Post-processed Images Research Articles

Early detection of small volume stroke and thromboembolic sources with computed tomography: Rationale and design of the ENCLOSE study.

BackgroundComputed tomography is the most frequently used imaging modality in acute stroke imaging protocols. Detection of small volume infarcts in the brain and cardioembolic sources of stroke is difficult with current computed tomography protocols. Furthermore, the role of computed tomography findings to predict recurrent ischemic stroke is unclear. With ENCLOSE, we aim to improve (1) the detection of small volume infarcts with thin slice computed tomography perfusion (CTP) images and thromboembolic source with cardiac computed tomography techniques in the acute stage of ischemic stroke and (2) prediction of recurrent ischemic stroke with computed tomography-derived predictors.Methods/design: ENCLOSE is a prospective multicenter observational cohort study, which will be conducted in three Dutch stroke centers (ClinicalTrials.gov Identifier: NCT04019483). Patients (≥18 years) with suspected acute ischemic stroke who undergo computed tomography imaging within 9 h after symptom onset are eligible. Computed tomography imaging includes non-contrast CT, CTP, and computed tomography angiography (CTA) from base of the heart to the top of the brain. Dual-energy CT data will be acquired when possible, and thin-slice CTP reconstructions will be obtained in addition to standard 5 mm CTP data. CTP data will be processed with commercially available software and locally developed model-based methods. The post-processed thin-slice CTP images will be compared to the standard CTP images and to magnetic resonance diffusion-weighted imaging performed within 48 h after admission. Detection of cardioembolic sources of stroke will be evaluated on the CTA images. Recurrence will be evaluated 90 days and two years after the index event. The added value of imaging findings to prognostic models for recurrent ischemic stroke will be evaluated.ConclusionThe aim of ENCLOSE is to improve early detection of small volume stroke and thromboembolic sources and to improve prediction of recurrence in patients with acute ischemic stroke.

Optimisation of the Half-Skip Total Focusing Method (HSTFM) parameters for sizing surface-breaking cracks

The Half-Skip Total Focusing Method (HSTFM) is an ultrasonic array post-processing (imaging) technique. The method allows surface-breaking cracks (SBCs) to be imaged and also sized using 6 dB drop rule. The HSTFM has previously been used to size SBCs initiating from flat and horizontal walls. However, there has been limited research to optimise the method in a rigours manner and quantitatively determine the performance of the HSTFM to size cracks accurately. In this paper, the SBCs characterization capability of the HSTFM was tested and applied on both numerically simulated and experimentally generated data. Under numerical simulation, considering the travel time of ultrasonic signals as per the ray theory, first, a mathematical framework was developed for the HSTFM imaging algorithm. Then, a quantitative parametric study, using the finite element method and point reflector model, was performed to evaluate the sizing capability of the HSTFM under different scenarios. These scenarios include the position of the ultrasonic array relative to the crack, the accuracy of the acoustic velocity, the height of the sample, the slope of the back wall, and the tilting angle of the defect. For each of the array configuration, the crack-sizing range (the smallest and largest Through Wall Extent (TWE) of a crack) that can be measured using the HSTFM was calculated. Thereafter, experimental validation was performed, where an excellent match with the numerical results was observed.

Detection and Condition Assessment of Icicle Bridging for Suspension Glass Insulator by Image Analysis

Icicles generated on the insulator sheds will constantly shorten the insulating gap distance between adjacent sheds as growth, thereby inducing significant decrease in electrical insulation of the insulators, icicle bridging even threatening the operating security of power systems. In order to evaluate whether the ice-covered insulator needs to deicing or the icicles bring in potential dangers, a study on detection and condition assessment of icicle bridging for ice-covered suspension glass insulator by image analysis is proposed in this article. First, the initial icicles regions are obtained by the local variation threshold segmentation algorithm based on the optimized texture energy image. Second, the insulator sheds are segmented and extracted based on the normalized color difference operator, and then the complete icicles regions are obtained through the image difference and postprocessing. Finally, the icicle length is calculated by finding its smallest axis-parallel enclosing rectangle, and two adjacent insulator sheds spacing which is calculated by ellipse fitting is used as bridging threshold, so the condition of icicle bridging can be defined as the safe, observation, and danger. The results demonstrate that the icicles can be effectively enhanced and accurately segmented by the presented method in this article, and the icicle bridging condition of ice-covered insulator can be assessed with average detection accuracy of 92.2% and average time consumption of 3.910 s, by which the safe operation of ice-covered insulator can be monitored and guaranteed.

