bluuebunny/crossref_metadata_2025_split huggingface dataset:
Impact of incidental magnetization transfer effects on inversion‐recovery sequences that use a fast spin‐echo readout
Authors: Meara Simon J.P. , Barker Gareth J. 
Published: September 2007

AbstractMultislice MR images obtained using a fast spin‐echo (FSE) readout are strongly affected by magnetization transfer (MT) effects, which will cause a decrease in the observed longitudinal relaxation times for tissues with a large bound water component. This is pertinent for FSE‐based inversion‐recovery (IR) sequences, as it would be expected to cause a change in the required inversion times. Furthermore, the effect will be greater as the number of slices that are acquired within the repetition time (TR) is increased. A pseudo‐3D IR‐FSE sequence was used to obtain images of a phantom consisting of thermally crosslinked bovine serum albumin. It was found that increasing the number of slabs acquired per TR period led to a decrease in the inversion time that maximally suppressed the signal from the MT phantom; this was not the case for water. This has important consequences for any IR imaging sequence that uses an FSE readout. Magn Reson Med 58:825–829, 2007. © 2007 Wiley‐Liss, Inc.
Selective parity RARE imaging
Authors: Norris David G. 
Published: September 2007

AbstractThis work describes a novel method for rapid acquisition with relaxation enhancement (RARE)/fast spin‐echo (FSE) imaging that removes the constraint of compliance with the Carr‐Purcell‐Meiboom‐Gill (CPMG) condition. In a multiecho sequence, echoes with either odd or even parities are acquired. The refocusing angles are chosen using a recursive algorithm, so that the signal amplitude satisfies a predetermined modulation function. In the examples given in this article an exponential decay to a plateau is used. At each echo the echo parity that gives the desired signal amplitude for the minimum refocusing angle is selected. It is further shown that in the presence of an initial magnetization having an arbitrary phase distribution, the complex conjugate of the signal of one echo parity has to be taken and its k‐space coordinates reversed. T‐weighted images are presented and initial applications to diffusion‐weighted imaging (DWI) and functional imaging shown. Magn Reson Med 58:643–649, 2007. © 2007 Wiley‐Liss, Inc.
MR diffusion tensor imaging study of postinfarct myocardium structural remodeling in a porcine model
Authors: Wu Ed X. , Wu Yin , Nicholls John M. , Wang Jie , Liao Songyan , Zhu Shuguang , Lau Chu‐Pak , Tse Hung‐Fat 
Published: September 2007

AbstractThis study aimed to investigate postinfarct left ventricular (LV) fiber structural alterations by ex vivo diffusion tensor imaging (DTI) in a porcine heart model. In vivo cardiac MR imaging was first performed to measure ventricular function in six adult pigs with septal infarction near apex induced by the LAD ligation 13 weeks earlier. Hearts were then excised from the infarct pigs (n = 6) and six intact controls (n = 6) and fixed in formalin. High‐resolution DTI was employed to examine changes in fractional anisotropy (FA), apparent diffusion coefficient (ADC), and transmural helix angle distribution in the infarct, adjacent and remote regions as compared to the sham regions in the controls. FA values were found to decrease in the infarct and differ between the adjacent and remote regions. ADC increase in the infarct region was substantial, while changes in the adjacent and remote regions were insignificant. Structurally, the double‐helix myocardial structure shifted toward more left‐handed around the infarcted myocardium. Accordingly, the histological analysis revealed clear fiber structural degradation in the adjacent region. These findings confirmed the subtle alterations in the myocardial fiber quality and structure not only in the infarcted but also in the surrounding noninfarcted myocardium or borderzone. Magn Reson Med 58:687–695, 2007. © 2007 Wiley‐Liss, Inc.
Assessment of metabolite quantitation reproducibility in serial 3D‐1H‐MR spectroscopic imaging of human brain using stereotactic repositioning
Authors: Langer Deanna L. , Rakaric Peter , Kirilova Anna , Jaffray David A. , Damyanovich Andrei Z. 
Published: September 2007

