bluuebunny/crossref_metadata_2025 huggingface dataset:
Real‐time position monitoring of invasive devices using magnetic resonance
Authors: Dumoulin C. L. , Souza S. P. , Darrow R. D.
Published: March 2007

Techniques which can be used to follow the position of invasive devices in real‐time using magnetic resonance (MR) are described. Tracking of an invasive device is made possible by incorporating one or more small RF coils into the device. These coils detect MR signals from only those spins near the coil. Pulse sequences which employ nonselective RF pulses to excite all nuclear spins within the field‐of‐view are used. Readout magnetic field gradient pulses, typically applied along one of the primary axes of the imaging system, are then used to frequency encode the position of the receive coil(s). Data are Fourier transformed and one or more peaks located to determine the position of each receiver coil in the direction of the applied field gradient. Subsequent data collected on orthogonal axes permits the localization of the receiver coil in three dimensions. The process can be repeated rapidly and the position of each coil can be displayed in real‐time.
Measurement of rat brain perfusion by NMR using spin labeling of arterial water: In vivo determination of the degree of spin labeling
Authors: Zhang Weiguo , Williams Donald S. , Koretsky Alan P.
Published: March 2007

In vivo NMR experiments are performed to determine the degree of spin labeling for measurement of tissue perfusion by NMR using spin labeling of arterial water by adiabatic fast passage. Arterial water spins are labeled using flow in the presence of a field gradient and B1 irradiation to fulfill the conditions for adiabatic fast passage spin inversion. It is demonstrated that the NMR‐measured tissue perfusion is not affected by changing the degree of spin labeling as long as the degree of spin labeling is determined and accounted for according to the model used for calculating perfusion. By measuring the degree of spin labeling with different arterial blood flow velocities induced by different arterial pCO2, it is also demonstrated that, when spin labeling is carried out by adiabatic fast passage, the degree of spin labeling is not affected by changes in arterial blood flow velocity over a broad range.
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

The 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

Measuring 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

The 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).
Optimization of flip angle for T1dependent contrast in MRI
Authors: Pelc Norbert J.
Published: March 2007

The flip angle which maximizes contrast between materials with different T1can be caculatd from the root of a cubic expression. A simple closed form expression can be used if contrast is defined in a differential sense and results in only slight contrast loss even with large T1 differences.
Nonaxial whole‐body instant imaging
Authors: Weisskoff Robert M. , Cohen Mark S. , Rzedzian Richard R.
Published: March 2007

We 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

A 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

The 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

The 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

The 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

The 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

A 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

Noninvasive 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

In 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

The 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

Some 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

We 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

We 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

A 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

The 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

A 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

The 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

The 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.
MR imaging of flow through tortuous vessels: A numerical simulation
Authors: van Tyen Rem , Saloner David , Jou Liang‐Der , Berger Stanley
Published: March 2007

A novel computer simulation technique is presented that allows the calculation of images from Magnetic Resonance Angiography (MRA) studies of blood flow in realistic curving and branching two‐dimensional vessel geometries. Fluid dynamic calculations provide flow streamlines through curved or branching vessels. MR simulations generate images for specific MR pulse sequence parameters. Simulations of steady flow in carotid bifurcation and carotid siphon geometries as imaged by a standard, flow‐compensated, spoiled gradient echo sequence illustrate the major features seen in clinical time of flight MRA studies. The simulations provide insight into a number of artifacts encountered in MRA such as displacement artifacts, signal pile‐up, truncation artifacts, and intravoxel phase dispersion.
Artifacts due to stimulus correlated motion in functional imaging of the brain
Authors: Hajnal Joseph V. , Myers Ralph , Oatridge Angela , Schwieso Jane E. , Young Ian R. , Bydder Graeme M.
Published: March 2007

To assess the effect of stimulus correlated motion on the appearance of functional magnetic resonance images, conventional visual and motor protocols were each performed by four normal volunteers and an image co‐registration technique was used to retrospectively monitor subject motion. In three studies synthetic data sets were constructed from single baseline images using the positional information obtained from the co‐registration procedure. Cumulative difference images were then created from both the synthetic and functional image sets. Stimulus correlated motion was detected in all eight studies and the synthetic cumulative difference images showed striking similarities to the equivalent functional images in each case.
Quantitative MRI of Gd‐DTPA uptake in tumors: Response to photo dynamic therapy
Authors: Kennedy S. D. , Szczepaniak L. S. , Gibson S. L. , Hilf R. , Foster T. H. , Bryant R. G.
Published: March 2007

