Magnetic resonance bone imaging: applications to vertebral lesions

Abstract

MR bone imaging is a recently introduced technique, that allows visualization of bony structures in good contrast against adjacent structures, like CT. Although CT has long been considered the modality of choice for bone imaging, MR bone imaging allows visualization of the bone without radiation exposure while simultaneously allowing conventional MR images to be obtained. Accordingly, MR bone imaging is expected as a new imaging technique for the diagnosis of miscellaneous spinal diseases. This review presents several sequences used in MR bone imaging including black bone imaging, ultrashort/zero echo time (UTE/ZTE) sequences, and T1-weighted 3D gradient-echo sequence. We also illustrate clinical cases in which spinal lesions could be effectively demonstrated on MR bone imaging, performed in most cases using a 3D gradient-echo sequence at our institution. The lesions presented herein include degenerative diseases, tumors and similar diseases, fractures, infectious diseases, and hemangioma. Finally, we discuss the differences between MR bone imaging and previously reported techniques, and the limitations and future perspectives of MR bone imaging.

Keywords: Bone imaging; CT-like MRI; MR imaging; Spine.

Fig. 1

Postprocessing used in the 3D-GRE sequence. Signals from TEs of 4.76, 9.53, 14.29, and 19.06 ms are added followed by a gray-scale reversal to obtain MR bone images

Fig. 2

Normal cervical and lumbar spine. Midsagittal MR bone image (a) of a 36-year-old male shows a normal appearance of the cervical spine. The anterior and posterior longitudinal ligaments are depicted as smooth linear lines (black arrows and white arrows, respectively). Midsagittal MR bone image (b) of the lumbar spine of a 39-year-old male similarly shows the anterior and posterior longitudinal ligaments (black arrows and white arrows, respectively). The bone cortex and trabeculae are delineated well at the cervical and lumbar spines. At the posterior part of many vertebral bodies, exits of the basivertebral veins are visualized as triangular or linear hypointense structures. The spinal cord shows hypointensity relative to the cerebrospinal fluid within the dural sac

Fig. 3

Modic type 2 change. Modic type endplate changes represent a classification for vertebral body endplate signal changes on MR imaging. Modic type 2 change represents red hemopoietic bone marrow conversion to yellow fatty marrow due to bone marrow ischemia. Sagittal T1-weighted (a), T2-weighted (b), and fat-suppressed T2-weighted (c) MR images of an 84-year-old male patient show signal changes compatible with fatty changes in the bone marrow (arrows). Sagittal MR bone image d shows sparse trabeculae (arrows)

Fig. 4

Modic type 3 change. Modic type 2 change represents subchondral bony sclerosis. Sagittal T1-weighted (a) and T2-weighted (b) MR images of an 84-year-old male patient show areas of hypointensity (arrows). Sagittal MR bone image c shows sclerotic changes as hyperintense areas (arrows)

Fig. 5

Lumbar disc herniation. Sagittal T2-weighted MR image a shows a herniated L4-5 disc in a 45-year-old male patient (arrow). Sagittal and axial MR bone images (b and c) show the herniated disc and preserved posterior longitudinal ligament (arrow)

Fig. 6

Ossification of the posterior longitudinal ligament. In diagnosing ossification of the posterior longitudinal ligament (OPLL), it is imperative to precisely assess the degree of ossification that causes spinal cord compression. Sagittal MR bone image a shows segmented OPLL at C2-C4 extending partially to C5 (arrows) in a 43-year-old male patient. Sagittal CT image b confirms the OPLL (arrows)

Fig. 7

Spondylolysis. Spondylolysis is a defect in the pars interarticularis of the neural arch often seen in the adolescent population. Sagittal MR bone image a obtained with the ZTE sequence at 1.5 T shows a defect in the pars interarticularis of L5 in a 19-year-old female patient (arrow). Sagittal CT bone image b shows the same finding (arrow). (Courtesy of Akira Fujikawa, MD, PhD, Self-Defense Forces Central Hospital, Tokyo, Japan)

Fig. 8

Plasma cell myeloma. Spinal metastasis is one of the common complications of plasma cell myeloma and often develops multiple destructive lesions. Sagittal fat-suppressed T2-weighted MR image shows numerous hyperintense lesions in the lumbar vertebrae and sacrum in a 60-year-old male patient (a). A mild compression fracture of the L5 body is also noted. Sagittal and axial MR bone images (b) and (c) show the lesions more clearly. Axial MR bone image (d) obtained at the same level after 3.5 months of chemotherapy shows the resolution of the lesions

Fig. 9

Recent pathologic compression fractures associated with old compression fractures. Sagittal T2-weighted MR image a shows compression fracture of Th11, Th12, L2, and L3 in a 77-year-old male patient with lung cancer (small arrows). Fluid sign is noted in the Th11 fracture (large arrow). Sagittal fat-suppressed T2-weighted MR image b shows the multiple fractures (arrows) and hypointensity in most parts of Th12, indicating old fracture (arrowhead). The hyperintensity of L2 and L3 suggests acute fracture. Part of Th11 also shows hyperintensity, suggesting recurrent acute fracture. On sagittal MR bone image c, the collapsed Th12 shows hyperintensity due to sclerosis. A tiny disruption of the cortex of L2 and L3 suggests a recent fracture (white arrows). Small hypointense lesions are probable metastatic foci from lung cancer (black arrows). Sagittal CT image d shows a sclerotic change of Th11 and Th12 as well as air indicating old fractures (large arrows). It also shows fracture of L2 and L3 with disruption of the cortex that is compatible with recent fracture as suggested on MR bone imaging (small arrows)

Fig. 10

Pyogenic spondylodiscitis. Sagittal fat-suppressed T2-weighted MR image (a) of a 64-year-old male patient shows abnormal hyperintensity in L1 and L2 vertebrae and the flattened L1-2 disc due to spondylodiscitis (arrows). Sagittal MR bone image (b) clearly shows the disrupted endplates of L1 and L2 vertebrae (arrowheads) and sparse trabeculae (arrows). Sagittal CT image (c) shows the corresponding destruction of the endplates of the L1 and L2 bodies facing the narrowed L1-2 disc (arrows)

Fig. 11

Hemangioma. Axial MR bone image (a) of an 84-year-old male shows a lucent lesion margin (arrow). Thickened internal trabeculae are also well visualized. Axial CT image (b) shows similar findings, but the lesion margin is unclear (arrow)