bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparison of 1H blood oxygen level–dependent (BOLD) and 19F MRI to investigate tumor oxygenation
Authors: Zhao Dawen , Jiang Lan , Hahn Eric W. , Mason Ralph P. 
Published: June 2009

AbstractFluorine‐19 [19F] MRI oximetry and 1H blood oxygen level–dependent (BOLD) MRI were used to investigate tumor oxygenation in rat breast 13762NF carcinomas, and correlations between the techniques were examined. A range of tissue oxygen partial pressure (pO2) values was found in the nine tumors while the anesthetized rats breathed air, with individual tumor pO2 ranging from a mean of 1 to 36 torr and hypoxic fraction (HF10) (<10 torr) ranging from 0% to 75%, indicating a large intra‐ and intertumor heterogeneity. Breathing oxygen produced significant increase in tumor pO2 (mean ΔpO2 = 50 torr) and decrease in HF10 (P < 0.01). 1H BOLD MRI observed using a spin echo‐planar imaging (EPI) sequence revealed a heterogeneous response and significant increase in mean tumor signal intensity (SI) (ΔSI = 7%, P < 0.01). R measured by multigradient‐echo (MGRE) MRI decreased significantly in response to oxygen (mean ΔR = −4 s−1; P < 0.05). A significant correlation was found between changes in mean tumor pO2 and mean EPI BOLD ΔSI accompanying oxygen breathing (r2 > 0.7, P < 0.001). Our results suggest that BOLD MRI provides information about tumor oxygenation and may be useful to predict pO2 changes accompanying interventions. Significantly, the magnitude of the BOLD response appears to be predictive for residual tumor HFs. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
Hybrid of opposite‐contrast MR angiography (HOP‐MRA) combining time‐of‐flight and flow‐sensitive black‐blood contrasts
Authors: Kimura Tokunori , Ikedo Masato , Takemoto Syuhei 
Published: June 2009

AbstractFor the purpose of visualizing low‐flow as well as high‐flow blood vessels without using contrast agents, we propose a new technique called a hybrid of opposite‐contrast MR angiography (HOP‐MRA). HOP‐MRA is a combination of standard time‐of‐flight (TOF) using a full first‐order velocity‐compensation for white‐blood (WB) and flow‐sensitive black‐blood (FSBB) techniques, which use motion‐probing gradients to introduce intravoxel flow dephasing. A dual‐echo three‐dimensional gradient echo sequence was used to reduce both imaging time and misregistration. HOP‐MRA images were obtained using a simple‐weighted subtraction (SWS) or a frequency‐weighted subtraction (FWS) applying different spatial filtering for WB and BB images. We then assessed the relationships among the contrast‐to‐noise ratios (CNR) of the blood‐to‐background signals for those three images. In both volunteer and clinical brain studies, low‐flow vessels were well visualized and the background signal was well suppressed by HOP‐MRA compared with standard TOF‐ or BB‐MRA. The FWS was better than the SWS when whole‐maximum intensity projection was performed on a larger volume including with different types of tissue. The proposed HOP‐MRA was proven to visualize low‐flow to high‐flow vessels and, therefore, demonstrates excellent potential to become a clinically useful technique, especially for visualizing collateral vessels which is difficult with standard TOF‐MRA. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
On the dual contrast enhancement mechanism in frequency‐selective inversion‐recovery magnetic resonance angiography (IRON‐MRA)
Authors: Vonken Evert‐jan , Korosoglou Grigorios , Yu Jing , Schär Michael , Weissleder Ralph , Stuber Matthias 
Published: June 2009

AbstractThe susceptibility of blood changes after administration of a paramagnetic contrast agent that shortens T1. Concomitantly, the resonance frequency of the blood vessels shifts in a geometry‐dependent way. This frequency change may be exploited for incremental contrast generation by applying a frequency‐selective saturation prepulse prior to the imaging sequence. The dual origin of vascular enhancement depending first on off‐resonance and second on T1 lowering was investigated in vitro, together with the geometry dependence of the signal at 3T. First results obtained in an in vivo rabbit model are presented. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
Incidental magnetization transfer contrast by fat saturation preparation pulses in multislice look‐locker echo planar imaging
Authors: Shin Wanyong , Gu Hong , Yang Yihong 
Published: June 2009

