What is the purpose of a gallium (Ga) scan?

Purpose of Gallium (Ga) Scan

A gallium scan is primarily used to detect areas of infection, inflammation, and certain types of cancer, particularly lymphoma, when other imaging modalities are inconclusive or contraindicated. 1

Main Clinical Applications

1. Infection Detection

• Spinal Infections:
  • Ga-67 scintigraphy combined with SPECT can detect spinal infections with 73% sensitivity and 81% specificity (when combined with Tc-99m-MDP bone scan) 1
  • Useful when MRI findings are equivocal or contraindicated 1
  • Particularly valuable in post-surgical spine patients where distinguishing between normal post-operative changes and infection is challenging 1

2. Cancer Detection and Monitoring

• Lymphoma:
  • High sensitivity (80-90%) for staging and follow-up of Hodgkin's disease 2
  • Particularly useful for evaluating residual mediastinal masses after treatment 2
  • SPECT imaging significantly increases sensitivity from 48% to 89% in lymphoma detection 3

3. Inflammatory Conditions

• Inflammatory Disorders:
  • Can detect inflammatory spondyloarthritis involving sternoclavicular and sternocostal joints 1
  • Helps differentiate between infectious and inflammatory conditions 1

Technical Aspects and Limitations

How It Works

• Gallium-67 citrate is injected intravenously and concentrates in areas of inflammation, infection, and certain tumors
• Imaging is typically performed 24-72 hours after injection 1
• Often combined with SPECT (Single Photon Emission Computed Tomography) to improve sensitivity 1, 3

Limitations

• Time-consuming procedure: Requires delayed imaging 24-72 hours after injection 1
• Moderate sensitivity: Less sensitive (73%) than MRI (96%) for spinal infections 1
• Interpretation challenges: Studies show significant variability in scan interpretation 4
• False negatives: May occur in leukopenic patients due to neutrophilic labeling mechanism 5
• Limited utility in some settings: Not cost-effective for routine staging of non-Hodgkin's lymphoma 6

Comparison with Other Imaging Modalities

MRI vs. Gallium Scan

• MRI is superior for spinal infections with 96% sensitivity and 94% specificity 1
• MRI provides better anatomical detail and can detect epidural abscess formation 1
• Gallium scan may be useful when MRI is contraindicated or inconclusive 1, 7

FDG-PET/CT vs. Gallium Scan

• FDG-PET/CT has largely replaced gallium scanning for many indications
• FDG-PET/CT shows higher sensitivity (94.8%) and specificity (91.4%) for spinal infections 1
• FDG-PET/CT offers faster results and better anatomical correlation 1

Bone Scan vs. Gallium Scan

• Bone scan has higher sensitivity (81.4%) but lower specificity (40.7%) for spine infection 1
• Combined Ga-67 and Tc-99m-MDP examination improves specificity to 81% 1
• Gallium scan normalizes earlier than bone scan after successful treatment of bone infection 5

Clinical Decision Algorithm

1. First-line imaging:

   • MRI without and with IV contrast for suspected spine infection 1, 7
   • CT or radiography for initial assessment of bone abnormalities 1

2. When to use gallium scan:

   • When MRI is contraindicated or inconclusive 1, 7
   • For monitoring treatment response in lymphoma patients 2
   • When multifocal infection is suspected 1
   • In post-surgical patients where distinguishing infection from normal post-operative changes is difficult 1

3. Consider combined imaging:

   • Combined Ga-67 and Tc-99m-MDP examination for improved specificity 1, 7
   • SPECT/CT for better anatomical localization 1, 3

In modern practice, gallium scanning has been largely replaced by more advanced imaging techniques like MRI and FDG-PET/CT for most indications, but it still maintains clinical utility in specific scenarios where these modalities are unavailable, contraindicated, or have yielded equivocal results.