bluuebunny/crossref_metadata_2025 huggingface dataset:
Activation of ARF6 by ARNO stimulates epithelial cell migration through downstream activation of both Rac1 and phospholipase D
Authors: Santy Lorraine C. , Casanova James E.
Published: July 2002

Migration of epithelial cells is essential for tissue morphogenesis, wound healing, and metastasis of epithelial tumors. Here we show that ARNO, a guanine nucleotide exchange factor for ADP-ribosylation factor (ARF) GTPases, induces Madin-Darby canine kidney epithelial cells to develop broad lamellipodia, to separate from neighboring cells, and to exhibit a dramatic increase in migratory behavior. This transition requires ARNO catalytic activity, which we show leads to enhanced activation of endogenous ARF6, but not ARF1, using a novel pulldown assay. We further demonstrate that expression of ARNO leads to increased activation of endogenous Rac1, and that Rac activation is required for ARNO-induced cell motility. Finally, ARNO-induced activation of ARF6 also results in increased activation of phospholipase D (PLD), and inhibition of PLD activity also inhibits motility. However, inhibition of PLD does not prevent activation of Rac. Together, these data suggest that ARF6 activation stimulates two distinct signaling pathways, one leading to Rac activation, the other to changes in membrane phospholipid composition, and that both pathways are required for cell motility.
Essential control of an endothelial cell ISOC by the spectrin membrane skeleton
Authors: Wu Songwei , Sangerman Jose , Li Ming , Brough George H. , Goodman Steven R. , Stevens Troy
Published: July 2002

Mechanism(s) underlying activation of store-operated Ca2+ entry currents, ISOC, remain incompletely understood. F-actin configuration is an important determinant of channel function, although the nature of interaction between the cytoskeleton and ISOC channels is unknown. We examined whether the spectrin membrane skeleton couples Ca2+ store depletion to Ca2+ entry. Thapsigargin activated an endothelial cell ISOC (−45 pA at −80 mV) that reversed at +40 mV, was inwardly rectifying when Ca2+ was the charge carrier, and was inhibited by La3+ (50 μM). Disruption of the spectrin–protein 4.1 interaction at residues A207-V445 of βSpIIΣ1 decreased the thapsigargin-induced global cytosolic Ca2+ response by 50% and selectively abolished the endothelial cell ISOC, without altering activation of a nonselective current through cyclic nucleotide–gated channels. In contrast, disruption of the spectrin–actin interaction at residues A47-K186 of βSpIIΣ1 did not decrease the thapsigargin-induced global cytosolic Ca2+ response or inhibit ISOC. Results indicate that the spectrin–protein 4.1 interaction selectively controls ISOC, indicating that physical coupling between calcium release and calcium entry is reliant upon the spectrin membrane skeleton.
Minimal Bystander Activation of CD8 T Cells during the Virus-induced Polyclonal T Cell Response
Authors: Zarozinski Christopher C. , Welsh Raymond M.
Published: July 2002

Acute infections with viruses such as lymphocytic choriomeningitis virus (LCMV) are associated with a massive polyclonal T cell response, but the specificities of only a small percentage of these activated T cells are known. To determine if bystander stimulation of T cells not specific to the virus plays a role in this T cell response, we examined two different systems, HY-specific T cell receptor (TCR)-transgenic mice, which have a restricted TCR repertoire, and LCMVcarrier mice, which are tolerant to LCMV. LCMV infection of HY-transgenic C57BL/6 mice induced antiviral CTLs that lysed target cells coated with two of the three immunodominant epitopes previously defined for LCMV (glycoprotein 33 and nucleoprotein 397). Although LCMV-induced cytotoxic T lymphocytes (CTLs) from C57BL/6 mice could lyse uninfected H-2k and H-2d allogeneic targets, LCMV-induced CTLs from HY mice lysed only the H-2kexpressing cells. The HY mice generated both anti-H-2k and anti-H-2d CTL in mixed leukocyte reactions, providing evidence that the generation of allospecific CTLs during acute LCMV infection is antigen specific. During the LCMV infection there was blastogenesis of the CD8+ T cell population, but the HY-specific T cells (as determined by expression of the TCR-α chain) remained small in size. To examine the potential for bystander stimulation under conditions of a very strong CTL response, T cell chimeras were made between normal and HY mice. Even in the context of a normal virus-induced CTL response, no stimulation of HY-specific T cells was observed, and HY-specific cells were diluted in number by day 9 after infection. In LCMV-carrier mice in which donor and host T cells could be distinguished by Thy1 allotypic markers, adoptive transfer of LCMV-immune T cells into LCMV-carrier mice, whose T cells were tolerant to LCMV, resulted in activation and proliferation of donor CD8 cells, but little or no activation of host CD8 cells. These results support the hypothesis that the massive polyclonal CTL response to LCMV infection is virus-specific and that bystander activation of non–virus-specific T cells is not a significant component of this response.
Proton Probing of the Charybdotoxin Binding Site of Shaker K+ Channels
Authors: Perez-Cornejo Patricia , Stampe Per , Begenisich Ted
Published: July 2002

