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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 at least enough energy to knock electron out of orbit (ionizing radiation)
        • Gamma ray and x-ray of same energy will appear alike but have different origin
          • Gamma: Originates from nucleus of atom, usually from radioactive decay
          • X-ray: Originates from interactions with atom's electron r
      • Gamma camera (Anger camera): Detection device capable of capturing and counting gamma rays
        • 2 types: Crystal + photomultiplier tubes (PMTs) (2-step process) or solid state detector (1-step process)
        • Sodium iodide crystal (scintillator) + PMTs
          • Thallium-doped sodium iodide crystal produces light photons when stimulated by gamma or x-ray photons
            • Thicker crystal is more sensitive (more counts stopped) but has lower resolution than thinner crystal
            • Thickness typically 3/8" based on primary use of Tc-99m (140 keV)
            • As electron falls back to lower energy level, low-energy photon (typically in visible spectrum) is emitted
          • PMTs collect light photons and convert them into electronic signals; sets of dynodes amplify signal
        • Solid state detector [e.g., CZT: Cadmium zinc telluride (CdZnTe)]: Collects gamma or x-ray photons and converts them directly into electronic signals
      • Collimator
        • Device attached to gamma camera image receptor that only allows gamma photons perpendicular to face of camera to reach camera crystal or solid state detector
        • 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 image receptor
            • Only allows gamma photons perpendicular to face of camera to reach crystal or solid state detector
          • Diverging: Hole columns are arranged in "V" with camera at narrow end and body at wider end; resulting images on camera are smaller than actual size
          • Converging: Hole columns are arranged in "V" with camera at wide end and body at narrow end; resulting images on camera are larger than actual 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): Thick; 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 100-300 keV
      • Best example: Tc-99m 140 keV, 6 hour t1/2
      • Other commonly used gamma camera imaging radionuclides
        • Ga-67: Primary output: 94, 184, and 296 keV; 79 hour t1/2
        • Tl-201: Primary output: 71, 135, and 167 keV; 73 hour t1/2
        • Xe-133: Primary output: 81 keV; 5.3 day t1/2
        • In-111: Primary output: 173 and 237 keV; 67 hour t1/2
      • Affordable and readily available

    IMAGING ANATOMY

    • General Anatomic Considerations

      CLINICAL IMPLICATIONS

      • Clinical Importance

        Selected References

        1. Mettler et al. Essentials of Nuclear Medicine and Molecular Imaging. Elsevier, 2018
        2. Cherry SR et al. Physics in Nuclear Medicine. Saunders, 2012
        3. Christian PE et al. Nuclear Medicine and PET: Technology and Techniques, 5th Edition. Mosby, 2004
        4. Karesh SM et al. Questions and Answers in Nuclear Medicine. Mosby, 1999
        5. Chandra. Nuclear Medicine Physics: The Basics, 5th Edition. Lippincott Williams & Wilkins, 1998
        6. 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 at least enough energy to knock electron out of orbit (ionizing radiation)
              • Gamma ray and x-ray of same energy will appear alike but have different origin
                • Gamma: Originates from nucleus of atom, usually from radioactive decay
                • X-ray: Originates from interactions with atom's electron r
            • Gamma camera (Anger camera): Detection device capable of capturing and counting gamma rays
              • 2 types: Crystal + photomultiplier tubes (PMTs) (2-step process) or solid state detector (1-step process)
              • Sodium iodide crystal (scintillator) + PMTs
                • Thallium-doped sodium iodide crystal produces light photons when stimulated by gamma or x-ray photons
                  • Thicker crystal is more sensitive (more counts stopped) but has lower resolution than thinner crystal
                  • Thickness typically 3/8" based on primary use of Tc-99m (140 keV)
                  • As electron falls back to lower energy level, low-energy photon (typically in visible spectrum) is emitted
                • PMTs collect light photons and convert them into electronic signals; sets of dynodes amplify signal
              • Solid state detector [e.g., CZT: Cadmium zinc telluride (CdZnTe)]: Collects gamma or x-ray photons and converts them directly into electronic signals
            • Collimator
              • Device attached to gamma camera image receptor that only allows gamma photons perpendicular to face of camera to reach camera crystal or solid state detector
              • 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 image receptor
                  • Only allows gamma photons perpendicular to face of camera to reach crystal or solid state detector
                • Diverging: Hole columns are arranged in "V" with camera at narrow end and body at wider end; resulting images on camera are smaller than actual size
                • Converging: Hole columns are arranged in "V" with camera at wide end and body at narrow end; resulting images on camera are larger than actual 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): Thick; 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 100-300 keV
            • Best example: Tc-99m 140 keV, 6 hour t1/2
            • Other commonly used gamma camera imaging radionuclides
              • Ga-67: Primary output: 94, 184, and 296 keV; 79 hour t1/2
              • Tl-201: Primary output: 71, 135, and 167 keV; 73 hour t1/2
              • Xe-133: Primary output: 81 keV; 5.3 day t1/2
              • In-111: Primary output: 173 and 237 keV; 67 hour t1/2
            • Affordable and readily available

          IMAGING ANATOMY

          • General Anatomic Considerations

            CLINICAL IMPLICATIONS

            • Clinical Importance

              Selected References

              1. Mettler et al. Essentials of Nuclear Medicine and Molecular Imaging. Elsevier, 2018
              2. Cherry SR et al. Physics in Nuclear Medicine. Saunders, 2012
              3. Christian PE et al. Nuclear Medicine and PET: Technology and Techniques, 5th Edition. Mosby, 2004
              4. Karesh SM et al. Questions and Answers in Nuclear Medicine. Mosby, 1999
              5. Chandra. Nuclear Medicine Physics: The Basics, 5th Edition. Lippincott Williams & Wilkins, 1998
              6. Early et al. Principles and Practice of Nuclear Medicine, 2nd Edition. Mosby, 1995.