bluuebunny/crossref_metadata_2025 huggingface dataset:
Trajectories in the Development of Islamic Theological Thought: the Synthesis ofKalām
Authors: Shah Mustafa
Published: July 2007

The field of Islamic theology (kalām) is not merely a receptacle for the presentation of the creedal statements and doctrinal catechisms of Islam; it derives itsraison d’êtrenot only from the articulation and elucidation of the doctrines of faith, but also by means of its rational and painstaking explication of dogma. While many of the dogmatic statements expressed in Islamic theology naturally emanate from a traditional substratum, countless more are the result of dialectical discussions as theologians expounded upon abstract constructs of religious dogma. Recent academic research is exploring the history, trends and conceptual achievements behind the Islamic experiment with theology, providing insights into the tradition's ability to integrate, refine and expand theological constructs. Scholars are also concerned with issues such as origins, authenticity and ascription, although such matters are not deflecting attention from the rich stock of resources and materialskalāmhas to offer.
The Impact of Complement Activation on Tumor Oxygenation During Photodynamic Therapy†
Authors: Cecic Ivana , Minchinton Andrew I. , Korbelik Mladen
Published: July 2007

The response to photodynamic therapy (PDT) mediated by photosensitizer Photofrin was examined with Lewis lung carcinomas growing in either complement‐proficient C57BL/6 (B6) or complement‐deficient complement C3 knockout (C3KO) mice. The results reveal that Photofrin‐PDT was more effective in attaining cures of tumors in C3KO than in B6 hosts. Colony‐forming ability of cells from tumors excised immediately after Photofrin‐PDT confirmed that the direct cell killing effect was more pronounced in C3KO than in B6 hosts. In contrast, PDT mediated by photosensitizer benzoporphyrin derivative (BPD) produced higher cure rates of tumors in B6 hosts than those in C3KO hosts. Determination of tumor C3 levels by ELISA showed that Photofrin‐PDT induced markedly more pronounced complement activation than BPD‐PDT. Measurements of tumor oxygen tension immediately after PDT by Eppendorf pO2 histograph showed that Photofrin‐PDT induced a marked decline in the oxygenation of tumors growing in B6 mice that was much less pronounced in C3KO hosts. With BPD‐PDT the oxygen tensions in tumors in B6 and C3KO hosts decreased to a similar extent. This study indicates that complement activation in PDT‐treated tumors that varies with different photosensitizers is an important determinant of tumor oxygen limitation effects directly associated with photodynamic action.
Ultraviolet B Irradiation Affects Resistance of Rainbow Trout (Oncorhynchus mykiss) Against Bacterium Yersinia ruckeri and Trematode Diplostomum spathaceum
Authors: Markkula S. Eveliina , Karvonen Anssi , Salo Harri , Tellervo Valtonen E. , Ilmari Jokinen E.
Published: July 2007

Ultraviolet B (UVB) radiation is known to have various effects on the immune system of fish, but the effect on the actual disease resistance has remained largely unknown. Here we studied the effect of UVB on the resistance of rainbow trout (Oncorhynchus mykiss) against a bacterium Yersinia ruckeri, the causative agent of enteric red mouth disease, and a trematode parasite Diplostomum spathaceum, which causes cataracts in fish. The fish were exposed to UVB irradiation seven times in 14 days, and inoculated intraperitoneally with Y. ruckeri on day 5 after the first irradiation. On day 2 postinfection (p.i.), the number of viable bacteria in the kidney was lower in UVB‐exposed than in unexposed fish. However, on day 8 p.i., UVB‐irradiated fish had not been able to clear remaining Y. ruckeri effectively, and had a slightly higher bacterial load than controls. A similar, although not significant, effect was seen in the bacterial numbers in spleen. In the other experiment, fish were exposed to UVB for six consecutive days and then exposed to D. spathaceum. A significantly higher number of parasites was detected in the eyes of irradiated fish, indicating reduced resistance against the pathogen. Furthermore, UVB‐irradiation altered the immunological and hematological parameters of fish, which also verified the immunomodulatory potential of UVB in the present study.
Quenching of Singlet Molecular Oxygen, O2(1Δg), by Dipyridamole and Derivatives
Authors: Oliveira Marilene Silva , Lima Michelle , Severino Divinomar , Baptista Maurício da Silva , Mascio Paolo Di , Tabak Marcel
Published: July 2007

