High-resolution Wall Research Articles

Efficient Synthesis of Water-Soluble Magnetic Nanoparticles and Its Application in MRI in the Detection of Intracranial Aneurysm

Magnetic nanoparticles were used in medical images, which could further improve image clarity, while watersoluble nanoparticles put forward more new requirements for the biocompatibility of nanoparticles. This research adopted a simple and novel method to prepare water-soluble iron oxide nanoparticles. First, transmission electron microscope (TEM) was used to analyze the size distribution of the prepared product; X-ray diffraction (XRD) was used to test the crystal structure of the prepared sample; the fast Fourier transform (FFT) spectrum was introduced to analyze the structural properties of the nanoparticles; the nanoparticle aqueous solutions of different concentrations were designed, and the impact of water-soluble nanoparticles on magnetic resonance imaging (MRI) was examined with the nuclear magnetic resonance spectrometer. At the same time, the prepared water-soluble nanoparticle solution was used for high-resolution tumor wall imaging of patients with unruptured intracranial aneurysm (IA) to compare the imaging effect of the aneurysm wall before and after the introduction of nanoparticles. In the material characterization test of nanoparticles, the prepared samples did not have certain iron oxide characteristic peaks, which means the synthesized iron oxide nanoparticles did not have a fixed crystal morphology. The samples tested by energy dispersive spectrometer (EDS) also contained Fe, O, C and Na. The average particle size was 5.8 nm. It was found under high-resolution TEM that the particle mirror spacing was 0.48 nm, which was consistent with the 111-crystal plane of Fe3O4; The magnetic hysteresis loop test confirmed that when the concentration of nanoparticles increased, the solution would form a magnetic fluid. When the concentration of aqueous solution of nanoparticles increased, the corresponding MRI signal would be significantly enhanced. It was used in the MR scan of patients with unruptured IA. Nanoparticle solution could increase the visibility of the aneurysm, and the image quality of the aneurysm wall could be significantly enhanced.

High-resolution wall temperature measurements with distributed fiber optic sensors

Conventional methods of surface temperature measurement are often unreliable, and other methods may not be practical in closed, high-temperature spaces. In this study, surface temperature measurements of the cooling panel of a natural circulation facility were performed with fiber optic distributed temperature sensors (DTS). High resolution surface temperature profiles of the cooling panel were acquired under two steady experimental conditions, and compared with measurements performed with nearby thermocouples. The total measurement error of the DTS results presented has been estimated to be ±4.4 °C. The results presented herein show that these DTS can reasonably measure surface temperature when installed with the methods developed in this study. Through the analysis of the DTS data collected, the interesting behavior of the cooling panel was revealed, providing new insights on the system's behavior that may be beneficial to the design and optimization of such heat transfer devices. These sensors can also provide the measurement density necessary for validation efforts with highly-resolved prediction methods such as finite element analysis (FEA) or computational fluid dynamics (CFD).

Local heat transfer coefficient measurements using thermal camera for upward flow of Freon 22 in a vertical tube at supercritical conditions and development of correlations

This paper presents experimental results obtained towards characterizing heat transfer behaviour in supercritical fluids employing R22 as a simulant fluid. It is well known that two regimes exist in supercritical heat transfer, viz., heat transfer enhanced regime and heat transfer deteriorated regime and very limited data exist in the heat transfer deteriorated regime. The use of thermal camera has resulted in obtaining high resolution wall temperature data leading to the identification of the bulk enthalpy at which the peak wall temperature occurs. The results bring out the effect of inlet temperature very precisely, on which not much information is available in the literature. Finally the work identifies a criterion for the onset of heat transfer deterioration and correlations to predict the complete heat transfer behaviour exhibited by supercritical fluids. These correlations are shown to predict satisfactorily with a large number of experimental data available in the literature.

