bluuebunny/crossref_metadata_2025 huggingface dataset:
Improved preparation of chick embryonic samples for magnetic resonance microscopy
Authors: Zhang Xiaowei , Yelbuz T. Mesud , Cofer Gary P. , Choma Michael A. , Kirby Margaret L. , Johnson G. Allan
Published: May 2003

Previous work demonstrated the power of three‐dimensional (3D) magnetic resonance microscopy (MRM) to follow complicated morphologic development in the embryonic cardiovascular system. In this study we describe a new dual‐contrast method for specimen preparation that combines perfusion fixation and immersion in fixative with macro‐ and small molecular gadolinium agents to provide enhanced definition of both the heart wall and chamber. MRM was performed at 9.4 T with image resolutions of 25, 31, and 50 μm isotropic voxels for three stages of chick embryos (day 4, day 5.5, and day 9), and compared to histological sections of the same embryos. The results show considerable improvement of image quality over previous efforts, with better signal‐to‐noise ratio (SNR) and contrast between the cardiac chamber and myocardial wall. Excellent correlation was shown between the MRM images and histological sections. Thus, 3D high‐resolution MRM in combination with the dual‐contrast technique is useful for acquiring quantitative 3D morphologic data regarding heart development. Magn Reson Med 49:1192–1195, 2003. © 2003 Wiley‐Liss, Inc.
Measuring the arterial input function with gradient echo sequences
Authors: van Osch Matthias J.P. , Vonken Evert‐jan P.A. , Viergever Max A. , van der Grond Jeroen , Bakker Chris J.G.
Published: May 2003

The measurement of the arterial input function by use of gradient echo sequences was investigated by in vitro and in vivo experiments. First, calibration curves representing the influence of the concentration of Gd‐DTPA on both the phase and the amplitude of the MR signal were measured in human blood by means of a slow‐infusion experiment. The results showed a linear increase in the phase velocity and a quadratic increase in ΔR as a function of the Gd‐DTPA concentration. Next, the resultant calibration curves were incorporated in a partial volume correction algorithm for the arterial input function determination. The algorithm was tested in a phantom experiment and was found to substantially improve the accuracy of the concentration measurement. Finally, the reproducibility of the arterial input function measurement was estimated in 16 patients by considering the input function of the left and the right sides as replicate measurements. This in vivo study showed that the reproducibility of the arterial input function determination using gradient echo sequences is improved by employing a partial volume correction algorithm based on the calibration curve for the contrast agent used. Magn Reson Med 49:1067–1076, 2003. © 2003 Wiley‐Liss, Inc.
Sensitive CEST agents based on nucleic acid imino proton exchange: Detection of poly(rU) and of a dendrimer‐poly(rU) model for nucleic acid delivery and pharmacology
Authors: Snoussi Karim , Bulte Jeff W.M. , Guéron Maurice , van Zijl Peter C.M.
Published: May 2003

It is shown that the exchange properties of the imino and hydroxyl protons of polyuridilic acid (poly(rU)) allow use of this compound as a chemical‐exchange saturation transfer (CEST) contrast agent. A proton/proton sensitivity enhancement factor of over 5000 per imino proton allowed the detection of a few micromolar of polymer (2000 uridine units; 644 kD) with a 50% change in the water signal. The enhancement factor would increase further at even lower concentrations, opening up the submicromolar range. When poly(rU) was complexed to a dendrimer carrying 250 positive charges, the stoichiometry was approximately one RNA for 10 dendrimers. The sensitivity enhancement was reduced but remained large (2300/imino proton), bringing enhanced CEST visibility to the dendrimers. The net charge of the complex was positive, suggesting that the complexed dendrimers would still interact with cell membranes, and that the RNA‐dendrimer complex could provide a model for a gene delivery system with good CEST visibility. Magn Reson Med 49:998–1005, 2003. © 2003 Wiley‐Liss, Inc.
B1AC‐MAMBA:B1array combined with multiple‐acquisition microB0array parallel magnetic resonance imaging
Authors: Paley Martyn N.J. , Lee Kuan J. , Wild James M. , Fichele Stanislao , Whitby Elspeth H. , Wilkinson Iain D. , Van Beek Edwin J. , Griffiths Paul D.
Published: May 2003

The combination of an in‐planeB1sensitivity encoding (SENSE) technique with a simultaneous multiple‐sliceB0field step technique (multiple‐acquisition microB0array (MAMBA)) has produced high scan time reduction factors (R ≤ 8). In this study, two slices were acquired simultaneously in combination with ×2 and ×4 SENSE in‐plane encoding using a MAMBA steppedB0field coil inside a four‐channel phased‐array coil system. Experiments were performed on a 1.5 T Infinion system (Philips Medical Systems, Cleveland, OH). The signal‐to‐noise ratio (SNR) was reduced with higher R factors, as was expected from the reduced number of acquisitions used to create the unaliased images. The combination of SENSE and MAMBA offers great promise for reducing scan times through parallel acquisition while at the same time reducing the number of RF channels required by a factor equal to the number of field steps employed. TheB1array combined with MAMBA (B1AC‐MAMBA) technique is applicable when the length of an object is much greater than its diameter, as in scanning limbs or in whole‐body screening for disease. Magn Reson Med 49:1196–1200, 2003. © 2003 Wiley‐Liss, Inc.
Receptor‐mediated endocytosis of iron‐oxide particles provides efficient labeling of dendritic cells for in vivo MR imaging
Authors: Ahrens E.T. , Feili‐Hariri M. , Xu H. , Genove G. , Morel P.A.
Published: May 2003

