Quantitative magnetic resonance imaging in the calcaneus and femur of women with varying degrees of osteopenia and vertebral deformity status

Behavior during aging of bone-marrow fatty-acids profile in women's calcaneus to search for early potential osteoporotic biomarkers: a 1H-MR Spectroscopy study

AIM

Identify new potential biomarkers of osteoporosis at an early stage, by magnetic resonance spectroscopy (MRS), studying early changes in the metabolic profile of bone-marrow fatty acids in women's calcanei during healthy aging and osteoporosis status.

METHODS

Single voxel MRS was performed by using a point resolved spectroscopy (PRESS) sequence at 3T. Thirty-four Caucasian women (age range: 22-59 years) were recruited to investigate calcaneus bone marrow. The cohort was constituted of four groups according to age, menopausal status, and T-score evaluated after a DXA examination on the femoral neck. Women were classified in young control (n = 11, mean age = 26.5 ± 3.8 y, age range: 22-34 years), perimenopausal groups (n = 11, mean age = 42.0 ± 3.6 y, age range: 37-47 years), postmenopausal group (n = 9, mean age = 55.4 ± 2.9 y, age range: 50-59 years, mean T-score = -1.70 ± 0.50) and osteoporotic group (n = 6, mean age = 53.0 ± 2.8 y, age range: 50-58 years, mean T-score = -2.54 ± 0.10). The total lipid content (TL), the Unsaturation Index (UI), and the fraction of unsaturated/polyunsaturated fatty acid (f_UFA and f_PUFA) were calculated.

RESULTS

TL was significantly correlated with age (r = 0.73, p < 0.001). TL increases linearly with age in the young + perimenopausal population (r = 0.92, p < 0.001) but this trend is not significant in the postmenopausal subject (r = 0.48, p = 0.07). No significant correlation was found between T-Score and TL in postmenopausal and osteoporotic women, whereas a significant correlation was found between TL and time interval (t_p) between the age at menopause and the age of the subject at the MRS examination. Conversely, no correlation was found between T-score and t_p. The unsaturation index (UI) does not significantly discriminate between osteoporotic, peri- and postmenopausal women. On the other hand, f_UFA is significantly different in peri-menopausal and osteoporotic subjects (p = 0.02), while f_PUFA is significantly different both between peri- and postmenopausal women (p = 0.05) and postmenopausal and osteoporotic subjects (p = 0.03). Both f_UFA and f_PUFA did not correlate with subjects' age.

CONCLUSION

In the female calcaneus, f_UFA and f_PUFA are promising measurable quantities for the characterization of bone marrow's composition potentially correlated with the development of osteoporosis, whereas UI does not differentiate between subjects of varying osteoporotic status. The fact that the TL in the calcaneus is correlated with t_p, indicates that active metabolic changes are still occurring in these subjects, giving complementary information to the DXA about the changes in bone marrow's composition which may affect the whole bone health.

Complexity and data mining in dental research: A network medicine perspective on interceptive orthodontics

Procedures and models of computerized data analysis are becoming researchers' and practitioners' thinking partners by transforming the reasoning underlying biomedicine. Complexity theory, Network analysis and Artificial Intelligence are already approaching this discipline, intending to provide support for patient's diagnosis, prognosis and treatments. At the same time, due to the sparsity, noisiness and time-dependency of medical data, such procedures are raising many unprecedented problems related to the mismatch between the human mind's reasoning and the outputs of computational models. Thanks to these computational, non-anthropocentric models, a patient's clinical situation can be elucidated in the orthodontic discipline, and the growth outcome can be approximated. However, to have confidence in these procedures, orthodontists should be warned of the related benefits and risks. Here we want to present how these innovative approaches can derive better patients' characterization, also offering a different point of view about patient's classification, prognosis and treatment.

Adding marrow R2∗ to proton density fat fraction improves the discrimination of osteopenia and osteoporosis in postmenopausal women assessed with 3D FACT sequence

OBJECTIVE

To evaluate the role of three-dimensional Fat Analysis & Calculation Technique sequence in improving the diagnostic accuracy for the detection of osteopenia and osteoporosis by simultaneous quantification of proton density fat fraction (PDFF) and fat-corrected R2∗.

METHODS

Fat Analysis & Calculation Technique imaging of lumbar spine was obtained in 99 postmenopausal women including 52 normal bone mass, 29 osteopenia, and 18 osteoporosis. The diagnostic performance of PDFF and R2∗ in the differentiation of different bone-density groups was evaluated with the receiver operating characteristic curve.

RESULTS

The reproducibility of PDFF and R2∗ measures was satisfactory with the root mean square coefficient of variation, 2.16% and 2.70%, respectively. The intra- and interobserver agreements for the PDFF and R2∗ were excellent with the intraclass correlation coefficient > 0.9 for all. There were significant differences in PDFF and R2∗ among the three groups (P < 0.05). Bone density had a moderate inverse correlation with PDFF (r  = -0.659) but a positive association with R2∗ (r = 0.508, P < 0.001). Adjusted for age, years since menopause and body mass index, odds ratios (95% confidence interval) for osteopenia and osteoporosis per standard deviation higher marrow PDFF and R2∗ were 2.9 (1.4-5.8) and 0.4 (0.2-0.8), respectively. The areas under the curve were 0.821 for PDFF, 0.784 for R2∗, and 0.922 for both combined for the detection of osteoporosis (P < 0.05). Similar results were obtained in distinguishing osteopenia from healthy controls.

CONCLUSIONS

Simultaneous estimation of marrow R2∗ and PDFF improves the discrimination of osteopenia and osteoporosis in comparison with the PDFF or R2∗ alone.

