bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractMaterial 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

AbstractThe 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

AbstractWe 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

AbstractWe 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

AbstractIschemic 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

AbstractAutomated 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

AbstractDynamic 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.
Organ‐specific effects of oxygen and carbogen gas inhalation on tissue longitudinal relaxation times
Authors: O'Connor James P.B. , Jackson Alan , Buonaccorsi Giovanni A. , Buckley David L. , Roberts Caleb , Watson Yvonne , Cheung Sue , McGrath Deirdre M. , Naish Josephine H. , Rose Chris J. , Dark Paul M. , Jayson Gordon C. , Parker Geoff J.M. 
Published: August 2007

AbstractMolecular oxygen has been previously shown to shorten longitudinal relaxation time (T1) in the spleen and renal cortex, but not in the liver or fat. In this study, the magnitude and temporal evolution of this effect were investigated. Medical air, oxygen, and carbogen (95% oxygen/5% CO2) were administered sequentially in 16 healthy volunteers. T1 maps were acquired using spoiled gradient echo sequences (TR = 3.5 ms, TE = 0.9 ms, α = 2°/8°/17°) with six acquisitions on air, 12 on oxygen, 12 on carbogen, and six to 12 back on air. Mean T1 values and change in relaxation rate were compared between each phase of gas inhalation in the liver, spleen, skeletal muscle, renal cortex, and fat by one‐way analysis of variance. Oxygen‐induced T1‐shortening occurred in the liver in fasted subjects (P < 0.001) but not in non‐fasted subjects (P = 0.244). T1‐shortening in spleen and renal cortex (both P < 0.001) were greater than previously reported. Carbogen induced conflicting responses in different organs, suggesting a complex relationship with organ vasculature. Shortening of tissue T1 by oxygen is more pronounced and more complex than previously recognized. The effect may be useful as a biomarker of arterial flow and oxygen delivery to vascular beds. Magn Reson Med 58:490–496, 2007. © 2007 Wiley‐Liss, Inc.
New algorithm for quantifying vascular changes in dynamic contrast‐enhanced MRI independent of absolute T1 values
Authors: Haacke E. Mark , Filleti Cristina L. , Gattu Ramtilak , Ciulla Carlo , Al‐Bashir Areen , Suryanarayanan Krithivasan , Li Meng , Latif Zahid , DelProposto Zach , Sehgal Vivek , Li Tao , Torquato Vidya , Kanaparti Rajesh , Jiang Jing , Neelavalli Jaladhar 
Published: August 2007

AbstractIn this work, we present a new method for predicting changes in tumor vascularity using only one flip angle in dynamic contrast‐enhanced (DCE) imaging. The usual DCE approach finds the tissue initial T1 value T1(0) prior to injection of a contrast agent. We propose finding changes in the tissue contrast agent uptake characteristics pre‐ and postdrug treatment by fixing T1(0). Using both simulations and imaging pre‐ and postadministration of caffeine, we find that the relative change (NR50) in the median of the cumulative distribution (R50) is almost independent of T1(0). Fixing T1(0) leads to a concentration curve c(t) more robust to the presence of noise than calculating T1(0). Consequently, the NR50 for the tumor remains roughly the same as the ideal NR50 when T1(0) is exactly known. Further, variations in eating habits are shown to create significant changes in the R50 response for both liver and muscle. In conclusion, analyzing data with fixed T1(0) leads to a more stable measure of changes in NR50 and does not require knowledge of T1(0). Both caffeine and eating introduce major changes in blood flow that can significantly modify the NR50 and lead to incorrect conclusions regarding drug treatment. Magn Reson Med 58:463–472, 2007. © 2007 Wiley‐Liss, Inc.
Parallel image reconstruction using B‐spline approximation (PROBER)
Authors: Petr Jan , Kybic Jan , Bock Michael , Müller Sven , Hlaváč Václav 
Published: August 2007

AbstractA new reconstruction method for parallel MRI called PROBER is proposed. The method PROBER works in an image domain similar to methods based on Sensitivity Encoding (SENSE). However, unlike SENSE, which first estimates the spatial sensitivity maps, PROBER approximates the reconstruction coefficients directly by B‐splines. Also, B‐spline coefficients are estimated at once in order to minimize the reconstruction error instead of estimating the reconstruction in each pixel independently (as in SENSE). This makes the method robust to noise in reference images. No presmoothing of reference images is necessary. The number of estimated parameters is reduced, which speeds up the estimation process. PROBER was tested on simulated, phantom, and in vivo data. The results are compared with commercial implementations of the algorithms SENSE and GRAPPA (Generalized Autocalibrating Partially Parallel Acquisitions) in terms of elapsed time and reconstruction quality. The experiments showed that PROBER is faster than GRAPPA and SENSE for images wider than 150 × 150 pixels for comparable reconstruction quality. With more basis functions, PROBER outperforms both SENSE and GRAPPA in reconstruction quality at the cost of slightly increased computational time. Magn Reson Med 58:582–591, 2007. © 2007 Wiley‐Liss, Inc.
Fluctuations in tumor blood perfusion assessed by dynamic contrast‐enhanced MRI
Authors: Brurberg Kjetil G. , Benjaminsen Ilana C. , Dørum Liv M.R. , Rofstad Einar K. 
Published: August 2007

