bluuebunny/crossref_metadata_2025 huggingface dataset:
Bound solitons with 103‐fs pulse width and 585.5‐fs separation from DI‐NOLM figure‐8 fiber laser
Authors: Gong Y. D. , Shum P. , Tang D. Y. , Lu C. , Cheng T. H. , Qi Z. W. , Guan Y. L. , Lai W. J. , Man W. S. , Tam H. Y.
Published: August 2003

Ultra‐short bound‐soliton pulses with pulse 103‐fs width and 585.5‐fs separation are observed experimentally from a figure‐8 passive mode‐locked fiber laser incorporated with a dispersion‐imbalanced nonlinear optical loop mirror (DI‐NOLM). To our knowledge, these are the most closely bound solitons produced from fiber laser to date, and the bound‐soliton separation and pulsewidth remains unchanged even after 1.2‐Km single‐mode fiber (SMF) transmission. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 39: 163–164, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11157
Steady‐state sequence synthesis and its application to efficient fat‐suppressed imaging
Authors: Overall William R. , Nishimura Dwight G. , Hu Bob S.
Published: August 2003

A new synthesis algorithm, based on the Shinnar‐Le Roux (SLR) transform, can be used to generate fully refocused steady‐state pulse sequences with arbitrary magnetization profiles as a function of off‐resonant precession. This is accomplished by appropriate periodic oscillation of the RF excitation magnitude and phase from echo to echo. The technique is applied to the design of refocused steady‐state free precession (SSFP) sequences with flat profiles, providing the opportunity for banding‐artifact‐free imaging with steady‐state contrast. The algorithm is also used to generate refocused‐SSFP sequences with an arbitrarily broad region of attenuated signal. These sequences are implemented and applied to the problem of steady‐state fat suppression. Preliminary results show signal levels that agree well with theory, and a broad region of suppressed signal at each echo. Total imaging time is kept identical to that of a standard refocused‐SSFP experiment through echo equalization and interleaving. 3D images from the leg of a normal volunteer acquired in 44 s demonstrate the applicability of the technique to fat‐suppressed imaging. Magn Reson Med 50:550–559, 2003. © 2003 Wiley‐Liss, Inc.
Assessment of regional systolic and diastolic dysfunction in familial hypertrophic cardiomyopathy using MR tagging
Authors: Ennis Daniel B. , Epstein Frederick H. , Kellman Peter , Fananapazir Lameh , McVeigh Elliot R. , Arai Andrew E.
Published: August 2003

Diastolic and systolic left ventricular (LV) dysfunction often significantly contribute to disabling symptoms in familial hypertrophic cardiomyopathy (FHC). This study compares regional LV function (midwall circumferential strain) during systole and diastole in eight FHC patients and six normal volunteers (NVs) using MR tagging. A prospectively‐gated fast gradient‐echo sequence with an echo‐train readout was modified to support complementary spatial modulation of magnetization (CSPAMM) tagging and full cardiac cycle data acquisition using the cardiac phase to order reconstruction (CAPTOR), thus providing tag persistence and data acquisition during the entire cardiac cycle. Total systolic strains in FHC patients were significantly reduced in septal and inferior regions (both P < 0.01). Early‐diastolic strain rates were reduced in all regions of the FHC group (all P < 0.03). The combination of CSPAMM and CAPTOR allows regional indices of myocardial function to be quantified throughout the cardiac cycle. This technique reveals regional differences in systolic and diastolic impairment in FHC patients. Magn Reson Med 50:638–642, 2003. Published 2003 Wiley‐Liss, Inc.
Lactate doublet quantification and lipid signal suppression using a new biexponential decay filter: Application to simulated and 1H MRS brain tumor time‐domain data
Authors: Serrai Hacene , Senhadji Lotfi , Wang Guoyu , Akoka Serge , Stroman Patrick
Published: August 2003

A new postprocessing filter based on the continuous wavelet transform (CWT) method modeled as a biexponential decay function to isolate the lactate doublet from overlapping lipid resonance(s) and estimate its magnetic resonance spectroscopy (MRS) parameters (signal amplitude, resonance frequencies, and apparent relaxation time (T)) is proposed. The new filter employs the same iterative process used in the previously single exponential decay filter. A comparison of the results obtained from application of both filters to simulated data and real 1H MRS data collected from human blood plasma and brain tumors demonstrates that the new filter provides a better estimate of MRS parameters of lactate, with less computation time. Furthermore, the results show that the new filter is less sensitive to noise and provides a direct estimate of J‐coupling value of the lactate doublet. Magn Reson Med 50:623–626, 2003. © 2003 Wiley‐Liss, Inc.
Analysis and generalized correction of the effect of spatial gradient field distortions in diffusion‐weighted imaging
Authors: Bammer R. , Markl M. , Barnett A. , Acar B. , Alley M.T. , Pelc N.J. , Glover G.H. , Moseley M.E.
Published: August 2003

