bluuebunny/crossref_metadata_2025_split huggingface dataset:
Multisection T1‐weighted hybrid‐rare: A pulse sequence for MR imaging of the entire liver during suspended respiration
Authors: Jara Hernán , Soto Jorge A. , Yu Beverly , Hentzen Peter C. , van Yperen Gert H. , Yucel E. Kent 
Published: March 2007

AbstractIt is shown that the maximum average‐data‐collection‐speed (ADCS) of multisection 2D hybrid‐RARE sequences is independent of TR and TEeff, and a monotonically increasing function of echo‐train‐length (ETL). This result was used in the design of an optimized T1‐weighted hybrid‐RARE sequence that produces 20 images of the abdomen in 31 s divided into four breath‐hold periods. The resulting ADCS is 58 lines in k‐space per second. Twenty‐four subjects (2 healthy volunteers and 22 patients) were imaged with a protocol that also included: (a) breath‐hold T1‐weighted FLASH which acquires data at 34 lines in k‐space per second (49 s scan time), and (b) T1‐weighted conventional spin‐echo (9:44 minutes scan time) with respiratory compensation. The experiments show that this T1‐weighted‐hybrid‐RARE sequence has: (1) a level of T1 weighting that is comparable with the conventional sequences, (2) very low vulnerability to susceptibility artifacts, (3) high data acquisition efficiency, and (4) higher SNR than T1‐weighted‐FLASH. In conclusion, the T1‐weighted‐hybrid‐RARE sequence described herein is an efficacious and reproducible technique for rapid imaging of the upper abdomen during suspended respiration.
Citrate signal enhancement with a homonuclear J‐refocusing modification to double‐echo PRESS sequences
Authors: Mulkern Robert V. , Bowers John L. , Peled Sharon , Kraft Robert A. , Williamson Daniel S. 
Published: March 2007

AbstractThe citrate signal at field strengths of whole body imagers arises from two sets of two strongly coupled methylene protons. This causes citrate spectra acquired with standard in vivo localization schemes like the double‐echo point resolved echo spectroscopy (PRESS) sequence to have complicated dependencies on timing parameters. A homonuclear J‐refo‐cused version of the double‐echo PRESS sequence that has previously been shown to completely remove J‐modulations from weakly coupled AX systems is considered for its potential in acquiring signal from the strongly coupled AB system of citrate. An analytic solution to the problem is derived with the density matrix formalism and verified both numerically and experimentally for 7 T conditions. The general expression for the AB signal is applied to study the 1.5 T citrate signal where a substantial signal enhancement over conventional double‐echo PRESS sequences is predicted and verified for echo times in the 150 to 300 ms range.
Commutator filter: A novel technique for the identification of structures producing significant susceptibility inhomogeneities and its application to functional MRI
Authors: Lai Song , Reichenbach Jürgen R. , Haacke E. Mark 
Published: March 2007

AbstractA robust postprocessing method to detect regions of magnetic field change is presented. High resolution gradient echo data is acquired to create a complex baseline image. From this image, two low resolution images are obtained by applying a low pass filter on the magnitude image and the complex image, respectively. Subtraction of the magnitude of the filtered complex image from the filtered magnitude image gives a new image called a commutator image in which regions of susceptibility‐induced field variation are greatly enhanced. Results on phantoms and applications to visualize paramagnetic venous blood vessels in the human brain are presented. The use of this technique on a 3D gradient echo data set represents a new approach to obtain an MR venogram. The application of this method to blood oxygenation level dependent (BOLD) functional brain MR imaging is demonstrated and the important role susceptibility plays in this model is verified.
Analysis of individual purine and pyrimidine nucleoside di‐ and triphosphates and other cellular metabolites in PCA extracts by using multinuclear high resolution NMR spectroscopy
Authors: Lutz Norbert W. , Yahi Nouara , Fantini Jacques , Cozzone Patrick J. 
Published: March 2007

AbstractThis work demonstrates thatindividualpurine and pyrimidine NDP and NTP can be assigned in high resolution31P NMR spectra from tissue extracts. To the best of our knowledge, it is shown for the first time that ATP, GTP, UTP, CTP, and the corresponding diphosphates can be quantitated in cell extracts without using HPLC or other biochemical methods. This work provides the basis for further optimization of nucleotide quantitation by31P NMR spectroscopy, and for a full assessment of this method. Furthermore, a new technique was developed for1H,31P, and13C NMR signal assignment and quantitation in cell extracts by using the same external reference capillary for all three nuclei. This allows for efficient, quantitative, multinuclear NMR spectroscopy without extract contamination by standard material.
Another interpretation of burst imaging as a variation of line projection imaging
Authors: Matsuda Tetsuya , Komori Masaru , Inoue Hiroshi , Hayashi Kohji , Kimura Toshihiko , Sasayama Shigetake 
Published: March 2007

