bluuebunny/crossref_metadata_2025 huggingface dataset:
A proposed structure–groundwater model: application to chalky media of the Paris Basin
Authors: Lallahem S. , Lamouroux Ch. , Mania J. , Hani A.
Published: August 2007

The groundwater flow in a fissured chalky environment at the northern border of the Paris Basin depends on several geological and hydrogeological parameters. Although the studied sector of the basin presents a homogeneous rock type, it is affected by a fracture network. In this type of environment, in which the permeability is low, the groundwater flow displays significant disruption, which is localized in the Fruges region (northern France). The interconnection of the discontinuities (network of fault and/or joints) is reliant on the structural control of groundwater flow through increases in the hydraulic connection between the unsaturated and the saturated zone. The methodology developed herein makes use of microstructural and regional analysis of the fracture patterns, and allowed consideration of the piezometric variations of the chalk aquifer during periods of low and high groundwater levels (April and October 2001) and a diagraphic representation of the estimated physical parameters (electrical resistivity). This enabled us to construct a ‘flow structure’ conceptual model in which we identify two types of faults: tight walls and flow paths that control the piezometric heads and the flow rate. Model validation was carried out on a similar sector. Copyright © 2007 John Wiley & Sons, Ltd.
Magnetic resonance imaging of vulnerable atherosclerotic plaques: Current imaging strategies and molecular imaging probes
Authors: Briley‐Saebo Karen C. , Mulder Willem J.M. , Mani Venkatesh , Hyafil Fabien , Amirbekian Vardan , Aguinaldo Juan Gilberto S. , Fisher Edward A. , Fayad Zahi A.
Published: August 2007

The vulnerability or destabilization of atherosclerotic plaques has been directly linked to plaque composition. Imaging modalities, such as magnetic resonance (MR) imaging, that allow for evaluation of plaque composition at a cellular and molecular level, could further improve the detection of vulnerable plaque and may allow for monitoring the efficacy of antiatherosclerotic therapies. In this review we focus on MR imaging strategies for the detection and evaluation of atherosclerotic plaques and their composition. We highlight recent advancements in the development of MR pulse sequences, computer image analysis, and the use of commercially available MR contrast agents, such as gadopentic acid (Gd‐DTPA), for plaque characterization. We also discuss molecular imaging strategies that are currently being used to design specific imaging probes targeted to biochemical and cellular markers of atherosclerotic plaque vulnerability. J. Magn. Reson. Imaging 2007;26:460–479. © 2007 Wiley‐Liss, Inc.
Maximizing contrast‐to‐noise ratio in ultra‐high resolution peripheral MR angiography using a blood pool agent and parallel imaging
Authors: Wang Maisie S. , Haynor David R. , Wilson Gregory J. , Leiner Tim , Maki Jeffrey H.
Published: August 2007

Purpose

To determine sequence parameters that maximize vascular contrast‐to‐noise (CNR) for ultra‐high resolution equilibrium phase (EP) peripheral imaging for the blood pool agent (BPA) Vasovist.

Materials and Methods

A model for maximizing CNR in EP MR angiography (MRA) is presented. Tissue relaxation times, coil geometry (g)‐factors, and clinical imaging requirements (voxel volume and scan time) were determined from human studies. Using these known values, parameters for TR, TE, bandwidth, flip angle (FA), and sensitivity encoding (SENSE) factor that maximized CNR were derived from the model. CNR was enhanced by using reduction in scan time gained from parallel imaging to increase TR and minimize bandwidth. A total of 10 patients were imaged using model‐derived EP CE‐MRA parameters.

Results

The model closely predicted experimental CNR data measured in two clinical studies (r2 = 0.85) and demonstrated an increase in CNR by a factor of 2.3 when subjects were imaged using optimal sequence parameters (P < 0.001). Thigh and calf data were acquired with voxel volumes on the order of 0.2 mm3 using a SENSE factor of 4.

Conclusion

Recommended imaging parameters for a 12‐channel and 18‐channel peripheral vascular coil at two doses of Vasovist (0.03 mmol/kg and 0.05 mmol/kg) are presented. J. Magn. Reson. Imaging 2007;26:580–588. © 2007 Wiley‐Liss, Inc.
Numerical simulation of in vitro pulsatile flow and its study using FRISK, a rapid phase contrast technique
Authors: Li Longchuan , Doyle Mark , Rayarao Geetha , Kortright Eduardo , Ito Yasushi , Anayiotos Andreas
Published: August 2007

Purpose

To test the potential of a phase contrast magnetic resonance (PC‐MR) sparse sampling technique, fragmented regional interpolation segmentation for k‐space (FRISK), to capture complex flow features within a breathhold duration by using numerical simulations and experimental approaches.

Materials and Methods

Computational fluid dynamics (CFD) data of three models were generated: a two‐chamber orifice flow model simulating valvular regurgitation, a femoral artery model, and a U‐shaped model simulating the aortic arch. These data were used to simulate conventional and FRISK PC‐MR data acquisitions. FRISK parameters can be adapted for different flow fields to capture either high temporal information or complexly varying spatial information with a temporal component or a mixture of both. In vivo PC‐MR images on a healthy volunteer were sampled to compare conventional PC‐MR with novel FRISK imaging.

Results

In our simulations of three representative models, when only the errors from different sampling sequences were considered, FRISK was shown to maintain or even improve data accuracy while cutting the scan time by at least 50% compared to corresponding conventional PC‐MR. By adapting the FRISK parameters for flowfields with different features, FRISK was capable of capturing in‐plane and through‐plane velocity information with excellent detail in approximately 20 heartbeats breathhold duration. The results of the in vivo MR experiment were consistent with the simulation results, showing that breathhold FRISK imaging improved spatial resolution of the data and maintained adequate temporal resolution compared with breathhold conventional imaging.

