bluuebunny/crossref_metadata_2025 huggingface dataset:
In obese Zucker rats, lipids accumulate in the heart despite normal mitochondrial content, morphology and long‐chain fatty acid oxidation
Authors: Holloway Graham P. , Snook Laelie A. , Harris Robert J. , Glatz Jan F. C. , Luiken Joost J. F. P. , Bonen Arend
Published: November 2010

Non‐technical summary

The storage of fat within the heart muscle has been associated with reductions in force production, which has implications for the ability of the heart to adequately pump blood. With the assistance of membrane proteins known as transport proteins, fats from the blood can be moved into heart muscle cells, where they can either be stored or used for generating energy (within a structure called mitochondria) to pump blood. We provide evidence that in obese animals more fat accumulates within the heart as a result of their increased transport across the membranes of heart cells, not due to reductions in mitochondrial number or function. The knowledge of why fat accumulates in the heart may provide insight into novel treatments/therapies, and the current study suggests therapies focused on limiting the entry of fats into the heart may restore the ability of the heart to pump blood.
Modeling and Experimental Validation of DNA Motion in Uniform and Nonuniform DC Electric Fields
Authors: David Regis A. , Jensen Brian D. , Black Justin L. , Burnett Sandra H. , Howell Larry L.
Published: November 2010

We are developing a new technique to insert foreign DNA into a living cell using a microelectromechanical system. This new technique relies on electrical forces to move DNA in a nonuniform electric field. To better understand this phenomenon, we perform integrated modeling and experiments of DNA electrophoresis. This paper describes the protocol and presents the results for DNA motion experiments using fabricated gel electrophoresis devices. We show that DNA motion is strongly correlated with ion transport (current flow) in the system. A better understanding of electrophoretic fundamentals allows for the creation of a mathematical model to predict the motion of DNA during electrophoresis in both uniform and nonuniform electric fields. The mathematical model is validated within 4% through comparison with the experimental results.
Vibration of a Multilayered Graphene Sheet With Initial Stress
Authors: Wang Lifeng , He Xiaoqiao
Published: November 2010

This paper reports an investigation on the vibration of an individual multilayered graphene sheet with initial stress, based on an elastic plate model and membrane model with simply supported ends, considering the van der Waals force interaction between all layers of graphene sheets. The effect of initial stress is more obviously with an increase of half wave numbers m and n. This investigation indicates that the stiffness D, effected by thickness choose, plays a dominant role in the lowest natural frequencies, and much weaker role in high order natural frequencies. The influence of the stiffness is more significant for all natural frequencies with an increase of half wave numbers m and n. The lowest natural frequency of a multilayered graphene sheet for a given combination of m and n is independent of the van der Waals interaction but all of the other higher natural frequencies are significantly dependent on this interaction.
Magnetic Drug Targeting in Partly Occluded Blood Vessels Using Magnetic Microspheres
Authors: Banerjee Moloy K. , Datta Amitava , Ganguly Ranjan
Published: November 2010

Magnetic drug targeting can be used for treating stenosis and thrombosis in partly occluded blood vessels. Herein, a numerical investigation of magnetic drug targeting using functionalized magnetic microspheres in partly occluded blood vessels is conducted. An Eulerian-Lagrangian technique is adopted to resolve the hemodynamic flow and the motion of the magnetic particles in the flow. An implantable cylindrical permanent magnet insert is used to create the requisite magnetic field. Targeted transport of the magnetic particles in a partly occluded vessel differs distinctly from the same in a regular unblocked vessel. Parametric investigation is conducted, and the influence of the flow Re, magnetic insert diameter, and its radial and axial position on the “targeting efficiency” is reported. Analysis shows that there exists an optimum regime of operating parameters for which deposition of the drug-carrying magnetic particles in a predesignated target zone on the partly occluded vessel wall can be maximized. The results provide useful design bases for an in vitro setup for the investigation of magnetic drug targeting in stenosed blood vessels.
Periodic Nanomechanical Stimulation in a Biokinetics Model Identifying Anabolic and Catabolic Pathways Associated With Cartilage Matrix Homeostasis
Authors: Saha Asit K. , Kohles Sean S.
Published: November 2010

Enhancing the available nanotechnology to describe physicochemical interactions during biokinetic regulation will strongly support cellular and molecular engineering efforts. In a recent mathematical model developed to extend the applicability of a statically loaded, single-cell biomechanical analysis, a biokinetic regulatory threshold was presented (Saha and Kohles, 2010, “A Distinct Catabolic to Anabolic Threshold Due to Single-Cell Static Nanomechanical Stimulation in a Cartilage Biokinetics Model,” J. Nanotechnol. Eng. Med., 1(3), p. 031005). Results described multiscale mechanobiology in terms of catabolic to anabolic pathways. In the present study, we expand the mathematical model to continue exploring the nanoscale biomolecular response within a controlled microenvironment. Here, we introduce a dynamic mechanical stimulus for regulating cartilage molecule synthesis. Model iterations indicate the identification of a biomathematical mechanism balancing the harmony between catabolic and anabolic states. Relative load limits were defined to distinguish between “healthy” and “injurious” biomolecule accumulations. The presented mathematical framework provides a specific algorithm from which to explore biokinetic regulation.
A Novel Method to Attenuate Protein Adsorption Using Combinations of Polyethylene Glycol (PEG) Grafts and Piezoelectric Actuation
Authors: Yeh Po-Ying , Kizhakkedathu Jayachandran N. , Chiao Mu
Published: November 2010