Preoperative Planning for the Foot and Ankle: A Technique Tip

Category:Other; Ankle; Midfoot/ForefootIntroduction/Purpose:Computed tomography (CT) advanced imaging techniques are a valuable tool for orthopedic surgeons when evaluating complex foot and ankle pathology. With advances in CT data processing, surgeons can create custom reformation of the imaging data in real time using postprocessing imaging tools. This article presents a technique describing how to manipulate CT data using two of these tools, multiplanar reformation (MPR) and maximal intensity projection (MIP), to better visualize pathology and allow a more definitive diagnosis preoperatively. Despite their availability on most modern picture archiving and communication systems, most surgeons across orthopaedics disciplines fail to utilize these powerful tools.Methods:Patients with complex midfoot deformities underwent CT scans for diagnosis and preoperative planning. Case 1 underwent percutaneous pinning of multiple metatarsal fractures. Post-operatively she had severe pain localized to the second and third metatarsals. A CT scan obtained in standard axes failed to interpret the multiplanar deformities when viewed initially on PACS. Using MPR/MIP, the axes were rotated to generate a detailed view of the deformities and subsequently template osteotomies. Case two underwent arthrodesis of the second and third tarsometatarsal (TMT) joints for an unstable Lisfranc injury. Post-operatively she presented with severe midfoot pain prohibiting her return to athletics. Radiographs demonstrated normal alignment with hardware obscuring the joints. Standard CT axes were difficult to interpret due to metal artifact and oblique planes of the TMT joints. MPR/MIP reformatting allowed metal artifact reduction through axes adjustment, improving visualization and facilitating diagnosis of nonunion of the second and third TMT fusions.Results:Case One:MIP/MPR allowed manipulation of the CT scan in the axial and coronal planes provided a sagittal reformat of the entire second and third metatarsals. The second metatarsal had a gradual plantarflexion malunion of the diaphysis. The third metatarsal had an acute plantarflexed deformity of the metatarsal neck. Reformatting provided an accurate preoperative template for planned dorsiflexion osteotomies. Case Two: Metal artifact and the oblique orientation of the TMT joints prevented evaluation of previous fusions. MIP/MPR reformatting provided axes which were perpendicular to the TMT joints decreased metal artifact and demonstrated nonunion of the previous fusions. Use of MIP/MPR in this case provided valuable diagnostic information regarding the source of pain and a plan for removal of hardware and revision TMT fusions.Conclusion:The MPR/MIP function is available in most PACS systems and allows customizable CT reformats. The technique is easy to learn and can be done quickly in the office or pre-operative setting. The technology has facilitated streamlined pre- operative planning and improvements in injury visualization numerous times, particularly in complex deformities and trauma. Using MIP/MPR reformats, the authors have been able to identify critical fracture lines and relationships between anatomic structures which may otherwise have been missed or less precisely understood. The authors hope that this article will enhance awareness and encourage others to utilize this powerful technology.

Two-dimensional iterative projection method for subsample speckle tracking of ultrasound images.

