bluuebunny/crossref_metadata_2025 huggingface dataset:
Self‐assembly multifunctional nanocomposites with Fe3O4 magnetic core and CdSe/ZnS quantum dots shell
Authors: Zhang Ying , Wang Shao‐Ning , Ma Song , Guan Jiao‐Jiao , Li Da , Zhang Xiang‐Dong , Zhang Zhi‐Dong
Published: October 2007

This paper describes a new method for self‐assembling multifunctional nanocomposites with a magnetic core of iron oxide Fe3O4 and a shell of CdSe/ZnS quantum dots (QDs). Two sol–gel processes were applied to form the uniform magnetic seeds (Fe3O4@SiO2‐SH) and then the thiol coordination was used to bind the CdSe/ZnS QDs to the surface of the seeds. The multifunctional nanocomposites were characterized by means of transmission electron microscopy, X‐ray diffraction, energy disperse spectroscopy, fluorescence spectroscopy, infrared spectroscopy, and superconducting quantum interference device (SQUID) magnetometer. The results showed that the magnetic Fe3O4 nanoparticles and the CdSe/ZnS fluorescent QDs were combined together. The nanocomposites were of spherical shape with a mean diameter of 25 nm and exhibited well magnetic response, photostability, chemical activity, and water miscibility. The method put forward here can also be extended to combine systems of other metal oxides and QDs to fabricate core‐shell nanocomposites with multifunction for biomedical applications. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2008
Estimation of shelf life of natural rubber latex exam‐gloves based on creep behavior
Authors: Das Srilekha Sarkar , Schroeder LeRoy W.
Published: October 2007

Samples of full‐length glove‐fingers cut from chlorinated and nonchlorinated latex medical examination gloves were aged for various times at several fixed temperatures and 25% relative humidity. Creep testing was performed using an applied stress of 50 kPa on rectangular specimens (10 mm × 8 mm) of aged and unaged glove fingers as an assessment of glove loosening during usage. Variations in creep curves obtained were compared to determine the threshold aging time when the amount of creep became larger than the initial value. These times were then used in various models to estimate shelf lives at lower temperatures. Several different methods of extrapolation were used for shelf‐life estimation and comparison. Neither Q‐factor nor Arrhenius activation energies, as calculated from 10°C interval shift factors, were constant over the temperature range; in fact, both decreased at lower temperatures. Values of Q‐factor and activation energies predicted up to 5 years of shelf life. Predictions are more sensitive to values of activation energy as the storage temperature departs from the experimental aging data. Averaging techniques for prediction of average activation energy predicted the longest shelf life as the curvature is reduced. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2008
Development of photoreceptor‐specific promoters and their utility to investigate EIAV lentiviral vector mediated gene transfer to photoreceptors
Authors: Nicoud Marjorie , Kong Jian , Iqball Sharifah , Kan On , Naylor Stuart , Gouras Peter , Allikmets Rando , Binley Katie
Published: October 2007

Background

We wanted to investigate the ability of recombinant equine infectious anemia virus (EIAV) vectors to transduce photoreceptor cells by developing a series of photoreceptor‐specific promoters that drive strong gene expression in photoreceptor cells.

Methods

Promoter fragments derived from the rhodopsin (RHO), the beta phosphodiesterase (PDE) and the retinitis pigmentosa (RP1) genes were cloned in combination with an enhancer element, derived from the interphotoreceptor retinoid‐binding protein gene (IRBP), into luciferase reporter plasmids. An in vitro transient reporter assay was carried out in the human Y‐79 retinoblastoma cell line. The optimal promoters from this screen were then cloned into the recombinant EIAV vector for evaluation in vivo following subretinal delivery into mice.

Results

All promoters maintained a photoreceptor‐specific expression profile in vitro and the gene expression was further enhanced in combination with the IRBP enhancer. The use of IRBP‐combined RHO or PDE promoters showed modest but exclusive expression in photoreceptors following subretinal delivery to mice. By contrast an EIAV vector containing the cytomegalovirus (CMV) promoter drove reporter gene expression in both photoreceptors and retinal pigment epithelium.

Conclusions

It may be possible to use recombinant EIAV vectors containing photoreceptor‐specific promoters to drive therapeutic gene expression to treat a range of retinal degenerative diseases where the photoreceptor cell is the primary disease target. Copyright © 2007 John Wiley & Sons, Ltd.
MR imaging of hepatocellular carcinoma: Relationship between lesion size and imaging findings, including signal intensity and dynamic enhancement patterns
Authors: van den Bos Indra C. , Hussain Shahid M. , Dwarkasing Roy S. , Hop Wim C.J. , Zondervan Pieter E. , de Man Robert A. , IJzermans Jan N.M. , Walker Craig W. , Krestin Gabriel P.
Published: October 2007

Purpose

To assess the relationship between lesion size and MR imaging findings of pathologically‐proven hepatocellular carcinoma (HCC).

Materials and Methods

In a retrospective, single‐center study, 37 consecutive patients were identified between 1999 and 2005 that underwent preoperative MRI and surgical resection of HCC. A total of 47 lesions (mean size = 6.85 cm, range = 1–25 cm) were assessed for signal intensity (SI), enhancement patterns, and secondary morphologic features. Interobserver rating, percentage enhancement, and contrast‐to‐noise‐ratio (CNR) were determined. Lesions were assessed for combinations of typical MRI features. Regression analysis was used to assess relations between MRI findings and tumor size.

