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At least 109 records · Page 6Linked to original sources

arXiv2013

AIR: fused Analytical and Iterative Reconstruction method for computed tomography

Purpose: CT image reconstruction techniques have two major categories: analytical reconstruction (AR) method and iterative reconstruction (IR) method. AR reconstructs images through analytical formulas, such as filtered backprojection (FBP) in 2D and Feldkamp-Davis-Kress (FDK) method in 3D, which can be either mathematically exact or approximate. On the other hand, IR is often based on the discrete forward model of X-ray transform and formulated as a minimization problem with some appropriate image regularization method, so that the reconstructed image corresponds to the minimizer of the optimization problem. This work is to investigate the fused analytical and iterative reconstruction (AIR) method. Methods: Based on IR with L1-type image regularization, AIR is formulated with a AR-specific preconditioner in the data fidelity term, which results in the minimal change of the solution algorithm that replaces the adjoint X-ray transform by the filtered X-ray transform. As a proof-of-concept 2D example of AIR, FBP is incorporated into tensor framelet (TF) regularization based IR, and the formulated AIR minimization problem is then solved through split Bregman method with GPU-accelerated X-ray transform and filtered adjoint X-ray transform. Conclusion: AIR, the fused Analytical and Iterative Reconstruction method, is proposed with a proof-of-concept 2D example to synergize FBP and TF-regularized IR, with improved image resolution and contrast for experimental data. The potential impact of AIR is that it offers a general framework to develop various AR enhanced IR methods, when neither AR nor IR alone is sufficient.

physics.med-ph↗

arXiv2013

Cyclostationary Approach for Heart and Respiration Rates Monitoring with Body Movement Cancellation Using Radar Doppler System

Heart and respiration rate measurement using Doppler radar is a non-contact and non-obstructive way for remote thorough-clothing monitoring of vital signs. The modulated back-scattered radar signal in the presence of high noise and interference is non-stationary with hidden periodicities, which cannot be detected by ordinary Fourier analysis. In this paper we propose a cyclostationary approach for such signals and show that by using non-linear transformation and then Fourier analysis of the radar signal, the hidden periodicities can be accurately obtained. Numerical results show that the vital signs can be extracted as cyclic frequencies, independent of SNR and without any filtering or phase unwrapping.

physics.med-ph↗

arXiv2013

Geometric analysis on the unidirectionality of the pulmonary veins for atrial reentry

It is widely believed that the pulmonary veins (PVs) of the atrium play the central role in the generation of atrial reentry leading to atrial fibrillation, but its mechanism has not been analytically explained. In order to improve the current clinical procedures for atrial reentry by understanding its mechanism, geometrical analysis is proposed on the conditions of conduction failure at the PVs and is validated by various computational modeling. To achieve this, a new analytic approach is proposed by adapting the geometric relative acceleration analysis from spacetime physics on the hypothesis that a large relative acceleration can translate to a dramatic increase in the curvature of the wavefront and subsequently to conduction failure. This analytic method is applied to a simplified model of the PV to reveal the strong dependency of the propagational direction and the magnitude of anisotropy for conduction failure. The unidirectionality of the PVs follows directly and is validated by computational tests in a T-shaped domain, computational simulations for three-dimensional atrial reentry and previous in-silico reports for atrial reentry.

physics.med-ph↗

arXiv2013

Elucidating the turbulence nature of the intracardiac flow: from medical images to multi-cycle Large Eddy Simulations

This brief article accompanies a fluid dynamics video presenting the results of a large-eddy simulation of the flow in a realistic left heart. The left heart geometry, from the pulmonary veins to the aortic root, is extracted from medical images and the endocardium movements are reconstructed through image registration. Large-eddy simulations are thus performed in a patient-specific heart model, where the patient-specific movements of the geometry are prescribed. The flow obtained is intermittent, showing both in the left atrium and in the left ventricle turbulent spots correlated to flow decelerations.

