Whole-body bone marrow DWI correlates with age, anemia, and hematopoietic activity

•Age, Hb, and RDW are the predominant predictors of bone marrow signals on DWI.•Low ADC and high visibility are relevant to young age, anemia and hematopoiesis.•Bone marrow ADCs were positively correlated with age and PDFF.•Fat-suppression methods and middle-age physiology may have affected the results. To identify the predictors of bone-marrow DWI signals from anthropometric, complete blood count (CBC), and C-reactive protein (CRP), and to evaluate the association with fat-content in patients. This retrospective study was approved by the institutional review board. A total of 113 consecutive tumor patients underwent whole-body PET/MRI. Apparent diffusion coefficient (ADC) and proton density fat fraction (PDFF) were measured and averaged in lumbar vertebrae (L3-5) and bilateral ilia. Due to respiratory motion, ribs were evaluated by 3-point visual scoring on DWI with b = 800 (1: invisible, 2: partially visible, 3: fully visible). The relationships between ADC/visual scores and anthropometric, CBC, CRP, and PDFF were examined. In females, the age-dependency was evaluated. Multi-regression analyses identified age as the strongest predictor of lumbar ADC (standardized coefficient: β = 0.45), followed by red cell distribution width (RDW) (β = −0.24), while age was the strongest predictor of iliac ADC (β = 0.43), followed by hemoglobin (Hb) (β = 0.22). RDW was the strongest predictor (β = 0.47) for rib visual score and age was the second (β = -0.39). ADC showed significant positive correlations with PDFF at L3-5 and ilium. Lumbar ADC showed a decreasing trend during middle age in females. Age, anemia (lower Hb), and increased hematopoietic activity (higher RDW) are the predominant predictors of ADC and the visibility of red marrow on DWI. Fat-suppression methods and bone-marrow physiology in middle-aged females may have affected the measured correlations between ADC and PDFF inconsistent with previous studies.