bluuebunny/crossref_metadata_2025 huggingface dataset:
Interventional cardiovascular procedures guided by real‐time MR imaging: An interactive interface using multiple slices, adaptive projection modes and live 3D renderings
Authors: Guttman Michael A. , Ozturk Cenghizhan , Raval Amish N. , Raman Venkatesh K. , Dick Alexander J. , DeSilva Ranil , Karmarkar Parag , Lederman Robert J. , McVeigh Elliot R.
Published: October 2007

Purpose

To develop and test a novel interactive real‐time MRI environment that facilitates image‐guided cardiovascular interventions.

Materials and Methods

Color highlighting of device‐mounted receiver coils, accelerated imaging of multiple slices, adaptive projection modes, live three‐dimensional (3D) renderings and other interactive features were utilized to enhance navigation of devices and targeting of tissue.

Results

Images are shown from several catheter‐based interventional procedures performed in swine that benefit from this custom interventional MRI interface. These include endograft repair of aortic aneurysm, balloon septostomy of the cardiac interatrial septum, angioplasty and stenting, and endomyocardial cell injection, all using active catheters containing MRI receiver coils.

Conclusion

Interactive features not available on standard clinical scanners enhance real‐time MRI for guiding cardiovascular interventional procedures. J. Magn. Reson. Imaging 2007. © 2007 Wiley‐Liss, Inc.
Anatomical distribution of 3He apparent diffusion coefficients in severe chronic obstructive pulmonary disease
Authors: Evans Andrea , McCormack David , Ouriadov Alexei , Etemad‐Rezai Roya , Santyr Giles , Parraga Grace
Published: October 2007

Purpose

To evaluate the anatomical distribution of apparent diffusion coefficients (ADC) using hyperpolarized helium‐3 (3He) MRI in chronic obstructive pulmonary disease (COPD).

Materials and Methods

Hyperpolarized 3He MRI was performed in eight healthy and seven COPD subjects under breathhold conditions in the supine position to determine ADC values from diffusion‐weighted images and evaluate anterior–posterior (AP) and superior–inferior (SI) differences.

Results

ADC differences between anterior and posterior slices, ΔAP, was 0.06 ±0.01 cm2/second for healthy volunteers and 0.04 ±0.02 cm2/second for COPD subjects and was significant for each subject (P < 0.01). The AP ADC gradient was –3.98 × 10–3 ±0.59 cm2/second/cm for healthy volunteers and –2.04 × 10–3 ±0.89 cm2/second/cm for COPD subjects. The difference in ADC between superior and inferior regions of interest (ROIs), ΔSI, was 0.02 ±0.02 cm2/second for healthy volunteers and 0.10 ±0.09 cm2/second for COPD subjects, which was significant for each subject (P < 0.05). The SI ADC gradient was –0.63 × 10–3 ±2.23 cm2/second/cm for healthy volunteers and –6.61 × 10–3 ±6.68 cm2/second/cm for COPD subjects. ΔAP, AP‐gradient, and SI‐gradient were significantly different between healthy volunteers and COPD subjects (P < 0.05).

Conclusion

In all subjects, ADC anatomical differences were significant and mean ADC was dependent on anatomic location and disease status. J. Magn. Reson. Imaging. © 2007 Wiley‐Liss, Inc.
Transcytolemmal water exchange in pharmacokinetic analysis of dynamic contrast‐enhanced MRI data in squamous cell carcinoma of the head and neck
Authors: Kim Sungheon , Quon Harry , Loevner Laurie A. , Rosen Mark A. , Dougherty Lawrence , Kilger Alex M. , Glickson Jerry D. , Poptani Harish
Published: October 2007

Purpose

To investigate the effect of transcytolemmal water exchange on the dynamic contrast‐enhanced (DCE) T1‐weighted MRI of human squamous cell carcinomas of the head and neck (HNSCC).

Materials and Methods

Nine patients with HNSCC nodal metastasis underwent pretreatment DCE‐MRI with a temporal resolution of 2.5 seconds and a spatial resolution of 1 mm × 1 mm × 5 mm at 1.5T. We used two pharmacokinetic models for data analysis: generalized kinetic model (GKM) without considering transcytolemmal water exchange and the shutter‐speed model (SSM), based on a two‐site exchange model for transcytolemmal water exchange. The results were compared in three subgroups of voxels in the tumor depending on the level of contrast enhancement.

Results

SSM was found to be a better fit for more than 75% of pixels of all subjects (P < 0.01) in terms of residual size and Bayesian information criterion (BIC). For all three subgroups based on the contrast enhancement, the median Ktrans values of SSM were 42% to 55% higher than those of GKM and the median ve values of SSM were 116% to 176% larger than those of GKM. The median Ktrans and ve of two models were found significantly different (P < 0.01). The median τi measured by SSM were from 211 to 364 msec.

Conclusion

The effect of transcytolemmal water exchange is an important factor that needs to be incorporated for adequate modeling of contrast enhancement dynamics measured by MRI of HNSCC. J. Magn. Reson. Imaging 2007. © 2007 Wiley‐Liss, Inc.
An integrated method for metabolite detection and identification using a linear ion trap/Orbitrap mass spectrometer and multiple data processing techniques: application to indinavir metabolite detection
Authors: Ruan Qian , Peterman Scott , Szewc Mark A. , Ma Li , Cui Dan , Humphreys W. Griffith , Zhu Mingshe
Published: October 2007

