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iterative reconstruction

Ye Tian, K C Erb, Ganesh Adluru, Devavrat Likhite, Apoorva Pedgaonkar, Michael Blatt, Srikant Kamesh Iyer, John Roberts, Edward DiBella
PURPOSE: To evaluate the use of three different pre-reconstruction interpolation methods to convert non-Cartesian k-space data to Cartesian samples such that iterative reconstructions can be performed more simply and more rapidly. METHODS: Phantom as well as cardiac perfusion radial datasets were reconstructed by four different methods. Three of the methods used pre-reconstruction interpolation once followed by a fast Fourier transform (FFT) at each iteration. The methods were: bilinear interpolation of nearest-neighbor points (BINN), 3-point interpolation, and a multi-coil interpolator called GRAPPA Operator Gridding (GROG)...
May 19, 2017: Medical Physics
Bryson Dietz, Eugene Yip, Jihyun Yun, B Gino Fallone, Keith Wachowicz
PURPOSE: This work presents a real-time dynamic image reconstruction technique, that combines compressed sensing and principal component analysis (CS-PCA), to achieve real-time adaptive radiotherapy with the use of a linac-magnetic resonance imaging system. METHODS: Six retrospective fully sampled dynamic data sets of patients diagnosed with non-small cell lung cancer were used to investigate the CS-PCA algorithm. Using a database of fully sampled k-space, principal components (PC's) were calculated to aid in the reconstruction of undersampled images...
May 19, 2017: Medical Physics
Michael T McCann, Michael Unser
We propose a new, cost-efficient method for computing back projections in parallel-ray X-ray CT. Forward and back projections are the basis of almost all X-ray CT reconstruction methods, but computing these accurately is costly. In the special case of parallel-ray geometry, it turns out that reconstruction requires back projection only. One approach to accelerate the back projection is through interpolation: fit a continuous representation to samples of the desired signal, then sample it at the required locations...
May 23, 2017: IEEE Transactions on Image Processing: a Publication of the IEEE Signal Processing Society
Dayu Yu, Fuchao Xu, Shuwei Zhang, Jixun Zhan
Nonribosomal peptide synthetases (NRPSs) assemble a large group of structurally and functionally diverse natural products. While the iterative catalytic mechanism of bacterial NRPSs is known, it remains unclear how fungal NRPSs create products of desired length. Here we show that fungal iterative NRPSs adopt an alternate incorporation strategy. Beauvericin and bassianolide synthetases have the same C1-A1-T1-C2-A2-MT-T2a-T2b-C3 domain organization. During catalysis, C3 and C2 take turns to incorporate the two biosynthetic precursors into the growing depsipeptide chain that swings between T1 and T2a/T2b with C3 cyclizing the chain when it reaches the full length...
May 23, 2017: Nature Communications
Zhencheng Fan, Yitong Weng, Guowen Chen, Hongen Liao
Three-dimensional (3D) visualization of preoperative and intraoperative medical information becomes more and more important in minimally invasive surgery. We develop a 3D interactive surgical visualization system using mobile spatial information acquisition and autostereoscopic display for surgeons to observe surgical target intuitively. The spatial information of regions of interest (ROIs) is captured by the mobile device and transferred to a server for further image processing. Triangular patches of intraoperative data with texture are calculated with a dimension-reduced triangulation algorithm and a projection-weighted mapping algorithm...
May 19, 2017: Journal of Biomedical Informatics
Dmitry Kurzhunov, Robert Borowiak, Marco Reisert, Axel Joachim Krafft, Ali Caglar Özen, Michael Bock
Oxygen metabolism is altered in brain tumor regions and is quantified by the cerebral metabolic rate of oxygen consumption (CMRO2). Direct dynamic (17)O MRI with inhalation of isotopically enriched (17)O2 gas can be used to quantify CMRO2; however, pixel-wise CMRO2 quantification in human brain is challenging due to low natural abundance of (17)O isotope and, thus, the low signal-to-noise ratio (SNR) of (17)O MR images. To test the feasibility CMRO2 mapping at a clinical 3 T MRI system, a new iterative reconstruction was proposed, which uses the edge information contained in a co-registered (1)H gradient image to construct a non-homogeneous anisotropic diffusion (AD) filter...
May 17, 2017: NeuroImage
Wanli Lu, Lei Li, Ailong Cai, Hanming Zhang, Linyuan Wang, Bin Yan
Iterative reconstruction algorithms for computed tomography (CT) through total variation (TV) regularization can provide accurate and stable reconstruction results. TV minimization is the L1-norm of gradient-magnitude images and can be regarded as a convex relaxation method to replace the L0 norm. In this study, a fast and efficient algorithm, which is named a weighted difference of L1 and L2 (L1 - αL2) on the gradient minimization, was proposed and investigated. The new algorithm provides a better description of sparsity for the optimization-based algorithms than TV minimization algorithms...