Dipyridamole (DIP) is known for its vasodilating and antiplatelet activity, exhibiting also a potent antioxidant effect, strongly inhibiting lipid peroxidation. This effect has been studied in mitochondria and a correlation between the DIP derivatives’ structure, the ability to bind to micelles and biological activity has been suggested. In the present work, the quenching of singlet molecular oxygen, O2(1Δg), by DIP and RA47 and RA25 derivatives was analyzed in acetonitrile (ACN) and aqueous acid solutions. Laser flash photolysis excitation of methylene blue (MB) was made at 532 nm and monomol light emission of O2(1Δg) was monitored at 1270 nm. Bimolecular quenching constants in ACN are consistent with an efficient physical quenching, presenting values a bit lower than the diffusion limit (kt = 3.4–6.8 × 108 m−1 s−1). The quenching process probably occurs via reversible charge transfer with the formation of an exciplex. Calculation of ΔGet associated with O2(1Δg) quenching corroborates with uncompleted electron transfer. In aqueous acid solutions (pH = 3.0), the kt values for DIP and derivatives are 20‐fold smaller when compared with ACN. The electrochemical properties of DIP in ACN are characterized by two consecutive one‐electron processes with half‐wave oxidation potentials of 0.30 and 0.67 V vs saturated calomel electrode (SCE). However, in an aqueous acid medium, a single oxidation wave is observed involving a two‐electron process (0.80 V vs SCE). Therefore, O2(1Δg) quenching is consistent with electrochemical data.
Phenotypic changes of morphologically identified guinea‐pig myenteric neurons following intestinal inflammation
Authors: Nurgali Kulmira , Nguyen Trung V. , Matsuyama Hayato , Thacker Michelle , Robbins Heather L. , Furness John B.
Published: July 2007

We investigated the responses of morphologically identified myenteric neurons of the guinea‐pig ileum to inflammation that was induced by the intraluminal injection of trinitrobenzene sulphonate, 6 or 7 days previously. Electrophysiological properties were examined with intracellular microelectrodes usingin vitropreparations from the inflamed or control ileum. The neurons were injected with marker dyes during recording and later they were recovered for morphological examination. A proportion of neurons with Dogiel type I morphology, 45% (32/71), from the inflamed ileum had a changed phenotype. These neurons exhibited an action potential with a tetrodotoxin‐resistant component, and a prolonged after‐hyperpolarizing potential followed the action potential. Of the other 39 Dogiel type I neurons, no changes were observed in 36 and 3 had increased excitability. The afterhyperpolarizing potential (AHP) in Dogiel type I neurons was blocked by the intermediate conductance, Ca2+‐dependent K+channel blocker TRAM‐34. Neurons which showed these phenotypic changes had anally directed axonal projections. Neither a tetrodotoxin‐resistant action potential nor an AHP was seen in Dogiel type I neurons from control preparations. Dogiel type II neurons retained their distinguishing AH phenotype, including an inflection on the falling phase of the action potential, an AHP and, in over 90% of neurons, an absence of fast excitatory transmission. However, they became hyperexcitable and exhibited anodal break action potentials, which, unlike control Dogiel type II neurons, were not all blocked by the h current (Ih) antagonist Cs+. It is concluded that inflammation selectively affects different classes of myenteric neurons and causes specific changes in their electrophysiological properties.
Multiple activation mechanisms of store‐operated TRPC channels in smooth muscle cells
Authors: Albert A. P. , Saleh S. N. , Peppiatt‐Wildman C. M. , Large W. A.
Published: July 2007

Store‐operated channels (SOCs) are plasma membrane Ca2+‐permeable cation channels which are activated by agents that deplete intracellular Ca2+ stores. In smooth muscle SOCs are involved in contraction, gene expression, cell growth and proliferation. Single channel recording has demonstrated that SOCs with different biophysical properties are expressed in smooth muscle indicating diverse molecular identities. Moreover it is apparent that several gating mechanisms including calmodulin, protein kinase C and lysophospholipids are involved in SOC activation. Evidence is accumulating that TRPC proteins are important components of SOCs in smooth muscle. More recently Orai and STIM proteins have been proposed to underlie the well‐described calcium‐release‐activated current (ICRAC) in non‐excitable cells but at present there is little information on the role of Orai and STIM proteins in smooth muscle. In addition it is likely that different TRPC subunits coassemble as heterotetrameric structures to form smooth muscle SOCs. In this brief review we summarize the diverse properties and gating mechanisms of SOCs in smooth muscle. We propose that the heterogeneity of the properties of these conductances in smooth muscle results from the formation of heterotetrameric TRPC structures in different smooth muscle preparations.
Laser‐induced thermal response and characterization of nanoparticles for cancer treatment using magnetic resonance thermal imaging
Authors: Elliott Andrew M. , Stafford R. Jason , Schwartz Jon , Wang James , Shetty Anil M. , Bourgoyne Chirs , O'Neal Patrick , Hazle John D.
Published: July 2007

Spherical nanoparticles with a gold outer shell and silica core can be tuned to absorb near‐infrared light of a specific wavelength. These nanoparticles have the potential to enhance the treatment efficacy of laser‐induced thermal therapy (LITT). In order to enhance both the potential efficacy and safety of such procedures, accurate methods of treatment planning are needed to predict the temperature distribution associated with treatment application. In this work, the standard diffusion approximation was used to model the laser fluence in phantoms containing different concentrations of nanoparticles, and the temperature distribution within the phantom was simulated in three‐dimensions using the finite element technique. Magnetic resonance temperature imaging was used to visualize the spatiotemporal distribution of the temperature in the phantoms. In most cases, excellent correlation is demonstrated between the simulations and the experiment ( mean error observed). This has significant implications for the treatment planning of LITT treatments using gold‐silica nanoshells.
Rejection and redistribution of scattered radiation in scan equalization digital radiography (SEDR): Simulation with spot images
Authors: Liu Xinming , Shaw Chris C.
Published: July 2007