A partial saturation method is described for obtaining rapid images of tissue 'H spin‐lattice relaxation rates following administration of the paramagnetic contrast agent gadolinium‐diethylenetriaminepentaacetate. The paramagnetic contribution to the relaxation rates is proportional to the concentration of contrast agent, making possible quantitative studies of paramagnetic contrast agent uptake or vessel leakage. Snapshot imaging capabilities are not required. Maps of contrast agent uptake rates are made in rat borne tumors before and following photodynamic therapy, which is known to cause vascular damage. Uptake efficiency is spatially heterogenous before and after therapy. Decreases in uptake rate are observed after two photo‐irradiation protocols, which differ by a factor of four in fluence rate but deliver the same total fluence. There is no apparent fluence rate dependence for changes in the uptake rates within 5 h after therapy. Whole tumor measurements of nucleotide triphosphates, inorganic phosphate, pH, and lactate made with NMR spectroscopy indicate that, while net ATP production is inhibited, lactate concentrations are not strongly affected by photodynamic therapy. The ratio of nucleotide triphosphates to inorganic phosphate falls to 0.21 ± 0.02 of initial values 5 h after tumors are treated with the lower fluence rate protocol, and falls to 0.40 ± 0.06 in tumors treated with the higher fluence rate.
Migration and chemical modification of silicone in women with breast prostheses
Authors: Garrido Leoncio , Pfleiderer Bettina , Jenkins Bruce G. , Hulka Carol A. , Kopans Daniel B.
Published: March 2007

Studies using magnetic resonance spectroscopy in human volunteers to evaluate their livers in vivo and to analyze their blood in vitro suggest that there are measurable amounts of silicon compounds in the blood of some women with implants and that there is migration of silicone to other organs such as the liver.
Proton NMR observation of glycogen in vivo
Authors: Chen Wei , Avison Malcolm J. , Bloch Gilles , Shulman Robert G.
Published: March 2007

Our previous solution studies of the proton relaxation properties of glycogen H1 have shown significant dipolar cross–relaxation with intra‐ring H2 and inter‐ring H4′ protons characterized by a correlation time τc= 2.7 × 10−9 s. This leads to a significant negative Nuclear Overhauser Enhancement (NOE) of glycogen H1 following either transient or steady state perturbations of the longitudinal magnetization of dipolar coupled protons, especially H2 and H4′. Here we use the NOE to edit selectively the H1 resonance of glycogen in the rat liver in vivo using a surface coil probe. The approach shows the possibility of measuring glycogen in vivo with high sensitivity using 1H NMR.
MR temperature mapping of focused ultrasound surgery
Authors: Cline Harvey E. , Hynynen Kullervo , Hardy Christopher J. , Watkins Ronald D. , Schenck John F. , Jolesz Ferenc A.
Published: March 2007

Deep lying soft tissue tumors may be treated by a nonincisional surgical procedure executed inside an MR imaging system using a thermal effect delivered by a focused ultrasound transducer. A prototype system is constructed to assess MRI thermal monitoring and the localization of the heat zone in muscle. The temperature distribution of the focal spot is imaged with MRI while mechanically moving the transducer with an hydraulic 3‐axis positioner. Acoustic power is applied with a spherical shell transducer using 1‐ to 10‐s duration pulses at frequencies of 1.5 MHz to selectively coagulate tissue at 60‐70°C. The procedure is monitored with a series of fast second gradient echo, T1‐weighted, temperature sensitive MR sequences. Acquisitions are optimized for high temperature sensitive images that yield the thermal diffusivity, heat flow time constant and the focal spot size in muscle. MR temperature maps of muscle provide localization and dosimetry both in the focal region and near field.
Measurement of GABA following GABA‐transaminase inhibition by gabaculine: A 1H and 31P NMR spectroscopic study of rat brain in vivo
Authors: Behar Kevin L. , Boehm Deborah
Published: March 2007

A selective 1H NMR spin‐echo editing method was used to detect the CCH, of GABA in rat brain in vivo before and after intravenous administration of the highly selective GABA transaminase inhibitor, gabaculine (3‐amino‐2,3‐dihydrobenzoic acid‐HCl; 100 mg/kg, intravenously). The effects of the inhibitor on high energy phosphates and pH, were determined by 31P NMR. GABA levels increased approximately linearly (r = 0.81 to 0.94; P < 0.0005) from 1.9 ± 0.4 μmol/g (pre‐gabaculine; mean ± SD) to between 6 and 8 μmollg after 4 hr at rates of accumulation of 1.1 to 2.9 μmol/hr/g. 1H NMR spectroscopic measurements of cerebral GABA and its rate of turnover offers a new approach in the study of GABA‐mediated processes in vivo.
Reduction of field of view for dynamic imaging
Authors: Hu Xiaoping , Parrish Todd
Published: March 2007

