Radiology 3: lesson & PP

• Major types of image receptors

  • Film based system
  • CR system
  • DR system
• Film based system

  • Dental x-ray film is typically found in two common sizes (size 2 and size 4)
  • Film is flexible which can be helpful for positioning
  • Chairside darkroom will be used to develop the film
• Exposing and viewing film based system

  1. Film is exposed with the convex dot at the rostral end of the mouth

  2. When viewing the film, the convex dot should be toward you

  3. Need to determine if it is a maxillary or mandibular image

  4. If maxillary, the cusps of the teeth should point towards the floor

  5. If mandibular, the cusp should be pointing towards the ceiling
• CR system

  • Similar to standard computerized radiography units
  • Processing unit is much smaller
  • Cassette is phosphor plate that is coved in plastic and must be run through the processor to produce a digital image
• DR system

  • Uses a direct receptor to produce an image immediately after the exposure
  • Plate is usually attached to a wire that goes directly to the computer
  • Digital receptor should be placed in a protective sleeve (plastic or vetwrap) to prevent damage
• Parallel Technique

  1. Can only be used for the caudal mandibular teeth

  2. Film or sensor will be placed parallel and directly behind the teeth

  3. Tube head is positioned perpendicular to the film
• Bisecting Angle Technique

  1. Must be utilized because the film or sensor cannot be placed directly behind the teeth (except for the mandibular teeth caudal to the 3rd premolar)

  2. Bisecting angle is created by the intersection of the long axis of the tooth and the plane of the film

  3. Tube head is positioned perpendicular to that line
• Occusual technique

  1. Places film on the occlusal plane

  2. Parallel to the palate

  3. Directs the beam at a right angle to the film

  4. Provides additional view of tooth, can get good views of incisors and sometimes canines

  5. Allows for imaging the nasal cavity
• Elongation


  Occurs when the x-ray beam is directed more towards the tooth axis and the resulting image will appear stretched
• Foreshortening


  Occurs when the x-ray beam is directed more towards the film or sensor and the resulting image will appear short
• Fluoroscopy


  The X-ray beam is projected up through the table to a screen above the patient
• The image projected is occurring as you see it
• Technician


  • Needs to be protected from primary radiation and scatter radiation by lead shields
• Fluoroscopy is a continuous exposure to x-rays. Extra care should be taken to protect yourself from overexposure
• Computed Tomography


  • Gantry: Contains x-ray tube and detectors that rotate around the patient
  • Cradle: Table that moves patient into gantry at specific intervals
• Transverse most common
• Magnetic Resonance Imaging

  • No x-rays/radiation
  • Powerful magnet aligns polar water molecules in tissues
  • Brief radio wave increases energy of water molecules
  • Scanner measures energy as it is released from the tissues
• Magnetic Resonance Imaging

  • Excellent for evaluating detail in water density tissues (soft tissues)
  • Multiple images taken in narrow slices
  • Images reconstructed by computer in any plane
• Ultrasonography


  • Transducer (probe): Emits a high-frequency sound = ultrasound, Receives the echo reflected back from tissues
  • Echo created depends on tissue density
• Ultrasound cannot penetrate air or bone
• Air (low density) scatters the sound and makes no echo
• Bone (high density) completely reflects the sound wave and prevents any evaluation beyond it
• Ultrasound is designed for soft tissues
• Echogenicity


  The amount of reflected sound, determined by the amount of liquids and solids in the tissue
• Echogenicity types

  • Hypoechoic: Shade(s) of gray
  • Hyperechoic: White or brighter than gray
  • Anechoic: Black/dark
  • Isoechoic: Has same brightness as surrounding structures
• Transducer characteristics

  • MHz = megaHertz: The frequency of the sound wave emitted
  • Penetration: The depth of tissue that may be imaged
  • Resolution: The amount of detail in the image
• Transducer selection

  • Low frequency 2.5-5.0 MHz: High penetration, low resolution, Large animals and large dog internal organs
  • Medium frequency 6-8 MHz: Moderate penetration and resolution, Cats and small dogs
  • High frequency 8-12 MHz: Low penetration, high resolution, Superficial structures: eye, neck, extremities
• Advantages of Ultrasonography

  • No radiation, Patient and technician safety, Allows continuous, moving, real time imaging, Non-invasive, Examine soft tissue without surgery/endoscopy, Safe for neonatal or debilitated patients, Portable
• Limitations of sonography

  • Poor assessment of gas and bone density tissues, Lungs, Gas filled bowel, Skull, spine and extremities, Large animals, Limited penetration, Poor resolution of internal organs
• Abdominal ultrasound

  Patient preparation: NPO 12 hours to reduce GI gas, Full abdominal clip and clean, Ultrasound gel (not EKG or lubricant gel), +/- sedation or anesthesia, Dorsal recumbency in trough for thorough exam, Lateral recumbency
• Echo

  Patient preparation: NPO not necessary, Clip small areas on each side of thorax behind elbow, Ultrasound gel, Light restraint, Lateral recumbency, Sector probe used to fit between ribs
• 1. mode (motion-mode)


  Single line scan, Scan traces across the screen over time (like an EKG), Can be combined with B-mode
• Large animal ultrasound

  Standing position, Common applications: Echocardiography, Abdominal exam, Tendons and ligaments, Reproductive exam with rectal linear array probe
• Linear array probe: muliple transducers in a line. Rectangular image
• Curved array probe: multiple transducers in a fan. curved image
• Sector prope: Transducers oscillate back and forth from a single point. Wedge shaped image