An antifouling treatment based on the combined effects of grafted polyethylene glycol (PEG) polymers and the application of vibration is reported. A gold-coated lead zirconate titanate piezoelectric composite was grafted with PEG used as a model substrate. The PEG grafted surfaces were thoroughly characterized by attenuated total reflectance-Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. In vitro protein adsorption onto PEG coated surfaces was studied with and without the application of vibration. Bovine serum albumin (BSA) adsorption onto PEG grafted surfaces followed a similar pattern as reported in literature. However, when piezoelectric vibration was applied on the PEG grafted surface, BSA desorption was observed. At very low graft densities, the vibration significantly reduced the BSA adsorption compared with high PEG graft densities. Theoretical calculations showed that the thickness of PEG layer on the surface was affecting vibration induced protein desorption.
Dielectric Properties of Electrospun PVP and PAN Nanocomposite Fibers at Various Temperatures
Authors: Khan W. S. , Asmatulu R. , Eltabey M. M.
Published: November 2010

Dielectric properties of electrospun polyvinylpyrrolidone (PVP) and polyacrylonitrile (PAN) nanocomposite fibers were determined as a function of temperature and concentration in order to explore the possibility of using them as dielectric materials in different industrial applications. Multiwall carbon nanotubes and Ni0.6Zn0.4Fe2O4 (NiZn ferrite) were individually dispersed into the polymeric solutions of PVP and PAN and were then electrospun at various conditions. Thin layers of films were placed between two parallel Al electrode plates of the capacitance bridge prior to the measurements. We determined that nanoscale inclusions and temperature mainly affect the dielectric properties of the nanocomposite fibers. The dielectric studies can provide critical information for many electronic applications, such as loss of a cable insulator, the impedance of a substrate, and the frequency of a dielectric resonator.
Toward Distinct Element Method Simulations of Carbon Nanotube Systems
Authors: Anderson Tyler , Akatyeva Evgeniya , Nikiforov Ilia , Potyondy David , Ballarini Roberto , Dumitrică Traian
Published: November 2010

We propose distinct element method modeling of carbon nanotube systems. The atomic-level description of an individual nanotube is coarse-grained into a chain of spherical elements that interact by parallel bonds located at their contacts. The spherical elements can lump multiple translational unit cells of the carbon nanotube and have both translational and rotational degrees of freedom. The discrete long ranged interaction between nanotubes is included in a van der Waals contact of nonmechanical nature that acts simultaneously with the parallel bonds. The created mesoscopic model is put into service by simulating a realistic carbon nanotube ring. The ring morphology arises from the energy balance stored in both parallel and van der Waals bonds.
GPU‐accelerated Monte Carlo convolution/superposition implementation for dose calculation
Authors: Zhou Bo , Yu Cedric X. , Chen Danny Z. , Hu X. Sharon
Published: November 2010

Purpose:

Dose calculation is a key component in radiation treatment planning systems. Its performance and accuracy are crucial to the quality of treatment plans as emerging advanced radiation therapy technologies are exerting ever tighter constraints on dose calculation. A common practice is to choose either a deterministic method such as the convolution/superposition (CS) method for speed or a Monte Carlo (MC) method for accuracy. The goal of this work is to boost the performance of a hybrid Monte Carlo convolution/superposition (MCCS) method by devising a graphics processing unit (GPU) implementation so as to make the method practical for day‐to‐day usage.

Methods:

Although the MCCS algorithm combines the merits of MC fluence generation and CS fluence transport, it is still not fast enough to be used as a day‐to‐day planning tool. To alleviate the speed issue of MC algorithms, the authors adopted MCCS as their target method and implemented a GPU‐based version. In order to fully utilize the GPU computing power, the MCCS algorithm is modified to match the GPU hardware architecture. The performance of the authors' GPU‐based implementation on an Nvidia GTX260 card is compared to a multithreaded software implementation on a quad‐core system.

Results:

A speedup in the range of 6.7–11.4× is observed for the clinical cases used. The less than 2% statistical fluctuation also indicates that the accuracy of the authors' GPU‐based implementation is in good agreement with the results from the quad‐core CPU implementation.

Conclusions:

This work shows that GPU is a feasible and cost‐efficient solution compared to other alternatives such as using cluster machines or field‐programmable gate arrays for satisfying the increasing demands on computation speed and accuracy of dose calculation. But there are also inherent limitations of using GPU for accelerating MC‐type applications, which are also analyzed in detail in this article.
Ultrafast treatment plan optimization for volumetric modulated arc therapy (VMAT)
Authors: Men Chunhua , Romeijn H. Edwin , Jia Xun , Jiang Steve B.
Published: November 2010

Purpose:

To develop a novel aperture‐based algorithm for volumetric modulated arc therapy (VMAT) treatment plan optimization with high quality and high efficiency.

