title: High-resolution three-dimensional macromolecular proton fraction mapping for quantitative neuroanatomical imaging of the rodent brain in ultra-high magnetic fields.
abstract: A well-known problem in ultra-high-field MRI is generation of high-resolution three-dimensional images for detailed characterization of white and gray matter anatomical structures. T1-weighted imaging traditionally used for this purpose suffers from the loss of contrast between white and gray matter with an increase of magnetic field strength. Macromolecular proton fraction (MPF) mapping is a new method potentially capable to mitigate this problem due to strong myelin-based contrast and independence of this parameter of field strength. MPF is a key parameter determining the magnetization transfer effect in tissues and defined within the two-pool model as a relative amount of macromolecular protons involved into magnetization exchange with water protons. The objectives of this study were to characterize the two-pool model parameters in brain tissues in ultra-high magnetic fields and introduce fast high-field 3D MPF mapping as both anatomical and quantitative neuroimaging modality for small animal applications. In vivo imaging data were obtained from four adult male rats using an 11.7T animal MRI scanner. Comprehensive comparison of brain tissue contrast was performed for standard R1and T2maps and reconstructed from Z-spectroscopic images two-pool model parameter maps including MPF, cross-relaxation rate constant, and T2of pools. Additionally, high-resolution whole-brain 3D MPF maps were obtained with isotropic 170µm voxel size using the single-point synthetic-reference method. MPF maps showed 3-6-fold increase in contrast between white and gray matter compared to other parameters. MPF measurements by the single-point synthetic reference method were in excellent agreement with the Z-spectroscopic method. MPF values in rat brain structures at 11.7T were similar to those at lower field strengths, thus confirming field independence of MPF. 3D MPF mapping provides a useful tool for neuroimaging in ultra-high magnetic fields enabling both quantitative tissue characterization based on the myelin content and high-resolution neuroanatomical visualization with high contrast between white and gray matter.
authors.affiliation: University of Washington, Department of Radiology, 850 Republican Street, Seattle, WA, USA; National Research Tomsk State University, Research Institute of Biology and Biophysics, 36 Lenina Avenue, Tomsk, Russia.
authors.forename: Anna V
authors.initials: AV
authors.lastname: Naumova
authors.affiliation: Institute of Cytology and Genetics, The Siberian Branch of the Russian Academy of Sciences, 10 Lavrentyeva Avenue, Novosibirsk, Russia.
authors.forename: Andrey E
authors.initials: AE
authors.lastname: Akulov
authors.affiliation: National Research Tomsk State University, Research Institute of Biology and Biophysics, 36 Lenina Avenue, Tomsk, Russia.
authors.forename: Marina Yu
authors.initials: MY
authors.lastname: Khodanovich
authors.affiliation: University of Washington, Department of Radiology, 850 Republican Street, Seattle, WA, USA; National Research Tomsk State University, Research Institute of Biology and Biophysics, 36 Lenina Avenue, Tomsk, Russia. Electronic address: yarnykh@uw.edu.
authors.forename: Vasily L
authors.initials: VL
authors.lastname: Yarnykh
mesh_terms: D000818:Animals; D066128:Gray Matter / Q000000981:diagnostic imaging*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D060328:Magnetic Phenomena; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D009186:Myelin Sheath; D011522:Protons; D051381:Rats; D017208:Rats, Wistar; D066127:White Matter / Q000000981:diagnostic imaging*
chemical_list: D011522:Protons
keywords: High-field MRI; Macromolecular proton fraction (MPF); Neuroimaging; Rat brain