bluuebunny/crossref_metadata_2025 huggingface dataset:
Resident Skin-specific γδ T Cells Provide Local, Nonredundant Regulation of Cutaneous Inflammation
Authors: Girardi Michael , Lewis Julia , Glusac Earl , Filler Renata B. , Geng Liping , Hayday Adrian C. , Tigelaar Robert E.
Published: July 2002

The function of the intraepithelial lymphocyte (IEL) network of T cell receptor (TCR) γδ+ (Vγ5+) dendritic epidermal T cells (DETC) was evaluated by examining several mouse strains genetically deficient in γδ T cells (δ−/− mice), and in δ−/− mice reconstituted with DETC or with different γδ cell subpopulations. NOD.δ−/− and FVB.δ−/− mice spontaneously developed localized, chronic dermatitis, whereas interestingly, the commonly used C57BL/6.δ−/− strain did not. Genetic analyses indicated a single autosomal recessive gene controlled the dermatitis susceptibility of NOD.δ−/− mice. Furthermore, allergic and irritant contact dermatitis reactions were exaggerated in FVB.δ−/−, but not in C57BL/6.δ−/− mice. Neither spontaneous nor augmented irritant dermatitis was observed in FVB.β−/− δ−/− mice lacking all T cells, indicating that αβ T cell–mediated inflammation is the target for γδ-mediated down-regulation. Reconstitution studies demonstrated that both spontaneous and augmented irritant dermatitis in FVB.δ−/− mice were down-regulated by Vγ5+ DETC, but not by epidermal T cells expressing other γδ TCRs. This study demonstrates that functional impairment at an epithelial interface can be specifically attributed to absence of the local TCR-γδ+ IEL subset and suggests that systemic inflammatory reactions may more generally be subject to substantial regulation by local IELs.
Gating Properties Conferred on Bk Channels by the β3b Auxiliary Subunit in the Absence of Its Nh2- and Cooh Termini
Authors: Zeng Xu-Hui , Ding J.-P. , Xia Xiao-Ming , Lingle Christopher J.
Published: July 2002

Both β1 and β2 auxiliary subunits of the BK-type K+ channel family profoundly regulate the apparent Ca2+ sensitivity of BK-type Ca2+-activated K+ channels. Each produces a pronounced leftward shift in the voltage of half-activation (V0.5) at a given Ca2+ concentration, particularly at Ca2+ above 1 μM. In contrast, the rapidly inactivating β3b auxiliary produces a leftward shift in activation at Ca2+ below 1 μM. In the companion work (Lingle, C.J., X.-H. Zeng, J.-P. Ding, and X.-M. Xia. 2001. J. Gen. Physiol. 117:583–605, this issue), we have shown that some of the apparent β3b-mediated shift in activation at low Ca2+ arises from rapid unblocking of inactivated channels, unlike the actions of the β1 and β2 subunits. Here, we compare effects of the β3b subunit that arise from inactivation, per se, versus those that may arise from other functional effects of the subunit. In particular, we examine gating properties of the β3b subunit and compare it to β3b constructs lacking either the NH2- or COOH terminus or both. The results demonstrate that, although the NH2 terminus appears to be the primary determinant of the β3b-mediated shift in V0.5 at low Ca2+, removal of the NH2 terminus reveals two other interesting aspects of the action of the β3b subunit. First, the conductance-voltage curves for activation of channels containing the β3b subunit are best described by a double Boltzmann shape, which is proposed to arise from two independent voltage-dependent activation steps. Second, the presence of the β3b subunit results in channels that exhibit an anomalous instantaneous outward current rectification that is correlated with a voltage dependence in the time-averaged single-channel current. The two effects appear to be unrelated, but indicative of the variety of ways that interactions between β and α subunits can affect BK channel function. The COOH terminus of the β3b subunit produces no discernible functional effects.
Two Temporal Phases of Light Adaptation in Retinal Rods
Authors: Calvert Peter D. , Govardovskii Victor I. , Arshavsky Vadim Y. , Makino Clint L.
Published: July 2002

Vertebrate rod photoreceptors adjust their sensitivity as they adapt during exposure to steady light. Light adaptation prevents the rod from saturating and significantly extends its dynamic range. We examined the time course of the onset of light adaptation in bullfrog rods and compared it with the projected onset of feedback reactions thought to underlie light adaptation on the molecular level. We found that adaptation developed in two distinct temporal phases: (1) a fast phase that operated within seconds after the onset of illumination, which is consistent with most previous reports of a 1–2-s time constant for the onset of adaptation; and (2) a slow phase that engaged over tens of seconds of continuous illumination. The fast phase desensitized the rods as much as 80-fold, and was observed at every light intensity tested. The slow phase was observed only at light intensities that suppressed more than half of the dark current. It provided an additional sensitivity loss of up to 40-fold before the rod saturated. Thus, rods achieved a total degree of adaptation of ∼3,000-fold. Although the fast adaptation is likely to originate from the well characterized Ca2+-dependent feedback mechanisms regulating the activities of several phototransduction cascade components, the molecular mechanism underlying slow adaptation is unclear. We tested the hypothesis that the slow adaptation phase is mediated by cGMP dissociation from noncatalytic binding sites on the cGMP phosphodiesterase, which has been shown to reduce the lifetime of activated phosphodiesterase in vitro. Although cGMP dissociated from the noncatalytic binding sites in intact rods with kinetics approximating that for the slow adaptation phase, this hypothesis was ruled out because the intensity of light required for cGMP dissociation far exceeded that required to evoke the slow phase. Other possible mechanisms are discussed.
Normality criteria for families of holomorphic mappings of several complex variables into 𝑃^{𝑁}(𝐶)
Authors: Tu Zhen-han
Published: July 2002