Methods:

The VMAT optimization problem is formulated as a large‐scale convex programming problem solved by a column generation approach. The authors consider a cost function consisting two terms, the first enforcing a desired dose distribution and the second guaranteeing a smooth dose rate variation between successive gantry angles. A gantry rotation is discretized into 180 beam angles and for each beam angle, only one MLC aperture is allowed. The apertures are generated one by one in a sequential way. At each iteration of the column generation method, a deliverable MLC aperture is generated for one of the unoccupied beam angles by solving a subproblem with the consideration of MLC mechanic constraints. A subsequent master problem is then solved to determine the dose rate at all currently generated apertures by minimizing the cost function. When all 180 beam angles are occupied, the optimization completes, yielding a set of deliverable apertures and associated dose rates that produce a high quality plan.

Results:

The algorithm was preliminarily tested on five prostate and five head‐and‐neck clinical cases, each with one full gantry rotation without any couch/collimator rotations. High quality VMAT plans have been generated for all ten cases with extremely high efficiency. It takes only 5–8 min on CPU (MATLAB code on an Intel Xeon 2.27 GHz CPU) and 18–31 s on GPU (CUDA code on an NVIDIA Tesla C1060 GPU card) to generate such plans.

Conclusions:

The authors have developed an aperture‐based VMAT optimization algorithm which can generate clinically deliverable high quality treatment plans at very high efficiency.
Model‐based measurements of the diameter of the internal carotid artery in CT angiography images
Authors: Gratama van Andel H. A. F. , Venema H. W. , Bol K. , Marquering H. A. , Majoie C. B. , den Heeten G. J. , Grimbergen C. A. , Streekstra G. J.
Published: November 2010

Purpose:

Computed tomography angiography (CTA) is often used to determine the degree of stenosis in patients that suffer from carotid artery occlusive disease. Accurate and precise measurements of the diameter of the stenosed internal carotid artery are required to make decisions on treatment of the patient. However, the inherent blurring of images hampers a straightforward measurement, especially for smaller vessels. The authors propose a model‐based approach to perform diameter measurements in which explicit allowance is made for the blurring of structures in the images. Three features of the authors' approach are the use of prior knowledge in the fitting of the model at the site of the stenosis, the applicability to vessels both with circular and noncircular cross‐section, and the ability to deal with additional structures close to the arteries such as calcifications.

Methods:

Noncircular cross‐sections of vessels were modeled with elliptic Fourier descriptors. When calcifications or other high‐intensity structures are adjacent to the lumen, both the lumen and the high‐intensity structures were modeled in order to improve the diameter estimates of the vessel. Measurements were performed in CT scans of a phantom mimicking stenosed carotids and in CTA scans of two patients with an internal carotid stenosis. In an attempt to validate the measurements in CTA images, measurements were also performed in three‐dimensional rotational angiography (3DRA) images of the same patients.

Results:

The validity of the approach for diameter measurements of cylindrical arteries in CTA images is evident from phantom measurements. When prior knowledge about the enhancement and the blurring parameter was used, accurate and precise diameter estimates were obtained down to a diameter of 0.4 mm. The potential of the presented approach, both with respect to the extension to noncircular cross‐sections and the modeling of adjacent calcifications, appears from the patient data. The accuracy of the size estimates in the patient images could not be unambiguously established because no gold standard was available and the quality of the 3DRA images was often suboptimal.

Conclusions:

The authors have shown that the inclusion ofa priori information results in accurate and precise diameter measurements of arteries with a small diameter. Furthermore, in patient data, the assumption of a circular cross‐section often appears to be too simple. The extension to noncircular cross‐sections and adjacent calcifications paves the way to realistic modeling of the carotid artery.
Evaluation of an improved algorithm for producing realistic 3D breast software phantoms: Application for mammography
Authors: Bliznakova K. , Suryanarayanan S. , Karellas A. , Pallikarakis N.
Published: November 2010

Purpose:

This work presents an improved algorithm for the generation of 3D breast software phantoms and its evaluation for mammography.

Methods:

The improved methodology has evolved from a previously presented 3D noncompressed breast modeling method used for the creation of breast models of different size, shape, and composition. The breast phantom is composed of breast surface, duct system and terminal ductal lobular units, Cooper's ligaments, lymphatic and blood vessel systems, pectoral muscle, skin, 3D mammographic background texture, and breast abnormalities. The key improvement is the development of a new algorithm for 3D mammographic texture generation. Simulated images of the enhanced 3D breast model without lesions were produced by simulating mammographic image acquisition and were evaluated subjectively and quantitatively. For evaluation purposes, a database with regions of interest taken from simulated and real mammograms was created. Four experienced radiologists participated in a visual subjective evaluation trial, as they judged the quality of the simulated mammograms, using the new algorithm compared to mammograms, obtained with the old modeling approach. In addition, extensive quantitative evaluation included power spectral analysis and calculation of fractal dimension, skewness, and kurtosis of simulated and real mammograms from the database.

