More Like this

1. Phase stabilization with motion compensated diffusion weighted imaging

   https://doi.org/10.1002/mrm.30218  

   Hannum, Ariel J; Cork, Tyler E; Setsompop, Kawin; Ennis, Daniel B (July 2024, Magnetic Resonance in Medicine)

   Abstract PurposeDiffusion encoding gradient waveforms can impartintra‐voxelandinter‐voxeldephasing owing to bulk motion, limiting achievable signal‐to‐noise and complicating multishot acquisitions. In this study, we characterize improvements in phase consistency via gradient moment nulling of diffusion encoding waveforms. MethodsHealthy volunteers received neuro () and cardiac () MRI. Three gradient moment nulling levels were evaluated: compensation for position (), position + velocity (), and position + velocity + acceleration (). Three experiments were completed: (Exp‐1) Fixed Trigger Delay Neuro DWI; (Exp‐2) Mixed Trigger Delay Neuro DWI; and (Exp‐3) Fixed Trigger Delay Cardiac DWI. Significant differences () of the temporal phase SD between repeated acquisitions and the spatial phase gradient across a given image were assessed. Resultsmoment nulling was a reference for all measures. In Exp‐1, temporal phase SD for diffusion encoding was significantly reduced with (35% oft‐tests) and (68% oft‐tests). The spatial phase gradient was reduced in 23% oft‐tests for and 2% of cases for . In Exp‐2, temporal phase SD significantly decreased with gradient moment nulling only for (83% oft‐tests), but spatial phase gradient significantly decreased with only (50% oft‐tests). In Exp‐3, gradient moment nulling significantly reduced temporal phase SD and spatial phase gradients (100% oft‐tests), resulting in less signal attenuation and more accurate ADCs. ConclusionWe characterized gradient moment nulling phase consistency for DWI. UsingM₁for neuroimaging andM₁ + M₂for cardiac imaging minimized temporal phase SDs and spatial phase gradients. 

   more » « less
2. The Effect of Secondary‐Phase Fraction on the Deformation of Olivine + Ferropericlase Aggregates: 1. Microstructural Evolution

   https://doi.org/10.1029/2022JB025723  

   Wiesman, Harison S.; Zimmerman, Mark E.; Kohlstedt, David L. (April 2023, Journal of Geophysical Research: Solid Earth)

   Abstract To study the microstructural evolution of polymineralic rocks, we performed deformation experiments on two‐phase aggregates of olivine (Ol) + ferropericlase (Per) with periclase fractions (f_Per) between 0.1 and 0.8. Additionally, single‐phase samples of both Ol and Per were deformed under the same experimental conditions to facilitate comparison of the microstructures in two‐phase and single‐phase materials. Each sample was deformed in torsion atT = 1523 K,P = 300 MPa at a constant strain rate up to a final shear strain of γ = 6 to 7. Microstructural developments, analyzed via electron backscatter diffraction (EBSD), indicate differences in both grain size and crystalline texture between single‐ and two‐phase samples. During deformation, grain size approximately doubled in our single‐phase samples of Ol and Per but remained unchanged or decreased in two‐phase samples. Zener‐pinning relationships fit to the mean grain sizes in each phase for samples with 0.1 ≤ f_Per≤ 0.5 and for those with 0.8 ≥ f_Per ≥ 0.5 demonstrate that the grain size of the primary phase is controlled by phase‐boundary pinning. Crystallographic preferred orientations, determined for both phases from EBSD data, are significantly weaker in the two‐phase materials than in the single‐phase materials. 

   more » « less
3. Evaluation of the robustness and accuracy of PCA-based algorithms for in-line Digital Holographic Microscopy

   https://doi.org/10.1364/3D.2023.JTu4A.35  

   Balachandran, K.; Castaneda, R.; Doblas, A. (January 2023, Optica Imaging Congress (3D, COSI, DH, FLatOptics, IS, pcAOP))

   This research undergraduate study evaluates the accuracy and robustness of a PCA-based phase reconstruction algorithm based on the number of phase-shifted images and the phase step for an in-line digital holographic microscope. 

   more » « less
4. Estimating Healthcare Expenditure Using Parametric Change Point Models

   https://doi.org/10.6339/24-JDS1157  

   Ghosh, Indranil; Zheng, Qi; Egger, Michael E; Kong, Maiying (December 2024, Journal of Data Science)

   Estimating healthcare expenditures is important for policymakers and clinicians. The expenditure of patients facing a life-threatening illness can often be segmented into four distinct phases: diagnosis, treatment, stable, and terminal phases. The diagnosis phase encompasses healthcare expenses incurred prior to the disease diagnosis, attributed to frequent healthcare visits and diagnostic tests. The second phase, following diagnosis, typically witnesses high expenditure due to various treatments, gradually tapering off over time and stabilizing into a stable phase, and eventually to a terminal phase. In this project, we introduce a pre-disease phase preceding the diagnosis phase, serving as a baseline for healthcare expenditure, and thus propose a five-phase to evaluate the healthcare expenditures. We use a piecewise linear model with three population-level change points and $4p$ subject-level parameters to capture expenditure trajectories and identify transitions between phases, where p is the number of covariates. To estimate the model’s coefficients, we apply generalized estimating equations, while a grid-search approach is used to estimate the change-point parameters by minimizing the residual sum of squares. In our analysis of expenditures for stages I–III pancreatic cancer patients using the SEER-Medicare database, we find that the diagnostic phase begins one month before diagnosis, followed by an initial treatment phase lasting three months. The stable phase continues until eight months before death, at which point the terminal phase begins, marked by a renewed increase in expenditures. 

   more » « less
5. Snapshot phase-shifting diffraction phase microscope

   https://doi.org/10.1364/OL.394033  

   Tian, Xiaobo; Liang, Rongguang (June 2020, Optics Letters)

   We propose a novel and simple snapshot phase-shifting diffraction phase microscope with a polarization grating and spatial phase-shifting technology. Polarization grating separates the incident beam into left and right circular polarization beams, one of which is used as the reference beam after passing through a pinhole. Four phase-shifted interferograms can be captured simultaneously from the polarization camera to reconstruct the high spatial resolution phase map. The principle is presented in this Letter, and the performance of the proposed system is demonstrated experimentally. Due to the near-common-path configuration and snapshot feature, the proposed system provides a feasible way for real-time quantitative phase measurement with minimal sensitivity to vibration and thermal disturbance. 

   more » « less