bluuebunny/crossref_metadata_2025_split huggingface dataset:
Contrast‐enhanced first pass myocardial perfusion imaging: Correlation between myocardial blood flow in dogs at rest and during hyperemia
Authors: Wilke N. , Simm C. , Zhang J. , Ellermann J. , Ya X. , Merkle H. , Path G. , Lüdemann H. , Bache R. J. , Uǧurbil K. 
Published: March 2007

AbstractThe sensitivity of contrast‐enhanced MR first pass perfusion imaging in detection and quantification of hypoperfused myocardium was evaluated using an instrumented, closed‐chest dog model where graded regional hypoperfusion was induced by applying predetermined levels of stenosis to the left anterior descending artery (LAD). All measurements were performed at rest and under stress induced by dipyridamole (DIP). Myocardial perfusion was assessed both with MR and radiolabeled microspheres injected immediately before the administration of the MR contrast agent. Ultrafast MR imaging was performed using a Turbo FLASH sequence with a 180° inversion prepulse. A Gd‐DTPA bolus was injected into the left atrium and T1‐weighted images were acquired with every heart beat. Signal intensity measured from the images in regions of the LAD and left circumflex (LCx) perfusion beds was plotted against time to generate signal intensity versus time curves (SI time curve). Various flow indices were derived according to the indicator dilution theory, and compared with and without volume correction due to vasodilation to the myocardial blood flow (MBF) calculated from radiolabeled microspheres. Correlation of the MR and MBF data demonstrated that different transmural and regional myocardial perfusion levels can be easily visualized in the perfusion images and accurately monitored by the SI time curves. Detection of the impairment of myocardial perfusion improved significantly after administration of DIP. The inverse mean transit time calculated from the SI time curve was found to yield a linear correlation to absolute MBF derived from the microsphere data. These results suggest that with intracardiac injections of exogenous contrast agent, myocardial perfusion can be assessed parametrically with first pass contrast enhanced ultrafast MRI.
Pitfalls in MR measurement of tissue blood flow with intravascular tracers: Which mean transit time?
Authors: Weisskoff Robert M. , Chesler David , Boxerman Jerrold L. , Rosen Bruce R. 
Published: March 2007

AbstractMeasuring tissue blood flow with NMR imaging of intravascular tracers is more difficult than measurements of tissue blood volume. One major obstacle to the application of the Central Volume Principle is the direct measurement of the mean transit time. In this note, we demonstrate that mean transit time (MTT), which relates tissue blood volume to blood flow via the Central Volume Principle, is not the first moment of the concentration‐time curve for MR or CT imaging of purely intravascular tracers. However, while first moment methods cannot be used by themselves to determine absolute flow, we show that transit curves may provide a useful relative measure of flow, for example, by considering ratios of the first moments.
Noninvaive observation of hepatic glycogen formation in man by13C MRS after Orl and intravenous glucose administration
Authors: Beckmann N. , Fried R. , Turkalj I. , Seeling J. , Keller U. , Stalder G. 
Published: March 2007

AbstractThe formation of glycogen in the liver of normal volunteers was followed noninvasively with 13C manetic resonance spectroscopy (MRS) under tow different conditions; a) intravenous infusion of [1‐13C] glucose under hyperglycemic and hyperinsullinemic clamp conditions, and b) oral Intake of glucose in the form of a bolus. For the intravenous infusion, [1‐13C]glucose with an enrichment level of 99% was employed. The C1 signals of α‐ and β‐glucose could be detected in the human liver already after an infusion period of 8 min. However, an increase in the glycogen signal was observed only after a prolonged infusion of about 60 min. Changes in the glycogen signal correlated well with the time course of insulin and glucagon during the measurement. Experiments showed also that liver glycogen formation in man can be followed noninvasively by13C‐MRS using nonlabeled glucose or [1‐13C]glucose with a low level of enrichment (6.6%). The use of nonlabeled glucose may therefore simplify the quantitation of net liver glycogen synthesis since it can be based directly on changes in the natural abundance 13C MRS glycogen signal, avoiding label dilution through the various metabolic pathways of glucose. The glucose uptake, estimated from the increase in the glycogen signal, was consistent with findings from more complex and invasive studies of glucose uptake in the liver. The average liver glycogen concentration in 12 h overnight fasted volunteers (n = 18) without any special dietary preparation was assessed to be 229 ± 34 mM (minimum = 160 mM; maximum = 274 mM).
Nonaxial whole‐body instant imaging
Authors: Weisskoff Robert M. , Cohen Mark S. , Rzedzian Richard R. 
Published: March 2007

