bluuebunny/crossref_metadata_2025_split huggingface dataset:
Localized proton MR spectroscopy of the human kidney in vivo by means of short echo time STEAM sequences
Authors: Dixon Ruth M. , Frahm Jens 
Published: March 2007

AbstractIn order to obtain proton magnetic resonance spectra from the normal human kidney in vivo, we employed a STEAM sequence with delay times TE= 10 ms and TM = 30 ms. Signals are attenuated during STEAM sequences by J‐coupling effects and by macroscopic movement of the sample. The combination of short echo times and respiratory triggering ensured that the kidney was stationary during the pulse sequence, and allowed us to detect strongly coupled resonances between 3 and 4.2 ppm. Analysis of spectra of extracts of bovine kidneys suggested that the renal MR‐visible metabolites could include the osmolytes betaine, myo‐inositol, and glycerophosphocholine. Four volunteers were subjected to overnight dehydration followed by rehydration, and we found that these signals increased significantly after dehydration, and decreased significantly 4 h after rehydration, thus supporting the assignment of the resonances as osmotically active metabolites.
Reduction of signal fluctuation in functional MRI using navigator echoes
Authors: Hu Xiaoping , Kim Seong‐Gi 
Published: March 2007

AbstractFunctional magnetic resonance imaging is sensitive to signal fluctuations due to physiological motion and system instability. In this paper, motion‐related signal fluctuations are studied, and a method that uses navigator echoes to monitor and compensate for signal fluctuations in a gradient‐echo sequence is described. The technique acquires a “navigator” signal before the application of the phase‐encoding and readout gradients and corrects the phase of the subsequently acquired imaging data. This technique was implemented on a 4 Tesla whole body system and validated on normal volunteers. With this technique, temporal fluctuations in image intensity were substantially reduced and improved functional activation maps were obtained.
Real time blood flow imaging by spiral scan phase velocity mapping
Authors: Gatehouse P. D. , Firmin D. N. , Collins S. , Longmore D. B. 
Published: March 2007

AbstractThe work describes the development of a novel sequence that uses rapid spiral k‐space sampling, combined with phase velocity mapping, for real time flow velocity imaging. The performance of the technique is assessed on phantoms for both through‐plane and in‐plane flows. The flow measurements compared well with those measured using a bucket and stopwatch. One advantage of the technique is that flow related signal loss is minimal due to the early acquisition of the center of k‐space data. Flow artifacts were observed for in‐plane flow and these were understood with the aid of computer simulations. In vivo studies involved cine velocity mapping in normal volunteers; aortic blood flow waveforms acquired by spiral scanning in two cardiac cycles compared well with data from a conventional gradient‐echo sequence. Potential applications of the method are demonstrated by studying the response of aortic flow to physical exercise and the real time monitoring of aortic flow during a valsalver maneuver.
Double‐echo multislice proton spectroscopic imaging using Hadamard slice encoding
Authors: Dreher Wolfgang , Leibfritz Dieter 
Published: March 2007

AbstractSimultaneous multislice proton spectroscopic imaging (SI) is presented using a pulse sequence with multifrequency selective RF excitation and Hadamard encoding in the slice direction, and conventional Fourier phase encoding in the in‐plane directions. Double‐echo data acquisition is used to increase the spectral information of the experiment. Tests on a phantom demonstrate the quality of the slice selection. Results of in vivo measurements on the healthy rat brain show that spectra with a high signal‐to‐noise ratio can be acquired from four slices within 32 min. The measurements were performed at 4.7 T using a field of view of 32 × 32 mm2, a slice thickness of 3 mm, and a voxel size of 12 μl. The proposed method is a useful alternative to sequential multislice SI and 3D SI. Furthermore, it is possible to combine sequential and simultaneous multi‐slice SI.
Studies on bromobenzene‐induced hepatotoxicity using in vivo MR microscopy with surgically implanted RF coils
Authors: Zhou Xiaohong , Maronpot Robert R. , Gofer Gary P. , Hedlund Laurence W. , Johnson G. Allan 
Published: March 2007

