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1
Zigunov, Fernando, e John Charonko. "One-Shot Omnidirectional Pressure Integration Through Matrix Inversion". Proceedings of the International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics 21 (8 luglio 2024): 1–14. http://dx.doi.org/10.55037/lxlaser.21st.41.
Testo completoAbstract (sommario):
In this work, we present a method to perform 2D and 3D omnidirectional pressure integration from velocity measurements with a single-iteration matrix inversion approach. This work builds upon our previous work, where the rotating parallel ray approach was extended to the limit of infinite rays by taking continuous projection integrals of the ray paths and recasting the problem as an iterative matrix inversion problem. This iterative matrix equation is now ``fast-forwarded'' to the ``infinity'' iteration, leading to a different matrix equation that can be solved in a single iteration, thereby presenting the same computational complexity as the Poisson equation. We observe computational speedups of $\sim10^6$ when compared to brute-force omnidirectional integration methods, enabling the treatment of grids of $\sim 10^9$ points and potentially even larger in a desktop setup at the time of publication. Further examination of the boundary conditions of our one-shot method shows that omnidirectional pressure integration implements a new type of boundary condition, which treats the boundary points as interior points to the extent that information is available.
2
Weglein, Arthur B. "A direct inverse method for subsurface properties: The conceptual and practical benefit and added value in comparison with all current indirect methods, for example, amplitude-variation-with-offset and full-waveform inversion". Interpretation 5, n. 3 (31 agosto 2017): SL89—SL107. http://dx.doi.org/10.1190/int-2016-0198.1.
Testo completoAbstract (sommario):
Direct inverse methods solve the problem of interest; in addition, they communicate whether the problem of interest is the problem that we (the seismic industry) need to be interested in. When a direct solution does not result in an improved drill success rate, we know that the problem we have chosen to solve is not the right problem — because the solution is direct and cannot be the issue. On the other hand, with an indirect method, if the result is not an improved drill success rate, then the issue can be either the chosen problem, or the particular choice within the plethora of indirect solution methods, or both. The inverse scattering series (ISS) is the only direct inversion method for a multidimensional subsurface. Solving a forward problem in an inverse sense is not equivalent to a direct inverse solution. All current methods for parameter estimation, e.g., amplitude-variation-with-offset and full-waveform inversion, are solving a forward problem in an inverse sense and are indirect inversion methods. The direct ISS method for determining earth material properties defines the precise data required and the algorithms that directly output earth mechanical properties. For an elastic model of the subsurface, the required data are a matrix of multicomponent data, and a complete set of shot records, with only primaries. With indirect methods, any data can be matched: one trace, one or several shot records, one component, multicomponent, with primaries only or primaries and multiples. Added to that are the innumerable choices of cost functions, generalized inverses, and local and global search engines. Direct and indirect parameter inversion are compared. The direct ISS method has more rapid convergence and a broader region of convergence. The difference in effectiveness increases as subsurface circumstances become more realistic and complex, in particular with band-limited noisy data.
3
Jones, Glyn M., e D. B. Jovanovich. "A ray inversion method for refraction analysis". GEOPHYSICS 50, n. 11 (novembre 1985): 1701–20. http://dx.doi.org/10.1190/1.1441861.
Testo completoAbstract (sommario):
A new technique is presented for the inversion of head‐wave traveltimes to infer near‐surface structure. Traveltimes computed along intersecting pairs of refracted rays are used to reconstruct the shape of the first refracting horizon beneath the surface and variations in refractor velocity along this boundary. The information derived can be used as the basis for further processing, such as the calculation of near‐surface static delays. One advantage of the method is that the shape of the refractor is determined independently of the refractor velocity. With multifold coverage, rapid lateral changes in refractor geometry or velocity can be mapped. Two examples of the inversion technique are presented: one uses a synthetic data set; the other is drawn from field data shot over a deep graben filled with sediment. The results obtained using the synthetic data validate the method and support the conclusions of an error analysis, in which errors in the refractor velocity determined using receivers to the left and right of the shots are of opposite sign. The true refractor velocity therefore falls between the two sets of estimates. The refraction image obtained by inversion of the set of field data is in good agreement with a constant‐velocity reflection stack and illustrates that the ray inversion method can handle large lateral changes in refractor velocity or relief.
4
Liu, Bin, Senlin Yang, Yuxiao Ren, Xinji Xu, Peng Jiang e Yangkang Chen. "Deep-learning seismic full-waveform inversion for realistic structural models". GEOPHYSICS 86, n. 1 (1 gennaio 2021): R31—R44. http://dx.doi.org/10.1190/geo2019-0435.1.
Testo completoAbstract (sommario):
Velocity model inversion is one of the most important tasks in seismic exploration. Full-waveform inversion (FWI) can obtain the highest resolution in traditional velocity inversion methods, but it heavily depends on initial models and is computationally expensive. In recent years, a large number of deep-learning (DL)-based velocity model inversion methods have been proposed. One critical component in those DL-based methods is a large training set containing different velocity models. We have developed a method to construct a realistic structural model for the DL network. Our compressional-wave velocity model building method for creating dense-layer/fault/salt body models can automatically construct a large number of models without much human effort, which is very meaningful for DL networks. Moreover, to improve the inversion result on these realistic structural models, instead of only using the common-shot gather, we also extract features from the common-receiver gather as well. Through a large number of realistic structural models, reasonable data acquisition methods, and appropriate network setups, a more generalized result can be obtained through our proposed inversion framework, which has been demonstrated to be effective on the independent testing data set. The results of dense-layer models, fault models, and salt body models that we compared and analyzed demonstrate the reliability of our method and also provide practical guidelines for choosing optimal inversion strategies in realistic situations.
5
Zhang, Yu, Guanquan Zhang e Norman Bleistein. "Theory of true-amplitude one-way wave equations and true-amplitude common-shot migration". GEOPHYSICS 70, n. 4 (luglio 2005): E1—E10. http://dx.doi.org/10.1190/1.1988182.
Testo completoAbstract (sommario):
One-way wave operators are powerful tools for forward modeling and migration. Here, we describe a recently developed true-amplitude implementation of modified one-way operators and present some numerical examples. By “true-amplitude” one-way forward modeling we mean that the solutions are dynamically correct as well as kinematically correct. That is, ray theory applied to these equations yields the upward- and downward-traveling eikonal equations of the full wave equation, and the amplitude satisfies the transport equation of the full wave equation. The solutions of these equations are used in the standard wave-equation migration imaging condition. The boundary data for the downgoing wave is also modified from the one used in the classic theory because the latter data is not consistent with a point source for the full wave equation. When the full wave-form solutions are replaced by their ray-theoretic approximations, the imaging formula reduces to the common-shot Kirchhoff inversion formula. In this sense, the migration is true amplitude as well. On the other hand, this new method retains all of the fidelity features of wave equation migration. Computer output using numerically generated data confirms the accuracy of this inversion method. However, there are practical limitations. The observed data must be a solution of the wave equation. Therefore, the data must be collected from a single common-shot experiment. Multiexperiment data, such as common-offset data, cannot be used with this method as presently formulated.
6
Zhang, Yu, Sheng Xu, Norman Bleistein e Guanquan Zhang. "True-amplitude, angle-domain, common-image gathers from one-way wave-equation migrations". GEOPHYSICS 72, n. 1 (gennaio 2007): S49—S58. http://dx.doi.org/10.1190/1.2399371.
Testo completoAbstract (sommario):
True-amplitude wave-equation migration provides a quality migrated image of the earth’s interior. In addition, the amplitude of the output provides an estimate of the angular-dependent reflection coefficient, similar to the output of Kirchhoff inversion. Recently, true-amplitude wave-equation migration for common-shot data has been proposed to generate amplitude-reliable, shot-domain, common-image gathers in heterogeneous media. We present a method to directly produce angle-domain common-image gathers from both common-shot and shot-receiver wave-equation migration. Generating true-amplitude, shot-domain, common-image gathers requires a deconvolution-type imaging condition using the ratio of the upgoing and downgoing wavefield, each downward-projected to the image point. Producing true-amplitude, angle-domain, common-image gathers requires, instead, the product of the upgoing wavefield and the complexconjugate of the downgoing wavefield in the imaging condition. Since multiplication is a more stable computational process than division, the new methods proposed provide more stable ways of inverting seismic data. Furthermore, the resulting common-image gathers can be directly used for migrated amplitude-variation-with angle analysis and tomography-based velocity analysis. Shot-receiver wave-equation migration requires new true-amplitude, one-way wave equations with one depth variable and transverse variables for the coordinates corresponding to sources and receivers, hence, two transverse coordinates in 2D and four transverse coordinates in 3D. We propose a modified double-square-root one-way wave equation to produce true amplitude common-image angle gathers. We also demonstrate the new methods with some synthetic examples. Some numerical examples show that the new methods we propose give better amplitude performance on the migrated angle gathers.
7
Dong, Wenjie, Mark Jeffrey Emanuel, Phillip Bording e Norman Bleistein. "A computer implementation of 2.5-D common‐shot inversion". GEOPHYSICS 56, n. 9 (settembre 1991): 1384–94. http://dx.doi.org/10.1190/1.1443158.
Testo completoAbstract (sommario):
The computer implementation of a two‐and‐one‐half dimensional (2.5-D) constant density prestack inversion formalism with laterally and depth‐dependent background propagation speed is a Kirchhoff‐type inversion, summing data from a line of receivers over traveltime curves in the depth‐dependent background medium with weights determined from Born/Kirchhoff inversion theory. This theory predicts that the output will be a reflector map with peak amplitudes on each reflector being in known proportion to the angularly dependent geometrical optics reflection coefficient. The 2.5-D feature provides for out‐of‐plane spreading correction consistent with the prescribed background medium. The method is applied to a synthetic data set and to a physically modeled data set generated at the Seismic Acoustic Laboratory. The graphical output demonstrates the validity of the formalism as a Kirchhoff migration. Parameter estimation for the synthetic data confirmed the theory. Parameter estimation for the experimental data was less successful, partially due to problems with amplitude control in the original experiment and partially due to the limited aperture of the common‐shot data, thereby suggesting that a common‐offset inversion might be more useful for parameter estimation.