By applying the heuristic principle in several complex variables obtained by Aladro and Krantz, we shall prove some normality criteria for families of holomorphic mappings of several complex variables into

P
N

(
C
)

P^N(C)

, the complex N-dimensional projective space, related to Green’s and Nochka’s Picard type theorems. The equivalence of normality to being uniformly Montel at a point will be obtained. Some examples will be given to complement our theory in this paper.
Periodic solutions to nonlinear one dimensional wave equation with 𝑋-dependent coefficients
Authors: Barbu V. , Pavel N.
Published: July 2002

This paper deals withtt-periodicity and regularity of solutions to the one dimensional nonlinear wave equation withxx-dependent coefficients
Finite element approximation of diffusion equations with convolution terms
Authors: Peszynska Malgorzata
Published: July 2002

Approximation of solutions to diffusion equations with memory represented by convolution integral terms is considered. Such problems arise from modeling of flows in fissured media. Convergence of the method is proved and results of numerical experiments confirming the theoretical results are presented. The advantages of implementation of the algorithm in a multiprocessing environment are discussed.
Rank one case of Dwork’s conjecture
Authors: Wan Daqing
Published: July 2002

In this paper, we prove the rank one case of Dwork’s conjecture on the

p
p

-adic meromorphic continuation of the pure slope L-functions arising from the slope decomposition of an overconvergent F-crystal. Further explicit information about zeros and poles of the pure slope L-functions are also obtained, including an application to the Gouvêa-Mazur type conjecture in this setting.
Existence of blow-up solutions in the energy space for the critical generalized KdV equation
Authors: Merle Frank
Published: July 2002

For the critical generalized Korteweg–de Vries equation, we establish blow-up in finite or infinite time inH1(R)H^1(\mathbf R)for initial data with negative energy, close to a soliton up to scaling and translation.
Purity of the stratification by Newton polygons
Authors: de Jong A. , Oort F.
Published: July 2002

Let

S
S

be a variety in characteristic

p
>
0

p>0

. Suppose we are given a nondegenerate

F
F

-crystal over

S
S

, for example the

i
i

th relative crystalline cohomology sheaf of a family of smooth projective varieties over

S
S

. At each point

s
s

of

S
S

we have the Newton polygon associated to the action of

F
F

on the fibre of the crystal at

s
s

. According to a theorem of Grothendieck the Newton polygon jumps up under specialization. The main theorem of this paper is that the jumps occur in codimension

1
1

on

S
S

(the Purity Theorem). As an application we prove some results on deformations of iso-simple

p
p

-divisible groups.
Post–Cytochrome c Protection from Apoptosis Conferred by a MAPK Pathway inXenopusEgg Extracts
Authors: Tashker Jessica S. , Olson Michael , Kornbluth Sally
Published: July 2002

In response to many different apoptotic stimuli, cytochrome c is released from the intermembrane space of the mitochondria into the cytoplasm, where it serves as a cofactor in the activation of procaspase 9. Inhibition of this process can occur either by preventing cytochrome c release or by blocking caspase activation or activity. Experiments involving in vitro reconstitution of apoptosis in cell-free extracts of Xenopus laevis eggs have suggested that extracts arrested in interphase are susceptible to an endogenous apoptotic program leading to caspase activation, whereas extracts arrested in meiotic metaphase are not. We report here that Mos/MEK/MAPK pathways active in M phase–arrested eggs are responsible for rendering them refractory to apoptosis. Interestingly, M phase–arrested extracts are competent to release cytochrome c, yet still do not activate caspases. Concomitantly, we have also demonstrated that recombinant Mos, MEK, and ERK are sufficient to block cytochrome c–dependent caspase activation in purified Xenopus cytosol, which lacks both transcription and translation. These data indicate that the MAP kinase pathway can target and inhibit post–cytochrome c release apoptotic events in the absence of new mRNA/protein synthesis and that this biochemical pathway is responsible for the apoptotic inhibition observed in meiotic X. laevis egg extracts.
An EXCEL template for calculation of enzyme kinetic parameters by non-linear regression.
Authors: Hern√°ndez A , Ruiz M T
Published: July 2002

MOTIVATION: An EXCEL template has been developed for the calculation of enzyme kinetic parameters by non-linear regression techniques. The tool is accurate, inexpensive, as well as easy to use and modify. AVAILABILITY: The program is available from http://www.ebi.ac.uk/biocat/biocat.html CONTACT: agustin. hernandez@bio.kuleuven.ac.be
Profile hidden Markov models.
Authors: Eddy S R
Published: July 2002

The recent literature on profile hidden Markov model (profile HMM) methods and software is reviewed. Profile HMMs turn a multiple sequence alignment into a position-specific scoring system suitable for searching databases for remotely homologous sequences. Profile HMM analyses complement standard pairwise comparison methods for large-scale sequence analysis. Several software implementations and two large libraries of profile HMMs of common protein domains are available. HMM methods performed comparably to threading methods in the CASP2 structure prediction exercise.
Registration of the expression patterns of Drosophila
segmentation genes by two independent methods
Authors: Myasnikova Ekaterina , Samsonova Anastassia , Kozlov Konstantin , Samsonova Maria , Reinitz John
Published: July 2002

Motivation: To construct an integrated map of Drosophila segmentation gene expression from partial data taken from individual embryos.