AbstractBurst imaging and DUFIS realize fast imaging without rapid switching of magnetic field gradients. In this paper, some new aspects of burst imaging are explored. Interestingly, when one‐dimensional Fourier transform is applied, Burst imaging becomes similar to line projection scanning, a concept proposed earlier by Mansfield and Maudsley (P. Mansfield, A. A. Maudsley, Planar spin imaging by NMR. J. Magn. Resort. 27, 101‐119 (1977)). The line scanning interpretation is applied to two‐dimensional Burst imaging, and the relationship between its two‐dimensional k‐space trajectory and line scanning interpretation is discussed.
Temporally resolved 3D phase‐contrast imaging
Authors: Wigström Lars , Sjöqvist Lars , Wranne Bengt 
Published: March 2007

AbstractA conventional 3D phase contrast acquisition generates images with good spatial resolution, but often gives rise to artifacts due to pulsatile flow. 2D cine phase contrast, on the other hand, can register dynamic flow, but has a poor spatial resolution perpendicular to the imaging plane. A combination of both high spatial and temporal resolution may be advantageous in some cases, both in quantitative flow measurements and in MR angiography. The described 3D cine phase contrast pulse sequence creates a temporally resolved series of 3D data sets with velocity encoded data.
An alternative to GRASE: Toward spin‐echo‐like contrast with independent reconstruction of gradient‐echo images
Authors: Keller Paul J. , Karis John P. , Fram Evan K. , Heiserman Joseph E. , Drayer Burton P. 
Published: March 2007

AbstractMultiple gradient echoes are generated for each RF echo of a Carr‐Purcell‐Meiboom‐Gill (CPMG) train. Independently, phase‐encoded fast spin‐echo images are obtained from the different gradient echoes. Presently, three images are formed from three gradient‐echoes from each of four RF echoes. The two peripheral gradient echo images are encoded for a late effective TE, then summed after reconstruction: this image has decreased fat intensity and increased susceptibility contrast compared with fast spin echo. The central gradient echoes yielded another image of intermediate contrast useful for neuroimaging. Raw data from the variously timed gradient echoes are not combined as they are in GRASE.
Arterial input functions from MR phase imaging
Authors: Akbudak Erbil , Conturo Thomas E. 
Published: March 2007

AbstractA method is presented for obtaining high‐sensitivity arterial input functions following bolus intravenous contrast agent administration. Arterial contrast agent is monitored by phase reconstruction of single‐shot echo‐planar images. During bolus injections of a gadolinium (Gd) agent in a baboon, data were acquired at the mid‐abdominal aorta, and magnitude and phase‐shift images were reconstructed. Pair‐wise image subtraction was used to minimize phase aliasing. The phase‐based method is shown to have a significant potential improvement in sensitivity compared to the magnitude approach. The phase method also has a general linear response to concentration. This method may have potential utility in quantitative imaging of blood flow and contrast agent kinetics.
Visualization of dedicated catheters using fast scanning techniques with potential for MR‐guided vascular interventions
Authors: Bakker Chris J. , Hoogeveen Romhild M. , Weber Jan , van Vaals Joop J. , Viergever Max A. , Mali Willem P. 
Published: March 2007

AbstractThis paper reports the development of dedicated catheters and real‐time MR scan techniques for guiding vascular interventional procedures. By way of phantom experiments, it is shown that proper modification of the magnetic properties of catheters allows their conspicuous and consistent visualization in subsecond 2D gradient echo images and phase contrast angiograms. Dynamic scan times as low as 0.5 s could be achieved by exploiting the keyhole technique and purposeful postprocessing. The temporal resolution and spatial resolution of the resultant scan protocol shows promise for adequate tracking of catheter manipulation.
MR spectroscopic imaging and diffusion‐weighted MRI for early detection of kainate‐induced status epilepticus in the rat
Authors: Ebisum Toshihiko , Rooney William D. , Graham Steven H. , Mancuso Anthony , Weiner Michael W. , Maudsley Andrew A. 
Published: March 2007

