Vertebral deformities and fractures are associated with MRI and pQCT measures obtained at the distal tibia and radius of postmenopausal women

Digital wrist tomosynthesis (DWT)-based finite element analysis of ultra-distal radius differentiates patients with and without a history of osteoporotic fracture

Despite effective therapies for those at risk of osteoporotic fracture, low adherence to screening guidelines and limited accuracy of bone mineral density (BMD) in predicting fracture risk preclude identification of those at risk. Because of high adherence to routine mammography, bone health screening at the time of mammography using a digital breast tomosynthesis (DBT) scanner has been suggested as a potential solution. BMD and bone microstructure can be measured from the wrist using a DBT scanner. However, the extent to which biomechanical variables can be derived from digital wrist tomosynthesis (DWT) has not been explored. Accordingly, we measured stiffness from a DWT based finite element (DWT-FE) model of the ultra-distal (UD) radius and ulna, and correlate these to reference microcomputed tomography image based FE (μCT-FE) from five cadaveric forearms. Further, this method is implemented to determine in vivo reproducibility of FE derived stiffness of UD radius and demonstrate the in vivo utility of DWT-FE in bone quality assessment by comparing two groups of postmenopausal women with and without a history of an osteoporotic fracture (Fx; n = 15, NFx; n = 51). Stiffness obtained from DWT and μCT had a strong correlation (R2 = 0.87, p < 0.001). In vivo repeatability error was <5 %. The NFx and Fx groups were not significantly different in DXA derived minimum T-scores (p > 0.3), but stiffness of the UD radius was lower for the Fx group (p < 0.007). Logistic regression models of fracture status with stiffness of the nondominant arm as the predictor were significant (p < 0.01). In conclusion this study demonstrates the feasibility of fracture risk assessment in mammography settings using DWT imaging and FE modeling in vivo. Using this approach, bone and breast screening can be performed in a single visit, with the potential to improve both the prevalence of bone health screening and the accuracy of fracture risk assessment.

Vertebral Deformity Measurements at MRI, CT, and Radiography Using Deep Learning

PURPOSE

To construct and evaluate the efficacy of a deep learning system to rapidly and automatically locate six vertebral landmarks, which are used to measure vertebral body heights, and to output spine angle measurements (lumbar lordosis angles [LLAs]) across multiple modalities.

MATERIALS AND METHODS

In this retrospective study, MR (n = 1123), CT (n = 137), and radiographic (n = 484) images were used from a wide variety of patient populations, ages, disease stages, bone densities, and interventions (n = 1744 total patients, 64 years ± 8, 76.8% women; images acquired 2005-2020). Trained annotators assessed images and generated data necessary for deformity analysis and for model development. A neural network model was then trained to output vertebral body landmarks for vertebral height measurement. The network was trained and validated on 898 MR, 110 CT, and 387 radiographic images and was then evaluated or tested on the remaining images for measuring deformities and LLAs. The Pearson correlation coefficient was used in reporting LLA measurements.

RESULTS

On the holdout testing dataset (225 MR, 27 CT, and 97 radiographic images), the network was able to measure vertebral heights (mean height percentage of error ± 1 standard deviation: MR images, 1.5% ± 0.3; CT scans, 1.9% ± 0.2; radiographs, 1.7% ± 0.4) and produce other measures such as the LLA (mean absolute error: MR images, 2.90°; CT scans, 2.26°; radiographs, 3.60°) in less than 1.7 seconds across MR, CT, and radiographic imaging studies.

CONCLUSION

The developed network was able to rapidly measure morphometric quantities in vertebral bodies and output LLAs across multiple modalities.Keywords: Computer Aided Diagnosis (CAD), MRI, CT, Spine, Demineralization-Bone, Feature Detection Supplemental material is available for this article. © RSNA, 2021.

Changes in bone microarchitecture following parathyroidectomy in patients with secondary hyperparathyroidism

Background

Secondary hyperparathyroidism (SHPT) in patients with chronic kidney disease (CKD) has a significant effect on bone, affecting both trabecular and cortical compartments. Although parathyroidectomy results in biochemical improvement in mineral metabolism, changes in bone microarchitecture as evaluated by high-resolution imaging modalities are not known. Magnetic resonance imaging (MRI) provides in-depth three-dimensional assessment of bone microarchitecture, as well as determination of mechanical bone strength determined by finite element analysis (FEA).

