Medical Imaging Flashcards
Why do Physical Therapists need to know how to view x-rays?
- more comprehensive evaluation is obtained
- PT will look at an x-ray for different reasons than a radiologist (alignment, fracture configuration, etc.)
- APTA seeks to allow PT’s to be able to order musculoskeletal radiographs
Who discovered X-rays?
Wilhelm Roentgen in 1895
Marie Curie discovered radioactive elements in 1898
X-Ray Wavelength
- Shorter the wavelength, the higher the energy and greater penetration of dense substances
- Produces ionization of atoms and molecules (loss of electrons)
- Results in a gray image on the radiograph
Production of a Radiograph
An x-ray beam source
A patient
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 and strike the anode
Attenuation
- Gradual loss of intensity as a result of passing through a medium
- How much attenuation depends on the density of the tissue
- Air is darker, bone is whiter
Radiodensity
- Refers to the amount of blackening on the radiograph
- Determines how much radiation will be absorbed
1) Radiolucent
2) Radiopague
-NOT photographs, but actually densographs
75% film-reading is knowledge of anatomy
Radiolucent
- Does not absorb much radiation
- Appears dark grey or black
ex) Air and Fat
Radiopaque
- Absorbs a lot of radiation
- Appears more white
ex) Metal and bone and teeth
Radiodensity determined by…
- Atomic weight
- Greater atomic weight = Greater radiodensity
- Lead used as a shielding device (high atomic weight) - Thickness of the object
- Thick object = more radiation absorbed = more radiodense
Density of tissues
- Greater density of tissue = less penetration of the x-rays
- Higher density tissues appear white
ex) Flat wedge vs. Upright wedge
Third Dimension Perception
- Need more than one radiograph to get information about a structure
- 2 projections are taken at 90° orientation (Minimizes 2D Error!)
Body Positioning
- Specific protocol for every body part to give best visualization w/ lowest # of radiographs
- Routine views: AP, lateral, & oblique
Anterioposterior (AP)
-Whiplash pts. to make sure Co & C2 are still intact
Posteroanterior (PA)
-Lung dysfunction
Tangetial
-Patella & Femur
aka “Sunrise” View
Axial
-Straight down from the top of patient
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
Film Markers
Patient ID Anatomical Side Markers (L/R) IR ER WB Erect, upright Decubitus (laying down) INSP/EXP Radiographers Initials
Image Quality Factors
- Controlled by varying the milliamperage (mA) & exposure time
- Distance of body part from beam affects this as well
- Underexposure: beam not on long enough
- Overexposure: beam on too long (more intensity)
Radiographic Contrast
- Greater variation in anatomy = higher contrast
- Chest = low contrast
- Skeleton = high contrast
Contrast
- Controlled by: kilovoltage (kVp)
- Higher kVp = greater energy of beam= greater penetration = more uniform picture = less variation in tissue absorption
From this, a low contrast radiograph occurs
General Rule
Use the highest kVp and lowest mA
Will yield the best diagnostic information necessary for patient intervention
Radiographic Distortion
Difference between the actual object and 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
Causes: Beam Source, Patient, Film, Alignment of the Body, Position of the Central Ray
Superimposition
- Anatomic structures are stacked on one another so the x-ray beam must penetrate multiple structures before arriving at the film plate.
- May create artificial lines, shapes, and forms that appear unrecognizable or pathological in nature.
- 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
ex) Osteoporosis
ABCD’S: Cartilage Space
- Joint space width
- Subchondral bone
- Epiphyseal plates: can tell their age by what age the plates fuse together in life
ABCD’S: Disc Space
-Only when valuating the cervical, thoracic, or lumbar spine
ABCD’S: Soft Tissue
- Muscles
- Fat pads
- Joint capsules
- Periostreum
- Mescellaneous soft tissue findings
Contrast-Enhanced Radiographs
- Radiolucent: Air
- Radiopaque: Barium sulfate or Iodide