Conclusion

FRISK, a new MRI sampling sequence that sparsely samples data and aligns acquired data during postprocessing, provides a scan time advantage of approximately a factor of 2 compared to conventional scans, and allowed rapid or breathhold scanning while obtaining acceptable accuracy. J. Magn. Reson. Imaging 2007;26:805–815. © 2007 Wiley‐Liss, Inc.
The pyramidal tract has a predictable course through the centrum semiovale: A diffusion‐tensor based tractography study
Authors: Yamada Kei , Kizu Osamu , Kubota Takao , Ito Hirotoshi , Matsushima Shigenori , Oouchi Hiroyuki , Nishimura Tsunehiko
Published: August 2007

Purpose

To identify reproducible anatomical landmarks that would allow predicting the course of the pyramidal tract (PT) through centrum semiovale.

Materials and Methods

A total of 20 normal volunteers (12 males, eight females) with a mean age of 34 years (range, 20–59 years) were scanned using a 1.5‐Tesla clinical MR unit to assess the trajectory of the PT. Neuroanatomical characteristics of the PT passing through the centrum semiovale were assessed by two independent observers. Tractography data of 10 consecutive patients with brain tumor were used to test the precision of anatomy‐based prediction of the tract location.

Results

On sagittal view, 95% of the PT depicted on tractography displayed a completely straight or primarily straight course through the supratentorial brain. In 98% of tracts, the bending point of the PT was identified ≤3 mm from the level of the anterior commissure‐posterior commissure (AC‐PC) plane. In 80% of PT, the intersection with the AC‐PC plane occurred midway between the AC and the PC as seen on the sagittal view. Evaluation of the PT in 10 patients with brain tumor revealed that the anatomy‐based prediction of PT on the contralesional hemisphere was not substantially deviated from the actual tractography depicted PT. PT on the lesional hemispheres, however, had deviations of various degrees.

Conclusion

The course of the PT through supratentorial brain can be predicted based on easily identifiable landmarks. This anatomy‐based prediction can be clinically applied for cases without substantial mass effect from a space occupying lesion. J. Magn. Reson. Imaging 2007;26:519–524. © 2007 Wiley‐Liss, Inc.
Automated analysis of contrast enhancement in breast MRI lesions using mean shift clustering for ROI selection
Authors: Stoutjesdijk Mark J. , Veltman Jeroen , Huisman Henkjan , Karssemeijer Nico , Barentsz Jelle O. , Blickman Johan G. , Boetes Carla
Published: August 2007

Purpose

To evaluate a new method for automated determination of a region of interest (ROI) for the analysis of contrast enhancement in breast MRI.

Materials and Methods

Mean shift multidimensional clustering (MS‐MDC) was employed to divide 92 lesions into several spatially contiguous clusters each, based on multiple enhancement parameters. The ROIs were defined as the clusters with the highest probability of malignancy. The performance of enhancement analysis within these ROIs was estimated using the area under the receiver operator characteristic curve (AUC), and compared against a radiologist's final assessment and a classifier using histogram analysis (HA). For HA, the first, second, and third quartiles were evaluated.

Results

MS‐MDC resulted in AUC = 0.88 with a 95% confidence interval (CI) of 0.81–0.95. The AUC for the radiologist's assessment was 0.93 (95%CI = 0.87–0.97). Best HA performance was found using the first quartile, with AUC = 0.79 (95%CI = 0.69–0.88). There was no significant difference between MS‐MDC and the radiologist (P = 0.40). The improvement of MS‐MDC over HA was significant (P = 0.018).

Conclusion

Mean shift clustering followed by automated selection of the most suspicious cluster resulted in accurate ROIs in breast MRI lesions. J. Magn. Reson. Imaging 2007;26:606–614. © 2007 Wiley‐Liss, Inc.
Dynamic T1 mapping predicts outcome of chemoradiation therapy in primary rectal carcinoma: Sequence implementation and data analysis
Authors: Kremser Christian , Trieb Thomas , Rudisch Ansgar , Judmaier Werner , de Vries Alexander
Published: August 2007

Purpose

To describe details about the implementation of a dynamic T1‐mapping technique and a simple data analysis strategy that can be used to predict therapy outcome in primary rectal carcinoma and to investigate the physiologic meaning of the obtained parameter.

Materials and Methods

Contrast‐enhanced dynamic T1 mapping was achieved with a snapshot fast low‐angle shot (FLASH) T1 mapping sequence implemented on a 1.5T MR scanner. This method was applied to 58 patients with primary rectal cancer before onset of chemoradiation therapy. A simple data analysis strategy based on the calculation of the maximum slope of the tissue concentration–time curve divided by the maximum of the arterial input function (AIF) was used as a measure of tumor microcirculation (PI values).

Results

The snapshot FLASH (SFL) T1‐mapping technique is accurate and sensitive enough to detect inhomogeneous uptake kinetics within tumor tissue. Classifying the patients into two groups according to therapy response showed lower mean PI values for responders as compared to nonresponders. PI was found to combine information about permeability surface area product (PS) and blood volume.

Conclusions

The described method based on dynamic T1 mapping has the potential to be a clinical tool for predicting therapy outcome of preoperative chemoradiation in patients with primary rectal carcinoma. J. Magn. Reson. Imaging 2007;26:662–671. © 2007 Wiley‐Liss, Inc.
A new EPI‐based dynamic field mapping method: Application to retrospective geometrical distortion corrections
Authors: Lamberton Franck , Delcroix Nicolas , Grenier Denis , Mazoyer Bernard , Joliot Marc
Published: August 2007

Purpose

To retrospectively correct for geometrical distortions, a new dynamic field mapping method suitable for dynamic single‐shot gradient‐echo type echo‐planar imaging (GRE‐EPI) is proposed.