Results: Spline and wavelet based registration techniques were developed to register Drosophila segmentation gene expression data. As ground control points for registration we used the locations of extrema on gene expression patterns, represented in 1D. The registration method was characterized by unprecedented high accuracy. A method for constructing the integrated pattern of gene expression at cellular resolution was designed. These patterns were constructed for 9 segmentation genes belonging to gap and pair-rule classes.

Availability: Programs running on SPARC/SunOS 5.0 platform or Alpha/DU 4.0E systems may be obtained from the authors.

Contact: myasnikova@fn.csa.ru

* To whom correspondence should be addressed.
Composing life
Authors: Segré Daniel , Lancet Doron
Published: July 2002

Textbooks often assert that life began with specialized complex molecules, such as RNA, that are capable of making their own copies. This scenario has serious difficulties, but an alternative has remained elusive. Recent research and computer simulations have suggested that the first steps toward life may not have involved biopolymers. Rather, non‐covalent protocellular assemblies, generated by catalyzed recruitment of diverse amphiphilic and hydrophobic compounds, could have constituted the first systems capable of information storage, inheritance and selection. A complex chain of evolutionary events, yet to be deciphered, could then have led to the common ancestors of today's free‐living cells, and to the appearance of DNA, RNA and protein enzymes.
Relative potential for selection of fluoroquinolone-resistant Streptococcus pneumoniae strains by levofloxacin: comparison with ciprofloxacin, sparfloxacin and ofloxacin
Authors: Drugeon H. B. , Juvin M. E. , Bryskier A.
Published: July 2002

The aim of this study was to evaluate the relative potential of levofloxacin to select for resistance in Streptococcus pneumoniae in comparison with ciprofloxacin, sparfloxacin and ofloxacin. Two S. pneumoniae strains were studied; HBD 153 (parental strain, serotype 3) and HBD 964 (selected from the parental strain in an experimental mouse peritonitis infection model). MICs for the two strains were, respectively: 2 and 2 mg/L for ciprofloxacin; 2 and 4 mg/L for ofloxacin; 0.5 and 1 mg/L for sparfloxacin; 2 and 2 mg/L for levofloxacin. In-vitro, with 4 × MIC as the selection concentration, no mutant was obtained with strain HBD 153 (mutation frequency <10 −8 ). With HBD 964, the mutation frequency was 9 × 10 −7 for ofloxacin, 10 −7 for ciprofloxacin, 4 × 10 −5 for sparfloxacin and <10 −8 for levofloxacin. In an immunosuppressed mouse peritonitis model (20 mice per dose), the S. pneumoniae strains were studied with sc doses of ciprofloxacin, sparfloxacin and ofloxacin at 50 mg/kg od, and with sc levofloxacin at a dose of 10 and 50 mg/kg od, or 10 and 50 mg/kg bid. The MICs for strains isolated after antibiotic treatment and the mutation frequencies at 4 × MIC were determined. Against HBD 153, sparfloxacin was the most active treatment, followed by levofloxacin 10 mg/kg and 50 mg/kg bid, but strains identical to HBD 964 (showing a resistant variant at 4 × MIC) were selected by sparfloxacin. Against HBD 964, levofloxacin (10 mg/kg and 50 mg/kg) was the most active drug. Highly resistant mutants were selected by ofloxacin and ciprofloxacin, but not by sparfloxacin and levofloxacin. In conclusion, the relative potential of levofloxacin to select for fluoroquinolone-resistant S. pneumoniae is lower than that of ciprofloxacin, ofloxacin and sparfloxacin both in vitro and in vivo.
Gulliver's further travels: the necessity and difficulty of a hierarchical theory of selection
Authors: Gould Stephen Jay
Published: July 2002