A new strategy using a hybrid linear ion trap/Orbitrap mass spectrometer and multiple post‐acquisition data mining techniques was evaluated and applied to the detection and characterization of in vitro metabolites of indinavir. Accurate‐mass, full‐scan MS and MS/MS data sets were acquired with a generic data‐dependent method and processed with extracted‐ion chromatography (EIC), mass‐defect filter (MDF), product‐ion filter (PIF), and neutral‐loss filter (NLF) techniques. The high‐resolution EIC process was shown to be highly effective in the detection of common metabolites with predicted molecular weights. The MDF process, which searched for metabolites based on the similarity of mass defects of metabolites to those of indinavir and its core substructures, was able to find uncommon metabolites not detected by the EIC processing. The high‐resolution PIF and NLF processes selectively detected metabolites that underwent fragmentation pathways similar to those of indinavir or its known metabolites. As a result, a total of 15 metabolites including two new indinavir metabolites were detected and characterized in a rat liver S9 incubation sample. Overall, these data mining techniques, which employed distinct metabolite search mechanisms, were complementary and effective in detecting both common and uncommon metabolites. In summary, the results demonstrated that this analytical strategy enables the high‐throughput acquisition of accurate‐mass LC/MS data sets, comprehensive search of a variety of metabolites through the post‐acquisition processes, and effective structural characterization based on elemental compositions of metabolite molecules and their product ions. Copyright © 2007 John Wiley & Sons, Ltd.
Identification of hexose diastereomers by means of tandem mass spectrometry of oxocarbenium ions followed by neural networks analysis
Authors: Madhusudanan K. P. , Srivastava Mukesh
Published: October 2007

The ion abundances in the tandem mass spectra of oxocarbenium ions generated from aldohexoses and ketohexoses under electrospray ionization conditions depend on their stereochemistry. The ratios of the abundances of two of the major ionsm/z85 and 91 are different in the aldohexoses and the ketohexoses. Principal component analysis (PCA) allowed visual differentiation of the hexose isomers. However, identification of an individual hexose was difficult. The data were subjected to neural network analysis (NNA) using a multilayer perceptron (MLP) model. The model was first trained using the data from the 11 hexoses and then used to identify the hexoses using fresh data acquired later. There was 100% identification of the various hexoses. The hexose units in methyl glucoside, mannoside and galactoside could also be identified accurately. The method can therefore be used for the characterization of hexose units from monosaccharides and glycosides. Copyright © 2007 John Wiley & Sons, Ltd.
On‐target sample preparation of 4‐sulfophenyl isothiocyanate‐derivatized peptides using AnchorChip Targets
Authors: Zhang Xumin , Rogowska‐Wrzesinska Adelina , Roepstorff Peter
Published: October 2007

De novo sequencing of tryptic peptides by post source decay (PSD) or collision induced dissociation (CID) analysis using MALDI TOF‐TOF instruments is due to the easy interpretation facilitated by the introduction of N‐terminal sulfonated derivatives. Recently, a stable and cheap reagent, 4‐sulfophenyl isothiocyanate (SPITC), has been successfully used for N‐terminal derivatization. Previously described methods have always used desalting and concentration by reverse‐phase chromatography prior to mass spectrometric analysis. Here we present an on‐target sample preparation method based on AnchorChip target technology. The method was optimized for reduction of by‐products and sensitivity with SPITC‐derivatized tryptic BSA peptides, and successfully applied to protein identification from silver‐stained two‐dimensional electrophoretic gels of fish liver extracts. The method is simple and sensitive and allowed protein identification based on de novo sequencing and BLAST search from species with limited sequence information. Copyright © 2007 John Wiley & Sons, Ltd.
Characterization of organosulfates from the photooxidation of isoprene and unsaturated fatty acids in ambient aerosol using liquid chromatography/(−) electrospray ionization mass spectrometry
Authors: Gómez‐González Yadian , Surratt Jason D. , Cuyckens Filip , Szmigielski Rafal , Vermeylen Reinhilde , Jaoui Mohammed , Lewandowski Michael , Offenberg John H. , Kleindienst Tadeusz E. , Edney Edward O. , Blockhuys Frank , Van Alsenoy Christian , Maenhaut Willy , Claeys Magda
Published: October 2007

In the present study, we have characterized in detail the MS2 and MS3 fragmentation behaviors, using electrospray ionization (ESI) in the negative ion mode, of previously identified sulfated isoprene secondary organic aerosol compounds, including 2‐methyltetrols, 2‐methylglyceric acid, 2‐methyltetrol mononitrate derivatives, glyoxal and methylglyoxal. A major fragmentation pathway for the deprotonated molecules of the sulfate esters of 2‐methyltetrols and 2‐methylglyceric acid and of the sulfate derivatives of glyoxal and methylglyoxal is the formation of the bisulfate [HSO4]− anion, while the deprotonated sulfate esters of 2‐methyltetrol mononitrate derivatives preferentially fragment through loss of nitric acid. Rational interpretation of MS2, MS3 and accurate mass data led to the structural characterization of unknown polar compounds in K‐puszta fine aerosol as organosulfate derivatives of photooxidation products of unsaturated fatty acids, i.e. 2‐hydroxy‐1,4‐butanedialdehyde, 4,5‐ and 2,3‐dihydroxypentanoic acids, and 2‐hydroxyglutaric acid, and of α‐pinene, i.e. 3‐hydroxyglutaric acid. The deprotonated molecules of the sulfated hydroxyacids, 2‐methylglyceric acid, 4,5‐ and 2,3‐dihydroxypentanoic acid, and 2‐ and 3‐hydroxyglutaric acids, showed in addition to the [HSO4]− ion (m/z 97) neutral losses of water, CO2 and/or SO3, features that are characteristic of humic‐like substances. The polar organosulfates characterized in the present work are of climatic relevance because they may contribute to the hydrophilic properties of fine ambient aerosol. In addition, these compounds probably serve as ambient tracer compounds for the occurrence of secondary organic aerosol formation under acidic conditions. Copyright © 2007 John Wiley & Sons, Ltd.
Amyloid β‐peptide activates nuclear factor‐κB through an N‐methyl‐D‐aspartate signaling pathway in cultured cerebellar cells
Authors: Kawamoto E. M. , Lepsch L. B. , Boaventura M. F. C. , Munhoz C. D. , Lima L. S. , Yshii L. M. , Avellar M. C. W. , Curi R. , Mattson M. P. , Scavone C.
Published: October 2007