8
Vigh, Denes, e E. William Starr. "3D prestack plane-wave, full-waveform inversion". GEOPHYSICS 73, n. 5 (settembre 2008): VE135—VE144. http://dx.doi.org/10.1190/1.2952623.
Testo completoAbstract (sommario):
Prestack depth migration has been used for decades to derive velocity distributions in depth. Numerous tools and methodologies have been developed to reach this goal. Exploration in geologically more complex areas exceeds the abilities of existing methods. New data-acquisition and data-processing methods are required to answer these new challenges effectively. The recently introduced wide-azimuth data acquisition method offers better illumination and noise attenuation as well as an opportunity to more accurately determine velocities for imaging. One of the most advanced tools for depth imaging is full-waveform inversion. Prestack seismic full-waveform inversion is very challenging because of the nonlinearity and nonuniqueness of the solution. Combined with multiple iterations of forward modeling and residual wavefield back propagation, the method is computer intensive, especially for 3D projects. We studied a time-domain, plane-wave implementation of 3D waveform inversion. We found that plane-wave gathers are an attractive input to waveform inversion with dramatically reduced computer run times compared to traditional shot-gather approaches. The study was conducted on two synthetic data sets — Marmousi2 and SMAART Pluto 1.5 — and a field data set. The results showed that a velocity field can be reconstructed well using a multiscale time-domain implementation of waveform inversion. Although the time-domain solution does not take advantage of wavenumber redundancy, the method is feasible on current computer architectures for 3D surveys. The inverted velocity volume produces a quality image for exploration geologists by using numerous iterations of waveform inversion.
9
Pan, Yudi, e Lingli Gao. "Random objective waveform inversion of surface waves". GEOPHYSICS 85, n. 4 (5 giugno 2020): EN49—EN61. http://dx.doi.org/10.1190/geo2019-0613.1.
Testo completoAbstract (sommario):
Full-waveform inversion (FWI) of surface waves is becoming increasingly popular among shallow-seismic methods. Due to a huge amount of data and the high nonlinearity of the objective function, FWI usually requires heavy computational costs and may converge toward a local minimum. To mitigate these problems, we have reformulated FWI under a multiobjective framework and adopted a random objective waveform inversion (ROWI) method for surface-wave characterization. Three different measure functions were used, whereas the combination of one measure function with one shot independently provided one of the [Formula: see text] objective functions ([Formula: see text] is the total number of shots). We have randomly chose and optimized one objective function at each iteration. We performed a synthetic test to compare the performance of the ROWI and conventional FWI approaches, which showed that the convergence of ROWI is faster and more robust compared with conventional FWI approaches. We also applied ROWI to a field data set acquired in Rheinstetten, Germany. ROWI successfully reconstructed the main geologic feature, a refilled trench, in the final result. The comparison between the ROWI result and a migrated ground-penetrating radar profile further proved the effectiveness of ROWI in reconstructing the near-surface S-wave velocity model. We also ran the same field example by using a poor initial model. In this case, conventional FWI failed whereas ROWI still reconstructed the subsurface model to a fairly good level, which highlighted the relatively low dependency of ROWI on the initial model.
10
Behura, Jyoti, e Roel Snieder. "Virtual Real Source: Source signature estimation using seismic interferometry". GEOPHYSICS 78, n. 5 (1 settembre 2013): Q57—Q68. http://dx.doi.org/10.1190/geo2013-0069.1.
Testo completoAbstract (sommario):
Knowledge of the seismic source signature is crucial in numerousproblems in exploration seismology, especially in full-waveform inversion. However, existing methods of source signature estimation like statistical methods and well-log-based methods suffer from several drawbacks arising from assumptions such as whiteness of the reflectivity series and the minimum-phase character of the wavelet. Also, estimation of the source signature using wave-theoretical methods requires the recording of the wavefield and its normal derivative or additional recordings above the receiver surface which are not always available. We introduce a method, called the Virtual Real Source, of extracting the source signature based on the theory of seismic interferometry, also known as the virtual source method. This method is independent of the assumptions and drawbacks of the above-mentioned methods. The only requirement for the method of Virtual Real Source is to have a virtual source location coincide with the physical shot position whose source signature is desired. The virtual source location does not necessarily have to be a zero-offset receiver because one can use interpolation for it. The source signature is extracted by deconvolving the real recording at a receiver from the virtual source recording. Through modeling examples, we show that Virtual Real Source produces accurate source signatures even for complicated subsurface structures and source signatures, and is robust in the presence of noise. Source signature of every shot in a survey can be extracted reliably as long as the source signatures have similar amplitude spectra. The phase spectrum of the source signature is always extracted accurately even if it varies randomly from one shot to another. The Virtual Real Source applied on a 2D streamer data set from the North Viking Graben in the North Sea extracts all the airgun signatures with the main pulse and the bubble oscillation.
11
Gras, Clàudia, Daniel Dagnino, Clara Estela Jiménez-Tejero, Adrià Meléndez, Valentí Sallarès e César R. Ranero. "Full-waveform inversion of short-offset, band-limited seismic data in the Alboran Basin (SE Iberia)". Solid Earth 10, n. 6 (30 ottobre 2019): 1833–55. http://dx.doi.org/10.5194/se-10-1833-2019.
Testo completoAbstract (sommario):
Abstract. We present a high-resolution P-wave velocity model of the sedimentary cover and the uppermost basement to ∼3 km depth obtained by full-waveform inversion of multichannel seismic data acquired with a 6 km long streamer in the Alboran Sea (SE Iberia). The inherent non-linearity of the method, especially for short-offset, band-limited seismic data as this one, is circumvented by applying a data processing or modelling sequence consisting of three steps: (1) data re-datuming by back-propagation of the recorded seismograms to the seafloor; (2) joint refraction and reflection travel-time tomography combining the original and the re-datumed shot gathers; and (3) full-waveform inversion of the original shot gathers using the model obtained by travel-time tomography as initial reference. The final velocity model shows a number of geological structures that cannot be identified in the travel-time tomography models or easily interpreted from seismic reflection images alone. A sharp strong velocity contrast accurately defines the geometry of the top of the basement. Several low-velocity zones that may correspond to the abrupt velocity change across steeply dipping normal faults are observed at the flanks of the basin. A 200–300 m thick, high-velocity layer embedded within lower-velocity sediment may correspond to evaporites deposited during the Messinian crisis. The results confirm that the combination of data re-datuming and joint refraction and reflection travel-time inversion provides reference models that are accurate enough to apply full-waveform inversion to relatively short offset streamer data in deep-water settings starting at a field-data standard low-frequency content of 6 Hz.
12
Da Silva, Curt, Yiming Zhang, Rajiv Kumar e Felix J. Herrmann. "Applications of low-rank compressed seismic data to full-waveform inversion and extended image volumes". GEOPHYSICS 84, n. 3 (1 maggio 2019): R371—R383. http://dx.doi.org/10.1190/geo2018-0116.1.
Testo completoAbstract (sommario):
Conventional oil and gas fields are increasingly difficult to explore and image, resulting in the call for more complex wave-equation-based inversion algorithms that require dense long-offset samplings. Consequently, there is an exponential growth in the size of data volumes and prohibitive demands on computational resources. We have developed a method to compress and process seismic data directly in a low-rank tensor format, which drastically reduces the amount of storage required to represent the data. Seismic data exhibit a low-rank structure in a particular transform domain, which can be exploited to compress the dense data in one extremely storage-efficient tensor format when the data are fully sampled or can be interpolated when the data have missing entries. In either case, once our data are represented in the compressed tensor form, we have developed an algorithm to extract source or receiver gathers directly from the compressed parameters. This extraction process can be done on the fly directly on the compressed data, and it does not require scanning through the entire data set to form shot gathers. We apply this shot-extraction technique in the context of stochastic full-waveform inversion as well as forming full subsurface image gathers through probing techniques and reveal the minor differences between using the full and compressed data, while drastically reducing the total memory costs.
13
Ben-Hadj-Ali, Hafedh, Stéphane Operto e Jean Virieux. "An efficient frequency-domain full waveform inversion method using simultaneous encoded sources". GEOPHYSICS 76, n. 4 (luglio 2011): R109—R124. http://dx.doi.org/10.1190/1.3581357.
Testo completoAbstract (sommario):
Three-dimensional full waveform inversion (FWI) still suffers from prohibitively high computational costs that arise because of the seismic modeling for multiple sources that is performed at each nonlinear iteration of FWI. Building supershots by assembling several sources allows mitigation of the number of simulations per FWI iteration, although it adds crosstalk artifacts because of interference between the individual sources of the supershots. These artifacts themselves can be reduced by encoding each individual source with a random phase shift during assembling of the sources. The source encoding method is applied to an efficient frequency-domain FWI, in which a limited number of discrete frequencies or coarsely sampled frequency groups are inverted successively following a multiscale approach. Random codes can be regenerated at each FWI iteration or for each frequency of a group during each FWI iteration, to favor the destructive summation of crosstalk artifacts over FWI iterations. Either a limited number of sources (partial assembling) or the total number of sources (full assembling) can be combined into supershots. Wide-aperture acquisition geometries such as land or marine node acquisitions are considered, to allow one to stack a large number of shots in the full computational domain and to test different partial assembling strategies involving sources that are close to or distant from each other. Two-dimensional case studies show that partial-source assembling of distant shots has a limited sensitivity to noise, for a computational saving that is roughly proportional to the number of shots assembled into the supershots. On the other hand, full assembling is more sensitive to noise, and it requires successive inversions of finely sampled frequency groups with a large number of FWI iterations. In contrast, refining the shot interval to improve the fold degrades the models when full assembling is applied to noisy data. Preliminary 3D application of the method leads to the same conclusions that 2D case studies do, with regard to the footprint of crosstalk noise in the imaging.