AbstractIn this study, it is demonstrated that fat saturation (FS) preparation (prep) pulses generate incidental magnetization transfer contrast (MTC) in multislice Look‐Locker (LL) imaging. It is shown that frequency‐selective FS prep pulses can invoke MTC through the exchange between free and motion‐restricted protons. Simulation reveals that the fractional signal loss by these MTC effects is more severe for smaller flip angles (FAs), shorter repetition times (TRs), and greater number of slices (SN). These incidental MTC effects result in a signal attenuation at a steady state (up to 30%) and a T1 measurement bias (up to 20%) when using inversion recovery (IR) LL echo‐planar imaging (EPI) sequences. Furthermore, it is shown that water‐selective MRI using binomial pulses has the potential to minimize the signal attenuation and provide unbiased T1 measurement without fat artifacts in MR images. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
Rapid estimation of cartilage T2 based on double echo at steady state (DESS) with 3 Tesla
Authors: Welsch Goetz H. , Scheffler Klaus , Mamisch Tallal C. , Hughes Timothy , Millington Steven , Deimling Michael , Trattnig Siegfried 
Published: June 2009

AbstractThe double‐echo‐steady‐state (DESS) sequence generates two signal echoes that are characterized by a different contrast behavior. Based on these two contrasts, the underlying T2 can be calculated. For a flip‐angle of 90°, the calculated T2 becomes independent of T1, but with very low signal‐to‐noise ratio. In the present study, the estimation of cartilage T2, based on DESS with a reduced flip‐angle, was investigated, with the goal of optimizing SNR, and simultaneously minimizing the error in T2. This approach was validated in phantoms and on volunteers. T2 estimations based on DESS at different flip‐angles were compared with standard multiecho, spin‐echo T2. Furthermore, DESS‐T2 estimations were used in a volunteer and in an initial study on patients after cartilage repair of the knee. A flip‐angle of 33° was the best compromise for the combination of DESS‐T2 mapping and morphological imaging. For this flip angle, the Pearson correlation was 0.993 in the phantom study (∼20% relative difference between SE‐T2 and DESS‐T2); and varied between 0.429 and 0.514 in the volunteer study. Measurements in patients showed comparable results for both techniques with regard to zonal assessment. This DESS‐T2 approach represents an opportunity to combine morphological and quantitative cartilage MRI in a rapid one‐step examination. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
Absolute temperature MR imaging with thulium 1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetramethyl‐1,4,7,10‐tetraacetic acid (TmDOTMA−)
Authors: James Judy R. , Gao Yong , Miller Michael A. , Babsky Andriy , Bansal Navin 
Published: June 2009

AbstractMR thermometry based on the water 1H signal provides high temporal and spatial resolution, but it has low temperature sensitivity (∼0.01 ppm/°C) and requires monitoring of another weaker signal for absolute temperature measurements. The use of the paramagnetic lanthanide complex, thulium 1,4,7,10‐ tetraazacyclo‐dodecane‐1,4,7,10‐tetramethyl‐1,4,7,10‐tetraac‐ etate (TmDOTMA−), which is ∼60 times more sensitive to temperature than the water 1H signal, is advanced to image absolute temperatures in vivo using water signal as a reference. The temperature imaging technique was developed using gradient echo and asymmetric spin echo imaging sequences on 9.4 Tesla (T) horizontal and vertical MR scanners. A comparison of regional temperatures measured with TmDOTMA− and fiber‐optic probes showed that the accuracy of imaging temperature is <0.3°C. The temperature imaging technique was found to be insensitive to inhomogeneities in the main magnetic field. The feasibility of imaging temperature of intact rats at ∼1.4 mmol/kg dose with ∼1‐mm spatial resolution in only 3 min is demonstrated. TmDOTMA− should prove useful for imaging absolute temperatures in deep‐seated organs in numerous biomedical applications. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
Correlative dynamic contrast MRI and microscopic assessments of tumor vascularity in RIP‐tag2 transgenic mice
Authors: Sennino Barbara , Raatschen Hans‐Juergen , Wendland Michael F. , Fu Yanjun , You Weon‐Kyoo , Shames David M. , McDonald Donald M. , Brasch Robert C. 
Published: June 2009

