bluuebunny/crossref_metadata_2025_split huggingface dataset:
Real‐time adaptive motion correction in functional MRI
Authors: Lee Christine C. , Jack Clifford R. , Grimm Roger C. , Rossman Phillip J. , Felmlee Joel P. , Ehman Richard L. , Riederer Stephen J. 
Published: March 2007

AbstractFunctional magnetic resonance imaging (fMRI) of the brain is often degraded by bulk head motion. Algorithms that address this by retrospective re‐registration of images in an fMRI time series are all fundamentally limited by any motion that occurs through‐plane. Here, a technique is described that can account for such motion by prospective. correction in real time. A navigator echo is used before every image acquisition to detect superior/inferior displacements of the head. The displacement information is then used to adjust the plane of excitation of the ensuing single‐shot echo‐planar fMRI axial image. These correction updates can be completed in 100 ms with motion sensitivity at least as small as 0.5 mm. The efficacy of this method is documented in phantom and human studies.
Oxidation of acetate in rabbit skeletal muscle: Detection by 13C NMR spectroscopy in vivo
Authors: Szczepaniak Lidia , Babcock Evelyn E. , Malloy Craig R. , Sherry A. Dean 
Published: March 2007

AbstractThe results of a proton‐decoupled and Overhauser‐enhanced 13C NMR study of acetate metabolism in skeletal muscle are reported. [2‐13C]Acetate was infused intravenously over 2 h into anesthetized rabbits, and skeletal muscle in the lateral thigh was monitored by 13C NMR spectroscopy at 4.7 T. Stable 13C enrichment in carbons 2, 3, and 4 of glutamate was observed at the end of the infusion, and the half‐time for enrichment was 17 min for glutamate C4 and 50 min for glutamate C2 and C3. The contribution of exogenous acetate to acetyl‐coenzyme A was nearly equal in skeletal muscle and heart in vivo (83–87%, measured in tissue extracts), comparable with earlier perfused heart studies in which acetate was the sole available substrate. Although relative flux through the combined anaplerotic pathways (relative to citric acid cycle flux) was higher in quiescent skeletal muscle (26%) compared with hearts (3%) from the same animals, actual anaplerotic flux was estimated to be substantially higher in heart than in skeletal muscle after correcting for differences in citric acid cycle flux in the two tissues.
Elimination of artifacts in short echo time 1H MR spectroscopy of the frontal lobe
Authors: Ernst Thomas , Chang Linda 
Published: March 2007

AbstractLocalized 1H spectra from the frontal part of the human brain are often distorted by “ghost” artifacts, especially with short echo time PRESS sequences. These artifacts are caused by insufficient dephasing of unwanted coherences involving magnetization in the sinuses and the mouth. Because the various unwanted coherences of a PRESS sequence are dephased differently, the order of the slice gradients has a pronounced effect on the spectral quality. For frontal voxels, the last slice gradient has to be applied in the axial direction. With this slice order, the major metabolites can be quantified with an interindividual variability of about 10%.
Noise in MRI
Authors: Macovski Albert 
Published: March 2007

AbstractThis study analyzes the signal‐to‐noise ratio (SNR) in magnetic resonance imaging. The factors that determine the SNR are derived starting from basic principles. The SNR, for a given object, is shown to be proportional to the voxel volume and the square root of the acquisition time. The noise generated by the body is derived using a cylindrical model and is shown to be proportional to the square of the radius and the square root of the length.
Pulmonary perfusion: Qualitative assessment with dynamic contrast‐enhanced MRI using ultra‐short TE and inversion recovery turbo FLASH
Authors: Hatabu Hiroto , Gaa Jochen , Kim Ducksoo , Li Wei , Prasad Pottumarthi V. , Edelman Robert R. 
Published: March 2007

