The impact of technical conditions of X-ray imaging on reproducibility and precision of digital computer-assisted X-ray radiogrammetry (DXR)

Objective To evaluate the reproducibility of imaging and analysis for bone mineral density (BMD) determination using digital computer-assisted X-ray radiogrammetry (DXR; Pronosco X-posure, version V.2, Sectra Pronosco, Denmark); to verify potential factors that influence BMD extrapolation such as tube voltage, film-focus distance (FFD), film quality and brand (Kodak T-MAT-Plus, Konika SRH, Agfa Scopix), imaging technology (conventional, digital), imaging system (Kodak, Agfa) and exposure level (mAs); and to clarify whether DXR analysis based on printouts of digital images is comparable to analysis of conventional images.Design and patients The hand of a cadaver was X-rayed using varied parameters: 4–8 mAs, 40–52 kV, 90–130 cm FFD. Radiographs under standardised conditions were performed 10 times using a conventional machine (Philips Super 80 CP) and the printouts of a digital system (Digital Diagnost Philips Optimus) for the analysis of reproducibility. One image was scanned and analysed 10 times additionally for imaging reproducibility.Results Reliability error of the system for the imaging process using conventional radiographs-rays was 0.49% (standard conditions: 6 mAs, 40 kV, 1 m FFD), using printouts of digital images was 2.89% (4 mAs, 42 kV, 1 m FFD) and regarding the analysis process was 0.22%. BMD calculation is not affected by alterations in FFD (precision error 1.21%), mAs (0.83%) or film quality/brand (0.38%), but differs significantly depending on tube voltage (2.70%). The system was not able to analyse conventional images with tube voltages of 49/52 kV.Conclusion DXR technology is stable with most of the tested parameters. Normative data should exclusively be used for calculations using similar tube voltage or correction factors. All other parameters had no significant influence on the BMD calculation. Reproducibility is high. For technical reasons it is not recommended to use the printouts of digital images for BMD determination.     

Comparative In vitro evaluation of two different preparations of small diameter polyurethane vascular grafts

Polyurethane (PU) frequently has been used to manufacture small diameter vascular grafts due to its good bicompatibility. In this study, sponge PU small diameter vascular grafts were fabricated from Pellethane 2103, as well as a self-synthesized PU, by utilization of a salt casting technique and by varying the salt/polymer ratios. Two types were made; one of them had a thin solid layer on the outer surface. The inner surface was identical and was coated with gelatin crosslinked by epoxide. Tensile properties, compliance, platelet activation, and endothelial cell attachment were evaluated in vitro. It was found that for the grafts with an outer nonporous coating, compliance could not be estimated from modulus due to anisotropy. The most compliance-matched grafts were made of self-synthesized polyurethane with a salt/polymer ratio 4 to 8 or Pellethane with a ratio 6 to 8 without the outer nonporous coating. The former had better elongation. Self-synthesized PU had lower platelet adhesion as well as more endothelial attachment than Pellethane. Porosity activated platelets strongly and reduced endothelial adhesion unless the surface was modified by the crosslinked gelatin layer. It was concluded that PU synthesized in our lab with a salt/polymer ratio of at least 4 and coated with epoxy crosslinked gelatin was a better substrate for preparation of small diameter vascular grafts.     

Alternative blood conduits: assessment of whether the porosity of synthetic prostheses is the key to long-term biofunctionality

The paper examines the effects of water permeability on solid particle (platelet) adhesion and lipid transport through the wall of a blood conduit. Also tested is the capacity of external supports to reduce lipid infiltration into venous grafts. The results indicate that water permeability not only facilitates particle adhesion, but also affects the spatial distribution of the adhesion. The presence of filtration flow leads to a concentration polarisation of atherogenic lipids at the blood/wall interface, with increased lipid concentration from the bulk value towards the interface, thus enhancing the drive potential for lipid infiltration into the vessel wall. An external support to a venous graft guards against excessive distention and significantly reduces lipid infiltration into the venous wall. These results strongly suggest that too high a water permeability or porosity can lead to the late failure of arterial grafting by affecting blood cell interaction with the graft and lipid infiltration into the wall. Therefore the pore structure of an arterial prosthesis is crucial to its long-term biofunctionality. Ideally, a synthetic prosthesis should display pores of adequate size and a structural network that promotes tissue ingrowth, while maintaining water porosity at a physiological level.     