AbstractThe purpose of this study was to define the feasibility of dynamic contrast‐enhanced magnetic resonance imaging (MRI) to estimate the vascular density and leakiness of spontaneous islet cell tumors in RIP‐Tag2 transgenic mice. Dynamic T1‐weighted spoiled gradient echo (SPGR) imaging at 2.0 T was performed in 17 RIP‐Tag2 mice using a prototype blood pool macromolecular contrast medium (MMCM), albumin‐(Gd‐DTPA)35. Kinetic analysis of the dynamic enhancement responses based on a two‐compartment model was used to estimate fractional plasma volume (fPV) and the coefficient of endothelial permeability (KPS) for each tumor. The MRI estimate of fPV was correlated on a tumor‐by‐tumor basis with corresponding microscopic measurements of vascular density. The fPV assays by MMCM‐enhanced imaging ranged from 2.4%–14.1% of tissue volume. Individual tumor fPV values correlated significantly (r = 0.79, P < 0.001) with the corresponding microscopic estimates of vascularity consisting of the combined area densities of lectin‐perfused microvessels plus erythrocyte‐stained blood lakes. A biotinylated derivative of the albumin‐based MMCM confirmed extravasation of the contrast agent from some tumor blood vessels and accumulation in 25% of blood lakes. The KPS values ranged from 0 (no detectable leak) to 0.356 mL/min/100 cm3. Dynamic MMCM‐enhanced MRI is feasible in RIP‐Tag2 pancreatic tumors, yielding estimates of vascular permeability and microscopically validated measurements of vascular richness. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
In vivo13C magnetic resonance spectroscopy of human brain on a clinical 3 T scanner using [2‐13C]glucose infusion and low‐power stochastic decoupling
Authors: Li Shizhe , Zhang Yan , Wang Shumin , Yang Jehoon , Ferraris Araneta Maria , Farris Amanda , Johnson Christopher , Fox Stephen , Innis Robert , Shen Jun 
Published: June 2009

AbstractThis study presents the detection of [2‐13C]glucose metabolism in the carboxylic/amide region in the human brain, and demonstrates that the cerebral metabolism of [2‐13C]glucose can be studied in human subjects in the presence of severe hardware constraints of widely available 3 T clinical scanners and with low‐power stochastic decoupling. In the carboxylic/amide region of human brain, the primary products of13C label incorporation from [2‐13C]glucose into glutamate, glutamine, aspartate, γ‐aminobutyric acid, and N‐acetylaspartate were detected. Unlike the commonly used alkanyl region where lipid signals spread over a broad frequency range, the carboxylic carbon signal of lipids was found to be confined to a narrow range centered at 172.5 ppm and present no spectral interference in the absence of lipid suppression. Comparison using phantoms shows that stochastic decoupling is far superior to the commonly used WALTZ sequence at very low decoupling power at 3 T. It was found that glutamine C1 and C5 can be decoupled using stochastic decoupling at 2.2 W, although glutamine protons span a frequency range of ≈700 Hz. Detailed specific absorption rate analysis was also performed using finite difference time domain numerical simulation. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
Breathhold multiecho fast spin‐echo pulse sequence for accurate R2 measurement in the heart and liver
Authors: Kim Daniel , Jensen Jens H. , Wu Ed X. , Sheth Sujit S. , Brittenham Gary M. 
Published: June 2009

AbstractMeasurement of proton transverse relaxation rates (R2) is a generally useful means for quantitative characterization of pathological changes in tissue with a variety of clinical applications. The most widely used R2 measurement method is the Carr‐Purcell‐Meiboom‐Gill (CPMG) pulse sequence but its relatively long scan time requires respiratory gating for chest or body MRI, rendering this approach impractical for comprehensive assessment within a clinically‐acceptable examination time. The purpose of our study was to develop a breathhold multiecho fast spin‐echo (FSE) sequence for accurate measurement of R2 in the liver and heart. Phantom experiments and studies of subjects in vivo were performed to compare the FSE data with the corresponding even‐echo CPMG data. For pooled data, the R2 measurements were strongly correlated (Pearson correlation coefficient = 0.99) and in excellent agreement (mean difference [CPMG – FSE] = 0.10 s–1; 95% limits of agreement were 1.98 and –1.78 s–1) between the two pulse sequences. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
Experimental determination of human peripheral nerve stimulation thresholds in a 3‐axis planar gradient system
Authors: Feldman Rebecca E. , Hardy Christopher J. , Aksel Bulent , Schenck John , Chronik Blaine A. 
Published: June 2009

