bluuebunny/crossref_metadata_2025 huggingface dataset:
Susceptibility changes following bolus injections
Authors: Albert Mitchell S. , Haung Wei , Lee Jing‐Huei , Patlak Clifford S. , Springer Charles S.
Published: March 2007

The general mechanism of bulk magnetic susceptibility (BMS) induced MRI contrast following a bolus injection is elaborated. Combining radiolabeled tracer data for the first pass of a bolus injection through the human brain with the application of Wiedemann's law allows us to calculate the lower limit for the time course of the vascular BMS following the injection of any contrast agent. Superparamagnetic Iron oxide particles produce a much larger effect than any mononuclear Ln(III) che‐late. We also calculate the BMS changes occurring after a dilution bolus injection (of isosmolal physiological saline) subsequent to a prior slow infusion of an intravascular contrast agent. This technique bears some resemblance to the increasingly important approach that exploits changes in only the level of blood oxygenation. The calculation indicates that contrast changes after the dilution bolus injection are smaller than those following Ln(III) agent injections but larger than those due to changes in blood oxygenation and suggests a way to possibly enhance the latter. We present an In vivo study demonstrating the dilution bolus injection technique in the mouse brain, and that features its rapid repeatability. Extrapolation of these results to the human, however, indicates that the saline volumes required for venous injections, except possibly for cardiac studies, would be prohibitively large. Smaller, catheter‐delivered arterial bolus injections are feasible. We also suggest a method for using an agent bolus injection to measure the parenchymal BMS, and thus the iron content, of pathologically iron‐loaded tissue.
Quantitative interpretation of magnetization transfer
Authors: Henkelman R. Mark , Huang Xuemei , Xiang Qing‐San , Stanisz G. J. , Swanson Scott D. , Bronskill Michael J.
Published: March 2007

Magnetization transfer contrast (MTC) experiments using off‐resonance irradiation have been performed with an agar gel model by systematically varying offset frequency, amplitude of the RF irradiation and gel concentration. The experimental results are shown to be quantitatively modelled by a two‐pool system consisting of a liquid pool with a Lorentzian line shape and a small semisolid pool with a Gaussian lineshape. The fitted model yields physically realistic fundamental parameters with a T2 of the semisolid pool of 13 μs. Further analysis shows that the off‐resonance irradiation MTC experiment has significant limitations in its ability to saturate the semisolid pool without directly affecting the liquid component.
An asymmetric slice profile: Spatial alteration of flow signal response in 3d time‐of‐flight NMR angiography
Authors: Matsuda Tetsuya , Morii Isao , Kohno Fujimasa , Asato Reinin , Ikezaki Yoshikazu , Yoshitome Eiji , Sasayama Shigetake
Published: March 2007

We introduce an asymmetric slice profile technique, which alters the spatial response of the flow signal in 3D time‐of‐flight NMR angiography. By gradually increasing the flip angle from the inflow to the outflow portions of the slab, the inflow refreshment effect is distributed over a wide slab thickness. The asymmetric slice profile is simply produced by using a Gaussian RF excitation with an overlapping presaturation. The spatial distribution of steady flow signal in a phantom study demonstrated an essential agreement with a numerical simulation. 3D time‐of‐flight NMR angiography of volunteers' heads using this technique provided a smooth vascular depiction over a wide slab thickness.
Blood flow measurement using variable velocity encoding in the RR interval
Authors: Buonocore Michael H.
Published: March 2007

Velocity‐encoded phase imaging using asynchronous gating requires input of a velocity encoding value to set the velocity sensitivity of the pulse sequence. The raw data interpolation and reconstruction scheme that the pulse sequence uses forces the encoding value to be constant throughout the RR interval. The sequence and the raw data interpolation scheme were modified to allow two velocity encodings during the RR interval. Two‐hundred cm/s encoding was used in systole, and 30 cm/s in diastole. Changing the encoding in diastole significantly improved the accuracy and precision of ascending aorta flow measurements.
Nonmagnetic hyperbaric chamber for in vivo NMR spectroscopy studies of small animals
Authors: Litt Lawrence , Xu Yan , Cohen Yoram , James Thomas L.
Published: March 2007

A description is given of the design, construction, and initial use of a polycarbonate resin hyperbaric chamber for in vivo NMR spectroscopy studies of anesthetized, ventilated rats in a horizontal bore 4.7 Tesla magnet. The chamber and its associated equipment, initially used for hyperbaric studies of rats in states of extreme hypercapnia, are also well suited for conventional hyperbaric studies, such as those related to hyperbaric oxygen therapy, oxygen toxicity, and diving. Basic technical challenges that required innovations involved: a) preservation of magnetic field homogeneity; b) avoidance of a metallic chamber body that would overload gradient and RF coils; c) physiological monitoring; and, d) remote control and stabilization of electromagnetic and physiologic factors (especially ventilatory stability) during pressure changes. A small paramagnetic bulk magnetic susceptibility shift from chamber‐associated hyperbaric oxygen was observed when chamber oxygen tensions were only one atmosphere. High‐quality NMR imaging and spectroscopy were demonstrated during hyperbaric conditions.
Spatially localized 31P NMR measurements of longitudinal relaxation rates in the canine myocardium
Authors: Rath D. P. , Abduljalil A. M. , Robitaille P.‐M. L.
Published: March 2007

