bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis and secretion of molecules exhibiting the HL1 epitope during development of the hyaline layer of the asteroid pisaster ochraceus
Authors: Pang T. , Crawford B.J. , Maghsoodi B. 
Published: November 2002

AbstractA complex ECM layer called the hyaline layer (HL) surrounds embryos and larvae of the starfish Pisaster ochraceus. When preserved by freeze substitution, the HL of a bipinnaria larva consists of six sublayers. From the plasmalemma outwards these are the intervillous layer (iv), the H3, H2, H1 sublayers that make up the supporting layer, a boundary layer (b) and the coarse outer meshwork (cm). HL development begins at fertilization when exocytosis of the cortical granules releases ECM into the perivitelline space and elevates the fertilization membrane. Over the course of early development the layers are added in a sequential manner and by hatching the embryo is surrounded by a thin HL containing most if not all of the layers. The layers thicken over the next few days. By the bipinnaria stage the larvae are surrounded by a thick six‐layered HL. HL1 is a monoclonal antibody that reacts against an epitope found in all regions of the HL of the bipinnaria larva except the H2 sublayer. Western blots show that it is present on several molecules during HL development. The number and pattern of the HL1‐labeled molecules change during development, suggesting that either new molecules are being produced or that some molecules are precursors of others. Light (immunofluorescence) and TEM (immunogold) studies using HL1 in the early stages of development show that HL1‐positive material is not present in the corticle granules and that it only begins to be manufactured and secreted in quantity in the blastula stage at 18–20 h. Following this it continues to be secreted at least as far as the bipinnaria stage. Molecules containing the HL1 antigen therefore do not appear to play a major role in early development of the HL but are necessary for later events. The results suggest that, like the sea urchin HL, the starfish HL undergoes a sequential organization of the different HL layers from ECM components, which are released into the perivitelline space. J. Morphol. 255:58–68, 2003. © 2002 Wiley‐Liss, Inc.
Caste morphology and development intermitogetonnr.planus(insecta, isoptera, rhinotermitidae)
Authors: Parmentier Dominique , Roisin Yves 
Published: November 2002

AbstractThe termite family Rhinotermitidae displays a wide diversity in its patterns of social organization in castes. The genusTermitogetonprobably branched off early in the evolution of this family. We studied the developmental pathways of a putative undescribed species from New Guinea,Termitogetonnrplanus. The development begins with two white inactive instars (larvae), the second of which possesses small wing buds. These are followed by a relatively homogenous group of active immature stages (pseudergates) among which a biometric study revealed the presence of four instars. The first of these instars possesses wing buds that regress at subsequent molts. The external morphology of older instars resembles that of higher termite workers. Older pseudergates can differentiate into presoldiers and then into soldiers, but they are also able to molt into a unique stage with long wing pads (nymph), preceding the imago. Colony maturity can be reached with about 103individuals. The sex ratio is near 1:1 in all castes except soldiers, among which females are more numerous than males. The caste pattern ofT.nr.planusis reminiscent of those of the Kalotermitidae and Termopsidae, and ofProrhinotermesamong the Rhinotermitidae. None of these taxa possess a true worker caste, permanently diverted from imaginal development: social tasks are done by unspecialized immatures that retain a full array of developmental options, including that of proceeding to the imago. The most remarkable trait ofT.nr.planusis the presence in all second‐instar individuals of wing buds that later regress to reappear in the single nymphal stage. We suggest that the traditional definitions of the terms larvae, nymphs, and pseudergates should be revised because they cannot be satisfactorily applied to the castes ofTermitogeton. J. Morphol. 255:69–79, 2003. © 2002 Wiley‐Liss, Inc.
Biflagellate spermatozoon of the poison‐dart frogsepipedobates femoralisandcolostethussp. (anura, dendrobatidae)
Authors: Aguiar– Odair , Garda Adrian A. , Lima Albertina P. , Colli Guarino R. , Báo Sônia N. , Recco‐Pimentel Shirlei M. 
Published: November 2002

