bluuebunny/crossref_metadata_2025_split huggingface dataset:
Estimation of total coronary artery flow using measurements of flow in the ascending aorta
Authors: Buonocore Michael H. 
Published: March 2007

AbstractThis paper describes a technique for estimation of total (right + left) coronary artery flow using MRI flow measurements in the ascending aorta. The technique is based on the principle that the flow in a vessel branch is equal to the difference of the net flow measured above and below the branch ostia. Aortic net flow is measured at four or more axial oblique slices from below the aortic valve to above the highest location of the coronary vessel ostia in late diastole. A flow model properly interprets the flow measurements in slices that contain the coronary ostia. Results in five normal subjects show that total coronary artery flow can be measured with a standard error of about 90 cc/min, 30% of total coronary artery flow. Potential clinical uses include noninvasive measurement of coronary flow reserve. Pulse sequence improvements are necessary to reduce examination time and improve accuracy and precision.
A dynamically adaptive imaging algorithm for wavelet‐encoded MRI
Authors: Panych Lawrence P. , Jolesz Ferenc A. 
Published: March 2007

AbstractA new adaptive algorithm based on wavelet‐encoded MRI is presented for application in dynamic imaging. This algorithm is adaptive because the strategy for updating image data in the dynamic series of images is determined by the processing of the most recently acquired data. The spatially selective multi‐resolution properties of the wavelet transform are exploited to selectively update only those regions of the field of view where change is actually occurring. A theoretical imaging model is presented to motivate use of the adaptive algorithm, and simulation results using both artificial and experimental wavelet‐encoded data are presented.
Minimization of dead‐periods in MRI pulse sequences for imaging oblique planes
Authors: Atalar Ergin , McVeigh Elliot R. 
Published: March 2007

AbstractWith the advent of breath‐hold MR cardiac imaging techniques, the minimization of TR and TE for oblique planes has become a critical issue. The slew rates and maximum currents of gradient amplifiers limit the minimum possible TR and TE by adding dead‐periods to the pulse sequences. We propose a method of designing gradient waveforms that will be applied to the amplifiers instead of the slice, readout, and phase encoding waveforms. Because this method ensures that the gradient amplifiers will always switch at their maximum slew rate, it results in the minimum possible dead‐period for given imaging parameters and scan plane position. A GRASS pulse sequence has been designed and ultra‐short TR and TE values have been obtained with standard gradient amplifiers and coils. For some oblique slices, we have achieved shorter TR and TE values than those for nonoblique slices.
The theory of shielded loop resonators
Authors: Harpen Michael D. 
Published: March 2007

AbstractWe present a mathematical model for shielded loop resonators. The model implies equivalent circuits for coaxial as well as flat Faraday shielded resonators under both balanced and unbalanced termination conditions. Expressions for impedance derived from the model are shown to agree well with observation using two test experimental resonators in a variety of experimental conditions.
1H NMR Detection of Lactate and Alanine in Perfused Rat Hearts during Global and Low Pressure Ischemia
Authors: Zhao Piyu , Storey Charles J. , Babcock Evelyn E. , Malloy Craig R. , Dean Sherry A. 
Published: March 2007

AbstractA spin‐echo method is presented for obtaining high resolution, 13C coupled, proton spectra of lactate and alanine in intact, beating rat hearts. All hearts were depleted of glycogen prior to prolonged perfusion with either 10 mM unenriched glucose or [1−13C]glucose to restore glycogen. These two groups of hearts were then examined by 1H NMR during prolonged global (zero flow) or low pressure (low flow) ischemia. During global ischemia, lactate was derived from both glucose and glycogen, with endogenous glycogen contributing twice as much lactate as exogenous glucose. During low perfusion pressure ischemia, however, lactate was derived exclusively from exogenous glucose. The entire pool of lactate (both 12C and 13C) was visible by NMR in intact, glucose perfused hearts while alanine was not detected. However, upon adding 10 mM pyruvate to the perfusate, the entire alanine pool became NMR visible while some of the lactate became NMR invisible. These observations indicate that the NMR visibility of small, usually highly mobile metabolites such as alanine and lactate is not always 100% in intact hearts and that the NMR visibility of these molecules may depend upon which exogenous substrate is presented to the heart.
Breath‐Hold 3D STAR MR Angiography of the Renal Arteries Using Segmented Echo Planar Imaging
Authors: Wielopolski Piotr A. , Adamis Mary , Prasad Pottumarthi , Gaa Jochen , Edelman Robert 
Published: March 2007