FLAX‐ISIS spatial localization was combined with inversion recovery to enable the measurement of spatially localized T1 values. This approach was applied to the transmural determination of creatine phosphate longitudinal relaxation times in the canine myocardium. By examining five voxels spanning the left myocardial wall, we observed that transmural T1 values for creatine phosphate ranged from 3.61 = 0.20 in the endocardium to 4.00 ± 0.20 in the epicardium at 4.7 Tesla. As such, the canine myocardium exhibits no transmural variation in the T1 values of creatine phosphate. This simple approach can be extended to enable the in vivo measurement of transmural enzymatic rates.
Stability and nonreactivity of ergothioneine in human erythrocytes studied by 1H NMR
Authors: Rae Caroline D. , Sweeney Kimberley J. E. , Kuchel Philip W.
Published: March 2007

The N(CH3)3 resonance of ergothioneine in 1H spin‐echo Fourier transform (SEFT) NMR spectra of red blood cells is usually a large singlet and it has been common practice to use this apparently unchanging resonance as an intensity reference. Recently, Reglinski et al. (Magn. Reson. Med. 6, 217–223 (1988)) have questioned this practice, reporting changes seen in the resonance in response to oxidative stress induced by arsenicals. We propose that the changes in the ergothioneine resonance that were reported are artifacts due to alterations in osmolality and magnetic susceptibility induced by the addition of nonisotonic solutions to red blood cell suspensions. These factors change the specific intensity of the intracellular resonances of all compounds. Ergothioneine was observed not to take part in any chemical reactions with arsenicals in free solution or in intact erythrocytes, and we conclude that ergothioneine may still be used as an internal intensity reference in 1H SEFT NMR spectra, bearing in mind the above physical factors.
In vivo degradation of silicones
Authors: Garrido Leoncio , Pfleiderer Bettina , Papisov Mikhail , Ackerman Jerome L.
Published: March 2007

29Si nuclear magnetic resonance (NMR) spectroscopy is applied to study the degradation of polysiloxanes (silicones) in vivo. Our results with animal models show that silicone migrates from the implant to the liver (29Si resonance at −20 ppm) and new silicon containing compounds form after the silicones are introduced into the rats. The new 29Si resonances in the chemical shift range of −40 to −85 ppm are related to hydrolyzed silicone, those at −90 to −115 ppm are indicative of the presence of silica (SiO2), and the peaks observed at −120 to −150 are related to high coordinated silicon complexes. These resonances are not present in the 29Si spectra of the silicones before implantation. Our findings demonstrate that silicones are not metabolically inert.
Transmural saturation transfer analysis of the creatine kinase system in the mammalian heart
Authors: Obitaille P.‐M. L. , Abduljalil A. , Rath D. , Zhang H. , Hamlin R. L.
Published: March 2007

31P NMR spatial localization and saturation transfer techniques were combined to enable the transmural measurement of the forward creatine kinase (CK) rate (ATP:creatine N‐phos‐photransferase, EC 2.7.3.2.) in the in vivo canine myocardium. Five epicardial towards endocardial regions of the left ventricle (LV) were simultaneously examined using spatially localized voxels. Although intralefl ventricular CP/ATP ratios were constant, the pseudo first order rate constant (K′) and the forward creatine kinase rate (Rt) displayed a 61% variation across the LV wall. Because CK levels and calculated [ADP], [CP]and pH are transmurally invariant in the normal left ventricle, the observed changes in the Rt could not be explained by changes in the absolute levels of these substrates and of creatine kinase. In addition, because myocardial oxygen consumption rates are known to be higher in the endocardium, these results imply that forward creatine kinase rates are not directly related to oxidative phosphorylation rates.
Responses of myocardial high energy phosphates and wall thickening to prolonged regional hypoperfusion induced by subtotal coronary stenosis
Authors: Zhang J. , Path G. , Chepuri V. , Xu Y. , Yoshiyama M. , Bache R. J. , From A. H. L. , Uǧurbil K.
Published: March 2007

The response of the myocardium to prolonged or chronic ischemia may differ from the well documented changes that occur acutely subsequent to the onset of hypoperfusion. Therefore, we have examined in an instrumented canine model and using spatially localized spectroscopy to achieve transmural differentiation, the myocardial HEP and Pi levels as well as wall thickening in situ during prolonged ischemia induced by sustained coronary artery stenosis. The results demonstrate that subtotal coronary artery occlusion causes immediate and transmurally inhomogeneous decreases in the myocardial HEP content and increase in the Pi /CP ratio; however, during prolonged mild hypoperfusion, metabolic changes occur which lead to statistically significant recovery of CP (but not ATP) and disappearance of Pi despite the persistence of reduced blood flow and oxygen supply. Upon release of the occlusion, the previously ischemic muscle recovered blood flow, and some (but not all) of its preischemic contractile function without parallel changes in the HEP levels. It is concluded that normal HEP and Pi levels cannot be equated with either the absence of underperfusion or insensitivity of NMR spectroscopy to ischemia. Rather, it is imperative that both functional and spectroscopic measurements are performed simultaneously to distinguish between ischemic myocardium which is adapted versus unadapted to the hypoperfusion.
Characterization of macromolecule resonances in the 1H NMR spectrum of rat brain
Authors: Behar Kevin L. , Ogino Takashi
Published: March 2007