AbstractThis study describes the spermatozoa of the dendrobatidsEpipedobates femoralisandColostethussp. using light and transmission electron microscopy. Both species possess a biflagellate spermatozoon, an unusual characteristic only previously reported in two anuran species belonging to the families Leptodactylidae and Racophoridae. The acrosomal complex of both species consists of a conical acrosomal vesicle and a subacrosomal cone, both of which cover the anterior portion of the nucleus, but to differing extents. In the midpiece, the centrioles are disposed parallel to each other and to the cell axis and give rise to two axonemes. Two paraxonemal rods were also seen entering the nuclear fossa. Both flagella are surrounded by a single mitochondrial collar. Each flagellum is formed by an axial fiber connected to the axoneme by an axial sheath; juxta‐axonemal fibers are absent. Our data seem to support thatEpipedobates femoralisshould be placed in a separate clade possibly related toColosthetusand that these two genera may not be monophyletic. J. Morphol. 255:114–121, 2003. © 2002 Wiley‐Liss, Inc.
Meiosis in the golden hamster: A confocal microscopy and flow cytometric analysis
Authors: Vigodner M. , Lewin L.M. , Shochat L. , Mittelman L. , Golan R. 
Published: November 2002

AbstractIn this study, confocal microscopy and flow‐cytometry were utilized to follow meiosis in hamster spermatogenesis. Confocal microscopy was used as an analytical tool to observe spermatocytes inside the tubules following meiotic progression consecutively at defined spermatogenic stages. To study spermatocyte differentiation, the structure of the synaptonemal complex was studied in detail at various stages of hamster spermatogenesis using the antibody against SC3 (the protein of axial/lateral element). The synaptonemal complex was observed from the leptotene stage until the first meiotic division with maximal staining in mid‐pachytene spermatocytes, suggesting a role for SC3 at this postrecombinational stage. In addition, 3‐dimensional (3D) images of synaptonemal complex were observed, providing information about spatial distribution of the chromosomes within the nuclei of spermatocytes at different stages of meiosis. Changes in spermatocyte sizes and DNA condensation allowed assessment of meiosis by flow cytometry. Changes in chromatin condensation at different stages of hamster meiosis were followed, revealing decondensation from early to late pachytene stages. The analysis also allowed a comparing of chromatin status of mitotic and meiotic chromosomes, confirming the less compact structure of the latter, possibly connected to increased transcriptional activity during meiosis. Mol. Reprod. Dev. 64: 86–95, 2003. © 2003 Wiley‐Liss, Inc.
Real‐time autoshimming for echo planar timecourse imaging
Authors: Ward Heidi A. , Riederer Stephen J. , Jack Clifford R. 
Published: November 2002

AbstractHead motion within an applied magnetic field alters the effective shim within the brain, causing geometric distortions in echo planar imaging (EPI). Even if subtle, change in shim can lead to artifactual signal changes in timecourse EPI acquisitions, which are typically performed for functional MRI (fMRI) or diffusion tensor imaging. Magnetic field maps acquired before and after head motions of clinically realistic magnitude indicate that motion‐induced changes in magnetic field may cause translations exceeding 3 mm in the phase‐encoding direction of the EPI images. The field maps also demonstrate a trend toward linear variations in shim changes as a function of position within the head, suggesting that a real‐time, first‐order correction may compensate for motion‐induced changes in magnetic field. This article presents a navigator pulse sequence and processing method, termed a “shim NAV,” for real‐time detection of linear shim changes, and a shim‐compensated EPI pulse sequence for dynamic correction of linear shim changes. In vivo and phantom experiments demonstrate the detection accuracy of shim NAVs in the presence of applied gradient shims. Phantom experiments demonstrate reduction of geometric distortion and image artifact using shim‐compensated EPI in the presence of applied gradient shims. In vivo experiments with intentional interimage subject motion demonstrate improved alignment of timecourse EPI images when using the shim NAV‐detected values to update the shim‐compensated EPI acquisition in real time. Magn Reson Med 48:771–780, 2002. © 2002 Wiley‐Liss, Inc.
Inductively coupled stent antennas in MRI
Authors: Quick Harald H. , Kuehl Hilmar , Kaiser Gernot , Bosk Silke , Debatin Jörg F. , Ladd Mark E. 
Published: November 2002