AbstractIntrasubject reproducibility of metabolite quantitation in three‐dimensional proton magnetic resonance spectroscopic imaging (3D‐MRSI) was investigated in 10 healthy volunteers over five separate sessions using two echo times (TEs): 144 and 30 ms. The use of a Gill‐Thomas‐Cosman (GTC) stereotactic head frame enabled precise subject repositioning and immobilization. Metabolite levels from each voxel in the volume of interest (VOI) were quantified using the Linear Combination of Model spectra (LCModel) analysis algorithm, and coefficients of variation (CVs) were calculated. Standard error estimates (%SD or Cramer‐Rao lower bounds) generated by LCModel were used as a confidence filter. The 95% confidence interval (CI) was found for each metabolite, providing an indication of the normal fluctuation expected for 3D‐MRSI. In vivo, median CVs at the %SD ≤ 20 level were found to be (%CV for TE = 144 and 30 ms, respectively): N‐acetyl‐aspartate plus N‐acetyl‐aspartyl‐glutamate (NAA): 10.2% and 13.5%; creatine plus phosphocreatine (Cr), 14.4% and 21.7%; and choline‐containing compounds (Cho), 15.2% and 18.4%. Relaxing the statistical filtering criteria to %SD ≤ 30 increased median CVs by less than 5% and permitted in vivo quantitation reproducibility to be evaluated for glutamine plus glutamate (Glx) and myoinositol (Ins) for TE = 30 ms, yielding CVs of 24.0% and 21.0%, respectively. Magn Reson Med 58:666–673, 2007. © 2007 Wiley‐Liss, Inc.
Cardiac and respiratory self‐gated cine MRI in the mouse: Comparison between radial and rectilinear techniques at 7T
Authors: Hiba Bassem , Richard Nathalie , Thibault Hélène , Janier Marc 
Published: September 2007

AbstractECG‐gated cardiac MRI in the mouse is hindered by many technical difficulties in ECG signal recording inside high magnetic field scanners. The present study proposes a robust rectilinear method of acquiring cardiac and respiratory self‐gated cine images in mouse hearts. In this approach, a motion‐synchronization MR signal is collected in the center of k‐space simultaneously with imaging data in each readout of a nontriggered rectilinear acquisition. This signal is then used for both cardiac and respiratory retrospective gating before cine image reconstruction. The value of this approach for overcoming ECG‐gating failure was demonstrated by performing cardiac imaging in eight mice with myocardial infarction. Comparison with an auto‐gated radial k‐space sampling technique, previously reported for cardiac applications in the mouse, found the rectilinear strategy more robust, thanks to a more reliable self‐gating signal, while the radial strategy was less sensitive to motion and flow artifacts. Magn Reson Med 58:745–753, 2007. © 2007 Wiley‐Liss, Inc.
Parallel MRI reconstruction using variance partitioning regularization
Authors: Lin Fa‐Hsuan , Wang Fu‐Nien , Ahlfors Seppo P. , Hämäläinen Matti S. , Belliveau John W. 
Published: September 2007

AbstractMultiple receivers can be utilized to enhance the spatiotemporal resolution of MRI by employing the parallel imaging technique. Previously, we have reported the L‐curve Tikhonov regularization technique to mitigate noise amplification resulting from the geometrical correlations between channels in a coil array. Nevertheless, one major disadvantage of regularized image reconstruction is lengthy computational time in regularization parameter estimation. At a fixed noise level, L‐curve regularization parameter estimation was also found not to be robust across repetitive measurements, particularly for low signal‐to‐noise ratio (SNR) acquisitions. Here we report a computationally efficient and robust method to estimate the regularization parameter by partitioning the variance of the noise‐whitened encoding matrix based on the estimated SNR of the aliased pixel set in parallel MRI data. The proposed Variance Partitioning Regularization (VPR) method can improve computational efficiency by 2–5‐fold, depending on image matrix sizes and acceleration rates. Our anatomical and functional MRI results show that the VPR method can be applied to both static and dynamic MRI experiments to suppress noise amplification in parallel MRI reconstructions for improved image quality. Magn Reson Med 58:735–744, 2007. © 2007 Wiley‐Liss, Inc.
Variable slew‐rate spiral design: Theory and application to peak B1 amplitude reduction in 2D RF pulse design
Authors: Xu Dan , King Kevin F. , Liang Zhi‐Pei 
Published: September 2007

