Analysis of ovariectomy and estrogen effects on body composition in rats by X-ray and magnetic resonance imaging techniques

Resistance of bone to fracture-bone strength-has been shown to depend on bo th the amount of bone and its architectural spatial organization, In vivo m agnetic resonance (MR) techniques have the capability of imaging bone tissu e, including the trabecular microarchitecture and the marrow composition, W e have applied in vivo and ex vivo MR methods to the tibia in an ovariectom ized rat model of osteoporosis, Specifically, in vivo high-resolution three -dimensional MR imaging and localized MRS were facilitated by specialized c oils and high field magnets, resulting in enhanced sensitivity of detection . As a result, in vivo and ex vivo differences in marrow composition were f ound between sham-ovariectomized, ovariectomized, and ovariectomized animal s treated with 17-beta-estradiol. Estrogen effects mere detected in vivo 7 days after surgery (3 days into treatment) as a decrease in the tibial fat signal level, The in vivo effects of ovariectomy mere observed 56 days afte r surgery as an increase in MR image fat signal level and spectral fat/wate r ratio in the proximal tibia, Ex vivo measurements of tibial marrow water signal discriminated clearly between the sham and ovariectomized groups and showed increased individual variations in the treatment group, Imaging fur ther showed that the highest fat content is observed in the epiphysis, Comp uted tomography confirmed ovariectomy-induced loss of bone in the proximal tibial metaphysis compared with the sham group, This loss of cancellous bon e with ovariectomy is consistent with the MR observations of increases in b oth fat and water in the metaphysis, These data showed that MR techniques c omplement X-ray techniques in the bone, water, and fat compositional analys is of the appendicular skeleton in response to ovariectomy and pharmacologi cal treatment.