Gallium-67 Imaging

  1. Physiology of Gallium-67
    1. Is an analog of Iron
    2. While many theories have been developed on the biopathway of gallium, it is still not completely understood
    3. This is what we know:
      1. Following Ga-67 injection binds to transferring (TF)
      2. Travels in the vascular pool
      3. Using the same mechanism of transportation as iron
      4. Patients with saturated iron binding sites have decreased tissue uptake and increased renal excretion
      5. When imaging infection
      6. Gallium binds to leukocytes via lactoferrin (LF) and TF binding sites. Thee leukocytes attack antigens in the human system
        1. 67Ga enters the infectious process through the intercellular fluid
        2. 67Ga uptake can be seen in an infection that has little blood flow
        3. Siderophores found in bacteria have a great affinity for iron, hence they pickup gallium
      7. Gallium also has a great affinity for certain types of tumors
        1. As gallium travels via TF and diffuses though loose endothelial junctions at the capillary level of the tumor cells
        2. TF receptors on tumor cells pick up gallium
        3. Then 67Ga enters the tumor cell and it concentrates in the lysosomes that have an affinity for TF and LF

      8. Normal distribution
        1. Since LF has a great affinity for lacrimal, salivary, nasopharynx, bone marrow, and spleen Ga-67 uptake is therefore noted in these areas
        2. Gallium also is seen in the liver, which is do the liver's ability to metabolize LT and TF
        3. Up to 24 hours post dose Ga67 is considered vascular therefore renal uptake noted as 15 to 25 % is filtered out of the human system. Post 24 hours renal uptake is considered abnormal
        4. At 24 hours uptake should also be seen in the myocardium and urinary bladder
        5. Gallium is also excreted through feces and activity is usually seen in the large bowel at 24 hour post dose and beyond
        6. Uptake in the lung for the first 24 hours following the injection is considered normal
        7. Skeletal uptake is also considered normal
        8. At 48 and 72 hours post dose images are considered "tissue" or perfusion imaging
  1. The imaging procedure
    1. The normal dose is 6 to 10 mCi
    2. Patient preparation
      1. Since gallium uptake is seen in the bowel there maybe some concern on differentiating fecal from tumor
      2. General, if the area of concern moves from one day?s imaging to the next it is considered to fecal activity, however, if it remains stationary it is thought to be tumor
      3. For additional calcification of possible tumor an enema maybe required
      4. Prior to the gallium injection a liver/spleen scan maybe considered in order to outline this anatomy. Why might this be important?
    3. While 6 and 24 hours images maybe taken for acute infection these images are not usually very helpful since gallium is still in the vascular pool causing a target to background problem
    4. Energy settings
      1. 96 keV with a 20% window
      2. 185 keV with a 20% window
      3. 300 keV with a 20% window
    5. Collimator - ME
    6. Whole body format
      1. Head to mid-thigh (unless disease is present in the appendages)
      2. Scan speed of 10 cm/minute or less
      3. 256 x 1024 matrix
    7. Spot imaging
      1. Matrix = 256
      2. 15 minutes per image
    8. Images should be taken at 24, 48, and 72 hours. Sometimes further delay images, up to 120 hours might be considered
  1. Comments on oncology
    1. Lymphomas and Hodgkin's disease
      1. Used for staging
      2. Approximately 75% of tumors are gallium avid
      3. False-positive rate is less than 6%
    2. For lung CA staging
      1. Sensitivity ranges from 100 to 93%
      2. Specificity ranges from 63 to 30%
    3. Primary hepatoma is about 90% sensitive
      1. Liver/spleen scan is suggested
      2. Sulfur colloid will be cold
      3. Ga-67 will be hot
      4. Lesions smaller than 2 cm are general not detected
    4. GI/GU tumors have poor sensitivity and specificity
    5. Melanoma
      1. 82% sensitive and 99% specific
      2. Tumor size must be at least 1 cm
    6. Head and neck tumors
      1. Overall sensitivity was 56%
      2. MRI and CT is the choice
    7. 67Ga in the imaging of oncologic disease has been at least somewhat replaced with PET/CT
  2. Comments on infectious imaging
    1. Sensitivity is approximately 90%
    2. 111In-WBC or 99mTc-WBC is preferred in the acute infection
    3. If the infection is greater than 2 weeks old it is considered chronic and Ga67 is preferred
    4. Gallium has a high avidity for osteomyelitis, septic arthritis, abscesses, pyelonephritis, and pneumocystis carinii (PCP)
    5. Gallium picks up 85 to 95% of PCP cases
    6. Negative for Kaposi sarcoma
    7. Gallium is also positive for certain pulmonary infections: sarcoidosis, idiopathic pulmonary fibrosis, and inflammation changes do to asbestosis
    8. Ga-67 is not effective for infections of the central nervous system

Return to the beginning of the document
Return to the Table of Content

Gallium Procedure

8/14