The anti‐scatter grid has been widely used to reject scatter and increase the perceptibility of a low‐contrast object in chest radiography; however, it also attenuated the primary x‐rays, resulting in a substantial loss of information and an increased relative noise level in heavily attenuated regions. A more dose efficient approach to scatter rejection is the slot‐scan imaging technique. Another problem in chest radiography is the low transmitted x‐ray intensity in heavily attenuating regions. It results in a higher relative noise level, thus limiting the contrast sensitivity. A solution to this problem is through the exposure equalization technique, with which the incident x‐ray intensity is regionally modulated to compensate for the differences of x‐ray attenuation due to the anatomic variation. We are in the process of implementing the scan equalization digital radiography (SEDR) technique, which combines the advantages of slot‐scan imaging and exposure equalization. However, associated with the use of exposure equalization is a redistribution of scattered radiation at the detector, which may impact on the benefit of using exposure equalization in conjunction with the slot‐scan imaging geometry. In order to understand the scatter properties and their impact in SEDR, we have used spot collimated digital radiographic images to synthesize simulated SEDR images with which scatter components, primary signals, and scatter‐to‐primary ratios (SPRs) were measured. It was shown that the anti‐scatter grid rejected approximately 70% and 80% of scattered radiation in lightly and heavily attenuated regions, respectively, while the slot‐scan method can reject as high as 95% (with slot width) of scattered radiation without attenuation of the primary x‐rays. Using a simple model for scatter effects, we have also estimated and compared the contrast‐to‐noise ratio degradation factors (CNRDFs, i.e., the fraction by which CNR is reduced). It was found that for quantum limited situations, the slot‐scan technique has resulted in a substantial improvement of the image quality, as indicated by higher estimated CNRDFs (less scatter). An estimated improvement of 40%–50% in the lungs, 50%–90% in the mediastinum, and 60%–110% in the subdiaphragm was achieved with the slot‐scan over the anti‐scatter grid method. Compared to slot‐scan imaging, SEDR resulted in higher SPRs in the lungs and lower SPRs in the mediastinum. In the subdiaphragmatic regions, the SPRs remain about the same. This corresponds to lower CNRDFs in the lungs, higher CNRDFs in the mediastinum, and about the same CNRDFs in the subdiaphragmatic regions. It was shown that although SEDR has resulted in minimum improvement over slot‐scan imaging in reducing the SPRs, it could improve the contrast sensitivity by raising the primary signal levels in heavily attenuating regions. This advantage needs to be further investigated in our continuing study of the SEDR technique.
Technical note: A physical phantom for assessment of accuracy of deformable alignment algorithms
Authors: Kashani Rojano , Hub Martina , Kessler Marc L. , Balter James M.
Published: July 2007

The purpose of this study was to investigate the feasibility of a simple deformable phantom as a QA tool for testing and validation of deformable image registration algorithms. A diagnostic thoracic imaging phantom with a deformable foam insert was used in this study. Small plastic markers were distributed through the foam to create a lattice with a measurable deformation as the ground truth data for all comparisons. The foam was compressed in the superior‐inferior direction using a one‐dimensional drive stage pushing a flat “diaphragm” to create deformations similar to those from inhale and exhale states. Images were acquired at different compressions of the foam and the location of every marker was manually identified on each image volume to establish a known deformation field with a known accuracy. The markers were removed digitally from corresponding images prior to registration. Different image registration algorithms were tested using this method. Repeat measurement of marker positions showed an accuracy of better than in identification of the reference marks. Testing the method on several image registration algorithms showed that the system is capable of evaluating errors quantitatively. This phantom is able to quantitatively assess the accuracy of deformable image registration, using a measure of accuracy that is independent of the signals that drive the deformation parameters.
Automatic segmentation of phase‐correlated CT scans through nonrigid image registration using geometrically regularized free‐form deformation
Authors: Shekhar Raj , Lei Peng , Castro‐Pareja Carlos R. , Plishker William L. , D'Souza Warren D.
Published: July 2007