AbstractThe development of intimal hyperplasia following stent deployment can lead to narrowing or even occlusion of the stent lumen. The underlying mechanisms leading to neointimal proliferation within stents remain largely unknown. Long‐term evaluation of stent patency requires a noninvasive means for assessing the stent lumen. MR angiography (MRA) has shown potential to provide noninvasive assessment of the vascular system. However, a detailed assessment of the stent lumen with MRI is often hampered by material‐dependent susceptibility artifacts, as well as by radiofrequency (RF) eddy currents generated inside the electrically conducting stent mesh. In this study, stent prototypes were designed to act as active resonant structures at the Larmor frequency of the MR system. Employing the principle of inductive coupling, the B1 fields of the stents were coupled to that of an outside surface coil. The stents thus acted as local RF signal amplifiers. Various stent designs were investigated regarding their coupling to an external coil, signal homogeneity, and suitability for mechanical expansion for implantation purposes. The dependency of flip angle amplification on the quality factor Q of the stents was systematically investigated. Phantom experiments revealed signal amplification in all stent prototypes. Signal enhancement inside and close to the surface of the stents enabled their localization with high contrast in MR images. In vivo imaging experiments in the iliac, renal, and splenic arteries of two pigs confirmed the in vitro findings. Wireless active visualization of stents allows for detailed analysis of the stent lumen with high contrast and spatial resolution. The proposed method could thus provide a powerful diagnostic means for the noninvasive long‐term follow‐up of stent patency, thereby enhancing our understanding of the mechanisms of restenosis. Magn Reson Med 48:781–790, 2002. © 2002 Wiley‐Liss, Inc.
Optimization of signal behavior in the transition to driven equilibrium in steady‐state free precession sequences
Authors: Hennig Juergen , Speck Oliver , Scheffler Klaus 
Published: November 2002

AbstractA new technique to avoid the initial signal fluctuations in steady‐state free precession (SSFP)‐sequences, such as trueFISP, FIESTA, and refocused FFE, is presented. The “transition into driven equilibrium” (TIDE) sequence uses modified flip angles over the initialization phase of a SSFP experiment, which not only avoids image artifacts but also improves the signal‐to‐noise ratio (SNR) and contrast behavior compared to conventional approaches. TIDE is demonstrated to be robust against variations of T1 and T2, and leads to a monotonous signal evolution for off‐resonance spins. The basic principles can also be applied repetitively to optimize continuous 3D acquisitions. Magn Reson Med 48:801–809, 2002. © 2002 Wiley‐Liss, Inc.
Variable‐density adaptive imaging for high‐resolution coronary artery MRI
Authors: Sussman Marshall S. , Stainsby Jeffrey A. , Robert Normand , Merchant Naeem , Wright Graham A. 
Published: November 2002

AbstractVariable‐density (VD) spiral k‐space acquisitions are used to acquire high‐resolution (0.78 mm), motion‐compensated images of the coronary arteries. Unlike conventional methods, information for motion compensation is obtained directly from the coronary anatomy itself. Specifically, periods of minimal coronary distortion are identified by applying the correlation coefficient template matching algorithm to real‐time images generated from the inner, high‐density portions of the VD spirals. Combining the data associated with these images together, high‐resolution, motion‐compensated coronary images are generated. Because coronary motion is visualized directly, the need for cardiac‐triggering, breath‐holding, and navigator echoes is eliminated. The motion compensation capability of the technique is determined by the inner‐spiral spatial and temporal resolution. Results indicate that the best performance is achieved using inner‐spiral images with high spatial resolution (1.6–2.9 mm), even though temporal resolution (four to six independent frames per second) suffers as a result. Image quality within the template region in healthy volunteers was found to be comparable to that achieved with cardiac‐triggered breath‐hold scans, although extended acquisition times of around 5 min were needed to overcome reduced SNR efficiency. Magn Reson Med 48:753–764, 2002. © 2002 Wiley‐Liss, Inc.
In vivo 3D MRI staining of mouse brain after subcutaneous application of MnCl2
Authors: Watanabe Takashi , Natt Oliver , Boretius Susann , Frahm Jens , Michaelis Thomas 
Published: November 2002