AbstractA new class of spiral trajectories called variable slew‐rate spirals is proposed. The governing differential equations for a variable slew‐rate spiral are derived, and both numeric and analytic solutions to the equations are given. The primary application of variable slew‐rate spirals is peak B1 amplitude reduction in 2D RF pulse design. The reduction of peak B1 amplitude is achieved by changing the gradient slew‐rate profile, and gradient amplitude and slew‐rate constraints are inherently satisfied by the design of variable slew‐rate spiral gradient waveforms. A design example of 2D RF pulses is given, which shows that under the same hardware constraints the RF pulse using a properly chosen variable slew‐rate spiral trajectory can be much shorter than that using a conventional constant slew‐rate spiral trajectory, thus having greater immunity to resonance frequency offsets. Magn Reson Med 58:835–842, 2007. © 2007 Wiley‐Liss, Inc.
Suitability of T1Gd as the “dGEMRIC index” at 1.5T and 3.0T
Authors: Williams Ashley , Mikulis Brandon , Krishnan Nitya , Gray Martha , McKenzie Charlie , Burstein Deborah 
Published: September 2007

AbstractDelayed gadolinium‐enhanced MRI of cartilage (dGEMRIC) is based on the theory that Gd‐DTPA2− will distribute in inverse relation to cartilage glycosaminoglycan (GAG). T1Gd (T1 after penetration of a 0.2 mmol/kg dose of Gd‐DTPA2−) has been used as the dGEMRIC index, although (1/T1Gd–1/T1o) should be more representative of Gd‐DTPA2− concentration (where T1o = T1 before contrast). T1o and T1Gd were measured in 20 volunteers at both 1.5T and 3T and the correlation between the metrics of T1Gd and (1/T1Gd–1/T1o) was calculated. There was a high correlation coefficient between the two metrics at both field strengths, with R = 0.94, 0.93, and 0.90 for central medial femur, posterior medial femur, and medial tibia, respectively, at 1.5T and 0.87, 0.94, 0.96 at 3T. In all cases P < 0.0001. Therefore, these data suggest that, for native cartilage, the current practice of measuring T1Gd (but not also T1o) is adequate at both 1.5T and 3T. Magn Reson Med 58:830–834, 2007. © 2007 Wiley‐Liss, Inc.
Magnetic nanoparticle labeling of mesenchymal stem cells without transfection agent: Cellular behavior and capability of detection with clinical 1.5 T magnetic resonance at the single cell level
Authors: Hsiao Jong‐Kai , Tai Ming‐Fong , Chu Hung‐Hao , Chen Shin‐Tai , Li Hung , Lai Dar‐Ming , Hsieh Sung‐Tsang , Wang Jaw‐Lin , Liu Hon‐Man 
Published: September 2007