Speckle tracking provides robust motion estimation necessary to create accurate post-processed images. These methods are known to be less accurate in the lateral dimension compared with the axial dimension due to the limitations on the lateral resolution of ultrasound scanning. This paper proposes a two-dimensional iterative projection (TDIP) algorithm using the Riesz transform to generate the analytic signals. The TDIP is an improvement to an already accurate speckle tracking algorithm called the phase coupled (PC) method. The PC method projects the intersection of gradients on the correlation map to the zero phase contour to estimate displacement. The TDIP method performs iterative projections and uses the aggregate of these projected locations to estimate the motion, in addition to rejecting inaccurate projections by checking them against the aggregate projection location. The TDIP additionally adopts the Riesz transform to generate two-dimensional analytic signals to improve lateral accuracy. The Riesz transform is a multidimensional extension of the Hilbert transform into the nD Euclidean space and therefore can be used to include data in both axial and lateral dimensions as opposed to the commonly used Hilbert transform which is one dimensional. The accuracy of the TDIP is quantitatively proven on simulated datasets from the Field II simulation program and on experimental data from two flow phantoms. At all cases, the TDIP is more accurate than the PC algorithm at two-dimensional displacement estimation. Graphical Abstract The lateral estimates from the Phase Coupled algorithm. This method uses the Hilbert transform for the analytic signal. There is large estimated motion within the flow blockage bounded by the red, fin shape in the center of the flow channel. The flow channel itself is also bounded by dashed, red lines. Graphical Abstract The lateral estimates from the TDIP method. This method is not tracking motion within the blockage in the center of the flow channel. The channel and the blockage are both bounded by dashed, red lines.

Simultaneous Diffusion and T1 Weighted Contrast Imaging for Human Brain Mapping

Introduction: Diffusion tensor imaging (DTI) is conventionally performed using echo planar imaging (EPI) for human brain mapping. However, EPI suffers from susceptibility distortion, requiring elaborate image post processing. Besides, DTI alone is limited in assessing gray and white matter boundaries of the brain, which is important for accurately imaging brain atrophy. The goal of this study was to design and evaluate simultaneous diffusion and T1 weighting high resolution imaging for human brain mapping. Materials and Methods: Three dimensional Magnetization-prepared rapid gradient-echo (3D MPRAGE) with T1 weighting, which is generally the method of choice for mapping gray and white matter structures in the brain, was extended to incorporate diffusion encoding using simulation and experiment to develop high resolution DTI and T1-weighted human brain data. Results: It is shown that the incorporation of DTI contrast (i.e. fractional anisotropy (FA) and mean diffusivity (MD)) into T1 weighted 3D MPRAGE using simulations as well as experimental results from in-vivo human brain studies at 4 Tesla magnetic field strength improves the contrast between gray and white matter sub-structural boundaries. Moreover, incorporating diffusion encoding into 3D MPRAGE avoids the inherent image distortions typically seen in EPI based DTI.Conclusion: This study suggests DTI weighted 3D MPRAGE combined with T1w is feasible for human brain imaging and expected to benefit improved assessment of gray/white matter boundaries.

Enhancement of low-spatial-frequency components by a new phase-contrast STEM using a probe formed with an amplitude Fresnel zone plate

Electron microscopy is a powerful tool for visualizing the shapes of sub-nanometer objects. However, Contrast Transfer Function (CTF) principally restricts lower frequency components in the image. To overcome this problem, phase-plate techniques have been proposed and currently Hole Free Phase Plate (HFPP) and Volta Phase Plate (VPP) are widely used especially for biological specimens to retrieve low frequency information of the sample’s potential distributions. In this report, we have developed a new phase-contrast scanning transmission electron microscope (STEM) in which a probe beam including side robes is formed with an amplitude Fresnel zone plate (FZP) and the interference patterns produced by the zero and first order diffracted waves generated by the FZP are detected. We name it FZP Phase Contrast STEM (FZP-PC-STEM) hereinafter. The amplitude FZP was manufactured by using focused ion beam (FIB) equipment, and the diffraction data were collected by using diffraction imaging technique. The validity of our proposed optical model was confirmed by comparing experimental and simulated images. Observations of carbon nanotube (CNT) bundles by using this method showed that the contrast of low-spatial-frequency components in the CNT image was significantly enhanced. This method does not, in principle, require the post-image processing used in the diffraction imaging method, and it can be easily introduced into pre-existing equipment without major modifications. The stability and robustness of the FZP inserted in condenser system were also confirmed during long-time operation. We expect that the FZP-PC-STEM will be widely applicable to high-contrast observations of low-Z samples with simple and easy operation.