physics.flu-dyn↗

arXiv2013

SQUID-based multichannel system for Magnetoencephalography

Here we present a multichannel system based on superconducting quantum interference devices (SQUIDs) for magnetoencephalography (MEG) measurements, developed and installed at Istituto di Cibernetica (ICIB) in Naples. This MEG system, consists of 163 full integrated SQUID magnetometers, 154 channels and 9 references, and has been designed to meet specifications concerning noise, dynamic range, slew rate and linearity through optimized design. The control electronics is located at room temperature and all the operations are performed inside a Magnetically Shielded Room (MSR). The system exhibits a magnetic white noise level of approximatively 5 fT/Hz1=2. This MEG system will be employed for both clinical and routine use. PACS numbers: 74.81.Fa, 85.25.Hv, 07.20.Mc, 85.25.Dq, 87.19.le, 87.85.Ng

physics.med-ph↗

arXiv2013

Fluid fragmentation from hospital toilets

Hospital-acquired infections represent significant health and financial burdens to society. Clostridium difficile (C. difficile) is a particularly challenging bacteria with the potential to cause severe diarrhea and death. One mode of transmission for C. difficile, as well as other pathogens, which has received little attention is the potential air contamination by pathogen-bearing droplets emanating from toilets. In the fluid dynamics video submitted to the APS DFD Gallery of Fluid Motion 2013, we present flow visualizations via high-speed recordings showing the capture of the product of the fluid fragmentation generated by hospital toilet high-pressure flushes. Important quantities of both large and small droplets are observed. We illustrate how high-pressure flushes and cleaning products currently used in hospital toilets result in aggravating, rather than alleviating, the suspension and recirculation of tenacious airborne pathogen-bearing droplets.

physics.flu-dyn↗

arXiv2013

Determination, Calculation and Representation of the Upper and Lower Sealing Zones During Virtual Stenting of Aneurysms

In this contribution, a novel method for stent simulation in preoperative computed tomography angiography (CTA) acquisitions of patients is presented where the sealing zones are automatically calculated and visualized. The method is eligible for non-bifurcated and bifurcated stents (Y-stents). Results of the proposed stent simulation with an automatic calculation of the sealing zones for specific diseases (abdominal aortic aneurysms (AAA), thoracic aortic aneurysms (TAA), iliac aneurysms) are presented. The contribution is organized as follows. Section 2 presents the proposed approach. In Section 3, experimental results are discussed. Section 4 concludes the contribution and outlines areas for future work.

cs.CV↗

arXiv2013

The "Life Potential": a new complex algorithm to assess "Heart Rate Variability" from Holter records for cognitive and diagnostic aims. Preliminary experimental results showing its dependence on age, gender and health conditions

Although HRV (Heart Rate Variability) analyses have been carried out for several decades, several limiting factors still make these analyses useless from a clinical point of view. The present paper aims at overcoming some of these limits by introducing the "Life Potential" (BMP), a new mathematical algorithm which seems to exhibit surprising cognitive and predictive capabilities. BMP is defined as a linear combination of five HRV Non-Linear Variables, in turn derived from the thermodynamic formalism of chaotic dynamic systems. The paper presents experimental measurements of BMP (Average Values and Standard Deviations) derived from 1048 Holter tests, matched in age and gender, including a control group of 356 healthy subjects. The main results are: (a) BMP always decreases when the age increases, and its dependence on age and gender is well established; (b) the shape of the age dependence within "healthy people" is different from that found in the general group: this behavior provides evidence of possible illness, and seems to justify the attribute of "life potential". A simplified "standard" procedure is then supplied to compute BMP values for a given subject, whereas BMP dependence on clinical status is now under investigation to make BMP a useful clinical tool.

physics.med-ph↗

arXiv2013

A Convex Optimization Approach to pMRI Reconstruction

In parallel magnetic resonance imaging (pMRI) reconstruction without using estimation of coil sensitivity functions, one group of algorithms reconstruct sensitivity encoded images of the coils first followed by the magnitude only image reconstruction, e.g. GRAPPA, and another group of algorithms jointly compute the image and sensitivity functions by regularized optimization which is a non-convex problem with local only solutions. For the magnitude only image reconstruction, this paper derives a reconstruction formulation, which is linear in the magnitude image, and an associated convex hull in the solution space of the formulated equation containing the magnitude of the image. As a result, the magnitude only image reconstruction for pMRI is formulated into a two-step convex optimization problem, which has a globally optimal solution. An algorithm based on split-bregman and nuclear norm regularized optimizations is proposed to implement the two-step convex optimization and its applications to phantom and in-vivo MRI data sets result in superior reconstruction performance compared with other algorithms.

