56 research outputs found
Iterative and discrete reconstruction in the evaluation of the rabbit model of osteoarthritis
Micro-computed tomography (”CT) is a standard method for bone morphometric evaluation. However, the scan time can be long and the radiation dose during the scan may have adverse effects on test subjects, therefore both of them should be minimized. This could be achieved by applying iterative reconstruction (IR) on sparse projection data, as IR is capable of producing reconstructions of sufficient image quality with less projection data than the traditional algorithm requires. In this work, the performance of three IR algorithms was assessed for quantitative bone imaging from low-resolution data in the evaluation of the rabbit model of osteoarthritis. Subchondral bone images were reconstructed with a conjugate gradient least squares algorithm, a total variation regularization scheme, and a discrete algebraic reconstruction technique to obtain quantitative bone morphometry, and the results obtained in this manner were compared with those obtained from the reference reconstruction. Our approaches were sufficient to identify changes in bone structure in early osteoarthritis, and these changes were preserved even when minimal data were provided for the reconstruction. Thus, our results suggest that IR algorithms give reliable performance with sparse projection data, thereby recommending them for use in ”CT studies where time and radiation exposure are preferably minimized. © 2018, The Author(s).Peer reviewe
Validity of self-reported exposure to shift work
OBJECTIVE: To evaluate the validity of widely used questionnaire items on work schedule using objective registry data as reference.
METHOD: A cohort study of hospital employees who responded to a self-administered questionnaire on work schedule in 2008, 2012 and 2014 and were linked to individual-level pay-roll-based records on work shifts. For predictive validity, leisure-time fatigue was assessed.
RESULTS: According to the survey data in 2014 (n=8896), 55% of the day workers had at least 1â
year of earlier shift work experience. 8% of the night shift workers changed to day work during the follow-up. Using pay-roll data as reference, questions on âshift work with night shiftsâ and âpermanent night workâ showed high sensitivity (96% and 90%) and specificity (92% and 97%). Self-reported âregular day workâ showed moderate sensitivity (73%), but high specificity (99%) and âshift work without night shiftsâ showed low sensitivity (62%) and moderate specificity (87%). In multivariate logistic regression analysis, the age-adjusted, sex-adjusted and baseline fatigue-adjusted association between âshift work without night shiftsâ and leisure-time fatigue was lower for self-reported compared with objective assessment (1.30, 95% CI 0.94 to 1.82, n=1707 vs 1.89, 95% CI 1.06 to 3.39, n=1627). In contrast, shift work with night shifts, compared with permanent day work, was similarly associated with fatigue in the two assessments (2.04, 95% CI 1.62 to 2.57, n=2311 vs 1.82, 95% CI 1.28 to 2.58, n=1804).
CONCLUSIONS: The validity of self-reported assessment of shift work varies between work schedules. Exposure misclassification in self-reported data may contribute to bias towards the null in shift work without night shifts
Determining collagen distribution in articular cartilage using contrast-enhanced micro-computed tomography
Objective: Collagen distribution within articular cartilage (AC) is typically evaluated from histological sections, e.g., using collagen staining and light microscopy (LM). Unfortunately, all techniques based on histological sections are time-consuming, destructive, and without extraordinary effort, limited to two dimensions. This study investigates whether phosphotungstic acid (PTA) and phosphomolybdic acid (PMA), two collagen-specific markers and X-ray absorbers, could (1) produce contrast for AC X-ray imaging or (2) be used to detect collagen distribution within AC. Method: We labeled equine AC samples with PTA or PMA and imaged them with micro-computed tomography (micro-CT) at pre-defined time points 0, 18, 36, 54, 72, 90, 180, 270 h during staining. The micro-CT image intensity was compared with collagen distributions obtained with a reference technique, i.e., Fourier-transform infrared imaging (FTIRI). The labeling time and contrast agent producing highest association (Pearson correlation, BlandeAltman analysis) between FTIRI collagen distribution and micro-CT -determined PTA distribution was selected for human AC. Results: Both, PTA and PMA labeling permitted visualization of AC features using micro-CT in non-calcified cartilage. After labeling the samples for 36 h in PTA, the spatial distribution of X-ray attenuation correlated highly with the collagen distribution determined by FTIRI in both equine (mean +/- S.D. of the Pearson correlation coefficients, r = 0.96 +/- 0.03, n = 12) and human AC (r = 0.82 +/- 0.15, n = 4). Conclusions: PTA-induced X-ray attenuation is a potential marker for non-destructive detection of AC collagen distributions in 3D. This approach opens new possibilities in development of non-destructive 3D histopathological techniques for characterization of OA. (C) 2015 The Authors. Published by Elsevier Ltd and Osteoarthritis Research Society International.Peer reviewe