Materials and Methods

The method requires a single volume additional acquisition and allows the extraction of a field map from each phase volume, assuming invariance across time of the echo time‐independent phase component. Performances of the method are assessed using three sets of experiments: the first tests the prerequisite and the modeling; the second tests the method with time‐dependent geometrical distortions; and the third presents a comparison with two other methods.

Results

Our results legitimize the modeling procedure and demonstrate that the dynamic method is less sensitive to noise than the other methods. A theoretical explanation for this is proposed in the discussion section.

Conclusion

Given the minor increase in the acquisition time, this method is well suited for functional magnetic resonance imaging; prospective direction. J. Magn. Reson. Imaging 2007;26:747–755. © 2007 Wiley‐Liss, Inc.
Automated method for accurate abdominal fat quantification on water‐saturated magnetic resonance images
Authors: Peng Qi , McColl Roderick W. , Ding Yao , Wang Jihong , Chia Jonathan M. , Weatherall Paul T.
Published: August 2007

Purpose

To introduce and evaluate the performance of an automated fat quantification method for water‐saturated magnetic resonance images.

Materials and Methods

A fat distribution model is proposed for fat quantification on water saturated magnetic resonance images. Fat from both full‐ and partial‐volume voxels are accounted for in this model based on image intensity histogram analysis. An automated threshold method is therefore proposed to accurately quantify total fat. This method is compared to a traditional full‐volume‐fat‐only method in phantom and human studies. In the phantom study, fat quantification was performed on MR images obtained from a human abdomen oil phantom and was compared with the true oil volumes. In the human study, results of the two fat quantification methods of six subjects were compared on abdominal images with different spatial resolutions.

Results

In the phantom study, the proposed method provided significantly more accurate estimations of true oil volumes compared to the reference method (P < 0.0001). In human studies, fat quantification using the proposed method gave much more consistent results on images with different spatial resolutions, and on regions with different degrees of partial volume averaging.

Conclusion

The proposed automated method is simple, rapid, and accurate for fat quantification on water‐saturated MR images. J. Magn. Reson. Imaging 2007;26:738–746. © 2007 Wiley‐Liss, Inc.
Effects of signal‐to‐noise ratio on the accuracy and reproducibility of diffusion tensor imaging–derived fractional anisotropy, mean diffusivity, and principal eigenvector measurements at 1.5T
Authors: Farrell Jonathan A.D. , Landman Bennett A. , Jones Craig K. , Smith Seth A. , Prince Jerry L. , van Zijl Peter C.M. , Mori Susumu
Published: August 2007

Purpose

To develop an experimental protocol to calculate the precision and accuracy of fractional anisotropy (FA), mean diffusivity (MD), and the orientation of the principal eigenvector (PEV) as a function of the signal‐to‐noise ratio (SNR) in vivo.

Materials and Methods

A healthy male volunteer was scanned in three separate scanning sessions, yielding a total of 45 diffusion tensor imaging (DTI) scans. To provide FA, MD, and PEV as a function of SNR, sequential scans from a scan session were grouped into nonintersecting sets. Analysis of the accuracy and precision of the DTI‐derived contrasts was done in both a voxel‐wise and region of interest (ROI)‐based manner.

Results

An upward bias of FA and no significant bias in MD were present as SNR decreased, confirming results from simulation‐based studies. Notably, while the precision of the PEV became worse at low SNR, no bias in the PEV orientation was observed. Overall, an accurate and precise quantification of FA values in GM requires substantially more SNR than the quantification of white matter (WM) FA values

Conclusion

This study provides guidance for FA, MD, and PEV quantification and a means to investigate the minimal detectable differences within and across scan sessions as a function of SNR. J. Magn. Reson. Imaging 2007;26:756–767. © 2007 Wiley‐Liss, Inc.
Evaluation of a resistance‐based model for the quantification of pulmonary arterial hypertension using MR flow measurements
Authors: Abolmaali Nasreddin , Seitz Uwe , Esmaeili Anoosh , Kock Martin , Radeloff Daniel , Ackermann Hanns , Vogl Thomas J.
Published: August 2007

Purpose

To establish an estimate for the mean pulmonary arterial pressure (mPAP) derived from noninvasive data acquired with magnetic resonance (MR) velocity‐encoded sequences.

Materials and Methods

In seven sedated pigs synchronous catheter‐based invasive pressure measurements (IPM) and noninvasive MR were acquired in the main pulmonary artery (MPA) at different severities of pulmonary arterial hypertension (PAH) that were caused by infusion of thromboxane A2 (TxA2). The invasively measured mPAP was correlated with the noninvasive MR velocity data and linear combination equations (LCE) were computed.

Results

Intravenously applied TxA2 induced a dose dependent level of severity of PAH with an mPAP of up to 54 mmHg without systemic effects. The acceleration time (AT) measured with MR demonstrated the best correlation with the mPAP (r2 = 0.75). The LCE with the highest correlation (R = 0.945, α < 0.01) between IPM and MR revealed a mean difference of 0, a SD of s = 4.66 and a maximal difference of 12.2 mmHg using the Bland‐Altman analysis.

Conclusion

Applying the identified LCE allowed the estimation of the mPAP in an acute and resistance‐based model of PAH with high accuracy using noninvasive MR velocity‐encoded sequences. J. Magn. Reson. Imaging 2007;26:646–653. © 2007 Wiley‐Liss, Inc.
MRI measurements of tumor size and pharmacokinetic parameters as early predictors of response in breast cancer patients undergoing neoadjuvant anthracycline chemotherapy
Authors: Yu Hon J. , Chen Jeon‐Hor , Mehta Rita S. , Nalcioglu Orhan , Su Min‐Ying
Published: August 2007

Purpose

To investigate the value of using changes in three parameters (tumor size, transfer constant (Ktrans), and rate constant (kep)) obtained after the first treatment‐cycle in predicting the final clinical response after two to four cycles of neoadjuvant anthracycline and cyclophosphamide (AC) chemotherapy.