physics.med-ph↗

arXiv2013

Rotating-crystal Malaria Diagnosis: Pre-clinical validation

Improving the efficiency of malaria diagnosis is one of the main goals of current malaria research. We have recently developed a magneto-optical (MO) method which allows high-sensitivity detection of malaria pigment (hemozoin) crystals via their magnetically induced rotation in blood. Here, we validate this technique on laboratory derived blood samples infected with \textit{Plasmodium falciparum}. Using two parasite cultures, the first containing mostly ring stages and the second corresponding to the end of the parasite life cycle, we demonstrate that our novel method can detect parasite densities as low as $\sim$40 and $\sim$10\,parasites per microliter of blood for ring and schizont stage parasites, respectively. This detection limit exceeds the performance of rapid diagnostic tests and competes with the threshold achievable by light microscopic observation of blood smears. Our method can be performed with as little as 50\,microliter of capillary blood and is sensitive to the presence of hemozoin micro-crystals down to ppm concentrations. The device, designed to a portable format for clinical and in-field tests, requires no special training of the operator or specific reagents, except for an inexpensive lysis solution to release intracellular hemozoin. Beyond diagnostics, this technique may offer an efficient tool to study hemozoin formation, trace hemozoin kinetics in the body and test susceptibility/resistance of parasites to new antimalarial drugs inhibiting hemozoin formation.

physics.med-ph↗

arXiv2014

A Study of Speed of the Boundary Element Method as applied to the Realtime Computational Simulation of Biological Organs

In this work, possibility of simulating biological organs in realtime using the Boundary Element Method (BEM) is investigated. Biological organs are assumed to follow linear elastostatic material behavior, and constant boundary element is the element type used. First, a Graphics Processing Unit (GPU) is used to speed up the BEM computations to achieve the realtime performance. Next, instead of the GPU, a computer cluster is used. Results indicate that BEM is fast enough to provide for realtime graphics if biological organs are assumed to follow linear elastostatic material behavior. Although the present work does not conduct any simulation using nonlinear material models, results from using the linear elastostatic material model imply that it would be difficult to obtain realtime performance if highly nonlinear material models that properly characterize biological organs are used. Although the use of BEM for the simulation of biological organs is not new, the results presented in the present study are not found elsewhere in the literature.

cs.CE↗

arXiv2013

Characteristics of multiplexing parallel beam (MPB) by using Monte Carlo simulation

It is discussed that the point spread function (PSF) of multiplexing parallel beam (MPB) is shift-invariant; the spatial resolution is linear as a function of depth h and the geometrical sensitivity is converged to a constant value at far field, by using Monte Carlo simulation in this work. The results indicate that the MPB collimator may maintain the same system characteristics as parallel beam (PB) collimator. Although the minimum standard deviation (SD) of MPB is more 3.7% than the PB with high sensitivity (HSPB), the improved resolution is 55.2% at h=160mm, compared with HSPB in this work. The reconstruction process also indicates that the convergence rate of MPB is slower than the HSPB because the projection counts are part of overlapping and the PSF of oblique PB (OPB) is asymmetrical. However the effective hole length is used in the calculation of the system matrix to correct for the penetration, which has a satisfactory result. From a visual assessment, the reconstructed image may well satisfy clinical criteria and it is therefore worth investigating this novel MPB collimator system for clinical imaging.

physics.med-ph↗

arXiv2013

A Fast local Reconstruction algorithm by selective backprojection for Low-Dose in Dental Computed Tomography

High radiation dose in computed tomography (CT) scans increases the lifetime risk of cancer, which become a major clinical concern. The backprojection-filtration (BPF) algorithm could reduce radiation dose by reconstructing images from truncated data in a short scan. In dental CT, it could reduce radiation dose for the teeth by using the projection acquired in a short scan, and could avoid irradiation to other part by using truncated projection. However, the limit of integration for backprojection varies per PI-line, resulting in low calculation efficiency and poor parallel performance. Recently, a tent BPF (T-BPF) has been proposed to improve calculation efficiency by rearranging projection. However, the memory-consuming data rebinning process is included. Accordingly, the chose-BPF (C-BPF) algorithm is proposed in this paper. In this algorithm, the derivative of projection is backprojected to the points whose x coordinate is less than that of the source focal spot to obtain the differentiated backprojection (DBP). The finite Hilbert inverse is then applied to each PI-line segment. C-BPF avoids the influence of the variable limit of integration by selective backprojection without additional time cost or memory cost. The simulation experiment and the real experiment demonstrated the higher reconstruction efficiency of C-BPF.