Osteoarthritis: New Strategies for Transport and Drug Delivery Across Length Scales

Osteoarthritis (OA) is the fourth leading cause of disability in adults. Yet, few viable pharmaceutical options exist for pain abatement and joint restoration, aside from joint replacement at late and irreversible stages of the disease. From the first onset of OA, as joint pain increases, individuals with arthritis increasingly reach for drug delivery solutions, from taking oral glycosaminoglycans (GAGs) bought over the counter from retail stores (e.g., Costco) to getting injections of viscous, GAG-containing synovial fluid supplement in the doctor's office. Little is known regarding the efficacy of delivery mode and/or treatment by such disease-modulating agents. This Review addresses the interplay of mechanics and biology on drug delivery to affected joints, which has profound implications for molecular transport in joint health and (patho)physiology. Multiscale systems biology approaches lend themselves to understand the relationship between the cell and joint health in OA and other joint (patho)physiologies. This Review first describes OA-related structural and functional changes in the context of the multilength scale anatomy of articular joints. It then summarizes and categorizes, by size and charge, published molecular transport studies, considering changes in permeability induced through inflammatory pathways. Finally, pharmacological interventions for OA are outlined in the context of molecular weights and modes of drug delivery. Taken together, the current state-of-the-art points to a need for new drug delivery strategies that harness systems-based interactions underpinning molecular transport and maintenance of joint structure and function at multiple length scales from molecular agents to cells, tissues, and tissue compartments which together make up articular joints. Cutting edge and cross-length and -time scale imaging represents a key discovery enabling technology in this process.

Simultaneous Quantification of Bone Edema/Adiposity and Structure in Inflamed Bone Using Chemical Shift-Encoded MRI in Spondyloarthritis

Purpose

To evaluate proton density fat fraction (PDFF) and R2* as markers of bone marrow composition and structure in inflamed bone in patients with spondyloarthritis.

Methods

Phantoms containing fat, water, and trabecular bone were constructed with proton density fat fraction (PDFF) and bone mineral density (BMD) values matching those expected in healthy bone marrow and disease states, and scanned using chemical shift‐encoded MRI (CSE‐MRI) at 3T. Measured PDFF and R2* values in phantoms were compared with reference FF and BMD values. Eight spondyloarthritis patients and 10 controls underwent CSE‐MRI of the sacroiliac joints. PDFF and R2* in areas of inflamed bone and fat metaplasia in patients were compared with normal bone marrow in controls.

Results

In phantoms, PDFF measurements were accurate over the full range of PDFF and BMD values. R2* measurements were positively associated with BMD but also were influenced by variations in PDFF. In patients, PDFF was reduced in areas of inflammation and increased in fat metaplasia compared to normal marrow. R2* measurements were significantly reduced in areas of fat metaplasia.

Conclusion

PDFF measurements reflect changes in marrow composition in areas of active inflammation and structural damage and could be used for disease monitoring in spondyloarthritis. R2* measurements may provide additional information bone mineral density but also are influenced by fat content. Magn Reson Med 79:1031–1042, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Feasibility of assessing bone matrix and mineral properties in vivo by combined solid-state 1H and 31P MRI

Purpose

To develop and evaluate an integrated imaging protocol for bone water and phosphorus quantification in vivo by solid-state ¹H and ³¹P MRI.

Materials and methods

All studies were HIPAA-compliant and were performed with institutional review board approval and written informed consent. Proton (¹H) ultra-short echo-time (UTE) and phosphorus (³¹P) zero echo-time (ZTE) sequences were designed and implemented on a 3 T clinical MR scanner to quantify bone water and mineral in vivo. The left tibia of ten healthy subjects (including both genders, 49±15 y/o) was examined with a custom-built ¹H/³¹P dual-frequency extremity RF coil. Total bone water (TW), water bound to the collagen matrix (BW) and bone ³¹P were quantified from MR images with respect to reference samples of known ¹H or ³¹P concentration, and pore water (PW) was subsequently determined from TW and BW. Porosity index (PI) was calculated as the ratio between UTE images acquired at two echo times. MRI parameters were compared with bone density measures obtained by high-resolution peripheral quantitative CT (HR-pQCT).

Results

The total scan time for the bone water and ³¹P quantification protocol was about 50 minutes. Average TW, BW, PW and ³¹P concentrations were 13.99±1.26, 10.39±0.80, 3.34±1.41 mol/L and 7.06±1.53 mol/L for the studied cohort, respectively, in good agreement with previous results conducted ex vivo. Average intra-subject coefficients of variation were 3.47%, 2.60% and 7.50% for TW, BW and PW and 5.60% for ³¹P. Negative correlations were observed between PW and vBMD (p<0.05) as well as between PI and ³¹P (p<0.05), while bone mineral content (BMC) estimated from ³¹P MRI and HR-pQCT were strongly positively correlated (p<0.0001).

Conclusion

This work demonstrates the feasibility of quantifying bone water and mineral phosphorus in human subjects in a single MRI session with a clinically practical imaging protocol.

Bone Marrow Lipid Profiles from Peripheral Skeleton as Potential Biomarkers for Osteoporosis: A 1H-MR Spectroscopy Study

RATIONALE AND OBJECTIVES

To characterize the lipidic profile of bone marrow in the calcaneus and femoral neck of healthy, osteopenic, and osteoporotic women, by using magnetic resonance spectroscopy (MRS) at 3T. The final goal was to identify specific metabolites with the potential ability to discriminate between healthy, osteopenic, and osteoporotic subjects.