The 1H NMR spectrum of the macromolecule fraction of rat brain cytosol was investigated following centrifugation and dialysis to remove low molecular weight metabolites and peptides (<3500 daltons). At least seven well resolved resonances were detected between 0.9 and 3.0 ppm in the 1H NMR spectrum of rat brain cytosol after dialysis, several of which cannot be observed in vivo due to overlap with N‐acetylaspartate, glutamate, glutamine, creatine, and yaminobutyric acid. Several cross‐peaks detected in 2D COSY spectra of the cytosolic macromolecule fraction coincided with those measured in a previous study of rat brain tissue in vitro and in situ (K. L. Behar, T. Ogino, Magn. Reson. Med. 17, 285 (1991)). Treatment of the cytosolic macromolecule fraction with a nonspecific protease permitted partial assignments of resonances in the 1H NMR spectrum to specific amino acids. Fractionation of the dialyzed cytosol of rat brain by gel filtration yielded qualitatively similar 1H NMR spectra for elution volumes corresponding to molecular masses from 12.5 kDa to over 100 kDa. The results indicate that many of the background nonmetabolite resonances observed in the 1H NMR spectrum of normal brain tissue arise from cytosolic proteins.
Quantification of tissue plasma volume in the rat by contrast‐enhanced magnetic resonance imaging
Authors: Kuwatsuru Ryohei , Shames David M. , Mühler Andreas , Mintorovitch Jan , Vexler Vladimir , Mann Jeffry S. , Cohn Frederic , Price David , Huberty John , Brasch Robert C.
Published: March 2007

Magnetic resonance imaging enhanced with a macromolecular contrast medium (MMCM), albumin‐Gd‐DTPA, was used to estimate the plasma volume in vivo in the myocardium, lung, liver, and skeletal muscle of 10 normal rats. The plasma volumes of the same tissues in a parallel group of six rats were estimated in vitro by a conventional radioisotopic technique (111In‐transferrin). Plasma volumes of myocardium, lung, liver, and skeletal muscle estimated by the MR technique (μl plas. ia cc‐1 of tissue) were 101,109,163, and 11.0, respectively, while plasma volumes measured by the In‐transferrin radioisotope technique (mg plasma g‐1 of tissue) were 78.6, 215,143, and 11‐2, respectively. Assuming a ratio of densities of aerated lung to blood of 0.45 and of other tissues to blood of 1.0, correlation between the methods was excellent (R2 = 0.99) indicating that MR imaging enhanced with MMCM permits reliable in vivo estimation of tissue plasma volume in the rat.
Processing strategies for time‐course data sets in functional mri of the human brain
Authors: Bandettini Peter A. , Jesmanowicz A. , Wong Eric C. , Hyde James S.
Published: March 2007

Image processing strategies for functional magnetic resonance imaging (FMRI) data sets acquired using a gradient‐recalled echo‐planar imaging sequence are considered. The analysis is carried out using the mathematics of vector spaces. Data sets consisting of N sequential images of the same slice of brain tissue are analyzed in the time‐domain and also, after Fourier transformation, in the frequency domain. A technique for thresholding is introduced that uses the shape of the response in a pixel compared with the shape of a reference waveform as the decision criterion. A method is presented to eliminate drifts in data that arise from subject movement. The methods are applied to experimental FMRI data from the motor—cortex and compared with more conventional image—subtraction methods. Several finger motion paradigms are considered in the context of the various image processing strategies. The most effective method for image processing involves thresholding by shape as characterized by the correlation coefficient of the data with respect to a reference waveform followed by formation of a cross‐correlation image. Emphasis is placed not only on image formation, but also on the use of signal processing techniques to characterize the temporal response of the brain to the paradigm.
MRI and MRS studies on the time course of rat brain lesions and the effect of drug treatment: Volume quantification and characterization of tissue heterogeneity by parameter selection
Authors: Pschorn Uwe , Körperich Hermann , Heymans Lothar , Subramanian Sankaran , Kuhn Winfried
Published: March 2007

Magnetic resonance imaging has been used to follow the time course of lesions induced in the rat brain as an animal model for characterization of the volume of the lesion. The dispersion in spin‐spin relaxation has been used to characterize the nature of the brain lesion. Parameter selective estimation of T2 quantitative determination of the lesion sire and volume selective in vivo proton spectroscopy have been employed for the purpose. The work has been carried out on rats which were subject to lesioning by ibotenic acid as a model for excitotoxicity and also on rats which doses of ibotenic acid and subsequent doses of the NMDA antagonist drug MK 801 (dizocilpine). The time course of the progress of the lesions in untreated animals and the effect of neuroprotection by MK 801 was continuously monitored in all test animals. Further, a relatively new inhalation anesthetic agent, isoflurane, has been employed. A more logical and semiquantitative T2 bandwidth demarkation useful in distinguishing different degrees of lesioning from the onset and up to the ‘edema’ stage through penumbra (mild lesion), medium degree lesion and severe lesion has been proposed.
Spin‐lattice relaxation time measurement by means of a TurboFLASH technique
Authors: Blüml Stefan , Schad Lothar R. , Stepanow Boris , Lorenz Walter J.
Published: March 2007

Rapid measurements of in vivo proton spin‐lattice relaxation times (T1) in human tissues were performed by magnetic resonance imaging in a 1.5 T whole‐body super‐conducting MR scanner. The measurements employ serial TurboFLASH imaging (Snapshot‐FLASH) with scan times for a single experiment below 4 s. Using centric phase encoding order, an appropriate fitling of the T1‐parameter from images with minimum motion artifacts is possible. Comparative T1‐determination with a multipoint inversion recovery and spin‐echo technique was performed on phantoms containing Gd‐DTPA solutions with different T1‐values. We found a maximum deviation of 3.3% for T1 < 1100 ms and of 12.1% for 1100 ms < T1 < 1700 ms from the results obtained by the IR technique. In vivo measurements of T1‐relaxation times were performed in white and grey matter, cerebrospinal fluid, kidney, liver, spleen, muscle, and bone marrow, and yielded values that are in good agreement with reported data.
Apparent diffusion coefficient mapping of experimental focal cerebral ischemia using diffusion‐weighted echo‐planar imaging
Authors: Dardzinski Bernard J. , Sotak Christopher H. , Fisher Marc , Hasegawa Yasuhiro , Li Lirnin , Minematsu Kazuo
Published: March 2007