AbstractUsing surgically implanted RF coils at 300 MHz, three‐dimensional microscopic MR images of rat liver were obtained in vivo to follow the development of pathology induced by bromobenzene exposure. Formalin fixed specimens of liver from these animals were also imaged using in vitro MR microscopy, followed by conventional optical microscopy. All MR images were acquired using a spin‐warp pulse sequence with TR = 950 ms and TE= 23 ms. The in vivo images were reconstructed as 2562 × 32 arrays with a voxel size of (50 μm)2 × 219 pm, while the in vitro images were reconstructed as 2562 × 128 arrays, giving an isotropic resolution at (39 μm)2. Based on results from six animals, we have found in all animals exposed to bromobenzene, image intensity decreased in specific hepatic tissue regions. These regions were well correlated to low signal intensity areas observed in in vitro MR images at higher resolution. Conventional optical microscopy indicated that the low signal intensity regions corresponded to areas of necrosis. The decrease in signal intensity is consistent with increased local diffusion coefficients as a result of necrosis. This study demonstrates that MR microscopy with implanted RF coils can be successfully used to follow tissue pathological changes in living tissues.
Measurement of the intracellular concentration of oxygen in a cell perfusion system
Authors: Chen Kai , Ng Cheng E. , Zweier Jay L. , Kuppusamy Periannan , Glickson Jerry D. , Swartz Harold M. 
Published: March 2007

Abstract[O2] was measured in the embedding material (alginate) in a typical apparatus for conducting studies of viable cells with NMR, using low frequency EPR. In suspension cultures respiration was independent of [O2] in the perfusing media down to about 1 μM while in alginate beads, the comparable value was 70 μM, indicating that the alginate was a very substantial barrier to the free diffusion of oxygen. With knowledge of [O2] in the various compartments, [O2] in the perfusing medium can be increased and the full power of NMR can be used to provide information on metabolism under various conditions. These results also provide evidence supporting the feasibility and usefulness of EPR techniques using nitroxides to measure [O2] in macroscopic samples such as NMR perfusion tubes. This technique is rapid, apparently nonperturbing, and enables one to differentiate between the concentrations of oxygen in different compartments.
Relaxivity enhancement of low molecular weight nitroxide stable free radicals: Importance of structure and medium
Authors: Vallet Patrick , van Haverbeke Yves , Bonnet Pierre Antoine , Subra Guy , Chapat Jean‐Pierre , Muller Robert N. 
Published: March 2007

AbstractThe longitudinal relaxivities of seven water‐soluble nitroxide derivatives ot low‐molecular weight have been measured at 5°C and 37°C in water and in serum between 0.01 and 200 MHz. The nuclear magnetic relaxation dispersion (NMRD) profiles show a clear relationship between the relaxivity observed in serum and the relative balance of the hydrophobichydrophilic character of the paramagnetic molecules. From the data analysis, contributions arising from a population of nitroxides characterized by reduced mobility can be extracted. The values of the correlation times are consistent with a system involving nitroxides adsorbed at the surface of albumin and magnetically interacting with the protons of hydrogen bonded water molecules.
T1 discrimination contributions to proton magnetization transfer in heterogeneous biological systems
Authors: Yang Hua , Schleich Thomas 
Published: March 2007

AbstractWater proton spin‐lattice relaxation times are commonly used as a guide in establishing the off‐resonance irradiation time as well as the repetition time of the magnetization transfer experiment. T1 discrimination effects occur if the motionally restricted spin bath longitudinal magnetization does not reach thermal equilibrium. In this study we developed the formalism necessary for the evaluation of T1 discrimination contributions to proton magnetization transfer arising from the use of a short repetition time relative to the spin‐lattice relaxation time of the motionally restricted spin bath. The results of computer simulation indicate that T1, discrimination contributions occur when the repetition time is small relative to the spin‐lattice relaxation time of the motionally restricted spin bath, and when the off‐resonance irradiation is weak and far off‐resonance. For somewhat longer repetition times, T1 discrimination contributions become important only when the cross relaxation rate is small, and the fractional amount of motionally restricted component large. The occurrence of T1 discrimination effects results in distortion of water proton intensity ratio dispersion curves thereby resulting in the estimation of erroneous magnetization transfer parameters, whereas in magnetization transfer contrast enhanced imaging, such contributions are manifested by a decrease in image contrast.
Projection‐reconstruction methods: Fast imaging sequences and data processing
Authors: Crémillieux Yannick , Briguet André , Deguin André 
Published: March 2007

AbstractNew, rapid two‐ and three‐dimensional imaging sequences based on steady‐state gradient echoes and projection‐reconstruction (PR) techniques are proposed. Quantitative studies show that fast PR sequences and classical, fast gradient‐echo Fourier transform sequences lead to identical contrasts. In order to minimize inhomogeneity effects, a particular focus has been placed on echo‐time reduction. The use of a weighting window permits one to acquire severely truncated echoes; partial k‐space scanning may be considered.
Studies of Gd‐DTPA relaxivity and proton exchange rates in tissue
Authors: Donahue Kathleen M. , Burstein Deborah , Manning Warren J. , Gray Martha L. 
Published: March 2007