AbstractWe demonstrate that whole‐body, single‐shot imaging is practical for imaging out of the central plane, including oblique axes. The technique is illustrated by images of the heart in the cardiac long‐ and short‐axis and by coronal images of the brain. Secondary gradients can produce additional image distortion and ghosting in these images. These artifacts are a direct consequence, predictable by Maxwell's equations, of the large gradients used in echo planar imaging. We show that these effects are, in general, made smaller by working at a high magnetic field.
K‐space substitution: A novel dynamic imaging technique
Authors: Jones R. A. , Haraldseth O. , Müller T. B. , Rinck P. A. , Øksendal A. N. 
Published: March 2007

AbstractA rapid dynamic imaging sequence has been developed in which only the 32 phase encoding steps that encode low spatial frequencies are collected for each dynamic image. These are substituted into a previously acquired, 128 × 128 raw data set prior to image reconstruction. In this way the dynamic information is retained while the overall appearance is improved in comparison with images obtained by zero filling to 128 × 128, leading to better qualitative evaluation. The limited k‐space sampling means that the technique is most effective for large homogeneous areas of signal change since fine changes in contrast are imperfectly recorded.
Pliosphocreatine T1 measurements with and without exchange in the heart
Authors: Friedrich Jan. , Nascimben Luigino , Liao Ronglih , Ingwall Joanne S. 
Published: March 2007

AbstractThe intrinsic phosphocreatine (PCr) T1 values measured by time‐dependent magnetization transfer in isolated perfused rat, hamster, and turkey hearts were indistinguishable. The value of 3.5 ± 0.3 s for the rat heart is similar to values measured by other magnetization transfer methods. Irreversibly inhibiting the phosphoryl exchange between PCr and ATP in the rat heart using iodoacetamide changed the apparent T1 values of the two exchanging species when measured by inversion recovery: The apparent T1 of PCr increased from 1.92 ± 0.06 s to 3.55 ± 0.06 s, in excellent agreement with the intrinsic T1, measured by magnetization transfer. The apparent T1 of [γ‐P]ATP decreased from 0.92 ± 0.07 s to 0.44 ± 0.03 s. The value for the T1 of [γ‐P]ATP in hearts with inhibited phosphoryl exchange was similar to T1 values for [α‐P]ATP and [β‐P]ATP, which remained unchanged. This illustrates that apparent T1 values for PCr and [γ‐P]ATP measured by inversion recovery in the presence of exchange are average T1 values in between the intrinsic values. The large differences between the intrinsic T1 measured by magnetization transfer and the T1 measured by inversion recovery makes the use of the appropriate value in different applications quantitatively important.
Fast echo‐shifted gradient‐recalled MRI: Combining a short repetition time with variable T2* weighting
Authors: Liu Guoying , Sobering Geoffrey , Olson Alan W. , Van Gelderen Peter , Moonen Chrit T. W. 
Published: March 2007

AbstractThe principles of a fast T2*‐sensitized MR imaging method (Moonen et al., Magn. Reson. Med. 26, 184 (1992)) are extended to further increase T2* sensitivity. It is shown that the period of T2*‐weighting can be lengthened by n TR‐periods by appropriate gradient schemes without RF refocusing resulting in progressively delayed gradient‐recalled echoes. This extension of the echo‐shifting concept thus introduces large flexibility in the choice of T2*‐weighting without changing total imaging time. The coherence pathway formalism is used to evaluate and describe the selection of the desired echo and the attenuation of unwanted coherences. The new techniques are demonstrated for tracking a bolus of susceptibility contrast agent in cat brain. Relative blood‐volume maps are derived with expected contrast between white and gray matter.
Double resonant quadrature birdcage
Authors: Fitzsimmons Jeffrey R. , Beck Barbara L. , Ralph Brooker H. 
Published: March 2007

