bluuebunny/crossref_metadata_2025_split huggingface dataset:
Changes in water diffusion due to Wallerian degeneration in peripheral nerve
Authors: Beaulieu Christian , Does Mark D. , Snyder Richard E. , Allen Peter S. 
Published: March 2007

AbstractThe authors report NMR measurements of the changes in water diffusion brought about by in vivo Wallerian degeneration due to either crush‐ or tie‐injuries in the sciatic nerve of the frog. Using a pulsed‐gradient spin‐echo sequence with a diffusion measurement time of 28 ms, the degree of diffusion coefficient anisotropy {D(longitudinal)/D(transverse)} 4 weeks after injury in both crush‐ and tie‐injured nerves (2.3 ± 0.4 and 1.7 ± 0.1, respectively) is significantly less than in normal frog sciatic nerve (3.9 ± 0.4). The decrease of anisotropy in the degenerated nerves is due to both a decrease in longitudinal diffusion and an increase in transverse diffusion. The changes in diffusion coefficients are compared with the degree of axonal and myelin breakdown observed in light and electron micrographs of the nerves.
Quantitative volumetric magnetization transfer analysis in multiple sclerosis: Estimation of macroscopic and microscopic disease burden
Authors: van Buchem Mark A. , McGowan Joseph C. , Kolson Dennis L. , Polansky Marcia , Grossman Robert I. 
Published: March 2007

AbstractMagnetization transfer imaging (MTI) has been shown to be sensitive to both macroscopic and microscopic disease in multiple sclerosis (MS). In this study three‐dimensional MTI was used to estimate the global burden of disease in large volumes of brain tissue. MTI was performed in 15 MS patients and 11 normal controls. In seven MS patients MTI was performed on two different occasions. MTI data were displayed as magnetization transfer ratio (MTR) histograms and analyzed. The peak height of the histograms, presumably reflecting the residual amount of normal brain tissue, was lower in MS patients as compared with normal controls (P < 0.001), and was found to correlate with the duration of disease (P < 0.05). A decrease of the MTR histogram peak height was observed in the course of the disease (P < 0.01). These findings suggest that in MS, volumetric MTI provides quantitative information reflecting the global burden of disease.
In vivo rapid magnetic field measurement and shimming using single scan differential phase mapping
Authors: Kanayamay Shoichi , Kuhara Shigehide , Satoh Kozo 
Published: March 2007

AbstractIn vivo shimming is a powerful tool for alleviating subjectdependent magnetic field distortions in MRI, although the usually lengthy procedure has limited its use. A magnetic field measurement method called single scan differential phase mapping that can reduce the measurement time of conventional methods by more than half when used with multiple gradient‐recalled echo imaging was developed. An automatic high‐order shimming using the present method was implemented in a commercial MRI system. In vivo field inhomogeneity features and the shimming performances were investigated. The method was found to be useful for improving the quality of echo‐planar images.
Simple measurement of scanner stability for functional NMR imaging of activation in the brain
Authors: Weisskoff Robert M. 
Published: March 2007

AbstractFunctional MR imaging (fMRI) of activation in the brain is one of the more demanding applications required of an NMR imaging instrument. Since the signal changes in activation imaging are quite small, any instrumental variations can easily compromise the fMRI contrast. The authors describe a simple method for measuring these scanner instabilities, which is implementable on all scanners, to determine whether instability is degrading the fMRI contrast‐to‐noise. In this method, a long time series of images is acquired with identical imaging parameters to the chosen fMRI scans, the fluctuations are measured as a function of region‐of‐interest (ROI) size, and compared with the single image SNR. By plotting these fluctuations versus ROI size, and comparing them with the theoretically approachable value, the impact of these fluctuations can be assessed. We also present a simplified version of the test, which can be implemented with minimal calculations.
Biopsy needle susceptibility artifacts
Authors: Ladd Mark E. , Erhart Peter , Debatin Jörg F. , Romanowski Benjamin J. , Boesiger Peter , McKinnon Graeme C. 
Published: March 2007