AbstractThe image intensity in many contrast agent perfusion studies is designed to be a function of bulk tissue T1, which is, in turn, a function of the compartmental (vascular, interstitial, and cellular) T1s, and the rate of proton exchange between the compartments. The goal of this study was to characterize the compartmental tissue Gd‐DTPA relaxivities and to determine the proton exchange rate between the compartments. Expressing [Gd‐DTPA] as mmol/liter tissue water, the relaxivities at 8.45 T and room temperature were: saline, 3.87 ± 0.06 (mM. s)−1 (mean ± SE; n = 29); plasma, 3.98 ± 0.05 (mM·s)−1 (n = 6); and control cartilage (primarily an interstitium), 4.08 f 0.08 (mM·s)−1 (n = 17), none of which are significantly different. The relexivity of cartilage did not change with compression, trypsinization, or equilibration in plasma, suggesting relaxivity is not influenced by interstitial solid matrix density, charge, or the presence of plasma proteins. T1 relaxation studies on isolated perfused hearts demonstrated that the cellular‐interstitial water exchange rate is between 8 and 27 Hz, while the interstitial‐vascular water exchange rate is less than 7 Hz. Thus, for Gd‐DTPA concentrations, which would be used clinicallly, the T1 relaxation rate behavior of intact hearts can be modeled as being in the fast exchange regime for cellular‐interstitial exchange but slow exchange for interstitial‐vascular exchange. A measured relaxivity of 3.82 ± 0.05 (mM·s)−1 (n = 8) for whole blood (red blood cells and plasma) and 4.16 ± 0.02 (mM·s)−1 (n = 3) for frog heart tissue (cells and interstitium) (with T1 and Gd‐DTPA concentration defined from the total tissue water volume) supports the conclusion of fast cellular‐extracellular exchange. Knowledge of the Gd‐DTPA relaxivity and maintaining Gd‐DTPA concentration in the range so as to maintain fast cellular‐interstitial exchange allows for calculation of bulk Gd‐DTPA concentration from bulk tissue T1 within a calculable error due to slow vascular exchange.
Dual interleaved 1H and proton‐decoupled‐31P in Vivo chemical shift imaging of human brain
Authors: Gonen Oded , Hu Jiani , Murphy‐Boesch Joseph , Stoyanova Radka , Brown Truman R. 
Published: March 2007

AbstractA technique is demonstrated to obtain interleaved proton (1H) and 1H‐decoupled phosphorus (31P) spectra of human brain using 2D CSI. A modified commercial full‐body imager and a dual‐tuned birdcage head‐coil were employed. Because proton relaxation times are shorter than those of phosphorus, TR(1H) can be chosen to be shorter than TR(31P), thus permitting a 1H acquisition to be inserted in each 31P cycle. The scheme results in significant time savings as both CSI data sets are obtained concurrently with patient loading, coil tuningi, shimming, and imaging needed to be done only once.
Abnormal cerebral metabolite concentrations in patients with probable alzheimer disease
Authors: Moats Rex A. , Ernst Thomas , Shonk Truda K. , Ross Brian D. 
Published: March 2007

AbstractTo establish whether recently described abnormalities of peak ratios are the result of changes in metabolite concentrations, quaintitative 1H magnetic resonance spectroscopy was performed in 10 patients with Alzheimer disease (AD) and seven normal elderly. CSF volumes, metabolite T1 and T2relaxation rates, ratios and concentrations of Kacetyl residues, creatine, choline residues, myeinositol, glutamine plus glutamate (Glx), and glucose were obtained. Difference spectroscopy and quantitative assays showed a 50% increase in myo‐inositol (6.4–9.8 mM; P < 0.005) and a decrease in N‐acetyl in occipital gray matter. A reduction in β,γ‐Glx and a significant increase in intracerebral [glucose], greater than attributable to CSF, were defined. Choline concentration increased with age, but was not elevated above normal in AD patients. These findings indicate the need for quantitative 1H MRS to substantiate metabolite ratios. The increased myo‐inositol concentration in AD is demonstrated by these studies.
Quantitative proton spectroscopy of canine brain: in Vivo and in Vitro correlations
Authors: Barker Peter B. , Breiter Steven N. , Soher Brian J. , Chatham John C. , Forder John R. , Samphilipo Michael A. , Magee Carolyn A. , Anderson James H. 
Published: March 2007