Results

On fat‐suppressed T2‐weighted (T2w) fast‐spin‐echo, smaller lesions had lower SI compared to larger lesions (P < 0.05). In the arterial phase, smaller lesions showed significantly higher percentage enhancement compared to larger lesions (P < 0.05). In the delayed phase, smaller lesions showed less pronounced washout (P < 0.05). Heterogeneity of the lesions, including fatty infiltration, internal nodules, or mosaic pattern, was observed significantly more frequently in larger lesions (P < 0.001). The classic combination of high T2w signal, strong arterial enhancement, and delayed phase washout was present in 23 of 44 lesions (52%).

Conclusion

Smaller HCC often showed lower SI on T2w, more intense arterial enhancement, and less pronounced delayed washout compared to larger HCC. J. Magn. Reson. Imaging 2007. © 2007 Wiley‐Liss, Inc.
MRI identification of the rostral‐caudal pattern of pathology within the corpus callosum in the cuprizone mouse model
Authors: Wu Qi‐Zhu , Yang Qing , Cate Holly S. , Kemper Dennis , Binder Michele , Wang Hong‐Xin , Fang Ke , Quick Melissa J. , Marriott Mark , Kilpatrick Trevor J. , Egan Gary F.
Published: October 2007

Purpose

To characterize and compare histological and MRI‐based changes within the corpus callosum (CC) in the cuprizone mouse model of multiple sclerosis (MS).

Materials and Methods

A total of 12 C57/BL6 mice were fed cuprizone from eight weeks of age for four weeks. One cohort of six cuprizone and two control mice were scanned with a T2‐weighted (T2W) sequence. The other cohort of six cuprizone and four control mice were scanned using a dual‐echo sequence for T2‐mapping and a diffusion‐weighted sequence with two orthogonal diffusion encoding directions to calculate water diffusivities parallel and perpendicular to the CC fiber (apparent diffusion coefficients [ADC]∥ and ADC⟂). After the mice were killed, the rostral‐caudal pattern of CC demyelination and other pathologies were examined using Luxol Fast Blue, neurofilament staining, and immunohistochemistry for microglia and were correlated with MRI.

Results

In contrast to control mice, T2W imaging (T2WI) hyperintensity, reduced ADC∥, and elevated ADC⟂ were detected in the CC of cuprizone‐fed mice, particularly in the caudal segment. The T2 value was increased in the entire CC. Marked demyelination, as well as axonal injury, microglia accumulation, and cellular infiltration were found in the caudal section of the cuprizone mouse CC. The rostral‐caudal pattern of abnormalities within the CC in MRI measurements correlated well with histopathological findings.

Conclusion

Noninvasive MRI using quantitative T2 and ADC mapping accurately characterized the rostral‐caudal pattern of CC demyelination and other pathologies in cuprizone challenged mice, and thus could provide an effective way to assess the structural response to experimental therapeutics being designed for the treatment of MS. J. Magn. Reson. Imaging 2007. © 2007 Wiley‐Liss, Inc.
Different strategies for MRI measurements of renal cortical volume
Authors: Karstoft Kristian , Lødrup Anders B. , Dissing Thomas H. , Sørensen Thomas S. , Nyengaard Jens R. , Pedersen Michael
Published: October 2007

Purpose

First, to measure renal cortical volume (Vc) using different MRI methods combined with a semiautomatic segmentation method. Second, to compare MRI measurements of Vc using the semiautomatic segmentation method with a manual segmentation method. Third, to evaluate the reproducibility of Vc measurements.

Materials and Methods

A total of 22 pigs, 13 with healthy kidneys and nine with diseased kidneys, underwent MRI with two non‐contrast‐agent methods (MRI100×900 and MRI300×1100) and one contrast‐agent method (MRIGd). For each of these methods, Vc was estimated using semiautomatic (Vc100×900, Vc300×1100, and VcGd), as well as manual (VcMANUAL) segmentation. Reference volumes were estimated by stereological means (VcSTEREOLOGY). MRI‐derived volumes were compared with reference volumes using a two‐tailed paired t‐test, and variances between methods were visualized with Bland Altman plots. Reproducibilities were analyzed using covariance analysis.

Results

Neither measurements of Vc100×900, Vc300×1100, nor VcGd differed markedly from VcSTEREOLOGY using semiautomatic segmentation. Vc was comparable when semiautomatic and manual segmentations were performed at the same scan. Reproducibility of MRI estimated Vc values offered intra‐ and interindividual differences <5%.

Conclusion

Vc can in both healthy and diseased kidneys be measured accurately with MRI using both semiautomatic and manual segmentation, and measurements can be obtained with a high reproducibility. Measurements of Vc100×900 may in the future become suitable in patients with chronic renal failure. J. Magn. Reson. Imaging 2007. © 2007 Wiley‐Liss, Inc.
Direct comparison of myocardial perfusion cardiovascular magnetic resonance sequences with parallel acquisition
Authors: Lyne Jonathan C. , Gatehouse Peter D. , Assomull Ravi G. , Smith Gillian C. , Kellman Peter , Firmin David N. , Pennell Dudley J.
Published: October 2007

Purpose

To directly compare the three main myocardial perfusion cardiovascular magnetic resonance (CMR) sequences incorporating parallel acquisition methods.

Materials and Methods

In 15 subjects (12 men, 57 ± 15.7 years) referred for diagnostic coronary angiography, we acquired first‐pass perfusion images (0.1 mmol/kg gadolinium‐DTPA) at rest and during adenosine (140 μg/kg/min) on three separate occasions using three sequences incorporating parallel acquisition methods and approximately equivalent spatiotemporal resolution: hybrid echo planar imaging (hEPI), steady‐state free precession (SSFP), and gradient echo imaging (GRE). We calculated the contrast‐to‐noise ratio (CNR) of each scan and blinded observers scored the presence and severity of artifacts (1, worst to 4, best), diagnostic confidence (0, low to 2, high), transmurality, area, and epicardial vessel territory of perfusion defects.