Results:

The results from the subjective evaluation strongly suggest that the new methodology for mammographic breast texture creates improved breast models compared to the old approach. Calculated parameters on simulated images such as exponent deducted from the power law spectral analysis and fractal dimension are similar to those calculated on real mammograms. The results for the kurtosis and skewness are also in good coincidence with those calculated from clinical images. Comparison with similar calculations published in the literature showed good agreement in the majority of cases.

Conclusions:

The improved methodology generated breast models with increased realism compared to the older model as shown in evaluations of simulated images by experienced radiologists. It is anticipated that the realism will be further improved using an advanced image simulator so that simulated images may be used in feasibility studies in mammography.
Dosimetric optimization of a conical breast brachytherapy applicator for improved skin dose sparing
Authors: Yang Yun , Rivard Mark J.
Published: November 2010

Purpose:

Both the AccuBoost® D‐shaped and round applicators have been dosimetrically characterized and clinically used to treat patients with breast cancer. While the round applicators provide conformal dose coverage, under certain clinical circumstances the breast skin dose may be higher than preferred. The purpose of this study was to modify the round applicators to minimize skin dose while not substantially affecting dose uniformity within the target volume and reducing the treatment time.

Methods:

In order to irradiate the intended volume while sparing critical structures such as the skin, the current round applicator design has been augmented through the addition of an internal truncated cone (i.e., frustum) shield. Monte Carlo methods and clinical constraints were used to design the optimal cone applicator. With the cone applicator now defined as the entire assembly including the surrounding tungsten‐alloy shell holding the HDR source catheter, the applicator height was reduced to diminish the treatment time while minimizing skin dose. Monte Carlo simulation results were validated using both radiochromic film and ionization chamber measurements based on established techniques.

Results:

The optimal cone applicators diminished the maximum skin dose by 15%–32% (based on the applicator diameter and breast separation) with the tumor dose reduced by less than 3% for a constant exposure time. Furthermore, reduction in applicator height diminished the treatment time by up to 30%. Radiochromic film and ionization chamber dosimetric results in phantom agreed with Monte Carlo simulation results typically within 3%. Larger differences were outside the treatment volume in low dose regions or associated with differences between the measurement and Monte Carlo simulation environments.

Conclusions:

A new radiotherapy treatment device was developed and dosimetrically characterized. This set of applicators significantly reduces the skin dose and treatment time while retaining uniform target dose.
Monte Carlo simulation of the effects of anode surface roughness on x‐ray spectra
Authors: Kákonyi Róbert , Erdélyi Miklós , Szabó Gábor
Published: November 2010

Purpose:

Spectral and angular distribution of the x‐ray beam generated by medical x‐ray tubes as a function of anode surface roughness was analyzed.

Methods:

Different sets of profiles such as ideal flat, regular profiles, and measured profiles adopted from the literature were analyzed by means ofMCNPX Monte Carlo simulator. The geometry used was simplified to separate different physical effects. A sphere centered on the origin of the coordinate system was divided into two hemispheres filled with tungsten and a vacuum, respectively. The studied anode surfaces were placed at the center of the plane of the hemisphere. The profiles were realized by means of the general lattice structure of the MCNPX. The energy and angular distributions of the excited photons were recorded with energy and angular resolutions of 0.5 keV and 1°, respectively, by means of point detectors. The range of the studied anode surface roughness was . The emission angle dependencies of the following quantities were analyzed: Half value layer (HVL) value, intensity, and spectral photon flux.

Results:

The analysis of the HVL of the x‐ray beam showed that around an emission angle of 5°, the hardness of the beam was practically independent of the surface roughness. The value of this emission angle depends on the filtration. Below this critical angle, the HVL value decreases, while at a higher emission angle, the beam becomes harder with increasing surface roughness. The intensity degradation saturates with increasing roughness. The position of the maximum spectral photon flux shifts to higher emission angles as the anode surface roughness increases. The surface roughness was found to be an inadequate quantity to describe the effect of anode surface roughness on x‐ray spectra since no definite connection was found between the values of the intensity degradation and surface roughness. At 120 kVp tube voltage and at a roughness value, the effect of anode surface roughness introduces a 5% and 12% intensity degradation at a 5° and 12° emission angle, respectively. However, it has a higher impact at low tube voltages , e.g., in mammography systems where the intensity degradation could even be 25% at the “newly” polished anode surface.

Conclusions:

The effects of anode surface roughness on x‐ray spectra were successfully simulated by a Monte Carlo method. It was proved that the effect of the anode surface roughness could not be modeled by simple filters made from the anode material. The surface roughness was found to be an inadequate quantity to describe the effect of anode surface roughness on x‐ray spectra.
Oblique incidence for broad monoenergetic proton beams
Authors: Jette David , Yuan Jiankui , Chen Weimin
Published: November 2010

Purpose:

The depth dose of a monoenergetic broad parallel proton beam has been modeled in a number of ways, but evidently not yet for oblique incidence. The purpose of this investigation is to find an accurate analytic formula for this case, which can then be used to model the depth dose of a broad beam with an initial Gaussian angular distribution.