14
Faucher, Florian, Giovanni Alessandrini, Hélène Barucq, Maarten V. de Hoop, Romina Gaburro e Eva Sincich. "Full reciprocity-gap waveform inversion enabling sparse-source acquisition". GEOPHYSICS 85, n. 6 (13 ottobre 2020): R461—R476. http://dx.doi.org/10.1190/geo2019-0527.1.
Testo completoAbstract (sommario):
The quantitative reconstruction of subsurface earth properties from the propagation of waves follows an iterative minimization of a misfit functional. In marine seismic exploration, the observed data usually consist of measurements of the pressure field, but dual-sensor devices also provide the normal velocity. Consequently, a reciprocity-based misfit functional is specifically designed, and it defines the full reciprocity-gap waveform inversion (FRgWI) method. This misfit functional provides additional features compared to the more traditional least-squares approaches, in particular, in that the observational and computational acquisitions can be different. Therefore, the positions and wavelets of the sources from which the measurements are acquired are not needed in the reconstruction procedure and, in fact, the numerical acquisition (for the simulations) can be chosen arbitrarily. Based on 3D experiments, FRgWI is shown to behave better than full-waveform inversion in the same context. It allows for arbitrary numerical acquisitions in two ways: when few measurements are given, a dense numerical acquisition (compared to the observational one) can be used to compensate. However, with a dense observational acquisition, a sparse computational one is shown to be sufficient, for instance, with multiple-point sources, hence reducing the numerical cost. FRgWI displays accurate reconstructions in both situations and appears more robust with respect to crosstalk than least-squares shot stacking.
15
Wellington, Paul, Romain Brossier e Jean Virieux. "Preconditioning full-waveform inversion with efficient local correlation operators". GEOPHYSICS 84, n. 3 (1 maggio 2019): R321—R332. http://dx.doi.org/10.1190/geo2018-0584.1.
Testo completoAbstract (sommario):
Full-waveform inversion (FWI) is an iterative locally linearized data-fitting technique. The FWI method attempts to move from an initial low-wavenumber representation of earth parameters to a broader representation of the medium. An issue with the method is that FWI is an ill-posed problem, oversampled for the numerical forward discretization. The success of the model parameter reconstruction can often be greatly affected by external factors such as the presence of noise in the input field data or other artifacts arising from the imaging condition present in the FWI gradient computation. We have developed a strategy for mitigating against the influence of such external factors by preconditioning the discrete data gradient using an efficient differential approach instead of the often used integral formulation. Such an application of a smoothing correlation operator allows one to use prior information to locally filter along expected geological dips while being consistent with faults. The application of this preconditioning strategy to real and synthetic 2D data sets illustrates how this incremental additional step makes the FWI workflow less sensitive to noise and spatial aliasing artifacts. Nothing prevents a possible 3D acoustic extension, thanks to the small added computer cost for this local filter application. Three-dimensional elastic FWI may require this inexpensive filtering strategy due to the prohibitive forward-modeling costs that could be partially mitigated by using a coarse shot increment in conjunction with gradient preconditioning.
16
Syamsuddin, Erfan, Sabrianto Aswad, Muhammad Alimuddin Hamzah Assegaf, Syamsurijal Rasimeng, Sakka Sakka, Syamsuddin Syamsuddin, Muhammad Nasri e Mufly Fadla Syihab. "Seismic Site Classification Using the Multichannel Analysis of Surface Waves Method". POSITRON 12, n. 2 (30 novembre 2022): 149. http://dx.doi.org/10.26418/positron.v12i2.53869.
Testo completoAbstract (sommario):
The soil has a variety of qualities that affect its ability to support the weight of a structure. One of these features is soil stiffness, which can be determined using the surface wave method to prevent soil collapse. Multichannel Analysis of Surface Waves (MASW) is one of the non-invasive methodologies used in this study to investigate subsurface structures in North Sumatra, Indonesia. This method utilizes the dispersion properties of Rayleigh waves, producing a dispersion curve to get the shear wave velocity (Vs) through inversion. The shear wave velocity can be used to examine the soil stiffness qualities. The dispersion curve explains the relationship between shear wave velocity and depth, which can subsequently be used as a site class parameter. This survey uses three lines with one shot for each line which uses thirty geophones. The seismic source used is a gun with the type M16.38 Cal. Each line consists of 30 geophones with a distance of 5 m. The entire track is 160 m long and lasts for 2048 seconds with a sampling rate of 0.00025 seconds. The average shear wave velocity measured at three measurements was 372.5 m/s on line P1, 347.1 m/s on line P2A, and 311.0 m/s on line P2B, respectively. Overall, the soil classification on the P1 line is class C, and the P2A and P2B lines are class D, which is suitable for development planning areas.
17
Trevithick, Alex, Matthew Chan, Michael Stengel, Eric Chan, Chao Liu, Zhiding Yu, Sameh Khamis, Manmohan Chandraker, Ravi Ramamoorthi e Koki Nagano. "Real-Time Radiance Fields for Single-Image Portrait View Synthesis". ACM Transactions on Graphics 42, n. 4 (26 luglio 2023): 1–15. http://dx.doi.org/10.1145/3592460.
Testo completoAbstract (sommario):
We present a one-shot method to infer and render a photorealistic 3D representation from a single unposed image (e.g., face portrait) in real-time. Given a single RGB input, our image encoder directly predicts a canonical triplane representation of a neural radiance field for 3D-aware novel view synthesis via volume rendering. Our method is fast (24 fps) on consumer hardware, and produces higher quality results than strong GAN-inversion baselines that require test-time optimization. To train our triplane encoder pipeline, we use only synthetic data, showing how to distill the knowledge from a pretrained 3D GAN into a feedforward encoder. Technical contributions include a Vision Transformer-based triplane encoder, a camera data augmentation strategy, and a well-designed loss function for synthetic data training. We benchmark against the state-of-the-art methods, demonstrating significant improvements in robustness and image quality in challenging real-world settings. We showcase our results on portraits of faces (FFHQ) and cats (AFHQ), but our algorithm can also be applied in the future to other categories with a 3D-aware image generator.
18
Aghayan, Afshin, Priyank Jaiswal e Hamid Reza Siahkoohi. "Seismic denoising using the redundant lifting scheme". GEOPHYSICS 81, n. 3 (maggio 2016): V249—V260. http://dx.doi.org/10.1190/geo2015-0601.1.
Testo completoAbstract (sommario):
Separating linear coherent noise, such as ground roll from reflections, remains a key challenge in seismic processing. By adapting the redundant lifting scheme (RLS), a wavelet transform method, to seismic data, we have determined how the wavelet domain can be used to suppress coherent and random noise. The RLS operates on a trace-by-trace basis decomposing each time series into wavelet-coefficient (WC) time series and consequently a single gather (in a shot, receiver, or common depth point domain) into a series of WC subgathers (SGs). The decomposition changes the relative magnitude of WCs of various events (reflection, head wave, ground roll, etc.) from one SG to another without affecting their moveout. In SG(s) in which the WCs of undesired events were significantly stronger than the desired events, the WCs can be surgically muted. Selective muting in carefully chosen SGs attenuates undesired events while having minimal effects on frequency spectra of the desired events. In addition, random noise can be suppressed in the individual SGs by designing a local thresholding mechanism (we have used modified Otsu thresholding) in combination with adaptive Wiener filtering. We have developed this approach of suppressing coherent and random noise in a step-by-step manner first using a synthetic shot gather, followed by demonstration on two real gathers. Our RLS-based denoising method has minimal effects on the lower end of signal frequency spectra, and it could be a valuable tool in a processor’s toolbox when data preconditioning for advanced processing such as waveform inversion, which benefits from low frequencies, is desired.
19
Zhang, Jie, e M. Nafi Toksöz. "Nonlinear refraction traveltime tomography". GEOPHYSICS 63, n. 5 (settembre 1998): 1726–37. http://dx.doi.org/10.1190/1.1444468.
Testo completoAbstract (sommario):
A few important issues for performing nonlinear refraction traveltime tomography have been identified. They include the accuracy of the traveltime and raypath calculations for refraction, the physical information in the refraction traveltime curves, and the characteristics of the refraction traveltime errors. Consequently, we develop a shortest path ray‐tracing method with an optimized node distribution that can calculate refraction traveltimes and raypaths accurately in any velocity model. We find that structure ambiguity caused by short and long rays in the seismic refraction method may influence the inversion solution significantly. Therefore, we pose a nonlinear inverse problem that explicitly minimizes the misfits of the average slownesses (ratios of traveltimes to the corresponding ray lengths) and the apparent slownesses (derivatives of traveltimes with respect to distance). As a result, we enhance the resolution as well as the convergence speed. To regularize our inverse problem, we use the Tikhonov method to avoid solving an ill‐posed inverse problem. Errors in refraction traveltimes are characterized in terms of a common‐shot error, a constant deviation for recordings from the same shot, and a relative traveltime‐gradient error with zero mean with respect to the true gradient of the traveltime curve. Therefore, we measure the uncertainty of our tomography solution using a nonlinear Monte Carlo approach and compute the posterior model covariance associated with two different types of random data vectors and one random model vector. The nonlinear uncertainty analysis indicates that the resolution of a tomography solution may not correspond to the ray coverage. We apply this tomography technique to image the shallow velocity structure at a coastal site near Boston, Massachusetts. The results are consistent with a subsequent drilling survey.
20
Endo, Yuto, Jun Tanida, Makoto Naruse e Ryoichi Horisaki. "Extrapolated Speckle-Correlation Imaging". Intelligent Computing 2022 (30 settembre 2022): 1–8. http://dx.doi.org/10.34133/2022/9787098.