MATERIALS AND METHODS

Sixty-two and thirty three postmenopausal women recruited to investigate calcaneus and femoral neck, respectively, underwent a bone mineral density (BMD) measurement to be classified as healthy subjects (n = 22), osteopenic (n = 45), or osteoporotic (n = 28) patients. MRS spectra were used to quantify and compare bone marrow fat resonances between the three BMD groups. Between-group differences were tested using a Welch analysis of variance. Multiple comparisons were made with the Games-Howell correction. Relationships between pairs of variables were assessed with linear correlation analysis. Reproducibility analysis was performed for all the lipid resonances in both sites.

RESULTS

The reproducibility was satisfactory. In femoral neck, methylene (L13), glycerol (L41, L43), and total lipid resonances were significantly lower in healthy as compared to osteoporotic subjects. On the other hand, in calcaneus, L13/glycerol significantly discriminated between osteopenic and osteoporotic subjects whereas L13/(unsaturated lipid) discriminated between healthy and osteopenic group. However, the reproducibility of both unsaturated lipid and glycerol resonances were less optimal.

CONCLUSIONS

MRS of bone marrow lipid profiles from peripheral skeletal sites may be a promising tool for screening of large population to identify individuals with or at risk for developing osteoporosis. Moreover, it provides information about the metabolic changes occurring in bone marrow with the development of osteoporosis, which are skeletal site dependent.

Focus on diffusion MR investigations of musculoskeletal tissue to improve osteoporosis diagnosis: a brief practical review

Nowadays, a huge number of papers have documented the ability of diffusion magnetic resonance imaging (D-MRI) to highlight normal and pathological conditions in a variety of cerebral, abdominal, and cardiovascular applications. To date, however, the role of D-MRI to investigate musculoskeletal tissue, specifically the cancellous bone, has not been extensively explored. In order to determine potentially useful applications of diffusion techniques in musculoskeletal investigation, D-MRI applications to detect osteoporosis disease were reviewed and further explained.

Characterization of trabecular bone density with ultra-short echo-time MRI at 1.5, 3.0 and 7.0 T--comparison with micro-computed tomography

The goal of this study was to test the potential of ultra-short echo-time (UTE) MRI at 1.5, 3.0 and 7.0 T for depiction of trabecular bone structure (of the wrist bones), to evaluate whether T2* relaxation times of bone water and parametric maps of T2* of trabecular bone could be obtained at all three field strengths, and to compare the T2* relaxation times with structural parameters obtained from micro-computed tomography (micro-CT) as a reference standard. Ex vivo carpal bones of six wrists were excised en bloc and underwent MRI at 1.5, 3.0 and 7.0 T in a whole-body MR imager using the head coil. A three-dimensional radial fat-suppressed UTE sequence was applied with subsequent acquisitions, with six different echo times TE of 150, 300, 600, 1200, 3500 and 7000 µs. The T2* relaxation time and pixel-wise computed T2* parametric maps were compared with a micro-computed-tomography reference standard providing trabecular bone structural parameters including porosity (defined as the bone-free fraction within a region of interest), trabecular thickness, trabecular separation, trabecular number and fractal dimension (Dk). T2* relaxation curves and parametric maps could be computed from datasets acquired at all field strengths. Mean T2* relaxation times of trabecular bone were 4580 ± 1040 µs at 1.5 T, 2420 ± 560 µs at 3.0 T and 1220 ± 300 µs at 7.0 T, when averaged over all carpal bones. A positive correlation of T2* with trabecular bone porosity and trabecular separation, and a negative correlation of T2* relaxation time with trabecular thickness, trabecular number and fractal dimension, was detected (p < 0.01 for all field strengths and micro-CT parameters). We conclude that UTE MRI may be useful to characterize the structure of trabecular bone, comparable to micro-CT.

Potential diagnostic role of the MRI-derived internal magnetic field gradient in calcaneus cancellous bone for evaluating postmenopausal osteoporosis at 3T

INTRODUCTION

Bone mineral density (BMD) result has a low predictive value on patients' risk for future fractures. Thus, new approaches for examining patients at risk for developing osteoporosis would be desirable. Magnetic resonance (MR) investigations in cancellous bone have been shown to yield useful quantitative information on both trabecular-bone microstructure and bone marrow composition. This work was undertaken to address the hypothesis that the effective internal magnetic field gradient (IMFG), a new MR parameter, discriminates between healthy, osteopenic and osteoporotic postmenopausal women, classified on the basis of bone mineral density (BMD) criteria. The work builds on preliminary results indicating that IMFG, measured in trabecular-bone pores and quantified by spin-echo decay and water diffusion MR near the bone-bone marrow interface depends on both the bone marrow water rate of diffusion and the magnetic susceptibility difference (ΔX) between water and bone.

MATERIALS AND METHODS

MR relaxometry, MR spectroscopy and diffusion-weighted MR imaging of the heel was performed in fifty-five women (mean age, 62.9±6.6years) at 3T. Moreover, in order to study the reproducibility of IMFG measurement, five young women (mean age 31.0±3.2years; age range, 28-36years) were scanned and rescanned. The study protocol was approved by the local Ethics Committee. Quantitative Computer Tomography (QCT) of the L1-L3 vertebral segments was performed to classify the postmenopausal women into three groups according to QCT BMD: healthy (n=8); osteopenic (n=25); and osteoporotic (n=22). In all subjects, BMD T-scores, marrow fat content (Mfc), T2*, apparent diffusion coefficient (ADC) and IMFG (estimated from the additional spin-echo decay due to diffusion of water in local magnetic field gradients), were assessed in the whole calcaneus as well as in three calcaneal subregions: subtalar, tuber calcaneus, and cavum calcaneus. Between-group comparisons to assess group differences and Pearson correlation analysis were performed. Short and long-term coefficients of variation (CVS and CVL, respectively) were evaluated in young subjects.