Amyloid β‐peptide (Aβ) likely causes functional alterations in neurons well prior to their death. Nuclear factor‐κB (NF‐κB), a transcription factor that is known to play important roles in cell survival and apoptosis, has been shown to be modulated by Aβ in neurons and glia, but the mechanism is unknown. Because Aβ has also been shown to enhance activation of N‐methyl‐D‐aspartate (NMDA) receptors, we investigated the role of NMDA receptor‐mediated intracellular signaling pathways in Aβ‐induced NF‐κB activation in primary cultured rat cerebellar cells. Cells were treated with different concentrations of Aβ1–40 (1 or 2 μM) for different periods (6, 12, or 24 hr). MK‐801 (NMDA antagonist), manumycin A and FTase inhibitor 1 (farnesyltransferase inhibitors), PP1 (Src‐family tyrosine kinase inhibitor), PD98059 [mitogen‐activated protein kinase (MAPK) inhibitor], and LY294002 [phosphatidylinositol 3‐kinase (PI3‐k) inhibitor] were added 20 min before Aβ treatment of the cells. Aβ induced a time‐ and concentration‐dependent activation of NF‐κB (1 μM, 12 hr); both p50/p65 and p50/p50 NF‐κB dimers were involved. This activation was abolished by MK‐801 and attenuated by manumycin A, FTase inhibitor 1, PP1, PD98059, and LY294002. Aβ at 1 μM increased the expression of inhibitory protein IκB, brain‐derived neurotrophic factor, inducible nitric oxide synthase, tumor necrosis factor‐α, and interleukin‐1β as shown by RT‐PCR assays. Collectively, these findings suggest that Aβ activates NF‐κB by an NMDA‐Src‐Ras‐like protein through MAPK and PI3‐k pathways in cultured cerebellar cells. This pathway may mediate an adaptive, neuroprotective response to Aβ. © 2007 Wiley‐Liss, Inc.
NR1 and GluR2 expression mediates excitotoxicity in chronic hypobaric hypoxia
Authors: Hota Sunil K. , Barhwal Kalpana , Singh Shashi. B. , Sairam M. , Ilavazhagan Govindasamy
Published: October 2007

Hypobaric hypoxia has been reported to cause memory dysfunction. The possible molecular mechanism involved, however, remains to be explored. The role that glutamate and its receptors play in causing excitotoxicity in ischemia and neurodegenerative diseases indicates the possible occurrence of a similar phenomenon in hypobaric hypoxia. The present study aimed to elucidate the molecular events occurring at glutamatergic synapses in hypobaric hypoxia using Sprague‐Dawley rats as a model system. The animals were exposed to an altitude of 7,600 m for different durations. Hypobaric hypoxia was found to cause oxidative stress, chromatin condensation, and neurodegeneration. A temporal change in the expression of the ionotropic receptors of glutamate was also observed. Expression of theN‐methyl‐D‐aspartate (NMDA) receptor increased, and expression of glutamate receptor subunit 2 of the α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazoleproprionate receptor decreased. We also observed increased activity of glutamate dehydrogenase, indicating greater synthesis and release of glutamate after 3 and 7 days of exposure. Administration of a selective NMDA antagonist during exposure was found to ameliorate neuronal degeneration, providing evidence for the occurrence of excitotoxicity in hypobaric hypoxia. Our study indicates that excitotoxicity occurs in hypobaric hypoxia. This study also indicates the appropriate period for drug administration during exposure to hypobaric hypoxia and establishes ionotropic receptors of glutamate as potential therapeutic targets for ameliorating high‐altitude‐induced cognitive dysfunction. © 2007 Wiley‐Liss, Inc.
Coherent structures in urban roughness sublayer turbulence
Authors: Christen Andreas , van Gorsel Eva , Vogt Roland
Published: October 2007

Data measured within and above an urban street canyon is used to analyse the importance of coherent structures in turbulent transfer. The atmosphere was probed simultaneously at six different heights from the base of the street canyon up to 2.2 times the mean building height. Integral length scales, joint probability densities, quadrant measures and wavelet‐based conditional sampling techniques are used to picture momentum and sensible heat exchange in the urban roughness sublayer. Layers directly at roof height show smallest length scales. With increasing distance from roofs, length scales increase, both up to higher levels above the roofs and also down to the base of the street canyon. Quadrant analysis indicates that turbulent momentum and sensible heat fluxes are strongly sweep‐dominated in large parts of the street canyon and close to the roofs. Only at the highest measurement levels do ejections slightly dominate exchange. Exchange is intermittent where length scales are largest, namely in the lower street canyon and at higher levels in the urban roughness sublayer. At rooftop, exchange is more efficient and least intermittent. A wavelet‐based detection is used to reconstruct time‐height cross‐sections of paired events measured at multiple levels simultaneously. Two types of sharp scalar fronts were identified—sweeps followed by ejections and ejections followed by sweeps. Both are important in transporting momentum and sensible heat. Copyright © 2007 Royal Meteorological Society
Amount of characteristic compounds in 15 cultivars of onion (Allium cepa L.) in controlled field trials
Authors: Vågen Ingunn M , Slimestad Rune
Published: October 2007

BACKGROUND: In order to develop the production of sweet onions (Allium cepa L.) and onions with a high content of flavonols and fibre in Norway, it was necessary to evaluate available cultivars with respect to their content of selected chemical compounds. A field trial with 15 different cultivars was conducted at Landvik in southern Norway. Compounds that reflect onion pungency and sweetness (pyruvate, sugars) and parameters known to have a beneficial impact on health (fructo‐oligosaccharides (FOS), flavonols, antioxidant capacity) were analysed.

