bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synchronized inversion recovery‐spin echo sequences for precise in vivo T1 measurement of human myocardium: A pilot study on 22 healthy subjects
Authors: Walker P. M. , Marie P. Y. , Mezeray C. , Bessieres M. , Escanyé J. M. , Karcher G. , Danchin N. , Mattei S. , Villemot J. P. , Bertrand A. 
Published: March 2007

AbstractAn ECG‐triggered, two‐sequence MRI technique is proposed for the precise measurement of proton T1 relaxation times of the human myocardium at a field strength of 0.5 T. The combination of an inversion recovery (IR) sequence and a spin echo (SE) sequence is not new. It is, however, rarely used in quantitative in vivo cardiac studies. Our approach employs a synchronization of the 90° read pulse to the systolic period. In a study of 22 healthy volunteers, the globally measured T1 value was estimated to be 714 ± 23 ms. Four of the volunteers also underwent additional imaging scans for the purposes of reproducibility assessment. The T1 precision was found to be 3.9 ± 1.1% for the IR/SE combination and 16.9 ± 5.3% for a combination of SE sequences. Total imaging time for the IR and SE sequences was 19.2 ± 3.0 mins. The relative rapidity of this classic technique and the T1 precision obtained give this technique an obvious application in the discrimination of normal and diseased myocardium. In the same study, valuable supplementary tissue characterization is provided by T2, calculated from the SE sequence. T2 was evaluated to be 50 ± 3 ms.
N‐acetyl‐L‐aspartate and acetate 1H NMR signal overlapping under mild acidic pH conditions
Authors: Marti Magali , Labouesse Julie , Canioni Paul , Merle Michel 
Published: March 2007

AbstractThe pH dependence of methyl proton chemical shifts of acetate, acetoacetate, N‐acetyl‐L‐aspartate (NAA), and N‐acetyl‐L‐aspartyl‐L‐glutamate (NAAG) were studied from pH 3 to pH 9. Only slight shifts of acetoacetate, NAA, and NAAG methyl signals were observed, whereas the acetate signal was largely shifted as a result of the titration of its acidic function. At pH 4.7, acetate and NAA methyl signals overlapped, whereas at more acidic pH, the acetate signal appeared downfield when compared to that of NAA. Results are discussed in terms of spectra misinterpretation risks linked to uncontrolled sample pH, on the one hand, and in terms of pH control and contamination by exogenous acetate during perchloric acid cell extract preparation, on the other.
Metabolic changes in the rat brain after acute and chronic ethanol intoxication: A 31P NMR spectroscopy study
Authors: Denays R. , Chao S. L. , Mathur‐Devré R. , Jeghers O. , Frühling J. , Noël P. , Ham H. R. 
Published: March 2007

AbstractIn this work, 31P phosphorus NMR (31P NMR) studies of the brain have been conducted in rats acutely and chronically intoxicated with ethanol. In both groups, changes in levels of high‐energy phosphates were observed: increase of phosphocreatinine (PCr)/β AaTP and PCr/inorganic phosphate (Pi) in acute and long‐term ethanol exposure, and decrease of Piβ ATP after acute ethanol administration. These changes in high‐energy phosphates, indicative of a reduction of adenosine triphosphate (ATP) and PCr consumption (PCr+ ADP + H+ ATP + Cr; ATP ADP + Pi), suggest a reduction of cerebral metabolism both in acute and chronic ethanol exposure. In addition, in the group of rats chronically intoxicated with ethanol, there were variations in phosphodiester peak intensities (decrease of phosphomonoester (PME)/phosphodiester (PDE), increase of PDE/β ATP), suggesting increased breakdown of membrane phospholipids. These changes could provide a metabolic explanation for the development of cerebral atrophy in chronic alcoholism.
Use of a projection reconstruction method to decrease motion sensitivity in diffusion‐weighted MRI
Authors: Gmitro Arthur F. , Alexander Andrew L. 
Published: March 2007

AbstractDiffusion‐weighted MRI is a clinically useful technique, but its utility is compromised by high sensitivity to patient motion. Use of radial‐scan data acquisition and projection reconstruction, rather than the conventional Fourier imaging method, can substantially reduce the sensitivity to global translational motion of the object. The basis of this concept and a demonstration of the technique in an animal imaging experiment are presented.
Changes in water diffusion and relaxation properties of rat cerebrum during status epilepticus
Authors: Zhong J. , Petroff O. A. C. , Prichard J. W. , Gore J. C. 
Published: March 2007