AbstractUnderstanding the appearance of thin metallic structures in magnetic resonance imaging is important for evaluating the potential role of MRI in guiding and monitoring percutaneous interventions. As most MR compatible instruments are made from materials with a susceptibility different from water, their visibility is enhanced beyond what is expected on the grounds of displaced water alone. Unfortunately, this artifactually enhanced visibility is not constant, but instead depends on a variety of factors. This article presents computer simulations of the image distortion resulting from magnetic susceptibility differences between a needle and the surrounding tissue. The simulations show not only an artifact size that is dependent on needle composition, orientation, and pulse sequence, but also a corresponding shift of the artifact center away from the actual center of the needle. These effects place limits on the accuracy of MRI‐guided needle tip placement.
Enhanced resolution of proton NMR spectra of malignant lymph nodes using magic‐angle spinning
Authors: Cheng Leo L. , Lean Cynthia L. , Bogdanova Anna , Wright S. Carter , Ackerman Jerome L. , Brady Thomas J. , Garrido Leoncio 
Published: March 2007

AbstractProton NMR spectroscopy has proven useful in the detection of cancer in lymph node tissue. However, due to the high fat content of this type of tissue, 2D 1H COSY measurements (requiring acquisition times of 4–5 h or longer) are necessary to obtain the spectral information necessary for diagnosis. T2‐filtered proton magic‐angle spinning (MAS) NMR spectros‐copy provides 1D spectra of lymph nodes in approximately 20 min with sufficient spectral resolution allowing for identification of changes in cellular chemistry due to the presence of malignant cells. MAS data from lymph nodes of five control and six rats with mammary adenocarcinoma (R13762) demonstrated increases in the signal intensity of resonances associated primarily with lactate (s̀ = 4.12 ppm) P < 0.0004, creatines/lysine (s̀ = 3.04 ppm) P < 0.0032, and glutamate/ glutamine (s̀ = 2.36 ppm) P < 0.0002 in metastatic compared with normal lymph nodes. The infiltration of lymph nodes by malignant cells is an important prognostic factor for many cancers. The rapid assessment of node tissue without the introduction of sampling errors (inherent in currently employed histological procedures) would allow postoperative therapy decisions to be made more efficiently.
Broadband decoupled, 1H‐localized 13C MRS of the human brain at 4 tesla
Authors: Gruetter Rolf , Adriany Gregor , Merkle Hellmut , Andersen Peter M. 
Published: March 2007

AbstractBroadband proton decoupling of the entire 13C spectrum was possible within power absorption guidelines and resulted in the detection of narrow (as low as 2–3 Hz), natural abundance signals from metabolites such as myo‐inositol, glutamate, N‐acetyl‐aspartate, and glutamine from 72 cm3 volumes in the human brain. To overcome the chemical shift displacement error, three‐dimensional localization on the 1H z magnetization was combined with polarization transfer. Efficiency of the heteronuclear localization method was demonstrated by the elimination of all scalp lipid resonances. A signal‐to‐noise ratio of 5:1 for 0.07 mM [13C] was achieved in 12 min, which is approximately a fivefold improvement over the sensitivity reported at 2.1 Tesla.
Gd‐DTPA2− as a measure of cartilage degradation
Authors: Bashir Adil , Gray Martha L. , Burstein Deborah 
Published: March 2007

AbstractGlycosaminoglycans (GAGs) are the main source of tissue fixed charge density (FCD) in cartilage, and are lost early in arthritic diseases. We tested the hypothesis that, like Na+, the charged contrast agent Gd‐DTPA2‐ (and hence proton T1) could be used to measure tissue FCD and hence GAG concentration. NMR spectroscopy studies of cartilage explants demonstrated that there was a strong correlation (r > 0.96) between proton T1 in the presence of Gd‐DTPA2‐ and tissue sodium and GAG concentrations. An ideal one‐compartment electrochemical (Donnan) equilibrium model was examined as a means of quantifying FCD from Gd‐DTPA2‐ concentration, yielding a value 50% less but linearly correlated with the validated method of quantifying FCD from Na+. These data could be used as the basis of an empirical model with which to quantify FCD from Gd‐DTPA2‐ concentration, or a more sophisticated physical model could be developed. Spatial distributions of FCD were easily observed in T1‐weighted MRI studies of trypsin and interleukin‐1 induced cartilage degradation, with good histological correlation. Therefore, equilibration of the tissue in Gd‐DTPA2‐ gives us the opportunity to directly image (through T1, weighting) the concentration of GAG, a major and critically important macromolecule in cartilage. Pilot clinical studies demonstrated Gd‐DTPA2‐ penetration into cartilage, suggesting that this technique is clinically feasible.
The NMR chemical shift pH measurement revisited: Analysis of error and modeling of a pH dependent reference
Authors: Ackerman Joseph J. H. , Soto Gabriel E. , Spees William M. , Zhu Zehua , Evelhoch Jeffrey L. 
Published: March 2007

