 This is a single-center cross-sectional imaging study in patients with localized bladder cancer undergoing neoadjuvant atezolizumab as part of a companion clinical trial NCT02451423; Phase 2 study of atezolizumab in non-metastatic bladder transitional cell carcinoma, and patients with locally advanced or metastatic bladder cancer receiving standard of care SOC atezolizumab. For the neoadjuvant cohort, study participants will undergo whole body PETPositron Emission TomographyMRMagnetic Resonance imaging with 18FF-AraG within 7 days of initiating atezolizumab and within 7 days before surgery. For the SOC cohort, study participants will undergo whole body PETMR imaging with 18FF-AraG within 7 days of initiating atezolizumab and between Day 14 and Day 21 of Cycle 1 atezolizumab. 