A review of the recent advances in magnetic resonance imaging in the assessment of osteoporosis

Abstract

Osteoporosis is a common metabolic disorder with considerable associated morbidity and mortality. The loss of bone mineral integrity and the resultant occurrence of atraumatic fractures are typically symptomatic of the disease. Currently skeletal status is commonly assessed using non-invasive conventional radiography and scintigraphy as well as densitometric techniques such as quantitative computed tomography and dual-energy X-ray absorptiometry. But, apart from gross bone mineral density, the fine structure of trabecular bone also plays an important role in defining the biomechanical competence of the skeleton. Recently attention has been focused on deriving measures that provide information about not only trabecular bone density but also microstructure. Magnetic resonance imaging (MRI) is one such new technique which potentially may provide information pertaining to bone density and structure as well as to occult fracture detection. Cortical bone produces a signal void in MR images, due to the fact that it contains very few mobile protons that give rise to a signal in MRI; also the MR relaxation time T2 of these protons is very short which produces a very fast decay of the MR signal during image acquisition. However, the trabecular bone network affects the MR properties of bone marrow. The difference in the magnetic properties of trabecular bone and bone marrow generates local imperfections in the magnetic field. The MR signal from bone marrow is modified due to these imperfections and the MR relaxation time T2 of marrow is shortened. The extent of relaxation time shortening and hence loss of signal intensity is proportional to the density of trabecular bone and marrow interfaces and their spatial architecture. Recent investigation in this area include studies aimed at quantifying marrow relaxation times and establishing their relationship to trabecular bone density and structure. In addition, with advances in imaging software and hardware, MR images at in-plane resolutions of 78-200 microns may be obtained. The trabecular bone structure is clearly revealed in such images and studies aimed at the development of high-resolution MRI techniques combined with quantitative image analysis techniques are currently under way. These potentially useful techniques for assessing osteoporosis and predicting fracture risk are reviewed in this paper.

In Vivo μMRI-Based Finite Element and Morphological Analyses of Tibial Trabecular Bone in Eugonadal and Hypogonadal Men Before and After Testosterone Treatment

“…2A). However, there was no significant increase in E 11 and G 31 after 24 mo of treatment. This observation might suggest that the effect of testosterone treatment on mechanical properties is anisotropic, in that the estimated elastic modulus of tibial trabecular bone with higher initial loss (E 11 , G 31 ) in testosterone deficiency is less recoverable with treatment.…”

“…CT and MRI are high-resolution imaging modalities that are now increasingly used for quantifying microstructural changes in trabecular bone architecture. (10)(11)(12)(13)(14)(15) MRI of trabecular bone actually images the bone marrow compartment instead of bone, whereas CT measures Xray attenuations of bone mineral. One of the advantages of MRI is its noninvasive property.…”

Bone densitometry: Clinical considerations

“…Thcrefore, although MRT cannot measure BMD, it can provide images of thc structurc of OP bone, such as morphologic changes in trabecular microarchitecture and occult fractures in the proximal femur (98). Based on its ability to differentiate physiochemical processes, it can also distinguish acute from chronic, or benign from malignant, vertebral fractures (99,100) and assist in thc diiignosis of transient OP of the hip (101). Although MRI cannot be used to measure quantitative bone density, it is currently used to diagnose subtle ostcoporotic fractures.…”

Quantitative imaging techniques for the assessment of osteoporosis and sarcopenia

“…The investigation of trabecular network with MRI is however, perhaps, less intuitive than with QCT and HR-pQCT because the physical principles underlying the generation of diagnostic images are complex and completely different from those of X-ray based techniques (126). In MRI, cortical bone appears dark (or as a signal void) due to the very small number of mobile protons and the extremely short T2 relaxation time; the trabecular bone network also appears as a signal void but the surrounding BM gives rise to a high signal, which intensity depends on the amount of fatty content (vs. hematopoietic BM) (102,127). Differences in diamagnetic susceptibility at the interfaces between BM and trabecular bone structure cause a reduction of marrow relaxation time T2*, and the extent of this decay depends on density and microarchitecture of the surrounding trabeculae (126) Today, high resolution MRI allows the depiction of trabecular bone density and structure in vitro and in vivo with a high spatial resolution (in-plane resolutions as high as 78 μm; slice thickness of approximately 300 μm) (8,102,128,129).…”