Proton magnetic relaxation in bone marrow related to age and bone mineral density: low-resolution in vitro studies

Detailed analysis of proton spin-spin and spin-lattice relaxation behaviors of the bone marrow in the presence of trabecular bone network was performe d at low-resolution (B-o = 0.496T) on rat vertebrae specimens deprived of s pinal cord. Two groups of samples, from young and old healthy animals, were investigated before cellular necrosis had started. BMD measurements were c arried out to quantify the expected age-related modifications of the trabec ular bone network. H-1-MR measurements were also performed on the same samp les, deprived of marrow and saturated with water, in order to control the v alidity of a possible interpretation of the marrow H-1-MR characteristics, in terms of marrow components, and to investigate the possible employment o f these samples to study the trabecular bone network properties. We pointed out that: 1) a bimodal distribution of T-2i and T-1i values (distinguishin g "fast" and "slow" relaxations) describes satisfactorily all the H-1-MR ex perimental decays; 2) age-related modifications of the trabecular bone netw ork are marked by correlate variations of the BMD value and of the proton s pin-spin relaxation rates in water saturated samples; 3) age-related modifi cations of marrow are underlined by variations of the average value of the "fast" T-2i and of the "slow" T-1i relaxation time distributions, which cou ld be attributed to the marrow components different from the fat granules o f the adipose cells. Our results suggest that studies in vitro on bone tissue, by H-1-MR techniq ues at low-resolution, may contribute to a better bone function characteriz ation and, therefore, to a better clinical utilization of MRI techniques. ( C) 2001 Elsevier Science Inc. All rights reserved.