New Perspectives in Imaging of the Bone Marrow

The bone marrow is one of the largest organs in the human body. In nearly every musculoskeletal imaging case, bone marrow is displayed as the area of main interest or the anatomical entity reflecting other pathologies. Therefore, it is of utmost importance to have a broad knowledge of this field in musculoskeletal magnetic resonance imaging (MRI). Recent developments such as diffusion and perfusion imaging as well as novel contrast agent applications are greatly enhancing the diagnostic imaging of the bone marrow.

Awareness of what constitutes normal marrow and an understanding of how marrow variants mimic disease are indispensable for the correct interpretation of various imaging modalities. This topic is addressed in the outstanding article contributed by Dr. Vande Berg et al. Metastases are the most common type of bone tumor and one of the leading indications for bone marrow MRI. They are most frequently located within the bone marrow at the site of hematopoiesis. Trabecular and cortical bone is not destroyed at an early stage after seeding of neoplastic cells within the bone marrow. Because MRI can detect the replacement of bone marrow soft tissue components in the absence of bone destruction, it is definitely superior to radiography and computed tomography (CT) in the assessment of skeletal metastases.

To fully exploit the potential provided by MRI, adequate pulse sequences have to be selected, as demonstrated by Dr. Vanel et al. Diffuse marrow changes may be due to multiple neoplastic but also to benign causes, such as stimulated hematopoiesis. MRI is not specific; however, when clinical information is provided, most cases can be interpreted correctly. Dr. Berger and coworkers provide in-depth information on selected topics, including Gaucher's disease, Hodgkin's disease and non-Hodgkin lymphoma, chronic lymphocytic leukemia, and alterations in bone marrow after different medication strategies. Multiple myeloma is a common bone marrow neoplasia of the elderly, discussed in the article I coauthored with Prof. Reiser. Imaging adds valuable information in the staging of patients with multiple myeloma. Whole-body multislice CT and whole-body MRI are being used more and more to replace conventional skeletal imaging, which is less sensitive in detecting bony involvement.

The advent of multichannel whole-body MRI (WB-MRI) systems enables bone marrow screening without the use of ionizing radiation and with high diagnostic accuracy. WB-MRI has been applied successfully in the screening of bone metastases and hematologic bone marrow diseases such as multiple myeloma, lymphoma, and histiocytosis X. Moreover, it was recently proposed for the assessment of primarily benign diseases predisposing for malignancy. Dr. Schmidt et al provide an overview of state-of-the-art whole-body imaging of the bone marrow and highlight present and potential future applications.

Diffusion-weighted imaging reflects the random motion of water molecules within tissue, and it has become a key technique for the early detection of brain infarction and the differentiation of various brain pathologies. Recently, diffusion-weighted imaging was introduced into the diagnostics of the bone marrow and has proved a valuable tool to solve diagnostic dilemmas. The article by Dr. Dietrich et al elucidates the physical principles of diffusion-weighted imaging and discusses the musculoskeletal applications, especially in the spine. Finally, Dr. Daldrup-Link and coworkers describe contrast agent applications, perfusion imaging, and new perspectives on molecular imaging of the bone marrow.

I would like to thank the editors for giving me the opportunity to serve as guest editor for this interesting topic and express my gratitude to the authors who contributed to this issue of Seminars in Musculoskeletal Radiology for their cooperation and excellent contributions.