Abstract Motion artifacts are a common finding during high-resolution peripheral quantitative computed tomography (HR-pQCT) image acquisitions. To date it is not clear (i) when to repeat an ...acquisition, (ii) when to exclude a motion-degraded dataset post hoc, and (iii) how motion induced artifacts impact measures of trabecular and cortical parameters. In this study we present inter- and intra-observer reproducibility of a qualitative image quality grading score and report the prevalence of repeat acquisitions in our population. Finally the errors in bone density and micro-architectural parameters estimated from repeat acquisitions with and without motion degradation are presented. The relationship between these errors and the image quality grade is evaluated for each parameter. Repeat acquisitions performed due to operator-observed motion in the reconstructed image occurred for 22.7% of the exams (29.7% radius, 15.7% tibia). Of this subset, 88 exams with repeat acquisitions had at least one acquisition graded 1 (best quality). In this subset, the percent differences in bone density and micro-architecture measures tended to increase as the relative image quality decreased. Micro-architectural parameters were more sensitive to motion compared to geometric and densitometric parameters. These results provide estimates of the error in bone quality measures due to motion artifacts and provide an initial framework for developing standardized quality control criteria for cross-sectional and longitudinal HR-pQCT studies.
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.
Summary
We investigated the sensitivity of distal bone density, structure, and strength measurements by high-resolution peripheral quantitative computed tomography (HR-pQCT) to variability in limb ...length. Our results demonstrate that HR-pQCT should be performed at a standard %-of-total-limb-length to avoid substantial measurement bias in population study comparisons and the evaluation of individual skeletal status in a clinical context.
Introduction
High-resolution peripheral quantitative computed tomography (HR-pQCT) measures of bone do not account for anatomic variability in bone length: a 1-cm volume is acquired at a fixed offset from an anatomic landmark. Our goal was to evaluate HR-pQCT measurement variability introduced by imaging fixed vs. proportional volumes and to propose a standard protocol for relative anatomic positioning.
Methods
Double-length (2-cm) scans were acquired in 30 adults. We compared measurements from 1-cm sub-volumes located at the default fixed offset, and the average %-of-length offset. The average position corresponded to 4.0% ± 1.1 mm for radius, and 7.2% ± 2.2 mm for tibia. We calculated the RMS difference in bone parameters and T-scores to determine the measurement variability related to differences in limb length. We used anthropometric ratios to estimate the mean limb length for published HR-pQCT reference data, and then calculated mean %-of-length offsets.
Results
Variability between fixed vs. relative scan positions was highest in the radius, and for cortical bone in general (RMS difference Ct.Th = 19.5%), while individuals had T-score differentials as high as +3.0 SD (radius Ct.BMD). We estimated that average scan position for published HR-pQCT reference data corresponded to 4.0% at the radius, and 7.3% at tibia.
Conclusion
Variability in limb length introduces significant bias to HR-pQCT measures, confounding cross-sectional analyses and limiting the clinical application for individual assessment of skeletal status. We propose to standardize scan positioning using 4.0 and 7.3% of total bone length for the distal radius and tibia, respectively.
Summary
Dairy protein but not plant protein was associated with bone strength of the radius and tibia in older men. These results are consistent with previous results in women and support similar ...findings related to fracture outcomes. Bone strength differences were largely due to thickness and area of the bone cortex.
Introduction
Our objective was to determine the association of protein intake by source (dairy, non-dairy animal, plant) with bone strength and bone microarchitecture among older men.
Methods
We used data from 1016 men (mean 84.3 years) who attended the Year 14 exam of the Osteoporotic Fractures in Men (MrOS) study, completed a food frequency questionnaire (500–5000 kcal/day), were not taking androgen or androgen agonists, and had high-resolution peripheral quantitative computed tomography (HR-pQCT) scans of the distal radius and distal or diaphyseal tibia. Protein was expressed as percentage of total energy intake (TEI); mean ± SD for TEI = 1548 ± 607 kcal/day and for total protein = 16.2 ± 2.9%TEI. We used linear regression with standardized HR-pQCT parameters as dependent variables and adjusted for age, limb length, center, education, race/ethnicity, marital status, smoking, alcohol intake, physical activity level, corticosteroids use, supplement use (calcium and vitamin D), and osteoporosis medications.