AbstractA standard differential calculus‐based propagation of error treatment is applied to the traditional chemical‐exchange Henderson‐Hasselbalch NMR pH model in which the reference shift is pH independent. It is seen naturally from this analysis that (i) the error minimum in derived pH occurs in the region where pH and indicator pKa are equal and that (ii) the dynamic range, or difference between the limiting chemical shifts of acid and base forms of indicator species, determines the insensitivity of the technique to propagation of errors. To extend the useful pH range and utility of NMR pH determination methodology, a more general model is developed in which the internal reference species is also considered as having a pH‐dependent chemical shift. Data from standard solution pH titrations are fitted to both models and parameters are estimated for the normally observed family of ionizable phosphorus metabolites (ATP, inorganic phosphate, phosphoethanolamine and phosphocholine) and the xenometabolite 2‐deoxyglucose‐6‐phosphate with either phospho‐creatine, the α‐phosphate of ATP, or H2O taken as the 31P or 1H chemical shift internal reference species as well as with an external reference.
The determination of myocardial viability using Gd‐DTPA in a canine model of acute myocardial ischemia and reperfusion
Authors: Pereira Raoul S. , Prato Frank S. , Wisenberg Gerald , Sykes Jane 
Published: March 2007

AbstractThe partition coefficient of Gd‐DTPA was thought to vary with the amount of cellular membrane damage after an acute myocardial infarction. The relationship between the partition coefficient of Gd‐DTPA (λ) and the uptake of 201TI (as a marker of tissue viability) was studied 2 h to 3 weeks after reperfusion of a 2‐h occlusion to the left anterior descending coronary artery in a canine model. Gd‐DTPA was infused as a bolus followed by a prolonged constant infusion, and this infusion protocol was optimized such that the concentration of Gd‐DTPA was directly related to λ. After this infusion, MR images of excised hearts showed regions of increased signal intensity corresponding to increased Gd‐DTPA concentration. At all time points, λ and 201TI uptake were strongly negatively correlated indicating that λ is an accurate indicator of myocardial viability. Furthermore, λ in the infarcted regions was increased relative to normal regions after 2 h of reperfusion and stayed elevated up to 3 weeks. At all time points, λ in the infarcted and normal regions were significantly different. As well, this data showed a trend that λ in infarcted regions decreased monotonically from 1 day to 3 weeks. This trend was confirmed with MR imaging by examining the change in signal intensity of in vivo images from 4 days to 3 weeks in two animals. These results suggest that MRI with Gd‐DTPA could be used to measure the extent of myocardial damage after an acute myocardial infarction.
Noninvasive measurement of the pH inside the gut by using pH‐sensitive nitroxides. An in vivo EPR study
Authors: Gallez Bernard , Mader Karsten , Swartz Harold M. 
Published: March 2007

AbstractThe use of pH‐sensitive probes permits the measurement of the proton activity in biological systems by EPR spectroscopy. To illustrate the potential of this technique for in vivo purposes, the authors took advantage of the oral administration of nitroxides to monitor the pH value inside the stomach of mice after administration of different antacidics. The results indicate that EPR can be a valuable tool to characterize the pH in vivo in a continuous and noninvasive way.
Tumor 31P NMR pH measurements in vivo: A comparison of inorganic phosphate and intracellular 2‐deoxyglucose‐6‐phosphate as pHnmr indicators in murine radiation‐induced fibrosarcoma‐1
Authors: Soto Gabriel E. , Zhu Zehua , Evelhoch Jeffrey L. , Ackerman Joseph J. H. 
Published: March 2007

