215 research outputs found
Characterization of a reproducible model of fracture healing in mice using an open femoral osteotomy
Purpose:
The classic fracture model, described by Bonnarens and Einhorn in 1984, enlists a blunt guillotine to generate a closed fracture in a pre-stabilized rodent femur. However, in less experienced hands, this technique yields considerable variability in fracture pattern and requires highly-specialized equipment. This study describes a reproducible and low-cost model of mouse fracture healing using an open femoral osteotomy.
Methods:
Femur fractures were produced in skeletally mature male and female mice using an open femoral osteotomy after intramedullary stabilization. Mice were recovered for up to 28 days prior to analysis with microradiographs, histomorphometry, a novel μCT methodology, and biomechanical torsion testing at weekly intervals.
Results:
Eight mice were excluded due to complications (8/193, 4.1%), including unacceptable fracture pattern (2/193, 1.0%). Microradiographs showed progression of the fracture site to mineralized callus by 14 days and remodelling 28 days after surgery. Histomorphometry from 14 to 28 days revealed decreased cartilage area and maintained bone area. μCT analysis demonstrated a reduction in mineral surface from 14 to 28 days, stable mineral volume, decreased strut number, and increased strut thickness. Torsion testing at 21 days showed that fractured femurs had 61% of the ultimate torque, 63% of the stiffness, and similar twist to failure when compared to unfractured contralateral femurs.
Conclusions:
The fracture model described herein, an open femoral osteotomy, demonstrated healing comparable to that reported using closed techniques. This simple model could be used in future research with improved reliability and reduced costs compared to the current options
Novel Moessbauer experiment in a rotating system and the extra-energy shift between emission and absorption lines
We present the results of a novel Mossbauer experiment in a rotating system,
implemented recently in Istanbul University, which yields the coefficient
k=0.69+/-0.02 within the frame of the expression for the relative energy shift
between emission and absorption lines dE/E=ku2/c2. This result turned out to be
in a quantitative agreement with an experiment achieved earlier on the subject
matter (A.L. Kholmetskii et al. 2009 Phys. Scr. 79 065007), and once again
strongly pointed to the inequality k>0.5, revealed originally in (A.L.
Kholmetskii et al. 2008 Phys. Scr. 77, 035302 (2008)) via the re-analysis of
Kundig experiment (W. Kundig. Phys. Rev. 129, 2371 (1963)). A possible
explanation of the deviation of the coefficient k from the relativistic
prediction k=0.5 is discussed.Comment: 21 pages, 8 figures, 3 table
Mineral maturity and crystallinity index are distinct characteristics of bone mineral
The purpose of this study was to test the hypothesis that mineral maturity and crystallinity index are two different characteristics of bone mineral. To this end, Fourier transform infrared microspectroscopy (FTIRM) was used. To test our hypothesis, synthetic apatites and human bone samples were used for the validation of the two parameters using FTIRM. Iliac crest samples from seven human controls and two with skeletal fluorosis were analyzed at the bone structural unit (BSU) level by FTIRM on sections 2–4 lm thick. Mineral maturity and crystallinity index were highly correlated in synthetic apatites but poorly correlated in normal human bone. In skeletal fluorosis, crystallinity index was increased and maturity decreased, supporting the fact of separate measurement of these two parameters. Moreover, results obtained in fluorosis suggested that mineral characteristics can be modified independently of bone remodeling. In conclusion, mineral maturity and crystallinity index are two different parameters measured separately by FTIRM and offering new perspectives to assess bone mineral traits in osteoporosis
Nonlinear Markov Random Fields Learned via Backpropagation
Although convolutional neural networks (CNNs) currently dominate competitions
on image segmentation, for neuroimaging analysis tasks, more classical
generative approaches based on mixture models are still used in practice to
parcellate brains. To bridge the gap between the two, in this paper we propose
a marriage between a probabilistic generative model, which has been shown to be
robust to variability among magnetic resonance (MR) images acquired via
different imaging protocols, and a CNN. The link is in the prior distribution
over the unknown tissue classes, which are classically modelled using a Markov
random field. In this work we model the interactions among neighbouring pixels
by a type of recurrent CNN, which can encode more complex spatial interactions.
