bluuebunny/crossref_metadata_2025 huggingface dataset:
Mapping of lateral geniculate nucleus activation during visual stimulation in human brain using fMRI
Authors: Chen Wei , Kato Toshinori , Zhu Xiao‐Hong , Strupp John , Ogawa Seiji , Uǧurbil Kǎmil
Published: March 2007

Functional magnetic resonance imaging has been successfully used to map the activation in the lateral geniculate nucleus (LGN) in both hemispheres as well as the primary visual cortex (V1) during a checkerboard visual stimulation. The average blood oxygenation level dependent (BOLD) change in LGN was less than that in V1. However, the BOLD temporal responses were similar between LGN and V1. The activation in the pulvinar nucleus during visual perception was also detected, and its activated location could be separated from LGN in 3D images. The LGN activation between intersubject and intrasubject multiple trials was compared. The results demonstrate that fMRI can reliably and robustly detect small subcortical nucleus activation in the human brain.
Bilateral imaging using separate interleaved 3D volumes and dynamically switched multiple receive coil arrays
Authors: Greenman Robert L. , Lenkinski Robert E. , Schnall Mitchell D.
Published: March 2007

Multiple receive coil arrays are often designed for unilateral imaging of anatomy having bilateral symmetry. A technique is described for extending the utility of such arrays to simultaneously image both bilaterally symmetric anatomical features. A separate, complete multiple receive coil array is placed at each location. Two separate, noncontiguous 3D volumes are then acquired, one at each location, in an interleaved fashion. High‐impedance blocking networks are alternately activated and deactivated to minimize coupling between the arrays. It is demonstrated that there is no degradation in image quality when compared to a unilateral exam. A general method for analyzing the interactions between separate multiple coil arrays is presented.
Right ventricular regional function using MR tagging: Normals versus chronic pulmonary hypertension
Authors: Fayad Zahi A. , Ferrari Victor A. , Kraitchman Dara L. , Young Alistair A. , Palevsky Harold I. , Bloomgarden Daniel C. , Axel Leon
Published: March 2007

Right ventricular (RV) regional function, in both normal and diseased states, is not well characterized. Using 1D MR myocardial tagging, RV and septal intramyocardial segmental shortening was noninvasively measured in ten healthy subjects and in seven patients with chronic pulmonary hypertension. The normal RV free wall regional shortening was not uniform. A pattern of increasing RV free wall short‐axis shortening was found from the RV outflow tract to the RV apex, and a more complex pattern of RV free wall long‐axis shortening was observed. Both regional short‐ and long‐axis shortening were globally reduced in pulmonary hypertension patients, with the greatest decreases in the RV outflow tract and in the basal septal wall region. Regional RV function can be quantitatively evaluated using MR tagging to determine the impact of chronic pulmonary hypertension on RV performance.
Off‐resonance experiments and contrast agents to improve magnetic resonance imaging
Authors: Bertini Ivano , Luchinat Claudio , Parigi Giacomo , Quacquarini Gea , Marzola Pasquina , Cavagna Friedrich M.
Published: March 2007

The effect of off‐resonance irradiation on the water proton NMR signal intensity has been investigated as follows: (a) in the presence of a paramagnetic probe like manganese(II); (b) in the presence of bovine serum albumin (BSA) and two gadolinium(III) complexes, Gd‐DTPA and Gd‐BOPTA; (c) in the presence of cross‐linked BSA and the two above‐mentioned gadolinium(III) complexes. The experimental data have been rationalized on the basis of the available theoretical models. The effectiveness of the two complexes as contrast agents for MRI has been predicted. It is shown that contrast agents providing comparable longitudinal and transverse relaxation rate enhancements are those of general interest for off‐resonance magnetization transfer‐MRI.
Probabilistic analysis of functional magnetic resonance imaging data
Authors: Frank Lawrence R. , Buxton Richard B. , Wong Eric C.
Published: March 2007

Probability theory is applied to the analysis of fMRI data. The posterior distribution of the parameters is shown to incorporate all the information available from the data, the hypotheses, and the prior information. Under appropriate simplifying conditions, the theory reduces to the standard statistical test, including the general linear model. The theory is particularly suited to handle the spatial variations in the noise present in fMRI, allowing the comparison of activated voxels that have different, and unknown, noise. The theory also explicitly includes prior information, which is shown to be critical in the attainment of reliable activation maps.
Quantitation of dexfenflurainine/d‐norfenfluramine concentration in primate brain using 19F NMR spectroscopy
Authors: Christensen James D. , Babb Suzann M. , Cohen Bruce M. , Renshaw Perry F.
Published: March 2007

Fluorine (19F) magnetic resonance spectroscopy (MRS) was used to quantify the combined concentration of the anorectic drug dexfenfluramine (DF) and its active metabolite d‐norfenfluramine (dNF) in rhesus monkey brain. The accuracy of the MRS technique was assessed by comparison with gas chromatography. Brain 19F MRS signals were converted to brain DF + dNF concentrations after correction for signal relaxation losses and drug distribution in nonbrain tissue. Gas chromatography (GC) was used to assay brain DF and dNF concentrations following MRS evaluation. DF + dNF concentrations measured by 19F MRS averaged 104 ± 36 μM (mean ± SD) and GC measurements averaged 71 ± 12 μM. Correction for the distribution of DF and its metabolites in nonbrain tissue yielded a DF + metabolite brain concentration that was within one standard deviation of the GC‐derived value. The concentration of DF plus dNF measured by 19F MRS was similar to or greater than the value obtained by GC, which indicates that DF and its active metabolite dNF are fully detected by 19F MRS in primate brain in vivo. The application of these techniques to human subjects should enable the measurement of low micromolar‐range brain concentrations of DF and other fluorinated drugs.
Determination of the intracellular sodium concentration in perfused mouse liver by 31P and 23Na magnetic resonance spectroscopy
Authors: Colet Jean‐Marie , Makos Janice D. , Malloy Craig R. , Sherry A. Dean
Published: March 2007