May 15, 2017: Journal of X-ray Science and Technology
Sergej Lebedev, Stefan Sawall, Michael Knaup, Marc Kachelrieß
PURPOSE: Optimization of the AIR-algorithm for improved convergence and performance. METHODS: The AIR method is an iterative algorithm for CT image reconstruction. As a result of its linearity with respect to the basis images, the AIR algorithm possesses well defined, regular image quality metrics, e.g. point spread function (PSF) or modulation transfer function (MTF), unlike other iterative reconstruction algorithms. The AIR algorithm computes weighting images α to blend between a set of basis images that preferably have mutually exclusive properties, e...
May 15, 2017: Zeitschrift Für Medizinische Physik
Marco Dal Maschio, Joseph C Donovan, Thomas O Helmbrecht, Herwig Baier
We introduce a flexible method for high-resolution interrogation of circuit function, which combines simultaneous 3D two-photon stimulation of multiple targeted neurons, volumetric functional imaging, and quantitative behavioral tracking. This integrated approach was applied to dissect how an ensemble of premotor neurons in the larval zebrafish brain drives a basic motor program, the bending of the tail. We developed an iterative photostimulation strategy to identify minimal subsets of channelrhodopsin (ChR2)-expressing neurons that are sufficient to initiate tail movements...
May 17, 2017: Neuron
Zhongshuai Zhang, Thomas Michaelis, Jens Frahm
BACKGROUND: Optimal control of minimally invasive interventions by hyperthermia requires dynamic temperature mapping at high temporal resolution. METHODS: Based on the temperature-dependent shift of the proton resonance frequency (PRF), this work developed a method for real-time MRI thermometry which relies on highly undersampled radial FLASH MRI sequences with iterative image reconstruction by regularized nonlinear inversion (NLINV). As a first step, the method was validated with use of a temperature phantom and ex vivo organs (swine kidney) subjected to heating by warm water or a pulsed laser source...
April 2017: Quantitative Imaging in Medicine and Surgery
Ute Lina Fahlenkamp, Ivan Diaz Ramirez, Moritz Wagner, Carsten Schwenke, Alexander Huppertz, Bernd Hamm, Alexander Lembcke
Background Computed tomography (CT) of the left atrium (LA) is performed prior to pulmonary vein isolation (PVI) to improve success of circumferential ablation for atrial fibrillation. The ablation procedure itself exposes patients to substantial radiation doses, therefore radiation dose reduction in pre-ablational imaging is of concern. Purpose To assess and compare diagnostic performance of low-radiation dose preprocedural CT in patients scheduled for PVI using two types of reconstruction algorithms. Material and Methods Forty-six patients (61 ± 10 years) scheduled for PVI were enrolled in this study irrespective of body-mass-index or cardiac rhythm at examination...
January 1, 2017: Acta Radiologica
Shabnam Khorasani Gerdekoohi, Naser Vosoughi, Kaveh Tanha, Majid Assadi, Pardis Ghafarian, Arman Rahmim, Mohammad Reza Ay
PURPOSE: Presence of photon attenuation severely challenges quantitative accuracy in single-photon emission computed tomography (SPECT) imaging. Subsequently, various attenuation correction methods have been developed to compensate for this degradation. The present study aims to implement an attenuation correction method and then to evaluate quantification accuracy of attenuation correction in small-animal SPECT imaging. METHODS: Images were reconstructed using an iterative reconstruction method based on the maximum-likelihood expectation maximization (MLEM) algorithm including resolution recovery...
May 16, 2017: Journal of Applied Clinical Medical Physics
Joonsung Lee, Narae Choi, Jin Keun Seo, Dong-Hyun Kim
PURPOSE: Magnetic Resonance Electrical Property Tomography (MREPT) is an emerging imaging modality using measured B1 maps from Magnetic Resonance Imaging (MRI) to measure a distribution of electric conductivity and permittivity of the subject at the Larmor frequency. Conventional MREPT approachesat single transmit channel system using the Helmholtz equation rely on an assumption that conductivity and permittivity of the subject are locally homogeneous. For small tissue structures and tissue boundaries, in which the assumption of locally homogeneous conductivity and permittivity does not hold, the reconstructed conductivity values deviated from the actual values, so called "Boundary Artifacts"...