AbstractThree‐dimensional (3D), cardiac triggered renal MR angiograms were acquired with excellent background suppression within a single breath‐hold of 18 to 30 s using signal targeting with alternating radiofrequency (STAR), a subtraction time‐of‐flight MR angiography technique, and a 3D scheme combining echo planar imaging (EPI) readouts and k‐space segmentation. The 3D STAR sequence was evaluated on 17 healthy individuals, 3 potential renal donors, and 2 patients with suspected renovascular hypertension. An inversion tag through the aorta was applied to produce the vascular contrast. After a suitable inflow time, 16 to 64 sections were encoded. An additional presaturation pulse applied over the imaging volume prior to tagging permitted improved background suppression by reducing signal variations from involuntary motion and changes in the cardiac period during breath‐holding. Intrarenal branches were observed consistently in all healthy individuals. Longer inflow times provided better depiction of the intrarenal vessels while shorter delays delineated the proximal renal branches with better signal‐to‐noise ratio. Breath‐hold and diastolic data collection reduced both blurring and flow related dephasing. Our results demonstrate excellent visualization of the renal arteries to the level of intrarenal branch vessels using the proposed technique.
Intracellular Volume Measurement and Detection of Edema: Multinuclear NMR Studies of Intact Rat Hearts during Normothermic Ischemia
Authors: Askenasy Nadir , Tassini Maria , Vivi Antonio , Navon Gil 
Published: March 2007

AbstractThe present study describes the cell volume dynamics in intact rat hearts, during ischemia and after reperfusion. Cell volumes were measured in isolated hearts by either 13C or 59Co NMR of mannitol or cobalticyanide, respectively, as extracellular markers and 1H NMR of water as the aqueous space marker. A constant volume chamber was built inside a 15‐mm NMR tube; the contents of the chamber were measured with and without a heart. The intracellular volume of isolated rat hearts was estimated to be 2.45 ± 0.13 ml/g dry weight. In the perfused heart, adenosine triphosphate (ATP) and phosphocreatine (PCr) concentrations were calculated to be 12.2 ± 0.7 and 16.1 ± 1.0 mM, respectively. Consecutive volume measurements showed cell swelling of 16% during 30 min of ischemia, which was reduced at reperfusion to 7%. After 30 min of reperfusion, ATP and PCr concentrations were 4.5 ± 0.8 and 8.1 ± 0.9 mM. It is concluded that: (1) cell swelling is an ischemic event, which is partially reversed by reperfusion; and (2) continuous measurement of cell volumes provides intracellular molar concentrations of metabolites, which are the physiologically significant parameters.
Quantitative Mapping of Ocular Oxygenation Using Magnetic Resonance Imaging
Authors: Berkowitz Bruce A. , Wilson Charles A. 
Published: March 2007

AbstractRetinal hypoxia is hypothesized to initiate angiogenesis, a leading cause of blindness in developed countries. Attempts to test this hypothesis suffer from the need to use highly invasive oxygen electrodes. In this communication, noninvasive and quantitative mapping of ocular oxygenation using magnetic resonance imaging is demonstrated for the first time.
Relative Concentrations of Proton MR Visible Neurochemicals in Gray and White Matter in Human Brain
Authors: Doyle Timothy J. , Bedell Barry J. , Narayana Ponnada A. 
Published: March 2007

AbstractThe relative distributions of N‐acetylaspartate (NAA) + N‐acetylaspartylglutamate (NAAG), creatine + phosphocreatine (Cr/PCr), and choline (Cho) in the gray and white matter of human brain were determined by utilizing proton magnetic resonance spectroscopic imaging (SI). The SI data was processed using an automated spectroscopic image processing algorithm, and image segmentation was performed using a supervised technique. Linear regression analysis indicated that the NAA + NAAG (2.01 ppm) and Cr/PCr (3.02 ppm) peaks are greater in gray matter compared with white matter. The large intersubject variation observed in the Cho (3.20 ppm) resonance prevented the assessment of its regional distribution with confidence.
RF Electric Field Mapping in MR Coils with a Quartz Crystal
Authors: Wang Dah‐Jyuu , Leigh John S. 
Published: March 2007