3D characterisation using plasma FIB-SEM: A large-area tomography technique for complex surfaces like black silicon

This paper demonstrates an improved method to accurately extract the surface morphology of black silicon (BSi). The method is based on an automated Xe+ plasma focused ion beam (PFIB) and scanning electron microscope (SEM) tomography technique. A comprehensive new sample preparation method is described and shown to minimize the PFIB artifacts induced by both the top surface sample-PFIB interaction and the non-uniform material density. An optimized post-image processing procedure is also described that ensures the accuracy of the reconstructed 3D surface model. The application of these new methods is demonstrated by applying them to extract the surface topography of BSi formed by reactive ion etching (RIE) consisting of 2 µm tall needles. An area of 320 µm2 is investigated with a controlled slice thickness of 10 nm. The reconstructed 3D model allows the extraction of critical roughness characteristics, such as height distribution, correlation length, and surface enhancement ratio. Furthermore, it is demonstrated that the particular surface studied contains regions in which under-etching has resulted in overhanging structures, which would not have been identified with other surface topography techniques. Such overhanging structures can be present in a broad range of BSi surfaces, including BSi surfaces formed by RIE and metal catalyst chemical etching (MCCE). Without proper measurement, the un-detected overhangs would result in the underestimation of many critical surface characteristics, such as absolute surface area, electrochemical reactivity and light-trapping.

Choriocapillaris flow deficit associated with intraretinal hyperreflective foci in intermediate age-related macular degeneration.

To evaluate the choriocapillaris (CC) flow deficit (FD) beneath drusen associated with overlying intraretinal hyperreflective foci (HRF). Patients with intermediate age-related macular degeneration (AMD) who had structural spectral-domain optical coherence tomography (SD-OCT) and OCT angiography (OCTA) using the Cirrus HD-OCT with AngioPlex software were retrospectively evaluated. A 6 × 6-mm-volume scan was used for the SD-OCT and OCTA. Post-imaging processing steps included generation of drusen map, identification of HRF, and generation of a signal-compensated CC slab prior to binarization and CC FD computation. The CC OCTA image was aligned with the drusen + HRF map to define regions of interest for CC FD measurement. The CC was quantified below drusen with and without overlying HRF and within a 150-μm-wide ring surrounding the drusen (unaffected by potential HRF-related shadowing), and across the entire 6 × 6 macular region. Fifty-three eyes with intermediate AMD were included, 25 eyes with HRF, and 28 eyes with no HRF. The mean ± SD FD% over the whole 6 × 6 macular region was 41.1 ± 3.4 in eyes with HRF compared with 39.5 ± 3.5 in eyes without HRF (p = 0.001). The mean ± SD CC FD% below drusen with HRF (54.4 ± 9.3) was significantly greater than below drusen without HRF (49.6 ± 9.5; p = 0.001). There was a strong positive correlation between the quantity of HRF and the extent of the CC FD (Pearson correlation = 0.81). Choriocapillaris flow deficits appear to be more severe in eyes with HRF and in particular directly below HRF. As HRF are thought to represent a higher risk or more advanced feature of intermediate AMD, these findings highlight the relationship between the severity of CC FD and overall severity of AMD.

Modulated radiation protocol achieves marked reduction of radiation exposure for chronic total coronary occlusion intervention.