Testo completoAbstract (sommario):
Imaging through scattering media is a longstanding issue in a wide range of applications, including biomedicine, security, and astronomy. Speckle-correlation imaging is promising for noninvasively seeing through scattering media by assuming shift invariance of the scattering process called the memory effect. However, the memory effect is known to be severely limited when the medium is thick. Under such a scattering condition, speckle-correlation imaging is not practical because the correlation of the speckle decays, reducing the field of view. To address this problem, we present a method for expanding the field of view of single-shot speckle-correlation imaging by extrapolating the correlation with a limited memory effect. We derive the imaging model under this scattering condition and its inversion for reconstructing the object. Our method simultaneously estimates both the object and the decay of the speckle correlation based on the gradient descent method. We numerically and experimentally demonstrate the proposed method by reconstructing point sources behind scattering media with a limited memory effect. In the demonstrations, our speckle-correlation imaging method with a minimal lensless optical setup realized a larger field of view compared with the conventional one. This study will make techniques for imaging through scattering media more practical in various fields.
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Billette, Frederic, Soazig Le Bégat, Pascal Podvin e Gilles Lambaré. "Practical aspects and applications of 2D stereotomography". GEOPHYSICS 68, n. 3 (maggio 2003): 1008–21. http://dx.doi.org/10.1190/1.1581072.
Testo completoAbstract (sommario):
Stereotomography is a new velocity estimation method. This tomographic approach aims at retrieving subsurface velocities from prestack seismic data. In addition to traveltimes, the slope of locally coherent events are picked simultaneously in common offset, common source, common receiver, and common midpoint gathers. As the picking is realized on locally coherent events, they do not need to be interpreted in terms of reflection on given interfaces, but may represent diffractions or reflections from anywhere in the image. In the high‐frequency approximation, each one of these events corresponds to a ray trajectory in the subsurface. Stereotomography consists of picking and analyzing these events to update both the associated ray paths and velocity model. In this paper, we describe the implementation of two critical features needed to put stereotomography into practice: an automatic picking tool and a robust multiscale iterative inversion technique. Applications to 2D reflection seismic are presented on synthetic data and on a 2D line extracted from a 3D towed streamer survey shot in West Africa for TotalFinaElf. The examples demonstrate that the method requires only minor human intervention and rapidly converges to a geologically plausible velocity model in these two very different and complex velocity regimes. The quality of the velocity models is verified by prestack depth migration results.
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Deng, Zhuofu, Binbin Wang, Heng Guo, Chengwei Chai, Yanze Wang e Zhiliang Zhu. "Unified Quantile Regression Deep Neural Network with Time-Cognition for Probabilistic Residential Load Forecasting". Complexity 2020 (22 gennaio 2020): 1–18. http://dx.doi.org/10.1155/2020/9147545.
Testo completoAbstract (sommario):
Residential load forecasting is important for many entities in the electricity market, but the load profile of single residence shows more volatilities and uncertainties. Due to the difficulty in producing reliable point forecasts, probabilistic load forecasting becomes more popular as a result of catching the volatility and uncertainty by intervals, density, or quantiles. In this paper, we propose a unified quantile regression deep neural network with time-cognition for tackling this challenging issue. At first, a convolutional neural network with multiscale convolution is devised for extracting more behavioral features from the historical load sequence. In addition, a novel periodical coding method marks the model to enhance its ability of capturing regular load pattern. Then, features generated from both subnetworks are fused and fed into the forecasting model with an end-to-end manner. Besides, a globally differentiable quantile loss function constrains the whole network for training. At last, forecasts of multiple quantiles are directly generated in one shot. With ablation experiments, the proposed model achieved the best results in the AQS, AACE, and inversion error, and especially the average of the AACE is grown by 34.71%, 75.22%, and 32.44% compared with QGBRT, QCNN, and QLSTM, respectively, indicating that our method has excellent reliability and robustness rather than the state-of-the-art models obviously. Meanwhile, great performances of efficient time response demonstrate that our proposed work has promising prospects in practical applications.
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Mi, Binbin, Jianghai Xia, Chao Shen, Limin Wang, Yue Hu e Feng Cheng. "Horizontal resolution of multichannel analysis of surface waves". GEOPHYSICS 82, n. 3 (1 maggio 2017): EN51—EN66. http://dx.doi.org/10.1190/geo2016-0202.1.
Testo completoAbstract (sommario):
The multichannel analysis of surface wave (MASW) method has been effectively and widely used to determine near-surface shear-wave velocity. Horizontal resolution of the MASW method represents the minimum horizontal length of recognizable geologic anomalous bodies on a pseudo-2D S-wave velocity [Formula: see text] section. Accurately assessing the achievable lateral resolution is one of the main issues in lateral variation reconstruction using the MASW method. It is difficult to quantitatively estimate the horizontal resolution of the MASW method because of the many influencing factors, such as parameters of the observation system, the depth of an anomalous body, and the velocity contrast between the anomalous body and the surrounding rocks. We first analyzed the horizontal resolution of the MASW method based on numerical simulation experiments. According to different influencing factors of the horizontal resolution, we established different laterally heterogeneous models and observation systems and then simulated several synthetic multichannel records with a finite-difference method along a linear survey line using the roll-along acquisition mode. After the extraction of dispersion curves of Rayleigh waves and inversion for S-wave velocity profiles for each synthetic shot gather, a pseudo-2D S-wave velocity section can be generated by aligning the 1D S-wave velocity models. Ultimately, we evaluated the horizontal resolution capability of the MASW method on pseudo-2D [Formula: see text] maps. Our numerical investigation results and field data analysis indicate that [Formula: see text] values on the maps are not the same as the true [Formula: see text] values for structures whose lateral dimension is shorter than a receiver spread length and that anomalous bodies, which are larger and have high velocity contrast, are easier to distinguish on [Formula: see text] maps with a shorter receiver spread length. The horizontal resolution decreases with the increasing depth and is approximately one-half of the shortest Rayleigh wavelength that can penetrate to the depth.
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Zwartjes, P., e A. Gisolf. "Fourier reconstruction of marine-streamer data in four spatial coordinates". GEOPHYSICS 71, n. 6 (novembre 2006): V171—V186. http://dx.doi.org/10.1190/1.2348633.
Testo completoAbstract (sommario):
Many methods exist for interpolation of seismic data in one and two spatial dimensions, but few can interpolate properly in three or four spatial dimensions. Marine multi-streamer data typically are sampled relatively well in the midpoint and absolute offset coordinates but not in the azimuth because the crossline shot coordinate is significantly under sampled. We approach the problem of interpolation of marine-streamer data in four spatial dimensions by splitting the problem into a 1D interpolation along the densely sampled streamers and a 3D Fourier reconstruction for the remaining spatial coordinates. In Fourier reconstruction, the Fourier coefficients that synthesize the nonuniformly sampled seismic data are estimated in a least-squares inversion. The method is computationally efficient, requires no subsurface information, and can handle uniform grids with missing data as well as nonuniform grids or random sampling. The output grid of the 1D interpolation in the first step is arbitrary. When the output grid has uniform inline midpoints spacing, the 3D Fourier reconstruction in the second step is performed in the crossline midpoint, absolute offset, and azimuth coordinates. When the first step outputs to uniform absolute offset, the 3D Fourier reconstruction handles the crossline/inline midpoint and the azimuth coordinates. In both cases, the main innovation is the inclusion of the azimuthal coordinate in the Fourier reconstruction. The azimuth multiplicity must be increased for the method to be successful, which means that overlap shooting is required. We have tested the algorithm on synthetic streamer data for which the proposed method outperforms an approach where the azimuthal coordinate is ignored. Potential applications are interpolation of marine streamer data to decrease the crossline source sampling for the benefit of 3D multiple prediction and regularization to reduce sampling-related differences in processing of time-lapse data.
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Li, Siwei, Alexander Vladimirsky e Sergey Fomel. "First-break traveltime tomography with the double-square-root eikonal equation". GEOPHYSICS 78, n. 6 (1 novembre 2013): U89—U101. http://dx.doi.org/10.1190/geo2013-0058.1.
Testo completoAbstract (sommario):
First-break traveltime tomography is based on the eikonal equation. Because the eikonal equation is solved at fixed-shot positions and only receiver positions can move along the raypath, the adjoint-state tomography relies on inversion to resolve possible contradicting information between independent shots. The double-square-root (DSR) eikonal equation allows not only the receivers but also the shots to change position, and thus describes the prestack survey as a whole. Consequently, its linearized tomographic operator naturally handles all shots together, in contrast with the shotwise approach in the traditional eikonal-based framework. The DSR eikonal equation is singular for the horizontal waves, which require special handling. Although it is possible to recover all branches of the solution through postprocessing, our current forward modeling and tomography focuses on the diving wave branch only. We consider two upwind discretizations of the DSR eikonal equation and show that the explicit scheme is only conditionally convergent and relies on nonphysical stability conditions. We then prove that an implicit upwind discretization is unconditionally convergent and monotonically causal. The latter property makes it possible to introduce a modified fast matching method thus obtaining first-break traveltimes efficiently and accurately. To compare the new DSR eikonal-based tomography and traditional eikonal-based tomography, we perform linearizations and apply the same adjoint-state formulation and upwind finite-differences implementation to both approaches. Synthetic model examples justify that the proposed approach converges faster and is more robust than the traditional one.
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Frazer, L. Neil, e Xinhua Sun. "New objective functions for waveform inversion". GEOPHYSICS 63, n. 1 (gennaio 1998): 213–22. http://dx.doi.org/10.1190/1.1444315.
Testo completoAbstract (sommario):
Inversion is an organized search for parameter values that maximize or minimize an objective function, referred to here as a processor. This note derives three new seismic processors that require neither prior deconvolution nor knowledge of the source‐receiver wavelet. The most powerful of these is the fourwise processor, as it is applicable to data sets from multiple shots and receivers even when each shot has a different unknown signature and each receiver has a different unknown impulse response. Somewhat less powerful than the fourwise processor is the pairwise processor, which is applicable to a data set consisting of two or more traces with the same unknown wavelet but possibly different gains. When only one seismogram exists the partition processor can be used. The partition processor is also applicable when there is only one shot (receiver) and each receiver (shot) has a different signature. In fourwise and pairwise inversions the unknown wavelets may be arbitrarily long in time and need not be minimum phase. In partition inversion the wavelet is assumed to be shorter in time than the data trace itself but is not otherwise restricted. None of the methods requires assumptions about the Green’s function.