Diffusion‐weighted, echo‐planar imaging (EPI) was used to map regional changes In the apparent diffusion coefficient (ADC) during experimental focal ischemia in the rat brain following permanent middle cerebral arterial occlusion (MCAO). Sixteen 64 × 64 diffusion‐weighted EPIs were acquired in 32 s with successively increasing amplitudes of the diffusion‐sensitive gradient pulses. A linear least‐squares regression algorithm was used to fit 15 of the 16 two‐dimensional matrices, on a pixel‐by‐pixel basis, to solve for the slope from which the ADC value was calculated. The correlation coefficient of the fit, R2 was used to filter the final ADC maps, and the ADCs were then scaled appropriately to be displayed in a 256 gray level format. Ranges (bins) of 0.05 × 10−3 mm2/s were then grouped and color coded to qualify and quantify the evolution of ischemia in the MCA territory. The percentage of area in the ischemic and contralateral hemispheres in seven ADC bins were calculated at 30, 60, and 120 min after MCAO for 10 animals and demonstrated a significant increase in ADC bins below 0.45 × 10−3 mm2/s and a decrease in bins above 0.50 × 10−3 mm2/s over the. The postmortem infarct area, as measured by TTC staining, was highly correlated with the portion of the ischemic hemisphere falling below ADC values of 0.55 × 10−3 mm2/s at 2 h after stroke onset. These studies suggest that focally ischemic brain tissue can be quantitatively subdivided according to ADC values and that ADC values below 0.55 × 10−3 mm2/s 2 h following ischemia highly predict infarction in a rat permanent occlusion stroke model.
Magnetic field distribution in models of trabecular bone
Authors: Ford J. Chetley , Wehrli Felix W. , Chung Hsiao‐Wen
Published: March 2007

A magnetostatic model consisting of a tetragonal lattice of struts of diamagnetic material, mimicking vertebral trabecular bone, was developed. The model allows estimation of the magnetic field histogram within the lattice's unit cell as a function of geometric parameters. The field was computed analytically from the induced magnetic surface charge density on the faces of the struts. The contribution from the induced magnetic field to the effective transverse relaxation rate, R2 was obtained as the mean decay rate of the Fourier transformed histograms, for both fixed and randomly oriented lattices. The model predicts the field distribution to increase with both strut thickness and density, paralleling material density. Finally, significant changes in R2′ are predicted at constant material density, in that the field distribution widens with simultaneously increasing strut number density and decreasing strut thickness.
Identification of vascular structures as a major source of signal contrast in high resolution 2D and 3D functional activation imaging of the motor cortex at l.5T preliminary results
Authors: Lai S. , Hopkins A. L. , Haacke E. M. , Li D. , Wasserman B. A. , Buckley P. , Friedman L. , Meltzer H. , Hedera P. , Friedland R.
Published: March 2007

We have measured the T2* signal response associated with cortical activation due to finger motion at 1.5 Tesla. Both thin slice 2D and 3D images show signal intensity changes which vary from 2% to 32% depending on volunteer, echo time, slice thickness, and in‐plane resolution. The largest signal change occurred for the thinnest slices and highest resolution (2 mm3). This is consistent with reducing partial volume effects and a simple difference in phase between the intravascular signal and surrounding parenchyma. No inflow enhancement was seen on the 2D or 3D scans, confirming the nature of the signal difference for this approach was due to local field in‐homogeneity effects. Using 3D imaging, multiple effects can be seen simultaneously. With a 3D MRA method, it was possible to locate the vessel that was the source of the T2* behavior; it was in each case a vein on the surface of the cortical parenchyma.
Analysis of saturated phosphatidylcholine in amniotic fluid by 31P NMR
Authors: Pearce J. M. , Krone J. T. , Pappas A. A. , Komoroski R. A.
Published: March 2007

A technique using solubilization with sodium cholate to resolve 31P NMR resonances of phospholipid molecular species was applied to amniotic fluid samples from 16 subjects. Gestational ages from 25 to 40 weeks were represented, and two subjects were sampled sequentially. Fitting of the partially resolved 31P NMR signal of phosphatidylcholine (PC) generated an estimate of percent disaturated acyl PC (%dsPC) which correlated more highly with gestational age than did several other potential indices of fetal lung maturation, such as the ratio of PC to inorganic phosphate from the solubilized spectra, or PC to sphingomyelin from extract spectra. In a few cases, enzyme‐catalyzed PC hydrolysis limited the precision, but did not appear to affect the accuracy, of the %dsPC estimates. Resolution of palmitoyl and oleoyl lyso‐PC species was observed for both the 1–and 2‐acyl isomers. Upfield shifts due to the presence of cis double bonds in the lone acyl chain of the lyso‐PCs were analogous to those observed for the diacyl PCs.
Differentiation of chronic lesions after stroke in stroke‐prone spontaneously hypertensive rats using diffusion weighted MRI
Authors: Takahashi M. , Fritz‐Zieroth B. , Chikugo T. , Ogawa H.
Published: March 2007

Apparent diffusion coefficients (ADCs) of tissue water were determined in chronic brain lesions of a rat stroke model, stroke‐prone spontaneously hypertensive rats and compared with histology. ADCs increased in the order control < edema < gliosis < cyst. The differences between individual groups were statistically significant. The increase in ADC is thought to mainly reflect a relative increase in the extracellular space in brain tissue. ADC values may be a clinically useful parameter for tissue characterization.
In Vivo proton spectroscopy and spectroscopic imaging of {1‐13C}‐g1ucose and its metabolic products
Authors: Van Zijl Peter C. M. , Scott Chesnick A. , Despres D. , Moonen Chrit T. W. , Rhiz‐Cabello J. , Van Gelderen P.
Published: March 2007

