Analysis Of Tomography Data Research Articles

Assessing the horizontal refraction of ocean acoustic tomography signals using high-resolution ocean state estimates.

The analysis of signals for acoustic tomography sent between a source and a receiver most often uses the unrefracted geodesic path, an approximation that is justified from theoretical considerations, relying on estimates of horizontal gradients of sound speed, or on simple theoretical models. To quantify the effects of horizontal refraction caused by a realistic ocean environment, horizontal refractions of long-range signals were computed using global ocean state estimates for 2004 from the Estimating the Circulation and Climate of the Ocean (ECCO2) project. Basin-scale paths in the eastern North Pacific Ocean and regional-scale paths in the Philippine Sea were used as examples. At O(5 Mm) basin scales, refracted geodesic and geodesic paths differed by only about 5 km. Gyre-scale features had the greatest refractive influence, but the precise refractive effects depended on the path geometry with respect to oceanographic features. Refraction decreased travel times by 5-10 ms and changed azimuthal angles by about 0.2°. At O(500 km) regional scales, paths deviated from the geodesic by only 250 m, and travel times deviated by less than 0.5 ms. Such effects are of little consequence in the analysis of tomographic data. Refraction details depend only slightly on mode number and frequency.

Imaging weak zones in the foundation using frequency domain attenuation tomography

Cross-hole imaging method using Time Domain (TD) and Frequency Domain (FD) parts of cross-hole radar tomography data acquired using Step Frequency Ground Penetrating Radar (SFGPR) was implemented. This method was adopted for imaging foundation of a dam to check if the foundation was free of geological weak zones. The dam site is characterised by massive and jointed-phyllites associated with major and minor shears. The cross-hole radar tomography data was acquired in the frequency bandwidth of 250 MHz, from the deepest level gallery up to a depth of 40 m in the foundation. In TD, first arrival time and amplitudes of radio waves were inverted using Simultaneous Iterative Reconstruction Technique (SIRT) resulting in velocity and attenuation tomograms. The tomograms showed nearly uniform velocity or attenuation structure in the respective tomographic plane. Subsequently, cross-hole radar tomography data was analysed in FD for a variation of spectrum-amplitude at different frequencies. Amplitudes picked at each single frequency were then inverted using SIRT for obtaining frequency domain attenuation tomogram (FDAT). The FDAT clearly showed presence of anomalous high attenuation zones in the depth range of 23–33 m of the tomographic plane. The anomalous zones in the attenuation tomogram are weak zones in the foundation. To validate the above observations, cross-hole seismic tomography was also done in the same boreholes. Cross-hole seismic tomography results showed low velocity (p-wave) zones around the same location corresponding to the high attenuation zone in FDAT, bringing the dormant weak zone to light. This enabled fine-tuning of the reinforcement design and strengthening the weak zone. This paper discusses the cross-hole radar tomography imaging method, the results of its application in imaging weak zones in the foundation and the comparison of cross-hole radar tomography results (in TD and FD) with the cross-hole seismic tomography results. • Cross-hole SFGPR tomography data analysis in TD and FD; FD attenuation (FDAT). • Inversion of TD and FD data by SIRT; TD - Velocity and Attenuation Tomograms. • FDAT (7.5-11 dB/m) at 200 MHz reveals weak zone in foundation. • Cross-hole P-wave low velocity (2200-3500 m/s) validates FDAT weak zone. • FDAT approach demonstrated in cross-hole imaging of dormant geological weak zone.