Dendritic cells (DCs) function as antigen presenting cells in vivo and play a fundamental role in numerous diseases. New methods are described for high‐efficiency intracellular labeling of DCs with superparamagnetic iron‐oxide (SPIO) utilizing a receptor‐mediated endocytosis (RME) mechanism. Bone marrow‐derived DCs or a fetal skin‐derived DC line were incubated with SPIO conjugated to anti‐CD11c monoclonal antibody (mAb) under conditions favoring RME. These cells exhibited approximately a 50‐fold increase in uptake relative to DCs incubated with SPIO without the mAb. Flow cytometry studies assaying cell surface markers showed a down‐modulation of CD11c, but no other changes in phenotype. Immunological function of the DCs was unmodified by the labeling, as determined by cytokine secretion assays. The RME mechanism was confirmed using electron microscopy, endocytosis inhibition assays, and incubation experiments with SPIO conjugated to mAbs against accessory molecules that are not expressed on DCs. Labeled DCs were injected into murine quadriceps and monitored in vivo for several days using MR microimaging at 11.7 T. DCs were observed to remain within the muscle for >24 hr. The use of RME is an efficient way to label immune cells for in vivo MRI and can be applied to a wide variety of cell types. Magn Reson Med 49:1006–1013, 2003. © 2003 Wiley‐Liss, Inc.
In vivo assessment of macromolecular content in articular cartilage of the goat knee
Authors: Laurent Didier , Wasvary James , Rudin Markus , O'Byrne Elizabeth , Pellas Theodore
Published: May 2003

Loss of proteoglycans (PGs) from the extracellular matrix of cartilage is an early event of osteoarthritis. The capability of Gd(DTPA)2–‐enhanced MRI to quantitatively assess PG content was explored in a goat model of cartilage degeneration. Partial to total PG depletion was induced by an intraarticular injection of papain 1 day prior to the MRI session. A close correlation was found between the extent of the PG loss and the Gd(DTPA)2–‐induced T1 decrease. Papain‐induced PG depletion was confirmed by post‐mortem histological and biochemical assessments. A 2‐hr delay after Gd(DTPA)2– injection was found to be optimal for an accurate quantitation of the cartilage defect. A series of knee flexions were performed post‐Gd(DTPA)2– injection to facilitate penetration of the contrast agent into cartilage. However, ΔT1's observed in cartilage of exercised goat knees were not affected by papain or IL1β pretreatment. Therefore, as long as a preinjection T1 map was obtained, the Gd(DTPA)2–‐enhanced MRI technique provided good sensitivity in detecting partial loss of PG in articular cartilage. This was true only when the animal was maintained in a resting state during diffusion of the Gd(DTPA)2–. This approach is of particular interest for long‐term evaluations of cartilage degeneration and regeneration. Magn Reson Med 49:1037–1046, 2003. © 2003 Wiley‐Liss, Inc.
Optimized spiral imaging for measurement of myocardial T2 relaxation
Authors: Foltz Warren D. , Al‐Kwifi Osama , Sussman Marshall S. , Stainsby Jeff A. , Wright Graham A.
Published: May 2003

Microcirculation oxygen levels and blood volumes should be reflected in measurements of myocardial T2 relaxation. This work describes the optimization of a spiral imaging strategy for robust myocardial T2 measurement to minimize the standard deviation of T2 measurement (σT2). Theoretical and experimental studies of blurring at muscle/blood interfaces enabled the derivation of parameter sets which reduce σ T2 to the level of 5%. T2 relaxation mapping within healthy volunteers provided estimation of residual σT2 within the optimized technique. The standard deviation in T2 measurement across regions of interest (ROIs) in different locations is about 9%. The standard deviation in T2 measurement in an ROI across different time points is about 5%. Magn Reson Med 49:1089–1097, 2003. © 2003 Wiley‐Liss, Inc.
Cluster analysis of BOLD fMRI time series in tumors to study the heterogeneity of hemodynamic response to treatment
Authors: Baudelet Christine , Gallez Bernard
Published: May 2003

BOLD‐contrast functional MRI (fMRI) has been used to assess the evolution of tumor oxygenation and blood flow after treatment. The aim of this study was to evaluate K‐means‐based cluster analysis as a exploratory, data‐driven method. The advantage of this approach is that it can be used to extract information without the need for prior knowledge concerning the hemodynamic response function. Two data sets were acquired to illustrate different types of BOLD fMRI response inside tumors: the first set following a respiratory challenge with carbogen, and the second after pharmacological modulation of tumor blood flow using flunarizine. To improve the efficiency of the clustering, a power density spectrum analysis was first used to isolate voxels for which signal changes did not originate from noise or linear drift. The technique presented here can be used to assess hemodynamic response to treatment, and especially to display areas of the tumor with heterogeneous responses. Magn Reson Med 49:985–990, 2003. © 2003 Wiley‐Liss, Inc.
Novel ROC‐type method for testing the efficiency of multivariate statistical methods in fMRI
Authors: Nandy Rajesh R. , Cordes Dietmar
Published: May 2003