For principled and substantially philosophical reasons, based largely on his reform of natural history by inverting the Paleyan notion of overarching and purposeful beneficence in the construction of organisms, Darwin built his theory of selection at the single causal level of individual bodies engaged in unconscious (and metaphorical) struggle for their own reproductive success. But the central logic of the theory allows selection to work effectively on entities at several levels of a genealogical hierarchy, provided that they embody a set of requisite features for defining evolutionary individuality. Genes, cell lineages, demes, species, and clades, as well as Darwin's favoured organisms, embody these requisite features in enough cases to form important levels of selection in the history of life. R. A. Fisher explicitly recognized the unassailable logic of species selection, but denied that this real process could be important in evolution because, compared with the production of new organisms within a species, the origin of new species is so rare, and the number of species within most clades so low. I review this and other classical arguments against higher–level selection, and conclude (in the first part of this paper) that they are invalid in practice for interdemic selection, and false in principle for species selection. Punctuated equilibrium defines the individuality of species and refutes Fisher's classical argument based on cycle time. In the second part of the paper, I argue that we have failed to appreciate the range and power of selection at levels above and below the organismic because we falsely extrapolate the defining properties of organisms to these other levels (which are characterized by quite different distinctive features), and then regard the other levels as impotent because their effective individuals differ so much from organisms. We would better appreciate the power and generality of hierarchical models of selection if we grasped two key principles: first, that levels can interact in all modes (positively, negatively, and orthogonally), and not only in the negative style (with a higher level suppressing an opposing force of selection from the lower level) that, for heuristic and operational reasons, has received almost exclusive attention in the existing literature; and second, that each hierarchical level differs from all others in substantial and interesting ways, both in the style and frequency of patterns in change and causal modes.
Supermolecular structure of photosystem II and location of the PsbS protein
Authors: Nield Jon , Funk Christiane , Barber James
Published: July 2002

This paper addresses the question of whether the PsbS protein of photosystem two (PS II) is located within the LHC II–PS II supercomplex for which a three–dimensional structure has been obtained by cryoelectron microscopy and single particle analysis. The PsbS protein has recently been implicated as the site for non–photochemical quenching. Based both on immunoblotting analyses and structural considerations of an improved model of the spinach LHC II–PS II supercomplex, we conclude that the PsbS protein is not located within the supercomplex. Analyses of other fractions resulting from the solubilization of PS II–enriched membranes derived from spinach suggest that the PsbS protein is located in the LHC II–rich regions that interconnect the supercomplex within the membrane.
Scaling in the growth of geographically subdivided populations: invariant patterns from a continent-wide biological survey
Authors: Keitt Timothy H. , Amaral Luis A. N. , Buldyrev Sergey V. , Stanley H. Eugene
Published: July 2002

We consider statistical patterns of variation in growth rates for over 400 species of breeding birds across North America surveyed from 1966 to 1998. We report two results. First, the standard deviation of population growth rates decays as a power–law function of total population size with an exponent β = 0.36 ± 0.02. Second, the number of subpopulations, measured as the number of survey locations with non–zero counts, scales to the 3/4 power of total number of birds counted in a given species. We show how these patterns may be related, and discuss a simple stochastic growth model for a geographically subdivided population that formalizes the relationship. We also examine reasons that may explain why some species deviate from these scaling laws.
Spinning an elastic ribbon of spider silk
Authors: Knight D. P. , Vollrath F.
Published: July 2002

The Sicarid spider
Loxosceles laeta
spins broad but very thin ribbons of elastic silk that it uses to form a retreat and to capture prey. A structural investigation into this spider's silk and spinning apparatus shows that these ribbons are spun from a gland homologous to the major ampullate gland of orb web spiders. The
Loxosceles
gland is constructed from the same basic parts (separate transverse zones in the gland, a duct and spigot) as other spider silk glands but construction details are highly specialized. These differences are thought to relate to different ways of spinning silk in the two groups of spiders.
Loxosceles
uses conventional die extrusion, feeding a liquid dope (spinning solution) to the slit–like die to form a flat ribbon, while orb web spiders use an extrusion process in which the silk dope is processed in an elongated duct to produce a cylindrical thread. This is achieved by the combination of an initial internal draw down, well inside the duct, and a final draw down, after the silk has left the spigot. The spinning mechanism in
Loxosceles
may be more ancestral.
Conserved and nonconserved features of the folding pathway of hisactophilin, a β‐trefoil protein
Authors: Liu Chengsong , Gaspar Joe A. , Wong Hannah J. , Meiering Elizabeth M.
Published: July 2002

Based on previous studies of interleukin‐1β (IL‐1β) and both acidic and basic fibroblast growth factors (FGFs), it has been suggested that the folding of β‐trefoil proteins is intrinsically slow and may occur via the formation of essential intermediates. Using optical and NMR‐detected quenched‐flow hydrogen/deuterium exchange methods, we have measured the folding kinetics of hisactophilin, another β‐trefoil protein that has <10% sequence identity and unrelated function to IL‐1β and FGFs. We find that hisactophilin can fold rapidly and with apparently two‐state kinetics, except under the most stabilizing conditions investigated where there is evidence for formation of a folding intermediate. The hisactophilin intermediate has significant structural similarities to the IL‐1β intermediate that has been observed experimentally and predicted theoretically using a simple, topology‐based folding model; however, it appears to be different from the folding intermediate observed experimentally for acidic FGF. For hisactophilin and acidic FGF, intermediates are much less prominent during folding than for IL‐1β. Considering the structures of the different β‐trefoil proteins, it appears that differences in nonconserved loops and hydrophobic interactions may play an important role in differential stabilization of the intermediates for these proteins.
Magnetic fields with photon beams: Dose calculation using electron multiple‐scattering theory
Authors: Jette David
Published: July 2002