AbstractDiffusion‐weighted (DW) imaging has been used to record changes associated with status epilepticus (SE) in rat brain. It was found that the apparent diffusion coefficient (ADC) of water in brain decreased14–18% during SE, and it fell a further 20–22% when the animals were sacrificed. The transverse decay time constant T2 showed corresponding reductions, but no significant changes were seen in relaxation times T1 or T2 values. Changes in ADC in status epilepticus are similar to those seen in stroke and ischemia but occur under very differ ret conditions of blood flow and metabolism.
Correction of phase effects produced by eddy currents in solvent suppressed 1H‐CSI
Authors: Roebuck Joseph R. , Hearshen David O. , O'Donnell Matthew , Raidy Tom 
Published: March 2007

AbstractAccurate phasing of MRS spectra is often difficult unless time varying phase effects produced by gradient‐induced eddy currents that persist during data acquisition are eliminated. This effect is particularly problematic in 1H‐CSI spectra where frequency shifts produced by static field inhomogeneity and phase shifts produced by eddy currents combine. In this paper we present a method that corrects both shifts and eliminates manual phasing of individual CSI spectra typically required to recover a pure absorption line shape. The method uses a time domain phase correction derived from the ambient water signal acquired under identical conditions (i.e., acquisition parameters, gradient sequence) as the solvent‐sup pressed CSI data. Results from CSI experiments on phantoms and in vivo solvent suppressed 1H‐CSI spectra from normal human brain are presented demonstrating the capabilities of the technique.
Snapshot MRI with T2*‐weighted magnetization preparation
Authors: Bendel Peter 
Published: March 2007

AbstractA method for encoding T2*‐dependent contrasts into the preparation period of magnetization‐prepared uitrafast MRI sequences is demonstrated and validated. The preparation block consists of a 90°—T—90°p sequence, where p is shifted by 90° for successive images. By adding two such successive images in quadrature, a combined image is obtained, in which the pixel intensities depend on the incoherent intravoxel dephasing that occurred during T in a way that is similar to the dependence on TE in a gradient‐echo sequence. The method could therefore be useful for applications that require very short repetition times for good temporal resolution, together with detection of T2*‐weighted contrasts, such as functional MRI in the brain.
Comparison of methods for the determination of absolute metabolite concentrations in human muscles by 31P MRS
Authors: Buchli Reto , Boesiger Peter 
Published: March 2007

AbstractIn order to determine metabolite concentrations in human skeletal muscles by in vivo 31P MRS, different quantification methods were analyzed with regard to the accuracy and reproducibility of results and the simplicity of handling. Each quantification method comprised a calibration strategy and a localization technique. Extensive in vivo and in vitro tests showed that homonuclear phantom‐based calibration strategies yielded significantly more accurate (lower systematic errors) and more reproducible (lower statistical errors) concentration estimates than heteronuclear strategies using internal water as a concentration standard. Additionally, the former strategies are easier to handle than the latter. Localization with the volume‐selective sequence lSlS yielded slightly more reproducible results than localization by surface coil. We conclude that phosphorus metabolite concentrations are determined most accurately with phantom‐based calibration strategies in combination with lSlS localization (measurement errors ≈ 5–7%).
Quantifying MRI geometric distortion in tissue
Authors: Sumanaweera Thilaka , Glover Gary , Song Samuel , Adler John , Napel Sandy 
Published: March 2007

AbstractWe present a method to quantify the MR field inhomogeneity geometric distortion to subplxel accuracy without using objects of known dimensions and without using an external standard such as CT. Our method may be used to quantify the geometric accuracy of MR images of anatomical structures of unknown geometry and also to test any geometry correction scheme. We have quantified the distortion in a tissue phantom and found the largest error to be approximately 2.8 pixels (1.8 mm) for B0 = 1.5 T, G = 3.13 mT/m and FOV = 160 × 160 × 70.7 mm3. We also found that our previously published correction technique reduced the largest error to 0.3 pixels (μ = 0.02 and σ = 0.07 pixels).
Simultaneous 31P NMR spectroscopy and EMG in exercising and recovering human skeletal muscle: Technical aspects
Authors: Vestergaard‐Poulsen P. , Thomsen C. , Sinkjær T. , Henriksen O. 
Published: March 2007