A combination of 31P and 23Na NMR spectroscopy has been used to quantify the concentration of intracellular sodium, [Na]IC in the isolated and perfused mouse liver. The 31P resonances of dimethyl methylphosphonate and LaDOTP5−, markers of total tissue space and extracellular space, respectively, were used to determine the intracellular liver volume. For a mean wet weight of 1.7 ± 0.3 g, the intracellular liver volume as measured by 31P NMR averaged 1.2 ± 0.2 ml. The amount of intracellular sodium was measured from the baseline‐resolved intracellular 23Na resonance during perfusion of the shift reagent, TmDOTP5−. These two measurements resulted in an NMR‐determined value for [Na]IC of 29.0 ± 5.2 mM. Separate measurement of total tissue Tm and Na by atomic absorption spectroscopy on the same samples provided an AAS‐determined value for [Na]Ic of 32.1 ± 7.4 mM. These results indicate that intracellular sodium in the isolated, perfused liver is 100% visible by 23Na NMR spectroscopy.
Measurement of changes in cerebral blood volume in spontaneously hypertensive rats following L‐arginine Infusion using dynamic susceptibility contrast MRI
Authors: Caramia Francesca , Yoshida Tazuka , Hamberg Leena M. , Huang Zihong , Hunter George , Wanke Isabel , Zaharchuk Greg , Moskowitz Michael A. , Rosen Bruce R.
Published: March 2007

To understand whether the NO‐dependent vasodilator L‐arginine was effective upon a chronically hypertensive cerebral capillary endothelium, dynamic susceptibility contrast MRI was used to measure the relative cerebral blood volume (rCBV) changes in nonischemic spontaneously hypertensive rats (SHRs). rCBV was measured in 11 rats at 4.7 T using fast gradient echo imaging with intravenous injection of Gd‐DTPA. Images were acquired before, immediately after, and up to 90 min after the infusion of 300 mg/kg L‐arginine (n = 7) or of an equivalent volume of saline (n = 4). L‐arginine increased rCBV in cortex beginning 10 min after infusion and reached significance after 30 min (P < 0.01), reached a peak of 1.24 ± 0.06 (mean ± SEM) times pre‐injection level after 50 min, and was sustained throughout the 90 min observation period. In contrast, the rCBV in the deeper gray matter (striatum) showed no statistically significant change over the 90 min observation period. While this is consistent with previous studies showing that L‐arginine infusion can directly modulate vascular tone and cerebral hemodynamics, it demonstrates that the effect is present only in cortex, and that it can occur also in the setting of a disturbed capillary endothelium.
Homonuclear J coupling effects in volume localized NMR spectroscopy: Pitfalls and solutions
Authors: Yablonskiy Dmitriy A. , Neil Jeffrey J. , Raichle Marcus E. , Ackerman Joseph J. H.
Published: March 2007

It has been observed that the signal amplitude of multiplet resonances such as the 1H doublet resonance of lactate varies with pulse sequence timing when echo‐driven volume selective methods such as point resolved spectroscopy are used. Herein a standard vectorial description is presented for the mechanism of this artifact, which results from the chemical shift between homonuclear scalar‐coupled (i.e., J coupled) nuclei. The chemical shift causes the extent of a signal phase modulation to vary for different spatial regions of the excited voxel. This variation results in spatial interference effects that can lead to marked loss of signal intensity as well as corruption of the size and shape of the voxel from which signal is obtained. The phenomenon is substantial at an imaging field of 1.5 T and becomes especially pronounced at higher field strengths. Several strategies to avoid the artifact are provided.
Functional MRI using steady‐state arterial water labeling
Authors: Talagala S. Lalith , Noll Douglas C.
Published: March 2007

Flow‐sensitive functional MRI (fMRI) was performed using steady‐state arterial water labeling (SS‐AWL). Arterial water labeling was accomplished by flow induced adiabatic fast passage. The signal intensity of the visual cortex in arterial water labeled images decreased by ˜1.4% during visual stimulation of the brain. Acquisition of arterial water unlabeled and labeled images allows measurement of relative cerebral blood flow increase during brain activation. During visual stimulation, cerebral blood flow in the visual cortex increased by 17 to 35% as measured by SS‐AWL. Quantitation of brain activation in terms of a physiological parameter using SS‐AWL will facilitate comparative fMRI studies under different conditions.
Identification of different lipid phases and calcium phosphate deposits in human carotid artery plaques by MAS NMR spectroscopy
Authors: Guo Wen , Morrisett Joel D. , Lawrie Gerald M. , DeBakey Michael E. , Hamilton James A.
Published: March 2007