Methods

We conducted a single-centre longitudinal study to evaluate changes in bone microarchitecture with MRI in patients with SHPT undergoing parathyroidectomy. MRI was performed at the distal tibia at baseline (time of parathyroidectomy) and at least 12 months following surgery. Trabecular and cortical topological parameters as well as bone mechanical competence using FEA were assessed.

Results

Fifteen patients with CKD (12 male, 3 female) underwent both MRI scans at the time of surgery and at least 12 months post-surgery. At baseline, 13 patients were on dialysis, one had a functioning kidney transplant, and one was pre-dialysis with stage 5 CKD. Seven patients received a kidney transplant following parathyroidectomy prior to follow-up MRI. MRI parameters in patients at follow up were consistent with loss in trabecular and cortical bone thickness (p = 0.006 and 0.03 respectively). Patients who underwent a kidney transplant in the follow-up period had reduction in trabecular thickness (p = 0.05), whereas those who continued on dialysis had reduction in cortical thickness (p = 0.04) and mechanical bone strength on FEA (p = 0.03).

Conclusion

Patients with severe SHPT requiring parathyroidectomy have persistent changes in bone microarchitecture at least 12 months following surgery with evidence of ongoing decline in trabecular and cortical thickness.

Differentiation Between Osteoporotic And Neoplastic Vertebral Fractures: State Of The Art And Future Perspectives

Vertebral fractures are a common condition, occurring in the context of osteoporosis and malignancy. These entities affect a group of patients in the same age range; clinical features may be indistinct and symptoms non-existing, and thus present challenges to diagnosis. In this article, we review the use and accuracy of different imaging modalities available to characterize vertebral fracture etiology, from well-established classical techniques, to the role of new and advanced imaging techniques, and the prospective use of artificial intelligence. We also address the role of imaging on treatment. In the context of osteoporosis, the importance of opportunistic diagnosis is highlighted. In the near future, the use of automated computer-aided diagnostic algorithms applied to different imaging techniques may be really useful to aid on diagnosis.

Effect of Low-Intensity Vibration on Bone Strength, Microstructure, and Adiposity in Pre-Osteoporotic Postmenopausal Women: A Randomized Placebo-Controlled Trial

There has been evidence that cyclical mechanical stimulation may be osteogenic, thus providing opportunities for nonpharmacological treatment of degenerative bone disease. Here, we applied this technology to a cohort of postmenopausal women with varying bone mineral density (BMD) T-scores at the total hip (-0.524 ± 0.843) and spine (-0.795 ± 1.03) to examine the response to intervention after 1 year of daily treatment with 10 minutes of vibration therapy in a randomized double-blinded trial. The device operates either in an active mode (30 Hz and 0.3 g) or placebo. Primary endpoints were changes in bone stiffness at the distal tibia and marrow adiposity of the vertebrae, based on 3 Tesla high-resolution MRI and spectroscopic imaging, respectively. Secondary outcome variables included distal tibial trabecular microstructural parameters and vertebral deformity determined by MRI, volumetric and areal bone densities derived using peripheral quantitative computed tomography (pQCT) of the tibia, and dual-energy X-ray absorptiometry (DXA)-based BMD of the hip and spine. Device adherence was 83% in the active group (n = 42) and 86% in the placebo group (n = 38) and did not differ between groups (p = .7). The mean 12-month changes in tibial stiffness in the treatment group and placebo group were +1.31 ± 6.05% and -2.55 ± 3.90%, respectively (group difference 3.86%, p = .0096). In the active group, marrow fat fraction significantly decreased after 12 months of intervention (p = .0003), whereas no significant change was observed in the placebo group (p = .7; group difference -1.59%, p = .029). Mean differences of the changes in trabecular bone volume fraction (p = .048) and erosion index (p = .044) were also significant, as was pQCT-derived trabecular volumetric BMD (vBMD; p = .016) at the tibia. The data are commensurate with the hypothesis that vibration therapy is protective against loss in mechanical strength and, further, that the intervention minimizes the shift from the osteoblastic to the adipocytic lineage of mesenchymal stem cells. © 2020 American Society for Bone and Mineral Research (ASBMR).

