bluuebunny/crossref_metadata_2025_split huggingface dataset:
Intravascular magnetic resonance imaging using a loopless catheter antenna
Authors: Ocali Ogan , Atalar Ergin 
Published: March 2007

AbstractRecently, intravascular catheter probes have been developed to increase signal‐to‐noise ratio (SNR) for MR imaging of blood vessels. Miniaturization of these catheter probes without degrading their performances is very critical in imaging small vessels such as coronary arteries. Catheter coils have a loop incorporated in their structure and have limitations in physical dimensions and electromagnetic properties. The use of a loopless intravascular catheter antenna is proposed to overcome these problems. The catheter antenna is essentially a dipole, which makes a very thin diameter possible, and its electronic circuitry can be placed outside the blood vessels without performance degradation. The theoretical foundation for the design and operation of the catheter antenna is presented. Several catheter antennae, as small as 1.5 French, were constructed and tested on phantoms and rabbits with great success. The catheter antenna has a simple structure and is easy to design, implement, and operate.
Cerebrospinal fluid‐suppressed high‐resolution diffusion imaging of human brain
Authors: Falconer James C. , Narayana Ponnada A 
Published: March 2007

AbstractA cerebrospinal fluid (CSF)‐suppressed flow‐attenuated inversion recovery (FLAIR) double‐shot diffusion echo‐planar imaging (EPI) sequence was developed and used, along with a non‐CSF‐suppressed version of the sequence, to determine the extent of the contribution of CSF partial‐volume averaging to the apparent diffusion coefficients (ADCs) of normal human brain in vivo. Regional analysis indicates that cortical gray matter and parenchymal tissues bordering the ventricles are most affected by CSF contamination, leading to elevated ADC values. Only slight differences in gray‐ and white‐matter average ADCs were detected after CSF suppression. The human brain average ADCs calculated from high‐resolution CSF‐sup‐pressed diffusion‐weighted images in these studies are similar to those reported in animals. FLAIR diffusion sequences remove CSF as a source of error in ADC determination and ischemic lesion discrimination in diffusion‐weighted images (DWI) and ADC maps.
Techniques for high‐speed cardiac magnetic resonance imaging in rats and rabbits
Authors: Rehwald Wolfgang G. , Reeder Scott B. , McVeigh Elliot R. , Judd Robert M 
Published: March 2007

AbstractProgress in research on hypertension, heart failure, aging, post‐infarct remodeling, and the molecular basis of cardiovascular diseases in general has been greatly facilitated in recent years by the development of specialized small‐mam‐mal models by selective breeding and/or genetic alteration. Routine noninvasive evaluation of cardiac function and perfusion in these animals models, however, is difficult using existing methods. In principle, MRI can be used for this purpose, but in practice this is difficult because of problems related to RF coils, cardiac gating, and imaging pulse sequences. In this article, solutions to these problems are described that have allowed us to use MRI to routinely image the hearts of rats and rabbits. Specifically described are four RF coils, cardiac gating schemes, and an imaging pulse sequence specially designed for cardiac imaging in these animals on a 4.7 T Omega chemical‐shift imaging (CSI) spectrometer. These techniques can be used to obtain, within 2 min, eight double‐oblique short‐axis images of the rat at different cardiac phases with 200 × 400μm in‐plane resolution and a slice thickness of 2 mm. Moreover, myocardial tissue tagging can be performed with tag thicknesses and separations comparable to those used routinely in humans. The technical information is presented in sufficient detail to allow researchers at other sites to reproduce the results. This information should facilitate the use of MRI for the noninvasive examination of cardiac function and perfusion, which can be combined with other established techniques for the study of cardiovascular disease in specialized animal models.
Decoupled automated rotational and translational registration for functional MRI time series data: The dart registration algorithm
Authors: Maas Luis C. , deB. Frederick Blaise , Renshaw Perry F. 
Published: March 2007