AbstractPrevious studies have shown that reduction of N‐acetyl‐aspartate (NAA) is correlated with the degree of neuronal loss at 3 days after kainate‐induced status epilepticus in the rat. In this study, magnetic resonance spectroscopic imaging (MRSI), measurement of NAA and lactate, T2‐weighted MRI, and diffusion‐weighted MRI were used to study early alterations in rat piriform cortex at 12 and 26 h after kainate administration. The major findings are that decreased NAA signal, increased lactate signal, and decreased apparent diffusion coefficient (ADC) were observed at 12 h, with little evidence of histological and T2‐weighted MRI changes. These results support the hypothesis that NAA, lactate signals, and ADC provide sensitive methods for detection of early and minimal brain damage in vivo.
Finger printing of mycobacterium tuberculosis in patients with intracranial tuberculomas by using in vivo, ex vivo, and in vitro magnetic resonance spectroscopy
Authors: Gupta Rakesh K. , Roy Raja , Dev Ravi , Husain Mazhar , Poptani Harish , Pandey Rakesh , Kishore Janak , Bhaduri Amiya P. 
Published: March 2007

AbstractIn vivo, ex vivo, and in vitro proton magnetic resonance spectroscopy was performed in 12 patients with intracranial tuberculomas with an aim of detecting the biochemical constituents of Mycobacterium tuberculosis in a granuloma. One dimensional (1D) single pulse and spin‐echo sequences and 2D correlative spectroscopy were used for the ex vivo study to confirm the resonances seen on in vivo study. Spectroscopic studies of the perchloric acid and lipid extract of granuloma and M. tuberculosis were performed to look for similarity of resonance. In vivo study showed the presence of lipids at 0.9, 1.3, 2.0, 2.8 ppm, and phosphoserine at 3.7 ppm. All these resonances were confirmed on ex vivo study. In addition, distinct resonances of serine and phenolic lipids were seen on ex vivo and in vitro study of tuberculous granuloma, which have not been observed in other intracranial tumors. Lipid extract of granuloma and M. tuberculosis showed phenolic lipids at 7.1 and 7.4 ppm, a constituent of the cell wall of the bacteria in a tuberculoma. It appears that it may be possible to finger print the biochemicals of the cell wall of M. tuberculosis in a tuberculous granuloma and thus may help in detection and diagnosis of such lesions.
2D locally focused MRI: Applications to dynamic and spectroscopic imaging
Authors: Yao Lian , Cao Yue , Levin David N. 
Published: March 2007

AbstractConventional magnetic resonance images have uniform spatial resolution across the entire field of view. A method of creating MR images with user‐specified spatial resolution along one dimension of the field of view was described recently by the authors. This paper presents the 2D generalization of this technique, which allows the user to specify arbitrary spatial resolution in arbitrary 2D regions. These images are reconstructed from signals that sparsely sample the k‐space representation of the image. Therefore, locally focused images can be acquired in less time than that required by Fourier imaging with uniformly high resolution. In this paper the authors show how to increase the temporal resolution of dynamic imaging (e.g., interventional imaging) by using high resolution in areas of expected change and lower resolution elsewhere. Alternatively, by matching the local spatial resolution to the expected edge content of the image, it is possible to avoid the localized truncation artifacts that mark Fourier images reconstructed from the same number of signals. For example, the authors show how proton spectroscopic images of the head may be improved by using high resolution in the neighborhood of scalp lipids that might otherwise cause truncation artifacts.
Biexponential diffusion attenuation in various states of brain tissue: Implications for diffusion‐weighted imaging
Authors: Niendorf Thoralf , Dijkhuizen Rick M. , Norris David G. , van Lookeren Campagne Menno , Nicolay Klaas 
Published: March 2007

AbstractDiffusion‐weighted single voxel experiments conducted at b‐values up to 1 × 104 smm−2 yielded biexponential signal attenuation curves for both normal and ischemic brain. The relative fractions of the rapidly and slowly decaying components (f1, f2)are f1 = 0.80 ± 0.02, f2 = 0.17 ± 0.02 in healthy adult rat brain and f1 = 0.90 ± 0.02, f2 = 0.11 ± 0.01 in normal neonatal rat brain, whereas the corresponding values for the postmortem situation are f1 = 0.69 ± 0.02, f2 = 0.33 ± 0.02. It is demonstrated that the changes in f1 and f2 occur simultaneously to those in the extracellular and intracellular space fractions (fex, fin) during: (i) cell swelling after total circulatory arrest, and (ii) the recovery from N‐methyl‐D‐aspartate induced excitotoxic brain edema evoked by MK‐801, as measured by changes in the electrical impedance. Possible reasons for the discrepancy between the estimated magnitude components and the physiological values are presented and evaluated. Implications of the biexponential signal attenuation curves for diffusion‐weighted imaging experiments are discussed.
Improving MR quantification of regional blood volume with intravascular T1 contrast agents: Accuracy, precision, and water exchange
Authors: Donahue Kathleen M. , Weisskoff Robert M. , Chesler David A. , Kwong Kenneth K. , Bogdanov Alexei A. , Mandeville Joseph B. , Rosen Bruce R. 
Published: March 2007