AbstractQuantitative, single‐voxel proton NMR spectroscopy of normal brain was performed in five adult beagle dogs using the cerebral water signal as an internal intensity reference. The same brain regions were then rapidly isolated and frozen using a pneumatic biopsy drill, perchloric acid extracted, and analyzed by biochemical assay and high‐resolution NMR spectroscopy. The concentrations of the major resonances in the in vivo and in vitro spectra were compared, and good agreement was found between the different measurements. The in vivo spectra contained three peaks at 3.21, 3.04, and 2.02 ppm, which are usually assigned to trimethylamines (TMA), creatines, and N‐acetyl derivatives (NAc), which corresponded to be the following metabolite concentration values: 1.7 ± 0.6, 7.7 ± 2.1, and 10.9 ± 2.7 μmol/g wet weight respectively. In vitro, the following metabolite concentrations were measured: glycerophosphocholine (GPC) 1.3 ± 0.2, phosphocholine (PC) 0.5 ± 0.1, phosphocreatine (PCr) 2.6 ± 0.4, creatine (Cr) 5.9 ± 1.4, and N‐Acetyl aspartate (NAA) 8.9 ± 1.8 μmol/g wet weight. Therefore, the 3.21 ppm resonance observed in the in vivo spectrum is predominantly GPC and PC in a ratio of 2.6:1, the 3.04 ppm resonance is Cr and PCr in a ratio of 2.3:1, and the 2.02 ppm resonance is predominantly (≈︁80%) NAA with small contributions from N‐acetylaspartyl‐glutamate (NAAG) and glutamate. The data presented here validate the technique of water referencing as a simple and convenient means of quantitating single‐voxel in vivo proton NMR spectra of the brain.
Three dimensional magnetic resonance microangiography of rat neurovasculature
Authors: Mellin Andrew F. , Cofer Gary P. , Smith Bradley R. , Suddarth Steven A. , Hedlund Laurence W. , Johnson G. Allan 
Published: March 2007

AbstractTechniques are described to perform three dimensional (3D) MR microangiography. We have combined the use of a blood pool agent (Gd‐DTPA‐complexed with bovine serum albumin), three dimensional Fourier encoding, careful animal stabilization, and volume rendering to permit imaging with voxels of 60 × 60 × 60 pm. 3DFT encoding has been performed at 7.1 T with very large arrays (256 × 512 × 512). Interactive volume rendering allows a number of unique display opportunities that effectively exploit these isotropic 3D arrays.
High frequency volume coils for clinical NMR imaging and spectroscopy
Authors: Vaughan J. Thomas , Hetherington Hoby P. , Otu Joe O. , Pan Jullie W. , Pohost Gerald M. 
Published: March 2007

AbstractA tuned transmission line resonator has been developed in theory and in practical design for the clinical NMR volume coil application at 4.1 tesla. The distributed circuit transmission line resonator was designed for high frequency, large conductive volume applications where conventional lumped element coil designs perform less efficiently. The resonator design has made use of a resonant coaxial cavity, which could be variably tuned to the Larmor frequency of interest by tunable transmission line elements. Large head‐ and body‐sized volumes, high efficiencies, and broad tuning ranges have been shown to be characteristic of the transmission line resonator to frequencies of 500 MHz. The B1 homogeneity of the resonator has been demonstrated to be a function of the electromagnetic properties of the load itself. By numerically solving Maxwell's: equations for the fully time‐dependent B1 field, coil homogeneity was predicted with finite‐element models of anatomic structure, and inhomogeneities corrected for. A how‐to exposition of coil design and construction has been included. Simple methods of quadrature driving and double tuning the transmission line resonator have also been presented. Human head images obtained with a tuned transmission line resonator at 175 MHz have clearly demonstrated uncompromised high field advantages of signal‐to‐noise and spatial resolution.
A modified quadrupole gradient set for use in high resolution MRI tagging
Authors: O'Dell Walter G. , Schoeniger Joseph S. , Blackband Stephen J. , McVeigh Elliot R. 
Published: March 2007

AbstractA special purpose gradient set with a Cos(20) current distribution has been constructed for high resolution MR imaging of small samples in a clinical Signa 1.5 T scanner using the existing gradient amplifiers. The X, Y, and Z gradient coils can attain gradient field strengths of 11.3, 4.7, and 15.2 G/cm at 100 amps current, respectively, with a slew rate of 20 G/cm/ms and usable ramp time of 150 μs. Field distortions are less than 2% over the central 8 cm of the bore, suitable for high resolution tagging of isolated canine hearts.
Interleaved echo planar flow quantitation
Authors: McKinnon Graeme C. , Debatin Jörg F. , Wetter Denis R. , von Schulthess Gustav K. 
Published: March 2007

