Role of endocortical contouring methods on precision of HR-pQCT-derived cortical micro-architecture in postmenopausal women and young adults

Validation of Bone Density and Microarchitecture Measurements of the Load-Bearing Femur in the Human Knee Obtained Using In Vivo HR-pQCT Protocol

High resolution peripheral quantitative computed tomography (HR-pQCT) was designed to study bone mineral density (BMD) and microarchitecture in peripheral sites at the distal radius and tibia. With the introduction of the second generation HR-pQCT scanner (XtremeCT II, Scanco Medical) that has a larger, longer gantry it is now possible to study the human knee in vivo using HR-pQCT. Previous validation of HR-pQCT measurements at the distal radius and tibia against micro-CT is not representative of the knee because the increased cross-sectional area, greater amount of soft tissue surrounding the scan region, and different imaging protocol result in potentially increased beam hardening effects and photon scatter and different signal-to-noise ratio. The objective of this study is to determine the accuracy of density and microarchitecture measurements in the human knee measured by HR-pQCT using an in vivo protocol. Twelve fresh-frozen cadaver knees were imaged using in vivo HR-pQCT (60.7 µm) protocol. Subsequentially, distal femurs were extracted and imaged using a higher resolution (30.3 µm) ex vivo protocol, replicating micro-CT imaging. Scans were registered so that agreement of density and bone microarchitecture measurements could be determined using linear regression and Bland-Altman plots. All density and microarchitecture outcomes were highly correlated between the 2 protocols (R² > 0.89) albeit with statistically significant differences between absolute measures based on paired t tests. All parameters showed accuracy between 4.5% and 8.7%, and errors were highly systematic, particularly for trabecular BMD and trabecular thickness (R² > 0.93). We found that BMD and microarchitecture measurements in the distal femur obtained using an in vivo HR-pQCT knee protocol contained systematic errors, and accurately represented measurements obtained using a micro-CT equivalent imaging protocol. This work establishes the validity and limitations of using HR-pQCT to study the BMD and microarchitecture of human knees in future clinical studies.

Precision of 3D Registration Analysis for Longitudinal Study of Second-Generation HR-pQCT

OBJECTIVE

The objective of this research was to develop 3D registration analysis method in longitudinal studies of high-resolution peripheral quantitative computed tomography (HR-pQCT), to analyze ranges of bone microstructure parameters in addition to standard parameters, and to test the precision of these measurements.

METHODS

Scans of HR-pQCT and analysis of bone microstructure were performed at 3 times in 15 subjects. The 3 images were matched 3-dimensionally, and bone microstructures were analyzed in the common region. In addition to standard measurement parameters of geometry, bone mineral density (BMD), trabecular bone, and cortical bone, parameters showing plate to rod-like structure, connectivity, cavity formation of trabecular bone, and bending stability of cortical bone were also measured. Precision was evaluated with the root mean square percent coefficient variance (RMS%CV).

RESULTS

RMS%CV was 0.1%-1.3% for geometry, 0.6%-1.9% for BMD, 0.8%-3.3% for trabecular bone, 2.1%-9.8% for additionally measured trabecular bone, 1.0%-3.4% for cortical bone excluding Ct.Po, 6.0%-6.1% for Ct.Po, and 0.8%-1.5% for additionally measured cortical bone. Precision was higher for 3D registration than for 2D registration in geometry, BV/TV, and Ct.Po.

CONCLUSIONS

3D registration analysis of a range of bone microstructural parameters in longitudinal analysis of HR-pQCT showed good precision, offering potential for contributing to future research on osteoporosis and bone metabolic diseases.

Guidelines for the assessment of bone density and microarchitecture in vivo using high-resolution peripheral quantitative computed tomography

INTRODUCTION

The application of high-resolution peripheral quantitative computed tomography (HR-pQCT) to assess bone microarchitecture has grown rapidly since its introduction in 2005. As the use of HR-pQCT for clinical research continues to grow, there is an urgent need to form a consensus on imaging and analysis methodologies so that studies can be appropriately compared. In addition, with the recent introduction of the second-generation HrpQCT, which differs from the first-generation HR-pQCT in scan region, resolution, and morphological measurement techniques, there is a need for guidelines on appropriate reporting of results and considerations as the field adopts newer systems.

