Notes on Medical Imaging Technologies and X-Ray Production

X-Ray Production

  • X-rays are produced, not stored.
  • Requirements for X-ray production:
    • A source of electrons.
    • A method to accelerate the electrons.
    • A mechanism to bring the electrons to a sudden stop.

X-Ray Tube

  • Components of the X-ray tube:
    • Cathode: The negative electrode providing the source of electrons.
    • Anode: The positive electrode where the electrons are decelerated, resulting in X-ray production.
    • Collimator: A device to focus and shape the X-ray beam.
  • Efficiency: Less than 1% of the energy used results in X-rays; over 99% is converted to heat.

Radiographic Imaging

  • Digital Imaging Types:
    • Computed Radiography (CR): Uses imaging plates coated with photostimulable phosphor.
    • Direct Digital Radiography (DR): A cassette-less system with direct image receptor.
Advantages of Digital Radiography
  • Elimination of film and chemicals.
  • Faster results for patients.
  • Ability to manipulate and adjust images.
  • Reduced patient dose and fewer repeats needed.
  • Awareness of "exposure creep" is necessary to avoid overexposure.
  • Elimination of fog and enhanced image storage capabilities.

Radiation Safety - ALARA

  • ALARA: As Low As Reasonably Achievable
    • Principle to minimize radiation exposure while obtaining high-quality diagnostic images.

X-Ray Exposure Factors

  • Milliamperes (mA): Controls the flow of electrons over time:
    • mAs=mAimestmAs = mA imes t (e.g., 600mAimes0.1s=60mAs600 mA imes 0.1 s = 60 mAs).
  • Kilovoltage Peak (kVp): Controls the penetrating ability of X-ray photons.
  • Distance: The distance from the X-ray source to the image receptor affects radiation intensity; more distance results in less radiation reaching the receptor due to beam divergence.

Characteristics of Radiographic Images

Image Brightness
  • determined by receptor exposure; brighter areas indicate less dense materials, darker areas indicate denser materials.
Image Contrast
  • Difference in brightness between light and dark areas; influenced by the anatomy being imaged and the X-ray settings.
Fog
  • A reduction in image quality caused by scatter radiation, which darkens the overall image; can be minimized using collimation or grids.
Spatial Resolution
  • Ability to see details; affected by:
    • Source-to-image distance (SID)
    • Motion of the subject
    • Pixel size, which cannot be controlled by the radiographer.
Distortion
  • False representation of objects:
    • Size distortion happens with increased object-to-image distance (OID).
    • Shape distortion caused by improper angling of the X-ray tube; can lead to foreshortening or elongation.

Specialized Imaging Equipment

Portable Radiography
  • Used for patients outside traditional settings; requires strict radiation safety measures.
Fluoroscopy
  • Provides real-time images; used in various procedures.
Other Imaging Technologies
  • CT: Cross-sectional imaging improving diagnosis.
  • MRI: Uses magnets and radio waves; no ionizing radiation.
  • Nuclear Medicine: Uses radiopharmaceuticals to visualize organs.
  • PET: Evaluates physiological functions.
  • Sonography: Employs high-frequency sound waves; used notably in obstetric imaging.

Image Storage

  • PACS: Picture Archiving and Communication System allows for digital image storage, enabled by networks connecting to hospital information systems (HIS) and radiology information systems (RIS).

Conclusion

  • Continual advances in imaging technologies demand that radiologic technologists remain educated in latest equipment and physics of imaging to ensure high-quality diagnostic functionalities.
    • The integration of computer technology is pivotal in modern diagnostic imaging.