AbstractThe purpose of this work was to evaluate the efficacy of labeling human mesenchymal stem cells (hMSCs) by ionic superparamagnetic iron oxide (SPIO) without a transfection agent and verifying its capability to be detected with clinical 1.5 T magnetic resonance (MR) at the single‐cell level. Human hMSCs were incubated for 24 h with an ionic SPIO, Ferucarbotran. The labeling efficiency of hMSCs was determined by iron content measurement spectrophotometrically, and the influence of labeling on cell behavior was ascertained by examination of cell viability using the trypan blue exclusion method, cell proliferation analysis using MTT (3‐(4,5‐Dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide) assay, mitochondrial membrane potential (MMP) change, differentiation capacity, and reactive oxygen species (ROS) production measured by dichlorofluorescein diacetate (DCFDA) fluorescent probe. Labeled hMSCs were scanned under 1.5 T MRI with three‐dimensional (3D) and two‐dimensional (2D) T2‐weighted gradient echo (GRE) pulse sequences. Human hMSC labeling without transfection agent was efficient. The iron content in hMSCs was 23.4 pg Fe/cell. No significant change was found in viability, proliferation, MMP change, ROS production, or differentiation capacity. About 45.2% of the hMSCs could be detected using 1.5 T MRI at the single cell level with 3D GRE and four repetitions. Magn Reson Med 58:717–724, 2007. © 2007 Wiley‐Liss, Inc.
Spin‐echo MRI underestimates functional changes in microvascular cerebral blood plasma volume using exogenous contrast agent
Authors: Mandeville Joseph B. , Leite Francisca P. , Marota John J.A. 
Published: September 2007

AbstractWhile most functional MRI studies using exogenous contrast agent employ gradient‐echo (GE) signal, spin echo (SE) imaging would represent an attractive alternative if its detection power were more comparable with GE imaging. This study demonstrates that SE methods systematically underestimate functional changes in microvascular cerebral blood plasma volume (CBV), so that SE detection power in brain tissue cannot match that provided by GE signal. Empirically, the in vivo response of SE‐CBV was about 40% smaller than that of GE‐CBV in rat brain at low basal values of CBV, a result that is consistent with physics predictions under the simplifying assumption of uniform vessel dilation. However, increasing values of basal CBV were associated with monotonically increasing mean vessel sizes and monotonically decreasing GE to SE ratios of functional changes in CBV (fCBV). This result suggests the presence of large but weakly reactive conduit vessels at high basal values of CBV. Hence, we conclude that GE imaging is the method of choice for functional MRI (fMRI) using exogenous contrast agent in most cases, although SE methods may represent a more spatially linear representation of underlying neural activity that becomes most apparent in regions with high basal CBV, such as the cortical surface. Magn Reson Med 58:769–776, 2007. © 2007 Wiley‐Liss, Inc.
Dynamic contrast‐enhanced myocardial perfusion MRI accelerated with k‐t sense
Authors: Plein Sven , Ryf Salome , Schwitter Juerg , Radjenovic Aleksandra , Boesiger Peter , Kozerke Sebastian 
Published: September 2007

AbstractIn the k‐t sensitivity encoding (k‐t SENSE) method spatiotemporal data correlations are exploited to accelerate data acquisition in dynamic MRI studies. The present study demonstrates the feasibility of applying k‐t SENSE to contrast‐enhanced myocardial perfusion MRI and using the speed‐up to increase spatial resolution. At a net acceleration factor of 3.9 (k‐t factor of 5 with 11 training profiles) accurate representations of dynamic signal intensity (SI) changes were achieved in computer simulations. In vivo, 5× k‐t SENSE was compared with 2× SENSE (identical acquisition parameters except for in‐plane spatial resolution = 1.48 × 1.48 mm2 vs. 2.64 × 2.64 mm2, respectively). In 10 volunteers no differences in myocardial SI profiles were found (relative peak enhancement = 151% vs. 149.7%, maximal upslope = 12.9%/s vs. 13.3%/s for 2× SENSE and 5× k‐t SENSE, respectively, all P > 0.05). Overall image quality was similar, but endocardial dark rim artifacts were reduced with k‐t SENSE. Signal‐to‐noise ratio (SNR) in the myocardium was greater with 5× k‐t SENSE by a factor of 1.36 ± 0.23 at peak contrast enhancement with the relative yield decreasing with increasing dynamics in the object in accordance to theory. Higher nominal acceleration factors of up to 10‐fold were shown to be feasible in computer simulations and in vivo. Magn Reson Med 58:777–785, 2007. © 2007 Wiley‐Liss, Inc.
MRI detection of paramagnetic chemical exchange effects in mice kidneys in vivo
Authors: Vinogradov Elena , He Huamei , Lubag Angelo , Balschi James A. , Sherry A. Dean , Lenkinski Robert E. 
Published: September 2007