Materials and Methods

Early changes in the three parameters were measured in 29 patients with invasive breast cancer by MRI after one cycle of treatment. Changes were then assessed for their predictive value of final clinical response and compared among patients with four different response patterns, Group 1 = responder (R) after one cycle and also R after four cycles, Group 2 = nonresponder (NR) after one cycle, but eventual R after four cycles, Group 3 = NR after one cycle and still NR after four cycles, and Group 4 = NR after one cycle and determined as NR after two cycles, being switched to the taxane regimen.

Results

Pearson's correlation analysis revealed significant correlation between early changes in tumor size and both pharmacokinetic parameters (r = 0.49 and P < 0.01 for Ktrans, r = 0.66 and P < 0.001 for kep). The areas under the receiver operating characteristic (ROC) curve differentiating between R (Groups 1+2) and NR (Groups 3+4) groups using changes in tumor size, Ktrans, and kep were 0.88 (standard error [SE] = 0.06, P < 0.0001), 0.63 (SE = 0.11, P = 0.11), and 0.77 (SE = 0.09, P = 0.001), respectively.

Conclusion

Early tumor size change in MRI after one cycle is better response predictor than that of either Ktrans or kep in breast cancer undergoing neoadjuvant chemotherapy using an AC regimen. J. Magn. Reson. Imaging 2007;26:615–623. © 2007 Wiley‐Liss, Inc.
Age, gender, and skeletal variation in bone marrow composition: A preliminary study at 3.0Tesla
Authors: Liney Gary P. , Bernard Clare P. , Manton David J. , Turnbull Lindsay W. , Langton Chris M.
Published: August 2007

Purpose

To evaluate the efficacy of MR Spectroscopy (MRS) at 3.0 Tesla for the assessment of normal bone marrow composition and assess the variation in terms of age, gender, and skeletal site.

Materials and Methods

A total of 16 normal subjects (aged between eight and 57 years) were investigated on a 3.0 Tesla GE Signa system. To investigate axial and peripheral skeleton differences, non‐water‐suppressed spectra were acquired from single voxels in the calcaneus and lumbar spine. In addition, spectra were acquired at multiple vertebral bodies to assess variation within the lumbar spine. Data was also correlated with bone mineral density (BMD) measured in six subjects using dual‐energy X‐ray absorptiometry (DXA).

Results

Fat content was an order of magnitude greater in the heel compared to the spine. An age‐related increase was demonstrated in the spine with values greater in men compared to female subjects. Significant trends in vertebral bodies within the same subjects were also shown, with fat content increasing L5 > L1. Population coefficient of variation (CV) was greater for fat fraction (FF) compared to BMD.

Conclusion

Significant normal variations of marrow composition have been demonstrated, which provide important data for the future interpretation of patient investigations. J. Magn. Reson. Imaging 2007;26:787–793. © 2007 Wiley‐Liss, Inc.
Study of ulnar variance with high‐resolution MRI: Correlation with triangular fibrocartilage complex and cartilage of ulnar side of wrist
Authors: Yoshioka Hiroshi , Tanaka Toshikazu , Ueno Teruko , Carrino John A. , Winalski Carl S. , Aliabadi Piran , Lang Philipp , Weissman Barbara N.
Published: August 2007

Purpose

To investigate correlations with ulnar variance and the triangular fibrocartilage complex (TFCC) or cartilage of ulnar side of the wrist on high‐resolution MRI with a microscopy coil.

Materials and Methods

We reviewed ulnar variance, TFCC, and cartilage of the ulnar side of the wrist in 93 subjects (29 asymptomatic volunteers and 64 patients with suspected TFCC injury) with high‐resolution MRI using a 47‐mm microscopy surface coil. All MR images were obtained with a 1.5 T scanner. Coronal 2D gradient recalled echo T2*‐weighted images were used for analysis. For qualitative analysis we measured ulnar variance, TFCC angle, thickness in the central portion of TFCC disc proper, and cartilage thickness of the lunate and the ulnar head on MRI and calculated the correlation coefficient between measured values. We also examined the relationship between ulnar variance and age or sex.

Results

High‐resolution MR images clearly demonstrated TFCC and cartilage of the wrist and ulnar variance. The mean ulnar variance on MRI was +0.26 mm (range, −4.59 to +3.71 mm). The mean TFCC angle and TFCC thickness were 23.9° (range, −4.6 to +54.1°) and 1.11 mm (range, 0.4 to 3.22 mm), respectively. Ulnar variance and TFCC angle were positively correlated (r = 0.84), and ulnar variance and TFCC thickness were negatively correlated (r = −0.71). However, ulnar variance and lunate or ulnar head cartilage thickness were not significantly correlated.

Conclusion

High‐resolution MRI with a microscopy coil is a useful tool for evaluating the relationship between ulnar variance and ulnar side structures. J. Magn. Reson. Imaging 2007;26:714–719. © 2007 Wiley‐Liss, Inc.
Astrocytes enhance long‐term survival of cholinergic neurons differentiated from human fetal neural stem cells
Authors: Jordan Paivi M. , Cain Lisa D. , Wu Ping
Published: August 2007

Establishment of an in vitro model of human cholinergic neurons would be highly desirable for understanding and developing treatment for Alzheimer's and motoneuron diseases. Previously we reported that the combination of basic fibroblast growth factor (bFGF), heparin, and laminin directs human fetal neural stem cells to form cholinergic neurons. One problem, however, is that long‐term in vitro survival of these cells is low. Our goal for this study was to determine whether astrocytes or their secreted factors enhance differentiation and survival of cholinergic neurons under long‐term differentiation conditions. We demonstrate here that astrocytes or astrocyte conditioned media did not enhance cholinergic differentiation but did increase the long‐term survival of differentiated human neural stem cells, particularly cholinergic neurons. We further show that astrocytes protected long‐term‐differentiated cells from apoptotic cell death, which is at least partially mediated by astrocyte‐secreted bFGF. Our findings indicate that long‐term survival of human stem cell‐derived cholinergic neurons requires trophic factors from nonneuronal cells. This data may provide insights into the development of an in vitro model of long‐term cultured human cholinergic neurons useful for understanding of the mechanisms of cholinergic differentiation and developing treatments for neurological diseases. © 2007 Wiley‐Liss, Inc.
Effects of heat stimulation via microwave applicator on cartilage matrix gene and HSP70 expression in the rabbit knee joint
Authors: Tonomura Hitoshi , Takahashi Kenji A. , Mazda Osam , Arai Yuji , Shin‐Ya Masaharu , Inoue Atsuo , Honjo Kuniaki , Hojo Tatsuya , Imanishi Jiro , Kubo Toshikazu
Published: August 2007

