Radio

• Diagnostic Imaging


  Non-invasive method of making medical images of the body to diagnose a disease
• Diagnostic Imaging Tests


  • X-ray
  • Ultrasound
  • Computed Tomography Scan
  • Magnetic Resonance Imaging
• 1. ray


  Discovered on November 8, 1896 by Wilhelm Conrad Roentgen, angiography was first described in 1896
• Basic Properties of X-ray

  • Have no charge
  • Have no mass
  • Travel at speed of light
  • Are invisible
  • Cannot be felt
  • Travel in a straight line
  • Cannot be deflected by magnetic fields
  • Penetrate all matter to some degree
  • Cause certain substance to fluoresce
  • Can expose photographic emulsions
  • Can ionize atoms
• Radiation Protection


  Goal in diagnostic radiology is to obtain maximum diagnostic information with minimal exposure of the patient, radiology personnel, and general public
• Radiation Units


  • Roentgen, rad, rem
  • Coulomb per kilogram, joule per kilogram
• Exposure Quantity


  Measurement based on the number of ion pairs produced in air by the oncoming radiation, absorbed dose not constant, dose equivalent
• ALARA


  Radiation safety principle
• Biologic Principles


  1. rays produce ionization in tissue
• Practical Considerations


  • Radiation workers in veterinary practices must be aware of the risk of radiation
  • Workers should be skilled
  • Workers should be instructed on the proper use and care of radiation protection devices
  • Pregnant and potentially pregnant women, individuals younger than 18 years old
• Measures to reduce radiation exposure

  • Distance
  • Time
  • Shielding
• Production of X-rays


  1. Electrons released from filament

  2. Tube voltage is applied across the x- ray tube. Electrons, therefore, are accelerated towards positively charged anode, which gives them a certain energy

  3. The electrons strike the anode and the energy released via interaction with the anode atoms produces x- ray photons
• Analog to Digital Conversion

  Analog information is transferred by a voltage or voltage pulse, analog signals that are acquired by medical imaging equipment are converted to digital data, disadvantage of analog format: electronic noise, disadvantage of digital data: potential for formation loss from sampling and quantization
• Computer Processing in Digital Imaging

  Computers are required to handle the large amount of digital data that form a digital image, each digital number is represented in a gray-scale image on a computer/video screen in the form of tiny squares called pixels, or picture elements
• Computed Radiography


  Imaging plate coated with photostimulable phosphors (crystals), exposed cassette is placed in the plate reader, plate reader extracts the imaging plate from the cassette and scans the plate with a red laser, converted into digital data & transferred to computer
• Direct Digital Radiography


  Uses an imaging plate designed with an array of detector elements, 2 main types of detectors: indirect - convert the x-ray energy into light then converted to electrical signal, direct - convert the x-ray energy directly to an electrical pulse, plate directly connected to computer
• Advantages of Digital Radiography

  • Linear response to x-ray intensity over a wide latitude
  • Decreased number of retakes
  • Digital radiography compensates for improper exposure techniques
  • Image windowing, biggest advantage
• Disadvantages of Digital Radiography

  • Do not have the degree of spatial resolution
  • Expensive
• Artifacts in Digital Radiography

  • Underexposure – resultant image appears grainy
  • Overexposure – soft tissue structures not visible
  • Processing artifacts
  • Image plate and plate reader artifacts
• Radiopaque

  Structures that are dense and resist the passage of x-ray, appear white
• Radiolucent


  Structures that are less dense and permit the x-ray beam to pass through them, appear black
• 3 Main Components of X-ray Exposure

  • KvP
  • mAs
  • Time
• KvP


  The power and strength of the x-ray beam, quality of the x-ray
• mAs


  The number of x-ray photons produced by the x-ray tube at the setting selected, quantity of the x-ray
• Time


  How long the exposure lasts
• Kilovolt Peak (kVp)


  Determines the quality of the beam, controls the contrast of the radiographic image
• Radiographic Geometry & Thinking in 3 Dimensions

  • Magnification and distortion
  • Unfamiliar image
  • Loss of depth and perception
  • Summation sign
  • Border effacement (silhouette sign)
• Unfamiliar Image


  Familiar object sometimes results in the object not being identifiable, patient positioning must be standardized
• Loss of Depth Perception

  Lost in radiograph, minimum of two views at 90-degree angle (orthogonal projections) required
• Summation Sign


  Results when parts of a patient or object in different planes are superimposed
• Border Effacement

  Occurs when two structures of the same radiopacity are in contact, inability to distinguish their margin, results in diseases masking normal radiographic structures
• Role of Perception in Interpretation

  Eyes and brain do not always perceive appearances accurately, viewing many radiographs can minimize perceptual inaccuracy
• Naming of Radiographic Projections

  Point of entrance to point of exit, names of lateral radiographs of the abdomen and thorax are abbreviated relative to the recumbency
• Lateral views of any part should be viewed with the cranial (rostral) aspect of the animal to the viewer's left
• Ventrodorsal or dorsoventral radiographs of the head, neck, or trunk should be placed with the cranial (rostral) part of the animal pointing up and with the left side of the animal to the viewer's right
• When viewing lateromedial or mediolateral radiographs of the extremities, including oblique projections, the radiograph should be placed on the illuminator with the proximal aspect of the limb pointing up and the cranial or dorsal aspect of the limb to the viewer's left