We have investigated the interaction of charybdotoxin (CTX) with Shaker K channels. We substituted a histidine residue for the wild-type phenylalanine (at position 425) in an inactivation-removed channel. The nature of the imidazole ring of the histidine provides the ability to change the charge on this amino acid side chain with solution hydrogen ion concentration. Wild-type, recombinant CTX blocked wild-type Shaker channels in a bimolecular fashion with a half-blocking concentration (Kd) of 650 nM (at a membrane potential of 0 mV). The F425H mutant channels were much more sensitive to CTX block with an apparent Kd (at pH 7.0) of 75 nM. Block of F425H but not wild-type channels was strongly pH sensitive. A pH change from 7 to 5.5 rendered the F425H channels >200-fold less sensitive to CTX. The pH dependence of CTX block was steeper than expected for inhibition produced by H+ ions binding to identical, independent sites. The data were consistent with H+ ions interacting with subunits of the channel homotetrameric structure. The in situ pK for the imidazole group on the histidine at channel position 425 was determined to be near 6.4 and the dissociation constant for binding of toxin to the unprotonated channel was near 50 nM. We estimate that the binding of a H+ ion to each subunit adds 0.8 kcal/mol or more of interaction energy with CTX. We used mutant toxins to test electrostatic and steric interactions between specific CTX residues and channel position 425. Our results are consistent with a model in which protons on F425H channel subunits interact with three positive charges on CTX at an effective distance 6–7 Å from this channel position.
Biophysical Properties of Connexin-45 Gap Junction Hemichannels Studied in Vertebrate Cells
Authors: Valiunas Virginijus
Published: July 2002

Human HeLa cells transfected with mouse Cx45 and rat RIN cells transfected with chicken Cx45 were used to study the electrical and permeability properties of Cx45 gap junction hemichannels. With no extracellular Ca2+, whole-cell recording revealed currents arising from hemichannels in both transfected cell lines. Multichannel currents showed a time-dependent activation or deactivation sensitive to voltage, Vm. These currents did not occur in nontransfected cells. The hemichannel currents were inhibited by raising extracellular Ca2+ or by acidification with CO2. The unitary conductance exhibited Vm dependence (i.e., γhc,main increased/decreased with hyperpolarization/depolarization). Extrapolation to Vm = 0 mV led to a γhc,main of 57 pS, roughly twice the conductance of an intact Cx45 gap junction channel. The open channel probability, Po, was Vm-dependent, declining at negative Vm (Po < 0.11, Vm < −50 mV), and increasing at positive Vm (Po ∼0.76, Vm > 50 mV). Moreover, Cx45 nonjunctional hemichannels appeared to mediate lucifer yellow (LY) and propidium iodide (PI) dye uptake from the external solution when extracellular Ca2+ level was reduced. Dye uptake was directly proportional to the number of functioning hemichannels. No significant dye uptake was detected in nontransfected cells. Cx45 transfected HeLa and RIN cells also allowed dye to leak out when preloaded with LY and then incubated in Ca2+-free external solution, whereas little or no dye leakage was observed when these cells were incubated with 2 mM external Ca2+. Intact Cx45 gap junction channels allowed passage of either LY or PI dye, but their respective flux rates were different. Comparison of LY diffusion through Cx45 hemichannels and intact gap junction channels revealed that the former is more permeable, suggesting that gap junction channel pores exhibit more allosterical restriction to the dye molecules than the unopposed hemichannel. The data demonstrate the opening of Cx45 nonjunctional hemichannels in vertebrate cells when the external Ca2+ concentration is reduced.
Oscillation of first order delay differential equations
Authors: Li Bingtuan
Published: July 2002

We introduce a new technique to analyze the generalized characteristic equations to obtain some infinite integral conditions for oscillation of the nonautonomous delay differential equations.
Chaos in the Lorenz equations: A computer assisted proof. Part II: Details
Authors: Mischaikow Konstantin , Mrozek Marian
Published: July 2002

Details of a new technique for obtaining rigorous results concerning the global dynamics of nonlinear systems is described. The technique combines abstract existence results based on the Conley index theory with rigorous computer assisted computations. As an application of these methods it is proven that for some explicit parameter values the Lorenz equations exhibit chaotic dynamics.
Reduction of elliptic curves over certain real quadratic number fields
Authors: Kida Masanari
Published: July 2002

The main result of this paper is that an elliptic curve having good reduction everywhere over a real quadratic field has a

2
2

-rational point under certain hypotheses (primarily on class numbers of related fields). It extends the earlier case in which no ramification at

2
2

is allowed. Small fields satisfying the hypotheses are then found, and in four cases the non-existence of such elliptic curves can be shown, while in three others all such curves have been classified.
Perspectives on American mathematics
Authors: Parshall Karen
Published: July 2002

A research-level community of mathematicians developed in the United States in the closing quarter of the nineteenth century. Since that time, American mathematicians have regularly paused to assess the state of their community and to reflect on its mathematical output. This paper analyzes a series of such reflections—beginning with Simon Newcomb’s thoughts on the state of the exact sciences in America in 1874 and culminating with the 1988 commentaries on the “problems of mathematics" discussed at Princeton’s bicentennial celebrations in 1946—against a backdrop of broader historical trends.
Modularity of certain potentially Barsotti-Tate Galois representations
Authors: Conrad Brian , Diamond Fred , Taylor Richard
Published: July 2002