The objective of this study was to investigate the effects of heat stimulation on the expression of extracellular matrix genes and heat‐shock protein 70 (HSP70) in rabbit articular cartilage in vivo. Heat stimulation was applied to the knee joints of Japanese white rabbits for 20 min using a microwave (MW) applicator (2.45‐GHz, 0–80 W). After 8–72 h, the articular cartilage was removed from the knee joints and proteins and total RNA were extracted. As controls, knee joints without heat stimulation were analyzed. The expression of HSP70 was confirmed by real‐time PCR and Western blotting. The expression of proteoglycan core protein (PG) and type II collagen (Col II) was quantified using real‐time PCR to assess cartilage matrix metabolism. Compared to controls, HSP70 expression was higher with more than 40 W of heat stimulation. The expression of PG and Col II mRNA was higher, with more than 20 W of heat stimulation and peaked with 40 W. When quercetin was used to inhibit the induction of HSP70 expression, PG mRNA expression did not increase. External MW application stimulated HSP70 expression in the articular cartilage in vivo. The expression of extracellular matrix genes was increased by appropriate heat stimulation. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:34–41, 2008
Use of a bioscaffold to improve healing of a patellar tendon defect after graft harvest for ACL reconstruction: A study in rabbits
Authors: Karaoglu Sinan , B. Fisher Matthew , Woo Savio L‐Y. , Fu Yin‐Chih , Liang Rui , Abramowitch Steven D.
Published: August 2007

Following harvest of a bone‐patellar tendon‐bone (BPTB) autograft, the central third of the patellar tendon (PT) does not heal well. The healing tissues also form adhesions to the fat pad and can cause abnormal patellofemoral joint motion. The hypotheses were that a bioscaffold could enhance patellar tendon healing through contact guidance and chemotaxis, and the scaffold could serve as a barrier to decrease adhesion formation between the neo‐PT and infrapatellar fat pad. In 20 New Zealand White rabbits, a central‐third PT defect was created. One strip of porcine small intestinal submucosa (SIS) was attached to both the anterior and posterior sides of the PT defect of the SIS‐treated group (n = 10). For comparison, a central defect was left nontreated (n = 10). At 12 weeks, histomorphology was examined using Masson's trichrome staining. The cross‐sectional area (CSA) was determined with a laser micrometer, and the central BPTB complexes were tested in uniaxial tension. SIS‐treated samples showed a greater amount of healing tissue with denser and well‐oriented collagen fibers and more spindle‐shaped cells. There was no noticeable adhesion formation in the SIS‐treated group. For the nontreated group, there were significantly more and diffuse adhesive formations. The SIS‐treated group also had a 68% increase in neo‐PT CSA, 98% higher stiffness, and 113% higher ultimate load than that in the nontreated group. SIS treatment increased the quantity of healing tissue, improved the histological appearance and biomechanical properties of the neo‐PT, and prevented adhesion formation between the PT and fat pad. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:255–263, 2008
Empirical relationships for soil organic carbon transport from agricultural watersheds in Ohio
Authors: Starr G. C. , Lal R. , Owens L. , Kimble J.
Published: August 2007

Improved quantification is needed for long‐term soil organic carbon (SOC) transport in runoff at watershed scales. Coshocton wheel samplers were used to collect runoff samples from no‐till and chisel‐till watersheds in corn (Zea mays) and soybean (Glycine max) rotations over 13 years. Samples were analyzed for SOC, N, P, K, and soil losses. The SOC losses, ranging from 0 to 357 kg ha−1 event−1, were correlated (r2 = 0·80–0·94) in power law relationships with N, P, K, soil loss, and runoff. Two events occurring in corn when soybean and cover crop residue were present in no‐till had combined SOC transport of 460 kg ha−1, nearly double the no‐till losses of a previous 11‐year period and 20 times higher than chisel‐till in the same events. Infrequent, extreme transport events that are not well characterized empirically, particularly in no‐till, can strongly influence hydrologic C transport from agriculture watersheds. Copyright © 2007 John Wiley & Sons, Ltd.
Faserverstärkte oxidkeramische Werkstoffe
Authors: Schmücker M.
Published: August 2007

Oxidkeramische Werkstoffe zeichnen sich durch hohe thermische und chemische Stabilität aus. Ein quasiduktiles Verformungsverhalten lässt sich durch den Einbau von hochfesten keramischen Langfasern erzielen. Voraussetzung für das quasiduktile, schadenstolerante Deformationsverhalten ist eine relativ schwache Faser/Matrix‐Bindung, damit Mechanismen wie Rissumleitung, Rissverzweigung oder Faser‐„Pull‐out”︁ greifen können. Die Bindung zwischen Fasern und Matrix lässt sich durch geeignete Faserbeschichtungen gezielt einstellen; in einem alternativen Konzept wird jedoch auf die Faserbeschichtung verzichtet und eine hochporöse Matrix eingesetzt. Oxidkeramische Faserverbundwerkstoffe mit hoher Matrixporosität zeigen bemerkenswerte mechanische Eigenschaften; gleichzeitig ist die Herstellung der Keramikverbunde verhältnismäßig einfach und preiswert. WHIPOX ist ein faserverstärkter oxidkeramischer Verbundwerkstoff mit poröser Matrix, der im Deutschen Zentrum für Luft‐ und Raumfahrt entwickelt wurde. Herstellung, Mikrostruktur und Eigenschaften von WHIPOX werden vorgestellt.
An integrated solution for NOx‐reduction and ‐control under lean‐burn conditions
Authors: Saruhan B. , Stranzenbach M. , Mondragón Rodríguez G. C.
Published: August 2007