RESULTS: The sweetest onions with respect to low content of pyruvate and high amount of fructose and glucose ranged in pyruvate content from 2.7 to 3.6 µmol mL−1. These cultivars were juicy and contained low amounts of FOS and total flavonols. The most pungent onions contained the highest amounts of FOS among the cultivars: 4.53, 3.80 and 5.81 g per 100 g fresh weight (FW) respectively. They also had a high content of flavonols (86.6, 159.2 and 97.6 mg per 100 g FW) and high dry weight content (14.6, 13.5 and 15.6 g per 100 g).

CONCLUSION: The sweetest onion cultivars were found to be ‘NUN 9746’, ‘Musica’, ‘Domenica Supersweet’, ‘Colossus’ and ‘Cronus’. The most pungent cultivars were ‘Powell Brown’ and ‘Tilbury’, which also contained the highest amounts of flavonols and gave the highest Trolox equivalent antioxidant capacity (TEAC) values among the 15 cultivars. Copyright © 2007 Society of Chemical Industry
Unsaturated Polyamides from Bio‐Based Z‐octadec‐9‐enedioic Acid
Authors: Pardal Francis , Salhi Slim , Rousseau Brigitte , Tessier Martine , Claude Sylvain , Fradet Alain
Published: October 2007

A series of polyamides based on Z‐octadec‐9‐enedioic acid, a bio‐based unsaturated monomer, and aliphatic‐, cycloaliphatic‐, or benzylic diamines were synthesized and characterized by 1H and 13C NMR analysis, size exclusion chromatography (SEC), DSC, and dynamic‐mechanical analysis (DMA). The high reaction temperature (250 °C) did not lead to the degradation of diacid unit double bonds and unsaturated polyamides were obtained. The aliphatic unsaturated polyamides are semi‐crystalline polymers of high molar mass, relatively flexible at room temperature. The cycloaliphatic unsaturated polyamides are semi‐crystalline or amorphous, present higher melting and glass transition temperatures and are much more rigid. The aliphatic and aliphatic–aromatic unsaturated polyamides present lower Tg and Tm as compared to their parent saturated polymers.

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Macromol. Chem. Phys. 21/2007
Authors: Kim Tae‐Ho , Lim Tae‐Wook , Park Yong‐Su , Shin Kyusoon , Lee Jong‐Chan
Published: October 2007

Front Cover: The cover illustrates a strategy for a simple preparation of the proton conductive composite membrane composed of poly(2,5‐benzimidazole) and zirconium pyrophosphate via a PPA direct casting method. The SEM image shows the zirconium pyrophosphate particles in the composite membrane when the content of the zirconium pyrophosphate is about 30 wt.‐%. Further details can be found in the article by T.‐H. Kim, T.‐W. Yim, Y.‐S. Park, K. Shin, and J.‐C. Lee* on page 2293.
Macromol. Chem. Phys. 21/2007
Authors: Huang Jinyu , Tang Chuanbing , Lee Hyungil , Kowalewski Tomasz , Matyjaszewski Krzysztof
Published: October 2007

Back Cover: Well‐defined nanostructured carbons were prepared by UV cross‐linking of micelles formed from block copolymers and molecular brushes containing polystyrene (PS) segments, synthesized by ATRP. After pyrolysis, the cross‐linked PS core was converted to partially graphitic nanostructured carbon, while the shell was sacrificed. Further details can be found in the article by J. Huang, C. Tang, H. Lee, T. Kowalewski, and K. Matyjaszewski* on page 2312.
Parallel Algorithm for Cell Dynamics Simulation of Block Copolymers
Authors: Guo Xiaohu , Pinna Marco , Zvelindovsky Andrei V.
Published: October 2007

Cell dynamics simulation (CDS) is a very promising approach to model dynamic processes in block copolymer systems at the mesoscale level. It is difficult to implement a real time and experimental‐scale simulation with traditional serial algorithms because of the expensive computation. A parallel, spatial decomposition‐based algorithm for large‐scale CDS is proposed. With the efficient strategy of domain decomposition and the fast method of neighbouring points location, we greatly reduce the calculating and communicating cost. The numerical results indicate that the proposed parallel algorithm can provide an efficient procedure for computer simulation of block copolymer systems of experimental size.

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Automatic plaque characterization employing quantitative and multicontrast MRI
Authors: Sun Binjian , Giddens Don P. , Long Robert , Taylor W. Robert , Weiss Diana , Joseph Giji , Vega David , Oshinski John N.
Published: October 2007

Multicontrast magnetic resonance imaging (MRI) has shown promise in identifying and characterizing atherosclerotic plaques. One of the limitations of this technique is the lack of a practical automated plaque characterization scheme. In the current study, a prior‐information‐enhanced clustering (PIEC) technique that utilizes both multicontrast MR images and quantitative T2 maps is proposed to characterize atherosclerotic plaque components automatically. The PIEC algorithm was assessed on computationally simulated images and multicontrast MRI data of coronary arteries. Multicontrast (T1‐, T2‐, partial T2‐, and proton density‐weighted) MR images were acquired from freshly excised human coronary arteries using a 4.7T small‐animal scanner. The T2 distribution for each plaque constituent was measured by exponentially fitting the signal from multiple MR images with different TEs and the same TR. The calculated T2 distributions were used as the a priori information and combined with the Fuzzy C‐Means (FCM)‐based clustering algorithm to characterize plaque constituents. The proposed PIEC technique appears to be a promising algorithm for accurate automated plaque characterization. Magn Reson Med, 2007. © 2007 Wiley‐Liss, Inc.
Intrinsic signal amplification in the application of 2D SENSE parallel imaging to 3D contrast‐enhanced elliptical centric MRA and MRV
Authors: Riederer Stephen J. , Hu Houchun Harry , Kruger David G. , Haider Clifton R. , Campeau Norbert G. , Huston John
Published: October 2007