Nonuniformities of magnetic field gradients can cause serious artifacts in diffusion imaging. While it is well known that nonlinearities of the imaging gradients lead to image warping, those imperfections can also cause spatially dependent errors in the direction and magnitude of the diffusion encoding. This study shows that the potential errors in diffusion imaging are considerable. Further, we show that retrospective corrections can be applied to reduce these errors. A general mathematical framework was formulated to characterize the contribution of gradient nonuniformities to diffusion experiments. The gradient field was approximated using spherical harmonic expansion, and this approximation was employed (after geometric distortions were eliminated) to predict and correct the errors in diffusion encoding. Before the corrections were made, the experiments clearly revealed marked deviations of the calculated diffusivity for fields of view (FOVs) generally used in diffusion experiments. These deviations were most significant farther away from the magnet's isocenter. For an FOV of 25 cm, the resultant errors in absolute diffusivity ranged from approximately –10% to +20%. Within the same FOV, the diffusion‐encoding direction and the orientation of the calculated eigenvectors can be significantly altered if the perturbations by the gradient nonuniformities are not considered. With the proposed correction scheme, most of the errors introduced by gradient nonuniformities can be removed. Magn Reson Med 50:560–569, 2003. © 2003 Wiley‐Liss, Inc.
Measuring the change in CBV upon cortical activation with high temporal resolution using look‐locker EPI and Gd‐DTPA
Authors: Francis S.T. , Pears J.A. , Butterworth S. , Bowtell R.W. , Gowland P.A.
Published: August 2003

A method of simultaneously measuring the changes in cerebral blood volume (CBV) and T that occur on brain activation with high temporal resolution was developed. The method involves measuring the change in the longitudinal relaxation time (T1) that occurs following a bolus injection of Gd‐DTPA and converting this measurement to a change in blood volume assuming fast exchange. The sequence was optimized for the measurement of changes in CBV with high temporal resolution. A change in CBV of 27 ± 4% on activation of the primary visual cortex (V1) was measured across four subjects. The time course of changes in T showed a poststimulus undershoot (P = 0.008) corresponding approximately to a period over which CBV was still elevated above baseline, but falling (P = 0.01). The effects of perfusion, nonfulfillment of the assumption of fast exchange and of intrinsic T1 changes on activation on the model used to calculate the change in CBV are discussed. Magn Reson Med 50:483–492, 2003. © 2003 Wiley‐Liss, Inc.
Fast proton spectroscopic imaging using steady‐state free precession methods
Authors: Dreher Wolfgang , Geppert Christian , Althaus Matthias , Leibfritz Dieter
Published: August 2003

Various pulse sequences for fast proton spectroscopic imaging (SI) using the steady‐state free precession (SSFP) condition are proposed. The sequences use either only the FID‐like signal S1, only the echo‐like signal S2, or both signals in separate but adjacent acquisition windows. As in SSFP imaging, S1 and S2 are separated by spoiler gradients. RF excitation is performed by slice‐selective or chemical shift‐selective pulses. The signals are detected in absence of a B0 gradient. Spatial localization is achieved by phase‐encoding gradients which are applied prior to and rewound after each signal acquisition. Measurements with 2D or 3D spatial resolution were performed at 4.7 T on phantoms and healthy rat brain in vivo allowing the detection of uncoupled and J‐coupled spins. The main advantages of SSFP based SI are the short minimum total measurement time (Tmin) and the high signal‐to‐noise ratio per unit measurement time (SNRt). The methods are of particular interest at higher magnetic field strength B0, as TR can be reduced with increasing B0 leading to a reduced Tmin and an increased SNRt. Drawbacks consist of the limited spectral resolution, particularly at lower B0, and the dependence of the signal intensities on T1 and T2. Further improvements are discussed including optimized data processing and signal detection under oscillating B0 gradients leading to a further reduction in Tmin. Magn Reson Med 50:453–460, 2003. © 2003 Wiley‐Liss, Inc.
Comparison of polarization transfer sequences for enhancement of signals in clinical 31P MRS studies
Authors: Mancini Laura , Payne Geoffrey S. , Leach Martin O.
Published: August 2003

Several 31P MRS studies in tumors in vivo have shown that levels of phosphocholine (PC) and other phosphomonoesters (PME) and phosphodiesters (PDE) are useful prognostic or early‐response indicators. To improve sensitivity for such measurements, four polarization transfer (PT) sequences (insensitive nuclei enhanced by PT (INEPT), distortionless enhancement by PT (DEPT), reverse‐INEPT, and heteronuclear single‐quantum coherence (HSQC)) were assessed theoretically and experimentally. The presence of homonuclear (1H‐1H) and heteronuclear (31P‐1H) couplings of similar magnitude makes theoretical analysis very sensitive to precise model parameters, especially for the 1H‐detected sequences. The 1H‐1H coupling causes the splitting of 1H peaks, and hence reduces the proton spectral resolution. This effect and a 50% signal loss from gradient‐enhanced water suppression negate the usual advantages of 1H‐detection. Among the PT methods, INEPT gave the higher signal enhancement. However, T2 losses during the long echo times (TEs) required by the weak coupling limited the resulting signals from PC. Magn Reson Med 50:578–588, 2003. © 2003 Wiley‐Liss, Inc.
Computation of the fractional anisotropy and mean diffusivity maps without tensor decoding and diagonalization: Theoretical analysis and validation
Authors: Hasan Khader M. , Narayana Ponnada A.
Published: August 2003

Diffusion tensor MRI (DT‐MRI) is a promising modality for in vivo mapping of the organization of deep tissues. The most commonly used DT‐MRI invariant maps are the mean diffusivity, μ(D), relative anisotropy (RA), and fractional anisotropy (FA). Because of the computational burden, anisotropy maps are generally computed offline. The availability of a simple procedure to compute RA, FA, and μ(D) online would make DT‐MRI more useful in clinical applications that require immediate feedback. In this study, analytical expressions that relate the commonly used tensor anisotropy measures obtained from the decoded and diagonalized DT with those obtained from the first and second moments of the measured diffusion‐weighted (DW) data are derived. Specifically, it is shown that for the principal icosahedron encoding scheme, RA is related to the mean and standard deviation (SD) of the DW measurements that can be computed online. Since FA is commonly used as an anisotropy measure, an analytical expression relating RA and FA was derived from the tensor invariants. These results were validated using both Monte Carlo simulations and high‐resolution, normal whole‐brain DT‐MRI measurements acquired with different b‐factors, encoding schemes, and signal‐to‐noise ratio (SNR) levels. The bias introduced by the rotationally variant encoding schemes into the diffusion measures is also investigated. Magn Reson Med 50:589–598, 2003. © 2003 Wiley‐Liss, Inc.
Contrast‐enhanced coronary artery imaging using 3D trueFISP
Authors: Deshpande Vibhas S. , Li Debiao
Published: August 2003

