From porous media to trabecular bone relaxation analysis: spatial variation of marrow 1H relaxation time distributions detected in vitro by quasi-continuous distribution analysis.

Quasi-continuous distributions of T(1) and T(2) of 1H nuclei were analyzed in vitro at 20MHz on some twenty fresh bone samples of pig femur. Large numbers of data points allowed a detailed investigation. Relaxation data were inverted by UPEN (Uniform PENalty inversion). In all samples the widths of the distributions, covering more than two decades, are not even close to being compatible with single exponential components. Moreover, the T(1) and T(2) distributions show enough character to distinguish the samples. We observe a spatial variation of these characteristics and in particular a second peak centered at 500-600 ms appearing in some proximal femur samples. The quasi-continuous distribution allows one to correlate the water content of the sample with parts of the distributions in specific time ranges. The signal fraction with T(1) values longer than a cutoff time of about 170 ms is in very good agreement with the water content of the samples and is significantly larger in the group of samples cored from proximal femur. Also T(2) distributions differentiate the samples, and the signal fraction with T(2) shorter than about 30 ms is significantly larger in the group of distal femur samples.