AbstractThe accurate assessment of pulmonary perfusion is especially important in the evaluation of patients with suspected pulmonary embolism, a common and potentially lethal disorder that can be treated by aggressive anticoagulation. In this study, we demonstrate for the first time the use of MR to image pulmonary perfusion in humans by using dynamic imaging after contrast administration. The technique, which uses an inversion recovery turbo FLASH sequence with ultrashort TE (1.4 ms) and 1‐s temporal resolution, was tested in a series of eight healthy subjects and in a porcine model of pulmonary embolism. After the administration of gadopentetate dimeglumine in humans and animal models, there was serial enhancement of the systemic veins, right atrium, right ventricle, and pulmonary arteries. The pulmonary arterial tree was visualized beyond the segmental branches, followed by a gradual diffuse increase in signal intensity of the lung parenchyma over a period of 4.0–7.0 s. Pulmonary circulation times ranged from 3.0–3.4 s. Whereas a high dose (20 or 40 ml) of contrast agent tended to produce the most intense parenchymal enhancement, a low dose (5 ml) was best for showing recirculation. In the animal model, a perfusion defect due to a pulmonary embolus was clearly shown and confirmed by cine angiography. It is concluded that MRI of lung perfusion is feasible. With further development, perfusion MRI could eventually have a significant clinical role in the diagnostic evaluation of pulmonary embolism.
Line scan diffusion imaging
Authors: Gudbjartsson Hákon , Maier Stephan E. , Mulkern Robert V. , Mórocz István Á. , Patz Samuel , Jolesz Ferenc A. 
Published: March 2007

AbstractA novel line scan diffusion imaging sequence (LSDI) is introduced. LSDI is inherently insensitive to motion artifacts and high quality diffusion maps of the brain can be obtained rapidly without the use of head restraints or cardiac gating. Results from a stroke study and abdominal diffusion images are presented. The results indicate that it is feasible to use the LSDI technique for clinical evaluation of acute ischemic stroke. In contrast to echo‐planar diffusion imaging, LSDI does not require modified gradient hardware and can be implemented on conventional scanners. Thus, LSDI should dramatically increase the general availability of robust clinical diffusion imaging.
Computation of flow pressure fields from magnetic resonance velocity mapping
Authors: Yang Guang‐Zhong , Kilner Philip J. , Wood Nigel B. , Underwood S. Richard , Firmin David N. 
Published: March 2007

AbstractMagnetic resonance phase velocity mapping has unrivalled capacities for acquiringin vivomulti‐directional blood flow information. In this study, the authors set out to derive both spatial and temporal components of acceleration, and hence differences of pressure in a flow field using cine magnetic resonance velocity data. An efficient numerical algorithm based on the Navier‐Stokes equations for incompressible Newtonian fluid was used. The computational approach was validated within vitroflow phantoms. This work aims to contribute to a better understanding of cardiovascular dynamics and to serve as a basis for investigating pulsatile pressure/ flow relationships associated with normal and impaired cardiovascular function.
A readout magnet for prepolarized MRI
Authors: Morgan Patrick , Conolly Steven , Scott Greig , Macovski Albert 
Published: March 2007

AbstractConventional MRI systems rely on large magnets to generate a field that is both strong and extremely uniform. This field is usually produced by a heavy permanent magnet or a cryogenically cooled superconductor. An alternative approach, called prepolarized MRI (PMRI), employs two separate fields produced by two different magnets. A strong and inhomogeneous magnetic field is used to polarize the sample. After polarization, a weak magnetic field is used for readout. These fields can be produced by two separate resistive electromagnets that cost significantly less than a single permanent or superconducting magnet. At Stanford, the authors are constructing a PMRI prototype scanner suitable for imaging human extremities roughly 20 cm in diameter. With this system the authors hope to demonstrate comparable image quality to MRI with reduced system cost. The authors' initial work on low‐frequency reception indicates that it will be possible to obtain comparable image signal‐to‐noise ratio to an MRI scanner operating at the same polarizing field strength. To reduce the capital cost of the system, the authors use resistive electromagnets. Here the authors discuss the full development of the readout magnet including important design considerations, shimming, and field plots. These encouraging results are an important step toward evaluating the cost effectiveness of PMRI.
Three‐dimensional strain‐rate imaging
Authors: Robson Matthew D. , Constable R. Todd 
Published: March 2007