AbstractTemporal heterogeneity in blood perfusion is a common phenomenon in tumors, but data characterizing the nature of the blood flow fluctuations are sparse. This study investigated the occurrence of blood flow fluctuations in A‐07 melanoma xenografts by using gadopentetate dimeglumine (Gd‐DTPA)‐based dynamic contrast‐enhanced MRI (DCE‐MRI). Each tumor was subjected to two DCE‐MRI acquisitions separated by 1 hour. The data were processed by Kety analysis and resulted in two E · F images (E is the initial extraction fraction of Gd‐DTPA and F is the perfusion) and two λ images (λ is the partition coefficient of Gd‐DTPA) for each tumor. The E · F images were used to determine the changes in blood perfusion arising in the time between the two imaging sequences. The λ images were used to control the reproducibility of the experimental procedure. The study showed that DCE‐MRI with subsequent Kety analysis is a useful method for detection of blood flow fluctuations in A‐07 tumors, and strongly suggested that the peripheral regions of A‐07 tumors are more exposed to temporal changes in blood perfusion than are the central regions. Magn Reson Med 58:473–481, 2007. © 2007 Wiley‐Liss, Inc.
Critical illness myopathy: Further evidence from muscle‐fiber excitability studies of an acquired channelopathy
Authors: Allen David C. , Arunachalam Ramamurthy , Mills Kerry R. 
Published: August 2007

AbstractRecent studies have demonstrated acquired muscle inexcitability in critical illness myopathy (CIM) and have used direct muscle stimulation (DMS) techniques to distinguish neuropathy from myopathy as a cause of weakness in the critically ill. The mechanisms underlying weakness in CIM are incompletely understood and DMS is only semiquantitative. We report results from a series of 32 patients with CIM and demonstrate significant slowing of muscle‐fiber conduction velocity (MFCV) and muscle‐fiber conduction block during the acute phase of CIM, which correlates with prolonged compound muscle action potential (CMAP) duration, clinical severity, and course. We also used a paired stimulation technique to explore the excitability of individual muscle fibers in vivo. We demonstrate altered muscle‐fiber excitability in CIM patients. Serial studies help define the course of these pathophysiological changes. Parallels are made between CIM and hypokalemic periodic paralysis. Our findings provide further evidence for muscle membrane dysfunction being the principal underlying abnormality in CIM. Muscle Nerve, 2007
Reduced Shh expression in TFF2‐overexpressing lesions of the gastric fundus under hypochlorhydric conditions
Authors: Minegishi Y , Suzuki H , Arakawa M , Fukushima Y , Masaoka T , Ishikawa T , Wright NA , Hibi T 
Published: August 2007

AbstractExpression of sonic hedgehog (Shh), a morphogen for the gastric fundic glands, is reduced in the atrophic mucosa that develops in association with Helicobacter pylori infection, resulting in impaired differentiation of the fundic gland cells, increased expression of trefoil factor family 2 (TFF2) and the formation of spasmolytic polypeptide (SP)‐expressing metaplasia (SPEM), a preneoplastic lesion. However, it is still unresolved whether H. pylori‐induced inflammation and the resultant reduction in parietal cell number or reduced parietal cell function per se reduces Shh expression. The present study was designed to clarify the expression of Shh and TFF2 in the context of parietal cell dysfunction in the absence of inflammation, using histamine H2 receptor‐knockout (H2R‐null) mice and an acid exposure model. Age‐matched H2R‐null mice and wild‐type (WT) mice were used. The expression of Shh and TFF2 mRNA was quantified by quantitative RT‐PCR. Immunohistochemistry was also performed to detect the expression of Shh, TFF2 and cell markers. To study the effects of acid exposure, HCl solution was administered to the animals. The H2R‐null mice exhibited higher gastric pH, increased TFF2 expression and reduced Shh expression. Impaired mucous neck‐to‐zymogenic cell differentiation was observed in the H2R‐null mice. Furthermore, Shh expression increased in the presence of gastric acid and showed a significant correlation with gastric surface pH. In conclusion, our results suggest that persistent parietal cell dysfunction alone (suppressed gastric acid secretion), in the absence of inflammation or parietal cell loss caused by H. pylori infection, may be sufficient to down‐regulate Shh expression in TFF2‐overexpressing preneoplastic lesions of the gastric fundus. Since exposure to acid restored fundic Shh expression, appropriate gastric acid secretion may play an important role in the morphogen dynamics involved in the maintenance of gastric fundic gland homeostasis. Copyright © 2007 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
Prognostic significance of myeloperoxidase expression in childhood acute myeloid leukemia
Authors: Roberson Jessica R. , Onciu Mihaela , Pounds Stanley , Rubnitz Jeffrey E. , Pui Ching‐Hon , Razzouk Bassem I. 
Published: August 2007