Methods:

The Bortfeld model of depth dose in a broad normally incident proton beam has been extended to the case of oblique incidence. This extension uses an empirically determined Gaussian parameter which (roughly) characterizes the off‐axis dose of a proton pencil beam. As with Bortfeld's work, the modeling is done in terms of parabolic cylinder functions. To obtain the depth dose for an initial angular distribution, the result is integrated over the angle of incidence, weighted by a Gaussian probability function. The predictions of the theory have been compared to MCNPX Monte Carlo calculations for four phantom materials (water, bone, aluminum, and copper) and for initial proton energies of 50, 100, 150, 200, and 250 MeV.

Results:

Comparisons of the depth dose predicted by this theory with Monte Carlo calculations have established that with very good accuracy, can be taken to be independent both of the depth and of the angle of incidence. As a function of initial proton range or of initial proton energy, has been found to obey a power law to very high accuracy. Good fits to Monte Carlo calculations have also been found for an initial Gaussian angular distribution.

Conclusions:

This investigation is the first step in the accurate modeling of a proton pencil beam with initial Gaussian angular distribution. It provides the longitudinal factor, with its Bragg peak buildup and sharp distal falloff. A transverse factor must still be incorporated into this theory and this will give the lateral penumbra of a collimated proton beam. Also, it will be necessary to model the dose of product particles from nuclear interactions of the proton beam. With the accurate modeling of a pencil beam, it will be possible to accurately take into account the effect of localized tissue inhomogeneities.
Three‐dimensional canine heart model for cardiac elastography
Authors: Chen Hao , Varghese Tomy
Published: November 2010

Purpose:

A three‐dimensional finite element analysis based canine heart model is introduced that would enable the assessment of cardiac function.

Methods:

The three‐dimensional canine heart model is based on the cardiac deformation and motion model obtained from the Cardiac Mechanics Research Group at UCSD. The canine heart model is incorporated into ultrasound simulation programs previously developed in the laboratory, enabling the generation of simulated ultrasound radiofrequency data to evaluate algorithms for cardiac elastography. The authors utilize a two‐dimensional multilevel hybrid method to estimate local displacements and strain from the simulated cardiac radiofrequency data.

Results:

Tissue displacements and strains estimated along both the axial and lateral directions (with respect to the ultrasound scan plane) are compared to the actual scatterer movement obtained using the canine heart model. Simulation and strain estimation algorithms combined with the three‐dimensional canine heart model provide high resolution displacement and strain curves for improved analysis of cardiac function. The use of principal component analysis along parasternal cardiac short axis views is also presented.

Conclusions:

A 3D cardiac deformation model is proposed for evaluating displacement tracking and strain estimation algorithms for cardiac strain imaging. Validation of the model is shown using ultrasound simulations to generate axial and lateral displacement and strain curves that are similar to the actual axial and lateral displacement and strain curves.
“SABER”: A new software tool for radiotherapy treatment plan evaluation
Authors: Zhao Bo , Joiner Michael C. , Orton Colin G. , Burmeister Jay
Published: November 2010

Purpose:

Both spatial and biological information are necessary in order to perform true optimization of a treatment plan and for predicting clinical outcome. The goal of this work is to develop an enhanced treatment plan evaluation tool which incorporates biological parameters and retains spatial dose information.

Methods:

A software system is developed which provides biological plan evaluation with a novel combination of features. It incorporates hyper‐radiosensitivity using the induced‐repair model and applies the new concept of dose convolution filter (DCF) to simulate dose wash‐out effects due to cell migration, bystander effect, and/or tissue motion during treatment. Further, the concept of spatial DVH (sDVH) is introduced to evaluate and potentially optimize the spatial dose distribution in the target volume. Finally, generalized equivalent uniform dose is derived from both the physical dose distribution (gEUD) and the distribution of equivalent dose in 2 Gy fractions and the software provides three separate models for calculation of tumor control probability (TCP), normal tissue complication probability (NTCP), and probability of uncomplicated tumor control . TCP, NTCP, and are provided as a function of prescribed dose and multivariable TCP, NTCP, and plots are provided to illustrate the dependence on individual parameters used to calculate these quantities. Ten plans from two clinical treatment sites are selected to test the three calculation models provided by this software.

Results:

By retaining both spatial and biological information about the dose distribution, the software is able to distinguish features of radiotherapy treatment plans not discernible using commercial systems. Plans that have similar DVHs may have different spatial and biological characteristics and the application of novel tools such as sDVH and DCF within the software may substantially change the apparent plan quality or predicted plan metrics such as TCP and NTCP. For the cases examined, both the calculation method and the application of DCF can change the ranking order of competing plans. The voxel‐by‐voxel TCP model makes it feasible to incorporate spatial variations of clonogen densities, radiosensitivities , and fractionation sensitivities as those data become available.