AbstractA rapid, in‐plane image registration algorithm that accurately estimates and corrects for rotational and translational motion is described. This automated, one‐pass method achieves its computational efficiency by decoupling the estimation of rotation and translation, allowing the application of rapid cross‐correlation and cross‐spectrum techniques for the determination of displacement parameters. k‐space regridding and modulation techniques are used for image correction as alternatives to linear interpolation. The performance of this method was analyzed with simulations and echo‐planar image data from both phantoms and human subjects. The processing time for image registration on a Hewlett‐Packard 735/125 is 7.5 s for a 128 × 128 pixel image and 1.7 s for a 64 × 64 pixel image. Imaging phantom data demonstrate the accuracy of the method (mean rotational error, −0.09°; standard deviation = 0.17°; range, −0.44° to + 0.31°; mean translational error = −0.035 pixels; standard deviation = 0.054 pixels; range, −0.16 to + 0.06 pixels). Registered human functional imaging data demonstrate a significant reduction in motion artifacts such as linear trends in pixel time series and activation artifacts due to stimulus‐correlated motion. The advantages of this technique are its noniterative one‐pass nature, the reduction in image degradation as compared to previous methods, and the speed of computation.
Normal myocardial perfwsion assessed with multishot echo‐planar imaging
Authors: Schwitter Jürg , Debatin Jorg F. , von Schulthess Gustav K. , McKinnon Graeme C. 
Published: March 2007

AbstractA new magnetic resonance imaging strategy is presented for accessing myocardial perfusion. Most previous work has relied on using T1‐weighted fast gradient‐echo imaging to monitor dynamically the signal changes during the passage of a contrast media bolus. However, the gradient‐echo approach is limited by an inability to image the entire heart with adequate temporal resolution.This paper focuses on a electrocardiogram‐gated multishot echo‐planar imaging sequence, using the simple strategy of using the intrinsic T1 weighting produced by a repetition time equal to the heart period. To quantitate the sequence's performance with respect to normal myocardial perfusion, seven volunteers were imaged, each with three different doses of the contrast medium gadolinium diethylenetriamine penta‐acetic acid (Gd‐DTPA). The first‐pass dynamics of the contrast were quantified in 13 regions per heart for each examination.In all volunteers, the complete heart could be covered, with five to seven slices, every two heartbeats. Enhancement was homogeneous throughout the left ventricular myocardium, with an enhancement of approximately 50% for the optimum contrast dose of 0.05 mmol/kg Gd‐DTPA.
Prospective adaptive navigator correction for breath‐hold MR coronary angiography
Authors: McConnell Michael V. , Khasgiwala Vaibhav C. , Savord Bernard J. , Chen Ming Hui , Chuang Michael L. , Manning Warren J , Edelman Robert R. 
Published: March 2007

AbstractCurrent MR coronary angiography (MRCA) methods use breath‐holding to minimize respiratory motion. A major limitation to this technique is misregistration between imaging slices due to breath‐hold variability. Prospective adaptive correction of image location using real‐time navigator measurement of diaphragm position is a potential method for improving slice registration in breath‐hold MRCA. Ten subjects underwent MRCA using an ECG‐gated, fat‐suppressed, segmented k‐space, gradient‐echo sequence. Transverse and coronal images were acquired using standard breath‐holding with and without prospective navigator correction. Breath‐hold MRCA with prospective navigator correction resulted in a 47% reduction in craniocaudal slice registration error compared to standard breath‐holding (0.9 ± 0.2 mm versus 1.7 2 0.4 mm, P = 0.04). Prospective adaptive navigator correction of image location significantly improves slice registration for breath‐hold MRCA and is a promising motion correction technique for cardiac MR.
Magnetization and diffusion effects in NMR imaging of hyperpolarized substances
Authors: Gao Jia‐Hong , Lemen Lisa , Xiong Jinhu , Patyal Baldev , Fox Peter T. 
Published: March 2007

AbstractThe special magnetization characteristics of hyperpolarized noble gases have led to an interest in using these agents for new MRI applications. In this note, the magnetization effects and NMR signal dependence of two noble gases, 3He and 129Xe, are modeled across a range of gradient‐echo imaging parameters. Pulse‐sequence analysis shows a wide variation in optimum flip angles between imaging of gas (e.g., 3He or 129Xe) in air spaces (e.g., trachea and lung) and in blood vessels. To optimize imaging of the air spaces, it is also necessary to reduce the otherwise substantial signal losses from diffusion effects by increasing voxel size. The possibility of using hyperpolarized 129Xe for functional MRI (fMRI) is discussed in view of the results from the blood flow analysis. The short‐lived nature of the hyperpolarization opens up new possibilities, as well as new technical challenges, in its potential application as a blood‐flow tracer.
Peak assignment in localized 1H MR spectra of human muscle based on oral creatine supplementation
Authors: Kreis Roland , Koster Markus , Kamber Matthias , Hoppeler Hans , Boesch Chris 
Published: March 2007