The receiver operating characteristic (ROC) method is a useful and popular tool for testing the efficiency of various diagnostic tests applicable to functional MRI (fMRI) data. Typically, the diagnostic tests are applied on simulated and pseudo‐human fMRI data, and the area under the ROC curve is used as a measure of the efficiency of the diagnostic test. The effectiveness of such a method depends on how well the simulated data approximate the real data. For multivariate statistical methods, however, this technique is usually inadequate, as the spatial dependence among voxels is ignored for simulated data. In this work a modified ROC method using real fMRI data with a broader scope is proposed. This method can be applied to most fMRI postprocessing techniques, including multivariate analyses such as canonical correlation analysis (CCA). Also, the relationship of the modified ROC method with the conventional ROC method is discussed in detail. Magn Reson Med 49:1152–1162, 2003. © 2003 Wiley‐Liss, Inc.
Extended field‐of‐view imaging with table translation and frequency sweeping
Authors: Zhu Yudong , Dumoulin Charles L.
Published: May 2003

A new method for MRI of an extended field of view (FOV) has been developed and validated. The method employs concurrent MR data acquisition and patient table motion. Table motion‐induced image artifacts are minimized by sweeping the frequency of the receiver at a rate matching the table's speed. Multiple regional images are collected and combined to reconstruct the full FOV. The imaging parameters and table speed are chosen to ensure that each regional image of the subject is collected while the corresponding anatomy is in the useable imaging volume of the scanner. Additional strategies are applied to further reduce field inhomogeneity‐induced artifacts, especially distortions due to gradient field nonlinearity. The method is robust and can be easily incorporated into most multislice 2D and volumetric 3D imaging pulse sequences. It is anticipated that this technique will be useful for a variety of applications, including angiographic runoffs, whole‐body screening, and short‐magnet imaging. Magn Reson Med 49:1106–1112, 2003. © 2003 Wiley‐Liss, Inc.
Method to determine in vivo the relaxation time T1 of hyperpolarized xenon in rat brain
Authors: Choquet Philippe , Hyacinthe Jean‐Noël , Duhamel Guillaume , Grillon Emmanuelle , Leviel Jean‐Louis , Constantinesco André , Ziegler Anne
Published: May 2003

The magnetic polarization of the stable 129Xe isotope may be enhanced dramatically by means of optical techniques and, in principle, hyperpolarized 129Xe MRI should allow quantitative mapping of cerebral blood flow with better spatial resolution than scintigraphic techniques. A parameter necessary for this quantitation, and not previously known, is the longitudinal relaxation time (T) of 129Xe in brain tissue in vivo: a method for determining this is reported. The time course of the MR signal in the brain during arterial injection of hyperpolarized 129Xe in a lipid emulsion was analyzed using an extended two‐compartment model. The model uses experimentally determined values of the RF flip angle and the T1 of 129Xe in the lipid emulsion. Measurements on rats, in vivo, at 2.35 T gave T = 3.6 ± 2.1 sec (±SD, n = 6). This method enables quantitative mapping of cerebral blood flow. Magn Reson Med 49:1014–1018, 2003. © 2003 Wiley‐Liss, Inc.
Microvascular BOLD contribution at 4 and 7 T in the human brain: Gradient‐echo and spin‐echo fMRI with suppression of blood effects
Authors: Duong Timothy Q. , Yacoub Essa , Adriany Gregory , Hu Xiaoping , Uǧurbil Kâmil , Kim Seong‐Gi
Published: May 2003

The BOLD signal consists of an intravascular (IV) and an extravascular (EV) component from both small and large vessels. Their relative contributions are dependent on field strength, imaging technique, and echo time. The IV and EV contributions were investigated in the human visual cortex at 4 and 7 T using spin‐echo and gradient‐echo BOLD fMRI with and without suppression of blood effects. Spin‐echo acquisition suppresses EV BOLD from large veins and reflects predominantly blood T2 changes and EV BOLD signal from small blood vessels. At a short echo time (32 ms), diffusion gradient‐based suppression of blood signals resulted in a 75% and 20% decrease in spin‐echo BOLD changes at 4 T and 7 T, respectively. However, at echo times (55–65 ms) approximating tissue T2 typically used for optimal BOLD contrast, these gradients had much smaller effects at both fields, consistent with the decreasing blood T2 with increasing field strength. Gradient‐echo BOLD percent changes, with relatively long echo times at both fields, were virtually unaffected by gradients that attenuated the blood contribution because the EV BOLD surrounding both large and small vessels dominated. These results suggest that spin‐echo BOLD fMRI at 4 and 7 T, with TE approximating tissue T2, significantly reduces nonspecific mapping signals from large vessels and significantly accentuates microvasculature contributions. Magn Reson Med 49:1019–1027, 2003. © 2003 Wiley‐Liss, Inc.
Mapping ischemic risk region and necrosis in the isolated heart using EPR imaging
Authors: Velayutham Murugesan , Li Haiquan , Kuppusamy Periannan , Zweier Jay L.
Published: May 2003

Reperfusion of ischemic tissue is a common event in the treatment of heart attack and stroke. To study disease pathogenesis, methods are required to measure tissue perfusion and area at risk, as well as localized regions of injury. While histology can provide this information, its destructive nature precludes assessment of time course. Thus, there is a critical need for a noninvasive technique to obtain this information. To map myocardial redox state as a possible index of cellular ischemia and viability, electron paramagnetic resonance (EPR) imaging experiments were performed on isolated rat hearts before and after the onset of regional ischemia using nitroxide spin labels. With coronary artery occlusion, the EPR images clearly showed the risk region as a void of lower intensity that reversed upon reperfusion. The extent of risk region in the heart was similar in EPR imaging and histological measurements. The unique information obtained regarding the time course of changes in redox metabolism of the risk region and normal myocardium can provide important insights regarding the mechanisms of myocardial injury during and following ischemia. Magn Reson Med 49:1181–1187, 2003. © 2003 Wiley‐Liss, Inc.
Spectral fitting: The extraction of crucial information from a spectrum and a spectral image
Authors: Mailer Colin , Robinson Bruce H. , Williams Benjamin B. , Halpern Howard J.
Published: May 2003