Metaibolism of {1−13C}‐glucose was studied in situ in cat brain usinig gradient‐enhanced proton‐detected heteronuclear spectroscopy. Proton detection of {1−13C}‐glucose, {3−13C}−lactaite, 4−{13C}‐glutamine, 4−{13C}‐glutamate and the combined signals 2−{13C}‐glutamate/glutamine and 3−(13C}‐glutamate/glutamine was achieved, despite the fact that some of the associated proton resonances are close to the water signal. Two‐dimensional {1H‐13C}‐spectra demonstrate the possibility of in situ spectral assignment with 1H sensitivity and 13C resolution. Spectroscopic images of glucose and its metabolic products were also acquired, showing the possibility to study spatial dependence of metabolism.
Intracellular labeling of T‐cells with superparamagnetic contrast agents
Authors: Yeh Tzu‐Chen , Zhang Weiguo , Ildstad Suzanne T. , Ho Chien
Published: March 2007

Isolated rat T‐cells have been labeled intracellularly, using endocytosis uptake of two superparamagnetic contrast agents, AquaMagl00 and BMS180549, which are both iron‐oxide particles coated with dextran. No deterioration of cell proliferation response to mitogen stimulation was observed alter labeling with either superparamagnetic contrast agent. AquaMag100 particles show aggregation and co‐precipitation in culture media for T‐cells. BMS180549 particles not only produce no observable aggregation or co‐precipitation, but also have a higher efficiency for labeling T‐cells than AquaPlag100. The efficiency of cell labeling was determined by measuring the decrease in the spin‐spin relaxation time of the water proton in cell samples containing 1 × 107 labeled T‐cells/milliliter of 2% w/w gelatin. After optimization of the labeling procedures, a shortening of the spin‐spin relaxation time by a factor of approximately 7 to 10 has been demonstrated. Under the present experimental conditions, the up‐regulation of low density lipoprotein receptor does not increase the labeling efficiency by endocytosis. Our results suggest that intracellular labeling of specific cell types can be achieved with good efficiency and the labeled cells can be detected by magnetic resonance imaging in rat testicles in vivo.
Experimental design of 31P MRS assessment of human forearm muscle function: Restrictions imposed by functional anatomy
Authors: Jeneson J. A. L. , van Dobbenburgh J. O. , van Echteld C. J. A. , Lekkerkerk C. , Janssen W. J. M. , Dorland L. , Berger R. , Brown T. R.
Published: March 2007

The restrictions imposed by the functional anatomy of the finger flexor muscles on the experimental design of 31P MRS assessment of human forearm muscle function employing surface coil localization and voluntary exercise were investigated. It was found that 31P MRS metabolic data of finger flexor muscle should be correlated with mechanical data of combined flexion of only the ring and little fingers, rather than all four fingers as has been commonly the case in previously reported studies.
Fast proton spectroscopic imaging using the sliced k‐space method
Authors: Norris David G. , Dreher Wolfgang
Published: March 2007

The use of one‐shot imaging methods for proton spectroscolpic imaging (1H‐SI) is examined. In particular the acquisition of Kx × Ky × Nt data points by means of Nt excitations, each acquiring a Kx, × Ky, k‐space slice, is advocated. A number of strategies for realising this experiment, and combining it with water suppression and volume‐selection are proposed. The practical implementation at 4.7 T for 1H‐Sl of the rat brain is described. Experimental results from a 32 × 32 spatial matrix with Nt = 64 are presented. Spectra obtained from volumes as low as 3.5 μl and within measuring times of as little as 3.8 min are shown. In these choline, creatine/phosphocreatine and N‐acetylaspartate are all clearly visible.
Simultaneous measurement of both lipid and lactate in isolated rat hearts by 1H NMR spectroscopy
Authors: Stewart Laura C. , Saunders John K. , Deslauriers Roxanne , Bourgeois Dominique , Nédélec Jean‐François J.
Published: March 2007

Myocardial lipid and lactate levels are sensitive indicators of biochemical status: lipid levels have been shown to increase in response to high fat diets, disease or metabolic stress and elevated lactate levels are indicative of reduced oxygen supply. Selective measurement of lactate or lipid levels by 1H NMR is not straightforward since both the lactate methyl group and lipid methylene groups resonate at 1.3 ppm. We have overcome this difficulty by employing spectral editing techniques to observe both lipid methylene and lactate methyl resonances, and have measured lipid and lactate levels in perfused rat hearts during control perfusion and in response to metabolic stress. Lactate increased during ischemia and decreased during reperfusion, and the ischemia‐induced increase is inhibited by iodoacetate, as expected. In contrast, lipid levels increased during ischemia and remained elevated during reperfusion. Hearts from rats fed high fat diet show elevated lipid levels during control perfusion. Data obtained by 1H NMR are consistent with biochemical data, validating the technique.
31P transverse relaxation times of ATP in human brain in vivo
Authors: Jung Wulf‐Ingo , Widmaier Stefan , Bunse Michael , Seeger Uwe , Straubinger Klaus , Schick Fritz , Küper Klaus , Dietze Günther , Lutz Otto
Published: March 2007