AbstractUncertainty regarding the intracellular/extracellular distribution of inorganic phosphate (Pi) in tumors has raised concerns that pH calculated from the tumor Pi chemical shift may not accurately represent the intracellular pH (pHin). This issue was addressed in subcutaneously transplanted murine radiation induced fibrosarcoma‐1 by directly comparing pH measured via Pi with pH measured via the in situ generated intracellular xenometabolite 2‐deoxyglucose‐6‐phosphate (2DG6P). In 131 comparative measurements employing eight tumor‐bearing mice under both control and hyperglycemic conditions (the latter to extend the range of tumor pH examined), the pH as derived from either 2DG6P or Pi showed only a small, but statistically significant, difference (0.07 ± 0.11 SD; P = 0.0001). Scatter in the comparative analysis over the pH range examined (ca. 5.5‐7.5) was not uniform. Above pH 6.6, 2DG6P indicated a pH lower than that of Pi by 0.088 ± 0.105 SD (n = 107, P = 0.0001); below pH 6.6, 2DG6P indicated a pH essentially identical to and not statistically different from that of Pi (mean difference 0.003 ± 0.128 SD (n = 24, P = 0.92)). Evidence is presented in support of this differential arising from a systematic measurement error due to peak overlap between 2DG6P and endogenous phosphomonoester species. These results support the use of Pi as a tumor 31P NMR pHin indicator, at least in RIF‐1 tumors under control and hyperglycemic conditions.
Three‐dimensional mapping of the static magnetic field inside the human head
Authors: Li Shizhe , Dardzinski Bernard J. , Collins Christopher M. , Yang Qing X. , Smith Michael B. 
Published: March 2007

AbstractFinite element analysis was used to calculate the static magnetic field within the three‐dimensional head model. Localized field distributions were evaluated by using the magnetic field histogram technique. Experimental field maps and histograms of the human head were also obtained to validate the simulation results. Field deviations and gradients inside the human head cause NMR signal frequency shifts and line broadening, respectively. Voxels 2 × 2 × 0.5 cm may have frequency differences of more than 2.0 ppm. The linewidth of a single voxel may be broadened by more than 0.5 ppm. Calculated and experimental field maps are in excellent agreement. The global field distortion in the human head is primarily due to the susceptibility difference between air and tissues and their corresponding geometrical shapes.
High resolution measurement of cerebral blood flow using intravascular tracer bolus passages. Part I: Mathematical approach and statistical analysis
Authors: Østergaard Leif , Weisskoff Robert M. , Chesler David A. , Gyldensted Carsten , Rosen Bruce R. 
Published: March 2007

AbstractThe authors review the theoretical basis of determination of cerebral blood flow (CBF) using dynamic measurements of nondiffusible contrast agents, and demonstrate how parametric and nonparametric deconvolution techniques can be modified for the special requirements of CBF determination using dynamic MRI. Using Monte Carlo modeling, the use of simple, analytical residue models is shown to introduce large errors in flow estimates when actual, underlying vascular characteristics are not sufficiently described by the chosen function. The determination of the shape of the residue function on a regional basis is shown to be possible only at high signal‐to‐noise ratio. Comparison of several nonparametric deconvolution techniques showed that a nonparametric deconvolution technique (singular value decomposition) allows estimation of flow relatively independent of underlying vascular structure and volume even at low signal‐to‐noise ratio associated with pixel‐by‐pixel deconvolution.
High resolution measurement of cerebral blood flow using intravascular tracer bolus passages. Part II: Experimental comparison and preliminary results
Authors: Østergaard Leif , Sorensen Alma Gregory , Kwong Kenneth K. , Weisskoff Robert M. , Gyldensted Carsten , Rosen Bruce R. 
Published: March 2007

AbstractThis report evaluates several methods to map relative cerebral blood flow (rCBF) by applying both parametric and non‐parametric techniques to deconvolve high resolution dynamic MRI measurements of paramagnetic bolus passages with noninvasively determined arterial inputs. We found a nonparametric (singular value decomposition (SVD)) deconvolution technique produced the most robust results, giving mean gray:white flow ratio of 2.7 ± 0.5 (SEM) in six normal volunteers, in excellent agreement with recent PET literature values for age‐matched subjects. Similar results were obtained by using a model‐dependent approach that assumes an exponential residue function, but not for a Gaussian‐shaped residue function or for either Fourier or regularization‐based model‐independent approaches. Pilot studies of our CBF mapping techniques in patients with tumor, stroke, and migraine aura demonstrated that these techniques can be readily used on data routinely acquired by using current echo planar imaging technology. By using these techniques, the authors visualized important regional hemodynamic changes not detectable with rCBV mapping algorithms.
ROC methods for evaluation of fMRI techniques
Authors: Sorenson James A. , Wang X. 
Published: March 2007