AbstractThe bioenergetics of human skeletal muscle can be studied by 31P NMR spectroscopy (31P‐MRS) and by surface electromyography (SEMG). Simultaneous 31P‐MRS and SEMG permit accurate and noninvasive studies of the correlation between metabolic and electrical changes in exercising and recovering human skeletal muscle, a relationship that is still poorly understood. This study describes the optimization of skeletal muscle 31P‐MRS in a whole‐body magnet, involving surface coil design, utilization of adiabatic radio frequency pulses and advanced time‐domain fitting, to the technical design of SEMG. A nonmagnetic ergometer was used for ankle dorsi‐flexions that activated only the anterior tibia1 muscle as verified by post exercise imaging. The coil design and the adiabatic sechltanh pulse improved sensitivity by 45% and 56% respectively, compared with standard techniques. Simultaneous electromyographic recordings did not deteriorate the NMR spectra. The VARPRO time domain fitting routine was very suitable for estimating 31P muscle spectra. With these methods it was possible to accurately estimate parameters describing metabolic and electrical changes during rest, exercise and the entire recovery period with a 20‐s time resolution on a standard 1.5 T whole‐body NMR scanner.
31P NMR spectroscopic studies of the effects of cyclophosphamide on perfused RIF‐1 tumor cells
Authors: Aiken Nanci R. , McGovern Kathy A. , Ng Cheng E. , Wehrle Janna P. , Glickson Jerry D. 
Published: March 2007

AbstractTo determine whether direct cellular effects of chemotherapy are responsible for 31P NMR spectral changes observed in treated tumors in vivo, RIF‐1 fibrosarcoma cells were examined in vitro before, during, and after treatment with 4‐hy‐droperoxycyclophosphamide (4‐HC), an activated form of cyclophosphamide. When RIF‐1 cells were treated with 4‐HC in a metabolically stable but nonproliferating state, the 31P NMR spectra were identical with those of untreated cells for up to 70 h. When actively proliferating RIF‐1 cells were treated with 4‐W, the intensities of the nucleotide triphosphate resonances, which increased linearly during control cell growth, remained constant for 50 h or longer. These studies demonstrate that the bioenergetic improvement observed following treatment of RIF‐1 tumors in vivo [S.‐J. Li, J.P. Wehrle, S.S. Rajan, R.G. Steen, J.D. Glickson, and J. Hilton, Cancer Res. 48, 4736 (1988)] does not result from direct effects of cyclophosphamide metabolites on RIF‐1 cell metabolism, but rather from indirect effects of treatment on tumor or host physiology. Key words: 31P NMR spectroscopy; RIF‐1 tumor cells; cyclophosphamide; cancer.
A Bayesian approach to subvoxel tissue classification in NMR microscopic images of trabecular bone
Authors: Wu Zhenyu , Chung Hsiao‐Wen , Wehrli Felix W. 
Published: March 2007

AbstractNMR microscopy is currently being used as an investigational tool for the evaluation of micromorphometric parameters of trabecular bone as a possible means to assess its strength. Since, typically, the image voxel size is not significantly smaller than individual trabecular elements, partial volume blurring can be a major complication for accurate tissue classification. In this paper, a Bayesian segmentation technique is reported that achieves improved subvoxel tissue classification. Each voxel is subdivided either into eight subvoxels twice the original resolution, or up to four subvoxels along the transaxial direction and the subvoxels optimally classified as either bone or marrow. Based on a statistical model for partial volume blurring, the likelihood for the number of marrow subvoxels in each voxel can be computed on the basis of its measured signal. To resolve the ambiguity of the location of the marrow subvoxels, a Gibbs distribution is introduced to model the interaction between the subvoxels. Neighboring subvoxel pairs with the same tissue label are encouraged, and pairs with distinct labels are penalized. The segmentation is achieved by maximizing thea posterioriprobability of the label image using the block ICM (iterative conditional mode) algorithm. The potential of the proposed technique is demonstrated in real and synthetic NMR microscopic images.
Simulation of spatial and contrast distortions in keyhole imaging
Authors: Spraggins Thomas A. 
Published: March 2007