Results

CNR was greatest with SSFP and least with hEPI (13.15 vs 7.85 P < 0.001). The most artifacts were recorded with SSFP and least with hEPI (2.00 vs 3.03 P < 0.001). Observers were significantly more confident in reporting hEPI images (1.6 hEPI vs 0.9 SSFP, P < 0.001). Results for GRE were intermediate for all assessments.

Conclusion

The hEPI sequence scored best for diagnostic performance despite the SSFP sequence having greater CNR. This trial favors hEPI for clinical myocardial perfusion CMR and suggests CNR should not be the sole criterion used to gauge the best candidate sequence. J. Magn. Reson. Imaging 2007. © 2007 Wiley‐Liss, Inc.
Magnetic resonance imaging assessment of a convective therapy delivery paradigm in a canine prostate model
Authors: Shetty Anil M. , Stafford R. Jason , Elliott Andrew M. , Kassouf Wassim , Brown Gordon A. , Stephens L. Clifton , Tinkey Peggy T. , Bidaut Luc , Pisters Louis L. , Hazle John D.
Published: October 2007

Purpose

To quantitatively investigate the feasibility of MRI as a tool for assessing the spatial distribution of a convectively delivered agent using a canine prostate model.

Materials and Methods

Canine prostates (ex vivo, n = 3; in vivo, n = 12) were injected under several injection paradigms with a solution of gadolinium‐DTPA for MR contrast and methylene blue as a grossly visible surrogate drug marker. Ex vivo and in vivo distributions were assessed at 1.5T and quantitatively compared.

Results

Measured distributions using MRI and methylene blue pathology photographs were analyzed using a Bland–Altman method. The fractional percentage volume covered (Vfrac) compared the measurements grossly: Pearson's correlation coefficients were R = 0.99 for ex vivo and R = 0.77 for in vivo (P < 0.05). The fractional percentage of area covered (Afrac) demonstrated the high degree of spatial correlation between individual slices: R = 0.93 for ex vivo and R = 0.98 for in vivo (P < 0.05). There was no statistically observable bias in scale or offset between the measurements.

Conclusion

Measured distributions using MRI and pathology were highly correlated and unbiased, indicating the potential of MRI as a tool for quantitative assessment of interstitial delivery of injected therapies in vivo. J. Magn. Reson. Imaging 2007. © 2007 Wiley‐Liss, Inc.
Pancreatic cancer: Correlation of MR findings, clinical features, and tumor grade
Authors: Elias Jorge , Semelka Richard C. , Altun Ersan , Tsurusaki Masakatsu , Pamuklar Ertan , Zapparoli Mauricio , Voultsinos Vasileios , Armao Diane M. , Rubinas Tara
Published: October 2007

Purpose

To assess the frequency of occurrence of poorly‐marginated and focally‐defined pancreatic ductal adenocarcinoma by MRI and to determine whether these appearances correlate with clinical features and histopathological grade.

Materials and Methods

Institutional review board with waiver of informed consent was obtained for this HIPAA compliant study. A total of 33 patients (16 female, 17 male, mean age = 63.5 ± 12.8, ranging from 41 to 80 years) with histopathologically‐proven pancreatic ductal adenocarcinoma who underwent MR examination between August 2000 and February 2005 were retrospectively evaluated. Clinical data and histopathological tumoral grade were obtained from clinical charts; nine of 33 patients were excluded of the histopathological evaluation since their diagnosis was performed by fine needle aspiration biopsy and it was not possible to obtain the histopathological grade. Two radiologists reviewed all cases independently to identify whether cancers were poorly‐marginated or focally‐defined. Agreement between radiologists was assessed using the kappa coefficient. The overall correlation between imaging findings, clinical features, and histopathological grade was assessed with contingency tables using the Fisher's exact test.

Results

Of the 33 patients, nine (27.2%) were classified as poorly‐marginated and 24 (72.8%) as focally‐defined. Agreement between the two reviewers was excellent (k = 0.92, 95% confidence interval (CI) = 0.78–1.0). Poorly‐marginated cancers exhibited well‐ to moderately‐differentiated histopathology in 71.4% of cases, while focally‐defined cancers had well‐ to moderately‐differentiated histopathology in 17.6% of cases, P = 0.02.

Conclusion

A poorly‐marginated appearance of pancreatic ductal carcinoma on MRI is not uncommon. These cancers exhibited statistically significant moderate‐ to well‐differentiated histopathology compared to focally‐defined cancers. J. Magn. Reson. Imaging 2007. © 2007 Wiley‐Liss, Inc.
Robust dynamic susceptibility contrast MR perfusion using 4D nonlinear noise filters
Authors: Kosior Jayme Cameron , Kosior Robert Karl , Frayne Richard
Published: October 2007

Purpose

To investigate if 4D (simultaneous space and time) nonlinear filtering techniques can produce more robust cerebral blood flow (CBF) estimates by reducing noise in acquired dynamic susceptibility contrast (DSC) MR perfusion data.

Materials and Methods

A digital anthropomorphic brain perfusion phantom was constructed to analyze filter performance by: 1) deriving anthropomorphic tissue volume fractions from a human subject and 2) simulating DSC‐MR perfusion signals for voxels with mixed tissue for various signal‐to‐noise ratios (SNRs). DSC‐MR data for 11 acute ischemic stroke patients were also acquired at 3T. CBF maps cross‐calibrated so that normal white matter CBF was 22 mL/minute/100 g were produced from DSC‐MR data without filtering and from 4D‐Gaussian and 4D‐bilateral noise‐filtered DSC‐MR data.

