185 research outputs found
A subspace-based resolution-enhancing image reconstruction method for few-view differential phase-contrast tomography
It is well known that properly designed image reconstruction methods can facilitate reductions in imaging doses and data-acquisition times in tomographic imaging. The ability to do so is particularly important for emerging modalities, such as differential x-ray phase-contrast tomography (D-XPCT), which are currently limited by these factors. An important application of D-XPCT is high-resolution imaging of biomedical samples. However, reconstructing high-resolution images from few-view tomographic measurements remains a challenging task due to the high-frequency information loss caused by data incompleteness. In this work, a subspace-based reconstruction strategy is proposed and investigated for use in few-view D-XPCT image reconstruction. By adopting a two-step approach, the proposed method can simultaneously recover high-frequency details within a certain region of interest while suppressing noise and/or artifacts globally. The proposed method is investigated by the use of few-view experimental data acquired by an edge-illumination D-XPCT scanner
A joint-reconstruction approach for single-shot edge illumination x-ray phase-contrast tomography
Edge illumination X-ray phase-contrast tomography (EIXPCT) is an imaging technique that estimates the spatially variant X-ray refractive index and absorption distribution within an object while seeking to circumvent the limitations of previous benchtop implementations of X-ray phase-contrast tomography. As with gratingor analyzer-based methods, conventional image reconstruction methods for EIXPCT require that two or more images be acquired at each tomographic view angle. This requirement leads to increased data acquisition times, hindering in vivo applications. To circumvent these limitations, a joint reconstruction (JR) approach is proposed that concurrently produces estimates of the refractive index and absorption distributions from a tomographic data set containing only a single image per tomographic view angle. The JR reconstruction method solves a nonlinear optimization problem by use of a novel iterative gradient-based algorithm. The JR method is demonstrated in both computer-simulated and experimental EIXPCT studies
Comparison of data-acquisition designs for single-shot edge-illumination X-ray phase-contrast tomography
Edge-illumination X-ray phase-contrast tomography (EIXPCT) is an emerging technique that enables practical phase-contrast imaging with laboratory-based X-ray sources. A joint reconstruction method was proposed for reconstructing EIXPCT images, enabling novel flexible data-acquisition designs. However, only limited efforts have been devoted to optimizing data-acquisition designs for use with the joint reconstruction method. In this study, several promising designs are introduced, such as the constant aperture position (CAP) strategy and the alternating aperture position (AAP) strategy covering different angular ranges. In computer-simulation studies, these designs are analyzed and compared. Experimental data are employed to test the designs in real-world applications. All candidate designs are also compared for their implementation complexity. The tradeoff between data-acquisition time and image quality is discussed
The stochastic digital human is now enrolling for in silico imaging trials -- Methods and tools for generating digital cohorts
Randomized clinical trials, while often viewed as the highest evidentiary bar
by which to judge the quality of a medical intervention, are far from perfect.
In silico imaging trials are computational studies that seek to ascertain the
performance of a medical device by collecting this information entirely via
computer simulations. The benefits of in silico trials for evaluating new
technology include significant resource and time savings, minimization of
subject risk, the ability to study devices that are not achievable in the
physical world, allow for the rapid and effective investigation of new
technologies and ensure representation from all relevant subgroups. To conduct
in silico trials, digital representations of humans are needed. We review the
latest developments in methods and tools for obtaining digital humans for in
silico imaging studies. First, we introduce terminology and a classification of
digital human models. Second, we survey available methodologies for generating
digital humans with healthy and diseased status and examine briefly the role of
augmentation methods. Finally, we discuss the trade-offs of four approaches for
sampling digital cohorts and the associated potential for study bias with
selecting specific patient distributions
Single-shot edge illumination x-ray phase-contrast tomography enabled by joint image reconstruction
Edge illumination x-ray phase-contrast tomography
(EIXPCT) is an emerging x-ray phase-contrast tomography
technique for reconstructing the complex-valued x-ray refractive
index distribution of an object. Conventional image
reconstruction approaches for EIXPCT require multiple
images to be acquired at each tomographic view angle.
This contributes to prolonged data-acquisition times and
elevated radiation doses, which can hinder in vivo applications.
In this work, a new “single-shot” method is proposed
for joint reconstruction (JR) of the real and imaginaryvalued
components of the refractive index distribution from
a tomographic data set that contains only a single image acquired
at each view angle. The proposed method is predicated
on a nonlinear formulation of the inverse problem that is
solved by using a gradient-based optimization method.
The method is validated and investigated using computersimulated
and experimental EIXPCT data sets
Predicting photooxidant concentrations in aerosol liquid water based on laboratory extracts of ambient particles
Aerosol liquid water (ALW) is a unique reaction medium,
but its chemistry is poorly understood. For example, little is known of
photooxidant concentrations – including hydroxyl radicals (⚫OH), singlet
molecular oxygen (1O2*), and oxidizing triplet excited states of
organic matter (3C*) – even though they likely drive much of ALW
chemistry. Due to the very limited water content of particles, it is
difficult to quantify oxidant concentrations in ALW directly. To predict
these values, we measured photooxidant concentrations in illuminated aqueous
particle extracts as a function of dilution and used the resulting oxidant
kinetics to extrapolate to ALW conditions. We prepared dilution series from
two sets of particles collected in Davis, California: one from winter (WIN)
and one from summer (SUM). Both periods are influenced by biomass burning,
with dissolved organic carbon (DOC) in the extracts ranging from 10 to 495 mg C
L−1. In the winter sample, the ⚫OH concentration is
independent of particle mass concentration, with an average value of 5.0 (± 2.2) × 10−15 M, while in summer ⚫OH increases
with DOC in the range (0.4–7.7) × 10−15 M. In both winter
and summer samples, 3C* concentrations increase rapidly with particle
mass concentrations in the extracts and then plateau under more
concentrated conditions, with a range of (0.2–7) × 10−13 M.
WIN and SUM have the same range of 1O2* concentrations, (0.2–8.5) × 10−12 M, but in WIN the 1O2* concentration
increases linearly with DOC, while in SUM 1O2* approaches a
plateau.
We next extrapolated the relationships of oxidant formation rates and sinks
as a function of particle mass concentration from our dilute extracts to the
much more concentrated condition of aerosol liquid water. Predicted ⚫OH
concentrations in ALW (including mass transport of ⚫OH from the
gas phase) are (5–8) × 10−15 M, similar to those in
fog/cloud waters. In contrast, predicted concentrations of 3C* and
1O2* in ALW are approximately 10 to 100 times higher than in
cloud/fogs, with values of (4–9) × 10−13 M and (1–5) × 10−12 M, respectively. Although ⚫OH is often considered
the main sink for organic compounds in the atmospheric aqueous phase, the
much higher concentrations of 3C* and 1O2* in aerosol liquid
water suggest these photooxidants will be more important sinks for many
organics in particle water.</p
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