An ECG‐triggered, segmented, magnetization‐prepared, 3D, trueFISP sequence was recently developed for coronary artery imaging. Fat saturation was achieved by a chemically selective fat saturation pulse, which is susceptible to field inhomogeneities. In addition, the blood–myocardial contrast was compromised because data were acquired during signal transience to steady state. The goals of this work were to investigate the potential benefits of T1‐shortening agents in improving blood–myocardial contrast, and to develop a technique to make fat suppression robust to resonance offsets for coronary artery imaging using trueFISP. A magnetization‐preparation scheme using saturation and inversion pulses was developed for simultaneous suppression of tissues over a wide range of T1's, including myocardium and fat. An additional advantage of this method is that it is insensitive to heart rate variations. Computer simulations were used to design the magnetization preparation, and volunteer studies were performed to compare precontrast imaging to contrast‐enhanced (CE) imaging. Results showed consistent fat suppression and a 78% increase in the blood–myocardial contrast‐to‐noise ratio (CNR) for postcontrast imaging over precontrast imaging. In conclusion, contrast agents are useful for trueFISP coronary artery imaging. Magn Reson Med 50:570–577, 2003. © 2003 Wiley‐Liss, Inc.
Morphological and carbogen‐based functional MRI of a chemically induced liver tumor model in mice
Authors: Thomas Carole D. , Chenu Evelyne , Walczak Christine , Plessis Marie‐José , Perin François , Volk Andreas
Published: August 2003

A multifocal mouse liver tumor model chemically induced with 5,9‐dimethyl‐7H‐dibenzo[c,g]carbazole was investigated by respiratory‐triggered morphological and functional MRI (fMRI) at 4.7 Tesla. The model is characterized by the presence of two tumor types: hypovascular cholangioma and vascularized hepatocellular carcinoma (HCC). Growth curves measured by 3D‐MRI showed limited growth of cholangiomas and rapid growth of HCCs after a latency of about 25 weeks. Functional imaging based on T‐weighted fast gradient‐echo MRI and carbogen breathing was optimized for liver imaging in mice. A response to carbogen was observed in HCCs but not in cholangiomas. Transversal analysis (50 HCCs) of signal change upon carbogen revealed four different types of response patterns: 1) signal increase upon carbogen administration (74%); 2) small or insignificant signal change (10%), 3) transient signal decrease and delayed increase (8%), and 4) signal decrease (8%). Longitudinal follow‐up of a subgroup (N = 17) showed that an initially observed type 1 response, attesting to the presence of a functional vasculature, remained stable for at least 3 weeks in 14 HCCs. A switch from a type 1 response to another response type may be useful for demonstrating, in a noninvasive manner, a disturbance of tumor vasculature induced by anti‐vascular or anti‐angiogenic therapy. Magn Reson Med 50:522–530, 2003. © 2003 Wiley‐Liss, Inc.
Diffusion in compartmental systems. I. A comparison of an analytical model with simulations
Authors: Meier Christian , Dreher Wolfgang , Leibfritz Dieter
Published: August 2003

This article examines the way in which microscopic tissue parameters affect the signal attenuation of diffusion‐weighted MR experiments. The influence of transmembrane water flux on the signal decay is emphasized using the Kärger equations, which are modified with respect to the cellular boundary restrictions for intra‐ and extracellular diffusion. This analytical approach is extensively compared to Monte‐Carlo simulations for a tissue model consisting of two compartments. It is shown that diffusion‐weighted MR methods provide a unique tool for estimation of the intracellular exchange time. Restrictions of applicability to in vivo data are examined. It is shown that the intracellular exchange time strongly depends on the size of a cell, leading to an apparent diffusion time dependence for in vivo data. Hence, an analytical model of a two‐compartment system with an averaged exchange time is inadequate for the interpretation of signal curves measured in vivo over large ranges of b‐values. Furthermore, differences of multiexponential signal curves, as obtained by different methods of diffusion weighting, can be explained by the influence of transmembrane water flux. Magn Reson Med 50:500–509, 2003. © 2003 Wiley‐Liss, Inc.
Diffusion in compartmental systems. II. Diffusion‐weighted measurements of rat brain tissue in vivo and postmortem at very large b‐values
Authors: Meier Christian , Dreher Wolfgang , Leibfritz Dieter
Published: August 2003

Diffusion‐weighted single‐voxel 1H spectroscopic measurements were performed on rat brain tissue in vivo and postmortem. Diffusion weighting was achieved by varying the diffusion time from 23 ms to 1.18 sec via the mixing time in a stimulated echo sequence. A series of constant gradient (cg‐) experiments of eight effective gradient strengths q̃2(q̃2 = γ2δ2g2) from 24.2 × 103 to 490.2 × 103 mm−2 was performed, resulting in a maximum attenuation factor of b = 580,000 s/mm2. A fit of three exponential terms was found to be appropriate to represent the attenuation signal over the whole b‐range. The behavior of the slowest decaying component can be fully understood in terms of a long time limit of a modified Kärger formalism for a two‐compartment system. This allowed estimation of the transmembrane water exchange rate: the intracellular exchange time was determined to be 622 ± 29 ms and 578 ± 20 ms in vivo and postmortem, respectively. Magn Reson Med 50:510–514, 2003. © 2003 Wiley‐Liss, Inc.
Arterial transit time imaging with flow encoding arterial spin tagging (FEAST)
Authors: Wang Jiongjiong , Alsop David C. , Song Hee Kwon , Maldjian Joseph A. , Tang Kathy , Salvucci Alana E. , Detre John A.
Published: August 2003