Accumulation of lipids in atherosclerotic plaques causes progressive narrowing of the arterial lumen, often followed by thrombosis and ischemia. Currently several different methods, most requiring disruption of the plaque, are used to study the physical properties of lipids accumulated in plaques, and lipid composition is typically determined by chemical analysis of completely disrupted plaques. In this study, 13C magic angle spinning NMR spectroscopy (MAS NMR) was used to determine in situ the lipid composition and molecular organization of all lipid phases in human carotid artery plaques (ex vivo). Protocols were developed to observe signals from one lipid phase without interference from other phases. In addition, 31P MAS NMR detected calcification in plaques by the signals from inorganic phosphate complexed to calcium. Together, 13C and 31P MAS NMR comprise a powerful nondisruptive approach for determining the quantity and phase state of components in arterial plaques.
Effects of endotoxin lung injury on NMR T2 relaxation
Authors: Cutillo Antonio G. , Chan Pei H. , Ailion David C. , Watanabe Suetaro , Albertine Kurt H. , Durney Carl H. , Hansen Christopher. B. , Laicher Gernot , Scheel Randall. F. , Morris Alan H.
Published: March 2007

The effects of endotoxin injury on lung NMR relaxation times (T1, CPMG T2, and Hahn decay constant (Hahn T2)) were studied in excised unperfused rat lungs. Blinded histologic examination showed no clear‐cut separation between endotoxin and control lungs. Morphometric lung tissue volume density and gravimetric lung water content did not differ significantly between the two groups. In contrast, the values of the fast, intermediate, and slow T2 components, obtained by multiexponential analysis of the CPMG decay curve, increased markedly after endotoxin administration, with minimal overlap between endotoxin and control values. The response of Hahn T2 was, in general, in the same direction as that of CPMG 72; however, Hahn T2 may be more affected by measurement errors and may be less sensitive to the presence of lung injury. t1 showed minimal changes after injury. The present data suggest that CPMG 72 measurements can consistently detect the presence of lung injury even when conventional histologic, morphometric, and gravimetric studies provide negative or equivocal results, and that the CMPG T2 method is superior, in this respect, to the Hahn decay method. T1 does not appear to be sensitive to lung injury in the absence of significant lung water accumulation.
A prospective approach to correct for inter‐image head rotation in FMRI
Authors: Lee Christine C. , Grimm Roger C. , Manduca Armando , Felmlee Joel P. , Ehman Richard L. , Riederer Stephen J. , Jack Clifford R.
Published: March 2007

Global head motion occurring between successive image acquisitions during a functional MRI time series can corrupt the signal of physiologic brain activation, potentially invalidating interpretation of the final activation map from that particular fMRI time series. By approximating the head as a rigid body, multiaxial global head motion can be decomposed into orthogonal linear and rotational components. This paper describes a method using orbital navigator echoes to provide prospective correction for both through–plane and in–plane inter–image head rotation in functional MRI. The dynamic detection and correction of rotation can be performed in <100 ms. Phantom experiments demonstrate accurate correction of rotational motion over a range of ±0.36° to ±12°. Imaging studies in volunteers document the feasibility of real–time prospective correction of rotational motion in vivo. Using a modified receiver operating characteristic method, motion–corrected functional MRI sensorimotor studies incorporating deliberate head rotations are shown to be superior to functional MRI time series acquired under similar conditions but without motion correction.
Improvement of spatial resolution of keyhole effect images
Authors: Oesterle Claudia , Hennig Jürgen
Published: March 2007

An algorithm is proposed which improves the spatial resolution of difference or effect images acquired with a keyhole sampling strategy. This new reconstruction algorithm uses a priori information about sharp structures in the observed signal changes from a high resolution reference scan. The potential of this algorithm even being able to deal with noisy effect images is illustrated by application to functional MRI data.
Variable TE gradient and spin echo sequences for in Vivo MR microscopy of short T2 species
Authors: Song Hee Kwon , Wehrli Felix W.
Published: March 2007

Collagen‐rich tissues such as skin or fibrous cartilage have very short T2 and thus, in order to be visible, demand a commensurate reduction in echo time. Whereas short echo time for imaging of humans is straightforward at large fields of view with currently available whole body gradient hardware, the problem is more challenging in the microscopic resolution regime (<100μm). In this work a simple approach consisting of shortening the echo time dynamically toward the lower spatial frequencies is described for three–dimensional partial flip‐angle gradient and spin‐echo sequences. Microimages obtained in vivo at 50 μm resolution on a 1.5 T whole body scanner are shown to afford a signal‐to‐noise gain of over 100% in the dermis of the human skin. A point–spread function analysis indicates that the variable echo time gradient–echo sequence produces a unique not previously reported off‐resonance artifact in the phase–encoding direction. The artifact results from the phase modulation occurring during the variable echo time and can manifest as both blurring and intensity fluctuations, as well as shifts of boundaries in the phase–encoding direction. However, for the on‐resonance condition, the images are free from these artifacts and exhibit significantly improved signal‐to‐noise ratio.
High‐resolution in vivo measurements of transverse relaxation times in rats at 7 Tesla
Authors: Crémillieux Yannick , Ding Shujun , Dunn Jeff F.
Published: March 2007