31P MRS examinations of the brain of 10 healthy volunteers were performed to determine T2 of the coupled ATP signals by use of the localized 90° ‐ TE/2 ‐ 2662 ‐ TE/2 ‐ acq frequency selective spin echo sequence for elimination of phase and intensity distortions. The T2 relaxation times obtained are much longer than usually assumed: γ‐ATP: 89 ± 9 ms; α‐ATP: 84 ± 6 ms; β‐ATP: 62 ± 3 ms.
A. functional MRI technique combining principles of echo‐shifting with a train of observations (PRESTO)
Authors: Liu Guoying , Sobering Geoffrey , Duyn Jeff , Moonen Chrit T. W.
Published: March 2007

We present a fast MRI technique sensitized to microscopic susceptibility effects. The method combines elements of echo‐shifted gradient‐recalled MR imaging (TE > TR) with the acquisition of multiple k‐space lines within a single TR‐period. The sequence results in a much reduced imaging time as compared with conventional gradient‐echo MRI methods. The feasibility of the method is demonstrated for susceptibility bolus tracking in the cat brain using an imaging time of 153 ms. The relative cerebral blood volume maps created with this method are comparable with those obtained with conventional methods.
Localized brain proton NMR spectroscopy in young adult phenylketonuria patients
Authors: Johannik K. , van Hecke P. , François B. , Marchal G. , Smet M‐H. , Jaeken J. , Breysem L. , Wilms G. , Baert A. L.
Published: March 2007

Localized proton magnetic resonance spectroscopy with short echo time (TE = 20 ms) was used to investigate biochemical changes in the cerebral white matter of 20 young adult patients (median 19 years) with phenylketonuria (PKU). Results were compared with those of a group of 12 age‐matched healthy volunteers (median 25 years). Concentrations of Nacetyl‐aspartate (NAA) and choline (Cho) relative to creatine (Cr) were unchanged. However, concentrations of inositol (Ins) relative to creatine were found to be significantly lower (P < 0.001) in the PKU patients (0.30 ± 0.09 versus 0.57 ± 0.17). Individual inositol concentrations did not correlate with age, diet, serum phenylalanine (Phe) levels or extent of pathological regions in the T,‐weighted images. The lack of correlation with individual data suggests that the decreased inositol concentration could be related to a metabolic deficiency during fetal development. No signal from the phenyl ring protons of phenylalanine was detected in the PKU patients (phenylalanine serum concentration ⩽ 1.27 mM), which suggests that concentration of phenylalanine may be lower in brain than in serum.
In vivo EPR studies of the metabolic fate of nitrosobenzene in the mouse
Authors: Fujii Hirotada , Zhao Baolu , Koscielniak Janusz , Berliner Lawrence J.
Published: March 2007

We report the first demonstration of EPR spectroscopy to study free radical reactions in live mice and excised muscle tissue resulting from the metabolism of nitrosobenzene. A broad three‐the EPR spectrum (aN = 11.6 G) appeared in the buttocks region of a mouse place in an L‐band loop gap resonator after intramuscular or intraperitoneal injection of 0.2 among nitrosobenzene. The signal intensity reached a maximum at 20 to 30 min and remained constant well beyond 2 h. If muscle tissue was dosed with nitrosobenzene and excised within 5 min, a similar three‐line X‐band EPR spectrum was obtained which was preceded by the rapid growth and subsequent decay of an EPR spectrum identical with that of the phenylhydronitroxide radical, which was presumably generated from reactions between nitrosobenzene and reducing agents in the blood or tissue such as NADH or ascorbic acid. A model system containing nitrosobenzene and unsaturated fatty acids (olive oil or animal fat) yielded an identical three‐line spectrum resulting from radical adducts of nitrosobenzene across the double bond. Overall, these results suggest that the most probable mechanism in vivo was nitrosobenzene covalently adding (“binding”) to polyunsaturated fatty acid clusters in fat or membranes.
Radioactive microsphere validation of a volume localized continuous saturation perfusion measurement
Authors: Walsh Edward G. , Minematsu K. , Leppo J. , Moore S. C.
Published: March 2007

Detre et al. (Magn. Reson. Med. 23, 37–45 (1992)) and Zhang et al., (Magn. Reson. Med. 25, 362 (1992)) have recently demonstrated a technique for the measurement of regional cerebral blood flow (rCBF) based on the continuous saturation (or inversion) of the arterial blood supply to the brain in rats at 4.7 T. In the work reported here, we combined this technique with volume localized (PRESS) readouts to benefit from recording “perfusion” signals averaged over a larger volume, resulting in rapid acquisition of data with sufficient signal‐to‐noise ratio for application at 2.0 T. In 10 baseline flow measurements, the mean error between the NMR technique and the microsphere flow measurement was −1.5% with a standard deviation of 15.2%. For five measurements obtained with occlusion of the middle cerebral artery, the mean error was −32.4 ± 20.2%. Perfusion measurements from a single animal under hyper‐capnic conditions indicated that the NMR technique could underestimate rCBF at high flow rates. An error analysis of the NMR perfusion model is also presented, along with results for typical parameters encountered at 2.0 T.
India ink: A potential clinically applicable EPR oximetry probe
Authors: Swartz Harold M. , Liu Ke Jian , Goda Fuminori , Walczak Tadeusz
Published: March 2007

Using a material that already is in widespread use in humans, India ink, the first EPR measurements in a human have been made, using the India ink in a pre‐existing tattoo. The EPR spectra of India ink are very sensitive to the partial pressure of oxygen (PO2), thereby making it feasible to use this approach to measure pO2 in tissues in patients. This potentially provides a means to measure this parameter directly with a sensitivity, accuracy, and repeatability that have not been available previously, and thereby to be able to individualize and guide treatment of diseases such as cancer and peripheral vascular insufficiency.
13C NMR study of the generation of C2‐ and C3,‐deuterated lactic acid by tumoral pancreatic islet cells exposed to D‐[1‐13C]‐, D‐[2‐13C]‐ and D‐[6‐13C]‐Glucose in 2H2O
Authors: Willem Rudolph , Biesemans Monique , Kayser François , Malaise Willy J.
Published: March 2007