We show that certain potentially semistable lifts of modular mod 

l
l

representations are themselves modular. As a result we show that any elliptic curve over the rational numbers with conductor not divisible by 27 is modular.
Two Splice Variants of Nopp140 inDrosophila melanogaster
Authors: Waggener John M. , DiMario Patrick J.
Published: July 2002

The Nopp140 gene of Drosophila maps within 79A5 of chromosome 3. Alternative splicing yields two variants. DmNopp140 (654 residues) is the sequence homolog of vertebrate Nopp140. Its carboxy terminus is 64% identical to that of the prototypical rat Nopp140. DmNopp140-RGG (688 residues) is identical to DmNopp140 throughout its first 551 residues, but its carboxy terminus contains a glycine/arginine-rich domain that is often found in RNA-binding proteins such as vertebrate nucleolin. Both Drosophilavariants localize to nucleoli in Drosophila Schneider II cells and Xenopus oocytes, specifically within the dense fibrillar components. In HeLa cells, DmNopp140-RGG localizes to intact nucleoli, whereas DmNopp140 partitions HeLa nucleoli into phase-light and phase-dark regions. The phase-light regions contain DmNopp140 and endogenous fibrillarin, whereas the phase-dark regions contain endogenous nucleolin. When coexpressed, bothDrosophila variants colocalize to HeLa cell nucleoli. Both variants fail to localize to endogenous Cajal bodies inXenopus oocyte nuclei and in HeLa cell nuclei. Endogenous HeLa coilin, however, accumulates around the periphery of phase-light regions in cells expressing DmNopp140. The carboxy truncation (DmNopp140ΔRGG) also fails to localize to Cajal bodies, but it forms similar phase-light regions that peripherally accumulate endogenous coilin. Conversely, we see no unusual accumulation of coilin in cells expressing DmNopp140-RGG.
Multi-query sequence BLAST output examination with MuSeqBox
Authors: Xing Liqun , Brendel Volker
Published: July 2002

Summary: MuSeqBox is a program to parse BLAST output and store attributes of BLAST hits in tabular form. The user can apply a number of selection criteria to filter out hits with particular attributes. MuSeqBox provides a powerful annotation tool for large sets of query sequences that are simultaneously compared against a database with any of the standard stand-alone or network–client BLAST programs. We discuss such application to the problem of annotation and analysis of EST collections.

Availability: The program was written in standard C++ and is freely available to noncommercial users by request from the authors. The program is also available over the web at http://bioinformatics.iastate.edu/bioinformatics2go/mb/MuSeqBox.html.

Contact: vbrendel@iastate.edu
Evaluation of computational metabolic-pathway predictions for
Helicobacter pylori
Authors: Paley Suzanne M. , Karp Peter D.
Published: July 2002

Motivation: We seek to determine the accuracy of computational methods for predicting metabolic pathways in sequenced genomes, and to understand the contributions of both the prediction algorithms, and the reference pathway databases used by those algorithms, to the prediction accuracy.

Results: The comparisons we performed were as follows. (1) We compared two predictions of the pathway complements of Helicobacter pylori that were computed by an early version of our pathway-prediction algorithm: prediction A used the EcoCyc E. coli pathway DB as the reference database (DB) for prediction, and prediction B used the MetaCyc pathway DB (a superset of EcoCyc) as the reference pathway DB. The MetaCyc-based prediction contained 75% more pathway predictions, but we believe a significant number of those predictions were false positives. (2) We compared two predictions of the pathway complement of H. pylori that used MetaCyc as the reference pathway DB, but that used different algorithms: the original PathoLogic algorithm, and an enhanced version of the algorithm designed to eliminate false-positive pathway predictions. The improved algorithm predicted 30\% fewer metabolic pathways than the original algorithm; all of the eliminated pathways are believed to be false-positive predictions. (3)~We compared the 98 pathways predicted by the enhanced algorithm with the results of a manual analysis of the pathways of H. pylori. Results: 40 of the computationally predicted pathways were consistent with the manual analysis, 13 pathways are considered false-positive predictions, and four pathways had partially overlapping topologies. Twenty-six predicted pathways were not mentioned in the manual analysis; we believe these are correct predictions by PathoLogic that were not found by the manual analysis. Five pathways from the manual analysis were not found computationally. Agreement between the computational and manual predictions was good overall, with the computational analysis inferring many pathways that the manual analysis did not identify. Ultimately the manual analysis is also partially speculative, and therefore is not an absolute measure of correctness. The algorithm is designed to err on the side of more false positives to bring more potential pathways to the user's attention. The resulting H. pylori pathway DB is freely available at http://ecocyc.org:1555/HPY/organism-summary?object=HPY.

Availability: The Pathway Tools software is freely available to academic users, and is available to commercial users for a fee. Contact pkarp@ai.sri.com for information on obtaining the software.