May 16, 2017: Medical Physics
Julien Pagniez, Louise Legrand, Suonita Khung, Jean-Baptiste Faivre, Alain Duhamel, Andreas Krauss, Jacques Remy, Martine Remy-Jardin
OBJECTIVE: The aim of the study was to compare iterative metallic artefact reduction (iMAR) and monochromatic imaging on metal artifact reduction. MATERIALS AND METHODS: Follow-up of 29 occluded pulmonary arteriovenous malformations was obtained with dual-energy computed tomography with reconstruction of averaged images using filtered back projection (group 1), iMAR (group 2), and creation of high-energy monoenergetic images (group 3). Two types of coils had been used: (a) nickel only (group A, n = 18) and (b) nickel and platinum (group B, n = 11)...
May 2017: Journal of Computer Assisted Tomography
Gerhard Jung, Martin Hanke, Friederike Schmid
In recent years it has become increasingly popular to construct coarse-grained models with non-Markovian dynamics in order to account for an incomplete separation of time scales. One challenge of a systematic coarse-graining procedure is the extraction of the dynamical properties, namely the memory kernel, from equilibrium all-atom simulations. In this paper we propose an iterative method for memory reconstruction from dynamical correlation functions. Compared to previously proposed non-iterative techniques, it ensures by construction that the target correlation functions of the original fine-grained systems are reproduced accurately by the coarse-grained system, regardless of time step and discretization effects...
May 15, 2017: Journal of Chemical Theory and Computation
Lu Ding, X Luis Dean Ben, Daniel Razansky
Optimal optoacoustic tomographic sampling is often hindered by the frequency-dependent directivity of ultrasound sensors, which can only be accounted for with an accurate three-dimensional (3D) model. Herein, we introduce a 3D modelbased reconstruction method applicable to optoacoustic imaging systems employing detection elements with arbitrary size and shape. The computational complexity and memory requirements are mitigated by introducing an efficient graphics processing unit (GPU)-based implementation of the iterative inversion...
May 12, 2017: IEEE Transactions on Medical Imaging
Mary Germino, Jean-Dominique Gallezot, Jianhua Yan, Richard Carson
Parametric images for dynamic positron emission tomography (PET) are typically generated by an indirect method, i.e., reconstructing a time series of emission images, then fitting a kinetic model to each voxel time activity curve. Alternatively, "direct reconstruction," incorporates the kinetic model into the reconstruction algorithm itself, directly producing parametric images from projection data. Direct reconstruction has been shown to achieve parametric images with lower standard error than the indirect method...
May 15, 2017: Physics in Medicine and Biology
Mai Le, Jeffrey A Fessler
Undersampling is an effective method for reducing scan acquisition time for MRI. Strategies for accelerated MRI such as parallel MRI and Compressed Sensing MRI present challenging image reconstruction problems with non-differentiable cost functions and computationally demanding operations. Variable splitting (VS) can simplify implementation of difficult image reconstruction problems, such as the combination of parallel MRI and Compressed Sensing, CS-SENSE-MRI. Combined with augmented Lagrangian (AL) and alternating minimization strategies, variable splitting can yield iterative minimization algorithms with simpler auxiliary variable updates...
March 2017: IEEE Transactions on Computational Imaging
Jeong Hee Yoon, Mi Hye Yu, Won Chang, Jin-Young Park, Marcel Dominik Nickel, Yohan Son, Berthold Kiefer, Jeong Min Lee
OBJECTIVES: The purpose of the study was to investigate the clinical feasibility of free-breathing dynamic T1-weighted imaging (T1WI) using Cartesian sampling, compressed sensing, and iterative reconstruction in gadoxetic acid-enhanced liver magnetic resonance imaging (MRI). MATERIALS AND METHODS: This retrospective study was approved by our institutional review board, and the requirement for informed consent was waived. A total of 51 patients at high risk of breath-holding failure underwent dynamic T1WI in a free-breathing manner using volumetric interpolated breath-hold (BH) examination with compressed sensing reconstruction (CS-VIBE) and hard gating...
May 11, 2017: Investigative Radiology
Juhun Lee, Robert M Nishikawa, Ingrid Reiser, Margarita L Zuley, John M Boone
We tested the agreement of radiologists' rankings of different reconstructions of breast computed tomography images based on their diagnostic (classification) performance and on their subjective image quality assessments. We used 102 pathology proven cases (62 malignant, 40 benign), and an iterative image reconstruction (IIR) algorithm to obtain 24 reconstructions per case with different image appearances. Using image feature analysis, we selected 3 IIRs and 1 clinical reconstruction and 50 lesions. The reconstructions produced a range of image quality from smooth/low-noise to sharp/high-noise, which had a range in classifier performance corresponding to AUCs of 0...
April 2017: Journal of Medical Imaging
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