Vertebral bone marrow fat quantification using single-voxel MRS is confounded by overlapping water-fat peaks and the difference in T2 relaxation time between water and fat components. The purposes of the present study were: (i) to determine the proton density fat fraction (PDFF) of vertebral bone marrow using single-voxel multi-TE MRS, addressing these confounding effects; and (ii) to investigate the implications of these corrections with respect to the age dependence of the PDFF. Single-voxel MRS was performed in the L5 vertebral body of 86 subjects (54 women and 32 men). To reliably extract the water peak from the overlying fat peaks, the mean bone marrow fat spectrum was characterized based on the area of measurable fat peaks and an a priori knowledge of the chemical triglyceride structure. MRS measurements were performed at multiple TEs. The T2 -weighted fat fraction was calculated at each TE. In addition, a T2 correction was performed to obtain the PDFF and the T2 value of water (T2w ) was calculated. The implications of the T2 correction were investigated by studying the age dependence of the T2 -weighted fat fractions and the PDFF. Compared with the PDFF, all T2 -weighted fat fractions significantly overestimated the fat fraction. Compared with the age dependence of the PDFF, the age dependence of the T2 -weighted fat fraction showed an increased slope and intercept as TE increased for women and a strongly increased intercept as TE increased for men. For women, a negative association between the T2 value of bone marrow water and PDFF was found. Single-voxel MRS-based vertebral bone marrow fat quantification should be based on a multi-TE MRS measurement to minimize confounding effects on PDFF determination, and also to allow the simultaneous calculation of T2w , which might be considered as an additional parameter sensitive to the composition of the water compartment.

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Bone consists of the mineralized component (i.e., cortex and trabeculae) and the non-mineralized component (i.e., bone marrow). Most of the routine clinical bone imaging uses X-ray-based techniques and focuses on the mineralized component. However, bone marrow adiposity has been also shown to have a strong linkage with bone health. Specifically, multiple previous studies have demonstrated a negative association between bone marrow fat fraction (BMFF) and bone mineral density. Magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) are ideal imaging techniques for non-invasively investigating the properties of bone marrow fat. In the present work, we first review the most important MRI and MRS methods for assessing properties of bone marrow fat, including methodologies for measuring BMFF and bone marrow fatty acid composition parameters. Previous MRI and MRS studies measuring BMFF and fat unsaturation in the context of osteoporosis are then reviewed. Finally, previous studies investigating the relationship between bone marrow fat, other fat depots, and bone health in patients with obesity and type 2 diabetes are presented. In summary, MRI and MRS are powerful non-invasive techniques for measuring properties of bone marrow fat in osteoporosis, obesity, and type 2 diabetes and can assist in future studies investigating the pathophysiology of bone changes in the above clinical scenarios.