AbstractThe goal of this work was to develop a comprehensive understanding of the relationship between vascular proton exchange rates and the accuracy and precision of tissue blood volume estimates using intravascular T1 contrast agents. Using computer simulations, the effects of vascular proton exchange and experimental pulse sequence parameters on measurement accuracy were quantified. T1 and signal measurements made in a rat model implanted with R3230 mammary adenocarcinoma tumors demonstrated that the theoretical findings are biologically relevant; data demonstrated that over‐simplified exchange models may result in measures of tumor, muscle, and liver blood volume fractions that depend on experimental parameters such as the vascular contrast concentration. As a solution to the measurement of blood volume in tissues with exchange that is unknown, methods that minimize exchange rate dependence were examined. Simulations that estimated both the accuracy and precision of such methods indicated that both the inversion recovery and the transverse‐spoiled gradient echo methods using a “noexchange” model provide the best trade‐off between accuracy and precision.
Pharmacokinetic changes induced by vasomodulators in kidneys, livers, muscles, and implanted tumors in rats as measured by dynamic Gd‐DTPA‐enhanced MRI
Authors: Su Min‐Ying , Wang Zhiheng , Roth Gerald M. , Lao Xiaoyan , Samoszuk Michael K. , Nalcioglu Orhan 
Published: March 2007

AbstractThe effects of three physiologically different vasomodulators, angiotensin II (a vasoconstrictor), hydralazine (a vasodilator), and histamine (a permeability modulator), on the pharmaco‐kinetics of entry of small molecules (measured by Gd‐DTPA concentration) into normal and abnormal tissue were studied in rats implanted with R3230 AC tumors. Sequential dynamic Gd‐DTPA‐enhanced MRI studies, one before and one after vasomodulator administration, were performed, and the signal intensities of various tissues analyzed. Angiotensin II (6 μg/kg) reduced blood flow in tumors, but increased it in muscles. Hydralazine (5 mg/kg) reduced blood flow in tumors, kidneys, and livers, and slowed Gd‐DTPA clearance from tumors, livers, and muscles. Histamine (25 μg/kg) increased renal blood flow, hastening Gd‐DTPA clearance causing reduced measurable blood flow in tumors and muscles. By simultaneously monitoring the effects in various tissues, the pharmacokinetic effect of each drug in the entire body could be obtained.
Lactate, N‐acetylaspartate, choline and creatine concentrations, and spin‐spin relaxation in thalamic and occipito‐parietal regions of developing human brain
Authors: Cady Ernest B. , Penrice Juliet , Amess Philip N. , Lorek Ann , Wylezinska Marzena , Aldridge Richard F. , Franconi Florence , Wyatt John S. , Reynolds E. Osmund R. 
Published: March 2007

AbstractPrevious studies of the brains of normal infants demonstrated lower lactate (Lac)/choline (Cho), Lac/creatine (Cr), and Lac/N‐acetylaspartate (Naa) peak‐area ratios in the thalamic region (predominantly gray matter) compared with occipitoparietal (mainly unmyelinated white matter) values. In the present study, thalamic Cho, Cr, and Naa concentrations between 32–42 weeks' gestational plus postnatal age were greater than occipito‐parietal: 4.6 ± 0.8 (mean ± SE), 10.5 ± 2.0, and 9.0 ± 0.7 versus 1.8 ± 0.6, 5.8 ± 1.5, and 3.4 ± 1.1 mmol/kg wet weight, respectively: Lac concentrations were similar, 2.7 ± 0.6 and 3.3 ± 1.3 mmol/kg wet weight, respectively. In the thalamic region, Cho and Naa T2s increased, and Cho and Lac concentrations decreased, during development. Lower thalamic Lac peak‐area ratios are principally due to higher thalamic concentrations of Cho, Cr, and Naa rather than less Lac. The high thalamic Cho concentration may relate to active myelination; the high thalamic Naa concentration may be due to advanced gray‐matter development including active myelination. Lac concentration is higher in neonatal than in adult brain.
Effect of 6‐aminonicotinamide on the pentose phosphate pathway: 31P NMR and tumor growth delay studies
Authors: Koutcher Jason A. , Alfieri Alan A. , Matei Cornelia , Meyer Kristen L. , Street James C. , Martin Daniel S. 
Published: March 2007

