397 research outputs found
Hear That Steamboat Whistle Blowing
https://digitalcommons.library.umaine.edu/mmb-vp/4473/thumbnail.jp
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Influence of Temperature Fields on the Processing of Polymer Powders by Means of Laser and Mask Sintering Technology
Besides their high potential for individual series-production, powder and beam based additive manufacturing
technologies, like laser and mask sintering, are in general still restricted to prototyping applications. This is a
result of multiple limitations concerning part properties (e.g. mechanical and geometrical), their insufficient
reproducibility due to transient thermal conditions and the limited range of available materials. The main focal
point of this paper is to show the influencing parameters (e.g. temperature fields in the building chamber) of
powder-based thermoplastic processing technologies on part properties, like porosity and surface quality, and
on the processability of further new polymers (e.g. polypropylene and polyoxymethylene).Mechanical Engineerin
Motion compensation with a scanned ion beam: a technical feasibility study
This is an Open Access article distributed under the terms of the Creative Commons Attribution Licens
4D treatment planning for scanned ion beams
At Gesellschaft fĂĽr Schwerionenforschung (GSI) more than 330 patients have been treated with scanned carbon ion beams in a pilot project. To date, only stationary tumors have been treated. In the presence of motion, scanned ion beam therapy is not yet possible because of interplay effects between scanned beam and target motion which can cause severe mis-dosage. We have started a project to treat tumors that are subject to respiratory motion. A prototype beam application system for target tracking with the scanned pencil beam has been developed and commissioned
Temporal Registration in In-Utero Volumetric MRI Time Series
We present a robust method to correct for motion and deformations in in-utero volumetric MRI time series. Spatio-temporal analysis of dynamic MRI requires robust alignment across time in the presence of substantial and unpredictable motion. We make a Markov assumption on the nature of deformations to take advantage of the temporal structure in the image data. Forward message passing in the corresponding hidden Markov model (HMM) yields an estimation algorithm that only has to account for relatively small motion between consecutive frames. We demonstrate the utility of the temporal model by showing that its use improves the accuracy of the segmentation propagation through temporal registration. Our results suggest that the proposed model captures accurately the temporal dynamics of deformations in in-utero MRI time series.National Institutes of Health (U.S.) (NIH NIBIB NAC P41EB015902)National Institutes of Health (U.S.) (NIH NICHD U01HD087211)National Institutes of Health (U.S.) (NIH NIBIB R01EB017337)Wistron CorporationMerrill Lynch Wealth Management (Fellowship
Temporal Registration in In-Utero Volumetric MRI Time Series
We present a robust method to correct for motion and deformations in in-utero volumetric MRI time series. Spatio-temporal analysis of dynamic MRI requires robust alignment across time in the presence of substantial and unpredictable motion. We make a Markov assumption on the nature of deformations to take advantage of the temporal structure in the image data. Forward message passing in the corresponding hidden Markov model (HMM) yields an estimation algorithm that only has to account for relatively small motion between consecutive frames. We demonstrate the utility of the temporal model by showing that its use improves the accuracy of the segmentation propagation through temporal registration. Our results suggest that the proposed model captures accurately the temporal dynamics of deformations in in-utero MRI time series.National Institutes of Health (U.S.) (NIH NIBIB NAC P41EB015902)National Institutes of Health (U.S.) (NIH NICHD U01HD087211)National Institutes of Health (U.S.) (NIH NIBIB R01EB017337)Wistron CorporationMerrill Lynch Wealth Management (Fellowship
GPU-based Low-dose 4DCT Reconstruction via Temporal Non-local Means
Four-dimensional computed tomography (4DCT) has been widely used in cancer
radiotherapy for accurate target delineation and motion measurement for tumors
in thorax and upper abdomen areas. However, 4DCT simulation is associated with
much higher imaging dose than conventional CT simulation, which is a major
concern in its clinical application. Conventionally, each phase of 4DCT is
reconstructed independently using the filtered backprojection (FBP) algorithm.
The basic idea of our new algorithm is that, by utilizing the common
information among different phases, the input information required to
reconstruct image of high quality, and thus the imaging dose, can be reduced.
We proposed a temporal non-local means (TNLM) method to explore the inter-phase
similarity. All phases of the 4DCT images are reconstructed simultaneously by
minimizing a cost function consisting of a data fidelity term and a TNLM
regularization term. We utilized a forward-backward splitting algorithm and a
Gauss-Jacobi iteration method to efficiently solve the minimization problem.
The algorithm was also implemented on graphics processing unit (GPU) to achieve
a high computational speed. Our reconstruction algorithm has been tested on a
digital NCAT thorax phantom in three low dose scenarios. Our new algorithm
generates visually much better CT images containing less image noise and
streaking artifacts compared with the standard FBP algorithm. Quantitative
analysis shows that much higher contrast-to-noise ratio and signal-to-noise
ratio can be obtained using our algorithm. The total reconstruction time for
all 10 phases of a slice ranges from 90 to 140 seconds on an NVIDIA Tesla C1060
GPU card.Comment: 14 pages, 4 figures, and 2 tables, accepted by Med. Phy
Assessment of dosimetric errors induced by deformable image registration methods in 4D pencil beam scanned proton treatment planning for liver tumours
PURPOSE: Respiratory impacts in pencil beam scanned proton therapy (PBS-PT) are accounted by extensive 4D dose calculations, where deformable image registration (DIR) is necessary for estimating deformation vector fields (DVFs). We aim here to evaluate the dosimetric errors induced by different DIR algorithms in their resulting 4D dose calculations by using ground truth(GT)-DVFs from 4DMRI. MATERIALS AND METHODS: Six DIR methods: ANACONDA, Morfeus, B-splines, Demons, CT Deformable, and Total Variation, were respectively applied to nine 4DCT-MRI liver data sets. The derived DVFs were then used as input for 4D dose calculation. The DIR induced dosimetric error was assessed by individually comparing the resultant 4D dose distributions to those obtained with GT-DVFs. Both single-/three-field plans and single/rescanned strategies were investigated. RESULTS: Differences in 4D dose distributions among different DIR algorithms, and compared to the results using GT-DVFs, were pronounced. Up to 40 % of clinically relevant dose calculation points showed dose differences of 10 % or more between the GT. Differences in V95(CTV) reached up to 11.34 ± 12.57 %. The dosimetric errors became in general less substantial when applying multiple-field plans or using rescanning. CONCLUSION: Intrinsic geometric errors by DIR can influence the clinical evaluation of liver 4D PBS-PT plans. We recommend the use of an error bar for correctly interpreting individual 4D dose distributions
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