RESULTS

Reproducibility of the IMFG measurement was satisfactory. No significant difference was found in the IMFG measurement performed in both calcaneus and subtalar calcaneal region between the two separate sessions comprised of five young women. Mfc did not significantly differ between groups. The IMFG in the subtalar region was significantly different between all three groups (P<0.01), being greatest in healthy women, intermediate in those with osteopenia, and lowest in osteoporotic subjects. Conversely neither T2* nor ADC is able to discriminate healthy subjects from those with osteopenia and osteoporosis. Increased inter-trabecular space, as it typically occurs in patients with osteoporosis, modifies water diffusion, conferring higher ADC values, thereby lowering the IMFG.

CONCLUSION

The IMFG measured in the calcaneal subtalar region shows a high ability in identifying healthy subjects. The new quantitative MR method based on measurement of the IMFG may provide a new means for assessing patients with osteoporosis.

Diffusion tensor imaging and magnetic resonance spectroscopy assessment of cancellous bone quality in femoral neck of healthy, osteopenic and osteoporotic subjects at 3T: Preliminary experience

We assessed the potential of diffusion tensor imaging (DTI) in combination with proton magnetic resonance spectroscopy (1H-MRS), in cancellous bone quality evaluation of the femoral neck in postmenopausal women.

INTRODUCTION

DTI allows for non-invasive microarchitectural characterization of heterogeneous tissue. In this work we hypothesized that DTI parameters mean diffusivity (MD) and fractional anisotropy (FA) of bone marrow water, can provide information about microstructural changes that occur with the development of osteoporosis disease. Because osteoporosis is associated with increased bone marrow fat content, which in principal can alter DTI parameters, the goal of this study was to examine the potential of MD and FA, in combination with bone marrow fat fraction (FF), to discriminate between healthy, osteopenic and osteoporotic subjects, classified according to DXA criteria.

MATERIALS AND METHODS

Forty postmenopausal women (mean age, 68.7 years; range 52-81 years), underwent a Dual-energy X-ray absorptiometry (DXA) examination in femoral neck, to be classified as healthy (n=12), osteopenic (n=14) and osteoporotic (n=14) subjects. 1H-MRS and DTI (with b value=2500 s/mm2) of femoral neck were obtained in each subject at 3T. The study protocol was approved by local Ethics Committee. MD, FA, FF and MD/FF, FA/FF were obtained and compared among the three bone-density groups. One-way ANOVA with multiple comparisons Bonferroni test and Pearson correlation analysis were applied. Receiver operating characteristic (ROC) curve analysis was also performed.

RESULTS

Reproducibility of DTI measures was satisfactory. CV was approximately 2%-3% for MD and 4%-5% for FA measurements. Moreover, no significant difference was found in both MD and FA measurements between two separate sessions (median 34 days apart) comprised of six healthy volunteers. FF was able to discriminate between healthy and osteoporotic subjects only. Conversely MD and FA were able to discriminate healthy from osteopenic and healthy from osteoporotic subjects, but they were not able to discriminate between osteopenic and osteoporotic patients. A significant correlation between MD and FF was observed in healthy group only. A moderate correlation was found between MD and T-score when all groups together are considered. No significant correlation was found between MD and T-score within groups. A significant positive correlation between FA and FF was found in both osteopenic and osteoporotic groups. Vice-versa no correlation between FA and FF was observed in healthy group. A high significant positive correlation was found between FA and T-score in all groups together, in healthy and in osteoporotic groups. MD/FF and FA/FF are characterized by a higher sensitivity and specificity compared to MD and FA in the discrimination between healthy, and osteoporotic subjects. MD/FF vs. FA/FF graph extracted from femoral neck, identify all healthy individuals according to DXA results.

CONCLUSION

DTI-(1)H-MRS protocol performed in femoral neck seems to be highly sensitive and specific in identifying healthy subjects. A MR exam is more expensive when compared to a DXA investigation. However, even though DXA BMD evaluation has been the accepted standard for osteoporosis diagnosis, DXA result has a low predictive value on patients' risk for future fractures. Thus, new approaches for examining patients at risk for developing osteoporosis would be desirable. Preliminary results showed here suggest that future studies on a larger population based on DTI assessment in the femoral neck, in combination with 1H-MRS investigations, might allow screening of high-risk populations and the establishment of cut-off values of normality, with potential application of the method to single subjects.

Magnetic resonance of calcified tissues

MRI of the human body is largely made possible by the favorable relaxation properties of protons of water and triacyl glycerides prevalent in soft tissues. Hard tissues--key among them bone--are generally less amenable to measurement with in vivo MR imaging techniques, not so much as a result of the lower proton density but rather due to the extremely short life-times of the proton signal in water bound to solid-like entities, typically collagen, or being trapped in micro-pores. Either mechanism can enhance T2 relaxation by up to three orders of magnitude relative to their soft-tissue counterparts. Detection of these protons requires solid-state techniques that have emerged in recent years and that promise to add a new dimension to the study of hard tissues. Alternative approaches to probe calcified tissues exploit their characteristic magnetic properties. Bone, teeth and extra-osseous calcium-containing biomaterials are unique in that they are more diamagnetic than all other tissues and thus yield information indirectly by virtue of the induced magnetic fields present in their vicinity. Progress has also been made in methods allowing very high-resolution structural imaging of trabecular and cortical bone relying on detection of the surrounding soft-tissues. This brief review, much of it drawn from work conducted in the author's laboratory, seeks to highlight opportunities with focus on early-stage developments for image-based assessment of structure, function, physiology and mechanics of calcified tissues in humans via liquid and solid-state approaches, including proton, deuteron and phosphorus NMR and MRI.