AbstractA method is presented for rapid blood flow quantitation. It combines multiple shot echo planar imaging principles with phase contrast velocity encoding gradients. Preliminary validation experiments performed on a flow phantom indicate a good correlation with actual flow values. Measurements of pulsatile flow in the ascending and descending aorta, acquired in just 4 s1 with a temporal resolution of 50 ms, are demonstrated.
Correlation of spectroscopy and magnetization transfer imaging in the evaluation of demyelinating lesions and normal appearing white matter in multiple sclerosis
Authors: Hiehle John F. , Lenkinski Robert E. , Grossman Robert I. , Dousset Vincent , Ramer Karen N. , Schnall Mitchell D. , Cohen Jeffrey A. , Gonzalez‐Scarano Francisco 
Published: March 2007

AbstractMagnetization transfer imaging (MT) and localized proton spectroscopy (1H‐MRS) were utilized in the evaluation of lesioins (high signal abnormalities on T2‐weighted images) and normal‐appearing white matter (NAWM) in multiple sclerosis (MI). Eleven patients with a clinical diagnosis of MS were independently evaluated with both 1H‐MRS and MT. The magnetization transfer ratio (MTR) of lesions was compared with the relative concentration of Kacetyl‐aspartate (NAA) and a composite peak at 2.1 to 2.6 ppm termed “marker peaks”. The MTR of white matter lesions in the MS patients was markedly decreased (6–34%; normal ≈︁42%), and correlated well with increase in the marker peaks region (0.94–3.89). There was no correlation between the relative concentration of NAA and MTR. Increased resonance peaks in the 2.1 to 2.6 ppm range and marked decreases in MTR may be a relatively specific indicators of demyelination.
Reconstructions of phase contrast, phased array multicoil data
Authors: Bernstein Matt A. , Grgic Mladen , Brosnan Thomas J. , Pelc Norbert J. 
Published: March 2007

AbstractWe present a reconstruction method for phased array multicoil data that is compatible with phase contrast MR angiography. The proposed algorithm can produce either complex difference or phase difference angiograms. Directional flow and quantitative information are preserved with the phase difference reconstruction. The proposed method is computationally efficient and avoids intercoil cancellation errors near the velocity aliasing boundary. Feasibility of the method is demonstrated on human scans.
Assessment of relative brain iron concentrations using T2‐weighted and T2*‐weighted MRI at 3 Tesla
Authors: Ordidge Roger J. , Gorell Jay M. , Deniau Jean C. , Knight Robert A. , Helpern Joseph A. 
Published: March 2007

AbstractIn this paper a new method is presented for the relative assessment of brain iron concentrations based on the evaluation of T2 and T2* ‐weighted images. A multiecho sequence is employed for rapid measurement of T2 and T2*, enabling calculation of the line broadening effect ( T2′). Several groups have failed to show a correlation between T2 and brain iron content. However, quantification of T2′, and the associated relaxation rate R2′, may provide a more specific relative measure of brain iron concentration. This may find application in the study of brain diseases, which cause associated changes in brain iron levels. A new method of field inhomogeneity correction is presented that allows the separation of global and local field inhomogeneities, leading to more accurate T2* measurements and hence, T2′ values. The combination of T2*, and T2‐weighted MRI methods enables the differentiation of Parlkinson's disease patients from normal age‐matched controls based on differences in iron content within the substantia nigra.
Dual‐echo MRI segmentation using vector decomposition and probability techniques: A two‐tissue model
Authors: Kao Yi‐Hsuan , Sorenson James A. , Bahn Mark M. , Winkler Stefan S. 
Published: March 2007

AbstractWe combined a vector decomposition technique with Gaussian probability thresholding in feature space to segment normal brain tissues, tumors, or other abnormalities on dual‐echo MR images. The vector decomposition technique assigns to each voxel a fractional volume for each of two tissues. A probability threshold, based on an assumed Gaussian probability density function describing random noise, isolates a region in feature space for fractional volume calculation that minimizes contamination from other tissues. The calculated fractional volumes are unbiased estimates of the true fractional volumes. The contrast‐to‐noise ratio (CNR) between tissues on the segmented images is the same as the Euclidean norm of CNRs in the original images. The method is capable of segmenting more than two tissues from a set ot dual‐echo images by sequentially analyzing different pairs of tissues. The model is analyzed mathematically and in experiments with a phantom. Two clinical examples are presented.