AbstractIn MRI, strong, rapidly switched gradient fields are desirable because they can be used to reduce imaging time, obtain images with better resolution, or improve image signal‐to‐noise ratios. Improvements in gradient strength can be made by either increasing the gradient amplifier strength or by enhancing gradient efficiency. Unfortunately, many MRI pulse sequences, in combination with high‐performance amplifiers and existing gradient hardware, can cause peripheral nerve stimulation (PNS). This makes improvements in gradient amplifiers ineffective at increasing safely usable gradient strength. Customized gradient coils are one way to achieve significant improvements in gradient performance. One specific gradient configuration, a planar gradient system, promises improved gradient strength and switching time for cardiac imaging. The PNS thresholds for planar gradients were characterized through human stimulation experiments on all three gradient axes. The specialized gradient was shown to have significantly higher stimulation thresholds than traditional cylindrical designs (y‐axis SRmin = 210 ± 18 mT/m/ms and ΔGmin = 133 ± 13 mT/m; x‐axis SRmin = 222 ± 24 mT/m/ms and ΔGmin = 147 ± 17 mT/m; z‐axis SRmin = 252 ± 26 mT/m/ms and ΔGmin = 218 ± 26 mT/m). This system could be operated at gradient strengths 2 to 3 times higher than cylindrical configurations without causing stimulation. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
Assessment of 31P relaxation times in the human calf muscle: A comparison between 3 T and 7 T in vivo
Authors: Bogner W. , Chmelik M. , Schmid A.I. , Moser E. , Trattnig S. , Gruber S. 
Published: June 2009

AbstractPhosphorus (31P) T1 and T2 relaxation times in the resting human calf muscle were assessed by interleaved, surface coil localized inversion recovery and frequency‐selective spin‐echo at 3 and 7 T. The obtained T1 (mean ± SD) decreased significantly (P < 0.05) from 3 to 7 T for phosphomonoesters (PME) (8.1 ± 1.7 s to 3.1 ± 0.9 s), phosphodiesters (PDE) (8.6 ± 1.2 s to 6.0 ± 1.1 s), phosphocreatine (PCr) (6.7 ± 0.4 s to 4.0 ± 0.2 s), γ‐NTP (nucleotide triphosphate) (5.5 ± 0.4 s to 3.3 ± 0.2 s), α‐NTP (3.4 ± 0.3 s to 1.8 ± 0.1 s), and β‐NTP (3.9 ± 0.4 s to 1.8 ± 0.1 s), but not for inorganic phosphate (Pi) (6.9 ± 0.6 s to 6.3 ± 1.0 s). The decrease in T2 was significant for Pi (153 ± 9 ms to 109 ± 17 ms), PDE (414 ± 128 ms to 314 ± 35 ms), PCr (354 ± 16 ms to 217 ± 14 ms), and γ‐NTP (61.9 ± 8.6 ms to 29.0 ± 3.3 ms). This decrease in T1 with increasing field strength of up to 62% can be explained by the increasing influence of chemical shift anisotropy on relaxation mechanisms and may allow shorter measurements at higher field strengths or up to 62% additional signal‐to‐noise ratio (SNR) per unit time. The fully relaxed SNR increased by +96%, while the linewidth increased from 6.5 ± 1.2 Hz to 11.2 ± 1.9 Hz or +72%. At 7 T 31P‐MRS in the human calf muscle offers more than twice as much SNR per unit time in reduced measurement time compared to 3 T. This will facilitate in vivo 31P‐MRS of the human muscle at 7 T. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
Visualization of seminiferous tubules in rat testes in normal and diseased conditions by high‐resolution MRI
Authors: Yamaguchi Masayuki , Mitsumori Fumiyuki , Watanabe Hidehiro , Takaya Nobuhiro , Minami Manabu 
Published: June 2009

AbstractRat seminiferous tubules were visualized for the first time using high‐spatial‐resolution MRI and their MRI features were investigated under normal and various kinds of pathological conditions. All testes images were obtained at 4.7 T with a dedicated quadrature surface coil. T2‐ and T‐weighted images with in‐plane resolution of 66 × 66 μm2 demonstrated numerous tubular structures with low‐signal‐intensity walls and high‐signal‐intensity lumens tightly packed throughout the entire testicle. The tubular structures were attributed to the seminiferous tubules in the histological specimens. In testicular ischemia, T‐weighted images demonstrated prominent low‐signal‐intensity bands along the radiate veins and normal‐appearing seminiferous tubules. As the ischemic condition persisted, the contour of the seminiferous tubules became less visible on both T2‐ and T‐weighted images, reflecting the disorganization of the seminiferous epithelia and severe interstitial edema. Changes in the images of testes treated with glycerol or diethylstilbestrol, a synthetic estrogen hormone, were also investigated. In the chronic spermatogenic impairment caused by these substances, extensive shrinkage of the seminiferous tubules was demonstrated. High‐resolution MRI aids in noninvasive evaluation of seminiferous tubules, and therefore has potential as a diagnostic test for human testes. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
In vivo detection of serine in the human brain by proton magnetic resonance spectroscopy (1H‐MRS) at 7 Tesla
Authors: Choi Changho , Dimitrov Ivan , Douglas Deborah , Zhao Chenguang , Hawesa Halima , Ghose Subroto , Tamminga Carol A. 
Published: June 2009

