What is the role of MRI in the workup of osteoporosis?

Updated: Jan 19, 2021
  • Author: Ali Nawaz Khan, MBBS, FRCS, FRCP, FRCR; Chief Editor: Felix S Chew, MD, MBA, MEd  more...
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Answer

Answer

Bone-mineral density (BMD) is the most important factor contributing to bone strength and the risk of fracture. However, studies have shown that changes in bone quality and structure, which influence both bone strength and individual risk of fracture, are independent of BMD. The influence of these other factors is thought to at least partially account for the observed overlap in bone-mineral measurements in patients with, and in those without, osteoporotic fractures, irrespective of measurement site or technique. Therefore, devising a method to assess bone quality and to quantify the trabecular bone structure may be what is important in assessing fracture risk. See also the Fracture Index WITH known Bone Mineral Density (BMD) calculator.

MRI is not yet in the mainstream use in the diagnosis of osteoporosis and is unlikely to become so because of its expense and the time required to obtain a scan. Even so, several noninvasive MR techniques have been shown to provide microstructural information about bone beyond simple bone densitometry. Newitt described a method for characterizing trabecular bone structure on high-resolution MRIs. [46]

Advances in MRI allow spatial resolutions of 80-150 µm and a section thickness of 300-700 µm, allowing resolution of the trabecular structure. Majumdar and Genant used MRI to quantify trabecular bone structure and bone density, both in vivo and in vitro. [47] They used both modified spin-echo and gradient-echo sequences to obtain the images, despite the fact that the technical parameters and the sequence-specific mechanisms affected the depiction of trabecular bone. They concluded that in conjunction with 3D image processing and an understanding of the mechanisms of image formation, these high-resolution images might be used to quantify trabecular bone architecture.

In addition to standard stereologic measures, other parameters may be derived from such images: trabecular bone volume; mean trabecular width; mean trabecular spacing; mean intercept length as a function of angle; parameters such as 3D connectivity, as measured by the Euler number; the fabric tensor in 3 dimensions; and texture-related parameters, such as fractals.

MRI is valuable in the assessment of vertebral body fractures, nonspinal insufficiency fractures, bone mass and strength, and bone marrow edema. The signal-intensity characteristics of bone marrow may allow the differentiation of neoplastic fractures from accompanying osteoporosis.

Because the features of osteoporotic fractures and fractures due to other infiltrative processes overlap, false-positive and false-negative results are possible.


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