AbstractThe electric field strength and distribution in MRI/MRS probes was assessed with a quartz crystal whose resonance frequency coincided with the probe frequency. A quartz crystal was used as the sensor because: (i) it was capable of producing a resonance signal when it was excited with a pulsed RF electric field; and (ii) the resonance signal was proportional to the square of the electric field strength (or RF excitation power). The sensor was placed in the vicinity of the MR coil under evaluation and was excited with a short RF pulse applied to the coil and, immediately after the pulse, the resonance signal induced was picked up by the same coil acting as a receiver coil. Intensities of the signals were used to assess the distribution of RF electric fields in the coil. This device is useful for probe design, particularly in the minimization of dielectric losses, which have been attributed to the presence of electric fields in MR coils.
Multislice first‐pass myocardial perfusion imaging on a conventional clinical scanner
Authors: Walsh Edward G. , Doyle Mark , Lawson Mark A. , Blackwell Gerald G. , Pohost Gerald M. 
Published: March 2007

AbstractA technique is demonstrated for the acquisition and processing of multislice, first‐pass contrast‐enhanced pelfusion images in the myocardium. The acquisition is a modification of “keyhole” imaging in which time series images are acquired by sampling a limited segment of k‐space, corresponding to the low spatial frequencies. In the modification demonstrated here, keyhole samples are divided into two groups that are sampled on alternate cardiac cycles. The alternate “missing” k‐space portions are synthesized by Fourier interpolation. Visualization of contrast agent accumulation by image subtraction is demonstrated. A motion artifact reduction process using time domain Fourier filtering is used to reduce artifacts from respiration. Studies were performed on 46 patients at 1.5 T using gadoteridol (0.05–0.1 mmol/kg) injected into the right antecubital vein in conjunction with radionuclide imaging. Fully concordant studies were noted in 27 of these patients. Remaining studies were either partially or completely discordant for reasons relating to the differing natures of radionuclide versus MR contrast agent characteristics.
Theory of 1/T1 and 1/T2 NMRD profiles of solutions of magnetic nanoparticles
Authors: Koenig Seymour H. , Kellar Kenneth E. 
Published: March 2007

AbstractOrganically coated iron oxide crystallites with diameters of 5–50 nm (“nanoparticles”) are potential magnetic resonance imaging contrast agents. 1/T1 and 1/T2 of solvent water protons are increased dramatically by magnetic interactions in the “outer sphere” environment of the nanoparticles; subsequent diffusive mixing distributes this relaxation throughout the solvent. Published theory, valid for the solute magnetic energy small compared with thermal energy, is applicable to small magnetic solutes (e.g., gadolinium and manganese diethylenetriaminopentaacetic acid, and nitroxide free radicals) at generally accessible fields (≤ 50 T). It fails for nanoparticles at fields above ˜0.05 T, i.e., at most imaging fields. The authors have reformulated outer sphere relaxation theory to incorporate progressive magnetic saturation of solute nanoparticles and, in addition, indicate how to use empirical magnetization data for realistic particles when their magnetic properties are not ideal. It is important to handle the effects of rapid thermally induced reorientation of the magnetization of the nanoparticles (their “superparamagnetism”) effectively, including their sensitivity to particle size. The theoretical results are presented as the magnetic field dependence (NMRD profiles) of 1/T1 and 1/T2, normalized to Fe content, for three sizes of particles, and then compared with the limited data extant for well‐characterized material.
In Vivo proton MR spectroscopy of human gliomas: definition of metabolic coordinates for multi‐dimensional classification
Authors: Hagberg Gisela , Burlina Alessandro P. , Mader Irina , Roser Werner , Radue Ernst W. , Seelig Joachim 
Published: March 2007

