Gallium-67 Imaging
- Physiology of Gallium-67
- Is an analog of Iron
- While many theories have been developed on the biopathway of gallium, it is still not completely understood
- This is what we know:
- Following Ga-67 injection binds to transferring (TF)
- Travels in the vascular pool
- Using the same mechanism of transportation as iron
- Patients with saturated iron binding sites have decreased tissue uptake and increased renal excretion
- When imaging infection
- Gallium binds to leukocytes via lactoferrin (LF) and TF binding sites. Thee leukocytes attack antigens in the human system
- 67Ga enters the infectious process through the intercellular fluid
- 67Ga uptake can be seen in an infection that has little blood flow
- Siderophores found in bacteria have a great affinity for iron, hence they pickup gallium
- Gallium also has a great affinity for certain types of tumors
- As gallium travels via TF and diffuses though loose endothelial junctions at the capillary level of the tumor cells
- TF receptors on tumor cells pick up gallium
- Then 67Ga enters the tumor cell and it concentrates in the lysosomes that have an affinity for TF and LF
- Normal distribution
- Since LF has a great affinity for lacrimal, salivary, nasopharynx, bone marrow, and spleen Ga-67 uptake is therefore noted in these areas
- Gallium also is seen in the liver, which is do the liver's ability to metabolize LT and TF
- 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
- At 24 hours uptake should also be seen in the myocardium and urinary bladder
- Gallium is also excreted through feces and activity is usually seen in the large bowel at 24 hour post dose and beyond
- Uptake in the lung for the first 24 hours following the injection is considered normal
- Skeletal uptake is also considered normal
- At 48 and 72 hours post dose images are considered "tissue" or perfusion imaging
- The imaging procedure
- The normal dose is 6 to 10 mCi
- Patient preparation
- Since gallium uptake is seen in the bowel there maybe some concern on differentiating fecal from tumor
- 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
- For additional calcification of possible tumor an enema maybe required
- Prior to the gallium injection a liver/spleen scan maybe considered in order to outline this anatomy. Why might this be important?
- 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
- Energy settings
- 96 keV with a 20% window
- 185 keV with a 20% window
- 300 keV with a 20% window
- Collimator - ME
- Whole body format
- Head to mid-thigh (unless disease is present in the appendages)
- Scan speed of 10 cm/minute or less
- 256 x 1024 matrix
- Spot imaging
- Matrix = 256
- 15 minutes per image
- Images should be taken at 24, 48, and 72 hours. Sometimes further delay images, up to 120 hours might be considered
- Comments on oncology
- Lymphomas and Hodgkin's disease
- Used for staging
- Approximately 75% of tumors are gallium avid
- False-positive rate is less than 6%
- For lung CA staging
- Sensitivity ranges from 100 to 93%
- Specificity ranges from 63 to 30%
- Primary hepatoma is about 90% sensitive
- Liver/spleen scan is suggested
- Sulfur colloid will be cold
- Ga-67 will be hot
- Lesions smaller than 2 cm are general not detected
- GI/GU tumors have poor sensitivity and specificity
- Melanoma
- 82% sensitive and 99% specific
- Tumor size must be at least 1 cm
- Head and neck tumors
- Overall sensitivity was 56%
- MRI and CT is the choice
- 67Ga in the imaging of oncologic disease has been at least somewhat replaced with PET/CT
- Comments on infectious imaging
- Sensitivity is approximately 90%
- 111In-WBC or 99mTc-WBC is preferred in the acute infection
- If the infection is greater than 2 weeks old it is considered chronic and Ga67 is preferred
- Gallium has a high avidity for osteomyelitis, septic arthritis, abscesses, pyelonephritis, and pneumocystis carinii (PCP)
- Gallium picks up 85 to 95% of PCP cases
- Negative for Kaposi sarcoma
- Gallium is also positive for certain pulmonary infections: sarcoidosis, idiopathic pulmonary fibrosis, and inflammation changes do to asbestosis
- Ga-67 is not effective for infections of the central nervous system
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Gallium Procedure
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