AbstractStrain‐rate imaging uses large velocity encoding gradients to obtain measurements of velocity that are extremely insensitive to the effects of random noise. The spatial differential of velocity yields the velocity gradient from which the strain‐rate and twist‐rate tensors can be determined. These tensors represent the distortion of the material and are of interest in the analysis of the dynamic behavior of living tissue (e.g., that of the myocardium). This work presents a new technique that uses the magnitude of the signal in the velocity encoded data to measure through‐plane velocity variations at the resolution of the voxel size. The magnitude of the MR signal contains information about the range of phases present within a voxel. When the phase is dependent on the velocity (as in phase velocity imaging), the magnitude contains information about the range of velocities within a voxel. The method presented in this work uses unbalanced slice‐refocusing gradients to sample the magnitude variation introduced by the interaction of velocity encoding gradients with spatially dependent velocities. The previously developed in‐plane velocity gradient methods can be easily integrated with this new through‐plane measurement to characterize the deformation of the myocardium in three spatial dimensions with high accuracy. The applicability of these methods is demonstrated theoretically, in phantoms and in vivo.
Dynamic electron spin resonance (ESR) imaging of the distribution of spin labeled dextran in a mouse
Authors: Kazama Shunsuke , Takashige Gou , Yoshioka Hisashi , Tanizawa Hisayuki , Ogata Tateaki , Koscielniak Janusz , Berliner Lawrence J. 
Published: March 2007

AbstractThe nitroxide group 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) was covalently bound to a dextran via an N‐acetamido linkage to produce a novel spin probe, TEMPO‐dextran (TEMPO‐DX), which circulates for long time periods in an animal without metabolic degradation. TEMPO‐DX was stable in mice, while small TEMPO analogs quickly disappeared after administration. Since dextran was reduced somewhat in size during synthesis, the resultant spin‐labeled dextran could be excreted through the kidney. A strong L‐band electron spin resonance signal was obtained shortly after Intravenous administration of TEMPO‐DX into the tail vein of a mouse, from which three‐dimensional images of specific organs were calculated. The signal was found to persist for well over 1 h.
Dynamic MR digital subtraction angiography using contrast enhancement, fast data acquisition, and complex subtraction
Authors: Wang Yi , Johnston Donald L. , Breen Jerome F. , Iii John Huston , Jack Clifford R. , Julsrud Paul R. , Kiely Michael J. , King Bernard F. , Riederer Stephen L. , Ehman Richard L. 
Published: March 2007

AbstractA dynamic MR angiography technique, MR digital subtraction angiography (MR DSA), is proposed using fast acquisition, contrast enhancement, and complex subtraction. When a bolus of contrast is injected into a patient, data acquisition begins, dynamically acquiring a thick slab using a fast gradient echo sequence for 10–100 s. Similar to x‐ray DSA, a mask is selected from the images without contrast enhancement, and later images are subtracted from the mask to generate angiograms. Complex subtraction is used to overcome the partial volume effects related to the phase difference between the flowing and stationary magnetization in a voxel. Vessel signal is the enhancement of flow magnetization resulting from the contrast bolus. MR DSA was performed in 28 patients, including vessels in the lungs, brains, legs, abdomen, and pelvis. All targeted vessels were well depicted with MR DSA. Corresponding dynamic information (contrast arrival time ta and duration of the arterial phase tav) was measured: ta/tav = 3.4/4.7 s for the lung, 10.3/4.9 s for the brain, 12.8/19.3 for the aorta, 15.2/12.6 s for the leg. MR DSA can provide dynamic angiographic images using a very short acquisition time.
Radial BURST imaging
Authors: Jakob Peter M. , Kober Frank , Haase Axel 
Published: March 2007

AbstractA radial BURST approach combining BURST excitations with projection reconstruction (PR) gradients for excitation and acquisition is introduced. With the application of PR gradients during excitation, the applied RF energy is distributed more homogeneously across the sample than in the initial BURST approach. Computer simulations of the radial BURST excitation scheme are presented and experimentally verified. Actual radial BURST implementation acquiring a 64 × 64 radial BURST image in 45 ms is reported. Extensions of the radial BURST imaging technique placing a magnetization preparation experiment in front of the whole imaging sequence are also described. Furthermore, the feasibility of combining radial BURST with a multishot approach is demonstrated.
Frequency offset corrected inversion (FOCI) pulses for use in localized spectroscopy
Authors: Ordidge Roger J. , Wylezinska Marzena , Hugg James W. , Butterworth Edward , Franconi Florence 
Published: March 2007