The relative signal‐to‐noise ratio (SNR) provided by 2D sensitivity encoding (SENSE) when applied to 3D contrast‐enhanced MR angiography (CE‐MRA) is studied. If an elliptical centric phase‐encoding order is used to map the waning magnetization of the contrast bolus to k‐space, the application of SENSE will reduce the degree of k‐space signal modulation, providing a signal amplification A over corresponding nonaccelerated acquisitions. This offsets the SNR loss in R‐accelerated SENSE due to

and the geometry (g) factor. The theoretical bound on A is R and is reduced from this depending on the properties of the bolus profile and the duration over which it is imaged. In this work a signal amplification of 1.14–1.23 times that of nonvascular background tissue is demonstrated in a study of 20 volunteers using R = 4 2D SENSE whole‐brain MR venography (MRV). The effects of a nonuniform g‐factor and inhomogeneity of background tissue are accounted for. The observed amplification compares favorably with the value of 1.31 predicted numerically from a measured bolus curve. Magn Reson Med 58:855–864, 2007. © 2007 Wiley‐Liss, Inc.
Vessel‐encoded arterial spin‐labeling using pseudocontinuous tagging
Authors: Wong Eric C.
Published: October 2007

A new signal‐to‐noise ratio (SNR) efficient method is introduced for the mapping of vascular territories based on pseudocontinuous arterial spin labeling (ASL). A pseudocontinuous tagging pulse train is modified using additional transverse gradient pulses and phase cycling to place some arteries in a tag condition, while others passing through the same tagging plane are in a control condition. This is combined with a Hadamard or similar encoding scheme such that all vessels of interest are fully inverted or relaxed for nearly all of the encoding cycles, providing optimal SNR. The relative tagging efficiency for each vessel is measured directly from the ASL data and is used in the decoding process to improve the separation of vascular territories. High SNR maps of left carotid, right carotid, and basilar territories are generated in 6 min of scan time. Magn Reson Med, 2007. © 2007 Wiley‐Liss, Inc.
MRI using a concentric rings trajectory
Authors: Wu Hochong H. , Lee Jin Hyung , Nishimura Dwight G.
Published: October 2007

The concentric rings two‐dimensional (2D) k‐space trajectory provides an alternative way to sample polar data. By collecting 2D k‐space data in a series of rings, many unique properties are observed. The concentric rings are inherently centric‐ordered, provide a smooth weighting in k‐space, and enable shorter total scan times. Due to these properties, the concentric rings are well‐suited as a readout trajectory for magnetization‐prepared studies. When non‐Cartesian trajectories are used for MRI, off‐resonance effects can cause blurring and degrade the image quality. For the concentric rings, off‐resonance blur can be corrected by retracing rings near the center of k‐space to obtain a field map with no extra excitations, and then employing multifrequency reconstruction. Simulations show that the concentric rings exhibit minimal effects due to T modulation, enable shorter scan times for a Nyquist‐sampled dataset than projection‐reconstruction imaging or Cartesian 2D Fourier transform (2DFT) imaging, and have more spatially distributed flow and motion properties than Cartesian sampling. Experimental results show that off‐resonance blurring can be successfully corrected to obtain high‐resolution images. Results also show that concentric rings effectively capture the intended contrast in a magnetization‐prepared sequence. Magn Reson Med, 2007. © 2007 Wiley‐Liss, Inc.
Short echo time 1H‐MRSI of the human brain at 3T with minimal chemical shift displacement errors using adiabatic refocusing pulses
Authors: Scheenen Tom W. J. , Klomp Dennis W. J. , Wijnen Jannie P. , Heerschap Arend
Published: October 2007

The chemical shift displacement error (CSDE) is an often‐underestimated problem in slice selection for localized proton spectroscopy at higher fields. With the proposed semi‐localized by adiabatic selective refocusing (LASER) pulse sequence, this problem is dealt with by using RF pulses with bandwidths in the order of 5 kHz. A combination of conventional nonadiabatic slice‐selective excitation of proton spins, together with double slice‐selective refocusing of the spins by two pairs of adiabatic full‐passage (APF) pulses, produces a spin echo in a volume of interest (VOI) at an echo time down to 30 ms. An illustration of the CSDE of conventional point‐resolved spectroscopy (PRESS) and the semi‐LASER sequence is shown with a measurement of the brain of a volunteer at 3T. With one application of the technique to a patient with a glioblastoma multiforme (GBM), its clinical functionality is demonstrated. With sharp selection profiles and a small CSDE, voxels close to the edge of the VOI can also be used for evaluation. With the additional advantage of being relatively insensitive for B1 inhomogeneities, the semi‐LASER technique can be viewed as a superior substitute for conventional PRESS MR spectroscopic imaging (MRSI) at 3T and beyond. Magn Reson Med, 2007. © 2007 Wiley‐Liss, Inc.
High‐resolution contrast‐enhanced MRI of atherosclerosis with digital cardiac and respiratory gating in mice
Authors: Alsaid Hasan , Sabbah Maher , Bendahmane Zakaria , Fokapu Odette , Felblinger Jacques , Desbleds‐Mansard Catherine , Corot Claire , Briguet André , Crémillieux Yannick , Canet‐Soulas Emmanuelle
Published: October 2007