A multi‐echo imaging sequence suitable for high‐resolution and accurate in vivo transverse relaxation time (T2) mapping has been implemented. The sequence was tested on phantoms and was used to measure T2 values in vivo in the rat brain, muscle, and fat at 7 T. Brain T2 maps are shown and regional variations in brain T2 are reported (41.8 ms in cortex, 47.9 ms in hippocampus). Results are compared to literature values obtained at lower field in vivo as well as high‐field T2 measurements on excised rat tissues. The reported T2 values are generally smaller compared to lower‐field‐strength literature values. A discussion of the possible causes of these field effects on T2 is included (dipolar interaction, fast chemical exchange, and diffusion in susceptibility gradients).
Identification of a high concentration of scyllo‐inositol in the brain of a healthy human subject using 1H‐ and 13C‐NMR
Authors: Seaquist Elizabeth R. , Gruetter Rolf
Published: March 2007

The peak at 3.35 ppm in the 1H‐NMR spectrum characteristic for scyllo‐inositol may be a marker for cerebral pathology, although it has a well‐known constant concentration relative to myo‐inositol. Such a peak was observed with an intensity at least 300% above normal in the brain of a healthy volunteer. The scyllo‐inositol signal was assigned based on the detection of a corresponding peak at 74.5 ppm in the 13C‐NMR spectrum and on the demonstration of singlet characteristics of the proton signal. The presence of substantial brain concentrations of scyllo‐inositol suggests that scyllo‐inositol metabolism may be regulated independently from myo‐inositol and that such concentrations are compatible with normal health.
Correction for variations in MRI scanner sensitivity in brain studies with histogram matching
Authors: Wang Liqun , Lai H‐Ming , Barker Gareth J. , Miller David H. , Tofts Paul S.
Published: March 2007

Quantitative comparisons of abnormalities in MRI scans between patients or within patients serially are affected by variations in MR scanner performance. A histogram matching method is proposed to correct for variation in scanner sensitivity. It is demonstrated that this histogram matching method reduced the variation in white matter intensities across normal subjects from 7.5 to 2.5% and provided a method to remove the threshold dependency in lesion volume measurement with global thresholding in patients with multiple sclerosis (MS). The effectiveness of the method was compared with three other possible correction schemes. The histogram matching method was shown to be 2 to 5 times better.
Correction of off resonance‐related distortion in echo‐planar imaging using EPI‐based field maps
Authors: Reber Paul J. , Wong Eric C. , Buxton Richard B. , Frank Lawrence R.
Published: March 2007

We present, here, a simple method for measurement and correction of off‐resonance related geometric distortion in echo‐planar imaging (EP1). This method uses high signal‐to‐noise ratio (SNR) EPI‐based field maps, rapidly acquired using a series of gradient recalled images collected across a range of TE values. This field map is distorted in the same manner as the EPI images to be unwarped, providing a direct look‐up table for the correct location of each pixel of data. This method adds very little scan time and is robust and easy to implement.
Gradient, high‐resolution, magic angle spinning 1H nuclear magnetic resonance spectroscopy of intact cells
Authors: Weybright Patrick , Millis Kevin , Campbell Natalee , Cory David G. , Singer Samuel
Published: March 2007

The application of new gradient, high‐resolution, magic angle spinning (MAS) 1H nuclear magnetic resonance (NMR) spectroscopy to the study of intact undifferentiated and differentiated NIH 3T3 F442A cells demonstrated improved spectral resolution and sensitivity compared with static studies. MAS of cells permits the detection and quantitation of many cellular metabolites that are not clearly resolved in nonspinning measurements and provides an improved visibility of phospholipids. Gradient, MAS enables the use of diffusion weighting for compartment assignment and the determination of mobility for many metabolites which are incompletely resolved using static techniques. The smaller, undifferentiated preadipocytes show no microscopic evidence of cell lysis after 2 h of MAS at 3.5 kHz and 82% of these cells remain viable by trypan blue exclusion. In contrast, 15‐19% of the larger, lipid‐laden differentiated adipocytes were found to suffer some degree of cell lysis with MAS. This new method is an attractive alternative to either nonspinning perfusion or extraction techniques for NMR studies of cells.
Self‐navigated spiral fMRI: Interleaved versus single‐shot
Authors: Glover Gary H. , Lai Song
Published: March 2007

This study compares the measured activation volumes in motor cortex as well as the fluctuation noise and off‐resonance characteristics for 1‐, 2‐, and 4‐shot spiral gradient‐recalled echo blood oxygen level dependent contrast functional magnetic resonance imaging (fMRI) acquisitions, under conditions of constant resolution and scan time and with two readout durations. Reconstructions were made with and without self‐navigator correction. It was found that the navigator correction provided a 50% reduction in image fluctuation noise with 4‐shot acquisitions, and that multishot acquisitions perform as well as single‐shot techniques when self‐navigation is employed. An analysis of blurring showed that off‐resonance Af causes blurring when Δf> 1/(2*Tad), whereTadis the readout duration. Off‐resonance effects were readily corrected during reconstruction with retrospective linear shim, even with the longer readout duration needed for single‐shot methods. With navigator and shim correction, single‐shot and multishot spiral methods are highly effective for fMRI acquisitions.
Correction of B1 inhomogeneities using echo‐planar imaging of water
Authors: Thulborn Keith R. , Boada Fernando E. , Shen Gary X. , Christensen James D. , Reese Timothy G.
Published: March 2007