Correlation of signal attenuation-based quantitative magnetic resonance imaging with quantitative computed tomographic measurements of subchondral bone mineral density in metacarpophalangeal joints of horses

OBJECTIVE

To evaluate the ability of signal attenuation-based quantitative magnetic resonance imaging (QMRI) to estimate subchondral bone mineral density (BMD) as assessed via quantitative computed tomography (QCT) in osteoarthritic joints of horses.

SAMPLE POPULATION

20 metacarpophalangeal joints from 10 horse cadavers.

PROCEDURES

Magnetic resonance (MR) images (dorsal and transverse T1-weighted gradient recalled echo [GRE] and dorsal T2*-weighted GRE fast imaging employing steady-state acquisition [T2*-FIESTA]) and transverse single-slice computed tomographic (CT) images of the joints were acquired. Magnetic resonance signal intensity (SI) and CT attenuation were quantified in 6 regions of interest (ROIs) in the subchondral bone of third metacarpal condyles. Separate ROIs were established in the air close to the joint and used to generate corrected ratios and SIs. Computed tomographic attenuation was corrected by use of a calibration phantom to obtain a K(2)HPO(4)-equivalent density of bone. Correlations between QMRI performed with different MR imaging sequences and QCT measurements were evaluated. The intraobserver repeatability of ROI measurements was tested for each modality.

RESULTS

Measurement repeatability was excellent for QCT (R(2) = 98.3%) and QMRI (R(2) = 98.8%). Transverse (R(2) = 77%) or dorsal (R(2) = 77%) T1-weighted GRE and QCT BMD measurements were negatively correlated, as were dorsal T2*-FIESTA and QCT (R(2) = 80%) measurements. Decreased bone SI during MR imaging linearly reflected increased BMD.

CONCLUSIONS AND CLINICAL RELEVANCE

Results of this ex vivo study suggested that signal attenuation-based QMRI was a reliable, clinically applicable method for indirect estimation of subchondral BMD in osteoarthritic metacarpophalangeal joints of horses.

Radiographic texture analysis of densitometric calcaneal images: relationship to clinical characteristics and to bone fragility

Osteoporotic fractures are related not only to bone mineral density (BMD) but also to bone structure or microarchitecture, which is not assessed routinely with currently available methods. We have developed radiographic texture analysis (RTA) for calcaneal images from a peripheral densitometer as an easy, noninvasive method for assessing bone structure. We conducted a cross-sectional study of the relationship between RTA and prevalent vertebral fractures (n = 148) among 900 subjects (ages 19 to 99 years, 94 males) referred for bone densitometry as part of their routine medical care. RTA features were derived from Fourier-based image analysis of the radiographic texture pattern (including root mean square, first moment, and power spectral analyses). RTA features were associated with age, weight, gender, and race, as well as glucocorticoid use. When controlling for clinical risk factors and BMD (or a summary measure calculated using FRAX algorithms), RTA features were significantly different for subjects with and without prevalent vertebral fractures [adjusted odds ratio (OR) = 1.5 per 1 standard deviation (SD) decrease in RTA feature beta, 95% confidence interval (CI) 1.2-1.8, p = .001]. Gender and use of pharmacologic therapy for osteoporosis did not significantly affect this association, suggesting that RTA can be applied to a wide range of densitometry patients. We conclude that RTA obtained using a portable instrument has a potential as a noninvasive method to enhance identification of patients at increased risk of osteoporotic fractures.

Considerations for development of surrogate endpoints for antifracture efficacy of new treatments in osteoporosis: a perspective

Because of the broad availability of efficacious osteoporosis therapies, conduct of placebo-controlled trials in subjects at high risk for fracture is becoming increasing difficult. Alternative trial designs include placebo-controlled trials in patients at low risk for fracture or active comparator studies, both of which would require enormous sample sizes and associated financial resources. Another more attractive alternative is to develop and validate surrogate endpoints for fracture. In this perspective, we review the concept of surrogate endpoints as it has been developed in other fields of medicine and discuss how it could be applied in clinical trials of osteoporosis. We outline a stepwise approach and possible study designs to qualify a biomarker as a surrogate endpoint in osteoporosis and review the existing data for several potential surrogate endpoints to assess their success in meeting the proposed criteria. Finally, we suggest a research agenda needed to advance the development of biomarkers as surrogate endpoints for fracture in osteoporosis trials. To ensure optimal development and best use of biomarkers to accelerate drug development, continuous dialog among the health professionals, industry, and regulators is of paramount importance.

Reproducibility and sources of variability in radiographic texture analysis of densitometric calcaneal images

Radiographic texture analysis (RTA) is a computerized analysis of the spatial pattern of radiographic images used as a way of evaluating bone structure. We have shown that RTA performed on high-resolution heel images obtained using a portable densitometer differentiates subjects with and without osteoporotic fractures. In the present study, short-term precision of RTA was examined on densitometric heel images obtained from 33 subjects scanned 8 times each, with 3 observers placing a region of interest (ROI) 3 times on each image. The long-term precision was examined on images obtained from 10 subjects 3 times on each of 3 days separated by 1 week, with 2 observers placing an ROI on each image. The RTA features examined included the root mean square (RMS) variation, a measure of the contrast between the light and dark areas of the image, the first moment of the power spectrum, a measure of the spatial frequency of the trabecular pattern, and Minkowski fractal (MINK), a measure of roughness/smoothness of the trabecular pattern. The precision of the RTA features expressed as coefficient of variation ranged between the lowest of 0.5-0.7% for MINK and the highest of 14-16% for RMS. The short- and long-term precision was similar, and was not significantly influenced by repositioning and rescanning, or by ROI placement by the same or different observers. Significant sources of variability of RTA were the between-subject differences and differences between regions of the heel, but not differences due to repositioning, rescanning in the same position, or ROI placement by the same or different observers. We conclude that technical aspects of image acquisition and processing are adequate to allow further development of RTA of the densitometric images for clinical application as a method for noninvasive assessment of bone structure.