Fracture Toughness of Acrylic PMMA Bone Cement: A Mini-Review

BackgroundAcrylic PMMA bone cement is an essential component in cemented implants and formed the cement-bone and cement-implant interfaces. The information on the fracture parameters of PMMA bone cement would be decisive for all doctors, researchers, and orthopaedic surgeons.PurposeThis review aims to indicate the parameters responsible for the variation in the fracture toughness of PMMA bone cement. This mini-review also points out some limitations of the earlier published research article, which can be added in the future analysis and can be helpful to get the more realistic data of the fracture parameters of PMMA bone cement.ConclusionDifferent mixing techniques, storage medium, temperature, loading conditions, frequency and environment, cement viscosity, type of specimen, and the ASTM standards (shape, size, and geometry), constituents, loading rate, and cement porosity were the critical parameters to affect the fracture toughness of PMMA bone cement. This study will also be helpful to increase the structural integrity of PMMA bone cement and the cemented implant.     

仿生矿化对PLGA支架材料孔隙率及生物力学性能的影响

目的通过聚乳酸-羟基乙酸(polylactide-co-glycolide,PLGA)的仿生矿化,对材料表面改性,检测矿化物组成,评价矿化对多孔材料孔隙率和生物力学性能的影响。方法PLGA经水解处理后在模拟体液(simulatedbodyfluid,SBF)中仿生矿化,应用扫描电镜、X射线衍射仪和红外光谱仪行矿化物形貌物相分析,比重法测量矿化前后材料孔隙率的变化,津岛生物力学测试仪测试材料矿化前后抗压强度的变化。结果PLGA在SBF中矿化后,表面可以形成明显的矿化层;矿化物主要成分为磷灰石,含有碳酸根成分,类似于人骨无机质。仿生矿化前后多孔PLGA孔隙率及生物力学性能无明显改变(P>0.05)。结论仿生矿化对三维多孔PLGA支架材料的孔隙表征和生物力学性能无影响,是表面改性的可行方法。     

The Mechanical Properties of Infrainguinal Vascular Bypass Grafts: Their Role in Influencing Patency

When autologous vein is unavailable, prosthetic graft materials, particularly expanded polytetrafluoroethylene are used for peripheral arterial revascularisation. Poor long term patency of prosthetic materials is due to distal anastomotic intimal hyperplasia. Intimal hyperplasia is directly linked to shear stress abnormalities at the vessel wall. Compliance and calibre mismatch between native vessel and graft, as well as anastomotic line stress concentration contribute towards unnatural wall shear stress. High porosity reduces graft compliance by causing fibrovascular infiltration, whereas low porosity discourages the development of an endothelial lining and hence effective antithrombogenicity. Therefore, consideration of mechanical properties is necessary in graft development. Current research into synthetic vascular grafts concentrates on simulating the mechanical properties of native arteries and tissue engineering aims to construct a new biological arterial conduit.     

Effect of process parameters on the characteristics of porous calcium phosphate ceramics for bone tissue scaffolds

Porous hydroxyapatite (HA) has already been widely used as a bone substitute due to its similarity with the mineral part of the bone. In this work, cylindrical tablets with micro and macro porosity were produced from stoichiometric and deficient hydroxyapatites by using naphthalene as porosifier agent. The influence of the processing parameters such as Ca/P ratio of start material, calcination temperature, and naphthalene content on the characteristics of porous calcium phosphate tablets was evaluated. Three mineral phases-HA, alpha-TCP (alpha tri-calcium phosphate), and beta-TCP (beta tricalcium phos-phate)-with variable contents were identified by x-ray diffraction (XRD) and Fourier-transformed infrared spectroscopy (FT-IR). Image analysis and density measurements were used to characterize sample porosity. As expected, the total porosity of the calcinated material is not dependent on the stoichiometry of the precursor hydroxyapatite. For calcium-deficient hydroxyapatite, the increase in naphthalene content contributes to stabilize alpha-TCP phase, altering the relative phases content.     