Bone Microarchitecture, Volumetric or Areal Bone Mineral Density for Discrimination of Vertebral Deformity in Adults: A Cross-sectional Study

INTRODUCTION/BACKGROUND

Both areal bone mineral density (aBMD) and bone microarchitecture have been associated with vertebral deformity (VD), but there are limited data on the utility of bone microarchitecture measures in combination with aBMD in discriminating VD. This study aimed to describe whether radial bone microarchitecture measures alone or in combinations with radial volumetric bone mineral density (vBMD) or spine aBMD can improve discrimination of VD in adults.

METHODS

Data on 196 subjects (mean age (standard deviation, SD) = 72 (7) years, female 46%) were utilized. VD of T4-L4 and spine aBMD were measured using dual-energy X-ray absorptiometry. VD was defined if anterior to posterior height ratio was more than 3-SD, 4-SD below, or >25% decrease compared with the sex-matched normal means. Bone microarchitecture parameters at distal radius were collected using high-resolution peripheral quantitative computed tomography and analyzed using StrAx.

RESULTS

The strongest associations were seen for the cortical thickness (odds ratios (ORs): 2.63/SD decrease for 25% and 2.38/SD decrease for 3-SD criterion) and compact cortical area (OR: 3.33/SD decrease for 4-SD criterion). The area under the receiver operating characteristic curve (AUC) for spine aBMD for VD was 0.594, 0.597, and 0.634 for 25%, 3-SD and 4-SD criteria, respectively (all p < 0.05). Compact cortical area, cortical thickness and compact cortical thickness alone had the largest AUCs for VD (0.680-0.685 for 25% criterion, 0.659-0.674 for 3-SD criterion, and 0.699-0.707 for 4-SD criterion). Adding spine aBMD or radial vBMD to each cortical measure did not improve VD discrimination (∆ AUC 0.8%-2.1%).

CONCLUSIONS

Cortical measures had the best utility for discriminating VD when used alone. Adding either spine aBMD or radial vBMD did not improve the utility of cortical measures.

Survey of MRI Usefulness for the Clinical Assessment of Bone Microstructure

Bone microarchitecture has been shown to provide useful information regarding the evaluation of skeleton quality with an added value to areal bone mineral density, which can be used for the diagnosis of several bone diseases. Bone mineral density estimated from dual-energy X-ray absorptiometry (DXA) has shown to be a limited tool to identify patients' risk stratification and therapy delivery. Magnetic resonance imaging (MRI) has been proposed as another technique to assess bone quality and fracture risk by evaluating the bone structure and microarchitecture. To date, MRI is the only completely non-invasive and non-ionizing imaging modality that can assess both cortical and trabecular bone in vivo. In this review article, we reported a survey regarding the clinically relevant information MRI could provide for the assessment of the inner trabecular morphology of different bone segments. The last section will be devoted to the upcoming MRI applications (MR spectroscopy and chemical shift encoding MRI, solid state MRI and quantitative susceptibility mapping), which could provide additional biomarkers for the assessment of bone microarchitecture.

MRI-derived porosity index is associated with whole-bone stiffness and mineral density in human cadaveric femora

Ultrashort echo time (UTE) magnetic resonance imaging (MRI) measures proton signals in cortical bone from two distinct water pools, bound water, or water that is tightly bound to bone matrix, and pore water, or water that is freely moving in the pore spaces in bone. By isolating the signal contribution from the pore water pool, UTE biomarkers can directly quantify cortical bone porosity in vivo. The Porosity Index (PI) is one non-invasive, clinically viable UTE-derived technique that has shown strong associations in the tibia with μCT porosity and other UTE measures of bone water. However, the efficacy of the PI biomarker has never been examined in the proximal femur, which is the site of the most catastrophic osteoporotic fractures. Additionally, the loads experienced during a sideways fall are complex and the femoral neck is difficult to image with UTE, so the usefulness of the PI in the femur was unknown. Therefore, the aim of this study was to examine the relationships between the PI measure in the proximal cortical shaft of human cadaveric femora specimens compared to (1) QCT-derived bone mineral density (BMD) and (2) whole bone stiffness obtained from mechanical testing mimicking a sideways fall. Fifteen fresh, frozen whole cadaveric femora specimens (age 72.1 ± 15.0 years old, 10 male, 5 female) were scanned on a clinical 3-T MRI using a dual-echo UTE sequence. Specimens were then scanned on a clinical CT scanner to measure volumetric BMD (vBMD) and then non-destructively mechanically tested in a sideways fall configuration. The PI in the cortical shaft demonstrated strong correlations with bone stiffness (r = -0.82, P = 0.0014), CT-derived vBMD (r = -0.64, P = 0.0149), and with average cortical thickness (r = -0.60, P = 0.0180). Furthermore, a hierarchical regression showed that PI was a strong predictor of bone stiffness which was independent of the other parameters. The findings from this study validate the MRI-derived porosity index as a useful measure of whole-bone mechanical integrity and stiffness.

