bluuebunny/crossref_metadata_2025 huggingface dataset:
Classification of trabecular structure in magnetic resonance images based on morphological granulometries
Authors: Chen Yidong , Dougherty Edward R. , Totterman Saara M. , Hornak Joseph P.
Published: March 2007

A new method of detecting structured changes in trabecular bone, such as those associated with osteoporosis, was evaluated on magnetic resonance images of the wrist. The method was based on gray‐scale morphological granulometries which classify image texture by iteratively filtering an image and measuring the rate of change of structural diminution in a filtered‐image sequence. A classification scheme capable of distinguishing structural changes in trabecular bone starting from normal trabeculae through sclerotic, cystic, and grossly porotic bone is presented. Results of the application of this technique to the evaluation of high resolution magnetic resonance images of the wrist are presented.
Simultaneous temperature and regional blood volume measurements in human muscle using an MRI fast diffusion technique
Authors: Morvan Daniel , Leroy‐Willig Anne , Malgouyres Agnès , Cuenod Charles A. , Jehenson Philippe , Syrota André
Published: March 2007

The thermal dependence of the translational diffusion coefficient and of the regional blood volume was investigated in vivo by using a special MR pulsed gradient technique with reduced sensitivity to bulk tissue motion. Measurements were done at 0.5 T, using a small gradient insert. The diffusion coefficient of muscle water was calibrated against thermocouple‐measured temperature in vitro, both with the muscle fibers parallel and perpendicular to the diffusion gradient.

The maximum muscle temperature variation obtained by percutaneous conduction was −8.8 ± 1.6°C under cooling and +3.7 ± 1.6°C under heating, from basal state. Simultaneously the fractional regional blood volume decreased by a factor of 3.5 under cooling and increased by a factor of 2.7 under heating.

Due to the interdependence of microcirculation and tissue temperature, this technique may be used to follow heat production or deposition in living tissue (muscle exercise, electromagnetic irradiation, etc.).
A highly sensitive lactate editing technique for surface coil spectroscopic imaging in vivo
Authors: Bourgeois Dominique , Kozlowski Piotr
Published: March 2007

A lactate editing sequence based on the use of spin‐locking pulses with surface coils is described. The sequence retains more than 90% of the available lactate magnetization and suppresses at least 95% of the lipid signal in a single scan and ca. 99.5% after a simple two step cycle. The technique allows simultaneous observation of lactate and uncoupled metabolites in the range 2 to 3 ppm. The sequence was combined with two‐dimensional spectroscopic imaging to obtain a lactate map of an ischemic rat brain in vivo.
Elimination of susceptibility distortions and reduction of diffusion attenuation in NMR microscopy by line‐narrowed 2DFT
Authors: Sharp J. C. , Bowtell R. W. , Mansfield P.
Published: March 2007

NMR imaging at high field strengths is adversely affected by magnetic susceptibility variations within the specimen. This is especially true in NMR microscopy. We present results using a line‐narrowed imaging sequence which overcomes the image distortions associated with the frequency encoded readout method. Signal attenuation due to diffusion in static magnetic field gradients is also reduced.
A technique for assessment of bone marrow composition using magnetic resonance phase interference at low field
Authors: Derby K. , Kramer D. M. , Kaufman L.
Published: March 2007

In disorders which involve the bone marrow, the fat/water ratio of the marrow is often an indicator of the progress of disease. A noninvasive method of monitoring this ratio in bone marrow could be clinically useful. We have investigated a method of bone marrow assessment, using magnetic resonance imaging at low field (0.064 Tesla). The method has been tested using calibrated phantoms; we also present results from normal human subjects.
Phosphonate‐modified Gd‐DTPA complexes. III: The detection of myocardial infarction by MRI
Authors: Adzamli I. Kofi , Blau Monte , Pfeffer Marc A. , Davis Michael A.
Published: March 2007

The potential of a phosphonate‐modified‐Gd‐DTPA for MR image enhancement of myocardial infarction has been demonstrated in imaging experiments on rats. The agent, 1‐hydroxy‐3‐aminopropane‐1, 1‐diphosphonate‐modified‐Gd‐DTPA (Gd‐DTPA‐HPDP) accumulates in two models of myocardial infarction, (i.e., drug‐induced diffusely infarcted whole hearts and in focal acute myocardial infarction from a left coronary artery ligation). The time course of the accumulation of the agent in the focal model of infarction and subsequent washout has also been followed in vitro. Results of this kinetics demonstrate that the agent first perfuses all normal fluid spaces and then slowly diffuses into the occluded zone where it is retained for a prolonged period, in sufficient quantities to be useful as an MRI contrast agent. Wash‐out of the agent from normal myocardium is fast and complete with MR signal returning to background in minutes.