A highly accurate line‐width simulation computer program is used that can account for both high amplitude and frequency of the Zeeman modulation in an electron paramagnetic resonance (EPR) experiment. This allows for the overmodulation of EPR lines to increase signal‐to‐noise ratio (SNR) in EPR spectra and spectroscopic images, without any sacrifice in the determination of the intrinsic line width (1/γ · T2e). The technique was applied to continuous‐wave EPR spectroscopic images of a narrow, single‐line trityl spin probe wherein a full EPR spectrum was extracted from each 3D spatial voxel. Typical improvements are a three‐ to fivefold increase in SNR in the high‐gradient projections in the image and a reduction in the standard deviation (SD), by a factor of 3, of the line widths in the low‐gradient domain. This method is a general one that is also applicable to the analysis of conventional 14N or 15N nitroxide spin probes. Magn Reson Med 49:1175–1180, 2003. © 2003 Wiley‐Liss, Inc.
Selective arterial spin labeling (SASL): Perfusion territory mapping of selected feeding arteries tagged using two‐dimensional radiofrequency pulses
Authors: Davies Nigel P. , Jezzard Peter
Published: May 2003

To date, most perfusion magnetic resonance imaging (MRI) methods using arterial spin labeling (ASL) have employed slab‐selective inversion pulses or continuous labeling within a plane in order to obtain maps derived from all major blood vessels entering the brain. However, there is great potential for gaining additional information on the territories perfused by the major vessels if individual feeding arteries could be tagged. This study demonstrates noninvasive arterial perfusion territory maps obtained using two‐dimensional (2D) selective inversion pulses. This method is designated “selective ASL” (SASL). The SASL method was used to tag the major arteries below the circle of Willis. A combination of 2D selective tagging and multislice readout allows perfusion territories to be clearly visualized, with likely applications to cerebrovascular disease and stroke. Magn Reson Med 49:1133–1142, 2003. © 2003 Wiley‐Liss, Inc.
Fast measurement of relaxation times by steady‐state free precession of 129Xe in carrier agents for hyperpolarized noble gases
Authors: Oregioni Alain , Parizel Nathalie , de Sousa Paulo Loureiro , Grucker Daniel
Published: May 2003

Hyperpolarized gases (129Xe and 3He) are being used increasingly in both MRI and NMR spectroscopy studies. However, it has been shown that carrier agents are required to preserve the long relaxation times of gases in biological fluids. Optimized gas transport can be achieved through controlled T1 and T2 measurements of 129Xe gas at equilibrium, using the steady‐state free precession method (SSFP). The accuracy of the method was proven with the use of CuSO4‐doped water samples and xenon dissolved in chloroform. The following T1 and T2 values were measured for xenon dissolved in a 30% intralipid emulsion: T1 = 29 ± 3 s; T2 = 1.0 ± 0.1 s. The values obtained in the intralipid emulsion contrast significantly with those obtained in conventional gas NMR experiments, in which it is commonly assumed that T1 = T2. This highlights the importance of obtaining accurate relaxation time measurements for medical applications of hyperpolarized gases. Magn Reson Med 49:1028–1032, 2003. © 2003 Wiley‐Liss, Inc.
Dynamic radial projection MRI of inhaled hyperpolarized 3He gas
Authors: Wild Jim M. , Paley Martyn N.J. , Kasuboski Larry , Swift Andrew , Fichele Stan , Woodhouse Neil , Griffiths Paul D. , van Beek Edwin J.R.
Published: May 2003

A radial projection sliding‐window sequence has been developed for imaging the rapid flow of 3He gas in human lungs. The short echo time (TE) of the radial sequence lends itself to fast repetition times, and thus allows a rapid update in the image when it is reconstructed with a sliding window. Oversampling in the radial direction combined with angular undersampling can further reduce the time needed to acquire a complete image data set, without significantly compromising spatial resolution. Controlled flow phantom experiments using hyperpolarized 3He gas exemplify the temporal resolution of the method. In vivo studies on three healthy volunteers, one patient with chronic obstructive pulmonary disease (COPD), and one patient with hemiparalysis of the right diaphragm demonstrate that it is possible to accurately resolve the passage of gas down the trachea and bronchi and into the peripheral lung. Magn Reson Med 49:991–997, 2003. © 2003 Wiley‐Liss, Inc.
Error reduction and parameter optimization of the TAPIR method for fast T1 mapping
Authors: Zaitsev M. , Steinhoff S. , Shah N.J.
Published: May 2003