To evaluate the feasibility of a new acquisition protocol to reduce radiation exposure. Percutaneous coronary interventions (PCI) for chronic total coronary occlusions (CTO) are characterized by the highest radiation exposure among PCI procedures. We analyzed 552 consecutive CTO procedures between January 2018 and October 2019. After 366 procedures (Group 1) a modified radiation acquisition protocol was implemented for the subsequent 186 procedures (Group 2). Besides a low fluoroscopy frame rate of 6/s and cine frame rate of 7.5/s for both groups, additional modifications consisted of increased copper filtering with lower entry dose in combination with a modified image postprocessing. Radiation exposure was assessed as air kerma (AK; mGy), and dose-area product (DAP; cGy*cm2 ). There was no significant difference in lesion or procedural complexity between the study groups with 46 and 43% of the procedures done via the retrograde approach. While fluoroscopy time remained similar (median: 32.7 vs. 34.3min), the protocol modifications resulted in a drastic reduction of AK by 68% from 2,040 (1,321-3,339) mGy to 655 (415-1,113) mGy (p < .001) without affecting the procedural success rate. DAP was equally decreased by 71%. These considerable reductions were observed even in obese patients of BMI > 30. In Group 2, not a single procedure exceeded the 5 Gy threshold as compared to 10.4% in Group 1. Radiation exposure decreased considerably with a new acquisition protocol without affecting procedure duration and success. These modifications were applicable also to patients with a high BMI.

Assessment of hessian-based Frangi vesselness filter in optoacoustic imaging

The Hessian-based Frangi vesselness filter is commonly used to enhance vasculature in optoacoustic (photoacoustic) images, but its accuracy and limitations have never been rigorously assessed. Here we validate the ability of the filter to enhance vessel-like structures in phantoms, and we introduce an experimental approach that uses measurements before and after the administration of gold nanorods (AuNRs) to examine filter performance in vivo. We evaluate the influence of contrast, filter scales, angular tomographic coverage, out-of-plane signals and light fluence on image quality, and gain insight into the performance of the filter. We observe the generation of artifactual structures that can be misinterpreted as vessels and provide recommendations to ensure appropriate use of Frangi and other vesselness filters and avoid misinterpretation of post-processed optoacoustic images.

Post-processing of face-on radiographic images for quantitative analysis in ablative Rayleigh-Taylor instability experiments

An experiment was performed at the National Ignition Facility investigating the ablative Rayleigh-Taylor instability’s dependence on initial conditions in the highly nonlinear stage. The detailed post-processing of the radiographic images which includes backlighter reconstruction, Wiener deconvolution of the raw data, and the calculation of a conversion factor from optical depth to physical units. The results of these calculations were fed into the primary analysis of the experimental data, with this manuscript serving as a supplemental reference to the primary paper [1].

Precision Digital Oncology: Emerging Role of Radiomics-based Biomarkers and Artificial Intelligence for Advanced Imaging and Characterization of Brain Tumors.

Advances in computerized image analysis and the use of artificial intelligence-based approaches for image-based analysis and construction of prediction algorithms represent a new era for noninvasive biomarker discovery. In recent literature, it has become apparent that radiologic images can serve as mineable databases that contain large amounts of quantitative features with potential clinical significance. Extraction and analysis of these quantitative features is commonly referred to as texture or radiomic analysis. Numerous studies have demonstrated applications for texture and radiomic characterization methods for assessing brain tumors to improve noninvasive predictions of tumor histologic characteristics, molecular profile, distinction of treatment-related changes, and prediction of patient survival. In this review, the current use and future potential of texture or radiomic-based approaches with machine learning for brain tumor image analysis and prediction algorithm construction will be discussed. This technology has the potential to advance the value of diagnostic imaging by extracting currently unused information on medical scans that enables more precise, personalized therapy; however, significant barriers must be overcome if this technology is to be successfully implemented on a wide scale for routine use in the clinical setting. Keywords: Adults and Pediatrics, Brain/Brain Stem, CNS, Computer Aided Diagnosis (CAD), Computer Applications-General (Informatics), Image Postprocessing, Informatics, Neural Networks, Neuro-Oncology, Oncology, Treatment Effects, Tumor Response Supplemental material is available for this article. © RSNA, 2020.

MRI Super-Resolution using Laplacian Pyramid Convolutional Neural Networks with Isotropic Undecimated Wavelet Loss.