Results

The nonlinear 4D‐bilateral filter yielded the lowest CBF root‐mean square error (RMSE) in the phantom experiments with noise (average RMSE across all tissues regions for no filtering, 4D‐Gaussian, and 4D‐bilateral was 5.3 mL/minute/100 g, 6.2 mL/minute/100 g, and 4.0 mL/minute/100 g, respectively) and had the best image quality in both the phantom and patient data.

Conclusion

Nonlinear 4D noise filters are better suited to the 4D nature of DSC‐MR data. Linear spatial filters are not appropriate and can produce larger CBF errors than without filtering. J. Magn. Reson. Imaging 2007. © 2007 Wiley‐Liss, Inc.
Assessment of solvent residues accessibility using three Sulfo‐NHS‐biotin reagents in parallel: application to footprint changes of a methyltransferase upon binding its substrate
Authors: Gabant Guillaume , Augier Julie , Armengaud Jean
Published: October 2007

NHS‐biotin modification as a specific lysine probe coupled to mass spectrometry detection is increasingly used over the past years for assessing amino acid accessibility of proteins or complexes as an alternative when well‐established methods are challenged. We present a strategy based on usage in parallel of three commercially available reagents (Sulfo‐NHS‐biotin, Sulfo‐NHS‐LC‐biotin, and Sulfo‐NHS‐LC‐LC‐biotin) to efficiently assess the solvent accessibility of amino acids using MALDI‐TOF mass spectrometry. The same qualitative pattern of reactivity was observed for these three reagents on the THUMPα protein at four reagent/polypeptide molar ratios (2 : 1, 6 : 1, 13 : 1, and 26 : 1). Peptide assignment of the detected ions gains in accuracy because of the triple redundancy due to specific increments of monoisotopic mass. These reagents are a good alternative to isotope labeling when using only a single MALDI‐TOF mass spectrometer. We observed that hydroxyl groups of serine and tyrosine residues were also modified by these Sulfo‐NHS‐biotin reagents. The low amount of protein required and the method's simplicity make this procedure accessible and affordable in order to obtain topological information on proteins difficult to purify. This method was used to identify two lysine residues of the TrmG10 methyltransferase from Pyrococcus abyssi that were differentially reactive, modified in the protein but not in the tRNA–protein complex. Copyright © 2007 John Wiley & Sons, Ltd.
Astrocytes stimulate interleukin‐17 and interferon‐γ production in vitro
Authors: Miljkovic Djordje , Momcilovic Miljana , Stojanovic Ivana , Stosic‐Grujicic Stanislava , Ramic Zorica , Mostarica‐Stojkovic Marija
Published: October 2007

Astrocytes play important roles in the complex and as yet not very well understood net of interactions among resident and infiltrating cells during central nervous system (CNS) inflammation. In such an intricate network, cytokines represent an essential means for intercellular communication, and astrocytes are able to affect their generation and/or release. Among various cytokines produced by infiltrating cells, interferon (IFN)‐γ and interleukin (IL)‐17 are the focus of this research, because they are pivotal cytokines of helper T‐cell type 1 (Th1) and helper T‐cell type 17 (Th17), respectively. Importantly, both Th1 and Th17 cells, as well as their cytokines, have been shown to be of importance for the pathogenesis of experimental autoimmune encephalomyelitis (EAE), an animal model of a prototypical CNS disease with inflammatory pathogenesis, multiple sclerosis. Therefore, the influence of astrocytes on the generation of IFN‐γ and IL‐17 in concanavalin A‐ and myelin basic protein‐stimulated lymph node cells of healthy rats and rats with developing EAE, respectively, was investigated in vitro. Astrocytes up‐regulated IL‐17 and IFN‐γ gene expression and protein synthesis in T cells, which coincided with astrocytes' ability to express IL‐23 subunit p19 and common IL‐12/IL‐23 subunit p40 but not IL‐12 subunit p35 in the cocultivations. These results suggest one more way in which astrocytes could contribute to the complex interactions during CNS inflammation. © 2007 Wiley‐Liss, Inc.
Lubrication performance of multialkylatedcyclopentane oils for sliding friction of steel under vacuum condition
Authors: Masuko Masabumi , Mizuno Hideaki , Suzuki Akihito , Obara Shingo , Sasaki Akira
Published: October 2007

Sliding friction experiments under vacuum lubricated with additive‐free multialkylatedcyclopentane (MAC) were carried out using a ball‐on‐disc tribometer with 440C stainless steel as the material of the specimen. Antiwear characteristics of additive‐free MAC during the steady friction region under vacuum were shown to be better than those of perfluoropolyether (PFPE). However, it was found that the friction coefficient lubricated with the additive‐free MAC under vacuum showed an initial seizure‐like high friction of approximately 0.2 at the beginning of the test, followed by a steady low friction of approximately 0.1. It was also found in contrast that PFPE did not show the initial seizure‐like high friction but maintained a lower friction coefficient than 0.1 throughout the experiment. The initial high wear volume lubricated with the additive‐free MAC was found to be related to the initial seizure‐like high friction. The tricresylphosphate formulation prevented the initial seizure‐like high friction. Copyright © 2007 John Wiley & Sons, Ltd.
Novel Amphiphilic Styrene‐Based Block Copolymers for Induced Surface Reconstruction
Authors: Funk Lutz , Brehmer Martin , Zentel Rudolf , Kang Huiman , Char Kookheon
Published: October 2007

This paper describes the synthesis of amphiphilic block copolymers by living radical polymerization (NMP) of new styrene‐like monomers. The polar monomers (ethylene oxide side chains and free hydroxyl‐ or amino‐groups after deprotection) were polymerized in a “protected form” to adjust the solubility of the monomers. In this way high molar mass polymers with a narrow polydispersity (around or below 1.2) were accessible. In the bulk state hydrophobic and hydrophilic domains demix. By exposing thin films of these polymers to vacuum (air) or alternatively to water or a hydrophilic surface it becomes possible to switch the surface polarity reversibly between contact angles of about 105° and 83° as a result of surface reconstruction. Through side chains of different length and with different functionalities, it was possible to adjust the glass transition temperatures to values between −2 °C to 140 °C for the hydrophilic blocks and −30 °C to 100 °C for the hydrophobic block. The wide range of the glass temperatures allowed it to find a block copolymer system with a slow kinetic concerning the surface reconstruction process, so that a mechanistic examination of the process by AFM was possible. It got, thereby, possible to detect the break‐up of the hydrophobic surface lamella and the upfold of the hydrophilic lamella in contact with water.