AbstractThe combined acquisition of proton images and localized spectra is considered essential to the application of NMR techniques to human and animal research. The ideal imaging/ spectroscopy coil for our purposes would be one that provides the highest possible signal‐to‐noise, high homogeneity, and operation on two or more frequencies without retuning requirements or cable changes. To address these needs we have developed a quadrature double‐tuned birdcage. We have incorporated our earlier work on the transformer coupled double‐tuned surface coil into the birdcage structure by placing two birdcages in a coaxial configuration. This structure resonates at 34.6 MHz (phosphorus resonance at 2.0 T) and 85.5 MHz (proton resonance at 2.0 T). The quadrature performance of this coil for phosphorus was excellent, with a signal‐to‐noise that was 133% of our linear reference. The proton performance was less efficient, with a signal to noise that was 67% of our linear reference, but still quite sufficient for imaging. A phosphorus spectra and proton image of a rat abdomen are shown.
In vivo proton spectroscopy of meningioma after preoperative embolization
Authors: Jüngling F. D. , Wakhloo A. K. , Hennig J. 
Published: March 2007

AbstractThe time course of proton spectra of meningloma after embolization has been followed using a localized PRESS experiment with 135 ms of echo time. The most conspicuous findings were the observation of transient lactate signal within 24 h after blocking of the capillary bed. After that time large aliphatic signals from necrosis were observed, whereas other metabolite signals vanished. It was demonstrated, that tumor necrosis as shown by proton spectroscopy is complete within 4 days. This finding is significant for the timing of surgery, which can be performed after this period.
Spatially resolved and localized real‐time velocity distribution
Authors: Irarrazabal Pablo , Hu Bob S. , Pauly John M. , Nishimura Dwight G. 
Published: March 2007

AbstractA technique is presented for collecting the spin velocity distribution as a function of position and time. It uses a multidimensional excitation pulse to select a cylinder, giving localization in two dimensions. Resolution in the third spatial dimension is achieved in the readout. During readout, an oscillating gradient encodes the acquired data in both one spatial (dimension (x) and one veioclty dimension (v). Two acquisitions (42 ms each) are needed to get a complete coverage of kx — kv, space, which makes this technique real‐time. The data is interpolated from the nonuniformly sampled kx, — kv, space to a Cartesian frame with a gridding scheme to take advantage of the Fast Fourier Transform. The technique was successfully applied to phantoms and normal volunteers, giving reasonable real‐time measurements of velocity.
Magnetic resonance microscopy in rat skeletal research
Authors: Kapadia Rasesh D. , High Wanda B. , Soulleveld Henk A. , Bertolini Don , Sarkar Susanta K. 
Published: March 2007

AbstractNoninvasive evaluation of skeletal tissue, particularly certain sites that tend to be predisposed to disease, is critical in understanding the pathogenesis, progression, and successful treatment of various diseases like osteoporosis, rheumatoid arthritis, and osteoarthritis. Although several noninvasive techniques are currently available to evaluate skeletal tissues, they all have critical limitations. We report here a systematic study to compare the morphological changes (overall profile and tissue architecture) in the proximal tibiae and coccygeal vertebrae of a young growing rat and an older retired female breeder rat using 2‐ and 3‐dimensional MR (magnetic resonance) microscopy and histology. We have obtained MR microimages of intact rat tibiae and vertebrae with resolution up to 24 24 250 μm and have found excellent correlations between MR microscopy results and histological assessment.
Transaminase reaction rates, transport activities and TCA cycle analysis by post‐steady state 13C NMR
Authors: Robitaille Pierre‐Marie L. , Rath Dipti P. , Skinner Thomas E. , Abduljalil Amir M. , Hamlin Robert L. 
Published: March 2007

AbstractIn this work, we present the post‐steady state analysis of the TCA cycle and a closed form solution to the rate of label washout from the C4 carbon of glutamic acid through the transaminases and the malate‐aspartate shuttle and then through α‐ketoglutarate dehydrogenase. We demonstrate using a model of this problem that the rate of label washout depends not only on the flux through α‐ketoglutarate dehydrogenase, but most importantly on the activity of the malate‐aspartate shuttle as determined by the forward and reverse fluxes through the transaminases and by the rate of transport of glutamate and a‐ketoglutarate across the mitochondrial membrane.
Doxorubicin‐mediated free radical generation in intact human tumor cells enhances nitroxide electron paramagnetic resonance absorption intensity decay
Authors: Voest E. E. , Van Faassen E. , Neijt J. P. , Marx J. J. M. , Van Asbeck B. S. 
Published: March 2007