AbstractReceiver operating characteristic (ROC) methods provide a standardized and statistically meaningful means for comparing signal‐detection accuracy. A brief overview of ROC methods is presented. Example applications include a comparison of four different postprocessing algorithms operating on simulated fMRI time‐course data sets and on human null data sets to which a simulated fMR response had been added. ROC methods also were used to reanalyze one data set from a previously published work. Additional ROC methods that also may be useful for fMRI comparisons are described.
Optimization of spoiled gradient‐echo phase imaging for in vivo localization of a focused ultrasound beam
Authors: Chung Andrew H. , Hynynen Kullervo , Colucci Vincent , Oshio Koichi , Cline Harvey E. , Jolesz Ferenc A. 
Published: March 2007

AbstractThe parameters of a spoiled gradient‐echo (SPGR) pulse sequence have been optimized for in vivo localization of a focused ultrasound beam. Temperature elevation was measured by using the proton resonance frequency shift technique, and the phase difference signal‐to‐noise ratio (SNRδ ϕ) was estimated in skeletal muscle and kidney cortex in 10 rabbits. Optimized parameters included the echo time equivalent to T*2of the tissue, the longest repetition time possible with a 20‐s sonication, and the flip angle equivalent to the Ernst angle. Optimal SPGR phase imaging can detect a sonication beam with a peak phase difference of 0.55 radian, which corresponds to a temperature elevation of 7.3°C. The sonication beam can be localized within one voxel (0.6 × 0.6 × 5 mm3) at power levels that are below the threshold for thermal damage of the tissue.
Assessment of microvascular integrity in the isolated perfused rat liver by contrast‐enhanced MRI. Attenuation of reperfusion injury by conjugated deferoxamine
Authors: Colet Jean‐Marie , Cetiner Erol , Hedlund Bo E. , Muller Robert N. 
Published: March 2007

AbstractReperfusion of an ischemic organ can lead to miorocirculatory impairment caused, in part, by the generation of reactive free radicals. The iron‐catalyzed formation of these deleterious substances can be counteracted by strong metal chelators like deferoxamine. In this study, the protective effect of deferoxamme conjugate was evaluated by assessment of the hepatic microcirculation in the post‐ischemic phase. Assessment of the microvasculature was performed by MRI on the isolated perfused rat liver. The restriction of sinusoids subsequent to reperfusion injury was demonstrated by the use of a particulate superparamagnetic contrast agent trapped in the microvasculature. The protective effect of conjugated deferoxamine was evaluated by both MRI and release of alanine aminotransferase. Contrast‐enhanced MRI demonstrated a marked impairment of the microcirculation subsequent to the unprotected reperfusion of the ischemic tissue. This injury was attenuated by deferoxamine conjugated to hydroxyethylstarch (HES‐DFO).
Interpretation of flow encoding and quantification in MRI: Time domain versus frequency domain
Authors: Peeters Frank , Luypaert Robert , Eisendrath Henri , Osteaux Michel 
Published: March 2007

AbstractThe traditional approach to flow effects in MRI is based on the gradient moment expansion. Recently, we have presented an alternative description by using linear response theory: the distortions of the velocity waveform induced by the gradient waveforms were analyzed in the frequency domain on the basis of the transfer function. In the present paper, we perform an analysis of flow encoding and quantification in the time domain, on the basis of the impulse response. The analysis shows that flow encoding should be interpreted as a weighted averaging process. Instantaneous flow encoding is determined by the centroid of the impulse response, but care should be taken regarding the physical meaning of the instant of encoding. The relationship of this approach to the frequency domain and gradient moment expansion approaches is clarified. By way of example, some interesting applications are investigated: asymmetrical phase encoding gradients to minimize misregistration and oscillating read‐out gradients for flow quantification. A variety of new applications are expected to derive from the combination of both the time and frequency domains.