Arterial spin labeling (ASL) perfusion imaging provides direct and absolute measurement of cerebral blood flow (CBF). Arterial transit time is a related physiological parameter reflecting the duration for the labeled spins to reach the brain region of interest. Most of the existing ASL approaches to assess arterial transit time rely on multiple measurements at various postlabeling delay times, and thus are vulnerable to motion artifact as well as computational error. We describe the use of flow encoding arterial spin tagging (FEAST) technique to measure tissue transit time, which can be derived from the ratio between the ASL signals measured with and without appropriate bipolar gradients. In the present study, we provided a theoretical framework and carried out an experimental validation during steady‐state imaging. The global mean tissue transit time was ∼1100 and 1400 ms for two conditions of bipolar gradients with specific encoding velocity (Venc) of 29 and 8 mm/sec, respectively. The mean tissue transit time measured within cerebral vascular territories was shortest in the deep middle cerebral artery (MCA) territory. Application of the FEAST technique in two patients with cerebrovascular disease demonstrated prolonged tissue transit times in the affected vascular territories which were consistent with results from other MR imaging modalities. Magn Reson Med 50:599–607, 2003. © 2003 Wiley‐Liss, Inc.
Breathhold abdominal and thoracic proton MR spectroscopy at 3T
Authors: Katz‐Brull Rachel , Rofsky Neil M. , Lenkinski Robert E.
Published: August 2003

The clinical utility of proton MR spectroscopy (1H‐MRS) has been well demonstrated in the brain, prostate, and breast. The aims of this work were to investigate 1) the feasibility of abdominal and thoracic 1H‐MRS at 3T, 2) the benefits of breathholding to MRS in these regions, and 3) the utility of multiple breathhold averaging for MRS. Breathholding either eliminated or markedly reduced phase and frequency shifts and outer voxel contamination that were associated with the motion of the abdomen and the thorax during breathing. Breathholding was found to be essential to spectroscopic investigation of the thorax. Spectra of renal cell carcinoma metastases in the abdomen and thorax were obtained utilizing multiple breathhold averaging. These spectra exhibited a resonance at 3.2 ppm attributed to the trimethylamine moiety of choline metabolites. The results of this study suggest a practical strategy for implementation of 1H‐MRS in the body. Magn Reson Med 50:461–467, 2003. © 2003 Wiley‐Liss, Inc.
Removing spikes caused by quantization noise from high‐resolution histograms
Authors: Tozer Daniel J. , Tofts Paul S.
Published: August 2003

A novel method is presented for the removal of spikes, caused by the division of two series of integers, from high‐resolution histograms. When two series of integers are divided the results take the form of a nonuniform distribution. Such a division is often used in medical imaging, due to the storage of most images as integers. An example of this is the division of the saturated and unsaturated signal intensities to obtain a magnetization transfer ratio. Histograms produced using these methods often contain spikes relating to the nonuniform distribution mentioned above. These spikes can have serious implications for certain histogram characteristics. Most commonly, peak height and location can be seriously distorted by these spikes, which have predictable locations. These spikes can be removed by the addition of uniformly distributed noise to the integer signal intensities before division. Magn Reson Med 50:649–653, 2003. © 2003 Wiley‐Liss, Inc.
High‐resolution magic angle spinning proton NMR analysis of human prostate tissue with slow spinning rates
Authors: Taylor Jennifer L. , Wu Chin‐Lee , Cory David , Gonzalez R. Gilberto , Bielecki Anthony , Cheng Leo L.
Published: August 2003

The development of high‐resolution magic angle spinning (HR‐MAS) NMR spectroscopy for intact tissue analysis and the correlations between the measured tissue metabolites and disease pathologies have inspired investigations of slow‐spinning methodologies to maximize the protection of tissue pathology structures from HR‐MAS centrifuging damage. Spinning sidebands produced by slow‐rate spinning must be suppressed to prevent their complicating the spectral region of metabolites. Twenty‐two human prostatectomy samples were analyzed on a 14.1T spectrometer, with HR‐MAS spinning rates of 600 Hz, 700 Hz, and 3.0 kHz, a repetition time of 5 sec, and employing various rotor‐synchronized suppression methods, including DANTE, WATERGATE, TOSS, and PASS pulse sequences. Among them, DANTE, as the simplest scheme, has shown the most potential in suppression of tissue water signals and spinning sidebands, as well as in quantifying metabolic concentrations. Magn Reson Med 50:627–632, 2003. © 2003 Wiley‐Liss, Inc.
Time‐resolved flow measurement in the isolated rat heart: Characterization of left coronary artery stenosis
Authors: Köhler Sascha , Hiller Karl‐Heinz , Jakob Peter M. , Bauer Wolfgang R. , Haase Axel
Published: August 2003