A methodology is presented for the reduction of both systematic and random errors in T1 determination using TAPIR, a Look‐Locker‐based fast T1 mapping technique. The relations between various sequence parameters were carefully investigated in order to develop recipes for choosing optimal sequence parameters. Theoretical predictions for the optimal flip angle were verified experimentally. Inversion pulse imperfections were identified as the main source of systematic errors in T1 determination with TAPIR. An effective remedy is demonstrated which includes extension of the measurement protocol to include a special sequence for mapping the inversion efficiency itself. Magn Reson Med 49:1121–1132, 2003. © 2003 Wiley‐Liss, Inc.
Macrophage infiltration into the rat knee detected by MRI in a model of antigen‐induced arthritis
Authors: Beckmann Nicolau , Falk Regina , Zurbrügg Stefan , Dawson Janet , Engelhardt Petra
Published: May 2003

Three‐dimensional (3D) MR images were obtained from the knees of rats in a model of antigen‐induced arthritis, elicited by the intraarticular administration of methylated bovine serum albumin (mBSA) to previously immunized rats. Superparamagnetic particles of iron oxide (SPIO) were administered i.v. 24 hr before each imaging session. Starting 4 days postantigen injection, images from arthritic knees exhibited distinctive signal attenuation in the synovium. This signal attenuation was significantly smaller in knees from animals treated with dexamethasone, a glucocorticosteroid, and completely absent in contralateral knees that had been challenged with vehicle. A significant negative correlation was found between the MRI signal intensity in the synovium and the histologically determined iron content in macrophages located in the same region. These results suggest the feasibility of detecting macrophage infiltration into the knee synovium in this model of antigen‐induced arthritis by labeling the cells with SPIO. This readout could provide an early marker of disease progression, before more aggressive changes like cartilage and bone erosion take place. Monitoring early changes associated with arthritis can have an impact in preclinical studies by shortening the duration of the experimental period and by facilitating the investigation of novel immunomodulatory therapies acting on macrophages. Also, the approach can be potentially adapted to clinical studies. Magn Reson Med 49:1047–1055, 2003. © 2003 Wiley‐Liss, Inc.
Circular spectrum mapping for intravoxel fiber structures based on high angular resolution apparent diffusion coefficients
Authors: Zhan Wang , Gu Hong , Xu Su , Silbersweig David A. , Stern Emily , Yang Yihong
Published: May 2003

A method is presented for mapping intravoxel fiber structures using spectral decomposition onto a circular distribution of measured apparent diffusion coefficients (ADCs). The zeroth‐, second‐, and fourth‐order harmonic components of the ADC distribution on the circle spanned by the major and median eigenvectors of the diffusion tensor can be used to provide quantitative indices for isotropic, linear, and fiber‐crossing diffusion, respectively. A diffusion‐weighted MRI technique with 90 encoding orientations was implemented to estimate the circular ADC distribution and calculate the circular spectrum. A digital phantom was used to simulate various diffusion patterns. Comparisons were made between the circular spectrum and regular DTI‐based index maps. The results indicated that the zeroth‐ and second‐order circular spectrum maps exhibited a strong consistency with the DTI‐based mean diffusivity and linear indices, respectively, and the fourth‐order circular spectrum map was able to identify the fiber crossings. MRI experiments were performed on seven healthy human brains using a 3T scanner. The in vivo fourth‐order maps showed significantly higher densities in several brain regions, including the corpus callosum, cingulum bundle, superior longitudinal fasciculus, corticospinal tract, and middle cerebellar peduncle, which indicated the existence of fiber crossings in these regions. Magn Reson Med 49:1077–1088, 2003. © 2003 Wiley‐Liss, Inc.
Reduction of spectral ghost artifacts in high‐resolution echo‐planar spectroscopic imaging of water and fat resonances
Authors: Du Weiliang , Du Yiping P. , Fan Xiaobing , Zamora Marta A. , Karczmar Gregory S.
Published: May 2003

Echo‐planar spectroscopic imaging (EPSI) can be used for fast spectroscopic imaging of water and fat resonances at high resolution to improve structural and functional imaging. Because of the use of oscillating gradients during the free induction decay (FID), spectra obtained with EPSI are often degraded by Nyquist ghost artifacts arising from the inconsistency between the odd and even echoes. The presence of the spectral ghost lines causes errors in the evaluation of the true spectral lines, and this degrades images derived from high‐resolution EPSI data. A technique is described for reducing the spectral ghost artifacts in EPSI of water and fat resonances, using echo shift and zero‐order phase corrections. These corrections are applied during the data postprocessing. This technique is demonstrated with EPSI data acquired from human brains and breasts at 1.5 Tesla and from a water phantom at 4.7 Tesla. Experimental results indicate that the present approach significantly reduces the intensities of spectral ghosts. This technique is most useful in conjunction with high‐resolution EPSI of water and fat resonances, but is less applicable to EPSI of metabolites due to the complexity of the spectra. Magn Reson Med 49:1113–1120, 2003. © 2003 Wiley‐Liss, Inc.
Fast measurement of intracardiac pressure differences with 2D breath‐hold phase‐contrast MRI
Authors: Thompson Richard B. , McVeigh Elliot R.
Published: May 2003