The specificity of Gd‐DTPA‐HPDP for soft‐tissue calcification and its retention within the infarcts permitted imaging at 1 to 2 h postinjection, (after unbound material has cleared the normal tissues). Infarcted tissue appeared as regions of increased signal intensity in T1‐weighted images (>200% enhancement), and correlated with histopathology. Unmodified Gd‐DTPA was not retained under identical conditions. Gd‐DTPA‐HPDP permits a more accurate infarct delineation than is possible with the unmodified agent.
A weighted least‐squares method for nuclear magnetic resonance velocity imaging
Authors: Caprihan A. , Icenogle M. V.
Published: March 2007

The phase method for velocity measurements in NMR imaging with more than two velocity encoding steps is discussed. The weighted least‐squares method takes into account the variation in the accuracy of phase calculations at a voxel with the size of the velocity encoding gradients. We choose the weights so that the method is equivalent to the method of maximum‐likelihood for high signal‐to‐noise ratios. We propose a method of implementation to minimize the problem of phase wrapping. We also discuss the number of velocity encoding steps, the choice of step size, and signal averaging, to improve the reproducibility of velocity measurements. Standard deviation images for the velocity have been calculated and used to reduce velocity noise by thresholding the velocity image.
Solvate structures in water‐methanol solutions of MRI contrast agents: Electron spin echo envelope modulation in gadolinium chelates
Authors: Clarkson R. B. , Hwang J.‐H. , Belford R. L.
Published: March 2007

Electron Spin Echo Envelope Modulation (ESEEM) data are reported for three gadolinium (III) chelates, Gd‐EDTA, Gd‐DTPA, and Gd‐TTHA, in frozen D2O/CH3OD glasses. This series includes Gd‐DTPA, an MRI contrast agent that is in clinical use. Three‐pulse electron spin echo modulation patterns can be modeled to yield geometrical information; e.g., distances and numbers of Gd+3‐OD interactions. Interpreted by a spherical shell model, the data for Gd‐TTHA are accounted for by Gd+3 surrounded by seven deuterons at an effective distance of 3.9 Å. We attribute these deuterons to second‐coordination sphere solvent molecules, since it is likely that Gd+3 is fully coordinated by a TTHA ligand. For analysis of ESEEM from Gd‐EDTA and Gd‐DTPA, the second‐sphere structures of Gd‐EDTA, Gd‐DTPA, and Gd‐TTHA are assumed equivalent. 2H‐ESEEM from inner‐sphere solvent molecules gives the effective distance between deuterons and Gd+3 to be ≈ 2.7 Å for the inner‐sphere water in both EDTA and DTPA complexes. The results of simulations also give the isotropic hyperfine and quadrupole coupling constants for solvent deuterium in these systems. Possible sources of error in the determination of r and q by this method are discussed.
A multispectral analysis of brain tissues
Authors: Fletcher Lynn M. , Barsotti John B. , Hornak Joseph P.
Published: March 2007

With the increasing use of three‐dimensional MRI techniques it is becoming necessary to explore automated techniques for locating pathology in the volume images. The suitability of a specific technique to locate and identify healthy tissues of the brain was examined as a first step toward eventually identifying pathology in images. This technique, called multispectral image segmentation, is based on the classification of tissue types in an image according to their characteristics in various spectral regions. The spectral regions chosen for this study were the hydrogen spin‐lattice relaxation time T1 spin‐spin relaxation time T2, and spin density, ϱ. Single‐echo, spin‐echo magnetic resonance images of axial slices through the brain at the level of the lateral ventricles were recorded on a 1.5 Tesla imager from 20 volunteers ranging in age from 17 to 72 years. These images were used to calculate the T1, T2, and ϱ images used for the classification. Tissue classification was performed by locating clusters of pixels in a threedimensional T1‐1‐T2‐1‐ρ histogram. Gray matter, white matter, cerebrospinal fluid, meninges, muscle, and adipose tissues were readily classified in magnetic resonance images of the volunteers with a single set of T1, T2, and ρ values. Cluster characteristics, such as size, shape, and location, provided information on the imaging procedure and tissue characteristics.
High‐precision MR velocity mapping by 3D‐fourier phase encoding with a small number of encoding steps
Authors: Bittoun Jacques , Bourroul Eric , Jolivet Odile , Idy‐Peretti Ilana , Mousseaux Elie , Tardivon Anne , Peronneau Pierre
Published: March 2007

The final result of Fourier velocity mapping is a set of images, each representing the spatial distribution of spins at a given velocity. To acquire data in a short time, the number of encoding gradient steps must be as small as possible, but this can mean sacrificing velocity resolution. We used interpolation methods to obtain high velocity resolution with a small number of encoding steps involving linear interpolation from 16 encoding steps or more and zero‐filling interpolation from two to eight encoding steps. Velocity measured by interpolated Fourier‐flow encoding agreed well with values obtained using a calibrated phantom. A simulation of noise on the images of the phantom showed that, for a given acquisition time, increasing number of encoding steps in the Fourier flow encoding gave better precision for velocity measurement than did averaging identical signals in phase‐mapping methods.
Gadolinium‐DTPA enhanced MRI demonstrates uterine vascular changes associated with artificially induced decidualization and ovoimplantation in rats
Authors: Hamilton G. S. , Kennedy T. G. , Norley C. J. D. , Karlik S. J.
Published: March 2007

Gadolinium‐DTPA enhanced magnetic resonance (MR) imaging has been used to demonstrate uterine vascular changes during ovoimplantation and artificially induced decidualization in rats. Evans blue dye and Gd‐DTPA were injected i.v. into rats 10 h after unilateral decidualization was induced by injection of sesame oil into the lumen of one uterine horn. Animals were killed various times later and uteri were removed, T1‐weighted proton imaging was performed, and mean image intensities for stimulated and control uterine horns were calculated by computer‐assisted image analysis. Macroscopic bluing confined to stimulated horns was apparent 5 min after tracer injection and increased in intensity until the experiment was terminated at 320 min. Analysis of MR images showed that mean image intensity of control horns did not change significantly at any time after injection of the Gd‐DTPA and Evans blue whereas mean image intensity of stimulated horns increased significantly by 5 min after injection, peaked at 20 min, and returned to values not different from controls by 320 min. T1‐weighted images of day 6 pregnant rats injected with Gd‐DTPA and Evans blue revealed patterns of image enhancement that matched those of macroscopic bluing. Uterine concentrations of radioactivity after injection of 153Gd‐DTPA indicated that increased extracellular fluid volume (ECFV) produces the image enhancement of stimulated horns since the tracer permeates the extracellular fluid of both horns. Gd‐DTPA‐enhanced MR imaging of uteri after deciduogenic stimulation revealed significant image enhancement for stimulated horns at both 9 and 27 h after stimulation. We conclude that Gd‐DTPA enhanced MR imaging allows the identification of uterine vascular changes during ovoimplantation and decidualization and that this methodology may be useful in both experimental and clinical settings.
Localized detection of glioma glycolysis using edited 1H MRS
Authors: Schupp Daniel G. , Merkle Hellmut , Ellermann Jutta M. , Ke Yong , Garwood Michael
Published: March 2007