Conclusions:

The new software incorporates both spatial and biological information into the treatment planning process. The application of multiple methods for the incorporation of biological and spatial information has demonstrated that the order of application of biological models can change the order of plan ranking. Thus, the results of plan evaluation and optimization are dependent not only on the models used but also on the order in which they are applied. This software can help the planner choose more biologically optimal treatment plans and potentially predict treatment outcome more accurately.
Reduction of excitation light leakage to improve near‐infrared fluorescence imaging for tissue surface and deep tissue imaging
Authors: Zhu Banghe , Rasmussen John C. , Lu Yujie , Sevick‐Muraca Eva M.
Published: November 2010

Purpose:

Fluorescence‐enhanced optical imaging using near‐infrared (NIR) light developed forin vivo molecular targeting and reporting of various diseases provides promising opportunities for diagnostic imaging. However, the measurement sensitivity of NIR fluorescence (NIRF) optical imaging systems is limited by the leakage of the strong backscattered excitation light through rejection filters. In this article, the authors present a systematic method for improving sensitivity and validating the NIRF optical imager currently used for clinical imaging of human lymphatic function.

Methods:

The proposed systemic method consists of an appropriate filter combination and a collimation optics adapted to an NIRF optical imager. The spectral contributions were first assessed due to the excitation light backscattered from the tissue and from non‐normal‐incidence of the excitation light on the optical filters used in the authors' NIRF clinical imaging system. Then two tests were conducted to assess the system with and without the components of appropriate filters combination and collimation optics using: (1) a phantom to evaluate excitation light leakage as a function of target depth and (2) deployment in an actual human study.

Results:

The phantom studies demonstrate as much as two to three orders of magnitude reduction in the transmission ratio, indicating that the excitation light leakage can be reduced upon using the appropriate filter combination and collimation optics while anin vivo investigatory human study confirms improved imaging.

Conclusions:

The method for reducing the excitation light leakage is presented for validating collected signals for fluorescence imaging.
Photoacoustic angiography of the breast
Authors: Kruger Robert A. , Lam Richard B. , Reinecke Daniel R. , Del Rio Stephen P. , Doyle Ryan P.
Published: November 2010

Purpose:

The authors report a noninvasive technique and instrumentation for visualizing vasculature in the breast in three dimensions without using either ionizing radiation or exogenous contrast agents, such as iodine or gadolinium. Vasculature is visualized by virtue of its high hemoglobin content compared to surrounding breast parenchyma. The technique is compatible with dynamic contrast‐enhanced studies.

Methods:

Photoacoustic sonic waves were stimulated in the breast with a pulsed laser operating at 800 nm and a mean exposure of 20 mJ/pulse over an area of. These waves were subsequently detected by a hemispherical array of piezoelectric transducers, the temporal signals from which were filtered and backprojected to form three‐dimensional images with nearly uniform k‐space sampling.

Results:

Three‐dimensional vascular images of a human volunteer demonstrated a clear visualization of vascular anatomy with submillimeter spatial resolution to a maximum depth of 40 mm using a 24 s image acquisition protocol. Spatial resolution was nearly isotropic and approached over a field of view.

Conclusions:

The authors have successfully visualized submillimeter breast vasculature to a depth of 40 mm using an illumination intensity that is 32 times less than the maximum permissible exposure according to theAmerican National Standard for Safe Use of Lasers. Clearly, the authors can achieve greater penetration depth in the breast by increasing the intensity and the cross‐sectional area of the illumination beam. Given the 24 s image acquisition time without contrast agent, dynamic, contrast‐enhanced, photoacoustic breast imaging using optically absorbing contrast agents is conceivable in the future.
Performance of the NIRS fast scanning system for heavy‐ion radiotherapy
Authors: Furukawa Takuji , Inaniwa Taku , Sato Shinji , Shirai Toshiyuki , Takei Yuka , Takeshita Eri , Mizushima Kota , Iwata Yoshiyuki , Himukai Takeshi , Mori Shinichiro , Fukuda Shigekazu , Minohara Shinichi , Takada Eiichi , Murakami Takeshi , Noda Koji
Published: November 2010

Purpose:

A project to construct a new treatment facility, as an extension of the existing HIMAC facility, has been initiated for the further development of carbon‐ion therapy at NIRS. This new treatment facility is equipped with a 3D irradiation system with pencil‐beam scanning. The challenge of this project is to realize treatment of a moving target by scanning irradiation. To achieve fast rescanning within an acceptable irradiation time, the authors developed a fast scanning system.

Methods:

In order to verify the validity of the design and to demonstrate the performance of the fast scanning prior to use in the new treatment facility, a new scanning‐irradiation system was developed and installed into the existing HIMAC physics‐experiment course. The authors made strong efforts to develop (1) the fast scanning magnet and its power supply, (2) the high‐speed control system, and (3) the beam monitoring. The performance of the system including 3D dose conformation was tested by using the carbon beam from the HIMAC accelerator.

Results:

The performance of the fast scanning system was verified by beam tests. Precision of the scanned beam position was less than ±0.5 mm. By cooperating with the planning software, the authors verified the homogeneity of the delivered field within ±3% for the 3D delivery. This system took only 20 s to deliver the physical dose of 1 Gy to a spherical target having a diameter of 60 mm with eight rescans. In this test, the average of the spot‐staying time was considerably reduced to, while the minimum staying time was .

