Molecular In Vivo Imaging of Bone Marrow Adipose Tissue
Purpose of Review
The in vivo study of molecular processes in human bone marrow is important for both diagnostics and understanding of disease pathophysiology. Traditionally, the hematopoietic component of the bone marrow has been a research focus, but recently, the role of bone marrow adipose tissue has been gaining interest in many applications. The purpose of the present review is to give an overview of existing imaging modalities allowing in vivo molecular imaging of bone marrow adipose tissue in humans with an emphasis on technical aspects: the characteristics of the extracted parameters and their application in bone marrow adipose tissue.
Magnetic resonance (MR) imaging (MRI) and spectroscopy (MRS) are the most frequently used imaging methods for the examination of bone marrow adipose tissue as they provide rich soft tissue contrast and come without ionizing radiation. Existing MR methods allow the extraction of many different measures including proton density fat fraction, fatty acid characteristics, and diffusion and perfusion properties. However, many available techniques have to be carefully adjusted to be used in the investigation of the fat signal component, especially in the presence of trabecular bone. Dual-energy computed tomography (DECT) is an emerging technique—not yet widely available—which appears to be a promising alternative to MR for rapid fat fraction assessment. Positron emission tomography (PET) allows additional functional metabolic imaging and therefore provides valuable additional information (e.g., glucose uptake) to MR-based parameters at the cost of ionizing radiation.
Bone marrow imaging still appears to be a niche with remaining technical challenges using existing imaging modalities. A good working knowledge of the underlying physical and technical principles is required as most techniques are yet not available out of the box and may need to be adjusted to fit the requirements for bone marrow adipose tissue imaging. In summary, MR, DECT, and PET enable the measurement of several inherently different parameters in in vivo molecular imaging of bone marrow adipose tissue. The growing interest for molecular imaging markers of bone marrow, thanks to its high metabolic and clinical significance, may eventually lead to new developments, as well as improvements of emerging techniques as soon as they become more broadly available.
KeywordsMolecular imaging Bone marrow adipose tissue Bone marrow fat Bone marrow adipocytes Magnetic resonance imaging Magnetic resonance spectroscopy
Compliance with Ethical Standards
All reported studies/experiments with human or animal subjects performed by the authors have been previously published and complied with all applicable ethical standards (including the Helsinki declaration and its amendments, institutional/national research committee standards, and international/national/institutional guidelines).
Conflict of Interest
Stefan Ruschke, Maximilian N. Diefenbach, Daniela Franz, and Thomas Braum declare no conflicts of interest. Dimitrios C. Karampinos reports grants from Philips Healthcare, during the conduct of study and outside the submitted work.
Human and Animal Rights and Informed Consent
This article does not contain any studies with human or animal subjects performed by any of the authors.
Papers of particular interest, published recently, have been highlighted as: • Of importance •• Of major importance
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