Atherosclerosis initially develops predominantly at the aortic root and carotid origin, where effective visualization in mice requires efficient cardiac and respiratory gating. The present study sought to first compare the high‐resolution MRI gating performance of two digital gating strategies using: 1) separate cardiac and respiratory signals (double‐sensor); and 2) a single‐sensor cardiorespiratory signal (ECG demodulation), and second, to apply an optimized processing technique to dynamic contrast‐enhanced (CE) carotid origin vessel‐wall imaging in mice. High‐resolution MR mouse heart and aortic arch images were acquired by ECG signal detection, digital signal processing, and gating signal generation modeled using Simulink (MathWorks, USA). Double‐sensor gating used a respiratory sensor while single‐sensor gating used breathing‐modulated ECG to generate a demodulated respiratory signal. Pre‐ and postcontrast T1‐weighted images were acquired to evaluate vessel‐wall enhancement with a gadolinium blood‐pool agent (P792; Guerbet, France) at the carotid origin in vivo in ApoE−/− and C57BL/6 mice, using the optimized cardiorespiratory gating processing technique. Both strategies provided images with improved spatial resolution, less artifacts, and 100% correct transistor‐to‐transistor logic (TTL) signals. Image quality allowed vessel‐wall enhancement measurement in all the ApoE−/− mice, with maximal (32%) enhancement 27 min postinjection. The study demonstrated the efficiency of both cardiorespiratory gating strategies for dynamic contrast‐enhanced vessel‐wall imaging. Magn Reson Med, 2007. © 2007 Wiley‐Liss, Inc.
Multiple reference tissue method for contrast agent arterial input function estimation
Authors: Yang Cheng , Karczmar Gregory S. , Medved Milica , Stadler Walter M.
Published: October 2007

A precise contrast agent (CA) arterial input function (AIF) is important for accurate quantitative analysis of dynamic contrast‐enhanced (DCE)‐MRI. This paper proposes a method to estimate the AIF using the dynamic data from multiple reference tissues, assuming that their AIFs have the same shape, with a possible difference in bolus arrival time. By minimizing a cost function, one can simultaneously estimate the parameters and underlying AIF of the reference tissues. The method is computationally efficient and the estimated AIF is smooth and can have higher temporal resolution than the original data. Simulations suggest that this method can provide a reliable estimate of the AIF for DCE‐MRI data with a moderate signal‐to‐noise ratio (SNR) and temporal resolution, and its performance increases significantly as the SNR and temporal resolution increase. As demonstrated by its clinical application, sufficient reference tissues can be easily obtained from normal tissues and subregions segmented from a tumor region of interest (ROI), which suggests this method can be generally applied to cancer‐based DCE‐MRI studies to estimate the AIF. This method is applicable to general kinetic models in DCE‐MRI, as well as other CE imaging modalities. Magn Reson Med, 2007. © 2007 Wiley‐Liss, Inc.
Three‐dimensional spiral technique for high‐resolution functional MRI
Authors: Hu Yanle , Glover Gary H.
Published: October 2007

For high‐resolution functional MRI (fMRI) studies, signal‐to‐noise ratio (SNR) plays an important role. Any method that results in an improvement in SNR will be able to improve the quality of activation maps. Three‐dimensional (3D) acquisition methods in general can provide higher SNR than that of 2D methods due to volume excitation. To demonstrate the superiority of 3D methods for high‐resolution fMRI scans, a comparison study between 3D and 2D spiral methods was performed using a contrast‐reversing checkerboard visual stimulus. A 3‐inch surface coil was used to limit the in‐plane FOV to 14 cm × 14 cm so that 32 1‐mm slices with an in‐plane voxel size of 1.1 mm × 1.1 mm could be acquired within 5.76 seconds. Results showed that average numbers of activated voxels were 407 and 841 for 2D and 3D methods, respectively (P < 0.01). Therefore, the 3D technique may be a useful alternative to the conventional 2D method for high resolution fMRI studies. Magn Reson Med 58:947–951, 2007. © 2007 Wiley‐Liss, Inc.
Using adiabatic inversion pulses for long‐T2 suppression in ultrashort echo time (UTE) imaging
Authors: Larson Peder E. Z. , Conolly Steven M. , Pauly John M. , Nishimura Dwight G.
Published: October 2007

Ultrashort echo time (UTE) imaging is a technique that can visualize tissues with sub‐millisecond T2 values that have little or no signal in conventional MRI techniques. The short‐T2 tissues, which include tendons, menisci, calcifications, and cortical bone, are often obscured by long‐T2 tissues. This paper introduces a new method of long‐T2 component suppression based on adiabatic inversion pulses that significantly improves the contrast of short‐T2 tissues. Narrow bandwidth inversion pulses are used to selectively invert only long‐T2 components. These components are then suppressed by combining images prepared with and without inversion pulses. Fat suppression can be incorporated by combining images with the pulses applied on the fat and water resonances. Scaling factors must be used in the combination to compensate for relaxation during the preparation pulses. The suppression is insensitive to RF inhomogeneities because it uses adiabatic inversion pulses. Simulations and phantom experiments demonstrate the adiabatic pulse contrast and how the scaling factors are chosen. In vivo 2D UTE images in the ankle and lower leg show excellent, robust long‐T2 suppression for visualization of cortical bone and tendons. Magn Reson Med 58:952–961, 2007. © 2007 Wiley‐Liss, Inc.
Diffusion properties of NAA in human corpus callosum as studied with diffusion tensor spectroscopy
Authors: Upadhyay Jaymin , Hallock Kevin , Erb Kelley , Kim Dae‐Shik , Ronen Itamar
Published: October 2007

