Allogeneic cell transplant expands bone marrow distribution by colonizing previously abandoned areas: an FDG PET/CT analysis.

Mechanisms of hematopoietic reconstitution after bone marrow (BM) transplantation remain largely unknown. We applied a computational quantification software application to hybrid FDG PET/CT images to assess activity and distribution of the hematopoietic system throughout the whole skeleton of recently transplanted patients. 34 patients underwent PET/CT 30 days after either adult stem cells (ACT, n=18) or cord blood transplantation (CBT, n=16). Our software automatically recognized compact (CBV) and trabecular bone (IBV) in CT slices. Within IBV, co-registered PET data were extracted to identify the active BM (ABM) from the inactive tissue. Patients were compared with 34 matched controls, chosen among a published normalcy database. Whole body ABM increased in ACT and CBT when compared to controls (12.4±3 and 12.8±6.8 vs 8.1±2.6 ml/Kg of ideal body weight, IBW, p<0.001). In long bones, ABM was three- and six-fold increased in CBT and ACT, respectively, in comparison with controls (0.9±0.9 and 1.7±2.5 vs. 0.3±0.3 ml/Kg IBW, p<0.01). These data document an unexpected distribution of transplanted BM into previously abandoned bone marrow sites.