METHODS

A joint working group between the International Osteoporosis Foundation, American Society of Bone and Mineral Research, and European Calcified Tissue Society convened in person and by teleconference over several years to produce the guidelines and recommendations presented in this document.

RESULTS

An overview and discussion is provided for (1) standardized protocol for imaging distal radius and tibia sites using HR-pQCT, with the importance of quality control and operator training discussed; (2) standardized terminology and recommendations on reporting results; (3) factors influencing accuracy and precision error, with considerations for longitudinal and multi-center study designs; and finally (4) comparison between scanner generations and other high-resolution CT systems.

CONCLUSION

This article addresses the need for standardization of HR-pQCT imaging techniques and terminology, provides guidance on interpretation and reporting of results, and discusses unresolved issues in the field.

Optimizing HR-pQCT workflow: a comparison of bias and precision error for quantitative bone analysis

Manual correction of automatically generated contours for high-resolution peripheral quantitative computed tomography can be time consuming and introduces precision error. However, bias related to the automated protocol is unknown. This study provides insight into error bias that is present when using uncorrected contours and inter-operator precision error based on operator training.

INTRODUCTION

High-resolution peripheral quantitative computed tomography workflow includes manually correcting contours generated by the manufacturer's automated protocol. There is interest in minimizing corrections to save time and reduce precision error; however, bias related to the automated protocol is unknown. This study quantifies error bias when contours are uncorrected and identifies the impact of operator training on bias and precision error.

METHODS

Forty-five radii and tibiae scans across a representative range of bone density were analyzed using the automated and manually corrected contours of three operators, with training ranging from beginner to expert, and compared with a "ground truth" to estimate bias. Inter-operator precision was measured across operators.

RESULTS

The tibia had greater error bias than the radius when contours were uncorrected, with compartmental bone mineral densities and cortical microarchitecture having greatest biases, which could have significant implications for interpretation of studies using this skeletal site. Bias and precision error were greatest when contours were corrected by the beginner operator; however, when this operator was removed, bias was no longer present and inter-operator precision was between 0.01 and 3.74% for all parameters except cortical porosity.

CONCLUSION

These findings establish the need for manual correction and provide guidance on operator training needed to maximize workflow efficiency.

Distal radius bone microarchitecture: what are the differences between age 25 and old age?

This study reported that the transitional zones in older adults were enlarged at the expense of the compact-appearing cortex with a greater porosity in all cortical sub-compartments. The magnitude of differences in areal and volumetric bone mineral density (aBMD, vBMD) between older and younger groups was similar.

INTRODUCTION

Aging is strongly associated with bone loss, but little is known about magnitudes of differences in bone microarchitectures, aBMD, and vBMD from peak bone mass (PBM) to senescence. We aimed to describe differences in aBMD, vBMD, and bone microarchitecture parameters at the distal radius between older and young adults.

METHODS

We compared 201 participants, aged 62-89 years (female 47%) and 196 participants, aged 24-28 years (female 38%). Bone microarchitecture parameters at distal radius were measured using high-resolution peripheral computed tomography (HRpQCT). aBMD was measured using dual-energy X-ray absorptiometry (DXA). Unpaired t tests and chi-square tests were used to compare differences in means and proportions as appropriate.

RESULTS

Older adults had thinner compact-appearing cortices with larger (cross-sectional area: outer 30.96 mm² vs. 28.38 mm², inner 36.34 mm² vs. 32.93 mm²) and thicker (outer 0.57 mm vs. 0.54 mm, inner 0.71 mm vs. 0.65 mm) transitional zones compared with young adults (all p < 0.05). Cortical porosity was modestly higher in older adults than in young adults (54% vs. 49%, p < 0.001). The magnitude of the difference in hip aBMD between older and young adults was slightly lower than of total radial vBMD (- 0.51 SD vs. - 0.78 SD).

CONCLUSION

Compared with young adults at the time of PBM, the transitional zones in older adults were enlarged at the expense of the compact-appearing cortex with a greater porosity in all cortical sub-compartments. The similar SD differences in aBMD and vBMD between older and younger groups suggest that the differences in bone area are not leading to major artefactual change in aBMD.

