Correction of QCT vBMD using MRI measurements of marrow adipose tissue

Abstract

Objective: Quantitative computed tomography (QCT) measurements of volumetric bone mineral density (vBMD) are subject to errors due to variations in the amount of bone marrow adipose tissue (BMAT). The purpose of our study was to describe and validate a novel method to correct lumbar spine trabecular vBMD measurements for BMAT using chemical shift-encoded magnetic resonance imaging (CSE-MRI).

Methods: CSE-MRI measurements of proton density fat fraction (PDFF) were used to correct QCT spine vBMD measurements for BMAT based on the H₂O and K₂HPO₄ basis set equivalent densities of bone, red and yellow bone marrow. BMAT corrected and uncorrected vBMD measurements of the L1 vertebra were compared with dual-energy QCT (DEQCT) measurements in 18 subjects (mean age: 68 y, range 60 to 93 y). A further 400 subjects (mean age: 53 y, range 21 to 82 y) had 120 kV_p single-energy QCT and CES-MRI scans of L2-L4 and the data used to simplify the adipose tissue correction by deriving a linear equation between the CSE-MRI vBMD correction and fractional BMAT content.

Results: Application of the CSE-MRI derived vBMD correction changed the bias (95% limits of agreement) compared with DEQCT from 26.7 (11.0 to 42.4) mg/cm³ to 2.2 (-9.5 to 13.9) mg/cm³ at 80 kV_p, and from 22.4 (3.3 to 41.6) mg/cm³ to 2.9 (-12.6 to 18.4) mg/cm³ at 120 kV_p. Data for the 400 subjects gave the following relationship valid at 120 kV_p: vBMD correction (mg/cm³) = -12.96 + 75.76 × BMAT.

Conclusion: CSE-MRI measurements of PDFF can be used to correct for BMAT content and improve the accuracy of lumbar spine QCT vBMD measurements calibrated using a K₂HPO₄ phantom.

Keywords: Bone density accuracy errors; Bone marrow adipose tissue; Chemical shift encoded magnetic resonance imaging; Proton density fat fraction; Quantitative computed tomography; Volumetric bone mineral density.