361 research outputs found
Noise2Filter: fast, self-supervised learning and real-time reconstruction for 3D Computed Tomography
At X-ray beamlines of synchrotron light sources, the achievable
time-resolution for 3D tomographic imaging of the interior of an object has
been reduced to a fraction of a second, enabling rapidly changing structures to
be examined. The associated data acquisition rates require sizable
computational resources for reconstruction. Therefore, full 3D reconstruction
of the object is usually performed after the scan has completed. Quasi-3D
reconstruction -- where several interactive 2D slices are computed instead of a
3D volume -- has been shown to be significantly more efficient, and can enable
the real-time reconstruction and visualization of the interior. However,
quasi-3D reconstruction relies on filtered backprojection type algorithms,
which are typically sensitive to measurement noise. To overcome this issue, we
propose Noise2Filter, a learned filter method that can be trained using only
the measured data, and does not require any additional training data. This
method combines quasi-3D reconstruction, learned filters, and self-supervised
learning to derive a tomographic reconstruction method that can be trained in
under a minute and evaluated in real-time. We show limited loss of accuracy
compared to training with additional training data, and improved accuracy
compared to standard filter-based methods
A computationally efficient reconstruction algorithm for circular cone-beam computed tomography using shallow neural networks
Circular cone-beam (CCB) Computed Tomography (CT) has become an integral part
of industrial quality control, materials science and medical imaging. The need
to acquire and process each scan in a short time naturally leads to trade-offs
between speed and reconstruction quality, creating a need for fast
reconstruction algorithms capable of creating accurate reconstructions from
limited data.
In this paper we introduce the Neural Network Feldkamp-Davis-Kress (NN-FDK)
algorithm. This algorithm adds a machine learning component to the FDK
algorithm to improve its reconstruction accuracy while maintaining its
computational efficiency. Moreover, the NN-FDK algorithm is designed such that
it has low training data requirements and is fast to train. This ensures that
the proposed algorithm can be used to improve image quality in high throughput
CT scanning settings, where FDK is currently used to keep pace with the
acquisition speed using readily available computational resources.
We compare the NN-FDK algorithm to two standard CT reconstruction algorithms
and to two popular deep neural networks trained to remove reconstruction
artifacts from the 2D slices of an FDK reconstruction. We show that the NN-FDK
reconstruction algorithm is substantially faster in computing a reconstruction
than all the tested alternative methods except for the standard FDK algorithm
and we show it can compute accurate CCB CT reconstructions in cases of high
noise, a low number of projection angles or large cone angles. Moreover, we
show that the training time of an NN-FDK network is orders of magnitude lower
than the considered deep neural networks, with only a slight reduction in
reconstruction accuracy
A reâevaluation of the Plenus Cold Event, and the links between CO2, temperature, and seawater chemistry during OAE 2
International audienceThe greenhouse world of the midâCretaceous (~94 Ma) was punctuated by an episode of abrupt climatic upheaval: Oceanic Anoxic Event 2 (OAE 2). Highâresolution climate records reveal considerable changes in temperature, carbon cycling, and ocean chemistry during this climatic perturbation. In particular, an interval of cooling has been detected in the English Chalk on the basis of an invasive boreal fauna and bulk oxygenâisotope excursions registered during the early stages of OAE 2âa phenomenon known as the Plenus Cold Event (PCE), which has tentatively been correlated with climatic shifts worldwide.Here we present new highâresolution neodymiumâ, carbonâ, and oxygenâisotope data, as well as elemental chromium concentrations and cerium anomalies, from the English Chalk exposed at Dover, UK, which we evaluate in the context of >400 records from across the globe. A negative carbonâisotope excursion that correlates with the original âPCEâ is consistently expressed worldwide, and CO2 proxy records, where available, indicate a rise and subsequent fall in CO2 over the Plenus interval. However, variability in the timing and expression of cooling at different sites suggests that, although seaâsurface paleoâtemperatures may reflect a response to global CO2 change, local processes likely played a dominant role at many sites. Variability in the timing and expression of changes in waterâmass character, and problems in determining the driver of observed proxy changes, suggest that no single simple mechanism can link the carbon cycle to oceanography during the Plenus interval and other factors including upwelling and circulation patterns were locally important. As such, it is proposed that the Plenus carbonâisotope event is a more reliable stratigraphic marker to identify the Plenus interval, rather than any climatic shifts that may have been overprinted by local effects