3D morphometric analysis of calcified cartilage properties using micro-computed tomography
Objective: Our aim is to establish methods for quantifying morphometric properties of calcified cartilage (CC) from micro-computed tomography (mu CT). Furthermore, we evaluated the feasibility of these methods in investigating relationships between osteoarthritis (OA), tidemark surface morphology and open subchondral channels (OSCCs). Method: Samples (n = 15) used in this study were harvested from human lateral tibial plateau (n = 8). Conventional roughness and parameters assessing local 3-dimensional (3D) surface variations were used to quantify the surface morphology of the CC. Subchondral channel properties (percentage, density, size) were also calculated. As a reference, histological sections were evaluated using Histopathological osteoarthritis grading (OARSI) and thickness of CC and subchondral bone (SCB) was quantified. Results: OARSI grade correlated with a decrease in local 3D variations of the tidemark surface (amount of different surface patterns (r(s) = -0.600, P = 0.018), entropy of patterns (EP) (r(s) = -0.648, P = 0.018), homogeneity index (HI) (r(s) = 0.555, P = 0.032)) and tidemark roughness (TMR) (r(s) = -0.579, P = 0.024). Amount of different patterns (ADP) and EP associated with channel area fraction (CAF) (r(p) = 0.876, P <0.0001; r(p) = 0.665, P = 0.007, respectively) and channel density (CD) (r(p) = 0.680, P = 0.011; r(p) = 0.582, P = 0.023, respectively). TMR was associated with CAF (r(p) = 0.926, P <0.0001) and average channel size (r(p) = 0.574, P = 0.025). CC topography differed statistically significantly in early OA vs healthy samples. Conclusion: We introduced a mu-CT image method to quantify 3D CC topography and perforations through CC. CC topography was associated with OARSI grade and OSCC properties; this suggests that the established methods can detect topographical changes in tidemark and CC perforations associated with OA. (c) 2018 The Authors. Published by Elsevier Ltd on behalf of Osteoarthritis Research Society International. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).Peer reviewe
Effects of Articular Cartilage Constituents on Phosphotungstic Acid Enhanced Micro-Computed Tomography
Contrast-enhanced micro-computed tomography (CE mu CT) with phosphotungstic acid (PTA) has shown potential for detecting collagen distribution of articular cartilage. However, the selectivity of the PTA staining to articular cartilage constituents remains to be elucidated. The aim of this study was to investigate the dependence of PTA for the collagen content in bovine articular cartilage. Adjacent bovine articular cartilage samples were treated with chondroitinase ABC and collagenase to degrade the proteoglycan and the collagen constituents in articular cartilage, respectively. Enzymatically degraded samples were compared to the untreated samples using CE mu CT and reference methods, such as Fourier-transform infrared imaging. Decrease in the X-ray attenuation of PTA in articular cartilage and collagen content was observed in cartilage depth of 0-13% and deeper in tissue after collagen degradation. Increase in the X-ray attenuation of PTA was observed in the cartilage depth of 13- 39% after proteoglycan degradation. The X-ray attenuation of PTA-labelled articular cartilage in CE mu CT is associated mainly with collagen content but the proteoglycans have a minor effect on the X-ray attenuation of the PTA-labelled articular cartilage. In conclusion, the PTA labeling provides a feasible CE mu CT method for 3D characterization of articular cartilage.Peer reviewe
Quantification of osteochondral tissue modifications during osteoarthritis using micro-computed tomography
Abstract
Osteoarthritis (OA) is a heterogenic joint disease significantly affecting the quality of life of a patient, causing pain and disability. OA causes degenerative changes to the structure and composition of articular cartilage and subchondral bone. Currently, effective treatments for OA are limited, partly due to limitations in defining the imaging biomarkers of early OA. Improvement of imaging modalities in OA research and clinical setup is a requirement for quantitating early OA-related tissue features. In the clinical and preclinical setup, computed tomography (CT) enables imaging of bone and, using specific contrast agents, articular cartilage. The aim of this study is to create and validate novel micro-computed tomography (μCT) methods to quantify OA-related features and modifications in articular cartilage and subchondral bone.
