Assessing the ADC of Bone-marrow on Whole-body MR Images in Relation to the Fat-suppression Method and Fat Content.

PURPOSE

To compare apparent diffusion coefficients (ADCs) of bone marrow on diffusion-weighted imaging (DWI) between two fat-suppression techniques, and to evaluate the association between bone-marrow ADCs and the proton density fat fraction (PDFF).

METHODS

Seventy-seven patients underwent whole-body DWI with short-inversion time inversion-recovery (STIR) (DWI) and/or STIR + selective water-excitation (spectral-spatial RF [SSRF]) (DWI). ADCs of lumbar vertebrae (L3 and L4) were compared between DWI and DWI, and correlated with the PDFF.

RESULTS

Lumbar ADCs obtained by DWI and DWI were significantly correlated (L3: r = 0.90, P < 0.0001, L4: r = 0.90, P < 0.0001). Lumbar ADCs (× 10 mm/s) obtained by DWI were significantly lower than those by DWI (L3: 479 ± 137 and 490 ± 148, P < 0.05, L4: 456 ± 114 and 471 ± 118, P < 0.005). Residual fat signals were more clearly observed on DWI than on DWI. The ADCs of L3 obtained by DWI and DWI exhibited significant positive correlations with the PDFF (r = 0.51, P < 0.0001, and r = 0.45, P < 0.0001, respectively), and the ADCs of L4 obtained by DWI and DWI exhibited significantly positive correlations with the PDFF (r = 0.40, P < 0.0005, and r = 0.40, P < 0.0005, respectively).

CONCLUSION

Irrespective of different fat-suppression methods, lumbar ADCs were positively correlated with the PDFF, being inconsistent with previous studies. Lumbar ADCs obtained by DWI were significantly lower than those obtained by DWI probably due to residual fat signals on DWI. However, this difference (< 4%) did not explain the positive correlation between lumbar ADC and PDFF.