Reliable interpretation of the MR signal intensity over the FOV of an image must consider the spatial heterogeneity of instrumental sensitivity. A major source of such variation is the nonuniformity of the B1 magnetic field of the radiofrequency coil. This heterogeneity can be minimized by coil design but is exaggerated by surface coils, which are used to maximize the signal‐to‐noise ratio for some applications. This paper describes a rapid method for mapping the B1 field over the sample of interest, using 1H echo‐planar imaging, to correct for B1 distortions. The method applies to 1H imaging and has been extended to non‐1H imaging by using dual‐frequency coils in which the B., distributions are matched for the 1H frequency and the frequency of interest. The approach is demonstrated in phantoms, animals, and humans and for sodium imaging.
MR‐microscopic visualization of anisotropic internal cartilage structures using the magic angle technique
Authors: Gründer Wilfried , Wagner Manuela , Werner Annett
Published: March 2007

NMR microscopic studies of articular cartilage at 7.1 T are presented. Using a special experimental design, T2‐weighted spin‐echo images of cartilage‐bone plugs were taken under variable angles with respect to the static magnetic field Bo to visualize the angular‐dependent representation of internal matrix structures mediated by the collagen network arrangement. To quantify the observed orientational effect in the MR images, exact measurements of the transverse relaxation time T2 were taken using the CPMG sequence. The NMR experiments show the strong influence of the cartilage orientation with respect to the static magnetic field on the inhomogeneous appearance of the articular cartilage in the MR image. Additionally performed polarization light microscopic investigations demonstrate the direct relation between the oriented collagenous structures and the anisotropic regions observed in the MR images. A simple cartilage matrix model derived from the experimental findings is proposed, and consequences for the clinical assessment of the articular joint are discussed.
Removal of local field gradient artifacts in T2*‐weighted images at high fields by gradient‐echo slice excitation profile imaging
Authors: Yang Qing X. , Williams Gerald D. , Demeure Roger J. , Mosher Timothy J. , Smith Michael B.
Published: March 2007

Development of high magnetic field MRI techniques is hampered by the significant artifacts produced by B0 field inhomogeneities in the excited slices. A technique, gradient‐echo slice excitation profile imaging (GESEPI), is presented for recovering the signal lost caused by intravoxel phase dispersion in T2*‐weighted images. This technique superimposes an incremental gradient offset on the slice refocusing gradient to sample Jr‐space over the full range of spatial frequencies of the excitation profile. A third Fourier transform of the initial two‐dimensional image set generates an image set in which the artifacts produced by the low‐order B0 inhomogeneity field gradients in the sample are separated and removed from the high‐order microscopic field gradients responsible for T2* contrast. Application to high field brain imaging, at 3.0 T for human and at 9.4 T for immature rat imaging demonstrates the significant improvement in quality of the T2*‐weighted contrast images.
Quantitation of intrinsic magnetic susceptibility‐related effects in a tissue matrix. Phantom study
Authors: Yablonskiy Dmitriy A.
Published: March 2007

A theoretical background and experimental method that allows a separation of intrinsic, tissue‐matrix‐specific magnetic‐field inhomogeneity effects from both macroscopic (large compared with voxel dimensions) and microscopic (on the order of molecular dimensions) inhomogeneities is proposed. Such separation allows one to take full advantage of these tissue‐matrix‐specific magnetic field inhomogeneity effects to extract information about tissue structure. A method to measure the volume fraction occupied by the susceptibility‐perturbing component in a tissue matrix, the R2′ relaxation rate constant, and the susceptibility difference between the bulk component and the susceptibility‐perturbing component in a tissue matrix has been developed and tested on phantoms. This method offers the potential to assess a variety of tissue parameters, including cerebral blood volume, blood volume and blood oxygenation‐level changes in functional MRI, the structure of trabecular bone, and other physiologically important issues.
Quantification of phosphorus metabolites from chemical shift imaging spectra with corrections for point spread effects and B1 inhomogeneity
Authors: Murphy Joseph , Jiang Hong , Stoyanova Radka , Brown Truman R.
Published: March 2007

A method is described for quantifying phosphorus metabolites in tissue using spectra localized with surface coils and chemical shift imaging (CSI) and assuming that metabolites are uniformly distributed within a well‐defined volume. An analytical expression is developed that yields a single numerical correction factor that takes into account the excitation and receiver profiles of the coil, T1 saturation, and point spread effects associated with Fourier transformation of CSI data. An external phosphorus standard is used to calibrate instrument gain and the B1 profile of the coil. For spherical samples, point spread effects can modulate the signal intensities of three‐dimensional CSI spectra from ‐32% to +54%, depending on the voxel size. Measurements of phantoms of known concentrations showed systematic variations of ± 10% and random errors of ± 5%. We have used this method to measure the concentration of phosphocreatine in the thigh muscle of normal volunteers.
Boron‐11 NMR of borocaptate: Relaxation and in vivo detection in melanoma‐bearing mice
Authors: Bendel Peter , Frantz Anatol , Zilberstein Judith , Kabalka George W. , Salomon Yoram
Published: March 2007