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Flexural Creep Behavior of Unidirectional and Cross‐Ply All‐Poly(propylene) (PURE®) Composites
Authors: Banik Kaushik , Abraham Thomas N. , Karger‐Kocsis József
Published: October 2007

The long‐term viscoelastic behavior of reinforced all‐poly(propylene) composites was studied by flexural creep tests. Both unidirectional and cross‐ply laminates were prepared from PURE® coextruded tapes by vacuum bag molding in an autoclave. The specimens were subjected to isothermal creep tests at different temperatures ranging from 20 to 80 °C under an applied load. The time‐temperature superposition principle was verified for the creep data. An Arrhenius type relationship was found to better describe the shift data obtained from the creep tests. The activation energies relating to the different reinforcement architecture and different relaxation process were calculated.

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SSFP and GRE phase contrast imaging using a three‐echo readout
Authors: Nielsen Jon‐Fredrik , Nayak Krishna S.
Published: October 2007

A technique for rapid in‐plane phase‐contrast imaging with high signal‐to‐noise ratio (SNR) is described. Velocity‐encoding is achieved by oscillating the readout gradient, such that each 2DFT phase‐encode is acquired three times following a single RF slice‐selective excitation. Three images are reconstructed, from which both flow velocity and local resonance offset are calculated. This technique is compatible with both gradient‐recalled echo (GRE) and balanced steady‐state free precession (SSFP) imaging using a single steady‐state. The proposed technique enables 1D velocity mapping with 40% higher temporal resolution and 80% higher SNR, compared to conventional PC‐MRI using bipolar velocity‐encoding gradient pulses. Magn Reson Med, 2007. © 2007 Wiley‐Liss, Inc.
Temporal ΔB0 and relaxation in the rat heart
Authors: Dortch Richard D. , Does Mark D.
Published: October 2007

Field maps of the induced main magnetic field offset (ΔB0) were measured in the rat heart at various points in the cardiac cycle for the purpose of identifying their effects on relaxation measurements. The mean ΔB0 of the left ventricle averaged across rats was found to be 0.11 ± 0.35 ppm and 0.19 ± 0.39 ppm at the onset of systole and diastole, respectively. The root mean square (RMS) variation in resonant frequency of the left ventricle averaged across rats was found to be 0.09 ± 0.05 ppm and 0.06 ± 0.04 ppm during systole and diastole, respectively. Temporal variations in ΔB0 could substantially affect quantitative MRI measurements. To assess this, transverse relaxation rates (R2 and R) were measured at different points in the cardiac cycle, and the effects of ΔB0 were estimated using measured field map data. For a given region of the left ventricle, ΔB0 induced a mean error across rats of ≤3.9% for R2 and ≤9.6% for R. For R measurements, the static component of the field inhomogeneity was found to be responsible for most of the error induced. Magn Reson Med 58:939–946, 2007. © 2007 Wiley‐Liss, Inc.
Accelerated 3D echo‐planar spectroscopic imaging at 4 Tesla using modified blipped phase‐encoding
Authors: Ebel Andreas , Schuff Norbert
Published: October 2007

Whole‐brain echo‐planar spectroscopic imaging (EPSI) often substantially lengthens MRI/MRSI (magnetic resonance spectroscopic imaging) protocols. To halve acquisition time, application of a blipped phase‐encoding (PE) gradient during the EPSI readout (RO) was previously suggested by PE of the even RO echoes in k‐space at an interstitial location along kPE, separated from the odd RO echoes, effectively reducing the number of PEs by a factor of 2. However, the approach is very susceptible to phase inconsistencies between even and odd RO echoes in the presence of B0 inhomogeneities and gradient imbalance, leading to ghosting in the PE direction. In this work, the blipped PE gradient is placed in between pairs of even/odd RO gradient lobes to avoid these problems. This approach is demonstrated in a phantom and in normal human brain in vivo at 4T. While the proposed method allows substantial reduction in metabolite ghosting, it may be limited by the presence of a relatively large spurious signal at the Nyquist frequency. Magn Reson Med 58:1061–1066, 2007. © 2007 Wiley‐Liss, Inc.
Viral capsids as MRI contrast agents
Authors: Liepold Lars , Anderson Stasia , Willits Deborah , Oltrogge Luke , Frank Joseph A. , Douglas Trevor , Young Mark
Published: October 2007