AbstractBackgroundThe percentage of myeloperoxidase (MPO)‐positive blast cells is associated with prognosis in adult acute myeloid leukemia (AML), but this association is unsubstantiated in pediatric AML.ProcedureWe retrospectively compared cytochemical MPO results with outcome in 154 patients younger than 21 years treated on three consecutive institutional protocols for newly diagnosed AML (1987–2001). Patients with FAB M0 and M7 AML (no MPO expression) or M3 AML (100% MPO expression) and Down's syndrome were excluded.ResultsMedian MPO expression was higher in FAB M2 subtype than in other subtypes (P < 0.0001) and differed significantly across cytogenetic risk groups (P = 0.002) with highest MPO expression among those with favorable karyotypes. The percentage of MPO‐positive blasts was not significantly associated with the probability of complete remission (P = 0.97), event‐free survival (P = 0.72), or survival (P = 0.76) in multivariate analyses that accounted for age, FAB subtype, presenting WBC count, cytogenetic and protocol treatment risk group. In analysis limited to patients with intermediate‐risk cytogenetics, higher MPO expression appeared to be associated with improved EFS (P = 0.06) but was not associated with remission induction rate (P = 0.16) or overall survival (P = 0.38).ConclusionsThe percentage of MPO‐positive blast cells is related to FAB subtype in pediatric AML but has limited prognostic relevance. Pediatr Blood Cancer 2008;50:542–548. © 2007 Wiley‐Liss, Inc.
Failure to lactate: A possible late effect of cranial radiation
Authors: Johnston Karen , Vowels Marcus , Carroll Susan , Neville Kristen , Cohn Richard 
Published: August 2007

AbstractWe conducted a retrospective review of the lactation experience of female survivors who received 24 Gy cranial radiotherapy as CNS prophylaxis for acute lymphoblastic leukemia in childhood prior to 1982 and who attend the Long‐Term Follow‐Up Clinic at Sydney Children's Hospital, Randwick, Australia. Median time since diagnosis is 28 years (range 25–37 years). Twelve have produced offspring. Ten report minimal or no breast changes during pregnancy and failure to lactate postpartum. All patients remain in remission. These data suggest a high risk of failure of lactation in women treated during childhood with 24 Gy cranial irradiation. Awareness of this possibility can assist in counseling. Pediatr Blood Cancer 2008;50:721–722. © 2007 Wiley‐Liss, Inc.
Clinical and laboratorial prediction of bone marrow involvement in children and adolescents with Hodgkin Lymphoma
Authors: Barros Mário Henrique M. , Zalcberg Ilana R. , Hassan Rocio 
Published: August 2007

AbstractBackgroundA risk group (RG) system to predict bone marrow involvement (BMI) based on clinical and laboratory parameters was previously shown to have prognostic value in adult patients with Hodgkin lymphoma (HL). Our aim was to test the applicability of BMI RG in an independent group of childhood and adolescent HL patients.ProcedureSeventy‐eight HL patients (range 3–18, median 14 years old) were retrospectively studied, including revision of histopathological diagnosis and bilateral BM biopsies. Patients were divided into BMI high‐, standard‐ and low‐RG.ResultsThe high‐RG included 29.5% of the patients, the standard‐RG, 32%, and the low‐RG, 38.5%. All the patients in the high‐RG had stage III or IV. The five children (6.4%) with BMI were included in the high‐RG (P = 0.001, χ2 test) and had stage IV (P < 0.00001, χ2 test). The BMI risk group out‐performed the clinico‐pathologic risk assessment in predicting BMI, showing 100% sensitivity, 75% specificity and a positive predictive value of 0.88. Neither BMI nor risk of BMI was statistically associated to age groups (≤14 years old or >14 years old), suggesting that age is not a risk factor for BMI in the pediatric population.ConclusionsThe application of BMI RG score was able to efficiently foresee BMI in a pediatric group of HL patients, adding independent information to clinico‐pathologic BMI risk assessment. Pediatr Blood Cancer 2008;50:765–768. © 2007 Wiley‐Liss, Inc.