Tumoral pancreatic islet cells of the RIN5mF line were incubated for 120 min in media prepared in 2H2O and containing D‐[1‐13C]glucose, and D‐[2‐13C]glucose, and D‐[6‐13C]glucose. The generation of C2‐ and C3‐ deuterated lactic acid was assessed by 13C NMR. The interpretation of experimental results suggests that a) the efficiency of deuteration on the C1 of D‐fructose 6‐phosphate does not exceed about 47% and 4% in the phosphoglucoisomerase and phosphomannoisomerase reactions, respectively; b) approximately 38% of the molecules of D‐glyceraldehyde 3‐phosphate generated from D‐glucose escape deuteration in the sequence of reactions catalyzed by triose phosphate isomerase and aldolase; and c) about 41% of the molecules of pyruvate generated by glycolysis are immediately converted to lactate, the remaining 59% of pyruvate molecules undergoing first a single or double back‐and‐forth interconversion with L‐alanine. It is proposed that this methodological approach, based on high resolution 13C NMR spectroscopy, may provide novel information on the regulation of back‐and‐forth interconversion of glycolytic intermediates in intact cells as modulated, for instance, by enzyme‐to‐enzyme tunneling.
Variable‐averaging RARE
Authors: Noll Douglas C.
Published: March 2007

The RARE method and its variants have become popular, rapid‐imaging alternatives to conventional spin‐echo imaging, particularly for long repetition time proton density and T2‐weighted imaging. One variant is to generate both early and late echo images using the same pulse sequence, which has the added benefit of reduced edge artifacts and blurring. Described in this paper is variable‐averaging RARE (VARARE), a method by which independent amounts of averaging can be set for the early and late echo images generated by a single scanning sequence. Through the use of this method, the signal‐to‐noise ratio (SNR) of late echo images can be improved without unnecessarily increasing the number of averages for the early echo image, thus saving scanning time. Comparisons to various alternatives are made with respect to scanning time and image quality. Phantom measurements and in vivo images are given to demonstrate the effectiveness of VA‐RARE as an efficient method for improving SNR of late echo time images in RARE imaging.
Transient cell depolarization after permanent middle cerebral artery occlusion: An observation by diffusion‐weighted MRI and localized 1H‐MRS
Authors: Gyngell Michael L. , Back Tobias , Hoehn‐Berlage Mathias , Kohno Kanehisa , Hossmann Konstantin‐Alexander
Published: March 2007

Focal cerebral ischemia causes rapid intensity changes in diffusion‐weighted images (DWI) and elevated lactate as detected by localized proton spectroscopy (1H‐MRS). To investigate whether such changes can also be evoked by peri‐ischemic depolarizations, we combined DWI and 1H‐MRS measurements with DC potential recordings. About 40 min after occlusion of the middle cerebral artery in a rat, a negative DC deflection was observed indicating transient cell depolarization. Coincidentally with the depolarization a transient increase of the DWI signal intensity and a partially reversible increase of lactate occurred in the periphery of the ischemic territory. These results show that peri‐ischemic depolarization, known to contribute to the evolution of cerebral infarction, evokes disturbances that can be detected by DWI and 1H‐MRS.
13C isotopomer analyses in intact tissue using {13C}homonuclear decoupling
Authors: Sherry A. Dean , Zhao Piyu , Wiethoff Andrea , Malloy Craig R.
Published: March 2007

Entry of 13C‐enriched acetyl‐CoA into the citric acid cycle results in scrambling of 13C into the various carbon positions of all intermediate pools. The eventual result is that the 13C resonances of all detectable intermediates or molecules exchanging with those intermediates appear as multiplets due to nearest neighbor spin‐spin couplings. We have previously shown that an isotopomer analysis of the glutamate 13C multiplets provides a history of 13C flow through the cycle pools and that relative substrate utilization and relative anaplerotic flux can be quantitated (C.R. Malloy, A.D. Sherry, and F.M.H. Jeffrey, Am. J. Physiol. 259, H987–H995 (1990)). A major limitation of the method for in vivo applications is spectral resolution of multiline resonances required for a complete isotopomer analysis. We now show that (13C)homonuclear decoupling of the glutamate C3 resonance collapses nine‐line C4 and C2 resonances into three‐line multiplets. We demonstrate that these three line 13C multiplets are well resolved in isolated, perfused rat hearts and present steady‐state equations that allow an isotopomer analysis from data obtained in intact tissue. This advancement offers for the first time the possibility of extending 13C isotopomer methods to complex metabolic conditions in vivo.
Determinants of anisotropic water diffusion in nerves
Authors: Beaulieu Christian , Allen Peter S.
Published: March 2007

We report NMR diffusion measurements of water in three central nervous system models, namely the nonmyelinated olfactory, and the myelinated trigeminal and optic nerves of the spotted and long‐nosed garfish. A similar degree of anisotropy of the average diffusion coefficients (DNMR) is observed for all three freshly excised nerve types (DNMR parallel)/DNMR‐(perpendicular) is 3.6 ± 1.2, 3.2 ± 0.9, and 2.6 ± 0.4 for the olfactory, trigeminal, and optic nerves, respectively). The anisotropy of DNHR for the nonmyelinated olfactory nerve argues strongly that myelin is not a necessary determinant of diffusional anisotropy in ordered axonal systems (even though it may contribute when present). Garfish nerves treated with vinblastine, in order to depolymerize microtubules and inhibit fast axonal transport, also exhibit diffusional anisotropy {DNMR(parallel)/DNMR (perpendicular) is 2.6 ± 0.4,2.8 ± 0.8, and 2.2 ± 0.7 for the olfactory, trigeminal, and optic nerves, respectively) thus excluding a significant role for microtubules and fast axonal transport in that observed anisotropy.
MRI characterization of diffusion coefficients in a rat spinal cord injury model
Authors: Ford John C. , Hackney David B. , Alsop David C. , Jara Hernan , Joseph Peter M. , Hand Christopher M. , Black Perry
Published: March 2007