Experimental study of air-cooled water condensation in slightly inclined circular tube using infrared temperature measurement technique

This study presents the results of an investigation of the air-cooled water condensation heat transfer characteristics inside a slightly inclined circular tube made of transparent Pyrex glass. The high-resolution wall temperature data and stratified film formations could be obtained with the assistance of an infrared (IR) thermometry technique and side-view visualization using a CCD camera. In all experimental cases, the condensation flow patterns were in the fully-stratified flow region. In addition, the experimentally measured void fraction corresponded well with the logarithmic mean void fraction model. The local temperature differences in the cooling air flow across the condenser tube and high-resolution temperature profiles on the tube’s outer wall were obtained in the experimental measurements. Under the experimental conditions of this study, the local heat flux distributions in the longitudinal direction of the test tube were strongly dependent on the cooling air velocity. And, with the help of IR thermometry, the tube outer wall temperature data at 45 local points could be measured. From the data, the asymmetry distribution of the local wall temperatures and the accurate location of the transition from two-phase mixture to single phase liquid inside the tube could be obtained. Also, the analysis of the thermal resistances by condensation, wall conduction and air convection showed that the air convective heat transfer behavior can play a dominant role to the local heat transfer characteristics. Finally, in order to obtain the local heat flux distribution along the tube’s outer wall, a two-dimensional computational fluid dynamics analysis was conducted. From this calculation, it was resulted that about 70% of total heat transfer rate from the tube surface was released through the tube region lower than the center point. These results were caused by the distribution of air convective heat transfer coefficient on the tube surface.

Abstract TP118: New Markers for Basilar Artery Atherosclerotic Plaque on Conventional T2-weighted MR Imaging

Backgrounds and purpose: In vivo visualization of intracranial atherosclerotic plaque has been studied with high-resolution wall MRI (HRMRI). However, HRMRI is not widely available in routine clinical practice. We hypothesized that increased outer wall and partial loss of flow-void of basilar artery (BA) in conventional T2 axial imaging might be suggestive of positive remodeling and atherosclerotic plaque. Methods: Using a consecutive stroke registry, patients with basilar artery atherosclerotic steno-occlusion were identified. Subjects with same range of age who were negative for abnormal wall thickening of the BA in HRMRI served as controls. Using conventional T2 axial images, maximal diameter and T2 plaque sign (an eccentric or complete obscuration of normal flow-related T2 signal void) within the BA were measured. We tested the diagnostic value of T2 plaque sign and maximal diameter to distinguish patients from controls. Results: Seventy-five patients (age range, 51-81) and 36 controls (50-81) were identified. Maximal diameter was significantly larger in patients than controls (3.87 ± 0.868 mm vs 2.68 ± 0.447 mm, p<0.001). Positivity of T2 plaque sign were 61.3% in patients with BA atherosclerosis, 71.2% in patients with >30% BA stenosis, 77.5% in >50% BA stenosis, and 96.3% in patients with >70% BA stenosis. Receiver operating characteristic curve showed high predictive power (the area under the curve 0.921, 95% CI 0.872 - 0.970, p<0.001) of maximal BA diameter to distinguish patients and controls with an optimal cutoff of 3.185 mm, (sensitivity, 78.7%; specificity, 94.4%). Sensitivity and specificity of T2 plaque sign were 61.3% and 100.0% for BA atherosclerosis of any degree. Increasing sensitivity and decreasing specificity were noted for the diagnosis of higher degree stenosis. Conclusion: Our data suggest that increased BA diameter and plaque sign on conventional T2 imaging are markers of basilar artery atherosclerosis. This would be helpful for earlier identification of causative stroke mechanism. Further study is needed for validation of these findings among different stroke etiologies.

Abstract 80: Early Intervention With High-Dose Statin Decreased the Plaque in Acute Stroke Patients With Intracranial Atherosclerosis: High-Resolution MR Wall Imaging Study