AbstractA single‐voxel proton magnetic resonance spectroscopy (1H‐MRS) filtering strategy for in vivo detection of serine (Ser) in human brain at 7T is proposed. Spectral difference of coupled resonances arising from different subecho times of triple refocusing at a constant total echo time (TE) was utilized to detect the Ser multiplet and cancel the overlapping creatine (Cr) 3.92‐ppm singlet via difference editing. Dependence of the Ser signal on subecho times was investigated using density‐matrix simulation incorporating the slice‐selective radio frequency (RF) pulses. The simulation indicated that the difference‐edited Ser CH2 multiplet at ∼3.96 ppm is maximized with (TE1, TE2, TE3) = (54, 78, 78) and (36, 152, 22) ms. The edited Ser peak amplitude was estimated, with both numerical and phantom analyses of the performance, as 83% with respect to 90° acquisition for a localized volume, ignoring relaxation effects. From the area ratio of the edited Ser and unedited Cr 3.03‐ppm peaks, assuming identical T1 and T2 between Ser and Cr, the Ser‐to‐Cr concentration ratio for the frontal cortex of healthy adults was estimated to be 0.8 ± 0.2 (mean ± SD; N = 6). Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.
T‐spline finite element method for the analysis of shell structures
Authors: Uhm Tae‐Kyoung , Youn Sung‐Kie 
Published: June 2009

AbstractA T‐spline surface is a nonuniform rational B‐spline (NURBS) surface with T‐junctions, and is defined by a control grid called T‐mesh. The T‐mesh is similar to a NURBS control mesh except that in a T‐mesh, a row or column of control points is allowed to terminate in the inner parametric space. This property of T‐splines makes local refinement possible. In the present study, shell formulation based on the T‐spline finite element method (FEM) is presented. Shell formulation based on NURBS or T‐splines has fundamental limitations because rotational DOFs, which are necessary in the shell formulation, cannot be defined on control points. In this study, the simple mapping scheme, in which every control point is mapped into one geometric point on the surface, is employed to eliminate the limitations. Using this mapping scheme, T‐spline FEM can be easily extended to the analysis of shells. The proposed shell formulation is verified through various benchmarking problems. This study is a part of the efforts by the authors for the integration of CAD–CAE processes. Copyright © 2009 John Wiley & Sons, Ltd.
Multi‐level incomplete factorizations for the iterative solution of non‐linear finite element problems
Authors: Janna Carlo , Ferronato Massimiliano , Gambolati Giuseppe 
Published: June 2009

AbstractSeveral engineering applications give rise quite naturally to linearized FE systems of equations possessing a multi‐level structure. An example is provided by geomechanical models of layered and faulted geological formations. For such problems the use of a multi‐level incomplete factorization (MIF) as a preconditioner for Krylov subspace methods can prove a robust and efficient solution accelerator, allowing for a fine tuning of the fill‐in degree with a significant improvement in both the solver performance and the memory consumption. The present paper develops two novel MIF variants for the solution of multi‐level symmetric positive definite systems. Two correction algorithms are proposed with the aim of preserving the positive definiteness of the preconditioner, thus avoiding possible breakdowns of the preconditioned conjugate gradient solver. The MIF variants are experimented with in the solution of both a single system and a long‐term quasi‐static simulation dealing with a multi‐level geomechanical application. The numerical results show that MIF typically outperforms by up to a factor 3 a more traditional algebraic preconditioner such as an incomplete Cholesky factorization with partial fill‐in. The advantage is emphasized in a long‐term simulation where the fine fill‐in tuning allowed for by MIF yields a significant improvement for the computer memory requirement as well. Copyright © 2009 John Wiley & Sons, Ltd.