In vivo 1H MRS can be used to detect and quantify the lactate resonance at 1.3 ppm provided that overlapping lipid resonances are eliminated. A homonuclear spectral editing method was developed to acquire uncontaminated 1H spectra of lactate with adiabatic pulses. An advantage of the adiabatic pulse sequence is the ability to induce uniform flip angles and to maximize sensitivity in applications employing surface coil transmitters which produce highly inhomogeneous B1. Glycolytic activity in an intracerebral C6 glioma in rats was monitored by using adiabatic editing sequences to observe [3‐13C]lactate produced from infused [1‐13C]glucose. Acute hyperglycemia (serum glucose >22 mM, n = 10) had no significant effect (P = 0.08) on the total ([12C]+ [13C]) tumor lactate signal intensity.
Novel approaches to low‐cost MRI
Authors: Macovski Albert , Conolly Steven
Published: March 2007

This paper presents a combination of speculative approaches, some related to earlier work and some apparently novel, which show great promise in providing a new class of MRI machines that would be considerably less expensive. This class would have advantages and disadvantages as compared to existing MRI, over and above that of low cost. The disadvantages include the apparent inability to perform classic spectroscopy, and limited flexibility in the area of selective excitation. The advantages include a fundamental immunity to inhoinogenelty and susceptibility problems, the ability to create a wide class of machines that are designed for specific anatomy‐related applications, the ability to design open machines for physician access, and improved capability for high speed imaging. Generic to all of the methods presented are a pulsed polarizing field and an oscillatory readout bias field. The pulsed field initially polarizes the magnetic moments. Sinat it is not on during the readout operation it has negligible homogeneity requirements since changes in the field amplitude will merely shade the image intensity. During readout a relatively low bias field is used. To enable the use of a relatively inhomogeneous bias field, an osciliatory field is used that has a zero average value. This prevents any long‐term buildup of phase errors due to a frequency error associated with inhomogeneity. Thus the average bias frequency will be determined solely by the frequency rather than the amplitude of the bias field. Three methods are described, all including the above features. The first two involve imaging in the laboratory frame, while the third involves imaging in the rotating frame. The second approach requires no RF excitation and the third approach uses RF bias and gradient signals. Some approaches to slice selection are described.
Development of the human brain: In vivo quantification of metabolite and water content with proton magnetic resonance spectroscopy
Authors: Kreis Roland , Ernst Thomas , Ross Brian D.
Published: March 2007

Cerebral metabolite concentrations and water content were measured by means of localized proton magnetic resonance spectroscopy in 50 children, while metabolite peak ratios in short echo time spectra were evaluated in 173 examinations. Normative curves for normal development were established for two cerebral locations. The current report presents the first study of absolute metabolite concentrations and T1‐and T2‐relaxation as a function of age. Myo‐inositol was found dominating the spectra at birth (12 mmoles/kg), while choline is responsible for the strongest peak in older infants (2.5 mmoles/kg). Creatine and N‐acetyl groups are at significantly lower concentrations in the neonate than in the adult (Cr: 6, NA: 5 mmoles/kg). NA and Cr are determined by gestational age, whereas the concentration of ml correlates best with postnatal age. Quantitative lH MRS is expected to be of particular value in diagnosis and monitoring of pathology in infants, since metabolite ratios are often misleading.
Metabolic assessment of a neuron‐enriched fraction of rat cerebrum using high‐resolution1H and13C NMR spectroscopy
Authors: Petroff Ognen A. C. , Pleban Lisa , Prichard James W.
Published: March 2007

This study explored the utility of1H and13C magnetic resonance spectroscopy to study a neuron‐enriched preparation made from rat cerebrum. The preparation contained high concentrations ofN‐acetylaspartate and γ‐aminobutyric acid and low concentrations of glutamine, indicating that it was in fact rich in neuronal cytosol. This was confirmed by immunohistochemical studies with antibodies to neuronal and glial markers. A method of metabolite quantification based on the creatine signal yielded metabolite concentrations similar to those of rat cerebrum, whereas concentrations based on the metabolite/protein ratio were five times lower, suggesting that much protein in the preparation was not associated with functioning cytoplasm. The metabolic competence of the preparation was assessed by quantitative measurements of its ability to convert 1−13C‐glucose into lactate, glutamate, aspartate, and other metabolites under well oxygenated conditions for 30 min. Calculated from the creatine standard, the mean glycolytic rate was the same as in a synaptosomal preparation studied under similar conditions and the same as rat cerebrumin vivo. Tricarboxylic acid cycle flux occurred at half the rate observed in the synaptosomal preparation and 16% of the basal cerebral metabolic ratein vivo.
Generalized matched filtering for time‐resolved MR angiography of pulsatile flow
Authors: Wang Yi , Weber David M. , Korosec Frank R. , Mistretta Charles A. , Grist Thomas M. , Shannon Swan J. , Turski Patrick A.
Published: March 2007

