Chemical shift imaging at 4.7 Tesla of thymus in young and old mice

We propose an experimental protocol, based on chemical shift magnetic reson ance imaging (CSI) that improves the methods presently available for the in vivo study of the thymus in small animals. Male Balb/c mice were examined in an imager-spectrometer equipped with a 4.7 T magnet. Three groups of ani mals with different ages were used: the first group consisted of 3-month-ol d mice (n = 5), the second group of 19-month-old mice (n = 5), and the thir d group of 26-month-old mice (n = 4). The identification of thymic parenchy ma was obtained by two (T1-weighted spin-echo and CSI water-selective) imag es. The T1-weighted spin-echo image provided a detailed anatomical descript ion of the organs located in the thorax. The CSI water-selective image prov ided a detailed description of thymic location, shape, and dimensions. The cross-sectional area of the thymus, measured from CSI images, showed a decr easing trend with increasing age. The values of the thymus-muscle contrast- to-noise ratio were measured in both spin echo and CSI images. While the co ntrast between thymus and muscle was greatly improved in the young and pres enescent group, the difference was not statistically significant in the sen escent group. In conclusion, the proposed method allows the study of thymic modification during the passage from young to pre-senescent age and from p resenescent to old age. This method could be useful in studies in which exp erimental manipulation or drug treatments produce changes in the dimension and fat content of this organ. The proposed protocol, based on CSI, appears to be an improved methodology for study of the thymus. J. Magn. Reson. Ima ging 1999;10:97-101. (C) 1999 Wiley-Liss, Inc.