Viral capsids have the potential for combined cell/tissue targeting, drug delivery, and imaging. Described here is the development of a viral capsid as an efficient and potentially relevant MRI contrast agent. Two approaches are outlined to fuse high affinity Gd3+ chelating moieties to the surface of the cowpea chlorotic mottle virus (CCMV) capsid. In the first approach, a metal binding peptide has been genetically engineered into the subunit of CCMV. In a second approach gadolinium‐tetraazacyclododecane tetraacetic acid (GdDOTA) was attached to CCMV by reactions with endogenous lysine residues on the surface of the viral capsid. T1 and T2 ionic relaxivity rates for the genetic fusion particle were R1 = 210 and R2 = 402 mM−1s−1 (R2 at 56 MHz) and for CCMV functionalized with GdDOTA were R1 = 46 and R2 = 142 mM−1s−1 at 61 MHz. The relaxivities per intact capsid for the genetic fusion were R1 = 36,120 and R2 = 69,144 mM−1s−1 (R2 at 56 MHz) and for the GdDOTA CCMV construct were R1 = 2,806 and R2 = 8,662 mM−1s−1 at 61 MHz. The combination of high relaxivity, stable Gd3+ binding, and large Gd3+ payloads indicates the potential of viral capsids as high‐performance contrast agents. Magn Reson Med 58:871–879, 2007. © 2007 Wiley‐Liss, Inc.
Parallel imaging reconstruction for arbitrary trajectories using k‐space sparse matrices (kSPA)
Authors: Liu Chunlei , Bammer Roland , Moseley Michael E.
Published: October 2007

Although the concept of receiving MR signal using multiple coils simultaneously has been known for over two decades, the technique has only recently become clinically available as a result of the development of several effective parallel imaging reconstruction algorithms. Despite the success of these algorithms, it remains a challenge in many applications to rapidly and reliably reconstruct an image from partially‐acquired general non‐Cartesian k‐space data. Such applications include, for example, three‐dimensional (3D) imaging, functional MRI (fMRI), perfusion‐weighted imaging, and diffusion tensor imaging (DTI), in which a large number of images have to be reconstructed. In this work, a systematic k‐space–based reconstruction algorithm based on k‐space sparse matrices (kSPA) is introduced. This algorithm formulates the image reconstruction problem as a system of sparse linear equations in k‐space. The inversion of this system of equations is achieved by computing a sparse approximate inverse matrix. The algorithm is demonstrated using both simulated and in vivo data, and the resulting image quality is comparable to that of the iterative sensitivity encoding (SENSE) algorithm. The kSPA algorithm is noniterative and the computed sparse approximate inverse can be applied repetitively to reconstruct all subsequent images. This algorithm, therefore, is particularly suitable for the aforementioned applications. Magn Reson Med, 2007. © 2007 Wiley‐Liss, Inc.
In vivo MR spectroscopic imaging of polyunsaturated fatty acids (PUFA) in healthy and cancerous breast tissues by selective multiple‐quantum coherence transfer (Sel‐MQC): A preliminary study
Authors: He Qiuhong , Shkarin Pavel , Hooley Regina J. , Lannin Donald R. , Weinreb Jeffrey C. , Bossuyt Veerle Ilse Julie
Published: October 2007

The spatial distribution of polyunsaturated fatty acids (PUFA) in healthy and cancerous human breast tissues was measured in vivo with a selective multiple‐quantum coherence transfer (Sel‐MQC) technique. This method selectively detected the olefinic methylene protons (‐CH = CH‐) of PUFA at 5.3 ppm that were coupled with allylic methylene protons (‐CH2‐CH2‐CH=) of unsaturated acyl chain at 2.8 ppm. Unwanted lipid coherences and tissue water signal were dephased in a single scan. Breast PUFA were mapped at 1 cm3 voxel resolution in sagittal slices of nine breasts in six healthy female volunteers that were compared to invasive ductal carcinoma (IDC) in one breast cancer patient. The healthy breast tissue displayed continuous PUFA distribution. In some individuals, PUFA appeared throughout the breast tissue; in others they were only located in the central breast area. Decreased PUFA levels were detected in the IDC of the breast cancer patient. The magnetic resonance spectroscopic imaging (MRSI) measurement was consistent with the histological findings, ultrasound, and mammography images. PUFA patterns are sensitive to abnormal breast tissue changes including malignant transformations, and thus may serve as a biomarker for early diagnosis and therapeutic monitoring of breast disease. Magn Reson Med, 2007. © 2007 Wiley‐Liss, Inc.
4D radial contrast‐enhanced MR angiography with sliding subtraction
Authors: Cashen Ty A. , Jeong Hyun , Shah Maulin K. , Bhatt Hem M. , Shin Wanyong , Carr James C. , Walker Matthew T. , Batjer H. Hunt , Carroll Timothy J.
Published: October 2007

A method is presented for high spatial and temporal resolution 3D contrast‐enhanced magnetic resonance angiography. The overall technique involves a set of interrelated components suited to high‐frame‐rate angiography, including 3D cylindrical k‐space sampling, angular undersampling, asymmetric sampling, sliding window reconstruction, pseudorandom view ordering, and a sliding subtraction mask. Computer simulations and volunteer studies demonstrated the utility of each component of the technique. Angiograms of one hemisphere of the intracranial vasculature were acquired with a pixel size of 1.1 × 1.1 × 2.8 mm and a frame rate of 0.35 sec based on a temporal resolution of 3.5 sec. Such a 3D time‐resolved, or “4D,” technique has the potential to noninvasively acquire diagnostic quality images of certain anatomic regions with a frame rate fast enough to not only ensure the capture of an uncontaminated arterial phase, but even demonstrate contrast bolus flow dynamics. Clinical applications include noninvasive imaging of arteriovenous shunting, which is demonstrated with a patient study. Magn Reson Med 58:962–972, 2007. © 2007 Wiley‐Liss, Inc.
Apparent transverse relaxation rate in human brain varies linearly with tissue iron concentration at 4.7 T
Authors: Mitsumori Fumiyuki , Watanabe Hidehiro , Takaya Nobuhiro , Garwood Michael
Published: October 2007