Conventional radiotherapy is planned using free‐breathing computed tomography (CT), ignoring the motion and deformation of the anatomy from respiration. New breath‐hold‐synchronized, gated, and four‐dimensional (4D) CT acquisition strategies are enabling radiotherapy planning utilizing a set of CT scans belonging to different phases of the breathing cycle. Such 4D treatment planning relies on the availability of tumor and organ contours in all phases. The current practice of manual segmentation is impractical for 4D CT, because it is time consuming and tedious. A viable solution is registration‐based segmentation, through which contours provided by an expert for a particular phase are propagated to all other phases while accounting for phase‐to‐phase motion and anatomical deformation. Deformable image registration is central to this task, and a free‐form deformation‐based nonrigid image registration algorithm will be presented. Compared with the original algorithm, this version uses novel, computationally simpler geometric constraints to preserve the topology of the dense control‐point grid used to represent free‐form deformation and prevent tissue fold‐over. Using mean squared difference as an image similarity criterion, the inhale phase is registered to the exhale phase of lung CT scans of five patients and of characteristically low‐contrast abdominal CT scans of four patients. In addition, using expert contours for the inhale phase, the corresponding contours were automatically generated for the exhale phase. The accuracy of the segmentation (and hence deformable image registration) was judged by comparing automatically segmented contours with expert contours traced directly in the exhale phase scan using three metrics: volume overlap index, root mean square distance, and Hausdorff distance. The accuracy of the segmentation (in terms of radial distance mismatch) was approximatelyin the thorax andin the abdomen, which compares favorably to the accuracies reported elsewhere. Unlike most prior work, segmentation of the tumor is also presented. The clinical implementation of 4D treatment planning is critically dependent on automatic segmentation, for which is offered one of the most accurate algorithms yet presented.
Physical characteristics of five clinical systems for digital mammography
Authors: Lazzari B. , Belli G. , Gori C. , Rosselli Del Turco M.
Published: July 2007

The purpose of this study was to evaluate and compare the physical characteristics of five clinical systems for digital mammography (GE Senographe 2000D, Lorad Selenia M‐IV, Fischer Senoscan, Agfa DM 1000, and IMS Giotto) currently in clinical use. The basic performances of the mammography systems tested were assessed on the basis of response curve, modulation transfer function (MTF), noise power spectrum, noise equivalent quanta (NEQ), and detective quantum efficiency (DQE) in an experimental setting closely resembling the clinical one. As expected, all the full field digital mammography systems show a linear response curve over a dynamic range from . The presampling MTFs at 2, 3, and were found to be respectively 0.78, 0.64, and 0.37 for GE Senographe 2000D; 0.92, 0.85, and 0.69 for Lorad Selenia and Agfa DM1000; 0.75, 0.63, and 0.42 for Fischer Senoscan; and 0.91, 0.82, and 0.61 for the IMS Giotto. According to the pixel size of each digital system, the presampling MTF was calculated within a range up to the Nyquist frequency ( for GE Senographe 2000D, for Lorad Selenia, for Fischer Senoscan, and for IMS Giotto detector). The NEQ becomes related to the exposure in a linear behavior starting from about for GE Senographe 2000D, for Lorad Selenia, for Agfa DM1000, for Fischer Senoscan, and for the IMS Giotto. Above those values, the systems can be considered “quantum noise limited,” that is the electronic noise is negligible if compared to the quantum noise. The DQE, for several emitted x‐ray spectra for each system, i.e., Mo–Mo, Mo–Rh, Rh–Rh, W–Al anode‐filter combination, hardened by poly(methylmethacrylate) (PMMA) was evaluated. For the five different systems, the DQE at close to zero spatial frequency ranges between 0.25 and 0.63 at entrance surface air kerma to the detectors. The results of our quantitative analysis demonstrated a higher DQE for direct conversion technology when compared to that of the indirect conversion. The NEQ behavior of each system can be exploited to select the optimum exposure level set in clinical practice to ensure minimum patient dose though adequate image quality. The detailed results of the physical characterization of the digital systems reported in this work allow the quantitative comparison of different technologies as well as the definition of reference values for subsequent quality control tests. The method developed in this work is suitable to be reproduced in any medical physics department for the previously described goals.
Automated detection and quantitative assessment of pulmonary airways depicted on CT images
Authors: Zheng Bin , Leader Joseph K. , McMurray Jessica M. , Park Sang Cheol , Fuhrman Carl R. , Gur David , Sciurba Frank C.
Published: July 2007

We developed and tested a fully automated computerized scheme that identifies pulmonary airway sections depicted on computed tomography (CT) images and computes their sizes including the lumen and airway wall areas. The scheme includes four processing modules that (1) segment left and right lung areas, (2) identify airway locations, (3) segment airway walls from neighboring pixels, and (4) compute airway sizes. The scheme uses both a raster scanning and a labeling algorithm complemented by simple classification rules for region size and circularity to automatically search for and identify airway sections of interest. A profile tracking method is used to segment airway walls from neighboring pixels including those associated with dense tissue (i.e., pulmonary arteries) along scanning radial rays. A partial pixel membership method is used to compute airway size. The scheme was tested on ten randomly selected CT studies that included 26 sets of CT images acquired using both low and conventional dose CT examinations with one of four reconstruction algorithms (namely, “bone,” “lung,” “soft,” and “standard” convolution kernels). Three image section thicknesses (1.25, 2.5, and ) were evaluated. The scheme detected a large number of quantifiable airway sections when the CT images were reconstructed using high spatial frequency convolution kernels. The detection results demonstrated a consistent trend for all test image sets in that as airway lumen size increases, on average the airway wall area increases as well and the wall area percentage decreases. The study suggested that CT images reconstructed using high spatial frequency convolution kernels and thin‐section thickness were most amenable to automated detection, reasonable segmentation, and quantified assessment when the airways are close to being perpendicular to the CT image plane.
A frequency‐based approach to locate common structure for 2D‐3D intensity‐based registration of setup images in prostate radiotherapy
Authors: Munbodh Reshma , Chen Zhe , Jaffray David A. , Moseley Douglas J. , Knisely Jonathan P. S. , Duncan James S.
Published: July 2007