Contact: paley@ai.sri.com; pkarp@ai.sri.com

* To whom correspondence should be addressed.
Promoter protection by a transcription factor acting as a local topological homeostat
Authors: Rochman Mark , Aviv Michal , Glaser Gad , Muskhelishvili Georgi
Published: July 2002

Binding of the Escherichia coli global transcription factor FIS to the upstream activating sequence (UAS) of stable RNA promoters activates transcription on the outgrowth of cells from stationary phase. Paradoxically, while these promoters require negative supercoiling of DNA for optimal activity, FIS counteracts the increase of negative superhelical density by DNA gyrase. We demonstrate that binding of FIS at the UAS protects the rrnA P1 promoter from inactivation at suboptimal superhelical densities. This effect is correlated with FIS‐dependent constraint of writhe and facilitated untwisting of promoter DNA. We infer that FIS maintains stable RNA transcription by stabilizing local writhe in the UAS. These results suggest a novel mechanism of transcriptional regulation by a transcription factor acting as a local topological homeostat.
Knowledge acquired and decisions made: triadic interactions during allogrooming in wild bonnet macaques, Macaca radiata
Authors: Sinha Anindya
Published: July 2002

The pressures of developing and maintaining intricate social relationships may have led to the evolution of enhanced cognitive abilities in many nonhuman primates. Knowledge of the dominance ranks and social relationships of other individuals, in particular, is important in evaluating one's position in the rank hierarchy and affiliative networks. Triadic interactions offer an excellent opportunity to examine whether decisions are taken by individuals on the basis of such knowledge. Allogrooming supplants among wild female bonnet macaques (
Macaca radiata
) usually involved the subordinate female of a grooming dyad retreating at the approach of a female dominant to both members of the dyad. In a few exceptional cases, however, the dominant member of the dyad retreated; simple non–cognitive hypotheses involving dyadic rank differences and agonistic relationships failed to explain this phenomenon. Instead, retreat by the dominant individual was positively correlated with the social attractiveness of her subordinate companion (as measured by the duration of grooming received by the latter from other females in the troop). This suggests that not only does an individual evaluate relationships among other females, but does so on the basis of the amount of grooming received by them. Similarly, the frequency of approaches received by any female was correlated with her social attractiveness when she was the dominant member of the dyad, but not when she was the subordinate. This indicated that approaching females might be aware of the relative dominance ranks of the two allogrooming individuals. In logistic regression analyses, the probability of any individual retreating was found to be influenced more by her knowledge of her rank difference with both the other interactants, rather than by their absolute ranks. Moreover, information about social attractiveness appeared to be used in terms of correlated dominance ranks. The nature of knowledge acquired by bonnet macaque females may thus be egotistical in that other individuals are evaluated relative to oneself, integrative in that information about all other interactants is used simultaneously, and hierarchical in the ability to preferentially use certain categories of knowledge for the storage of related information from other domains.
Neural coding of 3D features of objects for hand action in the parietal cortex of the monkey
Authors: Sakata Hideo , Taira Masato , Kusunoki Makoto , Murata Akira , Tanaka Yuji , Tsutsui Ken–ichiro
Published: July 2002

In our previous studies of hand manipulation task–related neurons, we found many neurons of the parietal association cortex which responded to the sight of three–dimensional (3D) objects. Most of the task–related neurons in the AIP area (the lateral bank of the anterior intraparietal sulcus) were visually responsive and half of them responded to objects for manipulation. Most of these neurons were selective for the 3D features of the objects. More recently, we have found binocular visual neurons in the lateral bank of the caudal intraparietal sulcus (c–IPS area) that preferentially respond to a luminous bar or plate at a particular orientation in space. We studied the responses of axis–orientation selective (AOS) neurons and surface–orientation selective (SOS) neurons in this area with stimuli presented on a 3D computer graphics display. The AOS neurons showed a stronger response to elongated stimuli and showed tuning to the orientation of the longitudinal axis. Many of them preferred a tilted stimulus in depth and appeared to be sensitive to orientation disparity and/or width disparity. The SOS neurons showed a stronger response to a flat than to an elongated stimulus and showed tuning to the 3D orientation of the surface. Their responses increased with the width or length of the stimulus. A considerable number of SOS neurons responded to a square in a random dot stereogram and were tuned to orientation in depth, suggesting their sensitivity to the gradient of disparity. We also found several SOS neurons that responded to a square with tilted or slanted contours, suggesting their sensitivity to orientation disparity and/or width disparity. Area c–IPS is likely to send visual signals of the 3D features of an object to area AIP for the visual guidance of hand actions.
Anechoic aquarium for ultrasonic neural telemetry
Authors: Mensinger Allen F. , Deﬃenbaugh Max
Published: July 2002