Generating flow‐specific images (arteriograms, venograms) with optimal signal‐to‐noise ratios for time‐resolved MR angiography is a conditional maximum problem, and its solutions are generalized matched filters. We have investigated six matched filters, corresponding to all possible combinations of three flow suppression conditions and two signal‐to‐noise ratio maximization procedures. Four of these matched filters correspond to previously described methods: the subtractive matched filter, the standard deviation, the global venous eigenirnage and the global arterial eigenimage. The two others are referred to here as the local venous eigenimage and the local arterial eigenimage. These six matched filters have been applied to 2D time‐resolved phase contrast angiographic data. The local arterial eigenimage is found to be the most effective in suppressing undesired venous flow and preserving desired arterial flow.
A potentially artifact‐free oral contrast agent for gastrointestinal MRI
Authors: Liebig Thomas , Stoupis Christophoros , Ros Pablo R. , Ballinger J. Ray , Briggs Richard W.
Published: March 2007

The combination of diamagnetic barium sulfate and superparamagnetic iron oxide (SPIO) in one suspension produces a macroscopic cancellation of positive and negative magnetic susceptibility components that can potentially eliminate susceptilbllity artifacts even with gradient echo pulse sequences. The relaxation properties that make the SPIO suspension a useful negative contrast agent are retained.
Sensitivity and localization enhancement in multinuclear in vivo NMR spectroscopy by outer volume presaturation
Authors: Shungu Dikoma C. , Glickson Jerry D.
Published: March 2007

Sampling of the entire brain tissue in 1H NMR metabolic studies is complicated by the presence of intense pericranial lipid and tissue water resonances, which can obscure metabolite resonances. This study extends the concept of localization by outer volume suppression (OVS) to achieve fully conformal in viuo localization, sampling at least 95% of rat brain with complete elimination of pericranial lipids. This has permitted acquisition of lipid‐free short echo time (7.5 ms), high spatial resolution 2D spectroscopic images exhibiting high sensitivity and information content in relatively short measurement time (68 min). Incorporation of spatially tailored OVS into existing methods (e.g., DRESS, STEAM, PRESS) extends their localization efficiency and performance. Two single spin‐echo localization sequences have been described that attain much shorter echo times or achieve better water suppression than PRESS. One of these sequences allows editing and relaxo‐metric studies of J‐coupled spins. The methods described are suitable for in vivo localization of most tissues and can be applied with any biologically important nucleus.
Estimation of metabolite concentrations from localized in vivo proton NMR spectra
Authors: Provencher Stephen W.
Published: March 2007

The LCModel method analyzes an in vivo spectrum as a Linear Combination of Model spectra of metabolite solutions in vitro. By using complete model spectra, rather than just individual resonances, maximum information and uniqueness are incorporated into the analysis. A constrained regularization method accounts for differences in phase, baseline, and lineshapes between the in vitro and in vivo spectra, and estimates the metabolite concentrations and their uncertainties. LCModel is fully automatic in that the only input is the time‐domain in vivo data. The lack of subjective interaction should help the exchange and comparison of results. More than 3000 human brain STEAM spectra from patients and healthy volunteers have been analyzed with LCModel. N‐acetylaspartate, cholines, creatines, myo‐inositol, and glutamate can be reliably determined, and abnormal levels of these or elevated levels of lactate, alanine, scyllo‐inositol, glutamine, or glucose clearly indicate numerous pathologies. A computer program will be available.
Resolution enhanced NMR spectroscopy in biological systems via magnetic susceptibility matched sample immersion chambers
Authors: Ballon D. , Mahmood U. , Jakubowski A. , Koutcher J. A.
Published: March 2007

A technique is described which reduced the magnetic susceptibility induced line broadening in NMR spectra obtained from three biological systems at 4.7 Tesla. Proton spectra from a sealed suspension of HL60 leukemic myeioblasts yielded minimum linewidths of 1.3 Hz at 200 MHz (0.0065 ppm) after 10 min of automated shimming. 31P spectra from an in vivo murine MCa mammary carcinoma yielded a well‐resolved phospharylcholine resonance without proton decoupling and with the resistive shim coil currents set to zero. 31P spectra from a perfused suspension of RIF‐1 fibrosarcoma cells exhibited a γ‐nucleoside triphosphate resonance which was resolved into purine and pyrimidine components.
NMR visibility studies of N‐δ proton of proximal histidine in deoxyhemoglobin in lysed and intact red cells
Authors: Wang Dah‐Jyuu , Nioka Shoko , Wang Zhiyue , Leigh John S. , Chance Britton
Published: March 2007

Recent in vivo 1H MRS studies of muscle oxygen levels by means of myoglobin (Mb) oxygenation have necessitated an investigation of the possible contamination from deoxy‐hemoglobin (Hb). To determine the contribution of Hb in these NMR measurements, we studied the NMR visibility of histidyl N‐δ proton of Hb in lysed and intact RBC (red blood cell) suspensions. We found that the visibility of deoxy‐Hb was significantly lower in intact RBCs (ca. 16%) than the solution form at an equivalent concentration of β heme‐iron, even though the visibility of deoxy‐Hb from lysed RBC and deoxy‐Mb was almost identical. Our study also shows that visibility increases with RBC swelling. Based on the difference in concentration and compartmentation, we conclude that less than 17% contribution from Hb is expected in Mb measurements in vivo. The possible mechanisms which cause the low visibility of Hb in RBCs are discussed.
Quantitative characterization of the eddy current fields in a 40‐cm bore superconducting magnet
Authors: Liu Q. , Hughes D. G. , Allen P. S.
Published: March 2007