In many radiotherapy clinics, geometric uncertainties in the delivery of 3D conformal radiation therapy and intensity modulated radiation therapy of the prostate are reduced by aligning the patient's bony anatomy in the planning 3D CT to corresponding bony anatomy in 2D portal images acquired before every treatment fraction. In this paper, we seek to determine if there is a frequency band within the portal images and the digitally reconstructed radiographs (DRRs) of the planning CT in which bony anatomy predominates over non‐bony anatomy such that portal images and DRRs can be suitably filtered to achieve high registration accuracy in an automated 2D‐3D single portal intensity‐based registration framework. Two similarity measures, mutual information and the Pearson correlation coefficient were tested on carefully collected gold‐standard data consisting of a kilovoltage cone‐beam CT (CBCT) and megavoltage portal images in the anterior‐posterior (AP) view of an anthropomorphic phantom acquired under clinical conditions at known poses, and on patient data. It was found that filtering the portal images and DRRs during the registration considerably improved registration performance. Without filtering, the registration did not always converge while with filtering it always converged to an accurate solution. For the pose‐determination experiments conducted on the anthropomorphic phantom with the correlation coefficient, the mean (and standard deviation) of the absolute errors in recovering each of the six transformation parameters were , , , , , and . The mutual information‐based registration with filtered images also resulted in similarly small errors. For the patient data, visual inspection of the superimposed registered images showed that they were correctly aligned in all instances. The results presented in this paper suggest that robust and accurate registration can be achieved with intensity‐based methods by focusing on rigid bony structures in the images while diminishing the influence of artifacts with similar frequencies as soft tissue.
Performance of a hybrid MC dose algorithm for IMRT optimization dose evaluation
Authors: Siebers Jeffrey V. , Kawrakow Iwan , Ramakrishnan V.
Published: July 2007

This paper presents a hybrid intensity modulated radiation therapy (IMRT) optimization strategy which combines the speed of pencil beam (PB) and the accuracy of Monte Carlo (MC) dose calculations. After an initial deliverable‐based optimization using a PB algorithm, doses are recomputed using theMC code to determine dose correction factors, which are then utilized during further PB‐based optimization. The hybrid method is benchmarked with respect to full MC deliverable‐based optimization for ten prostate and ten head‐and‐neck IMRT plans. Final optimized plans are compared in terms of dose‐volume indices used for the plan optimization. Dose prediction errors (DPEs) and optimization convergence errors (OCEs) at intermediate steps of the hybrid sequence are evaluated. The hybrid method is found to produce optimized plans that are clinically equivalent to full MC‐based optimization, yet requires only 40% of the number of MC dose calculations. With the hybrid strategy presented here, MC‐based optimization results are achieved inor less on a modest computing cluster. While the initial PB‐deliverable‐based optimization is found to have DPEs and OCEs of up torelative to theprescription doses, application of the first MC correction reduces the average DPEs to less thanfor the prostate plans and less thanfor the head and neck plans. The maximum observed DPE or OCE isafter 1 MC dose correction, indicating that a single MC dose calculation correction might be sufficient for IMRT optimization.
Numerical study of reflectance imaging using a parallel Monte Carlo method
Authors: Chen Cheng , Lu Jun Q. , Li Kai , Zhao Suisheng , Brock R. Scott , Hu Xin‐Hua
Published: July 2007

Reflectance imaging of biological tissues with visible and near‐infrared light has the significant potential to provide a noninvasive and safe imaging modality for diagnosis of dysplastic and malignant lesions in the superficial tissue layers. The difficulty in the extraction of optical and structural parameters lies in the lack of efficient methods for accurate modeling of light scattering in biological tissues of turbid nature. We present a parallel Monte Carlo method for accurate and efficient modeling of reflectance images from turbid tissue phantoms. A parallel Monte Carlo code has been developed with the message passing interface and evaluated on a computing cluster with 16 processing elements. The code was validated against the solutions of the radiative transfer equation on the bidirectional reflection and transmission functions. With this code we investigated numerically the dependence of reflectance image on the imaging system and phantom parameters. The contrasts of reflectance images were found to be nearly independent of the numerical aperture (NA) of the imaging camera despite the fact that reflectance depends on the NA. This enables efficient simulations of the reflectance images using an NA at 1.00. Using heterogeneous tissue phantoms with an embedded region simulating a lesion, we investigated the correlation between the reflectance image profile or contrast and the phantom parameters. It has been shown that the image contrast approaches 0 when the single‐scattering albedos of the two regions in the heterogeneous phantoms become matched. Furthermore, a zone of detection has been demonstrated for determination of the thickness of the embedded region and optical parameters from the reflectance image profile and contrast. Therefore, the utility of the reflectance imaging method with visible and near‐infrared light has been firmly established. We conclude from these results that the optical parameters of the embedded region can be determined inversely from reflectance images acquired with full‐field illumination at multiple incident angles or multiple wavelengths.
Hardware assessment using the multi‐module, multi‐resolution system : A signal‐detection study
Authors: Hesterman Jacob Y. , Kupinski Matthew A. , Clarkson Eric , Barrett Harrison H.
Published: July 2007