Multiple pairs of adiabatic passage pulses were implemented in a spin‐echo sequence to achieve accurate measurements of the apparent transverse relaxation time (T) in a short scan time. In experiments on agarose gel phantoms with T2 values ranging from 30 to 105 ms, the measured T values were in good agreement with transverse relaxation times measured with a nonselective Carr‐Purcell‐Meiboom‐Gill sequence. In experiments on normal human brain at 4.7 T, T values in five different gray matter regions were found to range from 38 ± 2 ms (globus pallidus) to 64 ± 2 ms (frontal cortex). The apparent relaxation rate (1/T) in these five regions showed strong correlation (r = 0.97) with published levels of iron (Fe) in those regions. The linear coefficient relating 1/T and [Fe] at 4.7 T was measured to be 0.551 (s · mg Fe/100 g f.w.)−1. When compared with the values obtained in a previous report for six different static fields (B0) up to 1.5 T, the current measurement confirms the linear dependence of the linear coefficient on B0 up to 4.7 T (r = 0.99). These results suggest that the T value in the human brain is predominantly affected by the nonhemin iron distribution. The strong correlation between the obtained T values and the regional iron concentrations suggests a role for this pulse sequence in quantifying in vivo brain iron at high magnetic field. Magn Reson Med 58:1054–1060, 2007. © 2007 Wiley‐Liss, Inc.
Spatial effects in the detection of γ‐aminobutyric acid: Improved sensitivity at high fields using inner volume saturation
Authors: Edden Richard A.E. , Barker Peter B.
Published: October 2007

The MEGA‐PRESS‐IVS method has been developed, which combines MEGA (a frequency‐selective editing technique) editing with the point‐resolved spectroscopy sequence (PRESS) and inner volume saturation (IVS) localization, reducing the deleterious effects of spatial variation in coupling evolution. The IVS method has been previously described for improved efficiency of lactate detection. The current study demonstrates that the combination of MEGA‐PRESS with IVS results in increased sensitivity for edited single‐voxel measurements of glutamate and γ‐aminobutyric acid (GABA). A four‐compartment model of coupling evolution is investigated through simple product operators and full spin‐system simulations and the predicted pattern of signal evolution is demonstrated through MEGA‐PRESS‐MRSI. MEGA‐PRESS‐IVS is then compared to MEGA‐PRESS in a phantom and an average signal increase of 24% is demonstrated in five healthy volunteers. Magn Reson Med, 2007. © 2007 Wiley‐Liss, Inc.
q‐space diffusion of myelin‐deficient spinal cords
Authors: Biton I.E. , Duncan I.D. , Cohen Y.
Published: October 2007

The apparent water diffusion anisotropy in white matter (WM) of excised spinal cords of myelin‐deficient (md) rats and their age‐matched controls was studied by high‐b‐value q‐space diffusion MRS and MRI at different diffusion times. Non‐monoexponential signal decay was observed at long diffusion times. The mean displacements in the md spinal cords were found to be higher than those of the controls. The apparent anisotropy (AA) of the fast‐diffusing component was found to decrease more dramatically with the increase in diffusion time for the md spinal cords as compared with controls, whereas the AA of the slow‐diffusing component in the controls was found to increase with the increase in diffusion time while that of the md cords decreased with the increase in diffusion time. When diffusion MRI was performed, similar diffusion anisotropy was extracted for the md and control spinal cords at diffusion times of 22 and 50 ms. Only at a diffusion time of about 200 ms was a significant difference obtained in the AA of the two groups. This originates from the much smaller increase in the mean displacement perpendicular to the fiber direction in the control group vs. the md group when the diffusion time was increased. Magn Reson Med 58:993–1000, 2007. © 2007 Wiley‐Liss, Inc.
Ultrashort echo time spectroscopic imaging (UTESI) of cortical bone
Authors: Du Jiang , Hamilton Gavin , Takahashi Atsushi , Bydder Mark , Chung Christine B.
Published: October 2007

Cortical bone in the mature skeleton has a short T2* and produces no detectable signal with conventional MR sequences. A two‐dimensional ultrashort echo time (UTE) sequence employing half radio frequency (RF) pulse excitations and radial ramp sampling reduces the effective TE to 8 μs and is capable of detecting signals from cortical bone. We propose a time‐efficient UTE spectroscopic imaging (UTESI) technique based on an interleaved variable TE acquisition, preceded by long T2* signal suppression using either a 90° pulse and gradient dephasing or an inversion pulse and nulling. The projections were divided into multiple groups with the data for each group being collected with progressively increasing TE and interleaved projection angles. The undersampled projections within each group sparsely covered k‐space. A view sharing and sliding window reconstruction algorithm was implemented to reconstruct images at each TE, followed by Fourier transformation in the time domain to generate spectroscopic images. T2* was quantified through either exponential fitting of the time domain images or line fitting of the magnitude spectrum. Relative water content and the resonance frequency shift due to bulk susceptibility were also evaluated. The feasibility of this technique was demonstrated with phantom and volunteer studies on a clinical 3T scanner. Magn Reson Med 58:1001–1009, 2007. © 2007 Wiley‐Liss, Inc.
Sodium renal imaging in mice at high magnetic fields
Authors: Neuberger Thomas , Gulani Vikas , Webb Andrew
Published: October 2007

This work presents the first sodium MRI functional renal study on a mouse model. The tissue sodium concentration was monitored during induced diuresis with furosemide. By using density‐weighted chemical shift imaging (DWCSI) at high field strength a temporal resolution of less than 5 min for three dimensional (3D) data sets with high spatial resolution was achieved. A maximum increase of 20% in the cortex and a decrease of 45% of the original signal strength in the medulla were observed. These findings correspond well with experiments conducted on much larger rodent models. Magn Reson Med 58:1067–1071, 2007. © 2007 Wiley‐Liss, Inc.
MR elastography of breast lesions: Understanding the solid/liquid duality can improve the specificity of contrast‐enhanced MR mammography
Authors: Sinkus Ralph , Siegmann Katja , Xydeas Tanja , Tanter Mickael , Claussen Claus , Fink Mathias
Published: October 2007