Total-Body PET Imaging of Musculoskeletal Disorders

Imaging of musculoskeletal disorders, including arthritis, infection, osteoporosis, sarcopenia, and malignancies, is often limited when using conventional modalities such as radiography, computed tomography (CT), and MR imaging. As a result of recent advances in Positron Emission Tomography (PET) instrumentation, total-body PET/CT offers a longer axial field-of-view, higher geometric sensitivity, and higher spatial resolution compared with standard PET systems. This article discusses the potential applications of total-body PET/CT imaging in the assessment of musculoskeletal disorders.

Bone microarchitecture in patients undergoing parathyroidectomy for management of secondary hyperparathyroidism

Background

Secondary hyperparathyroidism (SHPT) in patients with chronic kidney disease (CKD) leads to complex bone disease, affecting both trabecular and cortical bone, and increased fracture risk. Optimal assessment of bone in patients with CKD is yet to be determined. High-resolution magnetic resonance imaging (MRI) can provide three-dimensional assessment of bone microarchitecture, as well as determination of mechanical strength with finite element analysis (FEA).

Methods

We conducted a single-centre, cross-sectional study to determine bone microarchitecture with MRI in CKD patients with SHPT undergoing parathyroidectomy. Within two weeks of surgery, MRI was performed at the distal tibia and biochemical markers of SHPT (parathyroid hormone [PTH] and alkaline phosphatase [ALP]) were collected. Trabecular and cortical topological parameters as well as bone mechanical competence using FEA were assessed. Correlation of MRI findings of bone was made with biochemical markers.

Results

Twenty patients with CKD (15 male, 5 female) underwent MRI at the time of parathyroidectomy (16 on dialysis, 3 with functioning kidney transplant, one pre-dialysis with CKD stage 5). Median PTH at the time of surgery was 138.5 pmol/L [39.6–186.7 pmol/L]. MRI parameters in patients were consistent with trabecular deterioration, with erosion index (EI) 1.01 ± 0.3, and trabecular bone volume (BV/TV) 10.8 ± 2.9%, as well as poor trabecular network integrity with surface-to-curve ratio (S/C) 5.4 ± 2.3. There was also evidence of reduced cortical thickness, with CTh 2.698 ± 0.630 mm, and FEA demonstrated overall poor bone mechanical strength with mean elastic modulus of 2.07 ± 0.44.

Conclusion

Patients with severe SHPT requiring parathyroidectomy have evidence of significant changes in bone microarchitecture with trabecular deterioration, low trabecular and cortical bone volume, and reduced mechanical competence of bone.

A Vertebral Segmentation Dataset with Fracture Grading

Published under a CC BY 4.0 license. Supplemental material is available for this article.

MRI-Based Quantitative Osteoporosis Imaging at the Spine and Femur

Osteoporosis is a systemic skeletal disease with a high prevalence worldwide, characterized by low bone mass and microarchitectural deterioration, predisposing an individual to fragility fractures. Dual-energy X-ray absorptiometry (DXA) has been the clinical reference standard for diagnosing osteoporosis and for assessing fracture risk for decades. However, other imaging modalities are of increasing importance to investigate the etiology, treatment, and fracture risk. The purpose of this work is to review the available literature on quantitative magnetic resonance imaging (MRI) methods and related findings in osteoporosis at the spine and proximal femur as the clinically most important fracture sites. Trabecular bone microstructure analysis at the proximal femur based on high-resolution MRI allows for a better prediction of osteoporotic fracture risk than DXA-based bone mineral density (BMD) alone. In the 1990s, T₂ * mapping was shown to correlate with the density and orientation of the trabecular bone. Recently, quantitative susceptibility mapping (QSM), which overcomes some of the limitations of T₂ * mapping, has been applied for trabecular bone quantifications at the spine, whereas ultrashort echo time (UTE) imaging provides valuable surrogate markers of cortical bone quantity and quality. Magnetic resonance spectroscopy (MRS) and chemical shift encoding-based water-fat MRI (CSE-MRI) enable the quantitative assessment of the nonmineralized bone compartment through extraction of the bone marrow fat fraction (BMFF). Furthermore, CSE-MRI allows for the differentiation of osteoporotic vs. pathologic fractures, which is of high clinical relevance. Lastly, advanced postprocessing and image analysis tools, particularly considering statistical parametric mapping and region-specific BMFF distributions, have high potential to further improve MRI-based fracture risk assessments at the spine and hip. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY STAGE: 2.