The investigation of flow behavior in coronary arteries is of great importance for an understanding of heart failure and heart regulation mechanisms. The purpose of the present study was to demonstrate that flow velocity can be quantified in the coronary arteries of the isolated rat heart with high‐resolution phase contrast MRI. A phase contrast cine‐FLASH imaging sequence was used for flow quantification with an in‐plane resolution of 70 μm and a slice thickness of 500 μm. With time‐resolved measurements, coronary flow over the heart cycle was analyzed. Furthermore, the flow behavior in coronary stenosis was investigated and the degree of stenosis was quantified with MR phase contrast imaging. To achieve the required spatial resolution and a satisfactory signal‐to‐noise ratio, the experiments were performed at 11.75 T. Magn Reson Med 50:449–452, 2003. © 2003 Wiley‐Liss, Inc.
Magnetization transfer effect on the creatine methyl resonance studied by CW off‐resonance irradiation in human skeletal muscle on a clinical MR system
Authors: Renema W. Klaas Jan , Klomp Dennis W.J. , Philippens Mariëlle E.P. , van den Bergh Adrianus J. , Wieringa Bé , Heerschap Arend
Published: August 2003

Magnetization transfer (MT) between the mobile (MR‐visible) spin pool and immobile (MR‐invisible) spin pool of creatine (Cr) was studied on a clinical 1.5 T MR scanner in human skeletal muscle using continuous wave (CW) pre‐irradiation as the saturation method for the immobile pool. For this purpose, only slight modifications to the MR system were made. A specially designed electronic circuit was used to couple a CW amplifier to the RF channel of the scanner. The CW pulse power (γB2/2π) and pulse length were determined to be approximately 550 Hz and 3 s, respectively, for optimal signal attenuation of the Cr methyl signal. The bound Cr fraction in human gastrocnemius muscle was determined to be 0.4–1.3% using a two‐pool exchange model function to describe the MT effect. Magn Reson Med 50:468–473, 2003. © 2003 Wiley‐Liss, Inc.
Equilibrium water exchange between the intra‐ and extracellular spaces of mammalian brain
Authors: Quirk James D. , Bretthorst G. Larry , Duong Timothy Q. , Snyder Avi Z. , Springer Charles S. , Ackerman Joseph J.H. , Neil Jeffrey J.
Published: August 2003

This report describes the measurement of water preexchange lifetimes and intra/extracellular content in intact, functioning mammalian brain. Intra‐ and extracellular water magnetic resonance (MR) signals from rat brain in vivo were quantitatively resolved in the longitudinal relaxation domain following administration of an MR relaxation agent into the extracellular space. The estimated intracellular water content fraction was 81% ± 8%, and the intra‐ to extracellular exchange rate constant was 1.81 ± 0.89 s–1 (mean ± SD, N = 9), corresponding to an intracellular water preexchange lifetime of ∼550 ms. These results provide a temporal framework for anticipating the water exchange regime (fast, intermediate, or slow) underlying a variety of compartment‐sensitive measurements. The method also supplies a means by which to evaluate membrane water permeability and intra/extracellular water content serially in intact tissue. The data are obtained in an imaging mode that permits detection of regional variations in these parameters. Magn Reson Med 50:493–499, 2003. © 2003 Wiley‐Liss, Inc.
In vivo qualitative assessments of articular cartilage in the rabbit knee with high‐resolution MRI at 3 T
Authors: Laurent Didier , Wasvary James , O'Byrne Elizabeth , Rudin Markus
Published: August 2003

Proteoglycan (PG) loss and disruption of the collagen framework in cartilage are early events associated with osteoarthritis (OA). The feasibility of in vivo high‐resolution MRI assessments probing both macromolecules was explored in articular cartilage of the rabbit knee. One‐millimeter thick coronal images were obtained at 3 T with a 97 × 97 μm2 pixel size. A 22% decrease in the magnetization transfer (MT) exchange rate along with an ∼2‐fold greater Gd(DTPA)2‐‐induced decrease in T1 relaxation time were measured in response to papain injection 1 day prior to the MRI session, indicative of an alteration of collagen integrity and PG depletion, respectively. A two‐point method was tested as an alternative to the more time‐consuming multipoint method typically used to measure T1 changes. Kinetics of Gd(DTPA)2‐ uptake were observed with a 10‐min time resolution. The diffusive transport of Gd(DTPA)2‐ was characterized by a T1 decrease ∼2‐fold faster in papain‐treated knees. These data suggest that kinetics of tracer diffusion may be used as an informative marker of PG loss, in addition to the amplitude of T1 variations. When applied to a relevant OA model, the combination of MT and Gd(DTPA)2‐‐MRI may help in identifying new active compounds during efficacy studies on cartilage protection. Magn Reson Med 50:541–549, 2003. © 2003 Wiley‐Liss, Inc.
Model of the human vasculature for studying the influence of contrast injection speed on cerebral perfusion MRI
Authors: van Osch Matthias J.P. , Vonken Evert‐jan P.A. , Wu Ona , Viergever Max A. , van der Grond Jeroen , Bakker Chris J.G.
Published: August 2003

Simulations of dynamic susceptibility contrast (DSC) MRI are frequently performed by assuming a certain shape for the input function and the microvascular response function. However, to investigate the influence of parameters that will affect the shape of the input function, a more complex model of the human vasculature is required. In this study, a model of the human vasculature is proposed that consists of a network of vascular operators based on physiological data typical of a 35‐year‐old male subject. The simulated contrast passage curves were found to be within the range of observed contrast passage curves in a population of patients without vascular disease. The model was used to predict the effect of different injection speeds of the contrast agent on the accuracy of the perfusion experiment. It was found that injection speeds of <3 ml/s lead to an underestimation of the observed cerebral blood flow (CBF). Additionally, it was determined that decreasing the temporal resolution of the acquisition results in an underestimation of the CBF values, and an increase of the standard deviation (SD) of CBF measurements. Magn Reson Med 50:614–622, 2003. © 2003 Wiley‐Liss, Inc.
In vivo study of microcirculation in canine myocardium using the IVIM method†
Authors: Callot Virginie , Bennett Eric , Decking Ulrich K.M. , Balaban Robert S. , Wen Han
Published: August 2003