Conclusions:

As a result of this study, the authors verified that the new scanning delivery system can produce an accurate 3D dose distribution for the target volume in combination with the planning software.
Flow measurement in MRI using arterial spin labeling with cumulative readout pulses—Theory and validation
Authors: Wang Yi , Kim Seong‐Eun , DiBella Edward V. R. , Parker Dennis L.
Published: November 2010

Purpose:

This article systematically examines arterial spin labeling (ASL) as a flow quantification technique through theoretical simulation,in vitro, and in vivo experiment. The authors present a novel imaging pulse sequence design consisting of a single ASL magnetization preparation followed by Look‐Locker‐like image readouts. Bloch‐equation‐based modeling has been developed and validated using a hemodialyzer as a tissue‐mimicking flow phantom.

Methods:

After the single in‐plane slice‐selective double inversion magnetization preparation, multiple TFL readouts are acquired with linear k‐space ordering, causing a signal variation that depends on through‐slice flow velocity. Computer simulations were performed to assess the behavior of the flow‐dependent ASL signal as a function of varying imaging parameters. The signal was optimized by choosing imaging parameters that maximize the simulated flow‐sensitive signal. Furthermore, a hemodialyzer which mimics blood flow in human tissues was tested with a wide range of flow rates. An exponential curve fitting of the flow‐sensitive dynamics to the model derived from Bloch equations provides a method to estimate through‐slice velocity for varying flow rates on the hemodialyzer andin vivo human brain.

Results:

The flow dependency of the ASL signal and the sensitivity of the ASL signal to imaging parameters were demonstrated. Experimental results from a hemodialyzer when fitted with a Bloch‐equation‐based model provide flow measurements that are consistent with ground truth velocities. Human brain velocity mapping was obtained as well.

Conclusions:

The results provide evidence that the proposed pulse sequence design is an effective technique to measure total fluid flow through image voxels. The unique combination of the two main features, multiple‐image readout after a single ASL preparation and linear acquisition ordering in the phase encoding direction in TFL imaging, make this technique an appealing flow imaging method to quantify through‐plane flow in a time‐efficient manner.
Exploring the potential of context‐sensitive CADe in screening mammography
Authors: Tourassi Georgia D. , Mazurowski Maciej A. , Harrawood Brian P. , Krupinski Elizabeth A.
Published: November 2010

Purpose:

Conventional computer‐assisted detection (CADe) systems in screening mammography provide the same decision support to all users. The aim of this study was to investigate the potential of a context‐sensitive CADe system which provides decision support guided by each user's focus of attention during visual search and reporting patterns for a specific case.

Methods:

An observer study for the detection of malignant masses in screening mammograms was conducted in which six radiologists evaluated 20 mammograms while wearing an eye‐tracking device. Eye‐position data and diagnostic decisions were collected for each radiologist and case they reviewed. These cases were subsequently analyzed with an in‐house knowledge‐based CADe system using two different modes: Conventional mode with a globally fixed decision threshold and context‐sensitive mode with a location‐variable decision threshold based on the radiologists' eye dwelling data and reporting information.

Results:

The CADe system operating in conventional mode had 85.7% per‐image malignant mass sensitivity at 3.15 false positives per image (FPsI). The same system operating in context‐sensitive mode provided personalized decision support at 85.7%–100% sensitivity and 0.35–0.40 FPsI to all six radiologists. Furthermore, context‐sensitive CADe system could improve the radiologists' sensitivity and reduce their performance gap more effectively than conventional CADe.

Conclusions:

Context‐sensitive CADe support shows promise in delineating and reducing the radiologists' perceptual and cognitive errors in the diagnostic interpretation of screening mammograms more effectively than conventional CADe.
Geometrical and Monte Carlo projectors in 3D PET reconstruction
Authors: Aguiar Pablo , Rafecas Magdalena , Ortuño Juan Enrique , Kontaxakis George , Santos Andrés , Pavía Javier , Ros Domènec
Published: November 2010

Purpose: In the present work, the authors compare geometrical and Monte Carlo projectors in detail. The geometrical projectors considered were the conventional geometrical Siddon ray‐tracer (S‐RT) and the orthogonal distance‐based ray‐tracer (OD‐RT), based on computing the orthogonal distance from the center of image voxel to the line‐of‐response. A comparison of these geometrical projectors was performed using different point spread function (PSF) models. The Monte Carlo‐based method under consideration involves an extensive model of the system response matrix based on Monte Carlo simulations and is computed off‐line and stored on disk.

Methods: Comparisons were performed using simulated and experimental data of the commercial small animal PET scanner rPET.

Results: The results demonstrate that the orthogonal distance‐based ray‐tracer and Siddon ray‐tracer using PSF image‐space convolutions yield better images in terms of contrast and spatial resolution than those obtained after using the conventional method and the multiray‐based S‐RT. Furthermore, the Monte Carlo‐based method yields slight improvements in terms of contrast and spatial resolution with respect to these geometrical projectors.