We validate our proposed model on publicly available MR data, from different
centres, and show that it generalises across imaging protocols. This result
demonstrates a successful and principled inclusion of a CNN in a generative
model, which in turn could be adapted by any probabilistic generative approach
for image segmentation.Comment: Accepted for the international conference on Information Processing
in Medical Imaging (IPMI) 2019, camera ready versio
Partial Volume Segmentation of Brain MRI Scans of any Resolution and Contrast
Partial voluming (PV) is arguably the last crucial unsolved problem in
Bayesian segmentation of brain MRI with probabilistic atlases. PV occurs when
voxels contain multiple tissue classes, giving rise to image intensities that
may not be representative of any one of the underlying classes. PV is
particularly problematic for segmentation when there is a large resolution gap
between the atlas and the test scan, e.g., when segmenting clinical scans with
thick slices, or when using a high-resolution atlas. In this work, we present
PV-SynthSeg, a convolutional neural network (CNN) that tackles this problem by
directly learning a mapping between (possibly multi-modal) low resolution (LR)
scans and underlying high resolution (HR) segmentations. PV-SynthSeg simulates
LR images from HR label maps with a generative model of PV, and can be trained
to segment scans of any desired target contrast and resolution, even for
previously unseen modalities where neither images nor segmentations are
available at training. PV-SynthSeg does not require any preprocessing, and runs
in seconds. We demonstrate the accuracy and flexibility of the method with
extensive experiments on three datasets and 2,680 scans. The code is available
at https://github.com/BBillot/SynthSeg.Comment: accepted for MICCAI 202
High-spin States in \u3csup\u3e191, 193\u3c/sup\u3eAu and \u3csup\u3e192\u3c/sup\u3ePt: Evidence for Oblate Deformation and Triaxial Shapes
High-spin states of 191, 193Au and 192Pt have been populated in the 186W(11B, xn) and 186W(11B, p4n) reactions, respectively, at a beam energy of 68 MeV and their γ decay was studied using the YRAST Ball detector array at the Wright Nuclear Structure Laboratory at Yale University. The level scheme of 193Au has been extended up to Iπ = 55/2+. New transitions were observed also in 191Au and 192Pt. Particle-plus-Triaxial-Rotor (PTR) and Total Routhian Surface (TRS) calculations were performed to determine the equilibrium deformations of the Au isotopes. The predictions for oblate deformations in these nuclei are in agreement with the experimental data. Development of nonaxial shapes is discussed within the framework of the PTR model
Triaxial Deformation and Nuclear Shape Transition in \u3csup\u3e192\u3c/sup\u3eAu
Background: Nuclei in the A≈190 mass region show gradual shape changes from prolate through nonaxial deformed shapes and ultimately towards spherical shapes as the Pb region is approached. Exploring how this shape evolution occurs will help us understand the evolution of collectivity in this region.
Purpose: The level scheme of the 192Au nucleus in A ≈ 190 region was studied in order to deduce its deformations.
Methods: High-spin states of 192Au have been populated in the 186W(11B, 5n) reaction at a beam energy of 68 MeV and their γ decay was studied using the YRAST Ball detector array at the Wright Nuclear Structure Laboratory (WNSL), Yale University.
Results: Based on double and triple γ-ray coincidence data the level scheme of 192Au has been extended up to Iπ = 32+ at an excitation energy of ∼6 MeV.