High spatial resolution of Magnetic Resonance images (MRI) provide rich structural details to facilitate accurate diagnosis and quantitative image analysis. However the long acquisition time of MRI leads to patient discomfort and possible motion artifacts in the reconstructed image. Single Image Super-Resolution (SISR) using Convolutional Neural networks (CNN) is an emerging trend in biomedical imaging especially Magnetic Resonance (MR) image analysis for image post processing. An efficient choice of SISR architecture is required to achieve better quality reconstruction. In addition, a robust choice of loss function together with the domain in which these loss functions operate play an important role in enhancing the fine structural details as well as removing the blurring effects to form a high resolution image. In this work, we propose a novel combined loss function consisting of an L1 Charbonnier loss function in the image domain and a wavelet domain loss function called the Isotropic Undecimated Wavelet loss (IUW loss) to train the existing Laplacian Pyramid Super-Resolution CNN. The proposed loss function was evaluated on three MRI datasets - privately collected Knee MRI dataset and the publicly available Kirby21 brain and iSeg infant brain datasets and on benchmark SISR datasets for natural images. Experimental analysis shows promising results with better recovery of structure and improvements in qualitative metrics.

A Comprehensive Approach to Disentangle the Effect of Cerebellar Damage on Physical Disability in Multiple Sclerosis.

Cerebellar damage occurs frequently in multiple sclerosis (MS) patients, with a wide exhibition of symptoms particularly as impairments of balance and gait. Recent studies implementing new postprocessing magnetic resonance imaging (MRI) techniques showed how cerebellar subregional atrophy provides an explanation of disability in MS. The aim of this work was to evaluate the relationship between quantitative measures of physical disability, cerebellar subregional atrophy, and cerebellar peduncle disruption. Forty-nine MS patients and 32 healthy subjects as controls (HS) underwent a 3-Tesla MRI including 3D T1-weighted and diffusion tensor imaging. Patients underwent static posturography to calculate the body's center of pressure (COP) displacement, Expanded Disability Status Scale (EDSS), and 25-ft walking test (25-FWT). Cerebellar lobular volumes were automatically calculated using the Spatially Unbiased Infratentorial Toolbox. Tract-based spatial statistics (TBSS) in FSL was used to process diffusion tensor imaging (DTI) Fit-generated fractional anisotropy (FA) maps to assess structural connectivity of cerebellar peduncles. Stepwise multivariate linear regression analyses were used to explore relationships between variables. Cerebellar volumes (anterior and posterior, as well as lobular volumes from I to X) were significantly lower in patients with MS than HS (p < 0.05). FA in all cerebellar peduncles was lower in MS patients than in HS (p < 0.05). EDSS and 25-FWT showed an association with atrophy of lobule VIIIb (β = −0.37, p < 0.01, and β = −0.45, p < 0.001, respectively) COP measures inversely correlated with volume of lobules I–IV (β = −0.37, p < 0.01, and β = −0.36, p < 0.01). Lower FA in the three cerebellar peduncles of MS patients positively correlated with cerebellar lobular volumes. Our findings show how sensorimotor cerebellum atrophy and disruption of both afferent and efferent cerebellar connections contribute to physical disability in MS patients.

X-ray tomographic image post-processing and a new 2D LBM simulation for the determination of the porosity and the static airflow resistivity of an acoustic fibrous material

A set of X-ray tomographic images of a highly porous material composed of air-saturated coconut fibers is considered and used to estimate intrinsic characteristics of the material. Two physical properties are of interest: porosity and static airflow resistivity. For the porosity, two-dimensional gray-scale tomography images are obtained and post-processed to produce approximative black and white ones, unambiguously attributing distinct regions to fibers and air locations. The porosity is then directly deduced counting the black and white pixels. Several image processing algorithms are compared and associated porosities range from 0.76 to 0.97, depending on the method employed, while it is estimated to be 0.86 from our analysis. For the airflow resistivity, the idea followed here is to use the pattern of the post-processed images as the lattice in a Lattice Boltzmann Method (LBM) fluid dynamics computation. To our knowledge, the LBM has not been used in this context before. A new 2D implementation of the method is therefore developed and studied. After tuning computational parameters, we have estimated the airflow resistivity using ten images of our sample to be 1382±12Pa.s/m2. Both porosity and resistivity results are fully consistent with measurements obtained from a porosity-meter and a resistivity-meter, demonstrating the pertinence of X-ray tomography and the associated proposed methods.

