Continuous distribution analysis of marrow 1H magnetic resonance relaxation in bone

Longitudinal and transverse NMR relaxation of 1H nuclei were studied in vitro on fresh animal femur samples. A large number of data points were taken, starting at 100 μs for T1 by inversion-recovery, at 200 μs for T2 by single-echo sequences, and at 600 μs for T2 by CPMG echo-trains. Quasi-continuous distributions of relaxation times were computed, giving wide distributions for all samples. Bulk marrow removed from the medullary cavity showed T2 distributions from about 20 ms to 600 ms and T1 distributions from about 40 ms to 2 s. The 1H nuclei in trabecular bone samples, where marrow is confined, may show long tails for T2 at relaxation times down to 250 μs, the origin of which is still not known. These tails are absent in bulk marrow from the medullary cavity. The differences observed in T1 distributions among trabecular bone samples are in accordance with the different marrow compositions. Discrete exponential fits were computed also, and in most cases four discrete exponential components were required to fit the experimental data adequately. However, the discrete components do not seem to correspond to any physically distinguishable separate compartments.