AbstractIn this report, the On resonance PARamagnetic CHemical Exchange Effects (OPARACHEE) method was implemented in vivo using WALTZ‐16* as a preparation pulse with a standard spin echo sequence to detect the accumulation and clearance of the TmDOTA‐4AmC− in mouse kidney. The performance of the technique in vivo is described in terms of the magnitude of the contrast effect versus the bolus agent concentration and signal‐to‐noise ratio (SNR) levels. The lowest injected concentration of TmDOTA‐4AmC−, 200 μL of a 2‐mM stock solution (corresponds to ∼0.2 mM agent in plasma), reduced the total water signal in the kidney papilla by 45% 3 min after the a bolus injection. The results show that the OPARACHEE methodology employing low‐amplitude RF trains can detect paramagnetic exchanging agents in vivo. Magn Reson Med 58:650–655, 2007. © 2007 Wiley‐Liss, Inc.
RASER: A new ultrafast magnetic resonance imaging method
Authors: Chamberlain Ryan , Park Jang‐Yeon , Corum Curt , Yacoub Essa , Ugurbil Kamil , Jack Clifford R. , Garwood Michael 
Published: September 2007

AbstractA new MRI method is described to acquire a T2‐weighted image from a single slice in a single shot. The technique is based on rapid acquisition by sequential excitation and refocusing (RASER). RASER avoids relaxation‐related blurring because the magnetization is sequentially refocused in a manner that effectively creates a series of spin echoes with a constant echo time. RASER uses the quadratic phase produced by a frequency‐swept chirp pulse to time‐encode one dimension of the image. In another implementation the pulse can be used to excite multiple slices with phase‐encoding and frequency‐encoding in the other two dimensions. The RASER imaging sequence is presented along with single‐shot and multislice images, and is compared to conventional spin‐echo and echo‐planar imaging sequences. A theoretical and empirical analysis of the spatial resolution is presented, and factors in choosing the spatial resolution for different applications are discussed. RASER produces high‐quality single‐shot images that are expected to be advantageous for a wide range of applications. Magn Reson Med 58:794–799, 2007. © 2007 Wiley‐Liss, Inc.
Comparison of single‐ and dual‐tracer pharmacokinetic modeling of dynamic contrast‐enhanced MRI data using low, medium, and high molecular weight contrast agents
Authors: Orth Robert C. , Bankson James , Price Roger , Jackson Edward F. 
Published: September 2007

AbstractPharmacokinetic parameters corresponding to perfused microvascular volume determined from dynamic contrast‐enhanced (DCE) MRI data were compared to immunohistochemical measures of microvascular density (MVD) and perfused microvascular density. DCE MRI data from human mammary tumors (MDA‐MB‐435) implanted in nude mice using low (Gd‐DTPA, MW ≈0.6 kDa), medium (Gadomer‐17, MWeff ≈35 kDa), and high (PG‐Gd‐DTPA, MW ≈220 kDa) molecular weight contrast agents were analyzed with single‐ and dual‐tracer pharmacokinetic models. MVD values were determined by two manual counting methods, “hot spot” and summed region of interest (SROI). Pharmacokinetic parameters determined using the single‐tracer model (Gd‐DTPA [n = 15] and Gadomer‐17 [n = 13]) did not correlate with MVD measures using either manual counting method. For dual‐tracer studies (Gadomer‐17/Gd‐DTPA [n = 15] and PG‐Gd‐DTPA/Gd‐DTPA [n = 13]), pharmacokinetic parameters demonstrated a statistically significant correlation with MVD determined by the SROI method, but not the “hot spot” method. Ten mice successfully underwent intravital FITC‐labeled lectin perfusion with the hemisphere of highest lectin labeling correlating with pharmacokinetic parameter values in 9 of 10 tumors (single‐tracer Gd‐DTPA [n = 2], single‐tracer Gadomer‐17 [n = 3], and dual‐tracer Gadomer‐17/Gd‐DTPA [n = 5]). This study demonstrates that dual‐tracer DCE MRI studies yield pharmacokinetic parameters that correlate with immunohistochemical measures of MVD. Magn Reson Med 58:705–716, 2007. © 2007 Wiley‐Liss, Inc.
Assessment of human brain temperature by 1H MRS during visual stimulation and hypercapnia
Authors: Kauppinen Risto A. , Vidyasagar Rishma , Childs Charmaine , Balanos George M. , Hiltunen Yrjő 
Published: September 2007

