[Muscle mass measurement by DXA and MRI in non-human primates]. 
The global population is aging rapidly and, in Japan, the number of elderly has been steadily rising.  It is important to shrink the gap between the average lifespan and the number of years people can expect to remain healthy.  This links with improving the quality of life for the elderly and reducing social welfare spending.  Maintaining motor function is believed to be a key to extending the number of years a person remains healthy, but recent years have seen a rise in locomotive syndrome.  Decreases in muscle mass with age, and the deterioration in motor functions leads to sarcopenia.  However, there is a dearth of medicines for increasing muscle mass or muscular strength.  In this study, we used non-human primates (NHPs), which have similar anatomical features to humans and have advanced functional differentiation between the fore- and hindlimbs, to examine a highly accurate method of measuring muscle mass using Magnetic Resonance Imaging (MRI) and compared it to Dual Energy X-ray Absorptiometry (DXA) usually used in clinical settings.  The results showed that both MRI and DXA provided high repeatability.  Furthermore, correlation analysis between the amount of excised muscle for measurement and the results from MRI and DXA showed a high correlation at all sites examined, with the correlation coefficient higher for MRI than for DXA.  We expect that the establishment of a highly accurate method for measurement of muscle mass using MRI and DXA will give impetus to the development of drugs that target muscle mass.