CT Evaluation of Extra-articular Glenoid Neck Fractures

Medial translation of the glenoid is frequently described as the main mode of displacement after glenoid neck fracture. Indeed, plain radiographs typically show the glenoid medialized relative to the scapular body. However, whether this truly represents medialization of the glenoid relative to the axial skeleton or lateralization of the scapular body remains unclear. The goal of this investigation was to assess the relationship between the glenoid, the scapular body, and the axial skeleton in patients with glenoid neck fractures using computed tomographic data analysis with the contralateral shoulder serving as an internal control. Retrospective radiographic review. Two Level I trauma centers. Eighteen patients (5 women and 13 men; average age, 38.7 years; range, 17-75 years) admitted between January 2000 and March 2006 with isolated extra-articular glenoid neck fractures (OTA 14C1 fractures) and chest computed tomographic scans that included both shoulders. Glenoid to midline distance and scapular width. The injured glenoid was lateralized an average of 9.8 mm (range, 8 mm medialized to 23 mm lateralized) (P < 0.001). Relative to the uninjured side, glenoid medialization infrequently occurred (4 of 18 patients) and when present was less than 1 cm (range, 2-8 mm). Lateralization occurred more frequently (14 of 18 patients), with an average displacement of 13.7 mm (range, 1-23 mm). The injured scapula was shortened by an average of 3.3 mm (range, 18 mm shorter to 20 mm longer) (P = 0.09). In 15 of 18 patients, the scapular width was shortened by an average of 5.9 mm (range, 1-18 mm), whereas in only 3 of 18 patients was the injured scapular width longer, an average of 9 mm (range, 1-20 mm). In patients with glenoid neck fractures, pure medial translation of the glenoid relative to the axial skeleton rarely occurs. Instead, there is typically a component of shortening of the scapula width combined with lateralization of the scapular body.

Widespread abnormality of the γ-aminobutyric acid-ergic system in Tourette syndrome

Dysfunction of the γ-aminobutyric acid-ergic system in Tourette syndrome may conceivably underlie the symptoms of motor disinhibition presenting as tics and psychiatric manifestations, such as attention deficit hyperactivity disorder and obsessive-compulsive disorder. The purpose of this study was to identify a possible dysfunction of the γ-aminobutyric acid-ergic system in Tourette patients, especially involving the basal ganglia-thalamo-cortical circuits and the cerebellum. We studied 11 patients with Tourette syndrome and 11 healthy controls. Positron emission tomography procedure: after injection of 20 mCi of [(11)C]flumazenil, dynamic emission images of the brain were acquired. Structural magnetic resonance imaging scans were obtained to provide an anatomical framework for the positron emission tomography data analysis. Images of binding potential were created using the two-step version of the simplified reference tissue model. The binding potential images then were spatially normalized, smoothed and compared between groups using statistical parametric mapping. We found decreased binding of GABA(A) receptors in Tourette patients bilaterally in the ventral striatum, globus pallidus, thalamus, amygdala and right insula. In addition, the GABA(A) receptor binding was increased in the bilateral substantia nigra, left periaqueductal grey, right posterior cingulate cortex and bilateral cerebellum. These results are consistent with the longstanding hypothesis that circuits involving the basal ganglia and thalamus are disinhibited in Tourette syndrome patients. In addition, the abnormalities in GABA(A) receptor binding in the insula and cerebellum appear particularly noteworthy based upon recent evidence implicating these structures in the generation of tics.

Three-dimensional registration of tomography data for quantification in biomaterials science

AbstractThe paper shows the benefit of registration tools in the quantitative analysis of tomography data. For this purpose three-dimensional datasets, i.e. target design in rapid prototyping, hard X-ray tomography, and magnetic resonance tomography, were registered with rigid, affine and non-rigid algorithms. Using rigid registration, we aligned individual tomograms to obtain one three-dimensional dataset per specimen, compared human teeth to determine abrasion, and optimized the acquisition parameters in clinical computed tomography. Affine registration was used to determine the sintering-induced shrinkage of hydroxyapatite scaffolds. Using non-rigid registration, we gained insight into tumor morphology imaged by different modes of micro computed tomography. In addition, the fixation-induced shrinkage of tumor tissue and the local deformation of brain tissues as well as the shape changes in nickel titanium alloys were quantitatively determined. Three-dimensional registration is, therefore, a powerful means to count back any influence on morphology of tissues and to quantitatively compare data of different tomography modalities.