Intracranial atherosclerosis (ICAS) is a common stroke etiology, especially in Asians. Current guidelines emphasize statin therapy with intensive lipid lowering effects for risk reduction in atherosclerotic strokes. High-dose statin therapy regress coronary, carotid and aortic atherosclerotic plaques. However the role of statin in patients with ICAS remains unknown. Thus we aimed to evaluate the impact of early intervention with rosuvastatin (20mg/day) on the symptomatic intracranial atherosclerotic plaque, using high-resolution (HR) wall MRI. Fiffteen patients with acute infarcts caused by ICAS were enrolled. All patients were given high-dose statin, rosuvastatin 20mg/day and performed serial HR MRI with 3-T scanner including proton density/T2-weighted axial/sagittal, T1 FLAIR pre- and post-contrast sagittal/axial and 3-dimensional volumetric isotropic turbo spin echo acquisition images. Serial HR wall MRI were taken before and after 3~6 months of treatment (interval, 141±45 days). Intracranial artery at the maximal stenosis on MRA was analyzed in terms of vascular remodeling (plaque burden) and wall enhancement (plaque activation). Normal vessels were also assessed for reference values. Intracranial atherosclerotic plaques were compared before and after statin treatment. Both intracranial atherosclerotic plaque burden and activation can be regressed by high-dose statin therapy (Figure). Wall area, a representative of plaque burden, was decreased (pre- vs. post-statin treatment, 5.74±2.63mm2 vs. 4.64±2.58mm2; p=0.027). Enhanced area within the wall, an indicator of plaque activation, was also lowered (pre- vs. post-statin treatment, 3.46±2.15mm2 vs. 2.32±1.81mm2; p=0.013). No patients stop rosuvastatin during follow-up period. Early intervention with high-dose rosuvastatin in acute stroke patients with ICAS enabled significant reduction of the symptomatic intracranial atherosclerotic plaque during 6 months.

Tracerco Discovery: the world's first subsea computed tomography (CT) scanner for non-intrusive pipeline inspection

Tracerco Discovery is the world’s first subsea CT scanner, providing high-resolution wall integrity data plus detection of hydrates and other deposits for flow assurance purposes. It is deployed as a remotely operated vehicle (ROV) and the inspection is carried out from the outside of the pipeline. It is the only non-invasive technology capable of inspecting unpiggable coated pipelines and there is no need to remove and replace the pipe’s protective coating. Unpiggable pipelines, especially coated ones, have proven extremely difficult (and in most cases impossible) to inspect for integrity and wall loss issues. An externally deployed tool to do this is needed by the global pipeline industry. Gas hydrates and other pipeline deposits pose a large challenge for the oil and gas industry as they can form restrictions that can result in costly shutdowns and serious safety threats. It is, therefore, important to be able to locate such restrictions subsea with high accuracy to allow safe and efficient remediation operations. Discovery benefits: Production can continue and normal operations are not affected. A high-resolution tomographic image of wall thickness and pipe contents at each scanning location is provided to 2 mm resolution. Coating does not need to be removed. Suitable for gas, liquid, or multiphase flow. Suitable for rigid and flexible lines. Pipe-in-Pipe lines and pipe-bundles can be inspected to measure the wall thickness of outer and inner pipes. The presentation of this extended abstract covers the background of the development work, gives a description of the technology, and shows recent results.

High Resolution Wall and Lumen MRI of the Middle Cerebral Arteries at 3 Tesla

Background: Although black-blood MRI (BB-MRI) can identify plaques in the cervical carotid arteries, this modality has not been applied in intracranial arteries. We imaged the lumina and walls of stenotic middle cerebral arteries (MCAs) in symptomatic and asymptomatic patients using high-resolution BB-MRI, in order to characterize vulnerable plaques and to determine the diagnostic accuracy of BB-MRI in MCA stenosis. Methods: Multicontrast (T₁, T₂ and proton density)-weighted BB-MRIs were acquired in 15 patients with MCA stenosis and in 2 volunteers. Each MCA was classified into one of three groups based on MR angiographic findings and symptoms: normal, symptomatic stenosis, or asymptomatic stenosis. The plaque signal intensity was interpreted and the total wall thickness was measured at the most stenotic segment. These values were then compared between asymptomatic and symptomatic MCAs using t test. For assessment of lumen imaging, the MCA stenosis graded on BB-MR images was compared with that graded on conventional angiography (digital subtraction angiography). Results: Twenty-eight MCAs were evaluated (normal MCAs: 12, symptomatic stenoses: 7, and asymptomatic stenoses: 9). T₁- and/or T₂-hyperintense foci were demonstrated more frequently within the plaques of symptomatic stenoses than within the plaques of asymptomatic stenoses (57.1 vs. 22%). The total wall thickness in the symptomatic stenoses was significantly higher than that seen in the asymptomatic stenoses. The stenosis grade for the BB-MRI was significantly correlated with the digital subtraction angiography grade. Conclusion: High-resolution, multicontrast-weighted BB-MRI has the potential to characterize atherosclerotic plaques in the MCA and may be a useful modality for evaluating the degree of stenosis.

