RADIOLOGY LECTURE 7 ~~~~~~~

Intraoral Radiographs

• Two common types: Periapical and Bitewing
• Periapical: Shows full tooth anatomy; can image multiple teeth or a single tooth.
• Bitewing: Shows only tooth crowns and bone levels; film bites down on a peg.

Radiographic Techniques

• PA Mandible: Images mandible from posterior to anterior; detector on face outside patient's mouth.
• DPT/Panoramic: Patient bites on peg; detector and X-ray source rotate around the head at 180°; creates panoramic projection.
• Lateral Cephalogram: X-rays pass from one side of face to the other; primarily used by orthodontists; detector outside mouth.
• CBCT (Cone Beam CT): Produces cross-sectional and 3D images of teeth and jaws using multiple angles and higher radiation doses; modern technique.
• Image Types:
  • Intraoral: Periapical, bitewing, occlusal
  • Extraoral: DPT/Panoramic, PA mandible, lateral cephalogram
  • 3D Imaging: CBCT

Image Quality

• Goal: Geometric accuracy with minimal distortion.
• Radiolucency/Radiopacity:
  • Radiolucent: More X-rays hit the detector (darker).
  • Radiopaque: Fewer X-rays hit the detector (lighter).
  • Dense objects are radiopaque (absorb more X-rays); less dense objects are radiolucent (allow more X-rays to pass).
• Examples: Amalgam fillings are radiopaque.
• Distortion:
  • Increased distance from detector increases magnification and distortion.
  • Closer object/detector reduces divergence and distortion, resulting in higher accuracy.
  • X-ray beams need to be as perpendicular as possible to the detector to minimize distortion.
    • Parallel detector/object is not enough- beam isn't actually parallel.
• Image Accuracy vs Positioning: Objects should remain parallel and positioned as close to the detector as possible to minimize distortion.
• Minimizing Distortion:
  • Increase distance between x-ray source and detector.
  • Decrease distance of object and detector.

DPT (Panoramic) Specifics

• Focal Trough: The green area; the specific section/slice of anatomy that is in focus/imaging.

Image Types and Distortion

• Panoramics have some geometric distortion; intraoral generally more accurate.
• Overexposure/Underexposure:
  • Overexposure: Too much X-ray; dark image.
  • Underexposure: Too little X-ray; light image.

kV and Image Production

• kV (Kilovoltage): Changes X-ray beam intensity, affecting photon energy.
  • Increasing kV decreases contrast and patient dose (more photons reach detector).
  • Decreasing kV increases contrast and patient dose (more photons absorbed by patient).

Film Holders

• Film holders ensure detectors are parallel with each other.

Other Factors Affecting Image Quality

• Proximity of the object or X-ray tube to the detector.
• X-ray source further from detector results in less distortion; closer proximity causes more distortion (due to divergence)