Intracardiovascular blood pressure differences can be derived from velocity images acquired with phase‐contrast (PC) MRI by evaluating the Navier‐Stokes equations. Pressure differences within a slice of interest can be calculated using only the in‐plane velocity components from that slice. This rapid exam is proposed as an alternative to the lengthy 3D velocity imaging exams. Despite their good spatial coverage, the 3D exams are prone to artifacts and errors from respiratory motion and insufficient temporal resolution, and are unattractive in the clinical setting due to their excessive scan times (>10 min of free breathing). The proposed single‐slice approach requires only one or two breath‐holds of acquisition time, and the velocity data can be processed for the calculation of pressure differences online with immediate feedback. The impact of reducing the pressure difference calculation to two dimensions is quantified by comparison with 3D data sets for the case of blood flow within the cardiac chambers. The calculated pressure differences are validated using high‐fidelity pressure transducers both in a pulsatile flow phantom and in vivo in a dog model. There was excellent agreement between the transducer and PC‐MRI results in all of the studies. Magn Reson Med 49:1056–1066, 2003. Published 2003 Wiley‐Liss, Inc.
Changes in the proton T2 relaxation times of cerebral water and metabolites during forebrain ischemia in rat at 9.4 T
Authors: Lei Hao , Zhang Yi , Zhu Xiao‐Hong , Chen Wei
Published: May 2003

Proton T2 relaxation times of cerebral water and metabolites were measured before, during, and after transient forebrain ischemia in rat at 9.4 T using localized proton magnetic resonance spectroscopy (1H‐MRS) with Hahn echoes formed at different echo times (TEs). It was found that the T2 values of water and N‐acetyl aspartate (NAA) methyl, but not total creatine (tCr) methyl, decrease significantly (∼10%) during ischemia, and this T2 reduction is reversed by reperfusion. The T2 reduction observed for NAA was most likely caused by the extravascular component of the blood oxygenation level‐dependent (BOLD) effect induced by a drastically increased deoxyhemoglobin content during ischemia. The absence of T2 changes for tCr can probably be explained by the fact that the BOLD‐related T2 decrease was counterbalanced by the conversion of phosphocreatine (PCr) to creatine (Cr), which has a longer T2 than PCr, during ischemia. The changes in T2 should be taken into account for the quantification of metabolite concentrations during ischemia. Magn Reson Med 49:979–984, 2003. © 2003 Wiley‐Liss, Inc.
Anisotropic noise propagation in diffusion tensor MRI sampling schemes
Authors: Batchelor P.G. , Atkinson D. , Hill D.L.G. , Calamante F. , Connelly A.
Published: May 2003

The subject of this study is the controversial choice of directions in diffusion tensor MRI (DT‐MRI); specifically, the numerical algebra related to this choice. In DT‐MRI, apparent diffusivities are sampled in six or more directions and a least‐squares equation is solved to reconstruct the diffusion tensor. Numerical characteristics of the system are considered, in particular the condition number and normal matrix, and are shown to be dependent on the relative orientation of the tensor with respect to the laboratory frame. As a consequence, noise propagation can be anisotropic. However, the class of icosahedral direction schemes is an exception, and icosahedral directions have the same condition number and normal matrix for direction encoding as the ideal scheme with an infinite number of directions. This normal matrix and its condition number are rotationally invariant. Numerical simulations show that for icosahedral schemes with 30 directions the standard deviation of the fractional anisotropy is both low and nearly independent of fiber orientation. The recommended choice of directions for a DT‐MRI experiment is therefore the icosahedral set of directions with the highest number of directions achievable in the available time. Magn Reson Med 49:1143–1151, 2003. © 2003 Wiley‐Liss, Inc.
Reinforcing mechanism of anchors in slopes: a numerical comparison of results of LEM and FEM
Authors: Cai Fei , Ugai Keizo
Published: May 2003

This paper reports the limitation of the conventional Bishop's simplified method to calculate the safety factor of slopes stabilized with anchors, and proposes a new approach to considering the reinforcing effect of anchors on the safety factor. The reinforcing effect of anchors can be explained using an additional shearing resistance on the slip surface. A three‐dimensional shear strength reduction finite element method (SSRFEM), where soil–anchor interactions were simulated by three‐dimensional zero‐thickness elasto‐plastic interface elements, was used to calculate the safety factor of slopes stabilized with anchors to verify the reinforcing mechanism of anchors. The results of SSRFEM were compared with those of the conventional and proposed approaches for Bishop's simplified method for various orientations, positions, and spacings of anchors, and shear strengths of soil–grouted body interfaces. For the safety factor, the proposed approach compared better with SSRFEM than the conventional approach. The additional shearing resistance can explain the influence of the orientation, position, and spacing of anchors, and the shear strength of soil–grouted body interfaces on the safety factor of slopes stabilized with anchors. Copyright © 2003 John Wiley & Sons, Ltd.
Numerical solutions for flow in porous media
Authors: Wang J.G. , Leung C.F. , Chow Y.K.
Published: May 2003

A numerical approach is proposed to model the flow in porous media using homogenization theory. The proposed concept involves the analyses of micro‐true flow at pore‐level and macro‐seepage flow at macro‐level. Macro‐seepage and microscopic characteristic flow equations are first derived from the Navier–Stokes equation at low Reynolds number through a two‐scale homogenization method. This homogenization method adopts an asymptotic expansion of velocity and pressure through the micro‐structures of porous media. A slightly compressible condition is introduced to express the characteristic flow through only characteristic velocity. This characteristic flow is then numerically solved using a penalty FEM scheme. Reduced integration technique is introduced for the volumetric term to avoid mesh locking. Finally, the numerical model is examined using two sets of permeability test data on clay and one set of permeability test data on sand. The numerical predictions agree well with the experimental data if constraint water film is considered for clay and two‐dimensional cross‐connection effect is included for sand. Copyright © 2003 John Wiley & Sons, Ltd.
Glyph and hyperstreamline representation of stress and strain tensors and material constitutive response
Authors: Hashash Youssef M. A. , Yao John I‐Chiang , Wotring Donald C.
Published: May 2003