Spatial distribution of anisotropic acoustic impedance assessed by time-resolved 50-MHz scanning acoustic microscopy and its relation to porosity in human cortical bone

We used quantitative scanning acoustic microscopy (SAM) to assess tissue acoustic impedance and microstructure of cortical bone of human radii with the aim to provide data on regional distribution of acoustic impedance along the circumferential and across the radial directions in the entire cross-section of the radius diaphysis as well as to determine the range of impedance values in transverse (perpendicular to bone axis) and longitudinal (parallel to bone axis) cross-sections. Several microstructural features related to cortical porosity were analyzed in order to determine whether these features differ in different parts of the cortex and to assess the relationship between the microstructure and tissue acoustic impedance. Fifteen fresh bone specimens (human radius) were investigated using a SAM (center frequency of 50 MHz and -6 dB lateral resolution of approximately 23 microm). The sample acoustic impedance was obtained by means of a calibration curve correlating the reflected signal amplitude of reference materials with their corresponding well-known acoustic impedance. Tissue acoustic impedance and microstructural features were derived from the morphometric analysis of the segmented impedance images. A higher porosity was found in the inner cortical layer (mean+/-SD=8.9+/-2.3%) compared to the peripheral layer (2.7+/-1.5%) (paired t-test, p<10(-5)). ANOVA showed that most of the variance can be explained by the regional effect across the radial direction with a minor contribution due to between-sample variability. Similar to porosity, the number and diameter of pores were greater in the inner layer. In contrast to porosity, ANOVA showed that impedance variability can mostly be explained by between-specimen variability. Two-way ANOVA revealed that after compensation for the between-sample variability the variation in acoustic impedance across the radial direction was much larger than that along the circumferential direction. In addition to the significant difference between the inner cortical layer (8.25+/-0.4 Mrayl) and peripheral layer (8.0+/-0.5 Mrayl) (unilateral paired t-test, p<10(-4)), the values in the anterior region (8.2+/-0.5 Mrayl) were found to be significantly higher than those of the posterior region (7.9+/-0.6 Mrayl). Impedance mean value of longitudinal sections was lower than mean value measured in transverse cross-sections, resulting in an impedance acoustic anisotropy ratio of 1.17+/-0.03 in the inner cortical layer and 1.19+/-0.02 in the peripheral layer. SAM is a valuable tool to provide data on the spatial distribution of microstructural and microelastic bone properties that is useful to improve our understanding of the impact of bone microstructure on tissue material properties.     

Ex vivo lung sonography: morphologic-ultrasound relationship

Ultrasound (US) interstitial syndrome is a sonographic lung pattern characterized by the presence of acoustic artifacts (B-lines and white lung). The purpose of this study was to demonstrate how interstitial syndrome is determined by acoustic interactions in lungs of variable density and in healthy organs deflated to a nonphysiologic level of density. Normal rabbit lungs were studied ex vivo by US at varying known degrees of inflation, and their histologic appearances were described. In this experimental setting, US interstitial syndrome recognizes a mechanism related to tissue density or porosity. Artifacts (B-lines and white lung) appear in the normal rabbit lung through air-dependent increases in density. As in pathologic conditions, US interstitial syndrome can be reproduced in histologically normal lungs that are deflated to a critical level (>0.45 g/mL) of density, which is not achievable under physiologic conditions.     

Towards an acoustic model-based poroelastic imaging method: I. Theoretical foundation

The ultrasonic measurement and imaging of tissue elasticity is currently under wide investigation and development as a clinical tool for the assessment of a broad range of diseases, but little account in this field has yet been taken of the fact that soft tissue is porous and contains mobile fluid. The ability to squeeze fluid out of tissue may have implications for conventional elasticity imaging, and may present opportunities for new investigative tools. When a homogeneous, isotropic, fluid-saturated poroelastic material with a linearly elastic solid phase and incompressible solid and fluid constituents is subjected to stress, the behaviour of the induced internal strain field is influenced by three material constants: the Young's modulus (E(s)) and Poisson's ratio (nu(s)) of the solid matrix and the permeability (k) of the solid matrix to the pore fluid. New analytical expressions were derived and used to model the time-dependent behaviour of the strain field inside simulated homogeneous cylindrical samples of such a poroelastic material undergoing sustained unconfined compression. A model-based reconstruction technique was developed to produce images of parameters related to the poroelastic material constants (E(s), nu(s), k) from a comparison of the measured and predicted time-dependent spatially varying radial strain. Tests of the method using simulated noisy strain data showed that it is capable of producing three unique parametric images: an image of the Poisson's ratio of the solid matrix, an image of the axial strain (which was not time-dependent subsequent to the application of the compression) and an image representing the product of the aggregate modulus E(s)(1-nu(s))/(1+nu(s))(1-2nu(s)) of the solid matrix and the permeability of the solid matrix to the pore fluid. The analytical expressions were further used to numerically validate a finite element model and to clarify previous work on poroelastography.