The multi‐module, multi‐resolution system is used for hardware assessment in objective, task‐based signal detection studies in projection data. A phantom capable of generating multiple realizations of a random textured background is introduced. Measured backgrounds from this phantom are used along with simulated lumpy and uniform backgrounds to investigate signal‐to‐noise ratio as a function of exposure time. Results are shown to agree with theoretical predictions, exhibiting a power‐law like dependence previously seen for studies performed either in simulation or without an imaging system, and help validate the use of simulated lumpy backgrounds in observer studies. A second study looks at signal‐detection performance, measured by AUC (area under the receiver operating characteristic curve), in lumpy backgrounds for 20 aperture combinations as a function of lump size and signal size. Observer performance reveals an improvement in AUC for certain ranges of signal and lump combinations through the use of multiplexed, multiple‐pinhole apertures, indicating a need for task‐specific aperture optimization. The channelized Hotelling observer is used with Laguerre–Gauss channels for both observer studies. Methods for selection of number of channels and channel width are discussed.
Visibility of microcalcification in cone beam breast CT: Effects of x‐ray tube voltage and radiation dose
Authors: Lai Chao‐Jen , Shaw Chris C. , Chen Lingyun , Altunbas Mustafa C. , Liu Xinming , Han Tao , Wang Tianpeng , Yang Wei T. , Whitman Gary J. , Tu Shu‐Ju
Published: July 2007

Mammography is the only technique currently used for detecting microcalcification (MC) clusters, an early indicator of breast cancer. However, mammographic images superimpose a three‐dimensional compressed breast image onto two‐dimensional projection views, resulting in overlapped anatomical breast structures that may obscure the detection and visualization of MCs. One possible solution to this problem is the use of cone beam computed tomography (CBCT) with a flat‐panel (FP) digital detector. Although feasibility studies of CBCT techniques for breast imaging have yielded promising results, they have not shown how radiation dose and x‐ray tube voltage affect the accuracy with which MCs are detected by CBCT experimentally. We therefore conducted a phantom study using a FP‐based CBCT system with various mean glandular doses and kVp values. An experimental CBCT scanner was constructed with a data acquisition rate of 7.5 frames/s. 10.5 and diameter breast phantoms made of gelatin were used to simulate uncompressed breasts consisting of 100% glandular tissue. Eight different MC sizes of calcium carbonate grains, ranging from to , were used to simulate MCs. MCs of the same size were arranged to form a MC cluster and embedded in the breast phantoms. These MC clusters were positioned at away from the center of the breast phantoms. The phantoms were imaged at 60, 80, and . With a single scan , 300 projection images were acquired with , , and mean glandular dose limit for phantom and with , , and for phantom. A Feldkamp algorithm with a pure ramp filter was used for image reconstruction. The normalized noise level was calculated for each x‐ray tube voltage and dose level. The image quality of the CBCT images was evaluated by counting the number of visible MCs for each MC cluster for various conditions. The average percentage of the visible MCs was computed and plotted as a function of the MGD, the kVp, and the average MC size. The results showed that the MC visibility increased with the MGD significantly but decreased with the breast size. The results also showed that the x‐ray tube voltage affects the detection of MCs under different circumstances. With a 50% threshold, the minimum detectable MC sizes for the phantom were , , at 3, 6, and , respectively. Those for the phantom were 355 , 307 , 275 at 6, 12, and , respectively. With a 75% threshold, the minimum detectable MC sizes for the phantom were 367 , 316 , 265 at 3, 6, and , respectively. Those for the phantom were 377 , 334 , 300 at 6, 12, and , respectively.
Impact of inhomogeneity corrections on dose coverage in the treatment of lung cancer using stereotactic body radiation therapy
Authors: Ding George X. , Duggan Dennis M. , Lu Bo , Hallahan Dennis E. , Cmelak Anthony , Malcolm Arnold , Newton Jared , Deeley Matthew , Coffey Charles W.
Published: July 2007