Contrast-enhanced μCT methods for imaging the collagen (phosphotungstic acid (PTA) and phosphomolybdic acid (PMA)) and GAG (CA4+) content of the articular cartilage in vitro were validated against various reference methods measuring the biochemical composition of articular cartilage. To improve the μCT imaging of subchondral bone, grey-level co-occurrence matrix (GLCM) based analysis of sub-resolution features of subchondral bone was introduced. In addition, to test the translatability of the GLCM-based analysis to clinical resolution, sub-resolution features extracted from clinical cone-beam CT were validated against the subchondral bone morphometrics from the μCT.
PTA showed stronger association with the collagen content of the articular cartilage compared to PMA. PTA was also associated with collagen content even in degraded articular cartilage. CA4+ distribution was found to accumulate in chondrons and surrounding areas, suggesting that it is a prominent contrast agent for high-resolution μCT studies of chondrocytes. The GLCM-based analysis of subchondral bone provided information on cellular structure from μCT images and trabecular bone micro-structures from clinical CT images.
In conclusion, μCT imaging can provide quantitative information on the collagen content and chondrons of articular cartilage, as well as on osteocytes in subchondral bone. The methods presented here extend the tools for researchers to quantify osteochondral tissue modifications in OA. Furthermore, the developed image processing tools could be translatable to the clinical CT.TiivistelmĂ€
Nivelrikko on heterogeeninen niveltauti, joka huonontaa yksilön elĂ€mĂ€n laatua aiheuttaen kipua ja liikuntakyvyttömyyttĂ€. Nivelrikko aiheuttaa nivelkudosten rappeumaa vaikuttaen mm. ruston ja rustonalaisen luun rakenteeseen ja koostumukseen. Nivelrikon kudosmuutosten kuvantamisen kehittĂ€minen ja mÀÀrĂ€llinen tutkiminen taudin alkuvaiheissa tukisivat nykyisten nivelrikon hoitomenetelmien kehittĂ€mistĂ€. KliinisessĂ€ kĂ€ytössĂ€ ja perustutkimuksessa, tietokonetomografia (TT) mahdollistaa luukuvantamisen ja varjoaineita kĂ€ytettĂ€essĂ€ myös rustokuvantamisen. TĂ€mĂ€n vĂ€itöskirjan tavoitteena on esitellĂ€ ja validoida uusia mikrotietokonetomografia-menetelmiĂ€ (μTT) nivelrikon rusto- ja luumuutosten mÀÀrĂ€lliseen tutkimukseen.