Strong transverse magnetic fields can produce large dose enhancements and reductions in localized regions of a patient under irradiation by a photon beam. We have developed a new equation of motion for the transport of charged particles in an arbitrary magnetic field, incorporating both energy loss and multiple scattering. Key to modeling the latter process is a new concept, that of “typical scattered particles.” The formulas which we have arrived at are particularly applicable to the transport of, and deposition of energy by, Compton electrons and pair‐production electrons and positrons generated within a medium by a photon beam, and we have shown qualitatively how large dose enhancements and reductions can occur. A companion article examines this dose modification effect through systematic Monte Carlo simulations.
A three‐dimensional deformable model for segmentation of human prostate from ultrasound images
Authors: Ghanei Amir , Soltanian‐Zadeh Hamid , Ratkewicz Alexander , Yin Fang‐Fang
Published: July 2002

Segmentation of human prostate from ultrasound (US) images is a crucial step in radiation therapy, especially in real‐time planning for US image‐guided prostate seed implant. This step is critical to determine the radioactive seed placement and to ensure the adequate dose coverage of prostate. However, due to the low contrast of prostate and very low signal‐to‐noise ratio in US images, this task remains as an obstacle. The manual segmentation of this object is time consuming and highly subjective. In this work, we have proposed a three‐dimensional (3D) deformable surface model for automatic segmentation of prostate. The model has a discrete structure made from a set of vertices in the 3D space that form triangle facets. The model converges from an initial shape to its equilibrium iteratively, by a weighted sum of the internal and external forces. Internal forces are based on the local curvature of the surface and external forces are extracted from the volumetric image data by applying an appropriate edge filter. We have also developed a method for initialization of the model from a few initial contours that are drawn on different slices. During the deformation, a resampling procedure is used to maintain the resolution of the model. The entire model is applied in a multiscale scheme, which increases the robustness and speed, and guarantees a better convergence. The model is tested on real clinical data and initial results are very promising.
Feature space analysis: Effects of MRI protocols
Authors: Soltanian‐Zadeh Hamid , Peck Donald J.
Published: July 2002

We present a method for exploring the relationship between the image segmentation results obtained by an optimal feature space method and the MRI protocols used. The steps of the work accomplished are as follows. (1) Patients with brain tumors were imaged on a 1.5 T General Electric Signa MRI System using multiple protocols (T1 and T2‐weighted fast spin–echo and FLAIR). T1‐weighted images were acquired before and after gadolinium injection. (2) Image volumes were co‐registered, and images of a slice through the center of the tumor were selected for processing. (3) For each patient, several image sets were defined by selecting certain MR images (e.g., 4T2's+1T1, 4T2's+FLAIR, 2T2's+1T1). (4) Using each image set, the optimal feature space was generated and images were segmented into normal tissues and different tumor zones. (5) Segmentation results obtained using the different MRI sets were compared. Based on the analysis results from 27 image sets, we found that the locations of the clusters for the tumor zones and their corresponding regions in the image domain changed as a function of the MR images (MRI protocols) used. However, the segmentation results for the total lesion and normal tissues remained relatively unchanged.
Analysis of trabecular bone texture by modified Hurst orientation transform method
Authors: Podsiadlo P. , Stachowiak G. W.
Published: July 2002

There is a growing need for noninvasive and inexpensive methods that can effectively be used on a large scale, to detect an onset of early osteoarthritis in human knee joints. Of many possible options, fractal analysis of two‐dimensional projection x‐ray images of trabecular bone (TB) texture, appears as one of the best approaches. However, there are some problems associated with the characterization of the roughness and anisotropy of the bone texture. To resolve these problems, a modified Hurst orientation transform (HOT) method, previously developed by the authors, has been used in this study. The advantages of the HOT method over other techniques used to analyze bone texture, are that it calculates a two‐dimensional fractal dimension in all possible directions and also provides a measure of anisotropy for both surfaces exhibiting strong anisotropy and surfaces exhibiting weak anisotropy. In this study, the accuracy of the HOT method in measuring the bone texture roughness and anisotropy; together with the effects of image noise, blur, exposure, magnification, and projection angle on its performance were investigated. Computer‐generated images of fractal surfaces and x‐ray images obtained for a human tibia head were used. Results obtained show that the HOT method can effectively be used to characterize the roughness and anisotropy (isotropy) of TB texture.
Efficient simulation of SPECT down‐scatter including photon interactions with crystal and lead
Authors: de Jong Hugo W. A. M. , Wang Wen‐Tung , Frey Eric C. , Viergever Max A. , Beekman Freek J.
Published: July 2002

