Problem-solving techniques are performed in a suspected or known marrow lesion in a short period of time. Post-contrast (intravenous gadolinium) fat-suppressed T1W imaging should always include pre-contrast baseline fat-suppressed T1W imaging in at least one plane, with subtraction manipulation if possible. The conventional techniques include T1W (keep echo time, TE <8 ms on 1.5 T and <10 ms on 3 T) and T2W, fat-suppressed T2W, or short tau inversion recovery (STIR for STIR, keep TE ~25-35 ms to maintain good signal to noise ratio) pulse sequences. The imaging can be performed on 1.5 T or 3 T MR scanners. Attention to appropriate MR imaging technique is important. The initial evaluation may include radiography however, many bone marrow lesions are occult on conventional radiography and MR imaging might be the first modality on which they show up for the first time. In an adult, the red marrow is mainly located in the appendicular skeleton in the metaphysis and near the vertebral endplate (the methaphyseal equivalent), due to well-developed vascularity. In long bones, such as humerus and femur, crescentic subchondral area of residual red marrow is commonly present. Epiphysis and apophysis are the first to convert to yellow marrow, which usually happens in the first decade of life itself. After infancy, red marrow to yellow marrow conversion progresses from the periphery (appendicular skeleton) to the center (axial skeleton) and from the diaphysis to the metaphysis in long bones. Red marrow contains 40% fat cells, 40% water, and 20% hematopoietic cells, whereas yellow bone marrow is composed of 80% fat cells, 15% water, and 5% hematopoietic cells. The normal bone marrow is constituted in different proportions by red (hematopoietic bone marrow) and yellow marrow (hematopoietic inactive marrow), which have different MRI characteristics due to the different content of hematopoietic and fat cells.
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