The temporal and spatial dependence of the eddy current fields, generated by switching off x, y, and z gradients in a 40‐cm bore Bruker superconducting magnet, have been studied by measuring the offset frequency of the proton FID obtained from a small spherical sample. The measurements were made with the pre‐emphasis unit deactivated. The data obtained at each location were well fitted to a sum of four exponentially decaying components. The shortest decay is, in each case, associated with the decay of the current in the gradient coil itself, while the other decays are associated with three eddy currents with decay times ranging from 13 to 480 ms. Each of the three eddy currents generates an essentially uniform gradient for at least 4 cm on either side of the isocenter. However, when the eddy currents are generated by either the vertical transverse gradient or the longitudinal gradient, the eddy current gradients are also accompanied by a field shift.
Magnetization transfer affects the proton creatine/phosphocreatine signal intensity: In vivo demonstration in the rat brain
Authors: Dreher Wolfgang , Norris David G. , Leibfritz Dieter
Published: March 2007

The effect of off‐resonance preirradiation on proton spectra acquired from the healthy rat brain at 4.7 T is examined using a PRESS sequence. The creatin/phosphocreatine (Cr/PCr) signal at 3.0 ppm decreases in signal intensity for offset frequencies between ±10 kHz. This cannot be explained by RF bleedover, but is attributed to magnetization transfer between two pools of Cr/PCr, one with a long T2 relaxation time giving the observed NMR signal, the other corresponding to a broad resonance line being completely or partially saturated by off‐resonance preirradiation. Possible interpretations of these results are discussed.
Methods for reconstructing phase sensitive slice profiles in magnetic resonance imaging
Authors: Devoulon Philippe , Emsley Lyndon , Weber Peter , Meuli Reto , Decorps Michel , Bodenhausen Geoffrey
Published: March 2007

The experimental determination of slice profiles excited by applying radiofrequency pulses in the presence of a gradient generally results in magnitude profiles. The conditions necessary to obtain a phase‐sensitive picture of the profile of a slice are discussed. A distinction is made between the “excitation profile” (distribution of the transverse magnetization immediately after the RF pulse) and the “slice profile” (distribution after refocusing by gradient reversal and/or imperfect gradient switching). Methods are presented that allow one to obtain either the excitation profile or the slice profile. It is shown that phase encoding along the direction of the slice selection gradient provides a convenient protocol for obtaining the distribution of both the real and imaginary parts of the slice profile. The phase sensitive excitation profile can be obtained by frequency encoding. These methods were used to evaluate the performance of various shaped pulses.
Accurate T1 determination from inversion recovery images: Application to human brain at 4 Tesla
Authors: Kim Seong‐Gi , Hu Xiaoping , Ugurbil Kamil
Published: March 2007

It is well known that the signal polarity in inversion‐recovery (IR) images changes with inversion time, complicating the determination of T1 To avoid this problem, a simple subtraction method is implemented. In this method, k‐space data of the longest inversion time are subtracted from the corresponding data of each inversion time. This subtraction yields IR images of same polarity, making it straightforward to derive T1 using a standard fitting routine. Phantom T1 studies with IR Turbo‐FLASH images demonstrate that this technique is robust and accurate. Four Tesla T1 values of the human brain were also determined by this method to demonstrate its in vivo utility.
Rapid monitoring of changes in water diffusion coefficients during reversible ischemia in cat and rat brain
Authors: Davis D. , Ulatowski J. , Eleff S. , Izuta M. , Mori S. , Shungu D. , van Zijl P. C. M.
Published: March 2007

Changes in the diffusion constant of water during reversible brain ischemia and cardiac arrest were monitored with a 10‐s time resolution. Results (five cats, three rats) indicate that these changes are reversible and that the bulk of the changes are not caused by temperature or motion related to brain pulsations and blood flow. The rapid time course of the changes corresponds to the known time course for changes in energy state, signal transduction, and ionic homeostasis.
Surface coil cardiac tagging and 31P spectroscopic localization with B1‐insensitive adiabatic pulses
Authors: Hendrich Kristy , Xu Ya , Kim Seong‐Gi , Uǧurbil Kǎmil
Published: March 2007

A technique is presented for MRI tagging in the presence of inhomogeneous B1 fields. A rectangular tagging grid is produced with B1‐insensitive adiabatic pulses in a magnetization preparation period that precedes image acquisition. Phantom results demonstrate that the method is well‐suited to surface coil experiments. The technique is applied to a canine model of myocardial ischemia to track the spatially dependent wall motion of the left ventricle during the cardiac cycle. Transmural 31P spectra are acquired from the same double‐tuned surface coil, with tagging and spectroscopy performed for the first time, during normal, ischemic, and recovery conditions for the same animal.
Quadrupole gradient coil design and optimization: A printed circuit board approach
Authors: Chu Kenneth C. , Rutt Brian K.
Published: March 2007