AbstractGradient localized spectroscopy techniques suffer from a well documented spatial localization error caused by the difference in chemical shifts between resonances. This results in the acquisition of spectra from partially overlapping spatial regions of the sample, with each resonance representing a different region. The image‐selected in vivo spectroscopy technique uses hyperbolic secant inversion pulses, where the main limitation in reducing this error is in the RF power available for application of the selective RF pulse. This spatial localization error may be dramatically reduced by increasing, and temporally shaping, the gradient pulse during slice‐selective spin inversion. The performance of these RF pulses have been experimentally verified.
Effect of ovariectomy on magnetic resonance T2* in rat femur
Authors: Checkley David , Millest Andrew J. , Johnstone Donna , Waterton John C. 
Published: March 2007

AbstractMeasurements have been made in the rat femur in vivo and ex vivo by using an asymmetric spin echo technique of T2′, the susceptibility contribution to T2*. The trabecular spacing in this study in rat bone is considerably less than in previous studies in the human. A significant increase in T2′ was seen in vivo 3 mm proximal to the growth plate with ovariectomy (a model of osteopenia), from 8.1 ± 0.7 to 10.0 ± 0.6 ms. Parallel changes in trabecular bone mineral density measured by quantitative computed tomography were found. T2′ was higher in living bones than in the same bones measured post mortem.
Measurement of Gd‐DTPA dialysis clearance rates by using a look‐locker imaging technique
Authors: Niendorf Eric R. , Santyr Giles E. , Brazy Peter C. , Grist Thomas M. 
Published: March 2007

AbstractThe exponential clearance rate constant, (k), and filtration fraction (FF) have been measured for dialysis of Gadoliniumdiethylenetriaminepentaacetic acid (Gd‐DTPA) (Magnevist, Berlex, Wayne, NJ) solutions by using a Look‐Locker imaging technique under conditions of flow. The measured values of k for the Baxter CA‐50, CA‐110, and CA‐210 filters were 0.0037 ± 0.0003, 0.0057 ± 0.0017, and 0.0092 ± 0.0018 min−1, respectively, for dialysis of 4.0 liters of aqueous Gd‐DTPA solutions. The measured values of FF for the Baxter CA‐110 and CA‐210 filters were 0.060 ± 0.013 and 0.089 ± 0.015, respectively, for dialysis of aqueous Gd‐DTPA at 350 ml/min. The k and FF measurements agree with values that use inversion recovery (IR) on static samples obtained by drawing aliquots of solution during the course of dialysis. This in vitro experiment suggests that accurate in vivo measurements of filtration fraction and glomerular filtration rate (GFR) may be possible.
3D MR angiography of pulmonary arteries using realtime navigator gating and magnetization preparation
Authors: Wang Yi , Rossman Phillip J. , Grimm Roger C. , Wilman Alan H. , Riederer Stephen J. , Ehman Richard L. 
Published: March 2007

AbstractAn ECG‐triggered magnetization‐prepared segmented 3D fast gradient echo sequence was developed to perform pulmonary arterial MR angiography. A selective inversion recovery pulse was used in the magnetization preparation to suppress venous vasculature. A real‐time gating technique based on navigator echoes was implemented to reduce respiration effects. Pencil‐beam navigator echoes were acquired immediately before and after the readout train and processed in real‐time to dynamically measure the diaphragm position, which was used to control data acquisition with an accept‐or‐reject‐reacquire logic. In a study of 10 volunteers, a gated 3D acquisition with 28 slices required on average approximately 4 min of acquisition time, and six to seven segmental arteries related to the interlobar trunk of the pulmonary artery were depicted. The use of SIR pulse reduced venous signal by 99%. The gated acquisitions were superior to the ungated acquisitions (n = 10, P < 0.005). The real‐time navigator gating technique is effective for reduction of respiration effects and thereby makes high resolution 3D MRA of the pulmonary arteries feasible.
Cardiac magnetic resonance fluoroscopy
Authors: Debbins Josef P. , Riederer Stephen J. , Rossman Phillip J. , Grimm Roger C. , Felmlee Joel P. , Breen Jerome F. , Ehman Richard L. 
Published: March 2007