The purpose of this study is to assess the real target dose coverage when radiation treatments were delivered to lung cancer patients based on treatment planning according to the RTOG‐0236 Protocol. We compare calculated dosimetric results between the more accurate anisotropic analytical algorithm (AAA) and the pencil beam algorithm for stereotactic body radiation therapy treatment planning in lung cancer. Ten patients with non‐small cell lung cancer were given in three fractions using 6 and beams with 8–10 fields. The patients were chosen in accordance with the lung RTOG‐0236 protocol. The dose calculations were performed using the pencil beam algorithm with no heterogeneity corrections (PB‐NC) and then recalculated with the pencil beam with modified Batho heterogeneity corrections (PB‐MB) and the AAA using an identical beam setup and monitor units. The differences in calculated dose to 95% or 99% of the PTV, between using the PB‐NC and the AAA, were within 10% of prescribed dose . However, the minimum dose to 95% and 99% of PTV calculated using the PB‐MB were consistently overestimated by up to 40% and 36% of the prescribed dose, respectively, compared to that calculated by the AAA. Using the AAA as reference, the calculated maximum doses were underestimated by up to 27% using the PB‐NC and overestimated by 19% using the PB‐MB. The calculations of dose to lung from PB‐NC generally agree with that of AAA except in the small high‐dose region where PB‐NC underestimates. The calculated dose distributions near the interface using the AAA agree with those from Monte Carlo calculations as well as measured values. This study indicates that the real minimum PTV dose coverage cannot be guaranteed when the PB‐NC is used to calculate the monitor unit settings in dose prescriptions.
Multichannel detectors for profile measurements in clinical proton fields
Authors: Nichiporov Dmitri , Solberg Keith , Hsi Wen , Wolanski Mark , Mascia Anthony , Farr Jonathan , Schreuder Andries
Published: July 2007

Two beam profile measurement detectors have been developed at Indiana University Cyclotron Facility to address the need for a tool to efficiently verify dose distributions created with active methods of clinical proton beam delivery. The multipad ionization chamber (MPIC) has 128 ionization chambers arranged in one plane and is designed to measure lateral profiles in fields up to in diameter. The MPIC pads have a pitch for fields up to in diameter and a pitch for larger fields, providing the accuracy of field size determination about . The multilayer ionization chamber (MLIC) detector contains 122 small‐volume ionization chambers stacked at a step (water‐equivalent) for depth‐dose profile measurements. The MLIC detector can measure profiles up to in depth, and determine the 80% distal dose fall‐off with about precision. Both detectors can be connected to the same set of electronics modules, which comprise the detectors’ data acquisition system. The detectors have been tested in clinical proton fields produced with active methods of beam delivery such as uniform scanning and energy stacking. This article describes detector performance tests and discusses their results. The test results indicate that the MPIC and MLIC detectors can be used for dosimetric characterization of clinical proton fields. The detectors offer significant time savings during measurements in actively delivered beams compared with traditional measurements using a water phantom.
A post‐reconstruction method to correct cupping artifacts in cone beam breast computed tomography
Authors: Altunbas M. C. , Shaw C. C. , Chen L. , Lai C. , Liu X. , Han T. , Wang T.
Published: July 2007

In cone beam breast computed tomography (CT), scattered radiation leads to nonuniform biasing of CT numbers known as a cupping artifact. Besides being visual distractions, cupping artifacts appear as background nonuniformities, which impair efficient gray scale windowing and pose a problem in threshold based volume visualization/segmentation. To overcome this problem, we have developed a background nonuniformity correction method specifically designed for cone beam breast CT. With this technique, the cupping artifact is modeled as an additive background signal profile in the reconstructed breast images. Due to the largely circularly symmetric shape of a typical breast, the additive background signal profile was also assumed to be circularly symmetric. The radial variation of the background signals was estimated by measuring the spatial variation of adipose tissue signals in front view breast images. To extract adipose tissue signals in an automated manner, a signal sampling scheme in polar coordinates and a background trend fitting algorithm were implemented. The background fits compared with targeted adipose tissue signal value (constant throughout the breast volume) to get an additive correction value for each tissue voxel. To test the accuracy, we applied the technique to cone beam CT images of mastectomy specimens. After correction, the images demonstrated significantly improved signal uniformity in both front and side view slices. The reduction of both intraslice and interslice variations in adipose tissue CT numbers supported our observations.
The influence of patient centering on CT dose and image noise
Authors: Toth Thomas , Ge Zhanyu , Daly Michael P.
Published: July 2007

Although x‐ray intensity shaping filters (bowtie filters) have been used since the introduction of some of the earliest CT scanner models, the clinical implications on dose and noise are not well understood. To achieve the intended dose and noise advantage requires the patient to be centered in the scan field of view. In this study we explore the implications of patient centering in clinical practice. We scanned various size and shape phantoms on a GE LightSpeed VCT scanner using each available source filter with the phantom centers positioned at 0, 3, and below the center of rotation (isocenter). Surface doses were measured along with image noise over a large image region. Regression models of surface dose and noise were generated as a function of phantom size and centering error. Methods were also developed to determine the amount of miscentering using a scout scan projection radiograph (SPR). These models were then used to retrospectively evaluate 273 adult body patients for clinical implications. When miscentered by 3 and , the surface dose on a CTDI phantom increased by 18% and 41% while image noise also increased by 6% and 22%. The retrospective analysis of adult body scout SPR scans shows that 46% of patients were miscentered in elevation by with a mean position below the center of rotation (isocenter). The analysis indicated a surface dose penalty of up to 140% with a mean dose penalty of 33% assuming that tube current is increased to compensate for the increased noise due to miscentering. Clinical image quality and dose efficiency can be improved on scanners with bowtie filters if care is exercised when positioning patients. Automatically providing patient specific centering and scan parameter selection information can help the technologist improve workflow, achieve more consistent image quality and reduce patient dose.
Boundary element model for simulating sound propagation and source localization within the lungs
Authors: Ozer M. B. , Acikgoz S. , Royston T. J. , Mansy H. A. , Sandler R. H.
Published: July 2007

