High-resolution imaging of bone precursor cells within the intact bone marrow cavity of living mice.

Bone precursor cells (BPCs) play a critical role in bone maintenance and regeneration. Currently, no tool exists to study BPCs or other bone marrow cell types directly within their complex microenvironment. Here, we describe in vivo magnetic resonance imaging (MRI) of anatomical structures inside the medullary cavity of the mouse femur. We demonstrate that BPCs passively labeled with iron oxide-containing particles can be monitored by MRI within the intact bone marrow at an in-plane resolution of 43x25 microm. Anatomical detail provided by MRI is complemented by functional optical imaging of reporter gene expression. Single-cell dual iron oxide-reporter gene labeling has potential for combined cell tracking and cell biology studies. In summary, we describe a versatile platform suitable for studying the biology of many bone marrow cell types in living bone.