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We report a novel method for estimating fluorescence impulse response function (fIRF) from noise-corrupted time-domain fluorescence measurements of biological tissue. This method is based on the use of high-order Laguerre basis functions and a constrained least-squares approach that addresses the problem of overfitting due to increased model complexity. The new method was extensively evaluated on fluorescence data from simulation, fluorescent standard dyes, ex vivo tissue samples of atherosclerotic plaques and in vivo oral carcinoma. Current results demonstrate that this method allows for rapid and accurate deconvolution of multiple channel fluorescence decays without adaptively adjusting the Laguerre scale parameter. The appropriate choice of the scale parameter is essential for accurate ...

Physics in Medicine and Biology

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February 3, 2012
We present a new version of STIR (Software for Tomographic Image Reconstruction), an open source object-oriented library implemented in C++ for 3D positron emission tomography reconstruction. This library has been designed such that it can be used for many algorithms and scanner geometries, while being portable to various computing platforms. This second release enhances its flexibility and modular design and includes additional features such as Compton scatter simulation, an additional iterative reconstruction algorithm and parametric image reconstruction (both indirect and direct). We discuss the new features in this release and present example results. STIR can be downloaded from http://stir.sourceforge.net. PMID: 22290410 [PubMed - in process] (Source: Physics in Medicine and Biol...

Physics in Medicine and Biology

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February 3, 2012
Authors: Defrise M, Rezaei A, Nuyts J Abstract In positron emission tomography (PET), a quantitative reconstruction of the tracer distribution requires accurate attenuation correction. We consider situations where a direct measurement of the attenuation coefficient of the tissues is not available or is unreliable, and where one attempts to estimate the attenuation sinogram directly from the emission data by exploiting the consistency conditions that must be satisfied by the non-attenuated data. We show that in time-of-flight PET, the attenuation sinogram is determined by the emission data except for a constant and that its gradient can be estimated efficiently using a simple analytic algorithm. The stability of the method is illustrated numerically by means of a 2D simulation. ...

Physics in Medicine and Biology

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February 3, 2012
Authors: Jing Y, Meral FC, Clement GT Abstract This paper proposes the use of a k-space method to obtain the correction for transcranial ultrasound beam focusing. Mirroring past approaches, a synthetic point source at the focal point is numerically excited, and propagated through the skull, using acoustic properties acquired from registered computed tomography of the skull being studied. The received data outside the skull contain the correction information and can be phase conjugated (time reversed) and then physically generated to achieve a tight focusing inside the skull, by assuming quasi-plane transmission where shear waves are not present or their contribution can be neglected. Compared with the conventional finite-difference time-domain method for wave propagation simulation...

Physics in Medicine and Biology

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February 3, 2012
Authors: Kyriakou E, McKenzie DR Abstract Evidence that some lung tumors change shape during respiration is derived from respiratory gated CT data by statistical shape modeling and image manipulation. Some tumors behave as rigid objects while others show systematic shape changes. Two views of lung motion are presented to allow analysis of the results. In the first, lung motion is viewed as a wave motion in which inertial effects arising from mass are present and in the second it is a quasistatic motion in which the mass of the lung tissues is neglected. In the first scenario, the extremes of tumor compression and expansion are expected to correlate with maximum upward and downward velocity of the tumor, respectively. In the second, they should occur at end exhale and end inhale, re...

Physics in Medicine and Biology

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February 3, 2012
This study opens up the possibility of improved tumor ablation therapy via a combination of percutaneous ethanol injection and high-intensity focused ultrasound. PMID: 22290554 [PubMed - in process] (Source: Physics in Medicine and Biology)

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Physics in Medicine and Biology

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February 3, 2012
Authors: Laakso I, Hirata A Abstract From extremely low frequencies to intermediate frequencies, the magnitude of induced electric field inside the human body is used as the metric for human protection. The induced electric field inside the body can be computed using anatomically realistic voxel models and numerical methods such as the finite-difference or finite-element methods. The computed electric field is affected by numerical errors that occur when curved boundaries with large contrasts in electrical conductivity are approximated using a staircase grid. In order to lessen the effect of the staircase approximation error, the use of the 99th percentile electric field, i.e. ignoring the highest 1% of electric field values, is recommended in the ICNIRP guidelines. However, the 99...

Physics in Medicine and Biology

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February 3, 2012
This study reports on the electron slowing-down spectra and mean energy per ion pair, the W-value, in water for monoenergetic electron and photon sources calculated with Geant4-DNA. These quantities depend on electron energy, but not on spatial or angular variables which makes them a good choice for testing the model of energy transfer processes. The spectra also have a scientific value for radiobiological modeling as they describe the energy distribution of electrons entering small volumes, such as the cell nucleus. Comparisons of Geant4-DNA results with previous studies showed overall good agreement. Some differences in slowing-down spectra between Geant4-DNA and previous studies were found at 100 eV and at approximately 500 eV that were attributed to approximations in models of vibratio...

Physics in Medicine and Biology

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February 3, 2012
Authors: Provost J, Thiébaut S, Luo J, Konofagou EE Abstract Electromechanical Wave Imaging (EWI) is a non-invasive, ultrasound-based imaging method capable of mapping the electromechanical wave (EW) in vivo, i.e. the transient deformations occurring in response to the electrical activation of the heart. Optimal imaging frame rates, in terms of the elastographic signal-to-noise ratio, to capture the EW cannot be achieved due to the limitations of conventional imaging sequences, in which the frame rate is low and tied to the imaging parameters. To achieve higher frame rates, EWI is typically performed by combining sectors acquired during separate heartbeats, which are then combined into a single view. However, the frame rates achieved remain potentially sub-optimal and this approac...