Local heat flow and temperature fluctuations in wall and fluid in nucleate boiling systems

Recent numerical and experimental investigations to improve the understanding of the nucleate boiling heat transfer process mainly concentrate on the description or measurement of local transport phenomena. It is known from these investigations that the interaction between microscale evaporation and macroscale transient heat flow in the wall and the thermal boundary layer is a key aspect for our physical understanding of boiling processes. However reliable quantitative data on the local and transient heat distribution and storage in the heater wall and thermal boundary layer is rare. In this paper we summarize recent developments and present new numerical and experimental results in this specific field of research. A fully transient numerical model has been developed based on a previous quasi stationary model of Kern and Stephan (ASME J Heat Transf 125,1106–1115). It allows describing the transient heat and fluid flow during the entire periodic cycle of a growing, detaching and rising bubble including the waiting time between two successive bubbles from a single nucleation site. It contains a multiscale approach ranging from the nanometer to the millimeter scale for the detailed description of the relevant local phenomena. The detailed analysis of the computed transient temperature profiles in wall and fluid gives accurate information about the heat supply, temporal energy storage and evaporation. It is shown that during the bubble growth and detachment period more heat is consumed by evaporation than heat supplied to the overall system. Thus the wall and liquid thermal boundary layer cool down. After detachment, during the bubble rise period and waiting time, the evaporative heat flow decreases. In this period more heat is supplied to the overall system than consumed by evaporation, thus the wall and liquid thermal boundary layer heat up again. Experimental investigations with high resolution wall temperature measurements underneath a vapor bubble were performed in a micro-g environment and qualitatively confirm these numerical observations.

AeroMEMS sensor array for high-resolution wall pressure measurements

The measurement of wall pressure and wall pressure fluctuations in fluid mechanics is of great importance for the investigation of turbulent flow phenomena. This paper is focused on the design, fabrication and test of a micro electromechanical system (MEMS) pressure sensor array for high-resolution wall pressure measurements in turbulent flows. In contrast to pressure sensor arrays in literature this array is highly sensitive and can be flush mounted on top of a cylinder without using pin holes and flexible tubes. Employing silicon-on-insulator (SOI) technology and deep silicon etching the sensors developed achieve a pressure resolution of 0.5 Pa. Three different types of sensors, featuring a diaphragm thickness of 3 μm and diaphragm sizes of 500 μm, 700 μm, and 900 μm (square diaphragm), have been fabricated and characterized. Simulation of the dynamic behavior yields resonance frequencies of 50 kHz (900 μm-diaphragm), 82 kHz (700 μm-diaphragm), and 160 kHz (500 μm-diaphragm). Sensitivities of 12 μV/(VPa) (900 μm-sensor), 7 μV/(VPa) (700 μm-sensor), and 3 μV/(VPa) (500 μm-sensor) are obtained in measurement ranges of ±200 Pa, ±500 Pa, and ±1 kPa, respectively, featuring a non-linearity of less than 1%. The array was flush mounted on a cylinder (radius 60 mm, height 240 mm) and tested in a wind tunnel.

A second generation MEMS surface fence sensor for high resolution wall shear stress measurement

The measurement of the wall shear stress in fluid mechanics has important implications for the investigation of turbulent flow phenomena. An advanced version of the MEMS silicon surface fence sensor that measures this stress is presented herein. This sensor consists of a cantilever structure with a length of 5 mm, a height of 315 μm, and a thickness of 10 μm. Fluid flowing towards this structure causes it to bend. The resulting bending stress in the cantilever is measured with four piezoresistors, and this stress is correlated to the wall shear stress. The offset voltage has been reduced significantly. The sensor operates over a range of approximately −1 to +1 N/m 2 with a resolution of 10 mN/m 2.