Longitudinal and transverse relaxation rates for the 11B resonances in sodium borocaptate (BSH) at varying concentrations were measured in undiluted horse serum in a 4.7 Tesla field. The results could be fit by a model that assumes fast exchange of the BSH molecule between a free and a bound state, using values of 0.77 ± 0.7 MHz for the 11B quadrupole coupling constant and (6.3 ± 0.9) × 10−9 s for the rotational correlation time in the bound state. These results were used as a basis for assessing the requirements and limitations of quantitative determination of BSH concentrations in vivo, using 11B NMR. Surface coil 11B NMR spectroscopy was performed on a total of 14 mice injected with BSH. Some of the animals (n = 9) had implanted M2R melanoma tumors grown to various sizes in the rear thigh, in which case the surface coil was placed against the tumor, whereas for the other animals (without tumor), the coil was placed against the rear thigh muscle. NMR spectra were acquired under fully relaxed conditions. The spectra were quantitated by peak integration; apparent absolute BSH concentrations were derived by comparison with spectra from a phantom with known BSH concentration, using extrapolation of the time‐domain data to zero preacquisition delay. The results indicate significantly higher 11B BSH signal intensities in tumors, compared with muscle tissue, whereas the uptake and clearance kinetics were similar.
Spiral scanning with anisotropic field of view
Authors: King Kevin F.
Published: March 2007

Spiral scanning has been used to achieve much shorter scan times than conventional techniques for a wide range of applications. The major drawback with spiral scans is blurring from off‐resonant spins, which is proportional to the readout time. Blurring limits maximal spatial resolution and minimal scan time potentially achievable with spiral scanning. Anisotropic field of view is used in conventional scanning to improve image quality by matching /c‐space trajectory to object characteristics. Anisotropic field of view improves spatial resolution in spiral scanning without increasing scan time or blurring. The resolution improvement results from increased maximal k‐space radius allowed by the lower field of view. A field of view reduction by a factor of 2 in one direction provides up to 60% resolution improvement in that direction. Reduced SNR also results from non‐uniform /c‐space sampling.
Ultimate intrinsic signal‐to‐noise ratio in MRI
Authors: Ocali Ogan , Atalar Ergin
Published: March 2007

A method to calculate the ultimate intrinsic signal‐to‐noise ratio (SNR) in a magnetic resonance experiment for a point inside an arbitrarily shaped object is presented. The ultimate intrinsic SNR is determined by body noise. A solution is obtained by optimizing the electromagnetic field to minimize total power deposition while maintaining a constant right‐hand circularly polarized component of the magnetic field at the point of interest. A numerical approximation for the optimal field is found by assuming a superposition of a large number of plane waves. This simulation allowed estimation of the ultimate intrinsic SNR attainable in a human torso model. The performance of six coil configurations was evaluated by comparing the SNR of images obtained by the coils with the ultimate values. In addition, the behavior of ultimate intrinsic SNR was investigated as a function of main field strength. It was found that the ultimate intrinsic SNR increases better than linearly with the main magnetic field up to 10 T for our model. It was observed that for field strengths of 4 T or higher, focusing is required to reach the ultimate intrinsic SNR.
Experimental hypoxemic hypoxia: Changes in R2* of brain parenchyma accurately reflect the combined effects of changes in arterial and cerebral venous oxygen saturation
Authors: Lin Weili , Paczynski Richard P. , Celik Azim , Kuppusamy Karthikeyan , Hsu Chung Y. , Powers William J.
Published: March 2007

A two‐dimensionalT2*‐weighted gradient‐echo sequence was used to image the rat brain before and during graded hypoxemia. Changes inR2* (δR2*) with respect to the control state were calculated for brain parenchyma and were compared with changes in hemoglobin saturation measured from both arterial and jugular venous blood samples. δR2* was first correlated with the changes in arterial (δYa) and venous (δYv) hemoglobin saturations individually. Although a general trend toward a linear relationship with δR2* was observed for both δYa and δYv, neither alone was strong (correlation coefficientsr= 0.71 and 0.75 for δYa and δYv, respectively, and standard errors of the regression (SER) = 0.52 and 0.48 for δYa and δYv, respectively). However, when an “effective” cerebral blood hemoglobin saturation change (δYb) was constructed that takes into account the approximate weighting of the contributions from the arterial and venous phases of the circulation (δYb = 0.75 × δYv + 0.25 × δYa), a stronger correlation with δR2* was obtained and there was less variance (r= 0.87 and SER = 0.35). It is concluded that an appropriate weighting of the contributions of arterial and venous phases of the circulation must be taken into account in modeling the volume susceptibility effects of deoxyhemoglobin onR2* of brain parenchyma. In this way, a more accurate relationship between δR2* and δYb can be obtained.
Elasticity reconstructive imaging by means of stimulated echo MRI
Authors: Chenevert Thomas L. , Skovoroda Andrei R. , O′donnell Matthew , Emelianov Stanislav Y.
Published: March 2007

A method is introduced to measure internal mechanical displacement and strain by means of MRI. Such measurements are needed to reconstruct an image of the elastic Young's modulus. A stimulated echo acquisition sequence with additional gradient pulses encodes internal displacements in response to an externally applied differential deformation. The sequence provides an accurate measure of static displacement by limiting the mechanical transitions to the mixing period of the simulated echo. Elasticity reconstruction involves definition of a region of interest having uniform Young's modulus along its boundary and subsequent solution of the discretized elasticity equilibrium equations. Data acquisition and reconstruction were performed on a urethane rubber phantom of known elastic properties and an ex vivo canine kidney phantom using <2% differential deformation. Regional elastic properties are well represented on Young's modulus images. The long‐term objective of this work is to provide a means for remote palpation and elasticity quantitation in deep tissues otherwise inaccessible to manual palpation.
Reproducibility of intracranial volume measurement by unsupervised multispectral brain segmentation
Authors: Alfano Bruno , Quarantelli Mario , Brunetti Arturo , Larobina Michele , Covelli Eugenio M. , Tedeschi Enrico , Salvatore Marco
Published: March 2007