Cortical porosity assessment in the distal radius: A comparison of HR-pQCT measures with Synchrotron-Radiation micro-CT-based measures

OBJECTIVE

To determine the agreement between cortical porosity derived from high resolution peripheral quantitative computed tomography (HR-pQCT) (via standard threshold, mean density and density inhomogeneity methods) and synchrotron radiation micro-CT (SR-μCT) derived porosity at the distal radius.

METHODS

We scanned 10 cadaveric radii (mean donor age: 79, SD 11 years) at the standard distal region using HR-pQCT and SR-μCT at voxel sizes of 82 μm and 17.7 μm, respectively. Common cortical regions were delineated for each specimen in both imaging modalities. HR-pQCT images were analyzed for cortical porosity using the following methods: Standard threshold, mean density, and density inhomogeneity (via recommended and optimized equations). We assessed agreement in porosity measures between HR-pQCT methods and SR-μCT by reporting predicted variance from linear regression and mean bias with limits of agreement (LOA).

RESULTS

The standard threshold and mean density methods predicted 85% and 89% of variance and indicated underestimation (mean bias -9.1%, LOA -15.9% to -2.2%) and overestimation (10.4%, 4.6% to 16.2%) of porosity, respectively. The density inhomogeneity method with recommended equation predicted 89% of variance and mean bias of 14.9% (-4.3 to 34.2) with systematic over-estimation of porosity in more porous specimens. The density inhomogeneity method with optimized equation predicted 91% of variance without bias (0.0%, -5.3 to 5.2).

CONCLUSION

HR-pQCT imaged porosity assessed with the density inhomogeneity method with optimized equation indicated the best agreement with SR-μCT derived porosity.

Reliability of HR-pQCT Derived Cortical Bone Structural Parameters When Using Uncorrected Instead of Corrected Automatically Generated Endocortical Contours in a Cross-Sectional Study: The Maastricht Study

Most HR-pQCT studies examining cortical bone use an automatically generated endocortical contour (AUTO), which is manually corrected if it visually deviates from the apparent endocortical margin (semi-automatic method, S-AUTO). This technique may be prone to operator-related variability and is time consuming. We examined whether the AUTO instead of the S-AUTO method can be used for cortical bone analysis. Fifty scans of the distal radius and tibia from participants of The Maastricht Study were evaluated with AUTO, and subsequently with S-AUTO by three independent operators. AUTO cortical bone parameters were compared to the average parameters obtained by the three operators (S-AUTOmean). All differences in mean cortical bone parameters between AUTO and S-AUTOmean were < 5%, except for lower AUTO cortical porosity of the radius (- 16%) and tibia (- 6%), and cortical pore volume (Ct.Po.V) of the radius (- 7%). The ICC of S-AUTOmean and AUTO was > 0.90 for all parameters, except for cortical pore diameter of the radius (0.79) and tibia (0.74) and Ct.Po.V of the tibia (0.89), without systematic errors on the Bland-Altman plots. The precision errors (RMS-CV%) of the radius parameters between S-AUTOmean and AUTO were comparable to those between the individual operators, whereas the tibia RMS-CV% between S-AUTOmean and AUTO were higher than those of the individual operators. Comparison of the three operators revealed clear inter-operator variability. This study suggests that the AUTO method can be used for cortical bone analysis in a cross-sectional study, but that the absolute values-particularly of the porosity-related parameters-will be lower.

Precision of Second-Generation High-Resolution Peripheral Quantitative Computed Tomography: Intra- and Intertester Reproducibilities and Factors Involved in the Reproducibility of Cortical Porosity