This paper describes a simple technique that improves the temporal resolution for certain dynamic imaging applications. The technique is based on the assumption that the image to image intensity changes sought in dynamic imaging studies ire sometimes localized, and a smaller field of view can be used to reduce imaging time. Technical details and experimental results are presented. Experimental results show that this technique works reasonably well for in vivo applications.
ATP production rates as a function of force level in the human gastrocnemius/soleus using 31P MRS
Authors: Boska Michael
Published: March 2007

Net forward adenosine triphosphate (ATP) production rates were calculated from 31P nuclear magnetic resonance spectroscopy (MRS) kinetic data collected with 1–8 s time resolution during isometric voluntary contractions of the human gastrocnemius/soleus muscle group. Volume normalized muscle output (Newtons/ml) was then divided by the calculated net ATP use (mM/s) to estimate the metabolic economy (ME) (Newtons · s/μpmol ATP). The ATP production rates from anaerobic glycolysis (An Gly) and creatine kinase (CK) reactions are approximately half of the oxidative phosphorylation ATP production rates (Ox Phos) at the end of 90 s of isometric contractions for a series of force levels. However, ME was independent of the force level in these exercises. The correlation between MVC of healthy, trained subjects, and the maximal cross‐sectional area of the gastrocnemius/soleus shows an average of 21.2 ± 4.6 Newtons/cm2 (mean ± SD, N = 15). This was measured using a foot pedal with a transducer measurement point 10.6 cm above the heel. [ADP] versus Ox Phos ATP production rate fits a Michaelis‐Menten kinetic control equation with an offset (underestimation of Ox Phos) of 0.3 m, Ws and a Km, = 27 μM for ADP and a Vmax = 1.0 mM/s. This suggests that [ADP] is the controlling factor for mitochondrial function at the end of a 90 to 120 s isometric contraction in normal subjects at any force level. Quantitative measurements of the phosphorus metabolite concentrations were obtained from 20 individuals and these data are also reported.
Development and evaluation of tracking algorithms for cardiac wall motion analysis using phase velocity MR imaging
Authors: Constable R. Todd , Rath Kristina M. , Sinusas Albert J. , Gore John C.
Published: March 2007

Phase velocity magnetic resonance imaging (MRI) has shown considerable potential for tracking distinct regions of the myocardium throughout the cardiac cycle. Phase contrast MR imaging produces multiple images, each phase encoded for velocity in a different direction, in which individual pixels depict the local motion of the tissue. In this work we present in detail three algorithms for tracking motion based on these images. Both simulated and phantom data are used to examine some of the problems encountered in practice in tracking points based on velocity maps. Solutions to these problems are offered when possible. The impact of noise and low order phase errors in the data on each of the three tracking approaches is examined. In addition, problems due to tissue expansion and contraction, to 2D versus 3D tracking, and to round off errors from motion which is small relative to pixel size or slice thickness, are considered. An example using data obtainedin vivois included to demonstrate the efficacy of the best of the three tracking algorithms in measuring left ventricular circumferential shortening preinfarct and postinfarct in a canine model.
Observation of cardiac lipids in humans by localized 1H magnetic resonance spectroscopic imaging
Authors: den Hollander Jan A. , Evanochko William T. , Pohost Gerald M.
Published: March 2007

Different approaches are being explored for the noninvasive observation of myocardial lipids in the human heart by in vivo 1H NMR spectroscopy. One approach is to measure cardiac lipids using a combination of volume selection and 2D gradient phase encoding. From these data sets lipid images can be reconstructed. By comparing these lipid images with 1H MR scout images, it is demonstrated that these signals represent epicardial and pericardial lipid. By selecting a smaller bar‐shaped volume combined with 1D phase encoding or by using single volume techniques, it is possible to avoid most of the pericardial and epicardial lipid to obtain myocardial 1H NMR spectra of the human heart showing lipid signals, as well as trimethylamine and (phospho)creatine signals. These measurements demonstrate the feasibility of obtaining 1H NMR spectra of the human myocardium.
Quantitative in vivo tissue sodium concentration maps: The effects of biexponential relaxation
Authors: Boada Fernando E. , Christensen James D. , Huang‐Hellinger Frank R. , Reese Timothy G. , Thulborn Keith R.
Published: March 2007

