs
- Radiographs are not photographs
- represent tissue density
- Normal tissues are gray, with any observed density changes, one can assume pathology is present.
75% of film-reading skill is knowledge of anatomy.
Density of tissues
- The greater the density of the tissue, the less penetration of the x-rays
- Highest density tissues appear white [ex: teeth]
Third Dimension Perception
- Need more than one radiograph to get information about a structure
- One view is no view
-2 projections are taken at 90° orientation [Minimizes 2D Error]
2D Error
Avoid making definitive statements regarding anatomical relationships based on a single x-ray view
Body positioning
- specific
- provide best visualization of body area with least # of radiographs
- routine views: AP, lateral and oblique
Viewing Radiographs
- Place film on view box as if the viewer (you) are the x-ray beam
- Consider the area x-rayed
- Consider this area must be closest to the film to get an accurate picture
- Consider the x-rays must pass through the person to get to the film
Image Quality Factors -Radiographic Density
- Controlled by varying the milliamperage (mA) and exposure time
- Distance of body part from beam affects this as well
- Underexposure or Overexposure
Image Quality Factors -Radiographic Contrast
- Anatomical detail more visible on the x-ray
- Greater the variation in anatomical structures, the higher the contrast
- Chest radiograph = low contrast
- Skeleton = high contrast
Contrast
- Contrast is controlled by: kilovoltage (kVp)
- Higher the kVp, the greater the energy of the x-ray beam which causes greater penetration through the body parts.
- More penetration, more uniform is the picture & will have less variation in tissue absorption & a low contrast radiograph occurs
General Rule
Use the highest kVp and lowest mA which will yield the best diagnostic information necessary for pt intervention
Recorded Detail
-Lack of detail = Blur [Primary controlling factor is MOTION]
-Other Factors:
Beam source diameter
Distance between beam source and film
Distance b/w beam source and pt
Radiographic Distortion
- Difference b/w the actual object & it’s recorded image
- Radiographs are 30% larger than actual structure
- Shape Distortion:Unequal magnification of structure
- -Central ray accurate
- -More inclined the structure = greater distortion
Size Distortion
Enlargement
Elongation
Shortening
Radiographic Distortion Causes
Beam Source Patient Film Alignment of the Body Position of the Central Ray
Superimposition
- Occurs when anatomic structures are stacked or superimposed on one another so that the x-ray beam must penetrate multiple structures before arriving at the film plate.
- -This may create artificial lines, shapes, & forms that appear unrecognizable or pathological in nature.
- -Can also serve to falsely obscure pathology
- Again, 2-D representation of a 3-D structure.
Evaluating Plain Film Radiographs
ABCD’S:
- Alignment
- Bone Density
- Cartilage Space
- Disc Space
- Soft Tissue
ABCD’S: Alignment
- General structural architecture
- General contour of bone
- Alignment of bone relative to adjacent bones
ABCD’S: Bone Density
- General bone density
- Texture abnormalities
- Local bone density changes
ABCD’S: Cartilage Space
- Joint space width
- Subchondral bone
- Epiphyseal plates
Epiphyseal Plates
- growth plate
- Hyaline cartilage plate in the metaphysis at each end of a long bone.
ABCD’S: Soft Tissue
- Muscles
- Fat pads
- Joint capsules
- Periostreum
- Mescellaneous soft tissue findings
Contrast-Enhanced Radiographs
-Contrast medium injected or ingested into the body
Improves visualization in areas with low contrast
-Can be radiolucent: Air
-Can be radiopaque: Barium sulfate or Iodide
-Can be dual [ex: gastointestinal dual-contrast]