To assess the inter‐study variability of a recently published unsupervised segmentation method (Magn. Reson. Med. 1997;37:84–93), 14 brain MR studies were performed in five normal subjects. Standard deviations for absolute and fractional volumes of intracranial compartments, which reflect the experimental variability, were smaller than 16.5 ml and 1.1%, respectively. By comparing the experimental component of the variability with the variability observed in our reference database, an estimate of the biological variability of the intracranial fractional volumes in the database population was obtained.
Imaging asynchronous mechanical activation of the paced heart with tagged MRI
Authors: McVeigh Elliot R. , Prinzen Frits W. , Wyman Bradley T. , Tsitlik Joshua E. , Halperin Henry R. , Hunter William C.
Published: March 2007

A method for imaging the rapid temporal‐spatial evolution of myocardial deformations in the paced heart is proposed. High time resolution‐tagged MR images were obtained after stimulation of the myocardium with an MR‐compatible pacing system. The images were analyzed to reconstruct dynamic models of local 3D strains over the entire left ventricle during systole. Normal canine hearts were studied in vivo with pacing sites on the right atrium, left ventricular free wall and right ventricular apex. This method clearly resolved local variations in myocardial contraction patterns caused by ventricular pacing. Potential applications are noninvasive determination of electrical conduction abnormalities and the evaluation of new pacing therapies.
Sound generation in gradient coil structures for MRI
Authors: Mansfield Peter , Glover Paul M. , Beaumont Joanna
Published: March 2007

When supporting plates of plastic material are subjected to alternating transverse Lorentz forces while in a strong magnetic field normal to the plate surface, compressional waves within the solid produce a modulation of the plate surface that launches an acoustic wave in air along the magnetic field axis. We have extended our previous theory describing this process to include a detailed description of the formation of an acoustic interference pattern in air described by Fraunhofer diffraction at a distance from the plate surface. The extended theory predicts that the observed acoustic signal midpoint and normal to the plate surface gives a variation with frequency in approximate agreement with our previous measurements. The acoustic output off axis shows acoustic blazing that produces two main diffraction peaks with a splitting inversely proportional to the velocity of sound in the plate material. The new results could have important ramifications for the minimization of sound output in gradient coil design for MRI. A new arrangement of coils is proposed to ameliorate the acoustic output problem centrally and normal to the plate by extending the frequency response of the supporting plates to much higher frequencies. Also presented are estimates of the compressional wave velocities deduced from frequency response data recorded at the center‐point of a number of different plates.
Ultra‐fast velocity imaging in stenotically produced turbulent jets using RUFIS
Authors: Madio David P. , Gach H. Michael , Lowe Irving J.
Published: March 2007

A method for rapidly producing velocity images is presented. This sequence combines a modified bipolar gradient pulse to magnitude encode the velocity with the rotating ultra‐fast imaging sequence (RUFIS) to image the encoded spins. Velocity encoding is done in 3 msec, and RUFIS acquires 32 projections in 8 msec. The method is applied to turbulent jets associated with a 75% stenosis in a 15‐mm inner diameter glass pipe. Data is acquired upstream and downstream from the stenosis for Reynolds numbers from 560 to 3750. In addition, a robust method of reconstructing the unobserved short time region of a free induction decay is presented and incorporated into the image processing.
Gradient characterization using a Fourier‐transform technique
Authors: Alley Marcus T. , Glover Gary H. , Pelc Norbert J.
Published: March 2007

This paper describes a technique for characterizing the gradient subsystem of a magnetic resonance (MR) system. The technique uses a Fourier‐transform analysis to directly measure the k‐space trajectory produced by an arbitrary gradient waveform. In addition, the method can be easily extended to multiple dimensions and can be adapted to measuring residual gradient effects such as eddy currents. Several examples of gradient waveform and eddy‐current measurements are presented. Also, it is demonstrated how the eddy‐current measurements can be parameterized with an impulse‐response formalism for later use in system tuning. When compared to a peak‐fitting analysis, this technique provides a more direct extraction of the k‐space measurements, which reduces the possibility of analysis error. This approach also has several advantages as compared to the conventional eddy‐current measurement technique, including the ability to measure very short time constant effects.
Dynamic functional imaging of relative cerebral blood volume during rat forepaw stimulation
Authors: Mandeville Joseph B. , Marota John J. A. , Kosofsky Barry E. , Keltner John R. , Weissleder Ralph , Rosen Bruce R. , Weisskoff Robert M.
Published: March 2007

Dynamic measurements of regional changes in cerebral blood volume (CBV) were performed in rat models of hypercarbia and focal neuronal activation using T2‐weighted imaging after injection of an intravascular contrast agent with a very long blood half‐life. Calculated percent CBV change during hypercarbia was consistent with literature results from other non‐invasive modalities. Equivalent percent CBV increases were found using spin‐ and gradient‐echo images, suggesting proportional changes in blood volume for capillaries and small veins. During electrical stimulation of rat forepaw, focal CBV response to stimulation (24 ± 4%) was significantly delayed relative to blood oxygen level dependent (BOLD) signal after both onset and cessation of stimulation. Poststimulus CBV decay was temporally consistent with the BOLD poststimulus undershoot. The use of exogenous agent increased the functional contrast‐to‐noise ratio relative to BOLD imaging by 5.7 ± 1.3 at a magnetic field strength of 2 Tesla and 1.5 ± 0.2 at 4.7 Tesla.
On the nature and reduction of plaque‐mimicking flow artifacts in black blood MRI of the carotid bifurcation
Authors: Steinman David A. , Rutt Brian K.
Published: March 2007

