Introduction
Bone marrow adipose tissue (BMAT) research has witnessed considerable advances over the past two decades. The development of ex vivo and in vivo methods to assess BMAT have brought a new perspective into the bone-fat interaction, particularly regarding skeletal metabolism and integrity [1]. BMAT is no longer considered an inert filler of bone marrow space in response to ageing or decrease demand for erythrocyte production [2]. For instance, the accrual of BMAT in response to caloric restriction is a unique behavior of BMAT in contrast to white adipose tissue [3,4]. The increase of BMAT can be seen with ageing and in certain conditions such as immobility, anorexia nervosa, and medication use [∗[4], [5], [6], [7], ∗[8]].
Recent research suggests that BMAT may be a biomarker of osteoporosis, and therefore a possible target for its treatment [[9], [10], [11], [12], [13], ∗[14], [15]]. BMAT may also be involved in the pathophysiology of certain metabolic disorders. For instance, despite preserved bone mineral density (BMD) in type 2 diabetes mellitus or obesity, an increased risk of fracture has been reported [[16], [17], [18]], and the quantity and composition of BMAT may play a role in the pathogenesis of impaired bone health in these disorders [19,20].
Magnetic resonance imaging (MRI) and single-voxel proton magnetic resonance spectroscopy (1H-MRS) allow the non-invasive assessment of BMAT without ionizing radiation [21,22], while computed tomography (CT)-based techniques involve ionizing radiation. However, dual-energy CT (DECT) has the advantage of simultaneous assessment of BMAT and BMD [[23], [24], [25], ∗[26], ∗[27]].
Our aim is to discuss the role of different in vivo imaging techniques in quantifying BMAT with particular focus on MRI- and CT-based techniques. Of note, this review uses the nomenclature and terminology proposed by the International Bone Marrow Adiposity Society (BMAS) [28].