BCR and acute lymphoblastic leukemia: To address this question, we utilized intravital fast scanning two-photon phosphorescence lifetime imaging microscopy (FaST-PLIM) to image B-ALL cells and oxygen concentrations in the BM, in addition to pimonidazole staining to identify intracellular hypoxia, in the context of a transplantable BCR/ABL B-ALL mouse model (19, 29).