Quantitative susceptibility mapping (QSM) has been demonstrated to reveal excellent image contrast and can quantify the magnetic properties of white matter that is not easily revealed by DTI (1, 2). At ultra-high magnetic field strengths, increase of contrast-noise-ratio in susceptibility may allow the study of rodent neuroanatomy at better details. In this study, we demonstrate that whole brain cytoarchitecture can be revealed by QSM at 10-μm resolution at 9.4T. Using QSM, we are able to reveal exquisite anatomical details such as retina layers of the eyeball, glomeruli in olfactory bulb, barrel cortex, medium-sized spiny neurons in striatum, cell layers of cerebellum, and hippocampus. This ultra-high resolution QSM of the intact mouse brain is a powerful dataset to allow analysis and visualization of the brain cytoarchitecture in 3D.The animal was prepared under an approved protocol by the Duke Institutional Animal Care and Use Committee. An adult male C57BL/6 mouse (Charles River Labs, Durham, NC) was perfusion fixed with Gd contrast agent (ProHance; Bracco diagnostics, Princeton, NJ). The excised mouse brain was imaged in a 9.4 T (400 MHz) 8.9-cm vertical bore Oxford magnet with shielded gradients of 2200 mT/m. The specimen was scanned using a three-dimensional (3D) spoiled-gradient-recalled sequence with multiecho acquisition. The following MRI parameters were used: field of view (FOV) = 22×11×10 mm³ with 10-µm isotropic resolution, TE1/TE2 = 6.8/16.4 ms, pulse repetition time (TR) = 35 ms, flip angle = 90°. Total acquisition time for each individual scan was 10 hours 42 minutes. Nine signal averages were acquired to achieve adequate SNR. The raw phase was processed by Laplacian-based phase unwrapping and V_SHARP background phase removal. QSM maps were reconstructed using a two-level STAR-QSM algorithm (4) for reducing the streaking artifacts.The QSM images revealed detailed anatomical structures such as cell layers and individual glomeruli (Fig 1). Fig. 1A shows a representative susceptibility map in the axial slice. The susceptibility demonstrates a strong cell layer structure contrast and better delineation of anatomy. For example, dramatic retina cell layer of the eye ball, glomeruli in olfactory bulb (indicated by arrow), sinus structure, barrel cortex arrangement, small fiber bundles of striatal neurons cell layers in cerebellum and hippocampus are demonstrated by QSM maps (Fig. 1B-H). The glomeruli in olfactory bulb shows a strong diamagnetic susceptibility than surrounding tissues. In addition, barrel cortex barrel walls exhibit a paramagnetic susceptibility while barrel hollows show a relative diamagnetic susceptibility. The V-shaped dentate gyrus regions could be readily identified due to the strong contrast with respect to surrounding tissues in hippocampus.A number of studies have demonstrated the utility of DTI in understanding the global structure of the mouse brain and the intricate connectivity. One of the challenges of DTI is the limited resolution due to SNR constraints, e.g., 43-μm isotropic resolution is one of the highest achieved resolution of a mouse brain specimen (5). The work shown here has increased the spatial resolution to 10-μm isotropic by 3D multiecho GRE data. The susceptibility maps allow better delineation of anatomy, e.g., the olfactory bulb layers, retina layers, cortical layers, and cerebellum cell layers. Moreover, the high resolution helps reduce the ambiguity in following fiber tracts. It is demonstrated the utility of QSM in understanding small fiber bundles, e.g., in striatum, with several branches which is known a limitation for DTI. Ultra-high resolution QSM provides quantitative magnetic susceptibility in 3D that is virtually impossible to achieve by the conventional MRI.