Three different dual‐axis quadrupole gradient coils for quantitative high resolution MR imaging of small animals, phantoms and specimens were designed and built using printed circuit board technology. Numerical optimization of the conductor positions was used to increase the volume of 0.4% gradient uniformity by up to a factor of four. In one coil, the volume of 5% gradient uniformity occupied 88% and 83% of the overall diameter and length of the coil, respectively. A systematic error of 0.5% in the wire placement was shown to cause a reduction in the volume of 0.4% gradient uniformity by a factor of two, though the region of 5% gradient uniformity was not significantly affected. Heat transfer calculations were used to determine maximum peak and root‐mean‐squared currents that could safely be applied to the coils.
Sources of intensity nonuniformity in spin echo images at 1.5 T
Authors: Simmons Andrew , Tofts Paul S. , Barker Gareth J. , Arridge Simon R.
Published: March 2007

This manuscript describes a number of sources of nonuniformity for spin echo images at 1.5 T. Both coil tuning and crosstalk can have significant effects on image nonuniformity. For short repetition times, nonuniformity increases with decreasing TR, possibly due to gradient eddy currents. In sections of RF coils with poor RF uniformity, image nonuniformity varies with both echo time and the number of echoes in a multiecho sequence. For the particular imager used, there are small differences between transverse and sagittal/coronal nonuniformity. The temporal stability of image nonuniformity is very good. The use of uniform oil phantoms is shown to be superior to low pass filtered images for correction of image nonuniformity.
Spreading waves of decreased diffusion coefficient lifter cortical stimulation in the rat brain
Authors: Latour Lawrence L. , Hasegawa Yasuhiro , Formato James E. , Fisher Marc , Sotak Christopher H.
Published: March 2007

A method is demonstrated for the noninvasive detection and study of spreading cortical depression. Spreading depression (SD) was elicited in rats by topical application of potassium chloride to the exposed cortex. The apparent diffusion coefficient (Dapp) of water in a region of the cortex, measured using a PFG‐NMR spin echo sequence with an observation time of 40 ms, declines 35% within 30 s and recovers to the normal value within the next 30 s. The region of decreased Dapp was shown to be 2 mm in size and to move in the cortex, away from the point of application, with a uniform velocity of 3.3 ± 0.5 mm/min. The behavior of the affected region is consistent with other reports of the behavior of SD as monitored by electro‐physiological means. The technique can be implemented on currently available MRI equipment and makes possible the noninvasive study of SD in animal models of neurological disorders, their therapeutic intervention, and possibly the study of SD in humans.
Band‐selective spin echoes for in vivo localized 1H NMR spectroscopy
Authors: Shungu Dikoma C. , Glickson Jerry D.
Published: March 2007

This study describes a new single spin‐echo spatial localization sequence, BASSALE or BAnd‐Selective Spin echo Acquisition for Localized Editing, that overcomes a number of the limitations of the STEAM and PRESS volume selection pulse sequences. It achieves conformal volume localization in a single shot by spatially tailored suppression of all magnetization outside a 2D region of interest followed by selection of a single orthogonal slice. This separation of spatial localization from the echo formation process has permitted use of a spectrally selective cosine‐modulated sinc refocusing pulse to acquire localized 1H spectra with the water suppression efficiency of STEAM and the sensitivity of PRESS. Echoes formed by such spectrally selective pulses have been termed bandselective spin echoes. The BASSALE sequence attains shorter echo times than PRESS, inhibits scalar spin‐spin interactions to permit localized editing and T2 relaxometry of metabolites with J‐coupled spins (e.g., lactate), is insensitive to homonuclear multiple‐quantum and polarization transfer effects, and can be made sensitive or insensitive to spin displacement effects. Applications are shown both with phantoms and in situ in the rat brain.
In Vitro and in Vivo13C and 31P NMR analyses of phosphocholine metabolism in rat glioma cells
Authors: Gillies Robert J. , Barry Judith A. , Ross Brian D.
Published: March 2007

In ivivo magnetic resonance spectroscopy (MRS) has revealed that phsophomonoesters (PME) such as phosphocholine (PCho) and phosphoethanolamine (PEth) are elevated in tumalrs and rapidly proliferating tissues. The regulation of PME levels and their relationship to proliferation are not well known. In the present study, we investigated the regulation of PCho and PEth levels in rat glioma cells grown in vivo and in vitro using 31P and 13C MRS. However, the ability of cells to produce choline endogenously is variable. To fully understand regulation of PCho levels, it is necessary to characterize the activity of the endogenous pathway, if it exists. This was first investigated by following the metabolic fate of 13C‐labeled methionine of 9L glioma tumors in vivo. Our results indicate that there is a significant amount of de novo choline synthesis in ivivo. However, similar experiments performed in virro using cells cultured in bioreactors indicated that glioma cells themselves are unable to synthesize choline de novo, suggesting that the in vivo results were due to the involvement of extra‐tunnoral organs, e.g., liver. Further in vitro experiments demonstrated that the uptake and phosphorylation of physiologically relevant concentrations of exogenous choline is very active in these systems. Thus, it appears that the exogenous pathway for PCho biosynthesis predominates and regulates PCho levels in glioma cells. Our results also demonstrate that PCho levels are lowest, and PEth levels are highest, in non‐proliferating cells. These observations indicate that there is a decrease in the biosynthesis of PCho concomitant with a redulction in culture growth. The source of the increased PEth is, as yet, undefined.
Inversion recovery EPI of bolus transit in rat myocardium using intravascular and extravascular gadolinium‐based MR contrast media: Dose effects on peak signal enhancement
Authors: Wendland Michael F. , Saeed Maythem , Yu Kyle K. , Roberts Timothy P. L. , Lauerma Kirsi , Derugin Nikita , Varadarajan John , Watson Alan D. , Higgins Charles B.
Published: March 2007