An acoustic neural telemetry tag has been developed for recording from free–swimming aquatic animals. Microwire electrodes were implanted into the VIIIth nerve of the toadfish,
Opsanus tau
, and interfaced to the subdermally implanted tag. The telemetry tag frequency modulates the neural signal, converting it into a varying frequency, which is amplified and transmitted acoustically (centre frequency of 90 kHz and a 20 kHz bandwidth). This acoustic signal is detected by a receiver hydrophone, and the receiver reconstructs the full neural waveform from the acoustic signal. However, due to the multipath environment in the experimental aquarium, the acoustic signal is quickly degraded as the hydrophone is moved away from the source. In order to receive the signal independent of fish position, an anechoic aquarium was designed. Streams of microbubbles (
ca.
70 μm diameter) were generated to produce a curtain of sound–absorptive material along the walls and water surface of the aquarium. Microbubble generation significantly reduced the multipath artefacts, and allowed signal discrimination independent of fish and hydrophone position. The anechoic aquarium will allow the recording of neural activity from freeswimming fishes in quasi–natural habitats, thus allowing better understanding of the neural mechanisms of behaviour.
Does natural selection organize ecosystems for the maintenance of high productivity and diversity?
Authors: Giles Leigh Egbert , Vermeij Geerat Jacobus
Published: July 2002

Three types of evidence suggest that natural ecosystems are organized for high productivity and diversity: (i) changes not previously experienced by a natural ecosystem, such as novel human disturbances, tend to diminish its productivity and/or diversity, just as ‘random’ changes in a machine designed for a function usually impair its execution of that function; (ii) humans strive to recreate properties of natural ecosystems to enhance productivity of artificial ones, as farmers try to recreate properties of natural soils in their fields; and (iii) productivity and diversity have increased during the Earth's history as a whole, and after every major biotic crisis.

Natural selection results in ecosystems organized to maintain high productivity of organic matter and diversity of species, just as competition among individuals in Adam Smith's ideal economy favours high production of wealth and diversity of occupations. In nature, poorly exploited energy attracts more efficient users. This circumstance favours the opening of new ways of life and more efficient recycling of resources, and eliminates most productivity–reducing ‘ecological monopolies’. Ecological dominants tend to be replaced by successors with higher metabolism, which respond to more stimuli and engage in more varied interactions. Finally, increasingly efficient predators and herbivores favour faster turnover of resources.
High-Throughput Imaging of Brain Gene Expression
Authors: Brown Vanessa M. , Ossadtchi Alex , Khan Arshad H. , Cherry Simon R. , Leahy Richard M. , Smith Desmond J.
Published: July 2002

Voxelation is a new method for acquisition of three dimensional (3D) gene expression patterns in the brain. It employs high-throughput analysis of spatially registered voxels (cubes) to produce multiple volumetric maps of gene expression analogous to the images reconstructed in biomedical imaging systems. Using microarrays, 24 voxel images of coronal hemisections at the level of the hippocampus of both the normal human brain and Alzheimer's disease brain were acquired for 2000 genes. The analysis revealed a common network of coregulated genes, and allowed identification of putative control regions. In addition, singular value decomposition (SVD), a mathematical method used to provide economical explanations of complex data sets, produced images that distinguished between brain structures, including cortex, caudate, and hippocampus. The results suggest that voxelation will be a useful approach for understanding how the genome constructs the brain.

[All study results are available as a web supplement athttp://www.pharmacology.ucla.edu/smithlab/genome_research_data and at http://www.genome.org.]
Burst calculations for brachytherapy sources
Authors: Rivard Mark J.
Published: July 2002

Due to helium production following alpha decay, it is necessary to demonstrate the structural integrity of new sources at elevated temperatures for special form certification by the U.S. Department of Transportation. Effects of temperature, capsule composition, and capsule dimensions are examined and reduced to a simple mathematical model. This highly conservative model assumes that all gas products leaving the radioactive source wire are retained by the capsule, and upon elevation to a temperature of the capsule exhibits negligible expansion or change in internal volume and no increase in gas‐phase components due to vaporization of spontaneous fission products. The calculated maximum loadings for the ORNL‐made Applicator Tube and three proposed high dose rate sources encapsulated in (VariSource, microSelectron classic, and a novel design) were 10.8, 0.508, 0.708, and 2.12 mg respectively.
Feasibility of a semiconductor dosimeter to monitor skin dose in interventional radiology
Authors: Meyer Philippe , Regal Raymond , Jung Monique , Siffert Paul , Mertz Luc , Constantinesco André
Published: July 2002

The design and preliminary test results of a semiconductor silicon dosimeter are presented in this article. Use of this dosimeter is foreseen for real‐time skin dose control in interventional radiology. The strong energy dependence of this kind of radiation detector is well overcome by filtering the silicon diode. Here, the optimal filter features have been calculated by numerical Monte Carlo simulations. A prototype has been built and tested in a radiological facility. The first experimental results show a good match between the filtered semiconductor diode response and an ionization chamber response, within 2% fluctuation in a 2.2 to 4.1 mm Al half‐value layer (HVL) energy range. Moreover, the semiconductor sensor response is linear from 0.02 Gy/min to at least 6.5 Gy/min, covering the whole dose rate range found in interventional radiology. The results show that a semiconductor dosimeter could be used to monitor skin dose during the majority of procedures using x‐rays below 150 keV. The use of this device may assist in avoiding radiation‐induced skin injuries and lower radiation levels during interventional procedures.
Implementation of a cone‐beam reconstruction algorithm for the single‐circle source orbit with embedded misalignment correction using homogeneous coordinates
Authors: Karolczak Marek , Schaller Stefan , Engelke Klaus , Lutz Andreas , Taubenreuther Ulrike , Wiesent Karl , Kalender Willi
Published: July 2002