In diffusion tensor imaging (DTI) the anisotropic movement of water is exploited to characterize microstructure. One confounding issue of DTI is the presence of intra‐ and extracellular components contributing to the measured diffusivity. This causes an ambiguity in determining the underlying cause of diffusion properties, particularly the fractional anisotropy (FA). In this study an intracellular constituent, N‐acetyl aspartate (NAA), was used to probe intracellular diffusion, while water molecules were used to probe the combined intra‐ and extracellular diffusion. NAA and water diffusion measurements were made in anterior and medial corpus callosum (CC) regions, which are referred to as R1 and R2, respectively. FA(NAA) was found to be greater than FA(Water) in both CC regions, thus indicating a higher degree of anisotropy within the intracellular space in comparison to the combined intra‐ and extracellular spaces. A decreasing trend in the FA of NAA and water was observed between R1 and R2, while the radial diffusivity (RD) for both molecules increased. The increase in RD(NAA) is particularly significant, thus explaining the more significant decrease in FA(NAA) between the two regions. It is suggested that diffusion tensor spectroscopy of NAA can potentially be used to further characterize microscopic anatomic organization in white matter. Magn Reson Med 58:1045–1053, 2007. © 2007 Wiley‐Liss, Inc.
Improved suppression of plaque‐mimicking artifacts in black‐blood carotid atherosclerosis imaging using a multislice motion‐sensitized driven‐equilibrium (MSDE) turbo spin‐echo (TSE) sequence
Authors: Wang Jinnan , Yarnykh Vasily L. , Hatsukami Thomas , Chu Baocheng , Balu Niranjan , Yuan Chun
Published: October 2007

In this study, a turbo spin‐echo (TSE) based motion‐sensitized driven‐equilibrium (MSDE) sequence was used as an alternative black‐blood (BB) carotid MRI imaging scheme. The MSDE sequence was first optimized for more efficient residual blood signal suppression in the carotid bulb of healthy volunteers. Effective contrast‐to‐noise ratio (CNReff) and residual signal‐to‐noise ratio (SNR) in the lumen measured from MSDE images were then compared to those measured from inflow saturation (IS) and double inversion‐recovery (DIR) images. Statistically significant higher CNReff and lower lumen SNR were obtained from MSDE images. To assess MSDE sequence in a clinical carotid protocol, 42 locations from six subjects with 50% to 79% carotid stenosis by duplex ultrasound were scanned with both MSDE and multislice DIR. The comparison showed that MSDE images present significantly higher CNR and lower lumen SNR compared to corresponding multislice DIR images. The vessel wall area and mean wall thickness measurements in MSDE images were slightly but significantly lower than those obtained with other blood suppression techniques. In conclusion, in vivo comparisons demonstrated that MSDE sequence can achieve better blood suppression and provide a more accurate depiction of the lumen boundaries by eliminating plaque mimicking artifacts in carotid artery (CA) imaging. Magn Reson Med 58:973–981, 2007. © 2007 Wiley‐Liss, Inc.
Sparse MRI: The application of compressed sensing for rapid MR imaging
Authors: Lustig Michael , Donoho David , Pauly John M.
Published: October 2007

The sparsity which is implicit in MR images is exploited to significantly undersample k‐space. Some MR images such as angiograms are already sparse in the pixel representation; other, more complicated images have a sparse representation in some transform domain–for example, in terms of spatial finite‐differences or their wavelet coefficients. According to the recently developed mathematical theory of compressed‐sensing, images with a sparse representation can be recovered from randomly undersampled k‐space data, provided an appropriate nonlinear recovery scheme is used. Intuitively, artifacts due to random undersampling add as noise‐like interference. In the sparse transform domain the significant coefficients stand out above the interference. A nonlinear thresholding scheme can recover the sparse coefficients, effectively recovering the image itself. In this article, practical incoherent undersampling schemes are developed and analyzed by means of their aliasing interference. Incoherence is introduced by pseudo‐random variable‐density undersampling of phase‐encodes. The reconstruction is performed by minimizing the ℓ1 norm of a transformed image, subject to data fidelity constraints. Examples demonstrate improved spatial resolution and accelerated acquisition for multislice fast spin‐echo brain imaging and 3D contrast enhanced angiography. Magn Reson Med, 2007. © 2007 Wiley‐Liss, Inc.
Coronary magnetic resonance vein imaging: Imaging contrast, sequence, and timing
Authors: Nezafat Reza , Han Yuchi , Peters Dana C. , Herzka Daniel A. , Wylie John V. , Goddu Beth , Kissinger Kraig K. , Yeon Susan B. , Zimetbaum Peter J. , Manning Warren J.
Published: October 2007

Recently, there has been increased interest in imaging the coronary vein anatomy to guide interventional cardiovascular procedures such as cardiac resynchronization therapy (CRT), a device therapy for congestive heart failure (CHF). With CRT the lateral wall of the left ventricle is electrically paced using a transvenous coronary sinus lead or surgically placed epicardial lead. Proper transvenous lead placement is facilitated by the knowledge of the coronary vein anatomy. Cardiovascular MR (CMR) has the potential to image the coronary veins. In this study we propose and test CMR techniques and protocols for imaging the coronary venous anatomy. Three aspects of design of imaging sequence were studied: magnetization preparation schemes (T2 preparation and magnetization transfer), imaging sequences (gradient‐echo (GRE) and steady‐state free precession (SSFP)), and imaging time during the cardiac cycle. Numerical and in vivo studies both in healthy and CHF subjects were performed to optimize and demonstrate the utility of CMR for coronary vein imaging. Magnetization transfer was superior to T2 preparation for contrast enhancement. Both GRE and SSFP were viable imaging sequences, although GRE provided more robust results with better contrast. Imaging during the end‐systolic quiescent period was preferable as it coincided with the maximum size of the coronary veins. Magn Reson Med, 2007. © 2007 Wiley‐Liss, Inc.
Correction for artifacts induced by B0 and B1 field inhomogeneities in pH‐sensitive chemical exchange saturation transfer (CEST) imaging
Authors: Sun Phillip Zhe , Farrar Christian T. , Sorensen A. Gregory
Published: October 2007

