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


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.


CONCLUSIONS
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.
Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA.
Pouria
P
Mossahebi
Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA.
Andrew L
AL
Alexander
Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA.|Department of Biomedical Engineering, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA.
Aaron S
AS
Field
Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA.
Alexey A
AA
Samsonov
D000465:Algorithms; D001921:Brain / Q000033:anatomy & histology; D001931:Brain Mapping / Q000379:methods*; D002555:Cerebrospinal Fluid / Q000737:chemistry*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008954:Models, Biological; D019047:Phantoms, Imaging; D014867:Water / Q000737:chemistry
D014867:Water
CSF; MRI; cross-relaxation imaging; gray matter; nonexchanging; quantitative magnetization transfer; three-pool model