physics.med-ph↗

arXiv2013

Dictionary-Learning-Based Reconstruction Method for Electron Tomography

Electron tomography usually suffers from so called missing wedge artifacts caused by limited tilt angle range. An equally sloped tomography (EST) acquisition scheme (which should be called the linogram sampling scheme) was recently applied to achieve 2.4-angstrom resolution. On the other hand, a compressive sensing-inspired reconstruction algorithm, known as adaptive dictionary based statistical iterative reconstruction (ADSIR), has been reported for x-ray computed tomography. In this paper, we evaluate the EST, ADSIR and an ordered-subset simultaneous algebraic reconstruction technique (OS-SART), and compare the ES and equally angled (EA) data acquisition modes. Our results show that OS-SART is comparable to EST, and the ADSIR outperforms EST and OS-SART. Furthermore, the equally sloped projection data acquisition mode has no advantage over the conventional equally angled mode in the context.

cs.CV↗

arXiv2015

Optimization of Radiation Therapy Fractionation Schedules in the Presence of Tumor Repopulation

We analyze the effect of tumor repopulation on optimal dose delivery in radiation therapy. We are primarily motivated by accelerated tumor repopulation towards the end of radiation treatment, which is believed to play a role in treatment failure for some tumor sites. A dynamic programming framework is developed to determine an optimal fractionation scheme based on a model of cell kill due to radiation and tumor growth in between treatment days. We find that faster tumor growth suggests shorter overall treatment duration. In addition, the presence of accelerated repopulation suggests larger dose fractions later in the treatment to compensate for the increased tumor proliferation. We prove that the optimal dose fractions are increasing over time. Numerical simulations indicate potential for improvement in treatment effectiveness.

physics.med-ph↗

arXiv2013

Liquid-Solid Phase Transition Alloy as Reversible and Rapid Molding Bone Cement

Bone cement has been demonstrated as an essential restorative material in the orthopedic surgery. However current materials often imply unavoidable drawbacks, such as tissue-cement reaction induced thermal injuries and troublesome revision procedure. Here we proposed an injectable alloy cement to address such problems through its liquid-solid phase transition mechanism. The cement is made of a unique alloy BiInSnZn with a specifically designed low melting point 57.5°C. This property enables its rapid molding into various shapes with high plasticity. Some fundamental characteristics including mechanical strength behaviors and phase transition-induced thermal features have been measured to demonstrate the competence of alloy as unconventional cement with favorable merits. Further biocompatible tests showed that this material could be safely employed in vivo. In addition, experiments also found the alloy cement capability as an excellent contrast agent for radiation imaging. Particularly, the proposed alloy cement with reversible phase transition feature significantly simplifies the revision of cement and prosthesis. This study opens the way to implement alloy material as bone cement to fulfill diverse clinical needs.

cond-mat.mtrl-sci↗

arXiv2013

Development of a proton Computed Tomography (pCT) scanner at NIU

We describe the development of a proton Computed Tomography (pCT) scanner at Northern Illinois University (NIU) in collaboration with Fermilab and Delhi University. This paper provides an overview of major components of the scanner and a detailed description of the data acquisition system (DAQ).

physics.ins-det↗

arXiv2014

A Mathematical Programming Approach to the Fractionation Problem in Chemoradiotherapy

In concurrent chemoradiotherapy, chemotherapeutic agents are administered during the course of radiotherapy to enhance the primary tumor control. However, that often comes at the expense of increased risk of normal-tissue complications. The additional biological damage is mainly attributed to two mechanisms of action, which are the independent cytotoxic activity of chemotherapeutic agents and their interactive cooperation with radiation. The goal of this study is to develop a mathematical framework to obtain drug and radiation administration schedules that maximize the therapeutic gain for concurrent chemoradiotherapy. In particular, we analyze the impact of incorporating these two mechanisms into the radiation fractionation problem. Considering each mechanism individually, we first derive closed-form expressions for the optimal radiation fractionation regimen and the corresponding drug administration schedule. We next study the case in which both mechanisms are simultaneously present and develop a dynamic programming framework to determine optimal treatment regimens. Results show that those chemotherapeutic agents that interact with radiation may change optimal radiation fractionation regimens. Moreover, administration of chemotherapeutic agents possessing both mechanisms may give rise to optimal non-stationary radiation fractionation schemes.

physics.med-ph↗