A major image degrading factor in simultaneous Dual Isotope (DI) SPECT or simultaneous Emission–Transmission (ECT–TCT) imaging, is the detection of photons emitted by the higher energy isotope in the energy window used for imaging the lower energy isotope. In Tc‐99m/Tl‐201 DI‐SPECT typically tens of percents of the total detected down‐scatter is caused by lead x rays. In Tc‐99m/Gd‐153 ECT–TCT, a comparable fraction of the down‐scatter originates from Tc‐99m photons which only partly deposit their energy in the detector crystal (i.e., due to crystal interactions). Efficient simulation methods which model down‐scatter can be used to optimize DI‐SPECT or ECT–TCT imaging acquisition or reconstruction protocols. In this paper we adapt a previously proposed efficient down‐scatter simulation method, to include the interactions of photons with the detector crystal and collimator lead. To this end, point spread function tables including crystal and lead interactions are precalculated. Subsequently, photons are traced through the patient body until their last scatter position, and the precalculated responses are used to project the photons onto the detector plane, while photon attenuation in the patient is taken into account. The approach is evaluated by comparing simulated Tc‐99m down‐scatter projections with measured projections. Incorporation of photon interaction with crystal and lead leads to significantly improved accuracy of the shape of down‐scatter responses, while differences in total counts between simulated and measured projections typically decrease from tens of percents to a couple of percents. Calculating 60 down‐scatter projections of an extended distribution on a 64×64×64 grid takes about three minutes on a PC with two 1.2 GHz processors. We conclude that accurate and efficient simulation of down‐scatter is now possible including the major effects of the nonuniform mass density of the patient as well as photon interactions with the crystal and collimator lead.
Blind deblurring of spiral CT images—comparative studies on edge‐to‐noise ratios
Authors: Jiang Ming , Wang Ge , Skinner Margaret W. , Rubinstein Jay T. , Vannier Michael W.
Published: July 2002

A recently developed blind deblurring algorithm based on the edge‐to‐noise ratio has been applied to improve the quality of spiral CT images. Since the discrepancy measure used to quantify the edge and noise effects is not symmetric, there are several ways to formulate the edge‐to‐noise ratio. This article is to investigate the performance of those ratios with phantom and patient data. In the phantom study, it is shown that all the ratios share similar properties, validating the blind deblurring algorithm. The image fidelity improvement varies from 29% to 33% for different ratios, according to the root mean square error (RMSE) criterion; the optimal iteration number determined for each ratio varies from 25 to 35. Those ratios that are associated with most satisfactory performance are singled out for the image fidelity improvement of about 33% in the numerical simulation. After automatic blind deblurring with the selected ratios, the spatial resolution of CT is substantially refined in all the cases tested.
An investigation of the physical characteristics of 66Ga as an isotope for PET imaging and quantification
Authors: Graham M. C. , Pentlow K. S. , Mawlawi O. , Finn R. D. , Daghighian F. , Larson S. M.
Published: July 2002

Isotopes commonly used for PET imaging and quantification have a straightforward decay scheme involving “pure” positron (β+) emission, i.e., 95%–100% β+ abundance, with no additional gamma rays. 66Ga (Emax=4.2 MeV, T1/2=9.5 h) is a member of a category of isotopes with a lower abundance of β+'s (57%) and a more complicated spectrum involving combinations of gamma rays that are emitted in cascade. These additional gamma rays tend to cause a higher singles rate, resulting in more random coincidence events. The most abundant positron (51.5%) in the spectrum has one of the highest energies considered for PET imaging. For the purposes of monoclonal antibody dosimetry using 66Ga, it is important to verify the quantification in phantoms prior to initiating human studies. A series of quantitative phantom measurements were performed on the PC4600, a head‐optimized BGO based scanner with multiple detector rings. Count rate linearity was verified over concentrations ranging from 4.0 kBq/cc to 37 kBq/cc (0.11–1.0 μCi/cc); resolution averaged 16 mm full width half‐maximum in the x and y directions in both the direct and cross planes. Axial resolution was 14 mm. The range of the energetic positrons (up to 4.153 MeV, range 7.6 mm in tissue) was verified as a primary source of resolution degradation. Within the limits outlined above, 66Ga is a suitable isotope for use as 66Ga citrate or with monoclonal antibodies in the detection and staging of tumors and other lesions. In addition, the energetic positrons have possible therapeutic applications when used as a monoclonal antibody label.
The effect on dose to computed tomography phantoms of varying the theoretical x‐ray spectrum: A comparison of four diagnostic x‐ray spectrum calculating codes
Authors: Caon Martin , Bibbo Giovanni , Pattison John , Bhat Madhava
Published: July 2002

Theoretical x‐ray spectra calculated by four different codes for the same tube parameters are compared by calculating and measuring doses to computed tomography (CT) body and head phantoms. The effect on the 120 kV spectrum, and hence on the calculated dose, of varying the anode angle, tube voltage, and total filtration of the x‐ray tube is investigated. Codes used were those of Nowotny and Höfer (XCOMP), Boone, Iles, and Tucker et al. The code based on the work of Tucker et al. produced calculated doses noticeably lower than the other codes and compared best to the measured value. The variation in calculated dose between the Tucker code and the others is of the same order as the variation introduced by uncertainties in total filtration of about 20%, in peak tube voltage of and in change of anode angle from 7° to 13°.
Phantoms with10BF3detectors for boron neutron capture therapy applications
Authors: Alburger D. E. , Raparia D. , Zucker M. S.
Published: July 2002