AbstractSeveral multi‐dimensional statistical evaluation methods were applied to single‐voxel proton MR spectra of glial brain tumors and of healthy volunteers. Metabolic coordinates with histological relevance for future diagnosis were found by which spectra from controls, low‐grade tumors, and highgrade tumors were completely separated. Significant differences between low‐grade and high‐grade glioma patients and controls were found for several metabolic ratios by variance analysis. Cluster analysis both with and without principal component analysis was applied. The outcome of these two approaches depended mainly on the lipid‐to‐creatine ratio. Two other approaches, discriminant factor analysis and the orthonormal discriminant vector method were then used to find discriminatory metabolic coordinates. It turned out that a linear combination of all evaluable metabolic ratios made it possible to separate the three groups completely. On the basis of these results, a classification method that uses the entire proton MRS spectrum is proposed.
Noninvasive MRI thermometry with the proton resonance frequency method: Study of susceptibility effects
Authors: Poorter John De 
Published: March 2007

AbstractThe temperature dependence of proton resonance frequency (PRF) is related to the temperature dependence of the screening constant and of the volume susceptibility constant. To evaluate the relative importance, an experimental setup was designed allowing quantification of both effects in different tissues, notably pure water in a gel structure, and porcine muscle and fat tissue. The temperature varied from 28 to 44°C, a range significant for hyperthermia applications. Good agreement with results from the literature was obtained for water. Porcine muscle tissue behaves like water. Its screening constant varies linearly at a rate of 0.97 10‐8 (oC)‐1 and the effects of temperature‐induced changes of the susceptibility constant are negligible for muscle thermometry applications. The PRF‐temperature relation in fat tissue, however, is almost completely determined by susceptibility effects.
1H mrs of human brain abscesses in vivo and in vitro
Authors: Rémy Chantal , Grand Sylvie , Laï Ernest Sam , Belle ValéRie , Hoffmann Dominique , Berger FrançOis , Estève FrançOis , Ziegler Anne , Bas Jean‐FrsançOis Le , Benabid Alim L. , Décorps Michel , Segebarth Christoph M. 
Published: March 2007

AbstractFive patients, each with a brain abscess, were examined by means of 1H MR spectroscopic imaging in vivo. The aspirated pus was analyzed in vitro by means of 1D and 2D COSY 1H MRS. In addition to resonance lines from compounds (lactate, alanine and lipids) often found in the spectra from intracranial tumors, resonance lines were detected from a number of markers of infectious involvement (acetate, succinate, and various amino acids). These results suggest that 1H MRS in vivo might contribute in establishing noninvasively a differential diagnosis between brain abscess and tumor.
Ultra‐fast imaging using low flip angles and fids
Authors: Madio David P. , Lowe Irving J. 
Published: March 2007

AbstractA new ultra‐fast imaging technique that does not place extreme demands on the speed of the gradient system is described. When used with comparable MRI systems, the rotating ultra‐fast imaging sequence (RUFIS) can acquire images 4 to 5 times faster than gradient‐moment nulled EPI and more than twice as fast as DUFIS, OUFIS, or BURST techniques. Because the technique uses free induction decays instead of echoes, it can be made particularly insensitive to effects of motion, flow, and diffusion. Preliminary images of turbulent flow are presented to demonstrate this insensitivity. However, with appropriate encoding, flow effects may be imaged.
In vivo31p spectroscopy study of treated and untreated recovery of rat partial brain ischemia
Authors: Macri Maria Antonietta , Campanella Renzo , Luca Francesco De , Montalbano Antonio , Taggi Franco , Maraviglia Bruno 
Published: March 2007

AbstractQuantitative 31P NMR was used to follow the time variation of the hypometabolic response to hypoxic partial ischemia in an animal model. The purpose of the study was to establish the value of this repeated spectroscopy operating by means of a surface coil. It aimed at determining whether a therapeutic intervention could influence the transient changes occurring during the insult or early recovery. A pharmacological substance was thus used during a reversible forebrain ischemia, induced by a combination of vascular occlusion and mild hypoxia in two groups of rats. As an available and convenient example, L‐carnitine was chosen. Statistical analysis of the experimental results revealed a significant difference of the P1 and PCr levels between treated and untreated animals.
Simultaneous calculation of flow and diffusion sensitivity in steady‐state free precession imaging
Authors: Gudbjartsson HÁKon , Patz Samuel 
Published: March 2007