The intravoxel incoherent motion (IVIM) method was implemented in closed‐chest dogs to obtain measurements on microcirculation in the left ventricular wall in vivo. Specifically, it enabled us to measure the mean microflow velocity (400 ± 40 μm/s) and the vascular volume fraction (VVF) (11.1% ± 2.2%), and observe the directional preference of capillary orientation. The apparent diffusion coefficients (ADCs) of water along and perpendicular to myofibers were also measured. With vasodilatation by adenosine infusion, a 25% increase in the VVF and a 7% increase in the mean microflow velocity were observed, while no change in the ADC was detected. A 28.5% decrease of the ADC was observed postmortem. Magn Reson Med 50:531–540, 2003. Published 2003 Wiley‐Liss, Inc.
Isotropic susceptibility shift under MAS: The origin of the split water resonances in 1H MAS NMR spectra of cell suspensions
Authors: Chen Jin‐Hong , Enloe Brian M. , Xiao Yong , Cory D.G. , Singer Samuel
Published: August 2003

Bulk susceptibility variations in a multiphase system such as cultured cells and tissue have two manifestations: a dipolar field component outside the regular heterogenous region which introduces linebroadening, and an isotropic field part which results in a frequency shift. Previous NMR studies have emphasized the utility of magic angle spinning for averaging the dipolar component, particularly if the spins of interest are limited to one phase of a multiphase system such as a sample of liquid with air pockets or glass beads. However, in analyzing spectra from complex multiphase systems, such as cell suspensions and tissues, etc., the isotropic part is often neglected, leading to questionable interpretation of experimental results. The present study demonstrates that under magic angle spinning, the water resonance in NMR experiments of cell suspensions is split into two resolved peaks due to the isotropic susceptibility shift. These two peaks are assigned to a central core of cell free water and an outer cylindrical ring of tightly packed cells in close association with water. A comprehensive theory for this splitting is provided based on a coaxis cylinder model with different susceptibilities. The frequency difference is shown to be dependent on the susceptibility difference and also on the angle of the rotor in the magnetic field. The splitting distance of the two water peaks can be used to measure the susceptibility difference of water in these two phases. The susceptibility difference was measured for three different cell types: 3T3 F442A preadipocyte cells, mouse embryonic stem cells, and human red blood cells. Magn Reson Med 50:515–521, 2003. © 2003 Wiley‐Liss, Inc.
Block regional off‐resonance correction (BRORC): A fast and effective deblurring method for spiral imaging
Authors: Moriguchi Hisamoto , Dale Brian M. , Lewin Jonathan S. , Duerk Jeffrey L.
Published: August 2003

One primary disadvantage of spiral imaging is blurring artifact due to off‐resonance effects. The conventional frequency segmented off‐resonance correction method that is performed over the entire image is computationally intense due to the large number of fast Fourier transforms (FFTs) required. Here, a new fast off‐resonance correction method, block regional off‐resonance correction (BRORC), is presented. In this method, off‐resonance correction proceeds block‐by‐block through the reconstructed image with FFTs performed on matrices that are smaller than the full image matrix. The BRORC algorithm is typically several times more computationally efficient than the conventional off‐resonance correction algorithm. Additional computational reductions can be expected for the BRORC if only specific image regions require deblurring. The newly proposed off‐resonance correction method offers significant speed advantages and equivalent image quality when compared to conventional off‐resonance correction methods. Magn Reson Med 50:643–648, 2003. © 2003 Wiley‐Liss, Inc.
Effect of vascular crushing on FAIR perfusion kinetics, using a BIR‐4 pulse in a magnetization prepared FLASH sequence
Authors: Schepers Janneke , van Osch Matthias J.P. , Nicolay Klaas
Published: August 2003

Flow‐sensitive alternating inversion recovery (FAIR) perfusion imaging suffers from high vascular signal, resulting in artifacts and overestimation of perfusion. With TurboFLASH acquisition, crushing of vascular signal by bipolar gradients after each excitation is difficult due to the requirement of an ultrashort repetition time. Therefore, insertion of a preparation phase in the FAIR sequence, after labeling and prior to TurboFLASH acquisition, is proposed. A segmented adiabatic BIR‐4 pulse, interleaved with crusher gradients, was used for flow crushing. The effect of the crusher preparation is shown as a function of crusher strength for a flow phantom and in rat brain. Influence of crusher strength on the time‐dependent FAIR signal from rat brain was also measured. Signal from flowing spins in a flow phantom and from arterial spins in rat brain was significantly suppressed. Image quality was improved and the overestimation of perfusion at short inflow times was eliminated. Magn Reson Med 50:608–613, 2003. © 2003 Wiley‐Liss, Inc.
Magnetic resonance spectroscopic imaging reconstruction with deformable shape‐intensity models
Authors: Zhu Xiao‐Ping , Du An‐Tao , Jahng Geon‐Ho , Soher Brian J. , Maudsley Andrew A. , Weiner Michael W. , Schuff Norbert
Published: August 2003

A new method, based on a deformable shape‐intensity model (DSM), was developed to improve the signal‐to‐noise ratio (SNR) of multidimensional magnetic resonance spectroscopic imaging (MRSI) data sets without affecting spectral lineshapes and linewidths. Improvements with DSM, compared to digital filters using conventional signal apodization, were demonstrated on both simulated and experimental in vivo1H MRS images from 22 cognitively normal (CN) elderly subjects and 25 patients with Alzheimer's disease (AD). Simulated MRSI data showed that DSM achieved superior noise suppression compared to a matched apodization filter. Experimental MRSI data showed that SNR could be increased 2.1‐fold with DSM without distorting spectral resolution, thus maintaining all spectral features of the raw, unfiltered data. In conclusion, DSM should be used to achieve high SNR in reconstructing MRSI data. Magn Reson Med 50:474–482, 2003. © 2003 Wiley‐Liss, Inc.
Mapping of periodic waveforms using the ghost reconstructed alternating current estimation (GRACE) magnetic resonance imaging technique
Authors: Yang Hua , Cook Greg G. , Paley Martyn N.J.
Published: August 2003

