(A)Retroperitoneal lymph node metastasis with low tracer uptake(SUV max, 4.6; PET arrow)was confirmed by histopathology, however judged neg ative by 4 of 16(25%)observers(false negative).(B)Pelvic bone metastasis with small sclerotic lesion(CT arrow)but faint 68Ga PSMA 11 uptake(SUV max, 3.7; PET arrow)was confirmed by adequate PSA drop after external beam radiation therapy, however judged negative by 6 of 16(38%)observers(false negative).(C)Right L1 hemangioma with moderate uptake(SUV max, 5.6; PET arrow)was judged positive by 8 of 16(50%)observers(false positive).