Conclusions: The orthogonal distance‐based ray‐tracer and Siddon ray‐tracer using PSF image‐space convolutions represent satisfactory alternatives to factorizing the system matrix or to the conventional on‐the‐fly ray‐tracing methods for list‐mode reconstruction, where an extensive modeling based on Monte Carlo simulations is unfeasible.
Thoracic target volume delineation using various maximum‐intensity projection computed tomography image sets for radiotherapy treatment planning
Authors: Zamora David A. , Riegel Adam C. , Sun Xiaojun , Balter Peter , Starkschall George , Mawlawi Osama , Pan Tinsu
Published: November 2010

Purpose:

Four‐dimensional computed tomography (4D‐CT) is commonly used to account for respiratory motion of target volumes in radiotherapy to the thorax. From the 4D‐CT acquisition, a maximum‐intensity projection (MIP) image set can be created and used to help define the tumor motion envelope or the internal gross tumor volume (iGTV). The purpose of this study was to quantify the differences in automatically contoured target volumes for usage in the delivery of stereotactic body radiation therapy using MIP data sets generated from one of the four methods: (1) 4D‐CT phase‐binned (PB) based on retrospective phase calculations, (2) 4D‐CT phase‐corrected phase‐binned (PC‐PB) based on motion extrema, (3) 4D‐CT amplitude‐binned (AB), and (4) cine CT built from all available images.

Methods:

MIP image data sets using each of the four methods were generated for a cohort of 28 patients who had prior thoracic 4D‐CT scans that exhibited lung tumor motion of at least 1 cm. Each MIP image set was automatically contoured on commercial radiation treatment planning system. Margins were added to the iGTV to observe differences in the final simulated planning target volumes (PTVs).

Results:

For all patients, the iGTV measured on the MIP generated from the entire cine CT data set was the largest. Expressed as a percentage of , 4D‐CT iGTV (all sorting methods) ranged from 83.8% to 99.1%, representing differences in the absolute volume ranging from 0.02 to ; the largest average and range of 4D‐CT iGTV measurements was from the PC‐PB data set. Expressed as a percentage of (expansions applied to ), the 4D‐CT PTV ranged from 87.6% to 99.6%, representing differences in the absolute volume ranging from 0.08 to . Regions of the measured respiratory waveform corresponding to a rapid change of phase or amplitude showed an increased susceptibility to the selection of identical images for adjacent bins. Duplicate image selection was most common in the AB implementation, followed by the PC‐PB method. The authors also found that the image associated with the minimum amplitude measurement did not always correlate with the image that showed maximum tumor motion extent.

Conclusions:

The authors identified cases in which the MIP generated from a 4D‐CT sorting process under‐represented the iGTV by more than 10% or up to when compared to the . They suggest utilization of a MIP generated from the full cine CT data set to ensure maximum inclusive tumor extent.
Strategies for scatter correction in dual source CT
Authors: Petersilka M. , Stierstorfer K. , Bruder H. , Flohr T.
Published: November 2010

Purpose:

Dual source CT (DSCT) systems utilize two measurement systems (A) and (B) offset by about 90°. A special challenge in DSCT is cross‐scattered radiation, i.e., scattered radiation from x‐ray tube (B) detected in detector (A) and vice versa. Cross‐scattered radiation can produce artifacts and degrade the contrast‐to‐noise ratio (CNR) of the images. Correction algorithms are mandatory to mitigate the negative effects of cross‐scattered radiation. The purpose of this work is to describe and evaluate different methods for cross‐scatter correction in DSCT.

Methods:

The authors present two techniques for cross‐scatter correction in DSCT. The first technique (1) is model‐based. Assuming that cross‐scatter is predominantly surface scatter, adequate knowledge about the surface of the scattering object is sufficient to describe the magnitude and distribution of cross‐scatter. The relevant surface information is derived from an analysis of the raw‐data sinogram during the CT‐scan. The correction is performed by a table look‐up into previously measured and stored cross‐scatter distributions for a variety of objects with different surface characteristics. The second technique (2) is measurement‐based. Dedicated sensors outside the penumbra of the fan beam in the z direction on both detectors (A) and (B) are used for an online measurement of both cross‐scattered and forward scattered radiation during the CT‐scan. In addition to the two scatter‐correction techniques, the authors describe a low‐pass filter method for the scatter‐correction term with the goal to improve the CNR of the corrected images. This filter can be applied to both model‐based (1) and measurement‐based (2) scatter correction. Both scatter‐correction techniques (1) and (2) are quantitatively assessed and the performance of the low‐pass filter method is evaluated using DSCT data of phantoms (water cylinders and anthropomorphic phantoms) and DSCT patient scan data.

Results:

Both scatter‐correction techniques restore image contrasts and reduce cross‐scatter induced artifacts in DSCT images. The measurement‐based technique results in higher CNR than the model‐based technique if the proposed low‐pass filtering of the scatter‐correction term is applied. Low‐pass filtering improves the CNR of cross‐scatter‐correction approaches beyond the limits published in the literature [Engel et al., “X‐ray scattering in single‐ and dual‐source CT,” Med. Phys. 35(1), 318–332 (2008)].

Conclusions:

Both model‐based and measurement‐based scatter correction can mitigate the negative effects of cross‐scatter in DSCT. The application of low‐pass filtering to the scatter‐correction term improves the CNR whenever the ratio of scattered radiation to total signal is high, as in larger patients.