Abstract1H‐MR spectra of human skeletal muscle feature peak splittings due to dipolar coupling. Quantitative difference spectroscopy in a double‐blind cross‐over trial testing oral creatine supplementation revealed that most of the resonances affected by dipolar coupling can be assigned to creatine and/or phosphocreatine. The assignment was performed in two different skeletal muscles and confirmed by measurements at the magic angle where dipolar splittings vanish. Numerical spectral simulations revealed that the observed spectra are consistent with partly‐averaged dipolar coupling among methylene and methyl protons of (phospho)creatine. The possible nature of the molecular dynamics leading to incomplete dipolar averaging is discussed.
Simultaneous 3D NMR spectroscopy of proton‐decoupled fluorine and phosphorus in human liver during 5‐fluorouracil chemotherapy
Authors: Gonen Oded , Murphy‐Boesch Joseph , Li Chun‐Wei , Padavic‐Shaller Kristin , Negendank William G. , Brown Truman R. 
Published: March 2007

AbstractSimultaneous acquisition of 1H‐decoupled 31P and 19F 3D CSI is demonstrated in the liver of a patient undergoing 5‐fluorouracil chemotherapy. Both 31P and 19F shared the same voxel size (64 or 27 ml), bi‐level 1H‐decoupling and 0.35 s TR. The measurements were done in a 1.5 Tesla clinical imager with three radio‐frequency (RF) channels and a triple‐tuned surface‐coil. The overall MRI and MRS examination time was under 90 min. Simultaneous acquisition of 31P and 19F permits localized study of the influence of hepatic metabolism on the uptake and catabolism of fluoropyrimidine drugs without extra measurement time or higher SAR.
Neuronal nitric oxide synthase mutant mice show smaller infarcts and attenuated apparent diffusion coefficient changes in the peri‐infarct zone during focal cerebral ischemia
Authors: Zaharchuk Greg , Hara Hideaki , Huang Paul L. , Fishman Mark C. , Moskowitz Michael A. , Jenkins Bruce G. , Rosen Bruce R. 
Published: March 2007

AbstractDiffusion‐weighted MRI at 2 T was used to monitor and assess tissue damage after permanent middle cerebral artery occlusion (MCAO) in wild‐type (WT) and mice deficient in nitric oxide synthase gene expression (nNOS−). The ischemic lesion was evaluated 3 h after occlusion and subdivided into the lesion core and peri‐infarct zone based on the magnitude of the apparent diffusion coefficient (ADC) change. Infarct volume, measured by using histochemical staining 24 h after MCA occlusion, correlated best with MRI infarct volume as assessed by an ADC threshold of 25% decrease from baseline at 3 h. For ADC thresholds of greater than 25% decrease, lesion size was not significantly different in nNOS− and WT mice. However, brain tissue showing ADC decreases of 10–25% was significantly smaller in the ipsilateral hemisphere of mutants (27 · 2% and 21 · 2% in WT and nNOS−, respectively; P < 0.05). These findings occurred independently of infarct volume and are consistent with a smaller peri‐infarct zone in nNOS− mice. We postulate that the smaller peri‐infarct zone is a reflection of less severe metabolic disturbance after ischemia in nNOS− mice, possibly related to diminished production of nitric oxide (NO) or a related product. We conclude that magnetic resonance techniques previously used to assess ischemic damage in larger animals can be extended to the mouse, raising the possibility that the molecular mechanisms leading to ischemic damage can be examined by using genetically engineered mice.
The sensitivity of low flip angle RARE imaging
Authors: Alsop David C. 
Published: March 2007

AbstractIt is demonstrated that the stability of the Carr‐Purcell‐Mei‐boom‐Gill (CPMG) sequence reflects the existence of a steady state solution to the Bloch equations in the absence of T2 and T1 decay. The steady state theory is then used to evaluate the performance of low flip angle RARE imaging sequences with both constant and optimally varied refocusing flip angles. The theory is experimentally verified in phantoms and then optimized, single shot, low flip angle RARE is used to obtain artifact‐free images from the brain of a normal volunteer.
In vivo MR microscopy of the human skin
Authors: Song Hee Kwon , Wehrli Felix W. , Ma Jingfei 
Published: March 2007

