Test–Retest Reproducibility of In Vivo Magnetization Transfer Ratio and Saturation Index in Mice at 9.4 Tesla

Background: Magnetization transfer saturation (MTsat) imaging was developed to reduce T1 dependence and improve specificity to myelin, compared to the widely used MT ratio (MTR) approach, while maintaining a feasible scan time. As MTsat imaging is an emerging technique, the reproducibility of MTsat compared to MTR must be evaluated. Purpose: To assess the test–retest reproducibility of MTR and MTsat in the mouse brain at 9.4 T and calculate sample sizes potentially required to detect effect sizes ranging from 6% to 14%. Study Type: Prospective. Subjects: Twelve healthy C57Bl/6 mice. Field Strength/Sequence: 9.4 T; magnetization transfer imaging using FLASH-3D Gradient Echo; T2-weighted TurboRARE spin echo. Assessment: All mice were scanned at two timepoints (5 days apart). MTR and MTsat maps were analyzed using mean region-of-interest (ROIs: corpus callosum [CC], internal capsule [IC], hippocampus [HC], cortex [CX], and thalamus [TH]), and whole brain voxel-wise analysis. Statistical Tests: Bland–Altman plots were used to assess biases between test–retest measurements. Test–retest reproducibility was evaluated via between and within-subject coefficients of variation (bsCV and wsCV, respectively). Sample sizes required were calculated (significance level: 95%; power: 80%), given effect sizes ranging from 6% to 14%, using both between and within-subject approaches. Results were considered statistically significant at P ≤ 0.05. Results: Bland–Altman plots showed negligible biases between test–retest sessions (MTR: 0.0009; MTsat: 0). ROI-based and voxel-wise CVs revealed high reproducibility for both MTR (ROI-bsCV/wsCV: CC—4.5/2.8%; IC—6.1/5.2%; HC—5.7/4.6%; CX—5.1/2.3%; TH—7.4/4.9%) and MTsat (ROI-bsCV/wsCV: CC—6.3/4.8%; IC—7.3/5.1%; HC—9.5/6.4%; CX—6.7/6.5%; TH—7.2/5.3%). With a sample size of 6, changes on the order of 15% could be detected in MTR and MTsat, both between and within subjects, while smaller changes (6%–8%) required sample sizes of 10–15 for MTR, and 15–20 for MTsat. Data Conclusion: MTsat exhibited comparable reproducibility to MTR, while providing sensitivity to myelin with less T1 dependence than MTR. Evidence Level: 2. Technical Efficacy: Stage 1

High-resolution three-dimensional quantitative map of the macromolecular proton fraction distribution in the normal rat brain

The presented dataset provides a normative high-resolution three-dimensional (3D) macromolecular proton fraction (MPF) map of the healthy rat brain in vivo and source images used for its reconstruction. The images were acquired using the protocol described elsewhere (Naumova, et al. High-resolution three-dimensional macromolecular proton fraction mapping for quantitative neuroanatomical imaging of the rodent brain in ultra-high magnetic fields. Neuroimage (2016) doi: 10.1016/j.neuroimage.2016.09.036). The map was reconstructed from three source images with different contrast weightings (proton density, T1, and magnetization transfer) using the single-point algorithm with a synthetic reference image. Source images were acquired from a living animal on an 11.7 T small animal MRI scanner with isotropic spatial resolution of 170 µm3 and total acquisition time about 1.5 h. The 3D dataset can be used for multiple purposes including interactive viewing of rat brain anatomy, measurements of reference MPF values in various brain structures, and development of image processing techniques for the rodent brain segmentation. It also can serve as a gold standard image for implementation and optimization of rodent brain MRI protocols

High-resolution three-dimensional quantitative map of the macromolecular proton fraction distribution in the normal rat brain

The presented dataset provides a normative high-resolution three-dimensional (3D) macromolecular proton fraction (MPF) map of the healthy rat brain in vivo and source images used for its reconstruction. The images were acquired using the protocol described elsewhere (Naumova, et al. High-resolution three-dimensional macromolecular proton fraction mapping for quantitative neuroanatomical imaging of the rodent brain in ultra-high magnetic fields. Neuroimage (2016) doi: 10.1016/j.neuroimage.2016.09.036). The map was reconstructed from three source images with different contrast weightings (proton density, T1, and magnetization transfer) using the single-point algorithm with a synthetic reference image. Source images were acquired from a living animal on an 11.7 T small animal MRI scanner with isotropic spatial resolution of 170 µm3 and total acquisition time about 1.5 h. The 3D dataset can be used for multiple purposes including interactive viewing of rat brain anatomy, measurements of reference MPF values in various brain structures, and development of image processing techniques for the rodent brain segmentation. It also can serve as a gold standard image for implementation and optimization of rodent brain MRI protocols

High-resolution three-dimensional quantitative map of the macromolecular proton fraction distribution in the normal rat brain

The presented dataset provides a normative high-resolution three-dimensional (3D) macromolecular proton fraction (MPF) map of the healthy rat brain in vivo and source images used for its reconstruction. The images were acquired using the protocol described elsewhere (Naumova, et al. High-resolution three-dimensional macromolecular proton fraction mapping for quantitative neuroanatomical imaging of the rodent brain in ultra-high magnetic fields. Neuroimage (2016) doi: 10.1016/j.neuroimage.2016.09.036). The map was reconstructed from three source images with different contrast weightings (proton density, T1, and magnetization transfer) using the single-point algorithm with a synthetic reference image. Source images were acquired from a living animal on an 11.7 T small animal MRI scanner with isotropic spatial resolution of 170 µm3 and total acquisition time about 1.5 h. The 3D dataset can be used for multiple purposes including interactive viewing of rat brain anatomy, measurements of reference MPF values in various brain structures, and development of image processing techniques for the rodent brain segmentation. It also can serve as a gold standard image for implementation and optimization of rodent brain MRI protocols