AbstractIn this paper the authors quantitatively evaluate the combined effect of both flow and diffusion in steady‐state free precession (SSFP) imaging. A partition analysis (PA) is used to derive a fourth order approximation (in E2) of the signal in an echo SSFP sequence. The authors also introduce a novel very fast simulation technique, based on a circular convolution, which accurately accounts for both flow and diffusion. A 2D SSFP‐echo sequence was implemented to obtain experimental data from a phantom containing three different solutions. Excellent agreement between the theory and the experimental data was found. Then by using the simulation algorithm and experimental measurements of in vivo brain motion, the authors estimated the artifacts to be expected in SSFP diffusion imaging of the brain and found them to be comparable with those of pulsed gradient spin echo. Finally, the authors point out the equivalence between the flow sensitivity of SSFP and RF spoiling commonly used in fast imaging.
High resolution renal diffusion imaging using a modified steady‐state free precession sequence
Authors: Ding Shujun , Trillaud Herve , Yongbi Martin , Rolett Ellis L. , Weaver John B. , Dunn Jeff F. 
Published: March 2007

AbstractA modified steady‐state free precession (SSFP) diffusion sequence is proposed for high resolution renal imaging. A pair of bipolar diffusion gradients was used to minimize the errors in measured apparent diffusion coefficient (ADC) caused by variations in T1, T2, and RF flip angle that have been observed with previously employed SSFP diffusion sequences. Motion sensitivity was reduced by the use of compensated gradients, frame‐by‐frame averaging, and a repetition time of 22 ms, which for a single‐acquisition 128 × 128 image requires only 3 s. High resolution was achieved by signal averaging. The modified sequence was applied to in vivo diffusion measurements. In six normal rat kidneys the ADCs (mean±SD; × 10−3 mm2/s) of the cortex, outer medulla, and inner medulla were 2.28 ± 0.05, 2.38 ± 0.10, and 2.95 ± 0.05, respectively. The technique requires relatively large gradients to achieve adequate diffusion weighting.
MRS imaging using anatomically based K‐space sampling and extrapolation
Authors: Plevritis Sylvia K. , Macovski Albert 
Published: March 2007

AbstractA comprehensive strategy for the acquisition, reconstruction, and postprocessing of MR spectroscopic images is presented. The reconstruction algorithm is the most critical component of this strategy. It is assumes that the desired image is spatially bounded, meaning that the desired image contains an object that is surrounded by a background of zeros. The reconstruction algorithm relies on prior knowledge of the background zeros fork‐space extrapolation. This algorithm is a good candidate for proton MR spectroscopic image reconstruction because these images are often spatially bounded and prior knowledge of the zeros is easily obtained from a rapidly acquired high resolution conventional MRI. Although the reconstruction algorithm can be used with the standard 3DFTk‐space distribution, a distribution that relies on anatomical features that are likely to occur in the spectroscopic image can produce better results. Prior knowledge of these anatomical features is also obtained from a conventional MRI. Finally, the postprocessing component of this strategy is valuable for reducing subcutaneous lipid contamination. Overall, the comprehensive approach presented here produces images that are better resolved than standard approaches without increasing acquisition time or reducing SNR. Examples using NAA data are provided.
Coronary artery imaging at 0.5 t using segmented 3d echo planar imaging
Authors: Börnert Peter , Jensen Dye 
Published: March 2007

AbstractThe application of segmented 3D gradient echo EPI at 0.5 T for coronary artery imaging is described. Experiments were performed using fat suppression, ECG triggering, and a patient‐controlled breath‐holding scheme. This approach provides a sufficient signal‐to‐noise ratio for thin contiguous slices in conjunction with a phased array cardiac receive coil. Wide 3D volumes, covering the proximal branches of the coronary tree, were measured with a high spatial resolution. Such data sets can be used for subsequent vessel segmentation. Furthermore, data out of narrow 3D volumes were obtained containing fewer slices angulated in the direction of a selected coronary artery. This provides a good visualization of the selected vessel over several centimeters without the need for segmentation.