AbstractBrain temperature is determined by the interplay between the cerebral metabolic rate of oxygen (CMRO2) and cerebral blood flow (CBF). In this study, single‐voxel 1H nuclear MRS, with an accuracy of ±0.2°C for temperature determination, was used at 3 T to measure human brain temperature during visual stimulation (which increases both CBF and CMRO2) and hypercapnia (which increases CBF only). Visual stimulation had no detectable effect on brain temperature in the parenchyma showing blood oxygenation level dependent activation. Hypercapnia, leading to an increase in the end tidal CO2 by 8 ± 2 mm Hg above the baseline, caused a short‐lasting decrease in brain temperature of 0.30 ± 0.33°C. These results indicate that increased CBF may be a key factor, bringing about a small decrease in brain temperature during brain activation. However, the increase in CBF is not sufficient to lower brain temperature in the presence of a concomitant increase in endogenous heat production. Copyright © 2007 John Wiley & Sons, Ltd.
Boundary element analysis of three‐dimensional mixed‐mode thermoelastic crack problems using the interaction and energy domain integrals
Authors: Balderrama R. , Cisilino A. P. , Martinez M. 
Published: September 2007

AbstractA three‐dimensional boundary element method (BEM) implementation of the interaction integral methodology for the numerical analysis of mixed‐mode three‐dimensional thermoelastic crack problems is presented in this paper. The interaction integral is evaluated from a domain representation naturally compatible with the BEM, since stresses, strains, temperatures and derivatives of displacements and temperatures at internal points can be evaluated using the appropriate boundary integral equations. Several examples are analysed and the results compared with those available in the literature to demonstrate the efficiency and accuracy of the implementation to solve straight and curved crack‐front problems. Copyright © 2007 John Wiley & Sons, Ltd.
The role of social anxiety in volunteering
Authors: Handy Femida , Cnaan Ram A. 
Published: September 2007

AbstractThe volunteer management literature suggests that the most effective means of recruitment is personal asking. However, agencies that apply this method do not report the expected success in volunteer recruitment. Often they face the volunteer recruitment fallacy: those people assumed to be interested in volunteering do not necessarily volunteer. Based on the literature of shyness or social anxiety and on empirical observations, this article suggests that social anxiety often deters volunteering by new recruits. We hypothesize that people with greater levels of social anxiety will be less likely to volunteer. Furthermore, we hypothesize that people with high social anxiety will prefer to give monetary support to worthy causes rather than volunteer their time, and if they do choose to volunteer, they will do so alongside friends. Our hypotheses are supported based on the findings from a large‐scale nonrandom sample in North America. We suggest how to avoid the volunteer recruitment fallacy by creating a personal environment in which high‐social‐anxiety recruits feel safe and accepted. By removing the fear of being negatively judged by strangers as they enter the agency and creating a more personal approach, new recruits may have a higher probability of becoming long‐term and consistent volunteers.