Two acrylic cube phantoms have been constructed for BNCT applications that allow the depth distribution of neutrons to be measured with miniaturedetectors in 0.5‐cm steps beginning at 1‐cm depth. Sizes and weights of the cubes are 14 cm, 3.230 kg, and 11 cm, 1.567 kg. Tests were made with the epithermal neutron beam from the patient treatment port of the Brookhaven Medical Research Reactor. Thermal neutron depth profiles were measured with a baredetector at a reactor power of 50 W, and Cd‐covered detector profiles were measured at a reactor power of 1 kW. The resulting plots of counting rate versus depth illustrate the dependence of neutron moderation on the size of the phantom. But more importantly the data can serve as benchmarks for testing the thermal and epithermal neutron profiles obtained with accelerator‐based BNCT facilities. Such tests could be made with these phantoms at power levels about five orders of magnitude lower than that required for the treatment of patients with brain tumors.
Development of a high‐power water cooled beryllium target for use in accelerator‐based boron neutron capture therapy
Authors: Blackburn B. W. , Yanch J. C. , Klinkowstein R. E.
Published: July 2002

In order for ABNCT (accelerator‐based boron neutron capture therapy) to be successful, 10–16 kW or more must be dissipated from a target. Beryllium is well suited as a high‐power target material. Beryllium has a thermal conductivity of 200 W/mK at 300 K which is comparable to aluminum, and it has one of the highest strength to weight ratios of any metal even at high temperatures (100 MPa at 600 °C). Submerged jet impingement cooling has been investigated as an effective means to remove averaged power densities on the order ofwith local power densities as high asWater velocities required to remove these power levels are in excess of 24 m/s with volumetric flow rates of nearly 100 GPM. Tests on a prototype target revealed that the heat transfer coefficient scaled asWith jet‐Reynolds numbers as high asheat transfer coefficients ofwere achieved. With this type of cooling configuration 30 kW of power could be effectively removed from a beryllium target placed on the end of an accelerator. A beryllium target utilizing a proton beam of 3.7 MeV and cooled by submerged jet impingement could be used to deliver a dose of 13 RBE cGy/min mA to a tumor at a depth of 4 cm. With a beam power of 30 kW, 1500 cGy could be delivered in 14.2 min.
Computer‐aided diagnoses: Automatic detection of lung nodules
Authors: Carreira Marı́a J. , Cabello Diego , Penedo Manuel G. , Mosquera Antonio
Published: July 2002

This work describes a computational scheme for automatic detection of suspected lung nodules in a chest radiograph. A knowledge‐based system extracts the lung masks over which we will apply the nodule detection process. First we obtain the normalized cross‐correlation image. Next we detect suspicious regions by assuming a threshold. We examine the suspicious regions using a variable threshold which results in the growth of the suspicious areas and an increase in false positives. We reduce the large number of false positives by applying thefacetmodel to the suspicious regions of the image. An algorithmic classification process gives a confidence factor that a suspicious region is a nodule. Five chest images containing 30 known nodules were used as a training set. We evaluated the system by analyzing 30 chest images with 40 confirmed nodules of varying contrast and size located in various parts of the lungs. The system detected 100% of the nodules with a mean of six false positives per image. The accuracy and specificity were 96%.
Use of the fast Hartley transform for three‐dimensional dose calculation in radionuclide therapy
Authors: Erdi Alev K. , Yorke Ellen D. , Loew Murray H. , Erdi Yusuf Emre , Sarfaraz Mehrdad , Wessels Barry W.
Published: July 2002

Effective radioimmunotherapy may depend ona prioriknowledge of the radiation absorbed dose distribution obtained by trace imaging activities administered to a patient before treatment. A new, fast, and effective treatment planning approach is developed to deal with a heterogeneous activity distribution. Calculation of the three‐dimensional absorbed dose distribution requires convolution of a cumulated activity distribution matrix with a point‐source kernel; both are represented by large matrices (64×64×64). To reduce the computation time required for these calculations, an implementation of convolution using three‐dimensional (3‐D) fast Hartley transform (FHT) is realized. Using the 3‐D FHT convolution, absorbed dose calculation time was reduced over 1000 times. With this system, fast and accurate absorbed dose calculations are possible in radioimmunotherapy. This approach was validated in simple geometries and then was used to calculate the absorbed dose distribution for a patient's tumor and a bone marrow sample.
Systematic distortions in magnetic position digitizers
Authors: Birkfellner W. , Watzinger F. , Wanschitz F. , Enislidis G. , Kollmann C. , Rafolt D. , Nowotny R. , Ewers R. , Bergmann H.
Published: July 2002

Medical devices equipped with position sensors enable applications like image guided surgical interventions, reconstruction of three‐dimensional 3D ultrasound (US) images, and virtual or augmented reality systems. The acquisition of three‐dimensional position data in real time is one of the key technologies in this field. The systematic distortions induced by various metals, surgical tools, and US scan probes in different commercial electromagnetic tracking systems were assessed in the presented work. A precise nonmetallic six degree‐of‐freedom measurement rack was built that allowed a quantitative comparison of different electromagnetic trackers. Also, their performance in the presence of large metallic structures was quantified in a phantom study on an acrylic skull model in an operating room (OR). The trackers used were alternating current (ac) and direct current (dc) based systems. The ac trackers were, on average, distorted by 0.7 mm and 0.5° by metallic objects positioned at a distance greater than 120 mm between the geometrical center of the sample and the sensor. In the OR environment, the ac system exhibits mean errors ofandThe dc trackers are more sensitive to distortions caused by ferromagnetic materials (averaged value: 1.6 mm and 0.5° beyond a distance of 120 mm). The dc tracker shows no distortions from other conductive materials but was less accurate in the OR environment (typical error:and). At distances smaller than approximately 100 mm between sample and sensor error increases quickly. It is also apparent from our measurements that the influence of US scan probes is governed by their shielding material. The results show that surgical instruments not containing conductive material are to be preferred when using an ac tracker. Nonferromagnetic instruments should be used with dc trackers. Static distortions caused by the OR environment have to be compensated by precise calibration methods.
On‐line monitoring of radiotherapy beams: Experimental results with proton beams
Authors: Litzenberg D. W. , Roberts D. A. , Lee M. Y. , Pham K. , Vander Molen A. M. , Ronningen R. , Becchetti F. D.
Published: July 2002

