<P> Bone marrow derived stem cells have a wide array of application in regenerative medicine . </P> <P> Medical imaging may provide a limited amount of information regarding bone marrow . Plain film x-rays pass through soft tissues such as marrow and do not provide visualization, although any changes in the structure of the associated bone may be detected . CT imaging has somewhat better capacity for assessing the marrow cavity of bones, although with low sensitivity and specificity . For example, normal fatty "yellow" marrow in adult long bones is of low density (- 30 to - 100 Hounsfield units), between subcutaneous fat and soft tissue . Tissue with increased cellular composition, such as normal "red" marrow or cancer cells within the medullary cavity will measure variably higher in density . </P> <P> MRI is more sensitive and specific for assessing bone bone composition . MRI enables assessment of the average molecular composition of soft tissues, and thus provides information regarding the relative fat content of marrow . In adult humans, "yellow" fatty marrow is the dominant tissue in bones, particularly in the (peripheral) appendicular skeleton . Because fat molecules have a high T1 - relaxivity, T1 - weighted imaging sequences show "yellow" fatty marrow as bright (hyperintense). Furthermore, normal fatty marrow loses signal on fat - saturation sequences, in a similar pattern to subcutaneous fat . </P> <P> When "yellow" fatty marrow becomes replaced by tissue with more cellular composition, this change is apparent as decreased brightness on T1 - weighted sequences . Both normal "red" marrow and pathologic marrow lesions (such as cancer) are darker than "yellow" marrow on T1 - weight sequences, although can often be distinguished by comparison with the MR signal intensity of adjacent soft tissues . Normal "red" marrow is typically equivalent or brighter than skeletal muscle or intervertebral disc on T1 - weighted sequences . </P>

Where is yellow bone marrow located in adults