Table 3.
Common Molecular Imaging Radiotracers.
| Radiotracer | Imaging Technique | Cellular Parameter | Mechanism of Localization |
Strengths | Weaknesses |
|---|---|---|---|---|---|
| 99mTc-MDP | Bone Scintigraphy | Osteoblastic bone formation | Chemiabsorption onto hydroxyapatite crystals of the bone matrix | Inexpensive High sensitivity |
Low specificity, dependent on area of exposed bone surface |
| 18F-NaF | Bone Scintigraphy or PET | Osteoblastic bone formation | Binds to and engages exchange reaction with hydroxyapatite crystals to form hydroxyfluoroapatite and fluoroapatite in the bone matrix | Smaller molecule than MDP with faster uptake, fast renal clearance, less background | Dependent on area of exposed bone surface |
| 99mTc-HMPAO | Labeled WBC (in vitro) | WBC migration to site of infection | WBC response to infection | Specificity, same day diagnosis of DFI | Simultaneous dual-tracer approach is not possible. Intensive preparation Expensive |
| 111I-oxine | Labeled WBC (in vitro) | WBC migration to site of infection | WBC response to infection | Simultaneous dual-tracer approach is possible | Intensive preparation Expensive Low image quality |
| 18F-FDG | PET/CT | Glucose uptake and metabolism | Taken up by WBC or immune cells with increased glucose disposal | Sensitivity, inherently tomographic | Specificity, Availability, and cost |
| 67/68Ga-Citrate | Scintigraphy/SPECT/CT (67Ga) or PET/CT (68Ga) | WBC activity at site of infection | Iron mimetic. Binds to transferrin in circulating plasma. Binds to lactoferrin released from dying WBCs and bacterial siderophores at the site of infection | Detects low grade infection Low toxicity, Bone/soft tissue distinction |
Delayed imaging High radiation dose, Non-specific accumulation in sterile inflammation or osteoblasts in healing bone |