Upcoming emission regulations order highly effective NOx‐reduction systems in lean‐burn engines requiring new catalytic materials and integrated control of the reduction process. Thus, new approaches for NOx‐reduction and its monitoring over an On‐Board‐Diagnostic (OBD) system are suggested throughout the globe. A promising attempt is the development of a catalytic system having an integrated NOx‐sensor, based on selective catalytic reduction process and impedance sensors. The study displays the results achieved both with a perovskite type of self‐regenerative catalyst functioning by H2‐reductant and with impedance NOx‐sensors. The catalysts were tested at the temperature range of 150 °C to 360 °C yielding NOx conversion rates of 92 % with high selectivity to N2. Impedance sensors having NiCr2O4‐ and NiO‐SE and PYSZ‐ and FYSZ‐electrolytes are developed and tested at 600 °C under lean atmosphere (5 vol. % O2). Better sensing behaviour towards NO and lower cross‐selectivity towards O2, CO, CO2 and CH4 have been observed with sensors having NiO‐SE.
Vorhersagemodell für die Wachstumsraten kurzer Risse auf der Basis von Kmax‐konstant‐Versuchen an M(T)‐Proben
Authors: Tesch A. , Pippan R. , Trautmann K.‐H. , Döker H.
Published: August 2007

Das Ermüdungsrisswachstumsverhalten von kurzen Rissen in den Aluminiumlegierungen Al 6013‐T6 und Al 2524‐T351 wurde untersucht. Ziel war es die Ermüdungsrisswachstumsraten von kurzen Eckrissen bei Spannungsverhältnissen von R = 0,1, R = 0,7 und R = 0,8 zu bestimmen und einen Weg zu finden, diese Wachstumsraten auf der Grundlage von Ermüdungsrisswachstumskurven von langen Rissen vorherzusagen. In Kurzrissproben, ähnlich M(T)‐Proben, wurden an einer Seite einer Bohrung (Ø = 4,8 mm) durch zyklische Druckbelastungen (R = 20) Eckrisse eingebracht. Kerbe und Anrisse zusammen waren kleiner als 100 μm. Unter anderen Methoden wurde eine komplett neue Methode, ein fokussierter Ionenstrahl, verwendet, um die sehr kleinen Kerben (10 μm – 50 μm) in die Proben zu schneiden. Die Ergebnisse aus den Ermüdungsrisswachstumsversuchen mit den Kurzrissproben wurden mit Ermüdungsrisswachstumsdaten von Proben mit langen Rissen verglichen. Die kurzen Risse zeigten Rissfortschritt bei ΔK‐Werten unterhalb der Schwellenwerte für lange Risse beim gleichen Spannungsverhältnis. Sie wuchsen außerdem schneller als lange Risse bei den gleichen ΔK‐Werten und Spannungsverhältnissen. Ein Modell auf Basis von Kmax‐konstant‐Versuchen wurde entwickelt, mit welchem eine gute und konservative Vorhersage der Kurzrisswachstumsraten möglich ist.
Thermal conductivity issues of EB‐PVD thermal barrier coatings
Authors: Schulz U. , Rätzer‐Scheibe H.‐J. , Saruhan B. , Renteria A. F.
Published: August 2007

The thermal conductivity of electron‐beam physical vapor deposited (EB‐PVD) thermal barrier coatings (TBCs) was investigated by the Laser Flash technique. Sample type and methodology of data analyses as well as atmosphere during the measurement have some influence on the data. A large variation of the thermal conductivity was found by changes in TBC microstructure. Exposure at high temperature caused sintering of the porous microstructure that finally increased thermal conductivity up to 30 %. EB‐PVD TBCs show a distinct thickness dependence of the thermal conductivity due to the anisotropic microstructure in thickness direction. Thin TBCs had a 20 % lower thermal conductivity than thick coatings. New compositions of the ceramic top layer offer the largest potential to lower thermal conductivity. Values down to 0.8W/(mK) have been already demonstrated with virgin coatings of pyrochlore compositions.
Verfahren zur vollständigen Ermittlung der R‐Abhängigkeit des Rissausbreitungsverhaltens mit nur einer Probe
Authors: Tesch A. , Pippan R. , Döker H.
Published: August 2007

Ein neues Prüfungskonzept für Ermüdungsrisswachstumsversuche ermöglicht es mit nur einer Probe für den gesamten Bereich des Spannungsverhältnisses von R = 0,9 bis R = ‐1 Ermüdungsrisswachstumskurven (da/dN‐ΔK‐Kurven) für jedes beliebige R‐Verhältnis zu erstellen. Zusätzlich erhält man auch die Schwellenwerte der Spannungsintensitätsschwingbreite ΔKthals Funktion von R und Kmax. In Kombination mit einer Methode zur kontinuierlichen Risslängenbestimmung, wie der Gleichstrompotenzialmethode, erfordert dieses Verfahren sehr geringen Personal‐ und Zeitaufwand. Das Prüfungskonzept besteht aus einer Aneinanderreihung von Kmax‐konstant‐Versuchen. Da die Kmax‐Werte stufenweise ansteigen, sollte es bei diesem Verfahren keine Lastfolgeeffekte geben. Die ermittelten Daten stimmen sehr gut mit Ergebnissen aus da/dN‐ΔK‐Versuchen, die nach der ASTM Norm E 647 mit mehreren Proben durchgeführten wurden, überein. Die Versuche erfüllen alle Bedingungen der ASTM E 647.
WHIPOX®: Ein faserverstärkter oxidkeramischer Werkstoff für Hochtemperatur– Langzeitanwendungen
Authors: Göring J. , Hackemann S. , Kanka B.
Published: August 2007