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Tura, M. Ali C., Robert J. Greaves e Wafik B. Beydoun. "Crosswell seismic reflection/diffraction tomography: A reservoir characterization application". GEOPHYSICS 59, n. 3 (marzo 1994): 351–61. http://dx.doi.org/10.1190/1.1443597.
Testo completoAbstract (sommario):
A crosswell seismic experiment at the San Emidio oil field in Bakersfield, California, is carried out to evaluate crosswell reflection/diffraction tomography and image the interwell region to locate a possible pinchout zone. In this experiment, the two wells used are 2500 ft (762 m) apart, and the zone to be imaged is 11 000 ft (3350 m) to 13 000 ft (3960 m) deep. With the considered distances, this experiment forms the first large scale reservoir characterization application of crosswell reflection/diffraction tomography. A subset of the intended data, formed of two common receiver gathers and one common shot gather, was collected at the San Emidio oil field. The crosswell data display a wide variety of wave modes including tube waves, singly and multiply reflected/diffracted waves, and refracted waves. The data are processed using frequency filters, median filters, and spatial muting filters to enhance the reflected/diffracted energy. A 2-D layered velocity model with gradients is built using zero‐offset VSPs and full‐waveform acoustic logs from the two wells. This model is used to generate synthetic finite‐difference data for the field data acquisition geometry. The synthetic data are processed and imaged using the elastic ray‐Born 𝓁2-migration/inversion (ERBMI) method. A smooth 2-D velocity model incorporating only gradients and a few layers is used as a background model for the imaging. Considering the limited data acquisition geometry, synthetic data images compare favorably with the initial velocity model. With the encouraging results obtained from synthetic data, the ERBMI method, with the smooth background velocity model is used next to image the processed field data. Images obtained from the crosswell data show a good match with the reflected field in the zero‐offset VSPs and with migrated surface seismic data. From the interpretation of these images, the potential of this crosswell seismic method for answering questions regarding reservoir continuity and existence of pinchout zones can be seen.
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Sjöberg, Lars E., e Majid Abrehdary. "The uncertainty of CRUST1.0". Journal of Applied Geodesy 15, n. 2 (23 febbraio 2021): 143–52. http://dx.doi.org/10.1515/jag-2020-0049.
Testo completoAbstract (sommario):
Abstract As crustal structure models based on seismic and other data are frequently used as a-priori information for further geophysical and geological studies and interpretations (e. g., for gravity inversion), it is important to accurately document their qualities. For instance, the uncertainties in published crustal structures deeply affect the accuracies of produced Moho contour maps. The qualities in seismic crustal models arise from several factors such as the survey method, the spatial resolution of the survey (for example the spacing of the shot points and the recording stations), and the analytical techniques utilized to process the data. It is difficult to determine the uncertainties associated with seismic based crustal depth/Moho depth (MD) models, and even more difficult to use such data for estimating the Moho density contrast (MDC) and its accuracy. However, there is another important observable available today, namely global satellite gravitational data, which are fairly homogeneous v. r. t. accuracy and distribution over the planet. For instance, we find by simple error propagation, using the error covariance matrix of the GOCE TIM5 gravitational model, that this model can determine the MD to a global RMS error of 0.8 km with a resolution of about 1° for a known MDC of 200 kg / m 3 \text{kg}/{\text{m}^{3}} . However, the uncertainty in the MDC will further deteriorate the result. We present a new method for estimating the MD and MDC uncertainties of one model by comparing it with another (correlated or uncorrelated) model with known uncertainty. The method is applied in estimating the uncertainty for the CRUST1.0 MD model from four global models (CRUST19, MDN07, GEMMA1.0, KTH15C), yielding mean standard errors varying between 2 and 4.9 km in ocean regions and between 3.2 and 6.0 km on land regions with overall means of 3.8±0.4 and 4.8 ± 0.6 km 4.8\pm 0.6\hspace{0.1667em}\text{km} , respectively. Also, starting from the KTH15C MDC model, the mean standard error of CRUST1.0 MDC was estimated to 47.4 and 48.3 kg / m 3 \text{kg}/{\text{m}^{3}} for ocean and land regions, respectively.
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Ibrahim, Amr, Paolo Terenghi e Mauricio D. Sacchi. "Simultaneous reconstruction of seismic reflections and diffractions using a global hyperbolic Radon dictionary". GEOPHYSICS 83, n. 6 (1 novembre 2018): V315—V323. http://dx.doi.org/10.1190/geo2017-0655.1.
Testo completoAbstract (sommario):
We have developed a new transform with basis functions that closely resemble seismic reflections and diffractions. The new transform is an extension of the classic hyperbolic Radon transform and accounts for the apex shifts of the seismic reflection hyperbolas and the asymptote shifts of the seismic diffraction hyperbolas. The adjoint and forward operators of the proposed transform are computed using Stolt operators in the frequency domain to increase the computational efficiency of the transform. This new transform is used, in conjunction with a sparse inversion algorithm, to reconstruct common-shot gathers. Our tests indicate that this new transform is an efficient tool for interpolating coarsely sampled seismic data in cases in which one cannot use small data windows to validate the linear event assumption that is often made by Fourier-based reconstruction methods.
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Yan, Cui, Junjiao Hu, Yanyu Li, Xingzhi Xie, Zhimin Zou, Qiyu Deng, Xiaoyue Zhou, Xiaoming Bi, Mu Zeng e Jun Liu. "Motion-corrected free-breathing late gadolinium enhancement combined with a gadolinium contrast agent with a high relaxation rate: an optimized cardiovascular magnetic resonance examination protocol". Journal of International Medical Research 48, n. 10 (ottobre 2020): 030006052096466. http://dx.doi.org/10.1177/0300060520964664.
Testo completoAbstract (sommario):
Objective This prospective study investigated the feasibility of an optimized cardiovascular magnetic resonance (CMR) examination protocol using the motion-corrected (MOCO), balanced steady-state free precession (bSSFP), phase-sensitive inversion recovery (PSIR) sequence combined with a gadolinium contrast agent with a high relaxation rate in patients who cannot hold their breath. Methods Fifty-one patients with heart disease underwent CMR examinations twice and these were performed with different late gadolinium enhancement (LGE) imaging sequences (fast low-angle shot [FLASH] sequence vs. MOCO sequence) and different gadolinium contrast agents (gadopentetate dimeglumine vs. gadobenate dimeglumine) with a 48-hour interval. LGE image quality, total time spent in the whole study, and time taken to perform LGE imaging were compared for the two CMR examinations. Results LGE images with the MOCO bSSFP PSIR sequence showed significantly higher image quality compared with those with the segmented FLASH PSIR sequence. There was a significant difference between the total scan time for the two examinations and different LGE sequences. Conclusions The MOCO bSSFP PSIR sequence effectively improves the quality of LGE images. Changing the CMR scanning protocol by combining the MOCO bSSFP PSIR sequence with a gadolinium contrast agent with a high relaxation rate effectively shortens the scan time. Clinical trial registration number: ChiCTR-ROC-17013978.
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Langston, Charles A., e Mehari Melak Ayele. "Vertical seismic wave gradiometry: Application at the San Andreas Fault Observatory at Depth". GEOPHYSICS 81, n. 3 (maggio 2016): D233—D243. http://dx.doi.org/10.1190/geo2015-0404.1.
Testo completoAbstract (sommario):
We have developed vertical seismic wave gradiometry (VSWG) to estimate velocity, impedance, and attenuation structure in the vicinity of boreholes using borehole array waveforms of check-shot explosions near the borehole head. We have extended wave gradiometry (WG) theory from a purely local relation of the wavefield and wavefield spatial gradient to one that incorporated the ray ansatz over the length of the borehole for a traveling wave in a vertically inhomogeneous medium. We checked the ray assumption against acoustic full-wave synthetic seismograms, and it was found to yield robust measures of the medium velocity. Anelastic attenuation and impedance structure trade off, but in cases of high anelastic attenuation, realistic bounds can be placed on the seismic impedance that effectively constrains the average attenuation. We have applied these methods to data collected at the San Andreas Fault Observatory at Depth borehole in central California in 2005, and we found that the WG velocity estimate agreed well with the borehole acoustic log and previously determined vertical seismic profile results based on traveltime analysis except at the bottom of the hole, where refraction on a near-vertical fault affected the data. The average [Formula: see text] is approximately 20 in the frequency band of 10–30 Hz, and it is required to yield realistic values of impedance in the local medium. Application of VSWG yields appropriate, smoothed velocity models that can be used as an end product or as a starting model for full-wave inversion.
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Hall, Walter A., Haiying Liu, Alastair J. Martin, Robert E. MAxwell e Charles L. Truwit. "Brain biopsy sampling by using prospective stereotaxis and a trajectory guide". Journal of Neurosurgery 94, n. 1 (gennaio 2001): 67–71. http://dx.doi.org/10.3171/jns.2001.94.1.0067.
Testo completoAbstract (sommario):
Object. The authors describe their initial results obtained using a skull-mounted trajectory guide for intraoperative magnetic resonance (MR) imaging—guided brain biopsy sampling. The device was used in conjunction with a new methodology known as prospective stereotaxis for surgical trajectory alignment. Methods. Between January 1999 and March 2000, 38 patients underwent 40 brain biopsy procedures in which prospective stereotaxis was performed with the trajectory guide in a short-bore 1.5-tesla MR imager. In most cases, orthogonal T2-weighted half-Fourier acquisition single-shot turbo spin—echo (HASTE) images were used to determine the desired trajectory and align the device. The surgical trajectory was defined as a line connecting three points: the target, pivot, and alignment stem points. In all cases, surgical specimens were submitted for frozen section and pathological examination. Postoperative turbofluid-attenuated inversion-recovery and gradient-echo images were obtained to exclude the presence of hemorrhage. Trajectory determination and alignment was simple and efficient, requiring less than 5 minutes. Confirmatory HASTE images were obtained along the biopsy needle as it was being advanced or after reaching the target. All biopsy procedures yielded diagnostic tissue. One patient with a lesion near the motor strip experienced a transient hemiparesis of the hand related to passage of the biopsy needle, and another sustained a fatal postoperative myocardial infarction. No patient suffered a clinically significant or radiologically visible hemorrhage. Conclusions. In combination with prospective stereotaxis, the trajectory guide provided a safe and accurate way to perform brain biopsy procedures.