Tibial geometry is associated with failure load ex vivo: a MRI, pQCT and DXA study

We studied the relations between bone geometry and density and the mechanical properties of human cadaveric tibiae. Bone geometry, assessed by MRI and pQCT, and bone density, assessed by DXA, were significantly associated with bone's mechanical properties. However, cortical density assessed by pQCT was not associated with mechanical properties.

INTRODUCTION

The primary objective of this study was to determine the contribution of cross-sectional geometry (by MRI and pQCT) and density (by pQCT and DXA) to mechanical properties of the human cadaveric tibia.

METHODS

We assessed 20 human cadaveric tibiae. Bone cross-sectional geometry variables (total area, cortical area, and section modulus) were measured with MRI and pQCT. Cortical density and areal BMD were measured with pQCT and DXA, respectively. The specimens were tested to failure in a four-point bending apparatus. Coefficients of determination between imaging variables of interest and mechanical properties were determined.

RESULTS

Cross-sectional geometry measurements from MRI and pQCT were strongly correlated with bone mechanical properties (r(2) range from 0.55 to 0.85). Bone cross-sectional geometry measured by MRI explained a proportion of variance in mechanical properties similar to that explained by pQCT bone cross-sectional geometry measurements and DXA measurements.

CONCLUSIONS

We found that there was a close association between geometry and mechanical properties regardless of the imaging modality (MRI or pQCT) used.

The vertebral fracture cascade in osteoporosis: a review of aetiopathogenesis

Once an initial vertebral fracture is sustained, the risk of subsequent vertebral fracture increases significantly. This phenomenon has been termed the "vertebral fracture cascade". Mechanisms underlying this fracture cascade are inadequately understood, creating uncertainty in the clinical environment regarding prevention of further fractures. The cascade cannot be explained by low bone mass alone, suggesting that factors independent of this parameter contribute to its aetiopathogenesis. This review explores physiologic properties that may help to explain the vertebral fracture cascade. Differences in bone properties, including bone mineral density and bone quality, between individuals with and those without osteoporotic vertebral fractures are discussed. Evidence suggests that non-bone parameters differ between individuals with and those without osteoporotic vertebral fractures. Spinal properties, including vertebral macroarchitecture, intervertebral disc integrity, spinal curvature and spinal loading are compared in these groups of individuals. Cross-sectional studies also indicate that neurophysiologic properties, particularly trunk control and balance, are affected by the presence of a vertebral fracture. This review provides a synthesis of the literature to highlight the multi-factorial aetiopathogenesis of the vertebral fracture cascade. With a more comprehensive understanding of the mechanisms underlying this clinical problem, more effective preventative strategies may be developed to offset the fracture cascade.

Severity of vertebral fracture reflects deterioration of bone microarchitecture

INTRODUCTION

Bone microarchitecture, a component of bone strength, is generally measured on transiliac bone biopsy samples. The objective of this study was to determine whether assessment of four grades of vertebral fracture severity could serve as a noninvasive surrogate marker for trabecular bone volume and microarchitecture.

METHODS

Baseline vertebral fracture severity was determined by semiquantitative assessment of spine radiographs from 190 postmenopausal women with osteoporosis. Bone-structure indices were obtained by 2D histomorphometry and 3D microcomputed tomography (CT) analyses. Significance of differences was determined after adjusting for age, height, and lumbar spine bone mineral density.

RESULTS

There were significant (P < 0.05) trends in decreasing bone volume, trabecular number, and connectivity, and increasing trabecular separation with greater vertebral fracture severity. Histomorphometric bone volume was 25 and 36% lower (P < 0.05) in women with moderate and severe fractures than in women with no fractures, respectively. Compared with women without fractures, women with mild, moderate, and severe fractures had lower (P < 0.05) microCT bone volume (23, 30, and 51%, respectively).

CONCLUSIONS

Microarchitectural deterioration was progressively worse in women with increasing severity of vertebral fractures. We conclude that assessment of vertebral fracture severity is an important clinical tool to evaluate the severity of postmenopausal osteoporosis.

Quantitative MRI for the assessment of bone structure and function

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 R2', the recoverable component of the total transverse relaxation rate. Alternatively, the trabecular network can be quantified by high-resolution MRI (micro-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.

Radiographic texture analysis of densitometer-generated calcaneus images differentiates postmenopausal women with and without fractures

INTRODUCTION

Bone fragility is determined by bone mass, measured as bone mineral density (BMD), and by trabecular structure, which cannot be easily measured using currently available noninvasive methods. In previous studies, radiographic texture analysis (RTA) performed on the radiographic images of the spine, proximal femur, and os calcis differentiated subjects with and without osteoporotic fractures. The present cross-sectional study was undertaken to determine whether such differentiation could also be made using high-resolution os calcis images obtained on a peripheral densitometer.

METHODS

In 170 postmenopausal women (42 with and 128 without prevalent vertebral fractures) who had no secondary causes of osteoporosis and were not receiving treatment for osteoporosis, BMD of the lumbar spine, proximal femur, and os calcis was measured using dual energy x-ray absorptiometry. Vertebral fractures were diagnosed on densitometric spine images. RTA, including Fourier-based and fractal analyses, was performed on densitometric images of os calcis.

