Examples of fusion images from human epidermal growth factor receptor 2 (HER2) PET and MR imaging scans. (A) In a vertebral metastasis seen on MR imaging but unapproachable for biopsy, HER2 status was revealed by 89Zr-trastuzumab uptake on PET imaging. (B) Example of HER2-positive brain lesion undetected by conventional scans, revealed by 89Zr-trastuzumab PET imaging, and subsequently confirmed by MR imaging. Arrows indicate lesions. HER2, human epidermal growth factor receptor 2; 89Zr, zirconium-89. (From Dijkers EC, Oude Munnink TH, Kosterink JG, et al. Biodistribution of 89Zr-trastuzumab and PET imaging of HER2-positive lesions in patients with metastatic breast cancer. Clin Pharmacol Ther 2010;87(5):589; with permission.)