Late Maastrichtian carbon isotope stratigraphy and cyclostratigraphy of the Newfoundland Margin (Site U1403, IODP Expedition 342)
Earthâs climate during the Maastrichtian (latest Cretaceous) was punctuated by brief warming and cooling episodes, accompanied by perturbations of the global carbon cycle. Superimposed on a long-term cooling trend, the middle Maastrichtian is characterized by deep-sea warming and relatively high values of stable carbon-isotope ratios, followed by strong climatic variability towards the end of the Cretaceous. A lack of knowledge on the timing of climatic change inhibits our understanding of underlying causal mechanisms. We present an integrated stratigraphy from Integrated Ocean Drilling Program (IODP) Site U1403, providing an expanded deep ocean record from the North Atlantic (Expedition 342, Newfoundland Margin). Distinct sedimentary cyclicity suggests that orbital forcing played a major role in depositional processes, which is confirmed by statistical analyses of high resolution elemental data obtained by X-ray fluorescence (XRF) core scanning. Astronomical calibration reveals that the investigated interval encompasses seven 405-kyr cycles (Ma4051 to Ma4057) and spans the 2.8 Myr directly preceding the Cretaceous/Paleocene (K/Pg) boundary. A high-resolution carbon-isotope record from bulk carbonates allows us to identify global trends in the late Maastrichtian carbon cycle. Low-amplitude variations (up to 0.4â°) in carbon isotopes at Site U1403 match similar scale variability in records from Tethyan and Pacific open-ocean sites. Comparison between Site U1403 and the hemipelagic restricted basin of the Zumaia section (northern Spain), with its own well-established independent cyclostratigraphic framework, is more complex. Whereas the pre-K/Pg oscillations and the negative values of the Mid-Maastrichtian Event (MME) can be readily discerned in both the Zumaia and U1403 records, patterns diverge during a ~ 1 Myr period in the late Maastrichtian (67.8â66.8 Ma), with Site U1403 more reliably reflecting global carbon cycling. Our new carbon isotope record and cyclostratigraphy offer promise for Site U1403 to serve as a future reference section for high-resolution studies of late Maastrichtian paleoclimatic change
Templates as an aid in implantology
The number, position and angulation of implants are of major importance in loading of implants and surrounding bone and in esthetics. Especially in single tooth and partially edentulous cases correct positioning of implants takes a great deal of care. A template is a device that helps to achieve the proper amount of bone and the correct position and angulation of implants. The design and fabrication of radiographic templates, diagnostic templates and surgical templates are described, both in general and specifically for overdentures and non-removable implant-supported restorations.</p
Templates as an aid in implantology
The number, position and angulation of implants are of major importance in loading of implants and surrounding bone and in esthetics. Especially in single tooth and partially edentulous cases correct positioning of implants takes a great deal of care. A template is a device that helps to achieve the proper amount of bone and the correct position and angulation of implants. The design and fabrication of radiographic templates, diagnostic templates and surgical templates are described, both in general and specifically for overdentures and non-removable implant-supported restorations.</p
Templates as an aid in implantology
The number, position and angulation of implants are of major importance in loading of implants and surrounding bone and in esthetics. Especially in single tooth and partially edentulous cases correct positioning of implants takes a great deal of care. A template is a device that helps to achieve the proper amount of bone and the correct position and angulation of implants. The design and fabrication of radiographic templates, diagnostic templates and surgical templates are described, both in general and specifically for overdentures and non-removable implant-supported restorations.</p
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