AbstractFollow‐up T1‐weighted 3D gradient‐echo MRI (2.35 T) of murine brain in vivo (N = 5) at 120 μm isotropic resolution revealed spatially distinct signal increases 6–48 hr after subcutaneous application of MnCl2 (20 mg/kg). The effects result from a shortening of the water proton T1 relaxation time due to the presence of unchelated paramagnetic Mn2+ ions, which access the brain by systemic circulation and crossing of the blood–brain barrier (BBB). A pronounced Mn2+‐induced signal enhancement was first seen in structures without a BBB, such as the choroid plexus, pituitary gland, and pineal gland. Within 24 hr after administration, Mn2+ contrast highlighted the olfactory bulb, inferior colliculi, cerebellum, and the CA3 subfield of the hippocampus. The affinity of Mn2+ to various brain systems suggests the neuronal uptake of Mn2+ ions from the extracellular space and subsequent axonal transport. Thus, at least part of the Mn2+ contrast reflects a functional brain response of behaving animals, for example, in the olfactory system. In vivo MRI staining of the brain by systemic administration of MnCl2 may contribute to phenotyping mutant mice with morphologic and functional alterations of the central nervous system. Magn Reson Med 48:852–859, 2002. © 2002 Wiley‐Liss, Inc.
Single‐breathhold 3D‐trueFISP cine cardiac imaging
Authors: Jung Bernd A. , Hennig Jürgen , Scheffler Klaus 
Published: November 2002

AbstractCardiac MRI function measurements are typically based on multiple breathhold 2D sequences to acquire images of the entire heart. In the present study, the feasibility of a cine 3D TrueFISP technique in which several complete volumetric measurements may be obtained during a single breathhold is demonstrated. In contrast to 3D FLASH, the TrueFISP sequence offers an excellent contrast between the myocardium and the intraventricular cavity without the use of contrast agent. An ECG‐gated 3D cine TrueFISP sequence was implemented with a repetition time of 2.4–2.8 ms, which allows imaging of the complete heart within a single breathhold throughout 20–46 heartbeats with a 3D frame rate of 8–13 volumes per cardiac cycle and a spatial resolution of about 1.5 × 3.5 × 3.5 mm3. Breathhold volumetric cine imaging with the 3D TrueFISP technique holds promise for rapid and accurate evaluation of the cardiac regional wall motion and the calculation of cardiac volume and ejection fraction. Magn Reson Med 48:921–925, 2002. © 2002 Wiley‐Liss, Inc.
Homogeneous preparation encoding (HoPE) in multislice imaging
Authors: Fautz Hans‐Peter , Scheffler Klaus , Hennig Jürgen 
Published: November 2002

AbstractFast magnetization preparation techniques acquire a series of echoes after a single magnetization preparation. If these echoes are acquired from different slices using a multislice technique the change in the preparation state of the echoes due to relaxation effects leads to different contrast modification for each slice. Encoding different preparation states along the phase‐encoding direction of each slice instead of acquiring each slice in a different preparation state is introduced as a general concept to obtain images of identical contrast and point‐spread function. This can be realized either by cycling the slice excitation order several times over the total number of repetitions or by moving the point of time at which the preparation is applied within each repetition. One possible application of this method is chemical shift selective fat saturation imaging. A homogeneous fat suppression across a multislice volume could be achieved using a FLASH sequence at a repetition time of TR = 145 ms, including a single fat saturation preparation. Conventional fat saturated spin‐echo imaging at any TR can be accelerated significantly by reducing the number of applied preparations per repetition. A further application of the homogeneous preparation encoding (HoPE) method is described that encodes the spatial self‐saturation of the multislice excitation order homogeneously in all slices. Only a reduced number of slices of the total volume are excited in each repetition and the slice excitation order is continuously moved along the imaging volume. This method is applied for time of flight (TOF) imaging. Using a TONE‐like series of flip angles for the slice excitations of each repetition homogeneous TOF images can be obtained on the basis of a multislice acquisition. Magn Reson Med 48:745–752, 2002. © 2002 Wiley‐Liss, Inc.
GABAergic mechanisms of heroin‐induced brain activation assessed with functional MRI
Authors: Xi Zheng‐Xiong , Wu Gaohong , Stein Elliot A. , Li Shi‐Jiang 
Published: November 2002

AbstractHeroin has been hypothesized to activate opiate receptors and inhibit γ‐aminobutyric acid (GABA) release from inhibitory GABAergic interneurons which, in turn, activates dopamine projection cells. Since the distal sites and consequences of this disinhibition are not well understood on a systems level, heroin‐induced brain activity was measured using functional MRI (fMRI) in rats. A significant blood oxygen level‐dependent (BOLD) signal increase was seen in cortical regions, including prefrontal cortex, cingulate, and olfactory cortex following acute heroin administration. In contrast, a significant signal decrease was seen in several subcortical areas, including the caudate and putamen, nucleus accumbens, thalamus, and hypothalamus. Pretreatment of γ‐vinyl GABA (GVG), an irreversible GABA transaminase inhibitor, significantly attenuated the heroin‐induced BOLD signal changes. Pretreatment of naloxone, an opiate μ receptor antagonist, eliminated the heroin‐induced BOLD signal changes and posttreatment of naloxone reversed the heroin‐induced BOLD signal changes. It is suggested that the heroin‐induced negative and positive BOLD changes are due to direct inhibitory and indirect disinhibitory mechanisms of GABAergic activities. Administration of GVG altered these mechanisms and further suggested that involvement of the opiate's pharmacological actions can, at least in part, be mediated by inhibiting brain GABA release. Magn Reson Med 48:838–843, 2002. © 2002 Wiley‐Liss, Inc.
Real‐time quantification of T changes using multiecho planar imaging and numerical methods
Authors: Hagberg G.E. , Indovina I. , Sanes J.N. , Posse S. 
Published: November 2002