A new method of estimating alternating currents using ghost images created when the magnetic field from a fluctuating current modulates the phase of the magnetic resonance (MR) signal between successive phase‐encode views is described. The method, known as ghost reconstructed alternating current estimation (GRACE), may be useful for directly mapping fields, and hence current impulses produced by neuronal firing events when synchronized periodic modulation can be induced. Images were acquired on a 1.5 T MR system with small oil capsule phantoms and a single wire with an applied alternating current, placed perpendicular to the main field direction. Computer simulations of these experiments yielded ghost images that agreed with experimental results. A simulated ghost image resulting from an evoked neuronal waveform is also discussed. Weak magnetic fields were detected from both sinusoidal and square wave modulations. Magn Reson Med 50:633–637, 2003. © 2003 Wiley‐Liss, Inc.
Statistical motor unit number estimation: From theory to practice
Authors: Lomen‐Hoerth Catherine , Slawnych Michael P.
Published: August 2003

Statistical motor unit number estimation (MUNE) is one of several experimental techniques used to estimate the number of lower motor neurons innervating a given muscle. All are fairly reproducible and have been applied successfully in monitoring neurogenic disease progression. Quantitating the number of lower motor neurons is important, since the compound muscle action potential (CMAP) and strength may not change as rapidly over time due to the confounding effect of reinnervation. MUNE techniques differ in the way they obtain samples of surface‐recorded motor unit potentials (SMUP). Statistical MUNE is based on Poisson statistics, uses surface stimulation, and is useful in testing distal, superficial nerves. This review focuses on the theory behind the development of the technique, critiques the publications resulting from applying the technique in control and disease subjects, and discusses the future developments needed for clinical utility. Muscle Nerve 28: 263–272, 2003
Immunotherapy of idiopathic inflammatory neuropathies
Authors: Donofrio Peter D.
Published: August 2003

Evaluation of peripheral neuropathy is a common reason for referral to a neurologist. Recent advances in immunology have identified an inflammatory component in many neuropathies and have led to treatment trials using agents that attenuate this response. This article reviews the clinical presentation and treatment of the most common subacute inflammatory neuropathies, Guillain–Barré syndrome (GBS) and Fisher syndrome, and describes the lack of response to corticosteroids and the efficacy of treatment with plasma exchange and intravenous immunoglobulin (IVIG). Chronic inflammatory demyelinating polyneuropathy, although sharing some clinical, electrodiagnostic, and pathologic similarities to GBS, improves after treatment with plasma exchange and IVIG and numerous immunomodulatory agents. Controlled trials in multifocal motor neuropathy have shown benefit after treatment with IVIG and cyclophosphamide. Also discussed is the treatment of less common inflammatory neuropathies whose pathophysiology involves monoclonal proteins or antibodies directed against myelin‐associated glycoprotein or sulfatide. Little treatment data exist to direct the clinician to proper management of rare inflammatory neuropathies resulting from osteosclerotic myeloma; POEMS syndrome; vasculitis; Sjögren's syndrome; and neoplasia (paraneoplastic neuropathy). Muscle Nerve 28: 273–292, 2003
Inflammatory demyelination in a patient with CMT1A
Authors: Vital Anne , Vital Claude , Lagueny Alain , Ferrer Xavier , Ribière‐Bachelier Catherine , Latour Philippe , Petry Klaus G.
Published: August 2003

We report a case of Charcot‐Marie‐Tooth disease (CMT), with identified PMP22 gene duplication (CMT type 1A), and with evidence of an inflammatory demyelinating process superimposed on the course of the chronic genetic disease. Macrophage‐associated demyelination was observed on the peripheral nerve biopsy. This observation supports some experimental data from the literature and shows that there may be a genetic susceptibility to inflammatory demyelinating processes in certain CMT kindreds. Muscle Nerve 28: 373–376, 2003
Electromyography of the anal sphincter: Which muscle to examine?
Authors: Podnar Simon
Published: August 2003

Electromyographic examination of the deeper external anal sphincter (EAS) muscle is far more uncomfortable than of the subcutaneous muscle, so we tested the need for its examination. We compared the findings in 85 paired examinations of ipsilateral subcutaneous and deeper EAS muscles in 67 patients with a cauda equina lesion. When the other muscle was normal, the deeper or subcutaneous muscle was pathological in 18% or 13% of pairs, respectively. In addition, the subcutaneous EAS muscle was usually more severely affected than the deeper EAS muscle. Thus, examination of the deeper EAS muscle did not increase the sensitivity of MUP analysis significantly, and did not seem clinically necessary. Muscle Nerve 28: 377–379, 2003
Two novel mutations in the muscle glycogen phosphorylase gene in McArdle's disease
Authors: Gámez Josep , Rubio Juan C. , Martín Miguel A. , Fernández‐Cadenas Israel , Garcia‐Arumi Elena , Andreu Antoni L. , Arenas Joaquín
Published: August 2003