Results
Higher dairy protein intake was associated with higher estimated failure load at the distal radius and distal tibia radius effect size = 0.17 (95% CI 0.07, 0.27), tibia effect size = 0.13 (95% CI 0.03, 0.23), while higher non-dairy animal protein was associated with higher failure load at only the distal radius. Plant protein intake was not associated with failure load at any site.
Conclusion
The association between protein intake and bone strength varied by source of protein. These results support a link between dairy protein intake and skeletal health, but an intervention study is needed to evaluate causality.
Summary
In this study, we determined that operator positioning precision contributes significant measurement error in high-resolution peripheral quantitative computed tomography (HR-pQCT). Moreover, ...we developed software to quantify intra- and inter-operator variability and demonstrated that standard positioning training (now available as a web-based application) can significantly reduce inter-operator variability.
Introduction
HR-pQCT is increasingly used to assess bone quality, fracture risk, and anti-fracture interventions. The contribution of the operator has not been adequately accounted in measurement precision. Operators acquire a 2D projection (“scout view image”) and define the region to be scanned by positioning a “reference line” on a standard anatomical landmark. In this study, we (i) evaluated the contribution of positioning variability to in vivo measurement precision, (ii) measured intra- and inter-operator positioning variability, and (iii) tested if custom training software led to superior reproducibility in new operators compared to experienced operators.
Methods
To evaluate the operator in vivo measurement precision, we compared precision errors calculated in 64 co-registered and non-co-registered scan-rescan images. To quantify operator variability, we developed software that simulates the positioning process of the scanner’s software. Eight experienced operators positioned reference lines on scout view images designed to test intra- and inter-operator reproducibility. Finally, we developed modules for training and evaluation of reference line positioning. We enrolled six new operators to participate in a common training, followed by the same reproducibility experiments performed by the experienced group.
Results
In vivo precision errors were up to threefold greater (Tt.BMD and Ct.Th) when variability in scan positioning was included. The inter-operator precision errors were significantly greater than the short-term intra-operator precision (
p
< 0.001). New trained operators achieved comparable intra-operator reproducibility to experienced operators and lower inter-operator reproducibility (
p
< 0.001). Precision errors were significantly greater for the radius than for the tibia.
Conclusion
Operator reference line positioning contributes significantly to in vivo measurement precision and is significantly greater for multi-operator datasets. Inter-operator variability can be significantly reduced using a systematic training platform, now available online (
http://webapps.radiology.ucsf.edu/refline/
).
Understanding mechanisms controlling fluid injection-triggered seismicity is key in defining strategies to ameliorate it. Recent triggered events (e.g. Pohang, Mw 5.5) have exceeded predictions of ...average energy release by a factor of >1000x, necessitating robust methodologies to both define critical antecedent conditions and to thereby constrain anticipated event size. We define maximum event magnitudes resulting from triggering as a function of pre-existing critical stresses and fluid injection volume. Fluid injection experiments on prestressed laboratory faults confirm these estimates of triggered moment magnitudes for varied boundary conditions and injection rates. In addition, observed ratios of shear slip to dilation rates on individual faults signal triggering and may serve as a measurable proxy for impending rupture. This new framework provides a robust method of constraining maximum event size for preloaded faults and unifies prior laboratory and field observations that span sixteen decades in injection volume and four decades in length scale.
Ab initio second-order algebraic diagrammatic construction (ADC(2)) calculations using the resolution of the identity (RI) method have been performed on poly-(p-phenylenevinylene) (PPV) oligomers ...with chain lengths up to eight phenyl rings. Vertical excitation energies for the four lowest π–π* excitations and geometry relaxation effects for the lowest excited state (S1) are reported. Extrapolation to infinite chain length shows good agreement with analogous data derived from experiment. Analysis of the bond length alternation (BLA) based on the optimized S1 geometry provides conclusive evidence for the localization of the defect in the center of the oligomer chain. Torsional potentials have been computed for the four excited states investigated and the transition densities divided into fragment contributions have been used to identify excitonic interactions. The present investigation provides benchmark results, which can be used (i) as reference for lower level methods and (ii) give the possibility to parametrize an effective Frenkel exciton Hamiltonian for quantum dynamical simulations of ultrafast exciton transfer dynamics in PPV type systems.