The biexponential relaxation behavior of the sodium nucleus affects the accuracy of quantitative measurement of in vivo tissue sodium concentration (TSC). Theoretical analysis and in vivo experimental results are used to demonstrate the extent of the large bias in the measured TSC that arises when the relaxation behavior in vivo differs significantly from that of the calibration standards which is when a significant fraction of the total sodium signal decays with a relaxation time much shorter than the echo time (TE) used for imaging. This bias can be as large as 20% for measurements of TSC in a normal rat brain with TE = 2 ms. Our findings indicate that shortening the echo time (TE < 0.5 ms) by projection imaging is a reliable means of obtaining accurate in vivo estimates for TSC using MR.
Thin film high temperature superconducting RF coils for low field MRI
Authors: van Heteren John G. , James Timothy W. , Bourne Lincoln C.
Published: March 2007

We have built and tested a thin‐film high temperature superconducting (HTS) surface coil for MRI at 0.064T. When placed as close as possible to a conductive sample, the 6.7‐cm outer diameter HTS coil had a measured signal‐to‐noise ratio (SNR) 1.8; times higher than a room temperature copper coil of similar size and location. Our results predict that in some cases, SNR gains of about a factor of 2 can be attained in low‐field MRI systems by substituting HTS surface coils for copper coils.
Turbine flow sensor for volume‐flow rate verification in MR
Authors: Frayne Richard , Holdsworth David W. , Smith Robert F. , Kasrai Reza , Larsen Jan P. T. , Rutt Brian K.
Published: March 2007

A turbine flow sensor for MR flow experiments has been evalusted using reference volume‐flow rate measurements obtained using an electromagnetic (EM) flow meter measurements and simultaneous phase contrast (PC) MR acquisitions. After calibration, the device was found to have accuracy (compared with the EM flow meter), linearity, and precision of better than ±1%, ±3.5%, 3.5%, respectively, in constant flow mode (0 to 30 ml s−1). The frequency response of the flow sensor was flat (within ±10%) up to 13.9 Hz. Volume‐flow rate measurements on constant and simulated physiologic flow waveforms were in close agreement with both the electromagnetic (EM) flow meter and the gated MR PC estimates.
Magnetic resonance velocity imaging using a fast spiral phase contrast sequence
Authors: Pike G. Bruce , Meyer Craig H. , Brosnan Thomas J. , Pelc Norbert J.
Published: March 2007

Time‐resolved velocity imaging using the magnetic resonance phase contrast technique can provide clinically important quantitative flow measurements in vivo but suffers from long scan times when based on conventional spin‐warp sequences. This can be particularly problematic when imaging regions of the abdomen and thorax because of respiratory motion. We present a rapid phase contrast sequence based on an interleaved spiral k‐space data acquisition that permits time‐resolved, three‐direction velocity imaging within a breath‐hold. Results of steady and pulsatile flow phantom experiments are presented, which indicate excellent agreement between our technique and through plane flow measurements made with an in‐line ultrasound probe. Also shown are results of normal volunteer studies of the carotids, renal arteries, and heart.
Quantitative MRI of spinal cord injury in a rat model
Authors: Falconer James C. , Narayana Ponnada A. , Bhattacharjee Meena B. , Liu Shi‐J.
Published: March 2007

Sequential in vivo MRI studies of experimental spinal cord injuries (SCI) were performed using a three‐dimensional implementation of the FATE (Fast low‐Angle spin echo sequence with short TE) sequence. MRI‐observed pathology was quantified using a multispectral segmentation algorithm. Neurological analysis was performed on the same animals concurrently, in addition to end‐point histology, for comparison with quantitative MRI results. These studies suggest that it is possible to use MRI to detect the onset of secondary injury in the spinal cord. The data also indicate that early detection of MRI‐visible pathology may provide the necessary markers for predicting the long‐term level of neurologic deficit.
In vivo proton magnetic resonance spectroscopy detection of human alcohol tolerance
Authors: Chiu Talc‐Ming , Mendelson Jack H. , Woods Bryan T. , Teoh Siew Koon , Levisohn Lisi , Mello Nancy K.
Published: March 2007

Alcohol tolerance was ascertained with in vivo proton magnetic resonance spectroscopy (MRS) in men who regularly consumed either large (10–20 drinks/week) or small (2–4 drinks/week) amounts of beverage alcohol. Brain ethanol concentrations were determined by MRS, and blood ethanol levels were measured by gas chromatography after controlled ethanol administration (0.8 g/kg). Brain‐blood ethanol concentration ratios for heavy drinkers were significantly greater than ratios for occasional drinkers (P < 0.002). Inasmuch as ethanol tolerance covaries with the severity of dependence, MRS procedures may facilitate our understanding of alcohol tolerance and treatment of alcoholism.
Electrocardiogram acquisition during MR examinations for patient monitoring and sequence triggering
Authors: Felblinger Jacques , Lehmann Christoph , Boesch Chris
Published: March 2007

