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Medical Physics

New submissions

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New submissions for Mon, 19 Mar 18

[1]  arXiv:1803.05938 [pdf, other]
Title: Low Rank plus Sparse Decomposition of ODFs for Improved Detection of Group-level Differences and Variable Correlations in White Matter
Comments: 20 pages, 11 figures, 5 supplementary figures
Subjects: Medical Physics (physics.med-ph); Biological Physics (physics.bio-ph); Neurons and Cognition (q-bio.NC)

A novel approach is presented for group statistical analysis of diffusion weighted MRI datasets through voxelwise Orientation Distribution Functions (ODF). Recent advances in MRI acquisition make it possible to use high quality diffusion weighted protocols (multi-shell, large number of gradient directions) for routine in vivo study of white matter architecture. The dimensionality of these data sets is however often reduced to simplify statistical analysis. While these approaches may detect large group differences, they do not fully capitalize on all acquired image volumes. Incorporation of all available diffusion information in the analysis however risks biasing the outcome by outliers. Here we propose a statistical analysis method operating on the ODF, either the diffusion ODF or fiber ODF. To avoid outlier bias and reliably detect voxelwise group differences and correlations with demographic or behavioral variables, we apply the Low-Rank plus Sparse (L + S) matrix decomposition on the voxelwise ODFs which separates the sparse individual variability in the sparse matrix S whilst recovering the essential ODF features in the low-rank matrix L. We demonstrate the performance of this ODF L + S approach by replicating the established negative association between global white matter integrity and physical obesity in the Human Connectome dataset. The volume of positive findings agrees with and expands on the volume found by TBSS, Connectivity based fixel enhancement and Connectometry. In the same dataset we further localize the correlations of brain structure with neurocognitive measures such as fluid intelligence and episodic memory. The presented ODF L + S approach will aid in the full utilization of all acquired diffusion weightings leading to the detection of smaller group differences in clinically relevant settings as well as in neuroscience applications.

[2]  arXiv:1803.06008 [pdf, other]
Title: A unified image reconstruction framework for quantitative dual- and triple-energy CT imaging of material compositions
Comments: 24 pages, 11 figures. Accepted by Medical Physics
Subjects: Medical Physics (physics.med-ph)

Many clinical applications depend critically on the accurate differentiation and classification of different types of materials in patient anatomy. This work introduces a unified framework for accurate nonlinear material decomposition and applies it, for the first time, in the concept of triple-energy CT (TECT) for enhanced material differentiation and classification as well as dual-energy CT. The triple-energy data acquisition is implemented at the scales of micro-CT and clinical CT imaging with commercial "TwinBeam" dual-source DECT configuration and a fast kV switching DECT configuration. Material decomposition and quantitative comparison with a photon counting detector and with the presence of a bow-tie filter are also performed. The proposed method provides quantitative material- and energy-selective images examining realistic configurations for both dual- and triple-energy CT measurements. Compared to the polychromatic kV CT images, virtual monochromatic images show superior image quality. For the mouse phantom, quantitative measurements show that the differences between gadodiamide and iodine concentrations obtained using TECT and idealized photon counting CT (PCCT) are smaller than 8 mg/mL and 1 mg/mL, respectively. TECT outperforms DECT for multi-contrast CT imaging and is robust with respect to spectrum estimation. For the thorax phantom, the differences between the concentrations of the contrast map and the corresponding true reference values are smaller than 7 mg/mL for all of the realistic configurations. A unified framework for both dual- and triple-energy CT imaging has been established for the accurate extraction of material compositions; considering currently available commercial DECT configurations. The novel technique is promising to provide an urgently needed solution for several CT-based diagnosis and therapy applications.

[3]  arXiv:1803.06274 [pdf, ps, other]
Title: Frequency-modulated SSFP with radial sampling and subspace reconstruction: A time-efficient alternative to phase-cycled bSFFP
Subjects: Medical Physics (physics.med-ph)

Purpose: A novel subspace-based reconstruction method for frequency-modulated balanced steady-state free precession (fmSSFP) MRI is presented. In this work, suitable data acquisition schemes, subspace sizes, and efficiencies for banding removal are investigated.
Theory and Methods: By combining a fmSSFP MRI sequence with a 3D stack-of-stars trajectory, scan efficiency is maximized as spectral information is obtained without intermediate preparation phases. A memory-efficient reconstruction routine is implemented by introducing the low-frequency Fourier transform as a subspace which allows for the formulation of a convex reconstruction problem. The removal of banding artifacts is investigated by comparing the proposed acquisition and reconstruction technique to phase-cycled bSSFP MRI. Aliasing properties of different undersampling schemes are analyzed and water/fat separation is demonstrated by reweighting the reconstructed subspace coefficients to generate virtual spectral responses in a post-processing step.
Results: A simple root-of-sum-of-squares combination of the reconstructed subspace coefficients yields high-SNR images with the characteristic bSSFP contrast but without banding artifacts. Compared to Golden-Angle trajectories, turn-based sampling schemes were superior in minimizing aliasing across reconstructed subspace coefficients. Water/fat separated images of the human knee were obtained by reweighting subspace coefficients.
Conclusion: The novel subspace-based fmSSFP MRI technique emerges as a time-efficient alternative to phase-cycled bSFFP. The method does not need intermediate preparation phases, offers high SNR and avoids banding artifacts. Reweighting of the reconstructed subspace coefficients allows for generating virtual spectral responses with applications to water/fat separation.

Replacements for Mon, 19 Mar 18

[4]  arXiv:1706.09780 (replaced) [pdf, other]
Title: ENLIVE: An Efficient Nonlinear Method for Calibrationless and Robust Parallel Imaging
Comments: Submitted to Magnetic Resonance in Medicine as a Full Paper. Part of this work has been presented at the 25th ISMRM Annual Meeting. 24 pages, 10 figures
Subjects: Medical Physics (physics.med-ph)
[5]  arXiv:1802.06705 (replaced) [pdf]
Title: Microdosimetry in ion-beam therapy: studying and comparing outcomes from different detectors
Authors: Giulio Magrin
Comments: 23 pages; 6 figures; 2 tables; 1 Appendix
Subjects: Instrumentation and Detectors (physics.ins-det); Medical Physics (physics.med-ph)
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