Inversion recovery gradient recalled echo planar imaging (TI/TR/TE = 700/2000/10 ms) was used to dynamically monitor the first pass of an intravascular (GdDOTA‐polylysine) and an extravascular (GdDTPA‐BMA) contrast agent through normal rat myocardium. It was found that myocardial enhancement increased with dose of the intravascutar agent to a limiting value of ∼50% of fully relaxed intensity, consistent with enhancement of 40% of myocardial water content during the first pass. Larger doses produced no further increase in peak response. On the other hand, the extravascular agent caused incrementally increased enhancement throughout the dose range examined to a final value of 68 ± 2% of fully relaxed intensity. The profile of dose dependence for both agents was inconsistent with monoexponential T1 relaxation. It was concluded that (a) compartmentalization of myocardial water combined with restricted myocardial water diffusion limits the peak response during bolus transit; (b) extraction of the extravascular agent during transit elevates the peak response over that obtained from agent confined to the vascular volume; and (c) models that assume simple monoexponential r, relaxation to derive timedensity curves do not adequately describe the relationship between changes in signal intensity, R1 and contrast concentration.
Noninvasive measurement of renal hemodynamic functions using gadolinium enhanced magnetic resonance imaging
Authors: Dumoulin Charles L. , Buonocore Michael H. , Opsahl Lorinda R. , Katzberg Richard W. , Darrow Robert D. , Morris Thomas W. , Batey Charlotte
Published: March 2007

A technique for the assessment of single kidney hemodynamic functions utilizing a novel MR pulse sequence in conjuinction with MR contrast material administration is described. Renal extraction fraction (EF) is derived by measuring the concentration of the incoming contrast agent in the renal artery and the outgoing concentration in the renal vein. The glomerular filtration rate (GFR) can then be determined by the product of EF and renal plasma flow. A modified iniversion recovery MR pulse sequence is used to measure the T1 of moving blood. This pulse sequence uses a spatially nonselective inversion pulse. A series of small flip angle detection pulses are then used to monitor the recovery of longitudinal spin magnetization in an image plane intersecting the renal vessels. The recovery rate is measured in each vessel and the T1 of blood determined. These T1 measurements are then used to determine the ratio of contrast concentration in the renal arteries and veins. Blood flow measurements can be obtained simultaneously with T1 measurements by inserting flow‐encoding magnetic field gradients into the pulse seqiuence. Preliminary results in human volunteers suggest the feasibility of noninvasively determining hemodynamic functions with magnetic resonance.
Cholesterol effects on nonelectrolyte membrane transport in human erythrocytes: NMR magnetization transfer studies
Authors: Nouri‐Sorkhabi M. Hossein , Chapman Bogdan E. , Sullivan David R. , Kuchel Philip W.
Published: March 2007

The cholesterol content of human erythrocytes was altered by incubating them with sonicated dispersions of cholesterol/phosphatidylcholine at 37°C. 31P NMR saturation transfer experiments were used to measure the rate constant for efflux of dimethyl methylphosphonate (DMMP) from the cells, and thereby gain an estimate of the permeability coefficient. It was shown that up to 39% depletion of membrane cholesterol (cholesterol/phospholipid molar ratio of 0.46) increased the efflux rate constant and permeability coefficient of DMMP 1.55‐and 1.86‐fold, respectively. Enrichment of the membranes with cholesterol by 45% (cholesterol/phospholipid molar ratio of 1.57) on the other hand, decreased the efflux rate constant and permeability coefficient 1.63‐and 1.79‐fold, respectively. It was concluded that DMMP may be used as a probe molecule to study the functional consequences of changes in the lipid composition of erythrocytes in diseases that are associated with disorders of lipid metabolism.
Three‐dimensional time‐of‐flight MR angiography with variable TE (VARIETE) for fat signal reduction
Authors: Lin Weili , Haacke E. Mark , Tkach Jean A.
Published: March 2007

Uniform fat saturation over a large region of interest remains a problem in time‐of‐flight (TOF) magnetic resonance angiography applications. We demonstrate that a variable echo time with an opposed phase value at low spatial slice select frequencies can effectively reduce most of the fat signal in an otherwise standard three‐dimensional TOF acquisition. We evaluated this method at 1.5 T using a short TE = 5.3 ms and a long TE = 6.75 ms for different values of the slice encoding gradient (i.e., different k2 values). Shorter echo time (TE = 5.3 msec) was used at higher spatial slice select frequencies, but all echoes have the same gradient structures. By keeping the number of slice encoding steps with longer echoes to a minimum, field inhomogeneity effects on flow compensation remained small. A magnetization transfer saturation pulse was used to suppress signal of brain parenchyma. Overall, highly uniform and selective fat signal reduction was obtained while maintaining superior flow compensation in all volunteer studies.
Incorporation of Lactate Measurement in Multi‐Spin‐Echo Proton Spectroscopic Imaging
Authors: Duyn Jeff H. , Frank Joseph A. , Moonen Chrit T. W.
Published: March 2007

An improved multi‐slice, multi‐spin‐echo proton spectro‐scopic imaging method for human brain is presented. The technique allows the reconstruction of lactate images, along with choline plus creatine, N‐acetylaspartate, and lipid images from one single data set processed in three separate ways. The discrimination between resonances of lipid protons and lactate methyl protons is based on homonuclear spin‐spin coupling. The reliability of the separation of the lipid and lactate contribution depends on the T2 of the lipid resonances. Measurements were performed on a standard 1.5 Tesla clinical scanner on healthy volunteers and a patient with high grade CNS lymphoma, demonstrating the ability to obtain high quality metabolite maps within 11 min.
NMR Measurement of Perfusion Using Arterial Spin Labeling Without Saturation of Macromolecular Spins
Authors: Zhang Weiguo , Silva Afonso C. , Williams Donald S. , Koretsky Alan P.
Published: March 2007