Chemical exchange saturation transfer (CEST) imaging provides an indirect detection mechanism that allows quantification of certain labile groups unobservable using conventional MRI. Recently, amide proton transfer (APT) imaging, a variant form of CEST imaging, has been shown capable of detecting lactic acidosis during acute ischemia, providing information complementary to that of perfusion and diffusion MRI. However, CEST contrast is usually small, and therefore, it is important to optimize experimental conditions for reliable and quantitative CEST imaging. In particular, CEST imaging is sensitive to B0 and B1 field, while on the other hand; field inhomogeneities persist despite recent advances in magnet technologies, especially for in vivo imaging at high fields. Consequently, correction algorithms that can compensate for field inhomogeneity‐induced measurement errors in CEST imaging might be very useful. In this study, the dependence of CEST contrast on field distribution was solved and a correction algorithm was developed to compensate for field inhomogeneity‐induced CEST imaging artifacts. In addition, the proposed algorithm was verified with both numerical simulation and experimental measurements, and showed nearly complete correction of CEST imaging measurement errors caused by moderate field inhomogeneity. Magn Reson Med, 2007. © 2007 Wiley‐Liss, Inc.
Positive contrast visualization of iron oxide‐labeled stem cells using inversion‐recovery with ON‐resonant water suppression (IRON)
Authors: Stuber Matthias , Gilson Wesley D. , Schär Michael , Kedziorek Dorota A. , Hofmann Lawrence V. , Shah Saurabh , Vonken Evert‐Jan , Bulte Jeff W.M. , Kraitchman Dara L.
Published: October 2007

In proton magnetic resonance imaging (MRI) metallic substances lead to magnetic field distortions that often result in signal voids in the adjacent anatomic structures. Thus, metallic objects and superparamagnetic iron oxide (SPIO)‐labeled cells appear as hypointense artifacts that obscure the underlying anatomy. The ability to illuminate these structures with positive contrast would enhance noninvasive MR tracking of cellular therapeutics. Therefore, an MRI methodology that selectively highlights areas of metallic objects has been developed. Inversion‐recovery with ON‐resonant water suppression (IRON) employs inversion of the magnetization in conjunction with a spectrally‐selective on‐resonant saturation prepulse. If imaging is performed after these prepulses, positive signal is obtained from off‐resonant protons in close proximity to the metallic objects. The first successful use of IRON to produce positive contrast in areas of metallic spheres and SPIO‐labeled stem cells in vitro and in vivo is presented. Magn Reson Med 58:1072–1077, 2007. © 2007 Wiley‐Liss, Inc.
Incorporating contrast agent diffusion into the analysis of DCE‐MRI data
Authors: Pellerin Martin , Yankeelov Thomas E. , Lepage Martin
Published: October 2007

Standard two‐compartment pharmacokinetic models that describe the dynamic contrast‐enhanced magnetic resonance imaging (DCE‐MRI) time course of gadolinium diethylenetriamine pentaacetic acid (Gd‐DTPA) concentration in a tissue do not account for the passive diffusion of contrast agent (CA) from a well‐perfused to a less vascularized region. Even when the arterial input function (AIF) is perfectly known, the standard Tofts model returns inaccurate values of Ktrans (mean absolute relative difference [ARD] of 43%) from realistic simulated data where a well‐defined delineation exists between a well‐perfused and a poorly vascularized region. This contribution proposes a diffusion‐perfusion (DP) model in which diffusion of a low molecular weight CA is incorporated in the standard two‐compartment Tofts model. The proposed DP model reliably retrieved the values of Ktrans and ve (mean ARD of 16% and 17%, respectively) from simulated data. On mouse adenocarcinoma xenograft data showing evidence of CA diffusion, the standard model returned unphysical values of ve in the tumor core whereas the proposed DP model found values that were in the physical range (0 < ve < 1) throughout the tissue. In addition, Ktrans distributions from the DP model more closely corresponded to the observed sharp delineation between highly and poorly perfused areas observed in the mouse tumors. Magn Reson Med, 2007. © 2007 Wiley‐Liss, Inc.
A theoretical and experimental investigation of the tagging efficiency of pseudocontinuous arterial spin labeling
Authors: Wu Wen‐Chau , Fernández‐Seara María , Detre John A. , Wehrli Felix W. , Wang Jiongjiong
Published: October 2007

Arterial spin labeling (ASL) is capable of noninvasively measuring blood flow by magnetically tagging the protons in arterial blood, which has been conventionally achieved using instantaneous (PASL) or continuous (CASL) RF pulses. As an intermediate method, pseudocontinuous ASL (pCASL) utilizes a train of discrete RF pulses to mimic continuous tagging that is often unavailable on imagers due to the requirement of continuous RF transmit capabilities. In the present study, we implemented two versions of pCASL (balanced and unbalanced gradient waveforms in tag and control scans) for both transmit/receive coils and array receivers. Experimental data show a 50% ± 4% increase of signal‐to‐noise ratio (SNR) compared with PASL and a higher tagging efficiency than amplitude‐modulated (AM) CASL (80% vs. 68%). Computer simulations predict an optimal tagging efficiency of 85% for flow velocities from 10 to 60 cm/s. It is theoretically and experimentally demonstrated that the tagging efficiency of pCASL is dependent upon the resonance offset and flip angle of the RF pulse train. We conclude that pCASL has the potential of combining the merits of PASL, including less hardware demand and higher tagging efficiency, and CASL, which includes a longer tagging bolus and thus higher SNR. These improvements provide a better balance between tagging efficiency and SNR. Magn Reson Med 58:1020–1027, 2007. © 2007 Wiley‐Liss, Inc.