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de Bruin, C. G. M., C. P. A. Wapenaar e A. J. Berkhout. "Angle‐dependent reflectivity by means of prestack migration". GEOPHYSICS 55, n. 9 (settembre 1990): 1223–34. http://dx.doi.org/10.1190/1.1442938.
Testo completoAbstract (sommario):
Most present day seismic migration schemes determine only the zero‐offset reflection coefficient for each grid point (depth point) in the subsurface. In matrix notation, the zero‐offset reflection coefficient is found on the diagonal of a reflectivity matrix operator that transforms the illuminating source‐wave field into a reflected‐wave field. However, angle dependent reflectivity information is contained in the full reflectivity matrix. Our objective is to obtain angle‐dependent reflection coefficients from seismic data by means of prestack migration (multisource, multioffset). After downward extrapolation of source and reflected wave fields to one depth level, the rows of the reflectivity matrix (representing angle‐dependent reflectivity information for each grid point at that depth level) are recovered by deconvolving the reflected wave fields with the related source wave fields. This process is carried out in the space‐frequency domain. In order to preserve the angle‐dependent reflectivity in the imaging we must not only add all frequency contributions but we should extend the imaging principle by adding along lines of constant angle in the wavenumber‐frequency domain. This procedure is carried out for each grid point. The resulting amplitude information provides a rigorous approach to amplitude‐versus‐offset related methods. The new imaging technique has been tested on media with horizontal layers. However, with our shot‐record oriented algorithm it is possible to handle any subsurface geometry. The first tests show excellent results up to high angles, both in the acoustic and in the elastic case. With angle‐dependent reflectivity information it becomes feasible to derive detailed velocity and density information in a subsequent stratigraphic inversion step.
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Carpenter, Chris. "Sub-Basalt Imaging Reveals Deeper Plays Offshore India". Journal of Petroleum Technology 73, n. 02 (1 febbraio 2021): 66–67. http://dx.doi.org/10.2118/0221-0066-jpt.
Testo completoAbstract (sommario):
This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 30279, “Revealing Deeper Plays, Offshore Kutch, India: A Success Story of Sub-Basalt Imaging,” by S.K. Biswal, N.N.B. Naidu, and S. Basu, ONGC, et al., prepared for the 2020 Offshore Technology Conference Asia, originally scheduled to be held in Kuala Lumpur, 2-6 November. The paper has not been peer reviewed. Copyright 2020 Offshore Technology Conference. Reproduced by permission. The Deccan Traps volcanic province of India is considered one of the largest basalt-covered regions in the world but is essentially unexplored because of the limitations of conventional marine streamer P-wave seismic acquisition in imaging structures both intrabasalt and sub-basalt. In the complete paper, the authors demonstrate that, even with legacy marine streamer surveys, an appropriate work flow of combining suitable advanced technologies can help to overcome the long-standing challenges of sub-basalt imaging. The reprocessed data show clear uplift in sub-basalt imaging, and inversion results validate the quality of the new data in relation to the well logs. Introduction The Kutch offshore basin is characterized by the presence of the Deccan Traps, a large igneous province of up to 2000-m-thick basalt lava flows. These lava flows have hindered successful imaging of sub-basalt Mesozoic sediments for hydrocarbon exploration. To date, no single technique has been found to produce considerable improvements in deeper image quality. The solution lies in an appropriate combination of advanced technologies. The project consists of three legacy data sets acquired in 2004, 2010, and 2014 in the shallow-water area (water depth ranges from 25 to 50 m). Two of the surveys were shot in the north/south direction with six streamers having 100-m separation, 25-m shot spacing, 12.5-m receiver spacing, and 6-second record length. The third survey was acquired oblique to these with a similar acquisition geometry; however, it featured sparser 25-m receiver spacing and 8- second record length. These surveys were matched and merged before migration to ensure a seamless image across the surveys in the post-migration domain. A tailored processing work flow improved existing data quality significantly and provided new insights into the sub-basalt geology, thereby opening a new play to exploration and production. Challenges and Work Flow Sub-basalt imaging challenges include transmission losses, scattering, complex wave kinematics, prevalent multiples, interference effects, and variable illumination caused by high and variable acoustic impedance of thick heterogeneous basalt layers. The tertiary sedimentary sequences overlying the Deccan Trap consist predominantly of carbonates, shale, and fine-grained clastic sediments, accompanied by channels and nearly vertical faulting. The geological complexities from the water bottom to the base of the basalt present a substantial geophysical challenge to successful deeper imaging and require an appropriate work flow to mitigate them. Broadband processing, including de-ghosting, can increase the signal-to-noise ratio across the broad range of frequencies in the seismic bandwidth and can enhance the lower frequencies required to achieve enhanced imaging at sub-basalt targets. Demultiple methods can reduce the presence of surface-related and interbed multiples that prohibit reliable interpretation of Mesozoic sediment; imaging methods can focus the recorded data when used in conjunction with an accurate Earth model that captures the velocity complexities of carbonates, shale, basalt, channel, and faults.
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Rusconi, Chiara, Erika Ravelli, Livio Gargantini, Francesca Ganguzza, Denis Ciapanna, Cristiana Ticca, Mauro Turrini, Gianbattista Bertani, Angelo Vanzulli e Enrica Morra. "Skeletal Involvement in Advanced Stage Lymphomas: Role of Total Body Magnetic Resonance." Blood 110, n. 11 (16 novembre 2007): 4405. http://dx.doi.org/10.1182/blood.v110.11.4405.4405.
Testo completoAbstract (sommario):
Abstract Introduction: Skeletal localizations is reported in approximately 10–20% of cases of advanced stage malignant lymphomas. Detection of osseous involvement can change clinical stage and consequently determine the choice of treatment. Computed tomography (CT) is considered the gold standard for lymphoma staging and evaluation of treatment response; this technique, however, has a limited sensitivity in identifying extra-nodal disease, especially skeletal localizations. Positron emission tomography (PET) using fluorine-18 (FDG) has a higher sensitivity in recognizing bone involvement and is now a well-recognized diagnostic tool, complementary to CT. Total body magnetic resonance (MR) may rapresent a useful technique for detection and better characterization of tumoral bone lesions. In this report total body MR is compared with conventional imaging procedures (CT and PET) in the evaluation of Hodgkin (HL) and non Hodgkin lymphomas (NHL) with suspected skeletal involvement. Patients and methods: In the last year, 4 patients with diagnosis of HL, and 8 patients with diffuse large B cell lymphoma, with clinical signs or radiological findings suggesting skeletal involvement, underwent total body MR in addiction to standard staging techniques (CT and PET). All patients showed at diagnosis a systemic disease with nodal involvement. Total body MR was performed with a body coil (1.5 Tesla) and images were obtained by using fast spin-echo (FSE) short time inversion recovery (STIR) and spin-echo single-shot (SE-EPI-SSH) sequences diffusion weighted. MR was performed at diagnosis in 6 cases, at restaging in 4 cases and in two cases both at the onset and after treatment, for a total of 14 examinations. MR images were compared with those obtained from conventional imaging performed at the same time. Results: At diagnosis a total of 8 MR were performed, and multifocal skeletal involvement was detected in all cases. On the contrast, CT was negative in 6/8 cases, showing a lower sensitivity (25% vs. 100%); moreover, when positive (2/8 cases), CT detected a lower number of osseous localizations. PET was performed at diagnosis in 5 patients and resulted positive in 4 cases, identifying a minor extension of osseous involvement. At restaging 6 MR were performed: in 4 cases no skeletal lesions were detected, accordingly to CT and PET results, confirming the complete remission obtained after treatment. In the remaining two patients MR was persistently positive at restaging. PET showed a concordant result in one of these two cases, but detected less sites of involvement. Discussion: These data suggest that total body MR may play a role in investigating patients affected by malignant lymphoma with suspected skeletal involvement. FSE-STIR and SE-EPI-SSH sequences diffusion weighted can accurately detect and characterize the hyper-intensity of lymphoma bone lesions. On the contrary, CT sensitivity was very low for skeletal involvement (25%); it derives that this technique alone is unable to correctly evaluate disease extension, possibly resulting in patients under-treatment. PET findings regarding skeletal involvement are often concordant with total body MR, but a lower number of bone lesions is detected in the majority of cases.
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Huaroc Moquillaza, Elizabeth, Kilian Weiss, Jonathan Stelter, Lisa Steinhelfer, Yoo Jin Lee, Thomas Amthor, Peter Koken et al. "Accelerated liver water T1 mapping using single‐shot continuous inversion‐recovery spiral imaging". NMR in Biomedicine, 25 gennaio 2024. http://dx.doi.org/10.1002/nbm.5097.
Testo completoAbstract (sommario):
PurposeLiver T1 mapping techniques typically require long breath holds or long scan time in free‐breathing, need correction for inhomogeneities and process composite (water and fat) signals. The purpose of this work is to accelerate the multi‐slice acquisition of liver water selective T1 (wT1) mapping in a single breath hold, improving the k‐space sampling efficiency.MethodsThe proposed continuous inversion‐recovery (IR) Look‐Locker methodology combines a single‐shot gradient echo spiral readout, Dixon processing and a dictionary‐based analysis for liver wT1 mapping at 3 T. The sequence parameters were adapted to obtain short scan times. The influence of fat, inhomogeneities and TE on the estimation of T1 was first assessed using simulations. The proposed method was then validated in a phantom and in 10 volunteers, comparing it with MRS and the modified Look‐Locker inversion‐recovery (MOLLI) method. Finally, the clinical feasibility was investigated by comparing wT1 maps with clinical scans in nine patients.ResultsThe phantom results are in good agreement with MRS. The proposed method encodes the IR‐curve for the liver wT1 estimation, is minimally sensitive to inhomogeneities and acquires one slice in 1.2 s. The volunteer results confirmed the multi‐slice capability of the proposed method, acquiring nine slices in a breath hold of 11 s. The present work shows robustness to inhomogeneities ( , good repeatability ( and is in better agreement with MRS ( than is MOLLI ( . The wT1 maps in patients captured diverse lesions, thus showing their clinical feasibility.ConclusionA single‐shot spiral acquisition can be combined with a continuous IR Look‐Locker method to perform rapid repeatable multi‐slice liver water T1 mapping at a rate of 1.2 s per slice without a map. The proposed method is suitable for nine‐slice liver clinical applications acquired in a single breath hold of 11 s.
