Quantitative MRI for the assessment of bone structure and function

Abstract

Osteoporosis is the most common degenerative disease in the elderly. It is characterized by low bone mass and structural deterioration of bone tissue, leading to morbidity and increased fracture risk in the hip, spine and wrist-all sites of predominantly trabecular bone. Bone densitometry, currently the standard methodology for diagnosis and treatment monitoring, has significant limitations in that it cannot provide information on the structural manifestations of the disease. Recent advances in imaging, in particular MRI, can now provide detailed insight into the architectural consequences of disease progression and regression in response to treatment. The focus of this review is on the emerging methodology of quantitative MRI for the assessment of structure and function of trabecular bone. During the past 10 years, various approaches have been explored for obtaining image-based quantitative information on trabecular architecture. Indirect methods that do not require resolution on the scale of individual trabeculae and therefore can be practiced at any skeletal location, make use of the induced magnetic fields in the intertrabecular space. These fields, which have their origin in the greater diamagnetism of bone relative to surrounding marrow, can be measured in various ways, most typically in the form of R 0 2 , the recoverable component of the total transverse relaxation rate. Alternatively, the trabecular network can be quantified by high-resolution MRI (m-MRI), which requires resolution adequate to at least partially resolve individual trabeculae. Micro-MRI-based structure analysis is therefore technically demanding in terms of image acquisition and algorithms needed to extract the structural information under conditions of limited signal-to-noise ratio and resolution. Other requirements that must be met include motion correction and image registration, both critical for achieving the reproducibility needed in repeat studies. Key clinical applications targeted involve fracture risk prediction and evaluation of the effect of therapeutic intervention.

Reproducibility of the quantitative assessment of cartilage morphology and trabecular bone structure with magnetic resonance imaging at 7 T

“…The measurement of cartilage morphology may provide a biomarker for evaluating the long-term progression of OA. The measurement of trabecular bone structure with MRI offers a quantitative assessment of OP progression and therapeutic monitoring in patient studies [8]. In addition, the superior SNR of ultra-high-field strengths is expected to improve image quality and to assist in evaluating cross-correlations between cartilage and bone changes during the progression of OA [9,10].…”

Comparison of computed tomographic and magnetic resonance imaging in fracture healing after spinal injury

“…3 Although there has been limited use of MRI for the evaluation of fracture healing in the spine, MRI techniques have been validated for the assessment of trabecular and cortical bone structure with good reproducibility. [4][5][6] MRI does have an established use in the diagnosis of occult fractures in the scaphoid bone using the presence of T1-weighted low signal and high signal on T2-weighted fatsuppressed imaging for diagnosis. 7,8 MRI has also been used to evaluate for union in the femur and tibia.…”

Potential of PET-MRI for imaging of non-oncologic musculoskeletal disease

“…Although MRI is not typically associated with bone imaging, tissue diffusion (25) and ultra-short echo time (uTE) (26,27) methods are able to provide important information about bone strength and fracture risk. These methods as well as many other MRI applications in musculoskeletal imaging are discussed in numerous review papers on the topic (28)(29)(30). Because MRI can offer novel functional contrasts, its combination with PET offers powerful observations of distinct physiological processes occurring in bone and cartilage at the same time.…”

“…Unlike most methods that image bone structure, trabecular and cortical bone is mostly visualized with negative contrast on MRI. The trabecular network can be visualized as signal void surrounded by high-signal-intensity fatty bone marrow (30). This signal void is due to the low water content and very short T2 relaxation time of bone as well as susceptibility effects at the bone-bone marrow interface.…”