Cardiac‐gated black blood MRI of the carotid artery bifurcation in normal human subjects shows signal within the lumen suggesting wall thickening or atherosclerotic plaque. This signal was believed to be artifactual, arising from complex flow patterns present at the carotid bifurcation. Computer simulation of the hemodynamics and black blood multislice image acquisition in a model of the carotid bifurcation showed that these artifacts arise from spins recovering their signal within the slow, recirculating flow of the carotid bulb. The computed hemodynamics also suggested that these artifacts could be minimized or eliminated entirely by gating the acquisition of slices in the most artifact‐prone region of the carotid bulb within a 250‐ms window after peak systole. Application of these predictions to studies of normal volunteers showed that, in most cases, these flow artifacts in black blood MRI can be eliminated simply by altering the phase of the cardiac cycle to which the image acquisition is gated. The observation that the size and placement of the saturation slabs had little effect on these artifacts suggested that, in those cases in which recirculation persists throughout the cardiac cycle, either inversion‐recovery or presaturation within the bulb itself would be required to suppress them.
Calibration of the 1H decoupling field strength and experimental evaluation of the specific RF absorption rate in 1H‐decoupled human 13C‐MRS
Authors: van den Bergh Adrianus J. , van den Boogert Hendrikusy J. , Heerschap Arend
Published: March 2007

For patient safety in human 1H decoupled 13C‐MRS, it is absolutely necessary to evaluate the specific RF absorption rate (SAR) of the tissue exposed to 1H frequency irradiation. With the use of surface coils, the local SAR at the body surface is of most concern due to the inherent RF field inhomogeneity. An empirical procedure to spatially calibrate the decoupler power level and to evaluate the local SAR at the body surface is described. For head, liver, muscle gastrocnemius, and muscle vastus lateralis, the SAR at the body surface was estimated for an 1HJ13C double surface coil setup. Optimized duty cycle values obtained with this procedure show that broadband 1H‐decoupled 13C‐MR spectroscopy is clinically feasible at 1.5 T for such a coil configuration within safety guidelines. Key words: SAR; decoupling; 13C‐MRS; 1.5 T.
A localized double‐quantum filter for the in vivo detection of brain glucose
Authors: Keltner John R. , Wald Lawrence L. , Ledden Patrick J. , Chen Yin‐Ching Iris , Matthews Richard T. , Küestermann Eekkehard H. G. K. , Baker John R. , Rosen Bruce R. , Jenkins Bruce G.
Published: March 2007

A double‐quantum filter (DQF) sequence with PRESS localization was developed for in vivo detection of the glucose resonances in the 3.85‐ppm region of the brain proton spectrum. The efficiency and spectral editing characteristics were studied in phantom and animal experiments. Approximately 45% detection efficiency was achieved at 4.7 T with TE = 68 ms. Since the efficiency of the DQF method is dependent on the relative phases of the RF pulses, a phase calibration procedure was used to correct for phase shifts induced by the spatial localization. In addition to detecting the 3.85‐ppm glucose resonances with approximately 45% efficiency, the DQF sequence simultaneously detects 1.3‐ppm lactate resonance with approximately 20% efficiency. The use of the DQF technique for simultaneously monitoring both the input and output of anaerobic glycolysis in the brain was demonstrated by detecting brain glucose and lactate in the same acquisition after iv injection of glucose followed by the induction of global ischemia.
Sodium MRI of human articular cartilage in vivo
Authors: Reddy Ravinder , Insko Erik K. , Noyszewski Elizabeth A. , Dandora Rahul , Kneeland John B. , Leigh John S.
Published: March 2007

Preliminary results from in vivo sodium MRI of human patellar articular cartilage are presented. Sodium images generated of an in vitro bovine patella clearly distinguish the region of proteoglycan depletion from the region of healthy cartilage. This provides the first evidence that sodium imaging may be used to detect changes due to osteoarthritis in vivo. The process of optimizing imaging time and signal‐to‐noise ratio, as well as potential implications in the detection of osteoar‐thritic change, are discussed.
BASE imaging: A new spin labeling technique for measuring absolute perfusion changes
Authors: Schwarzbauer Christian , Heinke Wolfgang
Published: March 2007

A new technique for magnetic resonance imaging of absolute perfusion changes that uses magnetically labeled tissue water proton spins as a freely diffusible tracer is described. It consists of unprepared basis (BA) images that serve as a reference and selective (SE) inversion prepared images that are sensitive to perfusion changes. In the present study, the BASE technique was applied to functional neuroimaging. BA and SE images were alternatingly and repeatedly acquired during periods of visual stimulation and control. Visual stimulation was achieved with an alternating black/white checkerboard operating at a frequency of 8 Hz. Maps of the absolute cerebral blood flow changes (ACBF) were calculated from the image intensities of the corresponding BA and SE images. The individual mean values of ACBF measured in five healthy volunteers ranged from 69 ± 18 to 99 ± 26 ml/min/100 g. Since the BASE technique does not require nonselective spin inversion, it can be used with small transmit/receive head coils (e.g., surface coils). In addition, the BASE technique is robust against a mismatch of the inversion and detection slice profiles.