AbstractKeyhole imaging is a scheme introduced to improve temporal resolution in dynamic contrast‐enhanced MRI by a factor of four or more. A “full” acquisition before contrast administration is followed by truncated acquisitions sensitive primarily to changes in image contrast. Simulations of the point‐spread functions that obtain, and their effect on contrast and spatial resolution, reveal significant degradation only for the smallest objects. Our simulations also address the feasibility of three‐dimensional keyhole imaging, and demonstrate a potential 16‐fold increase in temporal resolution. This suggests roles for keyhole imaging in conventional (nondynamic) precon‐trast and postcontrast studies and other applications.
True myocardial motion tracking
Authors: Fischer Stefan E. , McKinnon Graeme C. , Scheidegger Markus B. , Prins Wim , Meier Dieter , Boesiger P. 
Published: March 2007

AbstractMyocardial tagging is a powerful tool for the assessment of in‐plane cardiac motion. However, for previous myocardial tagging techniques, the imaged slice is fixed with respect to the magnet coordinate system. Thus, images acquired at different heart phases do not always represent the same slice of the myocardium. A new myocardial tagging technique is presented, which takes the through‐plane motion into consideration. It involves tagging of the desired myocardial slice and applying a subtraction imaging technique to image just that part of the myocardium. The examination time can be reduced considerably by the acquisition of two one‐dimensionally tagged images. To increase the signal‐to‐noise ratio especially at later heart phases, variable imaging RF excitation flip angles are applied. To reduce motion artifacts a repetitive breathhold scheme was applied. in vivo results demonstrate that the tags can be accurately tracked within the entire heart period with a temporal resolution of 35 ms, even at a top basal level of the heart and right ventricle.
Three‐dimensional time‐of‐flight MR angiography using selective inversion recovery RAGE with fat saturation and ECG‐triggering: Application to renal arteries
Authors: Li Debiao , Haacke E. Mark , Mugler John P. , Berr Stuart , Brookeman James R. , Hutton Max C. 
Published: March 2007

AbstractA three‐dimensional (3D), ECG‐triggered, selective inversion recovery (SIR) rapid gradient‐echo (RAGE) technique is proposed to obtain MR angiograms of the main renal arteries. By using the selective inversion recovery and fat saturation, the background is significantly suppressed while blood maintains a high signal intensity as compared with conventional 3D time‐of‐flight (TOF) MR angiography. The sequence is ECG‐triggered so that blood in‐flow is maximized during systole, and intravoxel dephasing and pulsatile flow artifacts are minimized by collecting data during diastole. As a result, vessel boundary blurring and ghosting artifacts due to background motion are dramatically reduced, and the conspicuity and lumen definition of the arteries are significantly improved. High‐quality MR angiograms of the main renal arteries with excellent blood/tissue contrast and suppression of motion artifacts have been consistently obtained for normal volunteers, with the length of visualization being 51 ± 07 mm for the left, and 57 ± 06 mm for the right renal arteries, significantly greater than using conventional 3D TOF pulse sequences. Statistical analysis was performed by using a one‐sided Student's t test. Key words: renal artery; MR angiography; three‐dimensional MR imaging.
A microscope slide probe for high resolution imaging at 11.7 tesla
Authors: Glover P. M. , Bowtell R. W. , Brown G. D. , Mansfield Peter 
Published: March 2007

AbstractWe present details of a novel RF coil for use in NMR microscopy. This coil is an inductively coupled surface coil which is built into a standard microscope slide. The coil is highly sensitive and is also designed so that the sample to be imaged can be viewed under an optical microscope. This facility allows comparison of optical and NMR micrographs, as well as accurate sample positioning. Using the slide coil, images of onion epidermal cells with an in‐plane resolution of 4.5 μm have been produced.
Localized proton spectroscopy of focal brain pathology in humans: Significant effects of edema on spin–spin relaxation time
Authors: Kamada Kyousuke , Houkin Kiyohiro , Hida Kazutoshi , Matsuzawa Hitoshi , Iwasaki Yoshinobu , Abe Hiroshi , Nakada Tsutomu 
Published: March 2007