STATISTICAL ANALYSIS OF TOMOGRAPHIC RECONSTRUCTION ALGORITHMS BY MORPHOLOGICAL IMAGE CHARACTERISTICS

We suggest a procedure for quantitative quality control of tomographic reconstruction algorithms. Our task-oriented evaluation focuses on the correct reproduction of phase boundary length and has thus a clear implication for morphological image analysis of tomographic data. Indirectly the method monitors accurate reproduction of a variety of locally defined critical image features within tomograms such as interface positions and microstructures, debonding, cracks and pores. Tomographic errors of such local nature are neglected if only global integral characteristics such as mean squared deviation are considered for the evaluation of an algorithm. The significance of differences in reconstruction quality between algorithms is assessed using a sample of independent random scenes to be reconstructed. These are generated by a Boolean model and thus exhibit a substantial stochastic variability with respect to image morphology. It is demonstrated that phase boundaries in standard reconstructions by filtered backprojection exhibit substantial errors. In the setting of our simulations, these could be significantly reduced by the use of the innovative reconstruction algorithm DIRECTT.

Analysis of electrical resistance tomography (ERT) data using least-squares regression modelling in industrial process tomography

Analysis of electrical resistance tomography (ERT) data using least-squares regression modelling in industrial process tomographs has been tested. Potential differences measured between electrodes in rings have been used to carry out the regression modelling to investigate the location and size of a disturbance present in the system. Extensive experiments have been carried out with ERT to test a suitable regression algorithm to extract the disturbance. Current analysis has been performed for a single disturbance known to be present in the system. For the environment considered, the least-squares regression reported in this paper demonstrates an alternative approach for analysis of tomography data in industrial applications. The position (concentric or off-centre) and the size of the disturbance (in concentric cases) can be well defined by the reported regression modelling approach. However, it is still a challenge to define the size of the off-centre disturbance.

Elemental analysis of hair using PIXE-tomography and INAA

3D quantitative elemental maps of a section of a strand of hair were produced using a combination of PIXE-Tomography and simultaneous On/Off Axis STIM-Tomography at the University of Surrey Ion Beam Centre. The distributions of S, K, Cl, Ca, Fe and Zn were determined using the PIXE-T reconstruction package DISRA. The results were compared with conventional bulk PIXE analysis of tomographic data as determined using Dan32. The overall concentrations determined by PIXE were compared with elemental concentrations held in the University of Surrey Hair Database. All the entries currently in the database were produced using INAA. The merits and possible contributions of tomographic PIXE analysis to analysis of hair are discussed. The conclusions drawn from the PIXE-Tomography analysis can be used to argue for more stringent procedures for hair analysis at the University of Surrey.

Gravitational Granular Flow Dynamics Study Based on Tomographic Data Processing

This article presents capabilities of the application of electrical capacitance tomography (ECT) to hopper flow dynamics analysis. The two main goals are to demonstrate a number of tomographic data analysis methods in the application to core flow and to propose some simple parameters depicting this flow via funnel description. Experiments have been conducted for various diameters of hopper orifice using two types of materials with different physicochemical properties, rice and polyamide pellets. ECT allows noninvasive in situ measurement, visualization, and study to be carried out on nonconducting media such as particulate systems or powders. Tomographic images give valuable information about solids concentration distribution inside the measurement space delimited by electrodes. Proper interpretation of concentration changes during the hopper discharging allows the investigation of phenomenon dynamics to be performed. Data analysis consists of raw signal (the measured capacitances) interpretation and tomographic image post-processing manipulation. The present study focuses on the tracking of particulate concentration changes and the hopper discharge rate parameter proposition. Preliminary attempts at funnel propagation velocity measurements are presented here. On the other hand, funnel propagation velocity rate in the initial stage of hopper unloading is based on the calculation of transition time between characteristic points indicated on unloading dynamics diagram. Transition time is calculated using stochastic processes theory-based methods. The novel approach proposed by the authors is based on the estimation of velocity using just one plane of sensing electrodes in contrast to standard applied inter-plane correlation techniques. However, basic parameter estimators such as autocorrelation and variance are used in order to examine the gravitational flow as well.