AbstractA technique is described for high speed interactive imaging of the heart with either white or black blood contrast. Thirty‐two views of a segmented, magnetization‐prepared gradient echo sequence are acquired during diastole. Using three‐quarter partial Fourier sampling, data for a complete 128 × 128 image are acquired in three cardiac cycles. High speed reconstruction provides an image update of each cardiac cycle 159 ms after measurement. An independent graphical user interface facilitates interactive control of section localization and contrast by permitting pulse sequence parameter modification during scanning. The efficiency and image quality of the cardiac MR fluoroscopy technique were evaluated in 11 subjects. Compared with the conventional graphic prescription method, the cardiac fluoroscopy technique provides an approximate eightfold reduction in the time required to obtain subject‐specific double oblique sections. Image quality for these scout acquisitions performed during free breathing was sufficient to identify small cardiac structures.
High resolution intravascular MRI and MRS by using a catheter receiver coil
Authors: Atalar Ergin , Bottomley Paul A. , Ocali Ogan , Correia Luis C. L. , Kelemen Mark D. , Lima Joao A. C. , Zerhouni Elias A. 
Published: March 2007

AbstractPotentially important diagnostic information about atherosclerosis can be obtained by using magnetic resonance imaging and spectroscopy techniques. Because critical vessels such as the aorta, coronary arteries, and renal arteries are not near the surface of the body, surface coils are not adequate to increase the data quality to desired levels. A few catheter MR receiver coil designs have been proposed for imaging the walls of large blood vessels such as the aorta. These coils have limited longitudinal coverage and they are too thick to be placed into small vessels. A flexible, long and narrow receiver coil that can be placed on the tip of a catheter and will enable multi‐slice high resolution imaging of small vessels has been developed. The authors describe the theory of the coil design technique, derive formulae for the signal‐to‐noise ratio characteristics of the coil, and show examples of high resolution cross‐sectional images from isolated human aortas acquired by using this catheter coil. In addition, high resolution in vivo rabbit aorta images were obtained as well as a set of spatially resolved chemical shift spectra from a dog circumflex coronary artery.
Sensitivity‐enhanced echo‐planar MRI at 1.5T using a 5 × 5 mesh dome resonator
Authors: Meyer Kristen L. , Kim Karl , Li Tao , Tulipano Paola K. , Lee Kyoung‐Min , Delapaz Robert , Hirsch Joy , Ballon Douglas 
Published: March 2007

AbstractIn this work a 5 × 5 mesh dome resonator that has been optimized for functional brain imaging is presented. The resonator was reduced in length and diameter compared with previous versions to reduce sample losses, thus enhancing the signal‐to‐noise ratio of the acquired data. In addition, a 5 × 5 mesh design was employed, which offered improved axial homogeneity over an earlier 3 × 3 mesh version. The new resonator exhibited high sensitivity and good homogeneity over the brain volume, permitting analysis of functional activation over large areas of the cerebral cortex. In a direct comparison with a standard clinical head‐imaging resonator, the high sensitivity of the 5 × 5 mesh dome resonator resulted in greater statistical confidence in functional activation.
Wavelet encoding for 3D gradient‐echo MR imaging
Authors: Gelman Neil , Wood Michael L. 
Published: March 2007

AbstractAn implementation of wavelet encoding to resolve one spatial direction of a three‐dimensional gradient‐echo magnetic resonance image is described. This is the first report of the use of wavelet encoding with a relatively short repetition time for rapid image acquisition. An important feature of this implementation is that it allows wavelet‐encoded images to be reconstructed without phase correction. The images show no discernible degradation compared with images acquired with phase encoding or scaling‐function encoding instead of wavelet encoding. In addition to describing the implementation, typical sources of phase errors are investigated both theoretically and experimentally.
Fast 3D functional magnetic resonance imaging at 1.5 T with spiral acquisition
Authors: Yang Yihong , Glover Gary H. , van Gelderen Peter , Mattay Venkata S. , Santha Attanagoda K. S. , Sexton Roy H. , Ramsey Nick F. , Moonen Chrit T. W. , Weinberger Daniel R. , Frank Joseph A. , Duyn Jeff H. 
Published: March 2007

AbstractA new method to perform rapid 3D fMRI in human brain is introduced and evaluated in normal subjects, on a standard clinical scanner at 1.5 Tesla. The method combines a highly stable gradient echo technique with a spiral scan method, to detect brain activation related changes in blood oxygenation with high sensitivity. A motor activation paradigm with a duration of less than 5 min, performed on 10 subjects, consistently showed significant changes in signal intensity in the area of the motor cortex. In all subjects, these changes survived high statistical thresholds.