The purpose of this analysis is to explore the potential diagnostic gain provided by the viscoelastic shear properties of breast lesions for the improvement of the specificity of contrast enhanced dynamic MR mammography (MRM). The assessment of viscoelastic properties is done via dynamic MR elastography (MRE) and it is demonstrated that the complex shear modulus of in vivo breast tissue follows within the frequency range of clinical MRE a power law behavior. Taking benefit of this frequency behavior, data are interpreted in the framework of the exact model for wave propagation satisfying the causality principle. This allows to obtain the exponent of the frequency power law from the complex shear modulus at one single frequency which is validated experimentally. Thereby, scan time is drastically reduced. It is observed that malignant tumors obtain larger exponents of the power law than benign tumors indicating a more liquid‐like behavior. The combination of the Breast Imaging Reporting and Data System (BIRADS) categorization obtained via MRM with viscoelastic information leads to a substantial rise in specificity. Analysis of 39 malignant and 29 benign lesions shows a significant diagnostic gain with an increase of about 20% in specificity at 100% sensitivity. Magn Reson Med, 2007. © 2007 Wiley‐Liss, Inc.
Fast multislice mapping of the myelin water fraction using multicompartment analysis of T decay at 3T: A preliminary postmortem study
Authors: Du Yiping P. , Chu Renxin , Hwang Dosik , Brown Mark S. , Kleinschmidt‐DeMasters Bette K. , Singel Debra , Simon Jack H.
Published: October 2007

Quantitative mapping of the myelin water content can provide significant insight into the pathophysiology of several white matter diseases, such as multiple sclerosis and leukoencephalopathies, and can potentially become a useful clinical tool for early diagnosis of these diseases. In this study, multicompartment analysis of T decay (MCAT2*) was used for the quantitative mapping of myelin water fraction (MWF). T decay of each voxel at multiple slice locations was acquired in fixed human brains using a multigradient‐echo (MGRE) pulse sequence with alternating readout gradient polarities. Compared to prior techniques using Carr‐Purcell‐Meiboom‐Gill (CPMG) acquisition, the MGRE acquisition approach has: 1) a very short first echo time (≈2 ms) and echo‐spacing (≈1 ms), which allows for the acquisition of multiple sampling points during the fast decay of the myelin water signal; 2) a low RF duty cycle, which is especially important for achieving acceptable specific absorption rate (SAR) levels at high field strengths. Multicompartment analysis was then applied to the T decay in each pixel using a 3‐pool model of white matter to detect the signal arising from the myelin water, myelinated axonal water, and mixed water compartments. Magn Reson Med 58:865–870, 2007. © 2007 Wiley‐Liss, Inc.
Minimizing RF heating of conducting wires in MRI
Authors: Yeung Christopher J. , Karmarkar Parag , McVeigh Elliot R.
Published: October 2007

Performing interventions using long conducting wires in MRI introduces the risk of focal RF heating at the wire tip. Comprehensive EM simulations are combined with carefully measured experimental data to show that method‐of‐moments EM field modeling coupled with heat transfer modeling can adequately predict RF heating with wires partially inserted into the patient‐mimicking phantom. The effects of total wire length, inserted length, wire position in the phantom, phantom position in the scanner, and phantom size are examined. Increasing phantom size can shift a wire's length of maximum tip heating from about a half wave toward a quarter wave. In any event, with wires parallel to the scanner bore, wire tip heating is minimized by keeping the patient and wires as close as possible to the central axis of the scanner bore. At 1.5T, heating is minimized if bare wires are shorter than 0.6 m or between ≈2.4 m and ≈3.0 m. Heating is further minimized if wire insertion into phantoms equivalent to most aqueous soft tissues is less than 13 cm or greater than 40 cm (longer for fatty tissues, bone, and lung). The methods demonstrated can be used to estimate the absolute amount of heating in order to set RF power safety thresholds. Magn Reson Med 58:1028–1034, 2007. © 2007 Wiley‐Liss, Inc.
Enhanced spectral shaping in steady‐state free precession imaging
Authors: Çukur Tolga , Bangerter Neal K. , Nishimura Dwight G.
Published: October 2007

Balanced steady‐state free precession (SSFP) is hindered by the inherent off‐resonance sensitivity and unwanted bright fat signal. Multiple‐acquisition SSFP combination methods, where multiple datasets with different fixed RF phase increments are acquired, have been used for shaping the SSFP spectrum to solve both problems. We present a new combination method (weighted‐combination SSFP or WC‐SSFP) that preserves SSFP contrast and enables banding‐reduction and fat‐water separation. Methods addressing the banding artifact have focused on either getting robust banding‐reduction (complex‐sum SSFP) or improved SNR efficiency (sum‐of‐squares SSFP). The proposed method achieves both robust banding‐reduction and an SNR efficiency close to that of the sum‐of‐squares method. A drawback of fat suppression methods that create a broad stop‐band around the fat resonance is the wedge shape of the stop‐band leading to imperfect suppression. WC‐SSFP improves the suppression of the stop‐band without affecting the pass‐band performance, and prevents fat signal from obscuring the tissues of interest in the presence of considerable resonant frequency variations. The method further facilitates the use of SSFP imaging by providing a control parameter to adjust the level of banding‐reduction or fat suppression to application‐specific needs. Magn Reson Med, 2007. © 2007 Wiley‐Liss, Inc.