Tissue oxygen level dependent (TOLD) MRI utilizes that T1 is directly related with tissue pO2. TOLD MRI is acquired by gradient echo based with a minimized TE. However, T2* contribution may not fully be suppressed. Here, we investigated the modulations of longitudinal and transverse relaxation times with oxygen challenge (OC) and compared TOLD signals from FLASH, UTE, and TSE at 7 T and 15.2 T. At both magnetic fields, T2 did not change with tissue pO2 while T1 did. Spin echo and UTE appear to reflect true pO2 levels due to invariability in T2 during OC and minimized T2* with ultrashort TE, respectively.