An experimental study on the flow and heat transfer characteristics of an impinging jet

The flow and heat transfer characteristics of an impinging jet is investigated in two major stages. The first stage is about the investigation of the three dimensional mean flow and the turbulent flow quantities in free jet, stagnation and wall jet region. After a complete documentation of the flow field, the convective heat transfer coefficient distributions on the impingement plate are presented, during the second stage of the study. Heat transfer experiments using the new hue-capturing technique result in high resolution wall heating rate distributions. The technique is fully automated using a true color image processing system. The present heat transfer results are discussed in detail in terms of the flow characteristics. The measurements from the new method are compared with conventional heat flux sensors located on the same model. These heat transfer distributions are also compared with other studies available from the literature. The new non-intrusive heat transfer method is highly effective in obtaining high resolution heat transfer maps with good accuracy.

Spatial and temporal registration of cardiac SPECT and MR images: methods and evaluation.

Image registration may assist in the integration of information from multiple sources by allowing direct point-for-point comparisons of studies. To determine the usefulness of such a technique, a method for the spatial and temporal registration of four-dimensional single photon emission computed tomographic (SPECT) and magnetic resonance (MR) cardiac images was developed. Automatically detected left ventricular endocardial surfaces were used to determine the best transform between the two sets of surface points, and that transform was applied to the original SPECT image. A fused image created from the MR and the transformed SPECT images combined the information in both. The authors tested the method with seven patient studies. Registration reduced the distance between the MR and SPECT left ventricular endocardial surfaces by 30%, to an average of 2.7 mm. The authors found that, by using the fused images, perfusion abnormalities could be easily localized and correlated to high-resolution endocardial wall motion and systolic wall thickening.

Investigation of the Love Canal Area of the Niagara River for the Presence of Unknown Organic Contaminants

Abstract A qualitative analysis of organic contaminants in the Niagara River water by high resolution wall coated open tubular column (WCOT) gas chromatography with selective mass spectrometric detection is described. Qualitative analysis of organic pollutants in water is rather a complex task. After the collection of a large Volume of a water sample, the sample is usually run through several extraction and separation steps before identification. During these manipulations, losses of compounds may occur or new impurities may be introduced with various solvents. Therefore, simplification of this procedure is required. This paper describes the detection of all of the major compounds by gas Chromatographic separation combined with mass spectrometric detection (GC-MS). A major advantage is the minimum requirement for cleanup and the injection of a particular fraction extract onto the WCOT column. Dedicated mass Chromatograms of preselected masses at the mass range of the total ion current profile have been used for comparative measurements and identification. For the detection of trace pollutants, a preliminary separation into acidic, neutral, and basic fractions results in simplification of the analysis.

Determination of Magnetization Distribution in Thin Films Using Electron Microscopy

Some new developments are reported in the technique of observing magnetization in thin ferromagnetic films by transmission electron microscopy, and the results of some observations are described that contribute to an understanding of the magnetic character of thin films. Two modes of operation of a microscope are explained, one using projector magnification alone, and one using both objective and projector lenses. The intensity distribution images of the magnetization distribution in a thin film is derived from the Lorentz force acting on an electron passing through the film. The intensity distributions for some simple domain walls are computed and compared in various ways with experimental observations. A magnetization ripple model is proposed and justified to explain an intensity texture observed principally when projector magnification alone is used. The texture is shown to be an orthogonal map of the magnetization of the film, and to be of use in interpreting wall structures. High magnification and resolution wall micrographs are obtained using objective magnification, and a direct measurement of the wall thickness and shape can be made in this way. 180° walls in a Fe-Ni alloy film of about 200 A thickness are found to have a width of 2δ = 1500 A, using the wall model cot−1θ = −sinhx/δ. The effect of finite resolution on the measurements is discussed. It is shown that the magnetization distribution of a wall can be obtained from the measured intensity distribution by inverting the parametric equation solution for the intensity distribution.