Removal of cerebrospinal fluid partial volume effects in quantitative magnetization transfer imaging using a three-pool model with nonexchanging water component

• Published in: Magnetic resonance in medicine 2015-11, Vol.74 (5), p.1317-1326
• Main Authors: Mossahebi, Pouria, Alexander, Andrew L., Field, Aaron S., Samsonov, Alexey A.
• Format: Article
• Language: English
• Subjects: Algorithms; Brain - anatomy & histology; Brain Mapping - methods; Cerebrospinal Fluid - chemistry; cross-relaxation imaging; CSF; gray matter; Humans; Image Processing, Computer-Assisted - methods; Magnetic Resonance Imaging - methods; Models, Biological; MRI; nonexchanging; Phantoms, Imaging; quantitative magnetization transfer; three-pool model; Water - chemistry
• ISSN: 0740-3194; 1522-2594
• DOI: 10.1002/mrm.25516

Purpose Parameters of the two‐pool model describing magnetization transfer (MT) in macromolecule‐rich tissues may be significantly biased in partial volume (PV) voxels containing cerebrospinal fluid (CSF). The purpose of this study was to develop a quantitative MT (qMT) method that provides indices insensitive to CSF PV averaging. Theory and Methods We propose a three‐pool MT model, in which PV macro‐compartment is modeled as an additional nonexchanging water pool. We demonstrate the feasibility of model parameter estimation from several MT‐weighted spoiled gradient echo datasets. We validated the three‐pool model in numerical, phantom, and in vivo studies. Results PV averaging with the free water compartment reduces all qMT parameters, most significantly affecting macromolecular proton fraction (MPF) and cross‐relaxation rate. Monte‐Carlo simulations confirmed stability of the three‐pool model fit. Unlike the standard two‐pool model, the three‐pool model qMT parameters were not affected by PV averaging in simulations and phantom studies. The three‐pool model fit allowed CSF PV correction in brain PV voxels and resulted in good correlation with standard two‐pool model parameters in non‐PV voxels. Conclusion Quantitative MT imaging based on a three‐pool model with a non‐exchanging water component yields a set of CSF‐insensitive qMT parameters, which may improve MPF‐based assessment of myelination in structures strongly affected by CSF PV averaging such as brain gray matter. Magn Reson Med 74:1317–1326, 2015. © 2014 Wiley Periodicals, Inc.