pQCT bone geometry and strength: population epidemiology and concordance in Australian children aged 11-12 years and their parents

OBJECTIVES

To describe the epidemiology and concordance of bone health in a population-based sample of Australian parent-child dyads at child age 11-12 years.

DESIGN

Population-based cross-sectional study (the Child Health CheckPoint) nested between waves 6 and 7 of the Longitudinal Study of Australian Children (LSAC).

SETTING

Assessment centres in seven cities around Australia, February 2015-March 2016.

PARTICIPANTS

of all participating CheckPoint families (n=1874), bone data were available for 1222 dyads (1271 children, 50% girls; 1250 parents, 86% mothers).

OUTCOME MEASURES

Peripheral quantitative CT (pQCT) of the non-dominant leg scanned at the 4% (distal) and 66% (mid-calf) tibial sites. Stratec XCT 2000 software generated estimates of bone density, geometry and polar stress-strain index.Parent-child concordance were assessed using Pearson's correlation coefficients and multivariable linear regression models. Percentiles were determined using survey weights. Survey weights and methods accounted for LSAC's complex sampling, stratification and clustering within postcodes.

RESULTS

Concordances were greater for the geometric pQCT parameters (periosteal circumference 0.38, 95% CI 0.33 to 0.43; endosteal circumference 0.42, 95% CI 0.37 to 0.47; total cross-sectional area 0.37, 95% CI 0.32 to 0.42) than density (cortical density 0.25, 95% CI 0.19 to 0.30). Mother-child and father-child values were similar. Relationships attenuated only slightly on adjustment for age, sex and body mass index. Percentiles and concordance are presented for the whole sample and by sex.

CONCLUSIONS

There is strong parent-child concordance in bone geometry and, to a lesser extent, density even before the period of peak adolescent bone deposition. This geometrical concordance suggests that future intergenerational bone studies could consider using pQCT rather than the more commonly used dual X-ray absorptiometry (DXA).

Micro-Finite Element Analysis of the Proximal Femur on the Basis of High-Resolution Magnetic Resonance Images

PURPOSE OF REVIEW

Hip fractures have catastrophic consequences. The purpose of this article is to review recent developments in high-resolution magnetic resonance imaging (MRI)-guided finite element analysis (FEA) of the hip as a means to determine subject-specific bone strength.

RECENT FINDINGS

Despite the ability of DXA to predict hip fracture, the majority of fractures occur in patients who do not have BMD T scores less than - 2.5. Therefore, without other detection methods, these individuals go undetected and untreated. Of methods available to image the hip, MRI is currently the only one capable of depicting bone microstructure in vivo. Availability of microstructural MRI allows generation of patient-specific micro-finite element models that can be used to simulate real-life loading conditions and determine bone strength. MRI-based FEA enables radiation-free approach to assess hip fracture strength. With further validation, this technique could become a potential clinical tool in managing hip fracture risk.

Changes in bone microarchitecture following kidney transplantation-Beyond bone mineral density

Bone disease in kidney transplant recipients (KTRs) is characterized by bone mineral density (BMD) loss but bone microarchitecture changes are poorly defined. In this prospective cohort study, we evaluated bone microarchitecture using non-invasive imaging modalities; high-resolution magnetic resonance imaging (MRI), peripheral quantitative computed tomography (pQCT), dual energy X-ray absorptiometry (DXA), and the trabecular bone score (TBS) following kidney transplantation. Eleven KTRs (48.3 ± 11.2 years) underwent MRI (tibia), pQCT (radius) and DXA at baseline and 12 months post-transplantation. Transiliac bone biopsies, performed at transplantation, showed 70% of patients with high/normal bone turnover. Compared with baseline, 12-month MRI showed deterioration in indices of trabecular network integrity-surface to curve ratio (S/C; -15%, P = 0.03) and erosion index (EI; +19%, P = 0.01). However, cortical area increased (+10.3%, P = 0.04), with a non-significant increase in cortical thickness (CtTh; +7.8%, P = 0.06). At 12 months, parathyroid hormone values (median 10.7 pmol/L) correlated with improved S/C (r = 0.75, P = 0.009) and EI (r = -0.71, P = 0.01) while osteocalcin correlated with CtTh (r = 0.72, P = 0.02) and area (r = 0.70, P = 0.02). TBS decreased from baseline (-5.1%, P = 0.01) with no significant changes in BMD or pQCT. These findings highlight a post-transplant deterioration in trabecular bone quality detected by MRI and TBS, independent of changes in BMD, underlining the potential utility of these modalities in evaluating bone microarchitecture in KTRs.