Apparent diffusion coefficients (ADC) were measured in a rat spinal cord weight‐drop injury model. After sacrifice, the spinal cords were fixed in situ and excised for MR imaging and ADC measurement. Diffusion is anisotropic in normal gray and white matter. There were significant decreases in ADCs measured along the longitudinal axis of the injured cord and increases in ADCs measured transverse to the cord. Injured segments demonstrated reductions in diffusion anisotropy in the white matter. Diffusion was completely isotropic at the epicenter of the weight‐drop injury. Significant decreases in longitudinal ADC and increases in transverse ADC were observed in portions of the cord which appeared normal on conventional spin‐echo and calculated T2 images. Thus ADC measurement may complement routine imaging for evaluation of spinal cord injury.
A one‐dimensional velocity technique for NMR measurement of aortic distensibility
Authors: Hardy Christopher J. , Bolster Bradley D. , McVeigh Elliot R. , Adams William J. , Zerhouni Elias A.
Published: March 2007

A technique is presented for rapidly and noninvasively determining aortic distensibility, by NMR measurement of wave velocity in the aorta. A two–dimensional NMR selective‐excitation pulse is used to repeatedly excite a cylinder of magnetization in the aorta, with magnetization read out along the cylinder axis each time. A toggled bipolar flow‐encoding pulse is applied prior to readout, to produce a one‐dimensional phase‐contrast flow image. Cardiac gating and data interleaving are employed to improve the effective time resolution to 2 ms. Wave velocities are determined from the slope of the leading edge of flow measured on the resulting M‐mode velocity image. The technique is sensitive over a range of distensibilities from 10−8 to 10−3 m s2/kg. The average value in the descending thoracic aorta in seven normal subjects was found to be 4.8 × 10−5 m s2/kg, with a significant inverse correlation with age.
Tag contrast in breath‐hold CINE cardiac MRI
Authors: Reeder Scott B. , McVeigh Elliot R.
Published: March 2007

Contrast between tagged and nontagged myocardium was investigated using rapid gradient echo segmented k‐space CINE MRI. The transient behavior of magnetization was measured in stationary and moving phantoms using gradient recalled acquisition in steady‐state GRASS and spoiled GRASS (SPGR) sequences with TR ≈ 7 ms and TE ≈ 2.5 ms. Bloch equation simulations were used to compute theoretical results. Understanding the transient behavior of magnetization is important because tags only persist in the myocardium during the nonequilibrium transition to steady state. The transition to steady state for both SPGR and GRASS is reproducible after one heartbeat, and including unprocessed data from the first heartbeat leads to image artifacts. In a moving phantom, simulations and experimental results showed that GRASS and SPGR are essentially equivalent. Tag‐tissue contrast in SPGR was very sensitive to imaging tip angle. The optimum tip angle for the scanning parameters used in this study was 11°.
Detection of liver fibrosis with magnetic cross‐relaxation
Authors: Aisen Alex M. , Doi Kei , Swanson Scott D.
Published: March 2007

The utility of MRI using magnetization transfer (MT) enhanced pulse sequences to diagnose hepatic cirrhosis in a rat model was investigated. Hepatic T1 was measured with and without MT off‐resonance RF pulses in 17 treated and six control rats. The livers were evaluated histologically, and the hydroxyproline content quantitatively measured. We did not find a statistically significant linear correlation between the MR relaxation times and the degree of tissue injury. However, the MR measurements performed with MT were superior to those without differentiating the treated and control groups. Specifically, the T1 times were 695 ±76 ms for the treated group, versus 748 ± 61 ms in the controls; P= 0.095. The T1sat times were also lower in the treated group, with statistical significance: 367 ± 51 ms versus 421 ± 38 ms, P = 0.016. Finally, the change in the relaxation rates (the inverse of the relaxation times) with and without saturation were 1.31 ± 0.22 s−1 (treated group) versus 1.05 ± 0.12 s−1 (controls), which differed significantly, P= 0.001.
The effects of linearly increasing flip angles on 3D inflow MR angiography
Authors: Nägele Thomas , Klose Uwe , Grodd Wolfgang , Petersen Dirk , Tintera Jaroslav
Published: March 2007

As recently demonstrated, spin saturation effects in 3D time‐of‐flight (TOF) MR angiography (MRA) can be reduced by using RF pulses with linearly increasing flip angles (ramp pulses) in the main direction of flow. We developed a model for calculating the signal distribution of proton flow within the excitation volume (slab) for different ramp slopes and compared the results with the measured distribution for the lower‐leg arteries. The ramp pulses were generated using the Fourier transformation of the desired excitation profiles. With a bandwidth of 6 kHz and a pulse length of 2.56 ms satisfactory ramps with variable slopes were generated and applied in a standard flow‐compensated 3D FISP sequence. The effects on the signal distribution in the resulting angiograms of the lower limbs revealed a considerable reduction of saturation losses in agreement with the calculations. Calculated optimal ramp slopes are provided for flow velocities ranging from 5 to 50 cm/s and excitation volumes ranging from 5 to 25 cm.