Introduction Flashcards
Radiation
The transfer of energy as particles or electromagnetic (EM) waves
Ionizing radiation
Radiation with sufficient energy (>15eV) to cause3 an atom or molecule that it reacts with to lose an electron
Production of X-Ray
Occurs through the conversion of energy within particulate radiation (electrons) to electromagnetic energy (X-rays)
Focusing cup
Negatively charged, repels the electrons and “focuses” the electron cloud toward the anode
KeV
Kiloelectron volt
The measure of the energy of a photon or electromagnetic wave
KVp
Kilovoltage peak applied across the tube
Beam includes many other energy X rays
Average energy of the beam is 1/3 - 1/2 KVp
Photoelectric effect (PE)
Ion pair created
Photon totally absorbed and does not contribute to image formation
Compton scatter (CS)
Ion pair created
Only some of the photon (X-Ray) energy is absorbed, but still continues as a lower energy X-Ray photon in a new direction
Probability of interaction is proportional to physical density of the subject/ (Energy)
Increased kVp decreases likelihood of
Compton scatter
Increased KVP decreased likelihood of
Photoelectric effect
Increased atomic number
Increased likelihood of photoelectric effect
No effect on Compton
Thickness/density of object increases
Compton scatter
Latitude
Maximum difference in Radiographic density of anatomical structures that can be evacuees on a given radiograph
Inversely related to contrast with many shades of gray
High KVp, low mAS
Used to abdomen and thoracic evaluation
The ability of a film to record differences in density (recognizable differences in shades of gray
Increase KVp by 15%
One-half mAS
Contrast
Difference in the photo density between two adjacent anatomic stuctures Very short gra scale Low KVp, high mAS Used for musculoskeletal techniques Decrease KVp by 15% Done mAS
More scatter will be produced with increases in
KVp setting (beam energy) Field size (collimating on) Patient thickness
Reducing scatter after X-Ray productions
Grids
Air gap
Grids
Carefully fabricated series of radiopaque material (lead) alternated with strips of radiolucent material
Transmits only those X-rays on a straight line from the source to the image receptor
Grid ratio =
Height of strips / space between the space
Three components of the image recording system
Film
Intensifying screens
Cassette
Intensifying screens
Converts X-Ray energy into visible light which then exposes the film
Digital imaging and communications in medicine
DICOM
Protocol intended to standardize the way in which images are stored
Picture archive and communication system
PACS
Stage of DICOM images
Direct digital radiography
DR
X-rays converted to electronic signal
Immediate display (3-4 seconds)
Computed radiography
CR
Use cassettes with image plate
Phosphorescence records and stop later image
Read by “laser”
Similar to film-screen systems as far as workflow
Screen construction
Protective coating
Phosphor
Reflective layer
Base
Phosphor
High atomic number
Active layer
Emits layer
Rare Earth - older screens calcium tungstate
Screen speed
Relative number that identifies the efficiency of conversion of X-Radiatio into light
Determined by - phosphor type, crystal size, secondary factors
Advantages of intensifying screens
Decrease X-Ray dose to patient
Decrease X posture times
Increase image contrast
Disadvantages to intensifying screens
Decrease detail
Artifacts