An acoustic boundary element (BE) model is used to simulate sound propagation in the lung parenchyma. It is computationally validated and then compared with experimental studies on lung phantom models. Parametric studies quantify the effect of different model parameters on the resulting acoustic field within the lung phantoms. The BE model is then coupled with a source localization algorithm to predict the position of an acoustic source within the phantom. Experimental studies validate the BE-based source localization algorithm and show that the same algorithm does not perform as well if the BE simulation is replaced with a free field assumption that neglects reflections and standing wave patterns created within the finite-size lung phantom. The BE model and source localization procedure are then applied to actual lung geometry taken from the National Library of Medicine’s Visible Human Project. These numerical studies are in agreement with the studies on simpler geometry in that use of a BE model in place of the free field assumption alters the predicted acoustic field and source localization results. This work is relevant to the development of advanced auscultatory techniques that utilize multiple noninvasive sensors to construct acoustic images of sound generation and transmission to identify pathologies.
Steering vector sensor array elements with linear cardioids and nonlinear hippioids
Authors: Smith Kevin B. , van Leijen A. Vincent
Published: July 2007

The purpose of this work is to study the impact due to individual vector sensor element steering patterns on linear array beamforming. Standard, linear beamformers employ cardioid beampatterns for each vector sensor. In this work, a class of vector sensor element steering patterns beyond the standard cardioid was examined. The element weighting is nonlinear but nonadaptive, making it simple to implement in hardware processing. The new sensor steering patterns, referred to as hippioids, are products of cardioids and various powers of hippopedes. The angular resolution of individual sensors, the impact on angular resolution from arrays of varying aperture, and peak-to-sidelobe levels will serve as performance measures. An example of the differences in vector sensor steering patterns is provided using measured directional frequency and recorded buoy data.
Tongue movement kinematics in long and short Japanese consonants
Authors: Löfqvist Anders
Published: July 2007

This paper examines tongue movements in stop and fricative consonants where the duration of the oral closure/constriction for the consonant is varied for linguistic purposes. Native speakers of Japanese served as subjects. The linguistic material consisted of Japanese word pairs that only differed in the duration of the lingual consonant, which was either long or short. Recordings were made of tongue movements using a magnetometer system. Results show a robust difference in closure duration between the long and short consonants. Overall, the path of the tongue movement during the consonant was longer for the long than for the short consonant. All speakers decreased the speed of the tongue movement during the long consonant. These adjustments in tongue movements were most likely made to maintain the contact between the tongue and the palate for the closure and constriction.
On the modeling of the diffuse field sound transmission loss of finite thickness apertures
Authors: Sgard Franck , Nelisse Hugues , Atalla Noureddine
Published: July 2007

The modeling of the diffuse field sound transmission loss (TL) of apertures has been rarely considered in the literature. The aims of this paper are (i) to give a comprehensive review of the existing models, (ii) to propose a general efficient and rigorous numerical method to predict the diffuse field TL of apertures of rectangular and circular cross section, (iii) to provide the reader with numerical results regarding this indicator together with its relation with the normal incidence case for various geometrical configurations, and (iv) to conclude on the relevance of using such a sophisticated model compared to more classical normal incidence ones. The proposed approach is based on the description of the sound field inside the aperture in terms of propagating and evanescent acoustic modes. The radiation of the aperture is accounted for using a modal radiation impedance matrix. The coupled problem is solved in terms of modal contribution factors. The convergence of the approach is then investigated and the model is validated by comparisons with existing models for various configurations and excitations. Several numerical examples are provided regarding the normal incidence and diffuse field TL for various apertures and the relationship between these two indicators is discussed.
Autocorrelation based denoising of manatee vocalizations using the undecimated discrete wavelet transform
Authors: Gur Berke M. , Niezrecki Christopher
Published: July 2007

Recent interest in the West Indian manatee (Trichechus manatus latirostris) vocalizations has been primarily induced by an effort to reduce manatee mortality rates due to watercraft collisions. A warning system based on passive acoustic detection of manatee vocalizations is desired. The success and feasibility of such a system depends on effective denoising of the vocalizations in the presence of high levels of background noise. In the last decade, simple and effective wavelet domain nonlinear denoising methods have emerged as an alternative to linear estimation methods. However, the denoising performances of these methods degrades considerably with decreasing signal-to-noise ratio (SNR) and therefore are not suited for denoising manatee vocalizations in which the typical SNR is below 0dB. Manatee vocalizations possess a strong harmonic content and a slow decaying autocorrelation function. In this paper, an efficient denoising scheme that exploits both the autocorrelation function of manatee vocalizations and effectiveness of the nonlinear wavelet transform based denoising algorithms is introduced. The suggested wavelet-based denoising algorithm is shown to outperform linear filtering methods, extending the detection range of vocalizations.