High-resolution peripheral quantitative computed tomography (HR-pQCT) was upgraded to a second generation in 2014 with higher spatial resolution, faster scan time, and a different measurement algorithm. The purpose of this study was to investigate the precision of the second-generation HR-pQCT. The distal radius and tibia of 15 healthy men and women (age range of 20-74 yr, 8 men and 7 women) were scanned by second-generation HR-pQCT, and their geometry, bone mineral density (BMD), and the microstructure of trabecular and cortical bones were evaluated. Scans and measurements were performed by tester 1 at baseline and at 1 and 4 wk to evaluate intratester reproducibility, and by testers 2 and 3 one time each to evaluate intertester reproducibility. Reproducibility was evaluated by root mean square percent coefficient of variance (RMS%CV). Factors involved in the reproducibility of cortical porosity (Ct.Po) were also investigated. The ranges of RMS%CV were 0.2%-2.5% for geometry, 0.6%-1.7% for BMD, 0.7%-2.4% for trabecular bone, and 1.1%-1.3% for cortical thickness, showing excellent reproducibility. The range of RMS%CV for Ct.Po was 11.0%-13.3%, relatively higher than those for the other parameters. There was no apparent difference between intra- and intertester reproducibilities. There was no clear correlation between the percent coefficient of variance of Ct.Po and the subjects' background characteristics, motion artifact, and cortical bone structure. The reproducibility of the second-generation HR-pQCT was excellent in geometry, BMD, trabecular bone, and cortical thickness, with no apparent difference between intra- and intertester reproducibilities. Compared with the first-generation HR-pQCT, the reproducibility of trabecular bone was improved. The reproducibility of Ct.Po was insufficient and needed to be improved, and factors that influence its reproducibility were not clear.

Micro-structural bone changes in early rheumatoid arthritis persist over 1-year despite use of disease modifying anti-rheumatic drug therapy

Background

We used High Resolution – peripheral Quantitative CT (HR-pQCT) imaging to examine peri-articular bone quality in early rheumatoid arthritis (RA) and explore whether bone quality improved over 12-months in individuals receiving care consistent with practice guidelines.

Methods

A 1-year longitudinal cohort study (Baseline and 12-months) evaluating individuals with early RA compared to age/sex-matched peers. Personal demographic and health and lifestyle information were collected for all. Whereas, active joint count (AJC₂₈), functional limitation, and RA medications were also collected for RA participants. HR-pQCT imaging analyses quantified bone density and microstructure in the Metacarpal Head (MH) and Ultra-Ultra-Distal (UUD) radius at baseline and 12-months. Analyses included a General Linear Modelling repeated measures analyses examined main effects for disease, time, and interaction on bone quality.

Results

Participants (n = 60, 30 RA/30 NRA); 80% female, mean age 53 (varying from 21 to 74 years). At baseline, RA participants were on average 7.7 months since diagnosis, presenting with few active joints (AJC₂₈: 30% none, remaining 70% Median 4 active joints) and minimal self-reported functional limitation (mHAQ-DI_0–3: 0.56). At baseline, 29 of 30 RA participants had received one or more non-biologic disease-modifying anti-rheumatic drugs (DMARD);13 in combination with glucocorticoid and 1 in combination with a biologic medication. One participant only received glucocorticoid medication. Four RA participants withdrew leaving 26 pairs (n = 52) at 12-months; 23 pairs (n = 46) with UUD and 22 pairs (n = 44) with MH baseline and 12-month images to compare. Notable RA/NRA differences (p < 0.05) in bone quality at all three sites included lower trabecular bone density and volume, more rod-like trabeculae, and larger and more variable spaces between trabeculae; fewer trabeculae at the UUD and MH2 sites; and lower cortical bone density and volume in the MH sites. Rate of change over 12-months did not differ between RA/NRA participants which meant there was also no improvement over the year in RA bone quality.

Conclusions

Early changes in peri-articular bone density and microstructure seen in RA are consistent with changes more commonly seen in aging bone and are slow or resistant to recover despite well controlled inflammatory joint symptoms with early DMARD therapy.

Electronic supplementary material

The online version of this article (10.1186/s12891-017-1888-3) contains supplementary material, which is available to authorized users.

Precision of bone density and micro-architectural properties at the distal radius and tibia in children: an HR-pQCT study

Precision errors need to be known when monitoring bone micro-architecture in children with HR-pQCT. Precision errors for trabecular bone micro-architecture ranged from 1 to 8% when using the standard evaluation at the radius and tibia. Precision errors for cortical bone micro-architecture ranged from 1 to 11% when using the advanced cortical evaluation.

INTRODUCTION

Our objective was to define HR-pQCT precision errors (CV%_RMS) and least significant changes (LSCs) at the distal radius and tibia in children using the standard evaluation and the advanced cortical evaluation.

METHODS

We scanned the distal radius (7% of ulnar length) and tibia (8% of tibia length) of 32 children (age range 8-13; mean age 11.3; SD 1.6 years) twice (1 week apart) using HR-pQCT (XtremeCT1). We calculated root-mean-squared coefficients of variation (CV%_RMS) to define precision errors and LSC to identify differences required to detect change.