We present an efficient implementation of an approximate cone‐beam image reconstruction algorithm for application in tomography, which accounts for scanner mechanical misalignment. The implementation is based on the algorithm proposed by Feldkamp et al. [J. Opt. Soc. Am. A 6, 612–619 (1984)] and is directed at circular scan paths. The algorithm has been developed for the purpose of reconstructing volume data from projections acquired in an experimental x‐ray microtomography (μCT) scanner [Engelke et al., Der Radiologe 39, 203–212 (1999)]. To mathematically model misalignment we use matrix notation with homogeneous coordinates to describe the scanner geometry, its misalignment, and the acquisition process. For convenience analysis is carried out for x‐ray CT scanners, but it is applicable to any tomographic modality, where two‐dimensional projection acquisition in cone beam geometry takes place, e.g., single photon emission computerized tomography. We derive an algorithm assuming misalignment errors to be small enough to weight and filter original projections and to embed compensation for misalignment in the backprojection. We verify the algorithm on simulations of virtual phantoms and scans of a physical multidisk (Defrise) phantom.
Optimization of power deposition and a heating strategy for external ultrasound thermal therapy
Authors: Lin Win‐Li , Liang Tzu‐Chen , Yen Jia‐Yush , Liu Hao‐Li , Chen Yung‐Yaw
Published: July 2002

The purpose of this paper is to examine the thermal dose distribution, to configure the optimal absorbed power deposition, and to design an appropriate heating strategy for ultrasound thermal therapy. This work employs simulation programs, which are based on the transient bio‐heat transfer equation and an ideal absorbed power deposition or an ideal temperature elevation within a cube of tissue, to study the optimal absorbed power deposition. Meanwhile, a simplified model of a scanned ultrasound transducer power deposition (a cone with convergent/divergent shape) is used to investigate the heating strategy for a large tumor with a sequence of heating pulses. The distribution of thermal dose equivalence defined by Sapareto and Dewey [Int. J. Radiat. Oncol., Biol., Phys. 10, 787–800 (1984)] is used to evaluate the heating result for a set of given parameters. The parameters considered are the absorbed power density, heating duration, temperature elevation, blood perfusion, and the size of heating cube. The results demonstrate that the peak temperature is the key factor determining the thermal dose for this short‐duration heating. Heat conduction has a very strong influence on the responses of temperature and thermal dose for a small heating cube and the boundary portion of a large heating cube. Hence, for obtaining the same therapeutic result, a higher power density is required for these two conditions to compensate the great temperature difference between the heating cube and the surrounding tissue. The influence of blood perfusion on the thermal dose is negligible on the boundary portion of the heating cube, while in the central portion it may become a crucial factor as a lower power density is used in this portion to save the delivered energy. When using external ultrasound heating method to treat a large tumor, the size of heating unit, the sequence of heating pulses, and the cooling‐time interval between the consecutive heating pulses are the important factors to be determined to have an appropriate treatment within a reasonable overall treatment time.
Automated seed detection and three‐dimensional reconstruction. I. Seed localization from fluoroscopic images or radiographs
Authors: Tubic Dragan , Zaccarin André , Pouliot Jean , Beaulieu Luc
Published: July 2002

An automated procedure for the detection of the position and the orientation of radioactive seeds on fluoroscopic images or scanned radiographs is presented. The extracted positions of seed centers and the orientations are used for three‐dimensional reconstruction of permanent prostate implants. The extraction procedure requires several steps: correction of image intensifier distortions, normalization, background removal, automatic threshold selection, thresholding, and finally, moment analysis and classification of the connected components. The algorithm was tested on 75 fluoroscopic images. The results show that, on average, 92% of the seeds are detected automatically. The orientation is found with an error smaller than 5° for 75% of the seeds. The orientation of overlapping seeds (10%) should be considered as an estimate at best. The image processing procedure can also be used for seed or catheter detection in CT images, with minor modifications.
Microwave‐induced thermoacoustic tomography: Reconstruction by synthetic aperture
Authors: Feng Dazi , Xu Yuan , Ku Geng , Wang Lihong V.
Published: July 2002

We have applied the synthetic‐aperture method to linear‐scanning microwave‐induced thermoacoustic tomography in biological tissues. A nonfocused ultrasonic transducer was used to receive thermoacoustic signals, to which the delay‐and‐sum algorithm was applied for image reconstruction. We greatly improved the lateral resolution of images and acquired a clear view of the circular boundaries of buried cylindrical objects, which could not be obtained in conventional linear‐scanning microwave‐induced thermoacoustic tomography based on focused transducers. Two microwave sources, which had frequencies of 9 and 3 GHz, respectively, were used in the experiments for comparison. The 3 GHz system had a much larger imaging depth but a lower signal–noise ratio than the 9 GHz system in near‐surface imaging.
Electron beam transport in the presence of a strong, axial magnetic field
Authors: Kuperman Vadim Y.
Published: July 2002