When measuring perfusion by arterial spin labeling, saturation of tissue macromolecular spins during arterial spin labeling greatly decreases tissue water magnetization, reducing the sensitivity of the technique. In this work, a theory has been developed for perfusion measurement by arterial spin labeling without saturation of macromolecular spins. A two‐coil system was used to achieve arterial spin labeling without saturation of brain tissue macromolecular spins for NMR measurement of rat cerebral perfusion. The effects of crossrelaxation on the measurement of perfusion have been studied in the absence of macromolecular spin saturation, and it is demonstrated that at 4.7 Tesla, perfusion is underestimated by approximately 17% when the effect of cross‐relaxation is neglected in the calculation of perfusion. However, assuming water to be a freely diffusable tracer, the effect of cross‐relaxation is predicted to be flow independent, and it can, thus, be accounted for in the calculation of perfusion. The theory and experiments are presented to estimate tissue perfusion, magnetization transfer rate constants, and spin‐lattice relaxation times of water and macromolecular spins in rat brain.
NOE Enhancements and T1 Relaxation Times of Phosphorylated Metabolites in Human Calf Muscle at 1.5 Tesla
Authors: Brown Truman R. , Stoyanova Radka , Greenberg Tamela , Srinivasan Ravi , Murphy‐Boesch Joseph
Published: March 2007

Nuclear Overhauser effect (NOE) enhancements and relaxation times of 31P metabolites in human calf were measured in 12 volunteers (4 men and 8 women) at 1.5 T using a dual tuned four‐ring birdcage. The NOE enhancements of inorganic phosphate (P1), phosphocreatine (PCr), γ‐, α‐, and β‐nucleoside triphosphate (NTP) from 19 measurements were 0.51 ± 0.10, 0.64 ± 0.03, 0.53 ± 0.03, 0.56 ± 0.08, and 0.47 ± 0.05, respectively. The relaxation times were independent of proton irradiation and from 23 measurements were 3.49 ± 0.35, 4.97 ± 0.58, 4.07 ± 0.36, 2.90 ± 0.25, and 3.61 ± 0.25 s for P1, PCr, γ‐, α‐, and β‐NTP, respectively. No significant differences between gender and age were observed for either NOE enhancements or relaxation times. Also, among nine volunteers, we observed no significant differences in T1 between the coupled and decoupled cases.
BOLD Based Functional MRI at 4 Tesla Includes a Capillary Bed Contribution: Echo‐Planar Imaging Correlates with Previous Optical Imaging Using Intrinsic Signals
Authors: Menon Ravi S. , Ogawa Seiji , Hu Xiaoping , Strupp John P. , Anderson Peter , Uǧurbil Kǎmil
Published: March 2007

We show that the EPI time course in functional MR imaging at 4 Tesla displays a multiphasic response in response to photic stimulation. Focal areas of gray matter display an initial negative change in signal intensity that reaches a maximum of 1 % about 2 s after the onset of photic stimulation. This component then changes sign, reaching a positive maximum about 5 s after the onset of the stimulus. Other areas, including those where draining veins are visible, show only a positive signal change, reaching a maximum of about 6% after the onset of the visual stimulus. These time constants are in very good agreement with published data obtained with intrinsic optical mapping techniques, where a deoxygenation phase has been shown to occur in functionally specific cortical columns, followed by an increase in blood volume which is more distributed in nature. Thus, we believe there is strong evidence that a sensitivity to capillary oxygenation state is present in high S/N functional MR images obtained with EPI at 4 T.
Respiratory Blur in 3D Coronary MR Imaging
Authors: Wang Yi , Grist Thomas M. , Korosec Frank R. , Christy Paul S. , Alley Marcus T. , Polzin Jason A. , Mistretta Charles A.
Published: March 2007

3D MR imaging of coronary arteries has the potential to provide both high resolution and high signal‐to‐noise ratio, but it is very susceptible to respiratory artifacts, especially respiratory blurring. Resolution loss caused by respiratory blurring in 3D coronary imaging is analyzed theoretically and verified experimentally. Under normal respiration, the width for any Gaussian point spread function is increased to a new value that is at least several millimeters (about 3–4 mm). In vivo studies were performed to compare respiratory pseudo‐gated 3D acquisition with breath‐hold 2D acquisition. On average, the overall quality of a pseudo‐gated 3D image is worse than that of the corresponding breath‐hold 2D image (P = 0.005). In most cases, respiratory blur caused coronary arteries in pseudo‐gated 3D data to have lower resolution than in breathhold 2D data.
Susceptibility Artifact Reduction in Fat Suppression
Authors: Mao Jintong , Gao Jia‐Hong , Yan Hong , Ray Ballinger J.
Published: March 2007

Strong fat signal in regions where a large susceptibility difference exists, for instance at the interface between air and tissue near the maxillary sinus, may not be eliminated by currently available fat suppression techniques without sacrificing the overall quality of the images. In this article, we show that this fat signal, which appears as a susceptibility artifact, can be significantly reduced by using an optimized presaturation pulse with sharp edges and a broad bandwidth, while causing minimal disturbance of the water signal. Several optimized presaturation pulses can be reproduced by the Fourier coefficients provided in the Appendix.