New perspectives on bone marrow contrast agents and molecular imaging.

Magnetic resonance (MR) imaging of bone marrow provides a noninvasive diagnosis of the vascularity, cell quantity, and composition of the normal and pathological bone marrow. This article reviews new and evolving techniques for bone marrow MR imaging with a special focus on translational and clinical applications. Evaluations of bone marrow perfusion with standard small molecular contrast agents and, more recently, with macromolecular contrast agents are currently being applied for therapy monitoring. Cell-specific contrast agents are expected to improve the sensitivity and specificity of bone marrow MR imaging. Novel cellular and molecular imaging techniques for the depiction of cell metabolism and specific biochemical pathways are discussed. Cell tracking techniques may allow specific diagnoses of inflammatory processes as well as monitoring of novel therapies based on stem cells. Future developments of fusion imaging techniques and bifunctional contrast agents are directed to combine comprehensive information about bone marrow structure and function with targeted and image-guided therapies.