The reproducibility of measuring trabecular bone parameters using a commercially available high-resolution magnetic resonance imaging approach: A pilot study

Bone imaging is currently the best non-invasive way to assess changes to bone associated with aging or chronic disease. However, common imaging techniques such as dual energy x-ray absorptiometry are associated with limitations. Magnetic resonance imaging (MRI) is a radiation-free technique that can measure bone microarchitecture. However, published MRI bone assessment protocols use specialized MRI coils and sequences and therefore have limited transferability across institutions. We developed a protocol on a Siemens 3 Tesla MRI machine, using a commercially available coil (Siemens 15 CH knee coil), and manufacturer supplied sequences to acquire images at the tibia. We tested the reproducibility of the FSE and the GE Axial sequences and hypothesized that both would generate reproducible trabecular bone parameters. Eight healthy adults (age 25.5 ± 5.4 years) completed three measurements of each MRI sequence at the tibia. Each of the images was processed for 8 different bone parameters (such as volumetric bone volume fraction). We computed the coefficient of variation (CV) and intraclass correlation coefficients (ICC) to assess reproducibility and reliability. Both sequences resulted in trabecular parameters that were reproducible (CV <5% for most) and reliable (ICC >80% for all). Our study is one of the first to report that a commercially available MRI protocol can result in reproducible data, and is significant as MRI may be an accessible method to measure bone microarchitecture in clinical or research environments. This technique requires further testing, including validation and evaluation in other populations.

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Trabecular bone is difficult to measure using commercial MRI techniques

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Reproducibility of a MRI protocol measuring trabecular bone was assessed

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Tibia trabecular bone was reproducible using a knee coil and a FSE Axial sequence

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Tibia trabecular bone was reproducible using a knee coil and a GE Axial sequence

Accuracy of MRI-based finite element assessment of distal tibia compared to mechanical testing

High-resolution MRI-derived finite element analysis (FEA) has been used in translational research to estimate the mechanical competence of human bone. However, this method has yet to be validated adequately under in vivo imaging spatial resolution or signal-to-noise conditions. We therefore compared MRI-based metrics of bone strength to those obtained from direct, mechanical testing. The study was conducted on tibiae from 17 human donors (12 males and five females, aged 33 to 88years) with no medical history of conditions affecting bone mineral homeostasis. A 25mm segment from each distal tibia underwent MR imaging in a clinical 3-Tesla scanner using a fast large-angle spin-echo (FLASE) sequence at 0.137mm×0.137mm×0.410mm voxel size, in accordance with in vivo scanning protocol. The resulting high-resolution MR images were processed and used to generate bone volume fraction maps, which served as input for the micro-level FEA model. Simulated compression was applied to compute stiffness, yield strength, ultimate strength, modulus of resilience, and toughness, which were then compared to metrics obtained from mechanical testing. Moderate to strong positive correlations were found between computationally and experimentally derived values of stiffness (R²=0.77, p<0.0001), yield strength (R²=0.38, p=0.0082), ultimate strength (R²=0.40, p=0.0067), and resilience (R²=0.46, p=0.0026), but only a weak, albeit significant, correlation was found for toughness (R²=0.26, p=0.036). Furthermore, experimentally derived yield strength and ultimate strength were moderately correlated with MRI-derived stiffness (R²=0.48, p=0.0022 and R²=0.58, p=0.0004, respectively). These results suggest that high-resolution MRI-based finite element (FE) models are effective in assessing mechanical parameters of distal skeletal extremities.