Results of numerical analyses of boundary value problems in geomechanics include output of three‐dimensional stress and strain states. Two‐dimensional plots of stress–stress or stress–strain quantities, often used to represent such output, do not fully communicate the evolution of stress and strain states. This paper describes the use of glyphs and hyperstreamlines for the visual representation of three dimensional stress and strain tensors in geomechanics applications. Glyphs can be used to represent principal stress states as well as normal stresses at a point. The application of these glyphs is extended in this paper to represent strain states. The paper introduces a new glyph, called HWY glyph for the representation of shear tensor components. A load step‐based hyperstreamline is developed to show the evolution of a stress or strain tensor under a general state of loading. The evolution of stress–strain states from simulated laboratory tests and a general boundary value problem of a deep braced excavation are represented using these advanced visual techniques. These visual representations facilitate the understanding of complex multidimensional stress–strain soil constitutive relationships. The visual objects introduced in this paper can be applied to stress and strain tensors from general boundary value problems. Copyright © 2003 John Wiley & Sons, Ltd.
A diffusible signal attracts olfactory sensory axons toward their target in the developing brain of the moth
Authors: Oland Lynne A. , Pott Wendy M. , Howard Charles T. , Inlow Mark , Buckingham Jocelyn
Published: May 2003

The signals that olfactory receptor axons use to navigate to their target in the CNS are still not well understood. In the moth Manduca sexta, the primary olfactory pathway develops postembryonically, and the receptor axons navigate from an experimentally accessible sensory epithelium to the brain along a pathway long enough for detailed study of regions in which axon behavior changes. The current experiments ask whether diffusible factors contribute to receptor axon guidance. Explants were made from the antennal receptor epithelium and co‐cultured in a collagen gel matrix with slices of various regions of the brain. Receptor axons were attracted toward the central regions of the brain, including the protocerebrum and antennal lobe. Receptor axons growing into a slice of the most proximal region of the antennal nerve, where axon sorting normally occurs, showed no directional preference. When the antennal lobe was included in the slice, the receptor axons entering the sorting region grew directly toward the antennal lobe. Taken together with the previous in vivo experiments, the current results suggest that an attractive diffusible factor can serve as one cue to direct misrouted olfactory receptor axons toward the medial regions of the brain, where local cues guide them to the antennal lobe. They also suggest that under normal circumstances, in which the receptor axons follow a pre‐existing pupal nerve to the antennal lobe, the diffusible factor emanating from the lobe acts in parallel and at short range to maintain the fidelity of the path into the antennal lobe. © 2003 Wiley Periodicals, Inc. J Neurobiol 56: 24–40, 2003
In vivo dynamics of CNS sensory arbor formation: A time‐lapse study in the embryonic leech
Authors: Baker Michael W. , Kauffman Brent , Macagno Eduardo R. , Zipser Birgit
Published: May 2003

In the embryo of the leech Hirudo medicinalis, afferent projections of peripheral sensory neurons travel along common nerve tracts to the CNS, where they defasciculate, branch, and arborize into separate, modality‐specific synaptic laminae. Previous studies have shown that this process requires, at least in part, the constitutive and then modality‐specific glycosylations of tractin, a leech L1 homologue. We report here on the dynamics of growth of these projections as obtained by examining the morphology of single growing dye‐filled sensory afferents as a function of time. Using 2‐photon laser‐scanning microscopy of the intact developing embryo, we obtained images of individual sensory projections at 3 to 30 min intervals, over several hours of growth, and at different stages of development. The time‐lapse series of images revealed a highly dynamic and maturation‐state‐dependent pattern of growth. Upon entering the CNS, the growth cone‐tipped primary axon sprouted numerous long filopodial processes, many of which appeared to undergo repeated cycles of extension and retraction. The growth cone was transformed into a sensory arbor through the formation of secondary branches that extended within the ganglionic neuropil along the anterior‐posterior axis of the CNS. Numerous tertiary and quaternary processes grew from these branches and also displayed cycles of extension and retraction. The motility of these higher‐order branches changed with age, with younger afferents displaying higher densities and greater motility than older, more mature sensory arbors. Finally, coincident with a reduction in higher order projections was the appearance of concavolar structures on the secondary processes. Rows of these indentations suggest the formation of presynaptic en‐passant specializations accompanying the developmental onset of synapse formation. © 2003 Wiley Periodicals, Inc. J Neurobiol 56: 41–53, 2003
Structural and functional changes in the olfactory pathway of adult Drosophila take place at a critical age
Authors: Devaud Jean‐Marc , Acebes Angel , Ramaswami Mani , Ferrús Alberto
Published: May 2003