RESULTS

BMD at all three sites and all texture features was significantly different in subjects with and without fractures, with the most significant differences observed for the femoral neck and total hip measurements and for the RTA feature Minkowski fractal (p<0.001). In univariate logistic regression analysis, Minkowski fractal predicted the presence of vertebral fractures as well as femoral neck BMD (p<0.001). In multivariate logistic regression analysis, both femoral neck BMD and Minkowski fractal yielded significant predictive effects (p=0.001), and when age was added to the model, the effect of RTA remained significant (p=0.002), suggesting that RTA reflects an aspect of bone fragility that is not captured by age or BMD. Finally, when RTA was compared in 42 fracture patients and 42 nonfracture patients matched for age and BMD, the RTA features were significantly different between the groups (p=0.003 to p=0.04), although BMD and age were not.

CONCLUSION

This study suggests that RTA of densitometer-generated calcaneus images provides an estimate of bone fragility independent of and complementary to BMD measurement and age.

The effects of antifracture therapies on the components of bone strength: assessment of fracture risk today and in the future

OBJECTIVE

To summarize the current knowledge regarding the impact of the most common antifracture medications on the various determinants of bone strength.

METHODS

Relevant English-language articles acquired from Medline from 1966 to January 2005 were reviewed. Searches included the keywords bone AND 1 of the following: strength, remodeling, microcrack, structure, mineralization, collagen, organic, crystallinity, osteocyte, porosity, diameter, anisotropy, stress risers, or connectivity AND alendronate, estrogen, etidronate, hormone replacement therapy, parathyroid hormone, risedronate, OR teriparatide. Abstracts from relevant conference proceedings were also reviewed for pertinent information.

RESULTS

Antiresorptive therapies increase bone strength through decreasing bone turnover. This lower bone turnover results in a higher mean mineralization and decreases the number of active resorption pits within bone at any given time. These resorption pits are speculated to be areas of focal weakness and a higher number of them would, if all other things were equal, result in greater fragility. Parathyroid hormone therapy increases the rate of bone remodeling, which introduces many resorption pits, but this source of strength loss is thought to be compensated by rapid increases in bone mass.

CONCLUSIONS

Both the antiresorptives, particularly bisphosphonates, and the parathyroid hormone therapy increase bone strength; however, the changes that are elicited to achieve this differ significantly.

Parathyroid hormone as an anabolic skeletal therapy

The quest for effective treatment for osteoporosis merits great attention because of the widespread prevalence of this disease, which is not only associated with fragility fractures, but also with significant morbidity and mortality. The efficacy of the antiresorptive drugs in this disease is achieved by reducing bone turnover, increasing bone density and improving other aspects of bone quality. This article concentrates on another approach to the treatment of osteoporosis, namely the use of anabolic therapy, which has even greater prospects for improving bone quality. Parathyroid hormone (PTH) is currently available only as the recombinant amino-terminal fragment, PTH(1-34), known as teriparatide. The full-length molecule, human PTH(1-84), is currently being investigated, as are other PTH molecules. Teriparatide improves bone quality through actions on bone turnover, bone density, bone size and bone microarchitecture. In postmenopausal women with osteoporosis, teriparatide reduces the incidence of vertebral and nonvertebral fractures. In individuals who have previously been treated with an antiresorptive agent, the subsequent actions of teriparatide on bone density are transiently delayed if bone turnover has been markedly suppressed. Combination therapy with teriparatide or PTH(1-84) and an antiresorptive agent does not appear, at this time, to offer advantages over the use of PTH or an antiresorptive agent alone. However, in order to maintain the densitometric gains in bone density obtained with PTH, it is important to follow its use with that of an antiresorptive agent.

Population-based analysis of the relationship of whole bone strength indices and fall-related loads to age- and sex-specific patterns of hip and wrist fractures

In an age- and sex-stratified population sample (n = 700), we estimated fall-related loads and bone strength indices at the UDR and FN. These load/strength ratios more closely simulated patterns of wrist and hip fractures occurring in the same population than did measurement of vBMD.

INTRODUCTION

Areal BMD measurements, although associated with fracture risk, incompletely explain patterns of fragility fractures. Moreover, population-based assessments relating applied loads and whole bone strength to fracture patterns have not been made.

MATERIALS AND METHODS

Using QCT, we assessed volumetric BMD (vBMD), cross-sectional geometry, and axial (EA) and flexural (EI) rigidities (indices of bone's resistance to compressive and bending loads, respectively) at the ultradistal radius (UDR) and femoral neck (FN) and estimated the loads applied to the wrist and hip during a fall. We used fall load (FL)/bone strength ratios to estimate fracture risk.

RESULTS

vBMD in young adults was similar between sexes. Decreases in vBMD over life were also similar (30% and 28%) at UDR but were somewhat greater (46% and 34%) at FN in women versus men, respectively. In young adults, FL/strength ratios at UDR were 32-51% lower (better) in men than in women and increased (worsened) over life less in men (+4% to +22%) than in women (+20% to +33%). In young adults, FL/strength ratios at FN were only marginally better in men than in women but worsened less over life in men (+22% to +36%) than in women (+40% to +62%).

CONCLUSIONS

The 6:1 female preponderance and the virtual immunity of men for age-related increases in wrist fractures are largely explained by the more favorable FL/strength ratios at UDR in young adult men (because of larger bone size and more favorable geometry) versus women and to maintaining this advantage over life. The 2-fold lower incidence of hip fractures in men versus women is largely explained by age-related increases (worsening) of FL/bone strength ratios that are only one-half of the increases in women. The moderate increases in these ratios with aging are insufficient to explain the >4-fold increase in hip fracture incidence after age 75 in both sexes, suggesting contributions of other factors, especially the well-documented increased frequency of injurious falls among the elderly.