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Wang, Kunxi, Tianyue Hu e Shangxu Wang. "An unsupervised learning approach to deblend seismic data from denser shot coverage surveys". Geophysical Journal International, 15 giugno 2022. http://dx.doi.org/10.1093/gji/ggac222.
Testo completoAbstract (sommario):
Summary The simultaneous source data obtained by simultaneous source acquisition contain crosstalk noise and cannot be directly used in conventional data processing procedures. Therefore, it is necessary to deblend the blended wavefield to obtain the conventionally acquired single-shot recordings. In this study, we propose an iterative inversion method based on the unsupervised deep neural network (UDNN) to deblend the simultaneous source data from a denser shot coverage survey (DSCS). In the common receiver gather (CRG), the coherent effective signals in the blended data of the primary and secondary sources are similar. We exploit the excellent nonlinear optimization capability of the U-net network to extract similar coherent signals from the blended data of the primary and secondary sources by minimizing the total loss function. The proposed UDNN method does not need to use the raw unblended data as label data, which solves the problem of missing label data and is suitable for deblending the simultaneous source data in different work areas with complex underground structures. One synthetic data and one field data examples are used to prove that the proposed method can suppress crosstalk noise and protect weak effective signals effectively, and achieve good effectiveness for the separation of simultaneous source data.
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Wang, Kunxi, Tianyue Hu e Shangxu Wang. "Iterative deblending using unsupervised learning with double deep neural networks". GEOPHYSICS, 23 gennaio 2023, 1–76. http://dx.doi.org/10.1190/geo2022-0299.1.
Testo completoAbstract (sommario):
Simultaneous source acquisition technology can greatly improve seismic acquisition efficiency. However, due to continuous shooting and serious crosstalk noise of the adjacent sources in seismic data, simultaneous source data cannot be directly used in conventional data processing procedures. Therefore, simultaneous source data need to be deblended to obtain the conventional shot record. Under densely sampled sources (DSSs), we propose a novel unsupervised deep learning (UDL) method based on the double deep neural networks (DDNNs) for iterative inversion deblending of simultaneous source data. The proposed UDL, which is mainly composed of the residual neural network (R-net) and the U-net neural network, has excellent nonlinear optimization ability. The total loss function designed in this study can optimize the proposed UDL in the right direction and avoid the problem of overfitting. By minimizing the total loss function, the R-net and U-net branches of UDL can extract the coherent effective signals of all sources and suppress the crosstalk noise. The most prominent advantage of our proposed UDL method is that it does not require label data, and the training dataset does not contain raw unblended data, thus solving the problem of missing training datasets. The examples with two synthetic data and one field data are used to prove the effectiveness of iterative inversion deblending of simultaneous source data based on our proposed UDL method when sources are within a small distance of each other. By comparing our proposed UDL method with the traditional Curvelet-based and Contourlet-based methods, the superiority of our proposed method in the quality of separation results is demonstrated.
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Zhao, Mingyue, Daming Shen, Lexiaozi Fan, Kyungpyo Hong, Li Feng, Brandon C. Benefield, Bradley D. Allen, Daniel C. Lee e Daniel Kim. "Incorporation of view sharing and KWIC filtering into GRASP‐Pro improves spatial resolution of single‐shot, multi‐TI, late gadolinium enhancement MRI". NMR in Biomedicine, 24 ottobre 2023. http://dx.doi.org/10.1002/nbm.5059.
Testo completoAbstract (sommario):
AbstractWhile single‐shot late gadolinium enhancement (LGE) is useful for imaging patients with arrhythmia and/or dyspnea, it produces low spatial resolution. One approach to improve spatial resolution is to accelerate data acquisition using compressed sensing (CS). Our previous work described a single‐shot, multi‐inversion time (TI) LGE pulse sequence using radial k‐space sampling and CS, but over‐regularization resulted in significant image blurring that muted the benefits of data acceleration. The purpose of the present study was to improve the spatial resolution of the single‐shot, multi‐TI LGE pulse sequence by incorporating view sharing (VS) and k‐space weighted contrast (KWIC) filtering into a GRASP‐Pro reconstruction. In 24 patients (mean age = 61 ± 16 years; 9/15 females/males), we compared the performance of our improved multi‐TI LGE and standard multi‐TI LGE, where clinical standard LGE was used as a reference. Two clinical raters independently graded multi‐TI images and clinical LGE images visually on a five‐point Likert scale (1, nondiagnostic; 3, clinically acceptable; 5, best) for three categories: the conspicuity of myocardium or scar, artifact, and noise. The summed visual score (SVS) was defined as the sum of the three scores. Myocardial scar volume was quantified using the full‐width at half‐maximum method. The SVS was not significantly different between clinical breath‐holding LGE (median 13.5, IQR 1.3) and multi‐TI LGE (median 12.5, IQR 1.6) (P = 0.068). The myocardial scar volumes measured from clinical standard LGE and multi‐TI LGE were strongly correlated (coefficient of determination, R2 = 0.99) and in good agreement (mean difference = 0.11%, lower limit of the agreement = −2.13%, upper limit of the agreement = 2.34%). The inter‐rater agreement in myocardial scar volume quantification was strong (intraclass correlation coefficient = 0.79). The incorporation of VS and KWIC into GRASP‐Pro improved spatial resolution. Our improved 25‐fold accelerated, single‐shot LGE sequence produces clinically acceptable image quality, multi‐TI reconstruction, and accurate myocardial scar volume quantification.
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Avram, Alexandru V., Joelle E. Sarlls e Peter J. Basser. "Whole-Brain Imaging of Subvoxel T1-Diffusion Correlation Spectra in Human Subjects". Frontiers in Neuroscience 15 (11 giugno 2021). http://dx.doi.org/10.3389/fnins.2021.671465.
Testo completoAbstract (sommario):
T1 relaxation and water mobility generate eloquent MRI tissue contrasts with great diagnostic value in many neuroradiological applications. However, conventional methods do not adequately quantify the microscopic heterogeneity of these important biophysical properties within a voxel, and therefore have limited biological specificity. We describe a new correlation spectroscopic (CS) MRI method for measuring how T1 and mean diffusivity (MD) co-vary in microscopic tissue environments. We develop a clinical pulse sequence that combines inversion recovery (IR) with single-shot isotropic diffusion encoding (IDE) to efficiently acquire whole-brain MRIs with a wide range of joint T1-MD weightings. Unlike conventional diffusion encoding, the IDE preparation ensures that all subvoxel water pools are weighted by their MDs regardless of the sizes, shapes, and orientations of their corresponding microscopic diffusion tensors. Accordingly, IR-IDE measurements are well-suited for model-free, quantitative spectroscopic analysis of microscopic water pools. Using numerical simulations, phantom experiments, and data from healthy volunteers we demonstrate how IR-IDE MRIs can be processed to reconstruct maps of two-dimensional joint probability density functions, i.e., correlation spectra, of subvoxel T1-MD values. In vivo T1-MD spectra show distinct cerebrospinal fluid and parenchymal tissue components specific to white matter, cortical gray matter, basal ganglia, and myelinated fiber pathways, suggesting the potential for improved biological specificity. The one-dimensional marginal distributions derived from the T1-MD correlation spectra agree well with results from other relaxation spectroscopic and quantitative MRI studies, validating the T1-MD contrast encoding and the spectral reconstruction. Mapping subvoxel T1-diffusion correlations in patient populations may provide a more nuanced, comprehensive, sensitive, and specific neuroradiological assessment of the non-specific changes seen on fluid-attenuated inversion recovery (FLAIR) and diffusion-weighted MRIs (DWIs) in cancer, ischemic stroke, or brain injury.
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Sun, Jiaxing, Jidong Yang, Zhenchun Li, Jianping Huang, Jie Xu e Subin Zhuang. "Reflection and diffraction separation in the dip-angle common-image gathers using convolutional neural network". GEOPHYSICS, 24 ottobre 2022, 1–76. http://dx.doi.org/10.1190/geo2022-0157.1.
Testo completoAbstract (sommario):
In exploration seismology, reflections have been extensively used for imaging and inversion to detect hydrocarbon and mine resources, which are generated from subsurface continuous impedance interfaces. When the interface is not continuous and its size reduces to less than half wavelength, reflected wave becomes diffraction. Both reflections and diffractions can be used to image subsurface targets, and the latter is helpful to resolve small-scale discontinuities, such as fault plane, pinch-out, Karst caves and salt edge. However, the amplitudes of diffractions are usually much weaker than that of reflections. This makes it difficult to directly identify and extract diffractions from unmigrated common-shot or common-middle-point gathers. Integrating over opening-angle for constant reflector dip can produce a common-image gather in the dip-angle domain (DACIG). One DACIG represents the migrated traces at a fixed lateral position for different reflector dips. The reflection and diffraction have different geometrical characteristics in DACIG, which provides one opportunity to separate diffractions and reflections. In this study, we present an efficient and accurate diffraction separation and imaging method using convolutional neural network (CNN). The training dataset of DACIGs are generated using one pass of seismic modeling and migration for velocity models with and without artificial scatterers. Then, a simplified end-to-end CNN is trained to identify and extract reflections from the migrated DACIGs that contain both reflections and diffractions. Next, two adaptive subtraction strategies are presented to compute the diffraction DACIGs and stacked images, respectively. Numerical experiments for Marmousi-II and Sigsbee 2A models demonstrate that the proposed method can produce accurate reflection and diffraction separation results in DACIGs, and the stacked image shows a good resolution for subsurface small-scale discontinuities.