AbstractThe decay of nitroxide spin label electron paramagnetic resonance (EPR) absorption intensity was used to investigate the doxorubicin‐mediated intracellular generation of free radicals. The effects of 50–500 μg/ml doxorubicin on human tumor cells (MCF‐7, breast cancer cells, and HL‐60, promyelocytic leukemia, cells) were studied by measuring 2,2,6,64etramethylpip‐eridine‐1‐oxyl (TEMPO) absorption intensity decay (TAID) at a TEMPO concentration of 10 μM. Doxorubicin accelerated the TAID in both cell lines with a detection limit of 50 μg/ml for MCF‐7 cells and 500 μg/ml doxorubicin for HL‐60 cells. Preincubation of cells with the iron chelating agent, deferoxamine (5 mM), partially prevented the effects of doxorubicin on the TAID. Catalase and copper, zinc‐superoxide dismutase (Cu, Zn‐SOD) had no influence on the effects of doxorubicin on the TAID in intact cells. However, Cu, Zn‐SOD completely abolished the effects of doxorubicin on the TAID in a MCF‐7 cell‐free system. Our findings suggest that doxorubicin mediates the intracellular generation of O2 and that iron is involved in this process.
Pulsatile flow artifacts in 3D magnetic resonance imaging
Authors: Frank Lawrence R. , Buxton Richard B. , Kerber Charles W, 
Published: March 2007

AbstractSome of the important features of how pulsatile flow generates artifacts in three‐dimensional magnetic resonance imaging are analyzed and demonstrated. Time variations in the magnetic resonance signal during the heart cycle lead to more complex patterns of artifacts in 3D imaging than in 2D imaging. The appearance and location of these artifacts within the image volume are shown to be describable as displacements along a line in a plane parallel to that defined by the phase and volume encode directions. The angle of the line in the plane depends solely upon the imaging parameters while the ghost displacement along the line is proportional to the signal modulation frequency. Aliasing of these ghosts leads to a variety of artifact patterns which are sensitive to the pulsation period and repetition time of the pulse sequence. Numerical simulations of these effects were found to be in good agreement with experimental images of an elastic model of a human carotid artery under simulated physiological conditions and with images of two human subjects.
Techniques for the measurement of the local myocardial extraction efficiency for inert diffusible contrast agents such as gadopentate dimeglumine
Authors: Tong Chun Y. , Prato Frank S. , Wisenberg Gerald , Lee Ting Y. , Carroll Edwin , Sandler Daivid , Wills Jane 
Published: March 2007

AbstractWe have previously shown that the concentration of Gd‐DTPA as, a function of time ([Gd‐DTPA]t(t)) in the myocardium following an intravenous bolus injection of Gd‐DTPA can be moldered using the Modified Kety Equation. Fitting this model to measurements of [Gd‐DTPA]t(t) in a region of myocardium would allow the determination of myocardial distribution volume (λ) and the product of flow (F) and extraction efficiency (E), i.e., FE. Thus, to measure F,E must be known. We describe here techniques developed to measure local values of E in normal and diseased myocardium. These techniques are valid for any inert diffusible MR contrast agent.
Fast proton spectroscopic imaging of human brain using multiple spin‐echoes
Authors: Duyn Jeff H. , Moonen Chrit T. W. 
Published: March 2007

AbstractWe introduce a multi‐echo multi‐slice MR proton spectroscopic imaging method, which allows for a dramatic reduction of the measurement time by acquiring multiple spin‐echoes within a single repetition time. In the multi‐echo multi‐slice experiment discussed in this paper, a threefold reduction in measurement time is obtained by sacrificing some spectral resolution. Signal‐to‐noise ratio and spatial resolution are preserved. Metabolite images of N‐acetyl aspartate, and total choline + total creatine from multiple slices through the human brain are presented and compared with images obtained with a conventional single‐echo multi‐slice method.
A monitoring, feedback, and triggering system for reproducible breath‐hold MR imaging
Authors: Liu Yu L. , Riederer Stephen J. , Rossman Phillip J. , Grim Roger C. , Debbins Josef P. , Ehman Richard L. 
Published: March 2007

AbstractA technique is described that provides improved reproducibility of breath‐holding for MR image acquisition by monitoring the superior‐inferior (S/I) position of the diaphragm. The method incorporates detection of the level of inspiration using an MR signal, rapid display to the patient of diaphragm position to enable breath‐hold adjustment, and triggering of image data acquisition once appropriate position is attained. The response time of the system is short, approximately 10 ms. Studies in six volunteers using this method demonstrate a considerable decrease in the S/I range of diaphragm position over 10 consecutive periods of suspended respiration. The mean range is 1.3 mm with the system, while it is 8.3 mm without using it is expected that this method will be of assistance in many abdominal and cardiothoracic studies that use breath‐hold techniques.
Gd(DOTP)5‐ outer‐sphere relaxation enhancement promoted by nitrogen bases
Authors: Aime Silvio , Botta Mauro , Terreno Enzo , Anelli Pier Lucio , Uggeri Fulvio 
Published: March 2007