Summary
We investigated the characteristics and spatial distribution of cortical bone pores in postmenopausal women with type 2 diabetes (T2D). High porosity in the midcortical and periosteal layers ...in T2D subjects with fragility fractures suggests that these cortical zones might be particularly susceptible to T2D-induced toxicity and may reflect cortical microangiopathy.
Introduction
Elevated cortical porosity is regarded as one of the main contributors to the high skeletal fragility in T2D. However, to date, it remains unclear if diabetic cortical porosity results from vascular cortical changes or from an expansion in bone marrow space. Here, we used a novel cortical laminar analysis technique to investigate the characteristics and spatial radial distribution of cortical pores in a T2D group with prior history of fragility fractures (DMFx, assigned high-risk group) and a fracture-free T2D group (DM, assigned low-risk group) and to compare their results to non-diabetic controls with (Fx) and without fragility fractures (Co).
Methods
Eighty postmenopausal women (
n
= 20/group) underwent high-resolution peripheral quantitative computed tomography (HR-pQCT) of the distal tibia and radius. Cortical bone was divided into three layers of equal width including an endosteal, midcortical, and periosteal layer. Within each layer, total pore area (TPA), total pore number (TPN), and average pore area (APA) were calculated. Statistical analysis employed Mann-Whitney tests and ANOVA with post hoc tests.
Results
Compared to the DM group, DMFx subjects exhibited +90 to +365 % elevated global porosity (
p
= 0.001). Cortical laminar analysis revealed that this increased porosity was for both skeletal sites confined to the midcortical layer, followed by the periosteal layer (midcortical +1327 % TPA,
p
≤ 0.001, periosteal +634 % TPA,
p
= 0.002), and was associated in both layers and skeletal sites with high TPN (+430 % TPN,
p
< 0.001) and high APA (+71.5 % APA,
p
< 0.001).
Conclusion
High porosity in the midcortical and periosteal layers in the high-risk T2D group suggests that these cortical zones might be particularly susceptible to T2D-induced toxicity and may reflect cortical microangiopathy.
The production of cloned animals is, at present, an inefficient process. This study focused on the fetal losses that occur
between Days 30â90 of gestation. Fetal and placental characteristics were ...studied from Days 30â90 of gestation using transrectal
ultrasonography, maternal pregnancy specific protein b (PSPb) levels, and postslaughter collection of fetal tissue. Pregnancy
rates at Day 30 were similar for recipient cows carrying nuclear transfer (NT) and control embryos (45% 54/120 vs. 58% 11/19),
although multiple NT embryos were often transferred into recipients. From Days 30â90, 82% of NT fetuses died, whereas all
control pregnancies remained viable. Crown-rump (CR) length was less in those fetuses that were destined to die before Day
90, but no significant difference was found between the CR lengths of NT and control fetuses that survived to Day 90. Maternal
PSPb levels at Days 30 and 50 of gestation were not predictive of fetal survival to Day 90. The placentas of six cloned and
four control (in vivo or in vitro fertilized) bovine pregnancies were compared between Days 35 and 60 of gestation. Two cloned
placentas showed rudimentary development, as indicated by flat, cuboidal trophoblastic epithelium and reduced vascularization,
whereas two others possessed a reduced number of barely discernable cotyledonary areas. The remaining two cloned placentas
were similar to the controls, although one contained hemorrhagic cotyledons. Poor viability of cloned fetuses during Days
35â60 was associated with either rudimentary or marginal chorioallantoic development. Our findings suggest that future research
should focus on factors that promote placental and vascular growth and on fetomaternal interactions that promote placental
attachment and villous formation.
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