RESULTS

Precision errors ranged between 1-8 and 1-5% for trabecular bone outcomes (obtained with standard evaluation) and between 1.5-11 and 0.5-6% for cortical bone outcomes (obtained with advanced cortical evaluation) at the distal radius and tibia, respectively. Related LSCs ranged between 3-21 and 3-14% for trabecular bone outcomes and between 4-30 and 2-16% for cortical bone outcomes at the distal radius and tibia, respectively.

CONCLUSIONS

HR-pQCT precision errors were between 1 and 8% (LSC 3-21%) for trabecular bone outcomes and 1 and 11% (LSC 2-30%) for cortical bone outcomes at the radius and tibia in children. Cortical bone outcomes obtained using the advanced cortical evaluation appeared to have lower precision errors than cortical outcomes derived using the standard evaluation. These findings, combined with better-defined cortical bone contours with advanced cortical evaluation, indicate that metrics from advanced cortical evaluation should be utilized when monitoring cortical bone properties in children.

Cortical Bone Porosity: What Is It, Why Is It Important, and How Can We Detect It?

There is growing recognition of the role of micro-architecture in osteoporotic bone loss and fragility. This trend has been driven by advances in imaging technology, which have enabled a transition from measures of mass to micro-architecture. Imaging trabecular bone has been a key research focus, but advances in resolution have also enabled the detection of cortical bone micro-architecture, particularly the network of vascular canals, commonly referred to as 'cortical porosity.' This review aims to provide an overview of what this level of porosity is, why it is important, and how it can be characterized by imaging. Moving beyond a 'trabeculocentric' view of bone loss holds the potential to improve diagnosis and monitoring of interventions. Furthermore, cortical porosity is intimately linked to the remodeling process, which underpins bone loss, and thus a larger potential exists to improve our fundamental understanding of bone health through imaging of both humans and animal models.

In vivo precision of three HR-pQCT-derived finite element models of the distal radius and tibia in postmenopausal women

Background

The distal radius is the most common osteoporotic fracture site occurring in postmenopausal women. Finite element (FE) modeling is a non-invasive mathematical technique that can estimate bone strength using inputted geometry/micro-architecture and tissue material properties from computed tomographic images. Our first objective was to define and compare in vivo precision errors for three high-resolution peripheral quantitative computed tomography (HR-pQCT, XtremeCT; Scanco) based FE models of the distal radius and tibia in postmenopausal women. Our second objective was to assess the role of scan interval, scan quality, and common region on precision errors of outcomes for each FE model.

Methods

Models included: single-tissue model (STM), cortical-trabecular dual-tissue model (DTM), and one scaled model using imaged bone mineral density (E-BMD). Using HR-pQCT, we scanned the distal radius and tibia of 34 postmenopausal women (74 ± 7 years), at two time points. Primary outcomes included: tissue stiffness, apparent modulus, average von Mises stress, and failure load. Precision errors (root-mean-squared coefficient of variation, CV%_RMS) were calculated. Multivariate ANOVA was used to compare the mean of individual CV% among the 3 HR-pQCT-based FE models. Spearman correlations were used to characterize the associations between precision errors of all FE model outcomes and scan/time interval, scan quality, and common region. Significance was accepted at P < 0.05.

Results

At the distal radius, CV%_RMS precision errors were <9 % (Range STM: 2.8–5.3 %; DTM: 2.9–5.4 %; E-BMD: 4.4–8.7 %). At the distal tibia, CV%_RMS precision errors were <6 % (Range STM: 2.7–4.8 %; DTM: 2.9–3.8 %; E-BMD: 1.8–2.5 %). At the radius, Spearman correlations indicated associations between the common region and associated precision errors of the E-BMD-derived apparent modulus (ρ = −0.392; P < 0.001) and von Mises stress (ρ = −0.297; P = 0.007).

Conclusion

Results suggest that the STM and DTM are more precise for modeling apparent modulus, average von Mises stress, and failure load at the distal radius. Precision errors were comparable for all three models at the distal tibia. Results indicate that the noted differences in precision error at the distal radius were associated with the common scan region, illustrating the importance of participant repositioning within the cast and reference line placement in the scout view during the scanning process.