We have developed a method for measuring the electrocardiogram (ECG) continuously during MR examinations. In contrast to ECG acquisition by wires, our new method is to amplify and convert the ECG into an optical signal directly above the patient's heart. The optical signal is transmitted out of the magnet bore by optical fiber. The small and fixed dimensions of the ECG amplifier avoid interactions with the MR system because of shorter electrical structures and smaller enclosed areas. Tests of the proposed device in a 1.5 Tesla MR system show that continuous and reliable ECG monitoring and sequence triggering are possible.
Evaluation of cerebral gray and white matter metabolite differences by spectroscopic imaging at 4.1T
Authors: Hetherington Hoby P. , Mason Graeme F. , Pan Jullie W. , Ponder Steven L. , Vaughan J. Thomas , Twieg Donald B. , Pohost Gerald M.
Published: March 2007

Using a 4.1 T whole body system, we have acquired 1H spectroscopic imaging (SI) data of N‐acetyl (NA) compounds, creatine (CR), and choline (CH) with nominal voxel sizes of 0.5 cc (1.15 cc after filtering). We have used the SI data to estimate differences in cerebral metabolites of human gray and white matter. To evaluate the origin of an increased CWNA and CWNA ratios in gray matter relative to white matter, we measured the T1 and T2 of CR, NA, and CH in gray and white matter using moderate resolution SI imaging. In white matter the T2s of NA, CR, and CH were 233 ± 27,141 ± 18, and 167 ± 20 ms, respectively, and 227 ± 27,140 ± 16, and 189 ± 25 ms in gray matter. The T, values for NA, CR, and CH were 1267 ±141, 1487 ± 146, and 1111 ± 136 ms in gray matter and 1260 ± 154, 1429 & 233, and 1074 ± 146 ms in white matter. After correcting for T1 and T2 losses, creatine content was significantly lower in white matter than gray (P < e 0.01, t‐test), with a white/gray content ratio of 0.8, in agreement with biopsy and in vivo measurements at 1.5 and 2.0T.
Localized in vivo31P NMR spectroscopy of skin flap metabolism
Authors: Cheung Ada , Zhong Jianhui , Gore John C. , Cuono Charles B.
Published: March 2007

We have used a rectangular surface coil and chemical shift imaging to conduct in vivo localized 31P NMR metabolic studies in a rat dorsal skin flap model. This approach permits regional comparisons without manipulation of either coil position or subject within the magnet bore. Both the PCr:P1 ratio (reflecting ischemia insult) and the PCr:ATP ratio (reflecting phosphagen reserves) decreased as functions of time and distance from the vascular pedicle. The maximum change was nearly 6‐fold for the PCr:P, ratio, and 3‐fold for the PCr:ATP ratio. Signal contamination from subjacent muscle is constant and does not interfere with the metabolic evaluations of skin flaps. This technique may facilitate a better understanding of cutaneous metabolic derangements, such as burns and skin flaps used in reconstructive surgery, as well as studies of pharmacologic regimens developed for their treatment. It also holds potential for application in the study of congenital and neoplastic metabolic disorders of skin.
31P NMR investigation of energy metabolism in perifused MMQ cells
Authors: Goger Michael J. , Login Ivan S. , Fernandez Erik J. , Grisham Charles M.
Published: March 2007

The MMQ cell line is a unique prolactin‐secreting rat pituitary cell line. MMQ cells entrapped in agarose gel threads are metabolically active, as determined by the uptake and phosphorylation of creatine and the maintenance of high energy phosphates for over 15 h. Forskolin activates the catalytic subunit of adenylyl cyclase and, in MMQ cells, elevates the level of cAMP and stimulates prolactin secretion. 31P NMR spectroscopy was used to investigate the energy metabolism of the MMQ cells during stimulation by forskolin. The ability to measure small changes in the energy status of these cells was enhanced by increasing the PCr levels in the cells. Administration of forskolin to the perifused MMQ cells resulted in acute, reversible, and dose‐dependent changes in the 31P NMR spectra of the cells within 12 to 24 min of the beginning of forskolin exposure. Several lines of evidence indicate that the changes observed in the MMQ cells are the composite result of the interaction of forskolin with adenylyl cyclase and the plasma membrane glucose transporter. Also, preincubation of the MMQ cells with the dopamine agonist, bromocriptine, attenuates the forskolin‐stimulated decrease in the PCr resonance by approximately 50%. This attenuation indicates that the forskolin‐stimulated changes in energy metabolism are probably related to the prolactin secretion process.