Abstract6‐aminonicotinamide (6AN) has been shown to enhance radio‐sensitivity in vitro, although previous in vivo studies failed to show an effect. 31P NMR spectra were obtained by using a one‐dimensional chemical shift imaging technique on a first generation transplant of the CD8FI spontaneous mammary carcinoma tumor model. Spectra were obtained both before and 10 h after treatment with 6AN (20 mg/kg). Changes in pH, nucleoside triphosphate/inorganic phosphate, and phosphocreatine/inorganic phosphate measured at 10 h post‐6AN were not significant. A new peak was detected 10 h post‐6AN, which was assigned to 6‐phosphogluconate (6PG), indicating inhibition of the pentose phosphate pathway (PPP). Based on the spectral data demonstrating inhibition of the PPP at 10 h post‐6AN, tumor‐bearing mice were irradiated (15 Gy × 3 fractions) on Days 1, 10 or 11, and 21 10 h after administration of 6‐aminonicotinamide (20 mg/kg). Tumor‐bearing mice receiving 6AN alone (20 mg/kg × 3), radiation alone (15 Gy × 3), or saline were also studied. Tumor growth delay studies indicated that 6AN alone induced a small but significant tumor growth delay (4.3 ± 0.8 days). Radiation alone induced a tumor growth delay of 34.5 ± 2.7 days. Treatment with 6AN followed by radiation induced a tumor growth delay of 57.0 ± 3.8 days. This was significantly greater than the TGD values for treatment with 6AN alone or radiation (P < 0.01). No complete regressions were noted after treatment with 6AN or radiation alone. Concomitant therapy with 6AN plus radiation yielded 6/28 complete regressions (21%), which was significantly greater than radiation (P < 0.05) or 6AN alone (P < 0.01) on this mammary carcinoma.
Toward a quantitative assessment of diffusion anisotropy
Authors: Pierpaoli Carlo , Basser Peter J. 
Published: March 2007

AbstractIndices of diffusion anisotropy calculated from diffusion coefficients acquired in two or three perpendicular directions are rotationally variant. In living monkey brain, these indices severely underestimate the degree of diffusion anisotropy. New indices calculated from the entire diffusion tensor are rotationally invariant (RI). They show that anisotropy is highly variable in different white matter regions depending on the degree of coherence of fiber tract directions. In structures with a regular, parallel fiber arrangement, water diffusivity in the direction parallel to the fibers (D| ≈ 1400–1800 × 10−6 mm2/s) is almost 10 times higher than the average diffusivity in directions perpendicular to them ((D + D⊥′)/2 ≈ 150–300 × 10−6 mm2/s), and is almost three times higher than previously reported. In structures where the fiber pattern is less coherent (e.g., where fiber bundles merge), diffusion anisotropy is significantly reduced. However, RI anisotropy indices are still susceptible to noise contamination. Monte Carlo simulations show that these indices are statistically biased, particularly those requiring sorting of the eigenvalues of the diffusion tensor based on their magnitude. A new intervoxel anisotropy index is proposed that locally averages inner products between diffusion tensors in neighboring voxels. This “lattice” RI index has an acceptably low error variance and is less susceptible to bias than any other RI anisotropy index proposed to date.
Unraveling diffusion constants in biological tissue by combining Carr‐Purcell‐Meiboom‐Gill imaging and pulsed field gradient NMR
Authors: van Dusschoten Dagmar , Moonen Chrit T. W. , de Jager P. Adrie , Van As Henk 
Published: March 2007

AbstractA diffusion‐weighted multi‐spin‐echo pulse sequence is presented, which allows for simultaneous measurement ofT2, the fractional amplitude, and the diffusion constant of different fractions. Monte Carlo simulations demonstrate an improvement of this sequence with respect to the accuracy of diffusion constant and fractional amplitude for slow exchange. Examples are shown for a simple phantom containing two fractions. In addition, experiments on cat brain in healthy condition and following occlusion of the middle cerebral artery show that the fractional amplitude and the diffusion constant of cerebral spinal fluid and normal brain tissue can be analyzed within each pixel with acceptable accuracy.