Assessing the ADC of Bone-marrow on Whole-body MR Imagesin 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(STIR)) and/or STIR + selective water-excitation (spectral-spatial RF [SSRF]) (DWI(STIR+SSRF)). ADCs of lumbar vertebrae (L3 and L4) were compared between DWI(STIR) and DWI(STIR+SSRF), and correlated with the PDFF. Results: Lumbar ADCs obtained by DWI(STIR) and DWI(STIR+SSRF) were significantly correlated (L3: r = 0.90, P < 0.0001, L4: r = 0.90, P < 0.0001). Lumbar ADCs (× 10(-6) mm(2)/s) obtained by DWI(STIR) were significantly lower than those by DWI(STIR+SSRF) (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(STIR) than on DWI(STIR+SSRF). The ADCs of L3 obtained by DWI(STIR) and DWI(STIR+SSRF) 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(STIR) and DWI(STIR+SSRF) 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(STIR) were significantly lower than those obtained by DWI(STIR+SSRF,) probably due to residual fat signals on DWI(STIR). However, this difference (< 4%) did not explain the positive correlation between lumbar ADC and PDFF.