Conclusion: The results are discussed in the framework of pairing and deformation self-consistent total Routhian surface (TRS) and cranked shell model (CSM) calculations. The comparison of the experimental observations with the calculations indicates that this nucleus takes a nonaxial shape similar to other Au nuclei in this region
Determination of composition and structure of spongy bone tissue in human head of femur by Raman spectral mapping
Biomechanical properties of bone depend on the composition and organization of collagen fibers. In this study, Raman microspectroscopy was employed to determine the content of mineral and organic constituents and orientation of collagen fibers in spongy bone in the human head of femur at the microstructural level. Changes in composition and structure of trabecula were illustrated using Raman spectral mapping. The polarized Raman spectra permit separate analysis of local variations in orientation and composition. The ratios of ν2PO43−/Amide III, ν4PO43−/Amide III and ν1CO32−/ν2PO43− are used to describe relative amounts of spongy bone components. The ν1PO43−/Amide I ratio is quite susceptible to orientation effect and brings information on collagen fibers orientation. The results presented illustrate the versatility of the Raman method in the study of bone tissue. The study permits better understanding of bone physiology and evaluation of the biomechanical properties of bone
Mechanical model for a collagen fibril pair in extracellular matrix
In this paper, we model the mechanics of a collagen pair in the connective
tissue extracellular matrix that exists in abundance throughout animals,
including the human body. This connective tissue comprises repeated units of
two main structures, namely collagens as well as axial, parallel and regular
anionic glycosaminoglycan between collagens. The collagen fibril can be modeled
by Hooke's law whereas anionic glycosaminoglycan behaves more like a
rubber-band rod and as such can be better modeled by the worm-like chain model.
While both computer simulations and continuum mechanics models have been
investigated the behavior of this connective tissue typically, authors either
assume a simple form of the molecular potential energy or entirely ignore the
microscopic structure of the connective tissue. Here, we apply basic physical
methodologies and simple applied mathematical modeling techniques to describe
the collagen pair quantitatively. We find that the growth of fibrils is
intimately related to the maximum length of the anionic glycosaminoglycan and
the relative displacement of two adjacent fibrils, which in return is closely
related to the effectiveness of anionic glycosaminoglycan in transmitting
forces between fibrils. These reveal the importance of the anionic
glycosaminoglycan in maintaining the structural shape of the connective tissue
extracellular matrix and eventually the shape modulus of human tissues. We also
find that some macroscopic properties, like the maximum molecular energy and
the breaking fraction of the collagen, are also related to the microscopic
characteristics of the anionic glycosaminoglycan
A novel underuse model shows that inactivity but not ovariectomy determines the deteriorated material properties and geometry of cortical bone in the tibia of adult rats
Our goal in this study was to determine to what extent the physiologic consequences of ovariectomy (OVX) in bones are exacerbated by a lack of daily activity such as walking. We forced 14-week-old female rats to be inactive for 15 weeks with a unique experimental system that prevents standing and walking while allowing other movements. Tibiae, femora, and 4th lumbar vertebrae were analyzed by peripheral quantitative computed tomography (pQCT), microfocused X-ray computed tomography (micro-CT), histology, histomorphometry, Raman spectroscopy, and the three-point bending test. Contrary to our expectation, the exacerbation was very much limited to the cancellous bone parameters. Parameters of femur and tibia cortical bone were affected by the forced inactivity but not by OVX: (1) cross-sectional moment of inertia was significantly smaller in Sham-Inactive rat bones than that of their walking counterparts; (2) the number of sclerostin-positive osteocytes per unit cross-sectional area was larger in Sham-Inactive rat bones than in Sham-Walking rat bones; and (3) material properties such as ultimate stress of inactive rat tibia was lower than that of their walking counterparts. Of note, the additive effect of inactivity and OVX was seen only in a few parameters, such as the cancellous bone mineral density of the lumbar vertebrae and the structural parameters of cancellous bone in the lumbar vertebrae/tibiae. It is concluded that the lack of daily activity is detrimental to the strength and quality of cortical bone in the femur and tibia of rats, while lack of estrogen is not. Our inactive rat model, with the older rats, will aid the study of postmenopausal osteoporosis, the etiology of which may be both hormonal and mechanical
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