Software tools for quantification of X-ray microtomography at the UGCT

The technique of X-ray microtomography using X-ray tube radiation offers an interesting tool for the non-destructive investigation of a wide range of materials. A major challenge lies in the analysis and quantification of the resulting data, allowing for a full characterization of the sample under investigation. In this paper, we discuss the software tools for reconstruction and analysis of tomographic data that are being developed at the UGCT. The tomographic reconstruction is performed using Octopus, a high-performance and user-friendly software package. The reconstruction process transforms the raw acquisition data into a stack of 2D cross-sections through the sample, resulting in a 3D data set. A number of artifact and noise reduction algorithms are integrated to reduce ring artifacts, beam hardening artifacts, COR misalignment, detector or stage tilt, pixel non-linearities, etc. These corrections are very important to facilitate the analysis of the 3D data. The analysis of the 3D data focuses primarily on the characterization of pore structures, but will be extended to other applications. A first package for the analysis of pore structures in three dimensions was developed under Matlab ®. A new package, called Morpho+, is being developed in a C++ environment, with optimizations and extensions of the previously used algorithms. The current status of this project will be discussed. Examples of pore analysis can be found in pharmaceuticals, material science, geology and numerous other fields.

Three-Dimensional Compositional Characterization of High-k Gate Dielectrics with LEAP Atom Probe Tomography

Laser pulsed atom probe tomography (APT) is used to quantitatively analyze oxides of interest to enable the timely the development of high-k gate dielectric films. Specific analysis of hafnium dioxide films, provided by IBM and characterized using the local electrode atom probe (LEAP®), transmission electron microscopy (TEM), and Secondary Ion Mass Spectroscopy (SIMS) are compared and contrasted. A variety of LEAP tomography data analysis techniques will be discussed, including thickness measurements, surface definitions, and buried interface surface roughness calculations based on iso- chemical concentration surfaces. This work demonstrates the ability of the LEAP technique to rapidly and accurately characterize the complex composition and structure of novel high performance semiconductor devices with sub-nanometer resolution. The compositional and spatial information is used to quantify the differences which subtle surface preparation changes have upon the interfacial region for a high-k gate dielectric film.

Three-Dimensional Pore Structure of Chromatographic Adsorbents from Electron Tomography

The pore structure of chromatographic adsorbents directly influences macromolecular partitioning and transport in chromatography. Quantitative structural characterization of chromatographic media has generally been performed in terms of the mean pore size or, at best, the pore size distribution (PSD), but more detailed information on, e.g., connectivity has been lacking. We have applied electron tomography, a 3D TEM technique that views a sample from multiple perspectives and allows reconstruction of the volumetric structure, to capture the internal details of microporous chromatographic media with nanometer-scale resolution. Visualization of reconstructions of three adsorbents, Toyopearl SP-650 C, SP-550 C, and CM Sepharose FF, provides thorough and direct information on the geometry and the interconnectivity of the pore network. The structures are qualitatively consistent with in situ AFM images, and quantitative data for the porosities and PSDs from the analysis of tomographic data agree reasonably well with inverse size-exclusion chromatography results. For a more straightforward representation of the networking and size features of the disordered pore space, a 3D thinning algorithm was used to derive pore skeletons and consequently quantitative data on distributions of local path lengths, widths, tortuosities, and connectivities. Such enriched structural information can be instrumental in more discriminate structural evaluation and construction of engineered pore models for the study of solute intraparticle transport.

Applications of Data Assimilation to Analysis of the Ocean on Large Scales (gtSpecial IssueltData Assimilation in Meteology and Oceanography: Theory and Practice)