Am Institut für Werkstoff‐Forschung des Deutschen Zentrums für Luft‐ und Raumfahrt (DLR) wurde der oxidkeramische Faserverbundwerkstoff WHIPOX® (Wound Highly Porous Oxide Ceramic Matrix Composite) bis zur Bauteilreife entwickelt. Neben den Anwendungen in Fluggasturbinen, Wiedereintrittsfahrzeugen und bei Flugkörpern, die in interdisziplinären Projekten im DLR bearbeitet werden, wurde das Material auch für den Einsatz in nicht‐luft‐ und raumfahrtspezifischen Anwendungen erfolgreich getestet. Die spezifische und einzigartige Eigenschaftskombination der faserverstärkten Oxidkeramik ermöglicht neue innovative Lösungsansätze bei Materialproblemen im Industrieofenbau, metallurgischen Anlagenbau, in der Filtertechnik, beim Brandschutz, bei Katalysatoren und Rußfiltern, in der Elektrotechnik und bei medizinischen Anwendungen. Im Bereich des Industrieofenbaus werden bereits Hochgeschwindigkeitsbrennerdüsen von einem Keramikhersteller in Lizenz gefertigt.
Control of thermoelectric properties in ZrO2/CoSb3 nano‐dispersed composites
Authors: Stiewe C. , He Z. , Platzek D. , Karpinski G. , Müller E. , Li S. , Toprak M. , Muhammed M.
Published: August 2007

Nano‐dispersed ZrO2/CoSb3 composites of various composition were prepared by uniaxial hot pressing of nano‐sized powders of thermoelectric CoSb3 intermixed with ceramic nano‐powders. The phase purity, the microstructure, and the temperature dependent transport parameters of the composites were investigated. Non‐dispersed samples from nano‐sized CoSb3 powders show higher electrical conductivity compared to melt‐grown material which is attributed to the presence of a small excess of metallic Sb, but they exhibit lower thermal conductivity due to the fine‐grained structure. Addition of 5 at.‐% ZrO2 enhances the ratio of electrical to thermal conductivity, whereas hardly affects the Seebeck coefficient. In this manner the nano‐dispersion method provides an effective approach to improving the material´s thermoelectric performance.
Multiaxial thermo‐mechanical fatigue on material systems for gas turbines
Authors: Bartsch M. , Baufeld B. , Heinzelmann M. , Karlsson A. M. , Dalkilic S. , Chernova L.
Published: August 2007

Material systems made from nickel based superalloys with protective coatings have been tested in thermo‐mechanical fatigue with superposed thermal gradients, which generated multiaxial stress states. The testing conditions were selected for simulating the fatigue loading in the wall of an internally cooled gas turbine blade of an aircraft engine. After thermo‐mechanical testing the damage behaviour of the materials has been investigated by means of microscopic methods. The laboratory experiments have been accompanied by numerical simulations. Based on the results of the simulations and observed damage features the test parameters in subsequent laboratory tests have been controlled to facilitate the validation of models describing the initiation and propagation of damages. This contribution gives an overview over results on the influence of multiaxial stress states on (i) oriented deformation and coagulation of γ’‐precipitates (‘rafting’) in the substrate, (ii) on morphological instabilities of the surface of metallic oxidation protection coatings (‘rumpling’), and (iii) on crack initiation and growth in material systems with additional ceramic thermal barrier coating.
Lifetime‐determining spalling mechanisms of NiCoCrAlRE / EB‐PVD zirconia TBC systems
Authors: Fritscher K. , Schulz U. , Leyens C.
Published: August 2007

The mechanisms that control the lifetime of thermal barrier coating (TBC) systems have been traced by two particular overlay bondcoats serving as model systems: superalloy pins (IN100, CMSX‐4) with two alternative NiCoCrAlRE (RE: Hf, Y) bond coat compositions (i) NiCoCrAlY without and (ii) with co‐dopants of silicon and hafnium. On top an electron‐beam physical‐vapor deposited (EB‐PVD) yttria partially stabilized zirconia (YPSZ) TBC commonly mixed with 2 wt.% hafnia, or, rarely with 10 wt.%, was applied. The test pins were thermo‐cycled at 1100 and 1150 °C until failure. Identical lifetimes in cyclic tests on YPSZ TBCs with 2 (relatively high sintering rate) and 10 wt.% hafnia (relatively low sintering rate) preclude an effect of diffusion mechanisms of the YPSZ TBC on lifetime. The fit of lifetimes and test temperatures to Arrhenius‐type relationships gives activation energies for failure. These energies agree with the activation energies for anion and cation diffusion in alumina for the respective bondcoat variant:

(i) for the NiCoCrAlY/TBC system for O2‐ diffusion in alumina,

(ii) for the NiCoCrAlYSiHf/TBC system for Al3+ diffusion in alumina.