The olfactory system of several holometabolous insect species undergoes anatomical changes after eclosion of the imago, following those occurring during metamorphosis. In parallel, odor experience and learning performance also evolve with age. Here, we analyze the case of adult Drosophila females. Synaptogenesis in the antennal lobe (AL) starts in late pupa and continues during the first days of adult life, at the same time as the behavioral response to odors matures. Individual olfactory glomeruli (DM6, DM2, and V) display specific growth patterns between days 1 and 12 of adult life. Experience can modify the olfactory pathway both structurally and functionally as shown by adaptation experiments. The modifications associated with this form of nonassociative learning seem to take place at a critical age. Exposure to benzaldehyde at days 2–5 of adult life, but not at 8–11, causes behavioral adaptation as well as structural changes in DM2 and V glomeruli. Altered levels in intracellular cAMP, caused by dunce and rutabaga mutants, do not affect the normal changes in glomerular size, at least at day 6 of development, but they prevent those elicited by experience, establishing a molecular difference between glomerular changes of intrinsic versus environmental origin. Taken together, these data demonstrate an imprinting‐like phenomenon in the olfactory pathway of young Drosophila adults, and illustrate its glomerulus‐specific dynamics. © 2003 Wiley Periodicals, Inc. J Neurobiol 56: 13–23, 2003
Blocking sensory inputs to identified antennal glomeruli selectively modifies odorant perception in Drosophila
Authors: Devaud Jean‐Marc , Keane John , Ferrús Alberto
Published: May 2003

Neural coding of sensory input is a major unsolved issue in neuroscience. Current experimental methods rely on neural activity recording or visualization following sensory stimulation. Most of them, however, do not include behavioral correlates on the actual perception by the animal. We present a novel approach to address olfaction and coding in adult Drosophila. Sensory input was selectively blocked in two subsets of sensory neurons that project to different, albeit overlapping, groups of central targets, by means of tetanus toxin expressed under the control of the yeast transcription factor Gal4. Glomeruli DL1, DL2, VM1, and VM4 were tested following stimulation with benzaldehyde, ethyl acetate, propionic acid, butanol, or acetone at various concentrations. The behavioral response was found to be modified in an odorant‐specific and a concentration‐dependent manner. Sensory input to DL2 and, to a minor extent, VM1 and/or VM4, appear to be required for benzaldehyde perception, while acetone is processed through DL1. None of these glomeruli, however, seem necessary for butanol perception. In addition, sexual differences were observed for some stimuli. These results demonstrate the behavioral relevance of odor representation as maps of glomerular activity generated in the antennal lobes following specific sensory input. The strategy used here should be useful to characterize olfactory coding, as new and selective Gal4 lines become available. © 2003 Wiley Periodicals, Inc. J Neurobiol 56: 1–12, 2003
Endogenous neurotrophic factors enhance neurite growth by bag cell neurons of Aplysia
Authors: Vanmali Binaben H. , Romanova Elena V. , Messner Maria C. , Singh Mona , Maruniak Joel , Sweedler Jonathan , Kirk Mark D.
Published: May 2003

Mechanisms that regulate neurite outgrowth are phylogenetically conserved, including the signaling molecules involved. Here, we describe neurotrophic effects on isolated bag cell neurons (BCNs) of substrate‐bound growth factors endogenous to the sea slug Aplysia californica. Sheath cells dissociated from the pleural‐visceral connectives of the Aplysia CNS and arterial cells dissociated from the anterior aorta enhance neurite outgrowth when compared to controls, i.e., BCNs grown in defined medium alone. In addition, the substrate remaining after sheath cells or arterial cells are killed significantly enhances growth, relative to all other conditions tested. For instance, primary neurites are more numerous and greater in length for BCNs cultured on substrate produced by arterial cells. These results suggest that sheath and arterial cells produce growth‐promoting factors, some of which are found in the substrates produced by these cell types. Using matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS), we found that Aplysia collagen‐like peptides are produced by dissociated arterial cells, and therefore likely contribute to the observed growth effects. Collagen‐like peptides and other factors produced by sheath and arterial cells likely influence neurite growth in the Aplysia CNS during development, learning and memory, and regeneration after injury. © 2003 Wiley Periodicals, Inc. J Neurobiol 56: 78–93, 2003
Estrogen alters excitability but not morphology of a sexually dimorphic neuromuscular system in adult rats
Authors: Fargo Keith N. , Foster Allison M. , Harty Mark W. , Sengelaub Dale R.
Published: May 2003

In rats, motoneurons of the spinal nucleus of the bulbocavernosus (SNB) innervate the bulbocavernosus (BC) muscle, which surrounds the base of the penis. The SNB/BC is a sexually dimorphic, steroid‐sensitive neuromuscular system, which is critically important in male reproductive behavior. Androgens are necessary for the development, morphology, and function of the SNB/BC system. However, estradiol (E) is also necessary for the development of the SNB/BC system, and E is capable of maintaining BC EMG activity in adulthood. In this study, we used electrophysiological and anatomical methods to examine estrogenic effects on BC EMG activity. We used a modified H‐reflex testing method to investigate polysynaptic reflex characteristics in intact males, castrates, and castrates treated short term with estradiol benzoate (EB). Measures of EMG activity, response latency, and spike count were altered in castrates, but maintained in EB‐treated castrates to the levels of intact males. Furthermore, estrogenic effects were found in EMG activity that could be isolated to the periphery of the SNB/BC system. BC NMJ size and muscle fiber area have been demonstrated to be hormone sensitive, and we examined these for possible correlates of E's effects on BC EMG activity. BC muscles of intact males, castrates, and short‐term EB‐treated castrates were fixed and stained with zinc iodide and osmium tetroxide. NMJ size and muscle fiber area did not differ between groups. Together, these data suggest that E treatment results in changes in the neuromuscular periphery that maintain BC EMG activity, but this effect cannot be accounted for by changes in NMJ size or muscle fiber area. © 2003 Wiley Periodicals, Inc. J Neurobiol 56: 66–77, 2003