Experimental Observation of Flow Reversal in Thin Liquid Film Flow Falling on an Inclined Plate

A customized particle image velocimetry/planar laser induced fluorescence (PIV/PLIF) experimental method, aiming to capture transient hydrodynamics of solitary waves of inertia-dominated falling liquid films, is presented in this paper. A novel PIV/PLIF technique, which only uses one camera to capture simultaneously both particle image and fluorescence, and meanwhile a post-processing imaging method is also developed, which is able to simultaneously measure both internal velocity field in film and its topology. To validate the fidelity of the novel PIV/PLIF technique, a comparison between experimental results of streamwise velocity profile and film thickness and that of the Nusselt’s prediction at low Reynold number is carried out, and in addition, integral continuity is checked for transient wavy film, both of which shows that they are in good agreement. Based on experimental velocity fields and film topology, pressure distribution inside film is derived with the Poisson equation. Considering characteristics of traveling waves, the experimental results are presented respectively in spatial mode and temporal mode. In spatial mode, capillary wave dynamics are demonstrated out of velocity field, film topology and pressure distribution, which reveals that flow reversal occurs at capillary troughs. In temporal mode, the mechanism of flow reversal at capillary troughs is scrutinized on the basis of high-frequency velocity sampling and the derived pressure gradient. It is shown that flow reversal at capillary troughs is triggered due to occurrence of positive pressure gradient at the back side of the capillary wave crest, rather than the trough upstream as stated by the previous researchers. By elucidating the dynamics of flow reversal, mechanisms for the upper limit of Reynold number with respect to flow reversal underneath capillary wave trough were proposed, which might be the gradually saturated deceleration from the capillary curvature and shorten deceleration duration determined by the wave speed and capillary wave length. Our results should be of interest for optimization of the mass transport model of falling liquid films and shed light on the revealing of flow reversal mechanism.

How Do the Locking Screws Lock? A Micro-CT Study of 3.5-mm Locking Screw Mechanism.

To quantify the amount of the screw head thread and the plate hole thread connection in two 3.5 mm locking plates: Locking Compression Plate (LCP) and Polyaxial Locking System (PLS). A micro - CT scan of a screw head - plate hole connection was performed pre- and post destructive tests. Tests were performed on bone surrogates in a fracture gap model. The 3.5 LCP and 3.5 PLS plates, with 3 perpendicular screws per segment were used in a destructive static test. The 3.5 PLS plates with mono- and polyaxial screws were compared in a cyclic fatigue tests in two orthogonal directions. Pre - and post - test scan datasets were compared. Each dataset was converted into serial images depicting sections cut orthogonally to locking screw axis. The amount of engagement was detected through automated image postprocessing. The mean amount of the thread connection for the LCP was 28.85% before and 18.55% after destructive static test. The mean amount of the connection for the PLS was 16.20% before and 14.55% after destructive static test. When inserted monoaxially, the mean amount of the connection for the PLS screws was 14.4% before and 19.24% after destructive cyclic test. The mean amount of the connection for the polyaxial inserted PLS screws when loaded against plate thickness was 2.99% before and 2.08% after destructive cyclic test. The mean amount of the connection for the polyaxial inserted PLS screws when loaded against plate width was 3.36% before and 3.93% after destructive cyclic test. The 3D visualization of the thread connection showed that the initial interface points between screw head and plate hole are different for both LCP and PLS after the destructive testing. Depending on the type of applied force, there was either loss or increase of the contact. Micro-CT offers news possibilities in locking implant investigation. It might be helpful in better understanding the nature of locking mechanism and prediction of possible mode of failure in different systems.

