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Gamma Camera Imaging
Angela P. Bruner, PhD, DABR; John Bailey, MD
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KEY FACTS

  • Terminology

    TERMINOLOGY

    • Definitions

      • Gamma radiation
        • Electromagnetic radiation that has high enough energy to knock electron out of orbit or more (ionizing radiation)
        • Originates from nucleus of atom, usually from radioactive decay
        • Appear like x-rays at same energy but x-rays are produced by interactions with electron shells of atom
      • Gamma camera (Anger camera)
        • Detection device capable of capturing and counting gamma rays
        • Uses solid crystal, which energizes or ejects electrons when interact with gamma ray photon
        • Sodium iodide crystal (scintillator) + array of photomultiplier tubes (PMTs)
          • Thallium-doped sodium iodide crystal produces light when stimulated by gamma or x-ray photons
            • Thicker crystal is more sensitive (more counts stopped) but has lower resolution
            • Thickness typically 3/8" based on primary use of Tc-99m (140 keV)
          • PMTs gather light and convert it to electronic signal near location it was detected
            • Includes set of dynodes that amplify signal
        • As electron falls back to lower energy level, low-energy photon (typically in visible spectrum) is emitted, detected, and counted by PMT
      • Collimator
        • Device attached to gamma camera crystal front that only allows gamma photons perpendicular to face of camera to reach camera crystal
        • Designed as series of holes that allow gamma rays through inside metal honeycomb pattern
        • Designed to eliminate photons that would degrade image (e.g., scattered or off-angle)
        • Protects crystal face; typically designed with pressure sensor to prevent impact with patient or other objects
        • Collimators by shape
          • Parallel hole (most common type): Hole columns are all parallel to each other and perpendicular to gamma camera crystal
            • Only allows gamma photons perpendicular to face of camera to reach crystal
          • Diverging: Hole columns are arranged like a "V" with camera at narrow end and body at wider end; resulting images on camera are smaller than real size
          • Converging: Hole columns are arranged like a "V" with camera at wide end and body at narrow end; resulting images on camera are larger than real size
          • Pinhole: Exaggerated version of converging collimator where there is only 1 hole that converges out to width of camera to capture enlarged image
        • Collimators by energy and resolution (LEHR, MEGP, etc.)
          • Low energy (LE): Thin; used with Tc-99m or Tl-201
          • Medium energy (ME): Medium thickness; used with Ga-67 or In-111
          • High energy (HE): Thickest; used with I-131
          • High resolution (HR): Many holes and thick walls between hole columns; lower counts but increased image quality
          • Ultra high resolution (UHR): Many holes and thickest walls between hole columns; lower counts but increased image quality
          • General purpose (GP): Medium number of holes and medium thickness of walls; average between high resolution and high sensitivity
          • High sensitivity (HS): Thin walled between hole columns to allow for higher counts
    • Planar Imaging

      • Camera is placed in fixed position or single view over patient
        • Acquires image of radionuclide position in body from one orientation
    • Radionuclides Used for Gamma Camera Imaging

      • t1/2 short enough to see biological function
      • Primarily gamma-only emitter
        • Beta or alpha emitters better for radiation therapy than imaging
      • Preferably single energy or only a few energies between 100 and 300 keV
      • Best example: Tc-99m 140 keV, 6 hour t1/2
      • Other commonly used gamma camera imaging radionuclides
        • Ga-67: Primary output: 94, 184, & 296 keV; 79 hour t1/2
        • Tl-201: Primary output: 71, 135, & 167 keV; 73 hour t1/2
        • Xe-133: Primary output: 81 keV; 5.3 day t1/2
        • In-111: Primary output: 173 & 237 keV; 67 hour t1/2
      • Affordable and readily available

    IMAGING ANATOMY

    • General Anatomic Considerations

      CLINICAL IMPLICATIONS

      • Clinical Importance

        Selected References

        1. Cherry SR et al. Physics in Nuclear Medicine. Saunders, 2012
        2. Christian PE et al. Nuclear Medicine and PET: Technology and Techniques, 5th Edition. Mosby, 2004
        3. Karesh SM et al. Questions and Answers in Nuclear Medicine. Mosby, 1999
        4. Chandra. Nuclear Medicine Physics: The Basics, 5th Edition. Lippincott Williams & Wilkins, 1998
        5. Early et al. Principles and Practice of Nuclear Medicine, 2nd Edition. Mosby, 1995.
        Related Anatomy
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        References
        Tables

