The etiology and pathogenesis of osteoporosis has been extensively discussed. The relationship between bone blood circulation and the formation of bony trabeculae has been less understood. There is plenty of indirect evidence highly suggestive of the correlation between these two factors, such as: the number of blood vessels in the per unit area of the bone marrow was decreased in the osteoporotic bone, indicating the possible role of a microvascular defect in the pathogenesis of osteoporosis. Furthermore, the bone mineral density in severe arteriosclerotic patients was lower than in the less affected subjects. In a large scale epidemiologic study, diminished bone mineral density was strongly associated with increased deaths from stroke. Osteopenia was also associated with an increased risk of stroke. These reports highly suggest the effect of ischemia on bone metabolism and make the investigators more interested in further investigation.

A dynamic contrast-enhanced magnetic resonance (MR) study was used recently in evaluating the blood perfusion of bone tumors. This method also has a strong correlation with the microsphere blood flow measurements. The investigator (T.F. Shih) used the dynamic MR in her recent two researches:

1. To differentiate benign versus malignant spinal compression fractures.
2. To evaluate the blood perfusion of non-fractured, normal-appearing vertebral bodies and find its significant correlation with aging and sex.

The alterations of bone marrow perfusion are synchronous with the changes of bone mineral density. Thus, based on the investigators' previous research work, they propose to further explore the relationship between bone marrow perfusion and bone mineral density in different age groups.