Internal flow dynamics of spill-return pressure-swirl atomizers

The sprays produced by spill-return pressure-swirl atomizers are strongly dependent on the nature of the internal fluid dynamics. Several spill-return atomizers were compared in terms of the spatial and temporal behaviour of the internal air-core, liquid sheet thickness and its perturbations. The only difference amongst the test configurations was the geometrical arrangement of the spill-line (SL) orifice through which the liquid was spilled away. The flow field inside the swirl chamber was examined using high-speed imaging with image post processing using an in-house Matlab code and three orthogonal velocity components acquired using Laser Doppler Anemometry. The dimensions of the production atomizers did not allow direct visualization of their internal flow, so a scaled, modular, transparent plexiglass model was used. Its flow characteristics were equivalent to the original atomizer. The refractive index of the atomizer body was matched to the test liquid using a solution of 1-Bromonaphthalene and kerosene fuel type JET A-1. The test conditions were derived from the original atomizer and were limited to inlet port Reynolds numbers, from 700 to 2000 and spill-to-feed ratios, SFR, from 0 to 0.75. An inviscid analysis, originally derived for Simplex atomizers, was modified and applied to the spill-return version. This approach allows a theoretical prediction of the discharge coefficient and air-core diameter dependent solely on SFR. An axially located SL orifice inhibits any internal air-core forming in the swirl chamber. Off-axial SL orifices generate and stabilize the air-core, which leads to the regular formation of a liquid sheet and a high-quality spray. Nevertheless, some configurations changed the breakup nature of the liquid sheet and consequently the spray quality. Moreover, the turn-down ratio of the liquid supply rate and spray stability depend on the distance of the SL orifices from the swirl chamber centreline. The flow energy losses increase with SFR. The outcomes from this analysis allow the optimization of the SL configuration for specific application and extend the classical inviscid analysis.

Evaluation of superficial femoral artery-lesions after percutaneous transluminal angioplasty: color-coded summation images vs. monochromatic digital subtraction angiography

BackgroundPercutaneous transluminal angioplasty (PTA) is increasingly requested in the therapy of peripheral arterial occlusive disease. The evaluation of the technical result after balloon angioplasty with regard to bailout stenting is highly dependent on the operators´ subjective assessment and mainly based on the monochromatic digital subtraction angiography (DSA) images. The aim of this study was to compare color-coded single image as a novel diagnostic tool with monochromatic DSA for the analysis of flow limitation and need for stent implantation after PTA of superficial femoral artery (SFA) stenoses.MethodsDuring a period of 18 months, 213 SFA lesions were treated by PTA with a standard balloon in 170 patients, resulting in a total of 193 endovascular procedures. The median age of the patients was 77 years (range, 35–96 years). Median length of the treated lesions was 10.5 cm (range, 1.0–50 cm). Three interventional radiologists retrospectively evaluated the results of balloon angioplasty with monochromatic as well as post-processed color-coded DSA images for flow limitations to decide if subsequent stent implantation was necessary. Consensus reading of two experienced interventional radiologists 2 months after the initial review served as reference standard to perform a receiver operating characteristics (ROC) analysis.ResultsROC analysis for readers A, B and C showed area under the curve (AUC) values of 0.797, 0.865 and 0.804 for color-coded DSA and AUC values of 0.792, 0.843 and 0.872 for monochromatic DSA: a significant advantage of color-coded over conventional monochromatic DSA was not found for readers A and B (p > 0.05). Results of reader C were significantly better in the assessment of monochromatic images (p = 0.023). Diagnostic confidence using color-coded images was slightly higher than in monochromatic images (κ = 0.486 vs. κ = 0.459).ConclusionsIn this study, color coded DSA did not reveal to be superior to conventional monochromatic DSA when evaluating results of PTA and when deciding whether stent implantation is necessary or not. This technology, however, requires further experiences with special regard to homogeneously trained radiologists and to the time requirement.