SEM and EDS investigations of the thermally grown oxides (TGOs) confirm the mechanisms responsible for TBC failure as indicated by activation energies. Two categories of failure can be distinguished: (i) NiCoCrAlY coatings fail by an “adhesive mode of failure” along smooth bond coat/TGO interfaces driven by a critical TGO thickness. (ii) NiCoCrAlYSiHf coatings fail later and more reluctantly by a “cohesive” crack mode via de‐cohesion at the TGO/TBC interface. In the latter case a quasi‐integrity of the crack‐affected TGO is lengthily maintained up to failure by a crack‐pinning mechanism which runs via Al3+ supply from the bondcoat.
Joint design of trajectory and RF pulses for parallel excitation
Authors: Yip Chun‐Yu , Grissom William A. , Fessler Jeffrey A. , Noll Douglas C.
Published: August 2007

We propose an alternating optimization framework for the joint design of excitation k‐space trajectory and RF pulses for small‐tip‐angle parallel excitation. Using Bloch simulations, we show that compared with conventional designs with predetermined trajectories, joint designs can often excite target patterns with improved accuracy and reduced total integrated pulse power, particularly at high reduction factors. These benefits come at a modest increase in computational time. Magn Reson Med 58:598–604, 2007. © 2007 Wiley‐Liss, Inc.
Regularized, fast, and robust analytical Q‐ball imaging
Authors: Descoteaux Maxime , Angelino Elaine , Fitzgibbons Shaun , Deriche Rachid
Published: August 2007

We propose a regularized, fast, and robust analytical solution for the Q‐ball imaging (QBI) reconstruction of the orientation distribution function (ODF) together with its detailed validation and a discussion on its benefits over the state‐of‐the‐art. Our analytical solution is achieved by modeling the raw high angular resolution diffusion imaging signal with a spherical harmonic basis that incorporates a regularization term based on the Laplace–Beltrami operator defined on the unit sphere. This leads to an elegant mathematical simplification of the Funk–Radon transform which approximates the ODF. We prove a new corollary of the Funk–Hecke theorem to obtain this simplification. Then, we show that the Laplace–Beltrami regularization is theoretically and practically better than Tikhonov regularization. At the cost of slightly reducing angular resolution, the Laplace–Beltrami regularization reduces ODF estimation errors and improves fiber detection while reducing angular error in the ODF maxima detected. Finally, a careful quantitative validation is performed against ground truth from synthetic data and against real data from a biological phantom and a human brain dataset. We show that our technique is also able to recover known fiber crossings in the human brain and provides the practical advantage of being up to 15 times faster than original numerical QBI method. Magn Reson Med 58:497–510, 2007. © 2007 Wiley‐Liss, Inc.
Dynamic water changes in excised rat myocardium assessed by continuous distribution of T1 and T2
Authors: Bruvold Morten , Seland John Georg , Brurok Heidi , Jynge Per
Published: August 2007

Ischemic changes in excised rat myocardium were followed by series of T1 or T2 measurements from 1 to 60 min after isolated perfusion cessation, and the influence of manganese enhancement was investigated. An inverse Laplace transformation (ILT) of T1 or T2 data was used to resolve the number, time constants, and fractions of tissue water components in a continuous distribution. For T1 distributions, one single tissue component ∼900 ms was significantly shortened and dispersed by manganese enhancement (25 and 200 μM MnCl2). For T2 distributions, three tissue components (∼30, ∼100, and ∼350 ms) were obtained initially. The two shortest components merged after ∼10 min to one component (∼40 ms). Both T1 and T2 tissue components became shorter with time. In particular, the T2 distribution dynamics might be compatible with complex sequential changes in tissue water fractions during ischemia. Magn Reson Med 58:442–447, 2007. © 2007 Wiley‐Liss, Inc.
Volumetric texture analysis of breast lesions on contrast‐enhanced magnetic resonance images
Authors: Chen Weijie , Giger Maryellen L. , Li Hui , Bick Ulrich , Newstead Gillian M.
Published: August 2007

Automated image analysis aims to extract relevant information from contrast‐enhanced magnetic resonance images (CE‐MRI) of the breast and improve the accuracy and consistency of image interpretation. In this work, we extend the traditional 2D gray‐level co‐occurrence matrix (GLCM) method to investigate a volumetric texture analysis approach and apply it for the characterization of breast MR lesions. Our database of breast MR images was obtained using a T1‐weighted 3D spoiled gradient echo sequence and consists of 121 biopsy‐proven lesions (77 malignant and 44 benign). A fuzzy c‐means clustering (FCM) based method is employed to automatically segment 3D breast lesions on CE‐MR images. For each 3D lesion, a nondirectional GLCM is then computed on the first postcontrast frame by summing 13 directional GLCMs. Texture features are extracted from the nondirectional GLCMs and the performance of each texture feature in the task of distinguishing between malignant and benign breast lesions is assessed by receiver operating characteristics (ROC) analysis. Our results show that the classification performance of volumetric texture features is significantly better than that based on 2D analysis. Our investigations of the effects of various of parameters on the diagnostic accuracy provided means for the optimal use of the approach. Magn Reson Med 58:562–571, 2007. © 2007 Wiley‐Liss, Inc.
Pharmacokinetic modeling of dynamic contrast‐enhanced MRI of the hand and wrist in rheumatoid arthritis and the response to anti‐tumor necrosis factor‐α therapy
Authors: Hodgson Richard J. , Connolly Sylvia , Barnes Theresa , Eyes Brian , Campbell Robert S.D. , Moots Robert
Published: August 2007

Dynamic contrast‐enhanced MRI (DCE‐MRI) of the hand and wrist was performed in 11 patients with rheumatoid arthritis twice before and once 2 weeks after treatment with anti–tumor necrosis factor (TNF)‐α therapy. A rapid, T1‐weighted 3D spoiled gradient echo (SPGR) sequence was used for the dynamic imaging. T1 estimation was performed using similar images obtained at different flip angles. The relative radiofrequency field was estimated from the known T1 of the periarticular fatty marrow. The arterial input function (AIF) was measured at each examination, and normalized to the expected plasma concentration to reduce partial volume effects. Synovial enhancement was modeled to yield values for Ktrans, ve, and vp. Ktrans and ve showed good reproducibility. There was a significant decrease of about 20% in Ktrans after 2 weeks of treatment. This study demonstrates the potential of DCE‐MRI and pharmacokinetic modeling to study early changes in inflammatory activity in rheumatoid arthritis following treatment. Magn Reson Med 58:482–489, 2007. © 2007 Wiley‐Liss, Inc.