We report on a Spanish family with myophosphorylase (EC 2.4.1.1) deficiency (McArdle's disease). The proband and his symptomatic sister were compound heterozygous for two novel mutations: a T‐to‐G transversion in exon 14 (c1722 T>G) that changes a tyrosine to a stop codon (Y573X), and a G‐to‐A transition in exon 15 (c1827 G>A) that disrupts the consensus signal at the donor splicing site. These findings further expand knowledge of the genetic bases of muscle glycogen phosphorylase deficiency. Muscle Nerve 28: 380–382, 2003
Cyclosporin A treatment increases rat soleus muscle oxidative capacities
Authors: Sanchez Hervé , N'Guessan Benoit , Ribera Florence , Ventura‐Clapier Renée , Bigard Xavier
Published: August 2003

Previous studies suggested that administration of cyclosporin A (CsA), an immunosuppressive agent, contributes to the increased fatigability of heart transplant recipients. The aim of this study was to investigate whether CsA itself, without vehicle, affects the function of mitochondria maintained in situ, in rats treated with CsA (25mg/kg/day) dissolved in ethanol and olive oil. Treatment with CsA induced a 16% decrease in slow myosin heavy chain (MHC) associated with a 225% increase in fast MHCIIa. The proportion of fibers expressing type IIa MHC increased as a result of CsA treatment. Soleus from the CsA‐treated animals showed an increase in both basal (+85%) and maximal (+37%) mitochondrial respiration (P < 0.001), consistent with a 24% increase in citrate synthase activity, whereas the apparent Km for adenosine diphosphate was unchanged. By itself, CsA has no deleterious effects on muscle oxidative capacity but induces alterations in energy metabolism in accordance with the increased proportion of fast‐twitch oxidative fibers. Muscle Nerve 28: 324–329, 2003
A prospective evaluation of phrenic nerve conduction in multifocal motor neuropathy and chronic inflammatory demyelinating polyneuropathy
Authors: Macia Frederic , Le Masson Gwendal , Rouanet‐Larriviere Marie , Habonimana Desire , Ferrer Xavier , Marthan Roger , Lagueny Alain
Published: August 2003

The purpose of the study was to evaluate electrophysiologically phrenic nerve involvement in multifocal motor neuropathy (MMN) and chronic inflammatory demyelinating polyneuropathy (CIDP). The response latencies following phrenic nerve stimulation were increased in 11 of 14 (80%) patients in the CIDP group but in only 1 of 14 (8%) patients in the MMN group. The mean diaphragmatic compound muscle action potential (CMAP) was significantly lower in amplitude in the CIDP group compared to the MMN group and to a control group of 8 subjects (P < 0.001). There were no significant differences between the MMN and control groups. Only the reduction in CMAP amplitude correlated with the presence of restrictive lung function. Phrenic nerve conduction measurement should be performed more systematically, especially in CIDP and, when diaphragmatic CMAPs are reduced in amplitude, pulmonary function tests should be performed to look for a restrictive lung syndrome. Muscle Nerve 28: 319–323, 2003
Ventilatory dysfunction in mdx mice: Impact of tumor necrosis factor–alpha deletion
Authors: Gosselin Luc E. , Barkley Jacob E. , Spencer Melissa J. , McCormick Kathleen M. , Farkas Gaspar A.
Published: August 2003

Muscular dystrophy is associated with inflammation and fiber necrosis in the diaphragm that may alter ventilatory function. The purpose of this study was to determine to what extent in vivo ventilatory function in dystrophic (mdx) mice was compromised and to assess the impact of deletion of tumor necrosis factor–alpha (TNF‐α), a known proinflammatory cytokine, on ventilatory function, diaphragm contractility, and myosin heavy chain (MHC) distribution in 10–12‐month‐old mdx mice. Although the resting ventilatory pattern did not significantly differ between control and mdx mice, the ventilatory response to hypercapnia in mdx mice was significantly attenuated. Elimination of TNF‐α significantly improved the hypercapnic ventilatory response and diaphragm muscle maximal isometric force. Long‐term TNF‐α deletion also altered the myosin heavy chain isoform profile of the diaphragm. These data indicate that a blunted ventilatory response to hypercapnia exists in mdx mice, and that TNF‐α influences the progressive deterioration of diaphragm muscle in mdx mice. Muscle Nerve 28: 336–343, 2003
Neurophysiological changes in demyelinating and axonal forms of acute experimental autoimmune neuritis in the Lewis rat
Authors: Taylor Jude M. , Pollard John D.
Published: August 2003

Myelin‐sensitized T‐ and B‐cells (lymph node cells) induced experimental autoimmune neuritis (EAN) in Lewis rats after passive transfer to naive recipients. After 6 days, all recipient rats developed tail paresis that progressed to limb paresis within 12–72 h. Progressive nerve conduction changes consistent with demyelination in the sciatic nerve (conduction block and prolongation of the distal motor latencies) and lumbar nerve roots (initial low F‐wave frequencies followed by later prolongation in F‐wave latencies) were observed during the disease. For comparison, adoptive transfer experimental autoimmune neuritis (AT‐EAN) of differing disease severity was induced by titrating the dose of P2‐specific T‐cells. In contrast to EAN induced by myelin‐sensitized T‐ and B‐cells, AT‐EAN was predominantly associated with rapid nerve conduction changes consistent with axonal dysfunction and degeneration. These findings demonstrate that distinct forms of EAN with different pathophysiological mechanisms are induced by the passive transfer of P2‐specific T‐cell lines or myelin‐specific T‐cells and B‐cells. The electrophysiological changes in EAN induced by myelin‐specific T‐ and B‐cells are very similar to those seen clinically during acute inflammatory demyelinating polyneuropathy, whereas AT‐EAN has less resemblance to axonal forms of Guillain–Barré syndrome. Muscle Nerve 28: 344–352, 2003