Magnetic Resonance Imaging of the Bone Marrow in Hematologic Malignancies

Abstract

the bone marrow. All MR images shown were acquired with M a 1.5 T unit.AGNETIC RESONANCE (MR) imaging has become preferred over other imaging modalities in evaluating T1-weighted images. On T1-weighted MR images, tisdisease in the bone marrow. 1,2 It is a noninvasive technique sue contrast is determined primarily by T1 characteristics. that complements bone marrow aspirations and biopsies by Fat has a short T1 relaxation time and is hyperintense (bright) sampling a large volume of bone marrow and by providing on T1-weighted images. Fatty marrow, because it is cominformation that aids the diagnosis, staging, and follow-up posed primarily of fat, has a characteristic bright signal, of hematologic malignancies.similar to that of subcutaneous fat (Figs 1 and 2). Water, on The MR imaging appearance of the bone marrow depends the other hand, has a long T1 relaxation time and is hypoinon the presence and relative proportions of trabecular bone, tense (dark) on T1-weighted images. Tissues rich in free fat, and water. Each of these constituents of the bone marrow water, such as cerebrospinal fluid, are dark on T1-weighted produces a different MR signal. It is the summation of these images. Red marrow is composed of 40% water, 40% fat, signals that creates the final MR image. Because the bone and 20% protein. On T1-weighted images, red marrow is marrow is a dynamic organ that changes continuously from considerably darker than fatty marrow and has a signal intenbirth through life, the MR appearance of the bone marrow sity similar to or slightly higher than muscle (Figs 1 and 2). 2 varies with age. The predictable rate and patterns of redThe bright signal of fatty marrow facilitates the detection of (hematopoietic) to yellow (fatty) marrow conversion and the marrow lesions, the vast majority of which have a longer unique characteristics of red and yellow marrow on MR T1 relaxation time than fat. 2 However, marrow lesions may images have allowed for the mapping of their age-related have similar T1 relaxation times to red marrow, and their distributions in the skeleton.detection on a background of hematopoietic marrow may be Fatty replacement of the functioning hematopoietic mardifficult with T1-weighted MR images alone. row begins in the periphery of the appendicular skeleton and T2-weighted images. Fat has a short T2 relaxation time, proceeds centrally (Fig 1). In the long bones, fatty marrow which means that, on T2-weighted images, in which T2 first appears in the diaphyses and epiphyses and later in the characteristics prevail, fat is dark and the signal intensity of metaphyses. [2][3][4] The adult pattern of red and yellow marrow fatty marrow decreases (Fig 2). Water has a long T2 relaxdistribution is reached in the early 20s; hematopoietic maration time and is bright on T2-weighted images. The appearrow remains throughout life in the spine, sternum, ribs, pelance of red marrow on T2-weighted MR images varies vis, skull, calcaneus, and proximal metaphysis of the huslightly. 2 It usually shows a small increase in signal, b...

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