        Tables

        KEY FACTS

        • Terminology

          TERMINOLOGY

          • Definitions

            • Gamma radiation
              • Electromagnetic radiation that has high enough energy to knock electron out of orbit or more (ionizing radiation)
              • Originates from nucleus of atom, usually from radioactive decay
              • Appear like x-rays at same energy but x-rays are produced by interactions with electron shells of atom
            • Gamma camera (Anger camera)
              • Detection device capable of capturing and counting gamma rays
              • Uses solid crystal, which energizes or ejects electrons when interact with gamma ray photon
              • Sodium iodide crystal (scintillator) + array of photomultiplier tubes (PMTs)
                • Thallium-doped sodium iodide crystal produces light when stimulated by gamma or x-ray photons
                  • Thicker crystal is more sensitive (more counts stopped) but has lower resolution
                  • Thickness typically 3/8" based on primary use of Tc-99m (140 keV)
                • PMTs gather light and convert it to electronic signal near location it was detected
                  • Includes set of dynodes that amplify signal
              • As electron falls back to lower energy level, low-energy photon (typically in visible spectrum) is emitted, detected, and counted by PMT
            • Collimator
              • Device attached to gamma camera crystal front that only allows gamma photons perpendicular to face of camera to reach camera crystal
              • Designed as series of holes that allow gamma rays through inside metal honeycomb pattern
              • Designed to eliminate photons that would degrade image (e.g., scattered or off-angle)
              • Protects crystal face; typically designed with pressure sensor to prevent impact with patient or other objects
              • Collimators by shape
                • Parallel hole (most common type): Hole columns are all parallel to each other and perpendicular to gamma camera crystal
                  • Only allows gamma photons perpendicular to face of camera to reach crystal
                • Diverging: Hole columns are arranged like a "V" with camera at narrow end and body at wider end; resulting images on camera are smaller than real size
                • Converging: Hole columns are arranged like a "V" with camera at wide end and body at narrow end; resulting images on camera are larger than real size
                • Pinhole: Exaggerated version of converging collimator where there is only 1 hole that converges out to width of camera to capture enlarged image
              • Collimators by energy and resolution (LEHR, MEGP, etc.)
                • Low energy (LE): Thin; used with Tc-99m or Tl-201
                • Medium energy (ME): Medium thickness; used with Ga-67 or In-111
                • High energy (HE): Thickest; used with I-131
                • High resolution (HR): Many holes and thick walls between hole columns; lower counts but increased image quality
                • Ultra high resolution (UHR): Many holes and thickest walls between hole columns; lower counts but increased image quality
                • General purpose (GP): Medium number of holes and medium thickness of walls; average between high resolution and high sensitivity
                • High sensitivity (HS): Thin walled between hole columns to allow for higher counts
          • Planar Imaging

            • Camera is placed in fixed position or single view over patient
              • Acquires image of radionuclide position in body from one orientation
          • Radionuclides Used for Gamma Camera Imaging

            • t1/2 short enough to see biological function
            • Primarily gamma-only emitter
              • Beta or alpha emitters better for radiation therapy than imaging
            • Preferably single energy or only a few energies between 100 and 300 keV
            • Best example: Tc-99m 140 keV, 6 hour t1/2
            • Other commonly used gamma camera imaging radionuclides
              • Ga-67: Primary output: 94, 184, & 296 keV; 79 hour t1/2
              • Tl-201: Primary output: 71, 135, & 167 keV; 73 hour t1/2
              • Xe-133: Primary output: 81 keV; 5.3 day t1/2
              • In-111: Primary output: 173 & 237 keV; 67 hour t1/2
            • Affordable and readily available

          IMAGING ANATOMY

          • General Anatomic Considerations

            CLINICAL IMPLICATIONS

            • Clinical Importance

              Selected References

              1. Cherry SR et al. Physics in Nuclear Medicine. Saunders, 2012
              2. Christian PE et al. Nuclear Medicine and PET: Technology and Techniques, 5th Edition. Mosby, 2004
              3. Karesh SM et al. Questions and Answers in Nuclear Medicine. Mosby, 1999
              4. Chandra. Nuclear Medicine Physics: The Basics, 5th Edition. Lippincott Williams & Wilkins, 1998
              5. Early et al. Principles and Practice of Nuclear Medicine, 2nd Edition. Mosby, 1995.