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Reddy, Vivek Y., Elad Anter, Gediminas Rackauskas, Petr Peichl, Jacob S. Koruth, Jan Petru, Moritoshi Funasako et al. "Lattice-Tip Focal Ablation Catheter That Toggles Between Radiofrequency and Pulsed Field Energy to Treat Atrial Fibrillation". Circulation: Arrhythmia and Electrophysiology 13, n. 6 (giugno 2020). http://dx.doi.org/10.1161/circep.120.008718.
Testo completoAbstract (sommario):
Background: The tissue selectivity of pulsed field ablation (PFA) provides safety advantages over radiofrequency ablation in treating atrial fibrillation. One-shot PFA catheters have been shown capable of performing pulmonary vein isolation, but not flexible lesion sets such as linear lesions. A novel lattice-tip ablation catheter with a compressible 9-mm nitinol tip is able to deliver either focal radiofrequency ablation or PFA lesions, each in 2 to 5 s. Methods: In a 3-center, single-arm, first-in-human trial, the 7.5F lattice catheter was used with a custom mapping system to treat paroxysmal or persistent atrial fibrillation. Toggling between energy sources, point-by-point pulmonary vein encirclement was performed using biphasic PFA posteriorly and either temperature-controlled irrigated radiofrequency ablation or PFA anteriorly (RF/PF or PF/PF, respectively). Linear lesions were created using either PFA or radiofrequency ablation. Results: The 76-patient cohort included 55 paroxysmal and 21 persistent atrial fibrillation patients undergoing either RF/PF (40 patients) or PF/PF (36 patients) ablation. The pulmonary vein isolation therapy duration time (transpiring from first to last lesion) was 22.6±8.3 min/patient, with a mean of 50.1 RF/PF lesions/patient. Linear lesions included 14 mitral (4 RF/2 RF+PF/8 PF), 34 left atrium roof (12 RF/22 PF), and 44 cavotricuspid isthmus (36 RF/8 PF) lines, with therapy duration times of 5.1±3.5, 1.8±2.3, and 2.4±2.1 min/patient, respectively. All lesion sets were acutely successful, using 4.7±3.5 minutes of fluoroscopy. There were no device-related complications, including no strokes. Postprocedure esophagogastroduodenoscopy revealed minor mucosal thermal injury in 2 of 36 RF/PF and 0 of 24 PF/PF patients. Postprocedure brain magnetic resonance imaging revealed diffusion-weighted imaging+/fluid-attenuated inversion recovery- and diffusion-weighted imaging+/fluid-attenuated inversion recovery+ asymptomatic lesions in 5 and 3 of 51 patients, respectively. Conclusions: A novel lattice-tip catheter could safely and rapidly ablate atrial fibrillation using either a combined RF/PF approach (capitalizing on the safety of PFA and the years of experience with radiofrequency energy) or an entirely PF approach. Registration: URL: https://www.clinicaltrials.gov ; Unique identifiers: NCT04141007 and NCT04194307.
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Gröschel, Jan, Ralf-Felix Trauzeddel, Maximilian Müller, Florian von Knobelsdorff-Brenkenhoff, Darian Viezzer, Thomas Hadler, Edyta Blaszczyk, Elias Daud e Jeanette Schulz-Menger. "Multi-site comparison of parametric T1 and T2 mapping: healthy travelling volunteers in the Berlin research network for cardiovascular magnetic resonance (BER-CMR)". Journal of Cardiovascular Magnetic Resonance 25, n. 1 (14 agosto 2023). http://dx.doi.org/10.1186/s12968-023-00954-9.
Testo completoAbstract (sommario):
Abstract Background Parametric mapping sequences in cardiovascular magnetic resonance (CMR) allow for non-invasive myocardial tissue characterization. However quantitative myocardial mapping is still limited by the need for local reference values. Confounders, such as field strength, vendors and sequences, make intersite comparisons challenging. This exploratory study aims to assess whether multi-site studies that control confounding factors provide first insights whether parametric mapping values are within pre-defined tolerance ranges across scanners and sites. Methods A cohort of 20 healthy travelling volunteers was prospectively scanned at three sites with a 3 T scanner from the same vendor using the same scanning protocol and acquisition scheme. A Modified Look-Locker inversion recovery sequence (MOLLI) for T1 and a fast low-angle shot sequence (FLASH) for T2 were used. At one site a scan-rescan was performed to assess the intra-scanner reproducibility. All acquired T1- and T2-mappings were analyzed in a core laboratory using the same post-processing approach and software. Results After exclusion of one volunteer due to an accidentally diagnosed cardiac disease, T1- and T2-maps of 19 volunteers showed no significant differences between the 3 T sites (mean ± SD [95% confidence interval] for global T1 in ms: site I: 1207 ± 32 [1192–1222]; site II: 1207 ± 40 [1184–1225]; site III: 1219 ± 26 [1207–1232]; p = 0.067; for global T2 in ms: site I: 40 ± 2 [39–41]; site II: 40 ± 1 [39–41]; site III 39 ± 2 [39–41]; p = 0.543). Conclusion Parametric mapping results displayed initial hints at a sufficient similarity between sites when confounders, such as field strength, vendor diversity, acquisition schemes and post-processing analysis are harmonized. This finding needs to be confirmed in a powered clinical trial. Trial registration ISRCTN14627679 (retrospectively registered)
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Gröschel, Jan, Ralf-Felix Trauzeddel, Maximilian Müller, Florian von Knobelsdorff-Brenkenhoff, Darian Viezzer, Thomas Hadler, Edyta Blaszczyk, Elias Daud e Jeanette Schulz-Menger. "Multi-site comparison of parametric T1 and T2 mapping: healthy travelling volunteers in the Berlin research network for cardiovascular magnetic resonance (BER-CMR)". Journal of Cardiovascular Magnetic Resonance 25, n. 1 (14 agosto 2023). http://dx.doi.org/10.1186/s12968-023-00954-9.
Testo completoAbstract (sommario):
Abstract Background Parametric mapping sequences in cardiovascular magnetic resonance (CMR) allow for non-invasive myocardial tissue characterization. However quantitative myocardial mapping is still limited by the need for local reference values. Confounders, such as field strength, vendors and sequences, make intersite comparisons challenging. This exploratory study aims to assess whether multi-site studies that control confounding factors provide first insights whether parametric mapping values are within pre-defined tolerance ranges across scanners and sites. Methods A cohort of 20 healthy travelling volunteers was prospectively scanned at three sites with a 3 T scanner from the same vendor using the same scanning protocol and acquisition scheme. A Modified Look-Locker inversion recovery sequence (MOLLI) for T1 and a fast low-angle shot sequence (FLASH) for T2 were used. At one site a scan-rescan was performed to assess the intra-scanner reproducibility. All acquired T1- and T2-mappings were analyzed in a core laboratory using the same post-processing approach and software. Results After exclusion of one volunteer due to an accidentally diagnosed cardiac disease, T1- and T2-maps of 19 volunteers showed no significant differences between the 3 T sites (mean ± SD [95% confidence interval] for global T1 in ms: site I: 1207 ± 32 [1192–1222]; site II: 1207 ± 40 [1184–1225]; site III: 1219 ± 26 [1207–1232]; p = 0.067; for global T2 in ms: site I: 40 ± 2 [39–41]; site II: 40 ± 1 [39–41]; site III 39 ± 2 [39–41]; p = 0.543). Conclusion Parametric mapping results displayed initial hints at a sufficient similarity between sites when confounders, such as field strength, vendor diversity, acquisition schemes and post-processing analysis are harmonized. This finding needs to be confirmed in a powered clinical trial. Trial registration ISRCTN14627679 (retrospectively registered)
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Shah, Rushil, Apurva Sharma, Fabrizio Assis, Henrique Doria De Vasconcellos, Navya Alugubelli, Pallavi Pandey, Tauseef Akhtar et al. "Quality assessment of cardiac magnetic resonance myocardial scar imaging prior to ventricular arrhythmia ablation". International Journal of Cardiovascular Imaging, 4 novembre 2022. http://dx.doi.org/10.1007/s10554-022-02734-5.
Testo completoAbstract (sommario):
AbstractHigh-resolution scar characterization using late gadolinium enhancement cardiac magnetic resonance imaging (LGE-CMR) is useful for guiding ventricular arrhythmia (VA) treatment. However, imaging study quality may be degraded by breath-holding difficulties, arrhythmias, and implantable cardioverter-defibrillators (ICDs). We evaluated the effect of image quality on left ventricle (LV) base to apex scar interpretation in pre-VA ablation LGE-CMR. 43 consecutive patients referred for VA ablation underwent gradient-recalled-echo LGE-CMR. In ICD patients (n = 24), wide-bandwidth inversion-recovery suppressed ICD artifacts. In non-ICD patients, single-shot steady-state free-precession LGE-CMR could also be performed to reduce respiratory motion/arrhythmia artifacts. Study quality was assessed for adequate/limited scar interpretation due to cardiac/respiratory motion artifacts, ICD-related artifacts, and image contrast. 28% of non-ICD patients had studies where image quality limited scar interpretation in at least one image compared to 71% of ICD patient studies (p = 0.012). A median of five image slices had limited quality per ICD patient study, compared to 0 images per non-ICD patient study. Poorer quality in ICD patients was largely due to motion-related artifacts (54% ICD vs 6% non-ICD studies, p = 0.001) as well as ICD-related image artifacts (25% of studies). In VA ablation patients with ICDs, conventional CMR protocols frequently have image slices with limited scar interpretation, which can limit whole-heart scar assessment. Motion artifacts contribute to suboptimal image quality, particularly in ICD patients. Improved methods for motion and ICD artifact suppression may better delineate high-resolution LGE scar features of interest for guiding VA ablation.