An analytical model is presented that describes the effects of an applied longitudinal magnetic field and energy loss on the transport of relativistic electrons in a medium. By using a modified Fermi equation we derive analytical solutions for the distribution function of electrons. The obtained results can be used to predict the influence of longitudinal magnetic fields on the lateral spread of electrons in both coordinate space and velocity space.
Evaluation of a commercial three‐dimensional electron pencil beam algorithm
Authors: Muller‐Runkel Renate , Cho Sang‐Hyun
Published: July 2002

Results from beta testing of a commercially available three‐dimensional electron pencil beam algorithm (CMS FOCUS, Computerized Medical Systems, Inc. St. Louis, MO) are reported. Straight on beams were evaluated at normal and extended distances, and obliquely incident beams at angles up to 40°. Shaped electron fields with small circular cutouts, and narrow elongated, centered and offcentered, rectangular field shapes were investigated. Slab inhomogeneities were studied for lung and bone equivalent material, and isodose distributions for small inhomogeneities of these materials were compared with film and TLD measurements. All tests reported here were performed with electrons of 6, 12, and 20 MeV from a Cl‐1800 accelerator.
A novel approach to scatter measurement and correction in digital radiography
Authors: Maher Kieran P.
Published: July 2002

This thesis is directed at the development, evaluation, and application of a novel scatter measurement technique for digital radiography. The use of an aperture for scatter measurement is examined from both a theoretical and an experimental perspective. The theoretical consideration is based on a broad beam analytical model which predicts that scatter signals should be negligible at narrow beam sizes. The experimental examination is based on analyzing features in images of narrow apertures using a digital fluoroscopy system in simulated clinical imaging conditions. It is established that a narrow aperture can generate a scatter‐free signal which can be related to the open field signal to determine the scatter signal and that this method has advantages over the conventional approach in terms of practical simplicity, accuracy, and dose efficiency. This is achieved through examination of the signature of skirt data in images of apertures 0.5 to 10 mm in diameter and through determination of the air gap dependence of aperture signals and the densitometric fidelity of image data. The approach is extended to the development and evaluation of a computerized scatter correction scheme based on two‐dimensional interpolation of scatter samples determined using an array of apertures. The evaluation is directed at the physical imaging performance of the scheme and encompasses the image acquisition and processing stages of the scatter correction process. It is established that the scheme generates substantial improvement in broad‐area contrast, densitometric linearity, square wave response factor, and spatial uniformity, has no direct effect on edge sharpness and limiting resolution, and gives rise to a substantial increase in image mottle. This conclusion is valid for any correction scheme which involves subtraction of a smooth background image be it based on spatial domain convolution filtering, interpolated scatter sampling or other process. The performance of the scheme is also compared with that of a high ratio grid and with spatial domain convolution filtering.
Evaluation of helical computed tomography scan parameters for vascular imaging
Authors: Reynolds Dena M. , Hazle John D. , Johnston Dennis A. , Charnsangavej Chusilp
Published: July 2002

Helical x‐ray computed tomography (hCT) is the volume acquisition of image data in which the data set represents a series of projections obtained in a helical spatial distribution. Data acquisition times and spatial resolution are determined largely by two user defined parameters—collimation and pitch. Each combination of pitch and collimation results in a slice profile which can be considered as the apparent slice thickness. Careful selection of pitch and collimation allows the acquisition of up to 20 cm of axial data in a breathold or first pass of bolus contrast material. This makes helical CT an excellent technique for angiographic (CTA) studies. Additionally, slices can be reconstructed at any interval to reduce partial volume averaging, minimizing the beading artifacts seen in maximum intensity projections (MIP) when interslice resolution is poor. We have evaluated a range of collimation and pitches for clinical CTA. Additionally, three reconstruction filters were included to determine the optimal frequency (spatial) properties for these techniques. Objective and subjective analyses were performed. We found pitches of up to 1.5:1 to be acceptable for all collimations. For a given scan length ( direction), selection of thinner collimation and higher pitch resulted in better SNR and observer scoring for angiographic presentations.
Measurements of electron beam peak scatter factors
Authors: Ding G. X. , Cygler J. E.
Published: July 2002

We have measured the peak scatter factor (PSF) for electron beams which in analogy to photon beams is defined as the ratio of the absorbed dose to water at the depth of dose maximum in a water phantom to the absorbed dose in free air at the same location for a given incident beam. In this study we have measured the PSFs as a function of the incident electron beam energy and field size. We have used both an RK ionization chamber and a silicon diode as radiation detectors. After applying the water/air stopping power ratio and fluence correction factors to the ionization chamber readings, the values of measured PSFs by using two different detectors are in a good agreement. The results show that the value of PSF increases with the increase of the field size and decreases with the increase of the beam energy. The range of the variation with field size between and is 1.24–1.42, 1.15–1.30, 1.15–1.17 for 6, 11, and 20 MeV beams, respectively.
On‐line monitoring and PET imaging of the positron‐emitting activity created in tissue by proton radiotherapy beams
Authors: Litzenberg Dale William
Published: July 2002