Proton radiotherapy is a powerful tool in the local control of cancer. The advantages of proton radiotherapy over gamma‐ray therapy arise from the phenomenon known as the Bragg peak. This phenomenon enables large doses to be delivered to well‐defined volumes while sparing surrounding healthy tissue. To fully realize the potential of this technique the location of the high‐dose volume must be controlled very accurately. An imaging system was designed and tested to monitor the positron‐emitting activity created by the beam as a means of verifying the beam's range, monitoring dose, and determining tissue composition. The prototype imaging system consists of 12 pairs of cylindrical BGO detectors shielded in lead. Each crystal was 1.9 cm in diameter, 5.0 cm long, and separated by 0.5 cm from other detectors in the row. These are arranged in two rows, 60 cm apart, with the proton beam and tissue phantoms half‐way between and parallel to the detector rows. Experiments were conducted with 150 MeV continuous and macro‐pulsed proton beams which had beam currents ranging from 0.14 nA to 1.75 nA. The production and decay of short‐lived isotopes,andwas studied using 1 min irradiations with a continuous beam. These isotopes provide a significant signal on short time scales, making on‐line imaging possible. Macro‐pulsed beams, having a period of 10 s, were used to study on‐line imaging and the production and decay of long‐lived isotopes,andDecay data were acquired and on‐line images were obtained between beam pulses and indicate that range verification is possible, for a 150 MeV beam, after one beam pulse, to within the 1.2 cm resolution limit of the imaging system. 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. Over 80% of the initial positron‐emitting activity is fromwhile the remainder is primarilywith traces ofandRadioisotopic 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 inhomogenous treatment volumes may be identified and used to locate anatomic landmarks. Radioisotopic imaging also reveals thatis created well beyond the Bragg peak, apparently by secondary neutrons.
XINPUT: A program to edit“DOSRZ”input files
Authors: Lauterbach Marc H. , Lehmann Jörg , Rosenow Ulf F.
Published: July 2002

TheDOSRZuser code, which is part of theEGS4standard distribution, is widely used in medical physics for the calculation of dose deposition in cylindrical geometries. The code provides the use of advanced Monte‐Carlo techniques(PRESTA)and variance reduction methods. In the case of complex cylinder geometries the input of coordinates and radii is not only tedious but also prone to a high error rate. Coordinates are to be stated in absolute numbers. A change of one number, e.g., the slab thickness, requires the change of all subsequent numbers. Furthermore, parameters are only stated as numbers with no indication of their meaning. Obviously, there is a need for a user interface to facilitate the input forDOSRZand to largely reduce the possibility for errors. We, therefore, wrote a graphical user interface (GUI) consisting of an input mask, a coordinate input interpreter, and a two‐dimensional and/or pseudo‐three‐dimensional display section. The GUI is based on the scripting language Tcl/Tk, which runs under various platforms such asUNIX(LINUX),W95, andWin NT. It consists of a main window which provides common‐style menus and buttons to navigate through the edit dialog boxes. The most important tools are the region input, which enables the user to create the simulation geometry, and the graphics section where the scaled output can be displayed. Different media are shown in different colors which are user defined. Furthermore, the program contains some tools to reduce the probability of an erroneous input in theEGS4input file. Since Tcl/Tk is a modern scripting language, it offers advanced tools to create the GUI and to “glue” different applications to it.XInputmay also be considered as a model program for the development of a more general interface to other input areas of theEGS4simulation code.
An analytical model of a kilovoltage beam phase space
Authors: Monti di Sopra Fabrice , Keall Paul , Beckham Wayne
Published: July 2002

Our aim in this project was to quantify a kilovoltage beam phase space for use in dose calculations. The phase space was modeled by incorporating the following analytically derived x‐ray beam production properties: the intensity variation due to the heel effect, the energy variation due to the differing amount of target material traversed by the photons, and the finite source size. The initial energy spectrum used was generated using a computer program. A Monte Carlo code was adapted in order to examine the validity of the calculated phase space. Dose distributions calculated using the modeled phase space for 10×10 andfields show agreement with experimental values to within 2% and 4%, respectively, for the central 80% of the field size. Within the field but outside this range a maximum of 6% difference (for thefield) was observed, however, these values were in a region of sharp gradient and hence small geometric shift. The “tails” of the profiles were underpredicted by up to 6%. Due to uncertainties in experiment (3%) and Monte Carlo (1.5%), the modeled phase space is deemed acceptable for phantom andin‐vivodosimetric calculations within the field boundaries.