AbstractThe relaxation properties of Gd(DOTP)5− (1, 4, 7, 10‐tetra‐azacyclododecane‐N,N',N “,N”' ‐tetrakis(methylenephosphon‐ic acid)) have been investigated as a function of pH, temperature, concentration, and magnetic field strength. We have found that the complex has one exchangeable water molecule in1 its inner coordination sphere, at a distance of 3.26 Å from the metal ion, and it does not form oligomers in solution in the Concentration range 0.2 to 10 mM. The possible presence of two species in solution with an average fractional hydration number is also taken into accounts. The NMRD profiles were recorded at 5°C, 25°C, and 35°C and quantitatively analyzed in terms of the paramagnetic relaxation equations. Interestingly the addition to a solution of the Gd(lll)‐complex of nitrogen biases results in a marked relaxation enhancement, which shows a strong pH dependence with a maximum around pH = 9. The relaxivity gain has been shown to depend on outer‐sphere effects originating from multiple electrostatic interactions between the anionic complex and the organic cations that bring the exchangeable protons of the substrate molecules in tal close proximity with the paramagnetic center. High resolution NMR relaxation data for N‐methy1‐D(‐)‐glucamine suggest that the hydroxyl group on the β‐carbon plays a role in stabilizing the interaction, presumably through a hydrogen bond with an uncoordinated oxygen atom of the complex.
Imaging of human brain activity at 0.15 T using fluid attenuated inversion recovery (FLAIR) pulse sequences
Authors: Hajnal Joseph V. , Collins Alan G. , White Susan J. , Pennock Jacqueline M. , Oatridge Angela , Baudouin Christine J. , Young Ian R. , Bydder Graeme M. 
Published: March 2007

AbstractA 34% change in signal intensity correlated with visual stimulation was observed in the occipital lobes of three normal volunteers examined with MRI at 0.15 T using fluid attenuated inversion recovery pulse sequences. Similar results were observed at 1.0 T. A double difference technique in which difference images are themselves opposed provided an increase in sensitivity.
Polymetallic macromolecules are potential contrast agents of improved efficiency
Authors: Cavagna Frederich , Luchinat Claudio , Scozzafava Andrea , Xia Zhicheng 
Published: March 2007

AbstractThe commercial synthetic homopolypeptide polyaspartate (average MW = 30,000, approximately 220 monomers) in solution quantitatively binds up to 40 mol Gd2+ ions per mole of polyaspartate. The water proton relaxivity of the solutions is far higher than that of clinically used or commonly investigated gadolinium(III) complexes. It is shown that polymetallic macromolecular complexes combine the high relaxing efficiency of monometallic macromolecular complexes with the favorable metal/ligand mass ratio of small monometallic complexes.
Water diffusion and acute stroke
Authors: van Gelderen Peter , de Vleeschouwer Marloes H. M. , DesPres Daryl , Pekar James , van Zijl Peter C. M. , Moonen Chrit T. W. 
Published: March 2007

AbstractThe occlusion of the middle cerebral artery was used as an experimental acute stroke model in 30 cats. The diffusion of water was followed by diffusion‐sensitized MRI between 1 and 15 h after induction of stroke. It is demonstrated that images representing the trace of the diffusion tensor provide a much more accurate delineation of affected area than images representing the diffusion in one direction only. The reason is that the strong contrast caused by the anisotropy and orientation of myelin fibers is completely removed in the trace of the diffusion tensor. The trace images show a small contrast between white and gray matter. The diffusion coefficient of white matter is decreased in acute stroke to approximately the same extent as gray matter. It is further shown that the average lifetime of water in extra and intracellular space is shorter than 20 ms both for healthy and ischemic tissue indicating that myelin fibers are permeable to water. The anisotropy contrast did not change before or after induction of stroke, nor after sacrifice. Together, these observations are consistent with the view that the changes in water diffusion during acute stroke are directly related to cytotoxic oedema, i.e., to the change in relative volume of intra‐ and extracellular spaces. Changes in membrane permeability do not appear to contribute significantly to the changes in diffusion.