Physics in Medicine and Biology

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February 3, 2012
Authors: Lampe J, Bassoy C, Rahmer J, Weizenecker J, Voss H, Gleich B, Borgert J Abstract Magnetic particle imaging (MPI) is a new tomographic imaging method which is able to capture the fast dynamic behavior of magnetic tracer material. From measured induced signals, the unknown magnetic particle concentration is reconstructed using a previously determined system function, which describes the relation between particle position and signal response. After discretization, the system function is represented by a matrix, whose size can prohibit the use of direct solvers for matrix inversion to reconstruct the image. In this paper, we present a new reconstruction approach, which combines efficient compression techniques and iterative reconstruction solvers. The data compression is based...

Physics in Medicine and Biology

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February 3, 2012
Authors: Chaswal V, Thomadsen BR, Henderson DL Abstract The development and application of an automated 3D greedy heuristic (GH) optimization algorithm utilizing the adjoint sensitivity fields for treatment planning to assess the advantage of directional interstitial prostate brachytherapy is presented. Directional and isotropic dose kernels generated using Monte Carlo simulations based on Best Industries model 2301 I-125 source are utilized for treatment planning. The newly developed GH algorithm is employed for optimization of the treatment plans for seven interstitial prostate brachytherapy cases using mixed sources (directional brachytherapy) and using only isotropic sources (conventional brachytherapy). All treatment plans resulted in V100 > 98% and D90 > 45 Gy for the t...

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Physics in Medicine and Biology

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February 3, 2012
In this study, we developed a pencil beam algorithm for scanning proton dose calculation by focusing on properly modeling individual scanning spots. All modeling parameters required by the pencil beam algorithm can be generated based solely on a few sets of measured data. We demonstrated that low-dose halos in single-spot profiles in the medium could be adequately modeled with the addition of a modified Cauchy-Lorentz distribution function to a double-Gaussian function. The field size effects were accurately computed at all depths and field sizes for all energies, and good dose accuracy was also achieved for patient dose verification. The implementation of the proposed pencil beam algorithm also enabled us to study the importance of different modeling components and parameters at various b...

Physics in Medicine and Biology

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February 3, 2012
Authors: Pursiainen S, Lucka F, Wolters CH Abstract In electroencephalography (EEG) source analysis, a primary current density generated by the neural activity of the brain is reconstructed from external electrode voltage measurements. This paper focuses on accurate and effective simulations of EEG through the complete electrode model (CEM). The CEM allows for the incorporation of the electrode size, shape and effective contact impedance into the forward simulation. Both neural currents in the brain and shunting currents between the electrodes and the skin can affect the measured voltages in the CEM. The goal of this study was to investigate the CEM by comparing it with the point electrode model (PEM), which is the current standard electrode model for EEG. We used a three-dimension...

Physics in Medicine and Biology

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February 3, 2012
Authors: Russell G, Harkins KD, Secomb TW, Galons JP, Trouard TP Abstract A new finite difference (FD) method for calculating the time evolution of complex transverse magnetization in diffusion-weighted magnetic resonance imaging and spectroscopy experiments is described that incorporates periodic boundary conditions. The new FD method relaxes restrictions on the allowable time step size employed in modeling which can significantly reduce computation time for simulations of large physical extent and allow for more complex, physiologically relevant, geometries to be simulated. PMID: 22297418 [PubMed - in process] (Source: Physics in Medicine and Biology)

Physics in Medicine and Biology

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February 3, 2012
In biomedical research and practice, quantitative tests or biomarkers are often used for diagnostic or screening purposes, with a cut point established on the quantitative measurement to aid binary classification. This paper introduces an alternative to the traditional methods based on the Youden index and the closest‐to‐(0, 1) criterion for threshold selection. A concordance probability evaluating the classification accuracy of a dichotomized measure is defined as an objective function of the possible cut point. A nonparametric approach is used to search for the optimal cut point maximizing the objective function. The procedure is shown to perform well in a simulation study. Using data from a real‐world study of arsenic‐induced skin lesions, we apply the method to a measure of blo...

Statistics in Medicine

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February 3, 2012
How medicine, sports and society are trying to heal and protect the brains of millions amidst the growing awareness of the long-lasting effects of traumatic head injury [More] (Source: Scientific American - Official RSS Feed)

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Scientific American - Official RSS Feed

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February 3, 2012
Morning After The Morning's Trash In my last post , I focused on flaws in the medical device approval process. The Union of Concerned Scientists FDA at a Crossroads meeting also covered problems with drug approval. This is perhaps no better illustrated than by the disappointing decision by Secretary of Health Kathleen Sebelius to deny the emergency contraceptive, Plan B, over-the-counter status for women under the age of 17 . This was a particular disappointment to many because President Obama had promised that decisions at the FDA would be made based on science, rather than politics. Some of us, naively, hoped that change we can believe in was real, having forgotten that the Tooth Fairy wasn t. [More] (Source: Scientific American - Official RSS Feed)

Scientific American - Official RSS Feed

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February 3, 2012
126 new pubmed citations were retrieved for your search. Click on the search hyperlink below to display the complete search results: "Angew Chem Int Ed Engl"[ta] These pubmed results were generated on 2012/02/03PubMed, a service of the National Library of Medicine, includes over 15 million citations for biomedical articles back to the 1950's. These citations are from MEDLINE and additional life science journals. PubMed includes links to many sites providing full text articles and other related resources. (Source: Angewandte Chemie)

Angewandte Chemie

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February 3, 2012
This article is currently available as a free download on ingentaconnect (Source: Military Medicine)

Military Medicine

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February 3, 2012
This article is currently available as a free download on ingentaconnect (Source: Military Medicine)

Military Medicine

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February 3, 2012