AbstractConventional approaches to quantify whole brain T maps use nonlinear regression with intensive computational requirements that therefore likely limit quantitative T mapping for real‐time applications. To overcome these limitations an alternative method, NumART (NUMerical Algorithm for Real‐time T mapping) that directly calculates T by a linear combination of images obtained at three or more different echo times was developed. NumART, linear least‐squares, and nonlinear regression techniques were applied to multiecho planar images of the human brain and to simulated data. Although NumART may overestimate T, it yields comparable values to regression techniques in cortical and subcortical areas, with only moderate deviations for echo spacings between 18 and 40 ms. NumART, like linear regression, requires 2% of the computational time needed for nonlinear regression and compares favorably with linear regression due to its higher precision. The use of NumART for continuous on‐line T mapping in real time fMRI studies is shown. Magn Reson Med 48:877–882, 2002. © 2002 Wiley‐Liss, Inc.
Fast phase‐contrast velocity measurement in the steady state
Authors: Overall William R. , Nishimura Dwight G. , Hu Bob S. 
Published: November 2002

AbstractA new method of encoding flow velocity as image phase in a refocused steady‐state free precession (SSFP) sequence, called steady‐state phase contrast (SSPC), can be used to generate velocity images rapidly while retaining high signal. Magnitude images with refocused‐SSFP contrast are simultaneously acquired. This technique is compared with the standard method of RF‐spoiled phase contrast (PC), and is found to have more than double the phase‐signal to phase‐noise ratio (PNR) when compared with standard PC at reasonable repetition intervals (TRs). As TR decreases, this advantage increases exponentially, facilitating rapid scans with high PNR efficiency. Rapid switching between the two necessary steady states can be accomplished by the insertion of a single TR interval with no flow‐encoding gradient. The technique is implemented in a 2DFT sequence and validated in a phantom study. Preliminary results indicate that further TR reduction may be necessary for high‐quality cardiac images; however, images in more stationary structures, such as the descending aorta and carotid bifurcation, exhibit good signal‐to‐noise ratio (SNR) and PNR. Comparisons with standard‐PC images verify the PNR advantage predicted by theory. Magn Reson Med 48:890–898, 2002. © 2002 Wiley‐Liss, Inc.
Sensitivity‐encoded single‐shot spiral imaging for reduced susceptibility artifacts in BOLD fMRI
Authors: Weiger Markus , Pruessmann Klaas P. , Österbauer Robert , Börnert Peter , Boesiger Peter , Jezzard Peter 
Published: November 2002

AbstractSensitivity encoding (SENSE) with iterative image reconstruction was used to shorten the readout duration in single‐shot spiral imaging by a factor of 2. This enabled susceptibility‐related blurring and signal loss artifacts to be reduced and spatial resolution to be improved. As a beneficial side effect, the gradient duty cycle was also reduced. The spiral SENSE technique was applied to functional MRI (fMRI) with blood oxygen level‐dependent (BOLD) contrast and compared to a conventional spiral acquisition. Stimulation experiments were performed in seven volunteers using motor, visual, and taste paradigms. The signal‐to‐noise ratio (SNR) and signal‐to‐fluctuation‐noise ratio (SFNR) of the SENSE acquisitions were reduced by 20% and 13%, respectively, with respect to the longer readout. The overall activation detected was comparable to that of the conventional spiral acquisition, even though difficulties in reproducing the stimulation response hampered the evaluation. In some cases, the application of SENSE enabled recovery of activation in regions affected by signal loss due to field inhomogeneity. Magn Reson Med 48:860–866, 2002. © 2002 Wiley‐Liss, Inc.