Varjoaineavusteisia μTT in vitro menetelmiĂ€ ruston kollageenin (fosfovolframihappoa (PTA) ja fosfomolybdeenihappoa (PMA)) ja GAG (CA4+) jakauman mÀÀrĂ€lliseen tutkimukseen validoitiin useilla eri ruston biokemiallista koostumusta mittaavilla vertailumenetelmillĂ€. Rustonalaisen luun kuvantamista kehitettiin soveltamalla harmaasĂ€vyjen tekstuurianalyysiĂ€, jolla pyrittiin tunnistamaan kuva-alkiota pienempiĂ€ luurakenteita. Rustonalaisen luun μTT-kuvien analyysien tulokset validoitiin synkrotronisĂ€teilyyn perustuvan μTT:n avulla. LisĂ€ksi tekstuurianalyysin soveltuvuutta testattiin kliinisen resoluution kartiokeilan TT-kuville. Kuvista analysoituja tekstuuriparametrejĂ€ verrattiin μTT:lla mitattuun todelliseen rustonalaisen luun rakenteeseen.
VĂ€itöskirjan tulokset osoittavat, ettĂ€ PTA on spesifimpi kollageenille testatuista varjoaineista ja sen jakauma on verrannollinen kollageenijakaumaan jopa rappeutuneessa nivelrustossa. GAG-spesifisen varjoaineen CA4+:n todettiin kerÀÀntyvĂ€n myös kondroneihin, mikĂ€ viittaa siihen, ettĂ€ kyseinen varjoaine soveltuisi potentiaalisesti rustosolujen korkean resoluution μTT-tutkimuksiin. Rustonalaisen luun μTT-kuvista analysoitujen tekstuuriparametrien havaittiin olevan verrannollisia osteosyyttien tilavuusfraktion kanssa.
VĂ€itöskirjassa esitettyjen tulosten perusteella μTT-kuvantaminen tarjoaa kvantitatiivisen menetelmĂ€n nivelruston kollageenijakauman ja rustosolujen sekĂ€ rustonalaisen luun osteosyyttien tutkimuksiin. VĂ€itöskirjassa esitetyt menetelmĂ€t laajentavat jo olemassa olevaa tutkimusmenetelmien kirjoa nivelrikon aiheuttamien nivelrusto- ja luumuutosten tutkimuksessa. LisĂ€ksi kehitetyt kuva-analyysimenetelmĂ€t voivat tarjota tarkempaa tietoa kliinisestĂ€ TT:sta
An investigation of a hypocycloid mechanism based twin-rotor piston engine
A unique mechanism is investigated in this paper to show the working principles of a novel hypocycloid twin-rotor piston engine (HTRPE), which provides the basis for the structural design, kinematic and dynamical analysis necessary to realize the engine. As a critical system for the HTRPE, the differential velocity mechanism is examined first by decomposing it into two non-uniform motion mechanisms and one hypocycloid mechanism, which allows an evaluation of different options of design parameters. Then analytical expressions are derived to calculate the rotor angular velocities and the relative angular velocities of pairs of rotors for a detailed performance analysis. Based on the results of this analysis a prototype HTRPE is proposed and benchmarked with both a conventional reciprocating and a Wankel engine. It is shown that the new engine outperforms the other two engines in key engine features including combustion gas force transmission, volumetric change of working chambers, power frequency, piston velocity and displacement, demonstrating that HTRPE is very promising as a more energy efficient engine due to its high compactness and power density, and consequently lightweight design
Cellulose nanofiber aerogels impregnated with bio-based epoxy using vacuum infusion:structure, orientation and mechanical properties
Abstract
Cellulose nanofiber aerogels were used as preforms that were impregnated with a bio-epoxy resin via a widely used vacuum infusion process. The simple and straightforward nanocomposite processing approach resulted in an almost 70% improvement in the storage modulus of the polymer with only an 11.7 wt% cellulose nanofiber content. The nanofibers were well dispersed in the polymer matrix and the fiber structures were anisotropically aligned. The impregnation time of the aerogels was also significantly lower than that of the more commonly used nanopapers. It was thus shown that environmentally friendly and mechanically robust nanocomposites could be produced by impregnating cellulose nanofiber aerogels with a thermosetting resin using a processing approach that has potential to be scaled up for commercial use
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