An imaging system was designed and tested to monitor the positron‐emitting activity distribution created by proton radiotherapy beams during treatments. Decay data were acquired and imaged between beam pulses and after irradiation. The range of a 150 MeV proton beam may be verified after a single beam pulse to within the resolution of the imaging system, which was 1.2 cm. Over 80% of the initial positron‐emitting activity is from while the remainder is primarily with traces of and The dose delivered to the patient may also be monitored by observing the increase in the number of coincidence events detected between successive beam pulses. In some situations the width of the plateau region of a Spread‐Out Bragg Peak may be inferred from the fall of activity at the distal end of the distribution. Radioisotopic imaging may also be performed along the beam path by fitting decay data collected after the treatment is complete. Using this technique, it is shown that variations in elemental composition in inhomogeneous treatment volumes may be identified and used to locate anatomic landmarks. Radioisotopic imaging also reveals that is created well beyond the Bragg peak, apparently by secondary neutrons.
Calculating lens dose and surface dose rates from ophthalmic applicators using Monte Carlo modeling
Authors: Gleckler Mark , Valentine John D. , Silberstein Edward B.
Published: July 2002

Using a applicator for brachytherapy for the reduction of recurrence rates after pterygium excisions has been an effective therapeutic procedure. Accurate knowledge of the dose being applied to the affected area on the sclera has been lacking, and for decades inaccurate estimates for lens dose have thus been made. Small errors in the assumptions which are required to make these estimates lead to dose rates changing exponentially because of the attenuation of beta particles. Monte Carlo simulations have been used to evaluate the assumptions that are now being used for the calculation of the surface dose rate and the corresponding determination of lens dose. For an ideal applicator, results from this study indicate dose rates to the most radiosensitive areas of the lens ranging from 8.8 to 15.5 cGy/s. This range is based on different eye dimensions that ultimately corresponds to a range in distance between the applicator surface and the germinative epithelium of the lens of 2–3 mm. Furthermore, the conventional 200 cGy threshold for whole lens cataractogenesis is questioned for predicting complications from scleral brachytherapy. The dose to the germinative epithelium should be used for studying radiocataractogenesis.
Commissioning a p‐type silicon diode for use in clinical electron beams
Authors: Eveling J. N. , Morgan A. M. , Pitchford W. G.
Published: July 2002

Commissioning measurements were carried out on a p‐type silicon diode detector for use in patient monitoring in high energy electron beams. Characteristics specific to the diode were examined. The variation in diode sensitivity with dose per pulse was found to be less than 1% over a range 0.069–0.237 mGy/pulse. The diode exhibited a sensitivity variation with accumulated dose of 10% per kGy and a sensitivity variation with surface temperature of 0.26%/°C. The dependence of the diode response on the direction of the incident electron beam was investigated. Results were found to exceed the manufacturer's specifications. Output factors measured with the diode agree to within 1.5% of those measured with an NACP‐02 air ionization chamber. The detector showed a variation in response with energy of 0.8% over the energy range 4–15 MeV. Prior to introducing the diode into clinical use, an assessment of beam perturbation directly behind the diode was made. The maximum reduction in local dose directly behind the diode at a depth of 1.0 cm below the surface was approximately 13% at 4 and 15 MeV.
An artificial neural net and error backpropagation to reconstruct single photon emission computerized tomography data
Authors: Knoll Peter , Mirzaei Siroos , Müllner Angelika , Leitha Thomas , Koriska Karl , Köhn Horst , Neumann Martin
Published: July 2002

At present, algorithms used in nuclear medicine to reconstruct single photon emission computerized tomography (SPECT) data are usually based on one of two principles: filtered backprojection and iterative methods. In this paper a different algorithm, applying an artificial neural network (multilayer perception) and error backpropagation as training method are used to reconstruct transaxial slices from SPECT data. The algorithm was implemented on an Elscint XPERT workstation (i486, 50 MHz), used as a routine digital image processing tool in our departments. Reconstruction time for a matrix is approximately 45 s/transaxial slice. The algorithm has been validated by a mathematical model and tested on heart and Jaszczak phantoms. Phantom studies and very first clinical results octreotide SPECT, MDP bone SPECT) show in comparison with filtered backprojection an enhancement in image quality.
A high‐precision, high‐resolution and fast dosimetry system for beta sources applied in cardiovascular brachytherapy
Authors: Bambynek M. , Flühs D. , Quast U. , Wegener D. , Soares C. G.
Published: July 2002

A fast dosimetry system based on plastic scintillator detectors has been developed which allows three‐dimensional measurement of the radiation field in water of β‐sources appropriate for application in cardiovascular brachytherapy. This system fulfills the AAPM Task Group 60 recommendations for dosimetry of cardiovascular brachytherapy sources. To demonstrate the use of the system, measurements have been performed with an ‐wire source. The dose distribution was determined with a spatial resolution of better than 0.2 mm, with only a few minutes needed per scan. The scintillator dosemeter was absolutely calibrated in terms of absorbed dose to water with a precision of ±7.5%. The relative precision achievable is ±2.5%. The response of the system is linear within ±2% for dose rates from 0.5 mGy s−1 to 500 mGy s−1.