Trabecular bone volume fraction measurements of a large number of subjects using a compact MRI

Trabecular bone volume fraction (TBVF) and speed of sound (SOS) were measured for the right calcanei of 416 female volunteers. The TBVF was measured with a compact MRI developed in our laboratory. The SOS was measured with a commercial quantitative ultrasound system. It was observed that the correlation coefficient between TBVF and SOS and that between TBVF and age varied depending on the location of region of interest (ROI) in the calcaneus. As a result, an optimum circular ROI with a diameter of 20 mm was determined so that the correlation coefficients were maximized. In the optimum ROI, transverse relaxation time (T2) of the bone marrow protons of the calcaneus was found to be concentrated in a narrow range over the subjects. This result suggested that a 50% scan time reduction in the TBVF measurements could be made by skipping the T2 correction procedure.

Parathyroid hormone and teriparatide for the treatment of osteoporosis: a review of the evidence and suggested guidelines for its use

All therapies currently recommended for the management of osteoporosis act mainly to inhibit bone resorption and reduce bone remodeling. PTH and its analog, teriparatide [recombinant human PTH(1-34)], represent a new class of anabolic therapies for the treatment of severe osteoporosis, having the potential to improve skeletal microarchitecture. Significant reductions in both vertebral and appendicular fracture rates have been demonstrated in the phase III trial of teriparatide, involving elderly women with at least one prevalent vertebral fracture before the onset of therapy. However, there is as yet no evidence that the antifracture efficacy of PTH will be superior to the bisphosphonates, whereas cost-utility estimates suggest that teriparatide is significantly more expensive. Teriparatide should be considered as treatment for postmenopausal women and men with severe osteoporosis, as well as for patients with established glucocorticoid-induced osteoporosis who require long-term steroid treatment. Teriparatide should also be considered for the management of individuals at particularly high risk for fractures, including subjects who are younger than age 65 and who have particularly low bone mineral density measurements (T scores < or = 3.5). Teriparatide therapy is not recommended for more than 2 yr, based, in part, on the induction of osteosarcoma in a rat model of carcinogenicity. Total daily calcium intake from both supplements and dietary sources should be limited to 1500 mg together with adequate vitamin D intake (< or =1000 U/d). Monitoring of serum calcium may be safely limited to measurement after 1 month of treatment; mild hypercalcemia may be treated by withdrawing dietary calcium supplements, reducing the dosing frequency of PTH, or both. At present, concurrent therapy with antiresorptive therapy, particularly bisphosphonates, should be avoided, although sequential therapy with such agents may consolidate the beneficial effects upon the skeleton after PTH is discontinued.

Discriminatory Ability of Magnetic Resonance T2* Measurements in a Sample of Postmenopausal Women With Low-Energy Fractures

RATIONALE AND OBJECTIVES

We sought to assess the ability of magnetic resonance T2* measurements to discriminate between patients with and without osteoporotic fracture and compare the results with the discriminatory ability of speed of sound (SOS) measured at the phalanx and axial bone mineral density (BMD).

MATERIALS AND METHODS

T2* measurements of lumbar spine were obtained at 1.5 T in 26 postmenopausal women with osteoporotic fractures and 28 age-matched healthy control subjects. A multiecho gradient echo (MEGRE) pulse train sequence was used with echo times of 2.70-74.93 milliseconds using 2.33-millisecond interecho intervals. BMD measurements were made in the axial skeleton. SOS also was measured at the finger phalanges.

RESULTS

The in vivo short-term reproducibility for T2* was 1.85%. T2*, spinal BMD, total hip BMD, and SOS measurements were found to give comparable discrimination between normal and osteoporotic women with odds ratios of 2.6, 2.6, 3.2, and 2.2, respectively.

CONCLUSIONS

T2* measurements of lumbar spine are reproducible and capable of differentiating between postmenopausal women with and those without osteoporotic fractures.

Development of a compact MRI system for trabecular bone volume fraction measurements

A compact MRI system for measuring trabecular bone volume fraction (TBVF) of the calcaneus was developed with the use of a 0.21 T permanent magnet and portable MRI console. The entire system weighed < 600 kg and was installed in a 2 m x 2 m space. Two cross-sectional spin-echo images of a heel acquired with external reference phantoms (total measurement time = 5 min) were used to quantify the TBVF of the calcaneus. The linearity and reproducibility of the measurements were evaluated by means of proton density-adjusted phantoms. Comparative measurements with quantitative ultrasound (QUS) in groups of healthy female volunteers showed a relatively high positive correlation (R(2) = 0.4539, 0.2693) between TBVF and the speed of sound (SOS). These results demonstrate the potential of this new system for measuring bone density. Magn Reson Med 52:440-444, 2004.

Noninvasive assessment of bone structure

Bone fragility is determined by bone mass and trabecular structure. While bone mass can be readily measured as bone density, bone trabecular structure cannot be easily assessed by currently available methods. The realization of the importance of bone structure in determining fracture risk has led to the development of several imaging modalities aimed at evaluating the contribution of bone quality to its biomechanical strength and fragility. High-resolution magnetic resonance imaging and computed tomography have limited spatial resolution and high cost but have a potential to generate true three-dimensional images of trabecular structure in vivo. Bone radiographs subjected to various forms of texture analysis have higher resolution and lower cost but provide only a two-dimensional representation of bone structure. Both two- and three-dimensional methods have been shown to predict biomechanical strength in vitro and to differentiate between subjects with and without fractures in vivo. Therefore, all of these methods deserve closer evaluation and also need further technical improvements before they can be considered for use in clinical practice.