AbstractLocalized proton nuclear magnetic resonance (NMR) spectroscopy of human brain in two common focal pathologies producing brain edema (peritumor edema and acute edema–tous ischemic stroke) was performed utilizing point resolved spectroscopy (PRESS). The spectra obtained from the pathological tissues were characterized by a reduced N‐acetyl‐as–partate (NAA) to total creatine (Cr) ratio (NAA/Cr) and high level of lactate. While the spin lattice relaxation time (T1) of the main metabolite resonances, namely, those of NAA, Cr, and choline containing compounds (Cho), showed values similar to those of normal brain, the spin‐spin relaxation time (T2) of these metabolites exhibited a dramatic shortening in pathological tissues. Serial postoperative measurements of T2 in two patients with peritumor edema showed a gradual recovery of the T2 shortening corresponding to improvement of the edema. The majority of localized spectroscopy studies in humans is performed using a sequence which utilizes spin echo signals with a fixed single echo time. Hence, the signal intensities of the metabolite resonances obtained are inherently T2 dependent. The current study underscores that cautious interpretation of clinical data with respect to metabolite quantification is warranted.
A novel eddy current compensation scheme for pulsed gradient systems
Authors: Wysong R. E. , Madio D. P. , Lowe Irving J. 
Published: March 2007

AbstractWe describe a modified pre‐emphasis network that uses a number of fixed time constants, only whose amplitudes are adjustable. In comparison with variable time constant pre‐emphasis networks we have used, the fixed time constant network is more effective and easier to set on the fly. We have further developed a method to set the fixed time constant network mathematically using a linear least squares technique.
Off‐resonance spin locking for MR imaging
Authors: Santyr Giles E. , Fairbanks E. Jefferson , Kelcz Frederick , Sorenson James A. 
Published: March 2007

AbstractOff‐resonance spin locking is investigated as a low power method for achieving low field spin‐lattice relaxation contrast using high field clinical MR imaging systems (e.g., 1.5 tesla). Spin‐lattice relaxation times and equilibrium magnetizations in the off‐resonance rotating frame (T β) were measured for tissue‐mimicking phantom materials as a function of the ratio of the amplitude to the resonance offset of the spin‐locking pulse (f1/Δ). The phantom materials consisted of vegetable oil to simulate fat and two different gels containing 2% and 4% agar to simulate nonfatty tissues with different macromolecular compositions. These measurements were used to verify a signal strength equation for a multislice off‐resonance spin‐locking technique implemented on a clinical MR imaging system operating at 1.5 tesla. Although the oil showed little change in image contrast with increasing f1/Δ, the two gels demonstrated a strong variation which provided improved discrimination compared to T1‐weighted imaging. Off‐resonance spin locking is suggested as a method for improving delineation of breast lesions and a preliminary clinical example from a patient volunteer is presented.
Intravascular MR imaging in a porcine animal model
Authors: Martin Alastair J. , Henkelman R. Mark 
Published: March 2007

AbstractAn opposed solenoid intravascular receiver coil is used in a series of five pigs to generate images of the aorta. Severe ghosting artifacts are shown to occur if the motion of the intravascular coil is not restricted with respect to the vessel wall. Restricting coil motion and saturating the blood signal superior to the imaging plane are shown to produce high quality MR images. Layers within the artery wall could be discerned and the results of the in vivo analysis compared favorably with high resolution MR images of the corresponding tissue after excision.
Conditions for achieving artifact‐free T preparation in MRI
Authors: Zhang Weiguo 
Published: March 2007

AbstractA theoretical analysis of the stimulated gradient‐echo method for achieving T‐preparation in magnetic resonance imaging is performed. The results show that T‐weighting without the “shading effect” due to magnetic field variation can only be achieved if the dephasing requirement of the stimulated echo is satisfied. It is also shown that the effective echo‐time for T‐weighting depends on the polarities of the dephasing and the rephasing gradient pulses that generate the stimulated echo. The results from the theoretical analysis are experimentally validated.
A new 3D localization technique using quadratic field gradients
Authors: Wu Ed X. , Johnson Glyn , Hilal Sadek K. , Cho Zang‐Hee 
Published: March 2007

AbstractA new method of 3D spatial selection using pulsed quadratic field gradients is presented. Like previous pulsed quadratic gradient methods the new method requires only two RF pulses to achieve selection in three dimensions. Unlike previous methods, however, precise alignment of linear and quadratic gradient coils is not required. This characteristic allows the method to be used with small or surface quadratic gradient coils. The method is demonstrated on phantoms and rats.