La moelle osseuse est constituée de tissu graisseux (moelle jaune) en hypersignal T1 et en hyposignal sur les séquences qui saturent la graisse, et de cellules hématopoïétiques (moelle rouge) en hyposignal T1 et signal intermédiaire STIR. Leur quantité respective varie tout au long de la vie. La base de l’analyse du signal de la moelle osseuse repose en première intention sur les séquences pondérées en T1, complétées de séquences pondérées T2 avec saturation de graisse (ou sTlR) et de séquence de diffusion.

Normal bone marrow is divided into red and yellow marrow, according to how much fat it contains. Distribution varies with age: during infancy red marrow occupies the entire ossified skeleton except epiphyses and apophyses. Gradually red marrow decreases such that arround 25 years of age it is essentially present in the axial skeleton. The conversion of red to yellow begins indeed peripherally before occurring in the femur and humerus. Islands of red marrow may be seen anywhere in the skeleton, but typically in a subcortical situation or in subchondral crescents of the proximal humerus and femur. MRI reading of T1 and T2-weighted imaging with and without fat suppression is key to distinguishing normal from pathologic bone marrow content.