MRI assessment of bone structure and microarchitecture

Osteoporosis is a disease of weak bone and increased fracture risk caused by low bone mass and microarchitectural deterioration of bone tissue. The standard-of-care test used to diagnose osteoporosis, dual-energy x-ray absorptiometry (DXA) estimation of areal bone mineral density (BMD), has limitations as a tool to identify patients at risk for fracture and as a tool to monitor therapy response. Magnetic resonance imaging (MRI) assessment of bone structure and microarchitecture has been proposed as another method to assess bone quality and fracture risk in vivo. MRI is advantageous because it is noninvasive, does not require ionizing radiation, and can evaluate both cortical and trabecular bone. In this review article, we summarize and discuss research progress on MRI of bone structure and microarchitecture over the last decade, focusing on in vivo translational studies. Single-center, in vivo studies have provided some evidence for the added value of MRI as a biomarker of fracture risk or treatment response. Larger, prospective, multicenter studies are needed in the future to validate the results of these initial translational studies.

LEVEL OF EVIDENCE

5 Technical Efficacy: Stage 5 J. MAGN. RESON. IMAGING 2017;46:323-337.

A Comparison of Peripheral Imaging Technologies for Bone and Muscle Quantification: a Mixed Methods Clinical Review

PURPOSE OF REVIEW

Bone and muscle peripheral imaging technologies are reviewed for their association with fractures and frailty. A narrative systematized review was conducted for bone and muscle parameters from each imaging technique. In addition, meta-analyses were performed across all bone quality parameters.

RECENT FINDINGS

The current body of evidence for bone quality's association with fractures is strong for (high-resolution) peripheral quantitative computed tomography (pQCT), with trabecular separation (Tb.Sp) and integral volumetric bone mineral density (vBMD) reporting consistently large associations with various fracture types across studies. Muscle has recently been linked to fractures and frailty, but the quality of evidence remains weaker from studies of small sample sizes. It is increasingly apparent that musculoskeletal tissues have a complex relationship with interrelated clinical endpoints such as fractures and frailty. Future studies must concurrently address these relationships in order to decipher the relative importance of one causal pathway from another.

Adverse Fat Depots and Marrow Adiposity Are Associated With Skeletal Deficits and Insulin Resistance in Long-Term Survivors of Pediatric Hematopoietic Stem Cell Transplantation

Allogeneic hematopoietic stem-cell transplantation (alloHSCT) survivors treated with total body irradiation (TBI) exhibit bone deficits and excess adiposity, potentially related to altered mesenchymal stem cell differentiation into osteoblasts or adipocytes. We examined associations among fat distribution, bone microarchitecture, and insulin resistance in alloHSCT survivors after TBI. This was a cross-sectional observational study of 25 alloHSCT survivors (aged 12 to 25 years) a median of 9.7 (4.3 to 19.3) years after alloHSCT compared to 25 age-, race-, and sex-matched healthy controls. Vertebral MR spectroscopic imaging and tibia micro-MRI were used to quantify marrow adipose tissue (MAT) and trabecular microarchitecture. Additional measures included DXA whole-body fat mass (WB-FM), leg lean mass (Leg-LM), trunk visceral adipose tissue (VAT), and CT calf muscle density. Insulin resistance in alloHSCT survivors was estimated by HOMA-IR. AlloHSCT survivors had lower Leg-LM (p < 0.001) and greater VAT (p < 0.01), MAT (p < 0.001), and fat infiltration of muscle (p = 0.04) independent of WB-FM, versus matched controls; BMI did not differ. Survivors had lower bone volume fraction and abnormal microarchitecture including greater erosion and more rod-like structure versus controls (all p = 0.04); 14 had vertebral deformities and two had compression fractures. Greater WB-FM, VAT, MAT, and muscle fat infiltration were associated with abnormal trabecular microarchitecture (p < 0.04 for all). AlloHSCT HOMA-IR was elevated, associated with younger age at transplantation (p < 0.01), and positively correlated with WB-FM and VAT (both p < 0.01). In conclusion, the markedly increased marrow adiposity, abnormal bone microarchitecture, and abnormal fat distribution highlight the risks of long-term treatment-related morbidity and mortality in alloHSCT recipients after TBI. Trabecular deterioration was associated with marrow and visceral adiposity. Furthermore, long-term survivors demonstrated sarcopenic obesity, insulin resistance, and vertebral deformities. Future studies are needed to identify strategies to prevent and treat metabolic and skeletal complications in this growing population of childhood alloHSCT survivors.