Ultra-high-field MRI real-time imaging of HSC engraftment of the bone marrow niche.

The bone marrow (BM) undergoes extensive remodeling following irradiation damage. A crucial part of restoring homeostasis following irradiation is the ability of hematopoietic stem cells (HSCs) to home to and engraft specialized niches within the BM through a remodeling BM vascular system. Here we show that a combination of ultra-high-field strength magnetic resonance imaging (17.6 T, MRI) coupled with fluorescent microscopy (FLM) serves as a powerful tool for the in vivo imaging of cell homing within the BM. Ultra-high-field MRI can achieve high-resolution three-dimensional (3D) images (28 × 28 × 60 μm(3)) of the BM in live mice, sufficient to resolve anatomical changes in BM microstructures attributed to radiation damage. Following intra-arterial infusion with dsRed-expressing BM cells, labeled with superparamagnetic iron oxides, both FLM and MRI could be used to follow initial homing and engraftment of donor HSC to a limited number of preferred sites within a few cell diameters of the calcified bone-the endosteal niche. Subsequent histology confirmed the fidelity and accuracy of MRI to create non-invasive, high-resolution 3D images of donor cell engraftment of the BM in living animals at the level of single-cell detection.