It is commonplace to begin talks on this topic by noting that oceanographic data are too scarce and sparse to provide complete initial and boundary conditions for large-scale ocean models. Even considering the availability of remotely-sensed data such as radar altimetry from the TOPEX and ERS-1 satellites, a glance at a map of available subsurface data should convince most observers that this is still the case. Data are still too sparse for comprehensive treatment of interannual to interdecadal climate change through the use of models, since the new data sets have not been around for very long. In view of the dearth of data, we must note that the overall picture is changing rapidly. Recently, there have been a number of large scale ocean analysis and prediction efforts, some of which now run on an operational or at least quasi-operational basis, most notably the model based analyses of the tropical oceans. These programs are modeled on numerical weather prediction. Aside from the success of the global tide models, assimilation of data in the tropics, in support of prediction and analysis of seasonal to interannual climate change, is probably the area of large scale ocean modeling and data assimilation in which the most progress has been made. Climate change is a problem which is particularly suited to advanced data assimilation methods. Linear models are useful, and the linear theory can be exploited. For the most part, the data are sufficiently sparse that implementation of advanced methods is worthwhile. As an example of a large scale data assimilation experiment with a recent extensive data set, we present results of a tropical ocean experiment in which the Kalman filter was used to assimilate three years of altimetric data from Geosat into a coarsely resolved linearized long wave shallow water model. Since nonlinear processes dominate the local dynamic signal outside the tropics, subsurface dynamical quantities cannot be reliably inferred from surface height anomalies. Because of its potential for large scale synoptic coverage of the deep ocean, acoustic travel time data should be a natural complement to satellite altimetry. Satellite data give us vertical integrals associated with thermodynamic and dynamic processes, while acoustic travel times provide horizontal integrals from which dynamics of the deep ocean can be inferred. Linearized analysis indicates that detailed information can be retrieved by means of data assimilation from integral sources of data such as acoustic travel times. Static analysis of tomographic data without data assimilation cannot provide nearly so much detail. It can be shown that integrated quantities along the edges and diagonals of a simple square array combined with a linearized quasigeostrophic model is an observable system, down to scales much shorter than the dimensions of the array. Nonlinearities complicate the picture, but the linear results, along with a few preliminary numerical experiments give us cause for optimism.

Conventional and modern seismic investigations for rock quality determination at a dam site—a case history1

AbstractRefraction seismics and modern tomographic surveys were employed at the Platanovrissi dam site on the Nestos river in northern Greece in an effort to investigate the dynamic elastic properties and rockmass condition of gneiss‐schist outcropping in the area under investigation. Six seismic refraction traverses were run on the ground surface, inside the exploratory tunnels and between tunnels and the ground surface. The results provided information about the low‐velocity surface layer parameters and the stress relief zones on the walls of all the tunnels in which seismic tomography tests were performed. Ultrasonic tests, conducted both in situ and in the laboratory, enabled the determination of the ratio Vp/Vs and the Poisson's ratio calculation. From the tomography data analysis and the geological interpretation of the results, three main velocity zones, ranging between 3500 and 4000, 3000 and 3500 and less than 3000m/s, were detected in each tunnel. High‐velocity zones were found to be compatible with the hard rockmass of gneiss‐schist material, while moderate velocities are closely related to jointed and fractured zones. Finally, low‐velocity zones were well correlated with weathered gneiss‐schist material.

An iterative approach to curved ray reconstruction of birefringent fields

The transmission of polarized light through non-homogeneous birefringent fields is examined, and an iterative approach for incorporating ray curvature into the analysis of tomographic data is proposed. The method extends strain-gradient theory and applies iterative algorithms which have been used by other researchers to reconstruct fields which are non-homogeneous but optically Isotropic. Optical anisotropy is incorporated by using a light propagation model which includes both bending and separation of initially coincident light ray pairs. To illustrate the method, data are generated computationally and are analysed to determine the bending moment in a prismatic beam and the forces acting on a diametrically loaded disc.

Combined surface display and reformatting for the three-dimensional analysis of tomographic data.

Radiologic examinations increasingly are based on sequences of cross-sectional images. In current clinical applications, the three-dimensional (3D) relationships contained in these examinations must be inferred by the observer through analysis of multiple two-dimensional (2D) images. In this article, methods for the direct display of 3D gray-level data are investigated. In the chosen approach, the 3D presentation of bone and skin surface serves to orient the viewer, while planar reformation and/or transparent projections can be applied for the assessment of soft-tissue structures in regions of interest. The resulting images represent the original image data in a way that is more suitable for observation of 3D relationships than the conventional cross-sectional viewing mode. This may facilitate the diagnostic process and enhance the interpretability of the images. Routine clinical application of this technique requires special computer hardware. Research applications, however, can be performed within tolerable times (10-30 sec/view) with computers found in radiologic research environments.