AbstractThe requirements for imaging the skin are dictated by the organ's layered structure, which extends only a few millimeters from the surface and thus demands extremely high resolution in this direction. While less critical, resolution in the remaining two dimensions determines whether the skin's accessory structures can be resolved. The problem is compounded by short transverse relaxation times, in particular of the dermis, the structure of most clinical interest. In this work images of the normal human skin were obtained in vivo at voxel sizes as small as 19 × 78 × 800 μm3, by means of customized 3D gradient and partial flip‐angle spin‐echo pulse sequences and very small transmit/receive coils on a 1.5T clinical imager equipped with high‐power whole‐body gradients. Structures resolved include hair follicles and the sublayers of the dermis. The very short time constant for the major component (91 %) for transverse relaxation in the dermis (T2* ∼10 ms) suggests the potential of substantial gains in achievable signal‐to‐noise ratio by shortening the echo time.
In vivo23Na NMR studies of myotonic dystrophy
Authors: Kushnir Tammar , Knubovets Tatyana , Itzchak Yacov , Eliav Uzi , Sadeh Menachem , Rapoport Lubov , Kott Edna , Navon Gil 
Published: March 2007

AbstractMyotonic dystrophy is an inherited multi‐system disease. Its pathophysiology leading to muscle malfunction and damage is not well understood. 23Na NMR spectroscopy was applied here for an in vivo comparative study of the calf muscles of 7 myotonic dystrophy patients at various stages of the disease and 11 healthy volunteers. Both the total sodium content, expressed as the ratio of the 23Na and 1H water signals, and the fast transverse relaxation time, T21, determined from the triple quantum‐filtered spectra, increased in correlation with the severity of the disease. The results demonstrate that 23Na NMR enables the quantitation of myotonic dystrophy progression.
In vivo observation of anisotropic motion of brain water using 2H double quantum filtered NMR spectroscopy
Authors: Assaf Yaniv , Navon Gil , Cohen Yoram 
Published: March 2007

AbstractThe 2H DQF NMR spectra of deuterated water molecules were measured for the first time in in vivo rat brain. The observation of the DQF signal indicates that there is a water population that exhibits anisotropic motion. The characteristics of the DQF spectra premortem and postmortem are very similar (lineshape and relaxation times). In the 1st h there is a 10–15% decrease in the signal intensity of the DQF spectra followed by a gradual but a much slower decrease in the DQF signal intensity that reaches 65–70% of its initial value after only 12 h. When the brains were kept at 4°C, a 40% decrease in the DQ signal intensity was observed only after 7 days. Mechanical chopping of the brain tissues causes an immediate loss of more that 97% of the DQ signals. The slow, temperature‐sensitive decay of the signal, and its sensitivity to mechanical treatment point out that these signals originate from water molecules that interact with structural components in the brain. The characteristics of the DQF spectra depend on the amount of bulk water as exemplified by increased residual quadrupolar interaction and relaxation rates obtained when dehydrating the brain tissue.
Proton MR spectroscopy of the normal human prostate with an endorectal coil and a double spin‐echo pulse sequence
Authors: Heerschap Arend , Jager Gerrit J. , Van Der Graaf Marinette , Barentsz Jelle O. , Ruijs Sjef H. J. 
Published: March 2007

AbstractThis report describes the use of an endorectal coil and a double spin‐echo pulse sequence for localized 1H MR spectroscopy of the normal prostate in volunteers. The spectra showed well‐resolved signals for citrate, (phospho)choline, and creatine protons. Additional signals were assigned to taurine and myoinositol protons. J modulation of the main and outer peaks of citrate could be monitored in vivo. Apparent relaxation times T1 and T2 have been estimated for the methyl protons of cholines and creatine. An effective T1 relaxation time was estimated for the main peaks of the citrate multiplet. Ratios of the integrals of these resonances have been evaluated, and tissue contents of choline and creatine were estimated using the H2O signal as an internal reference. Spectro‐scopic imaging experiments revealed a lower relative citrate signal in central parts of the prostate than in peripheral parts.
Quantitation of T2′ anisotropic effects on magnetic resonance bone mineral density measurement
Authors: Yablonskiy Dmitriy A. , Reinus William R. , Stark Helmut , Haacke E. Mark 
Published: March 2007

AbstractIn this paper, the authors quantitate the anisotropy of susceptibility effects in an uniaxial trabecular bone model and show its relevance to clinical MR bone mineral density measurements. A physical model is described that quantitates the anisotropic MR behavior of uniaxial trabecular bone. To test the model, a phantom of parallel polyethylene filaments was scanned every 15° between 0° and 90° with respect to the system's main magnetic field (B0). The distal radial metaphysis of a healthy female volunteer was scanned in orthogonal projections. The signal from each phantom image and each radial image was separated in a pixel‐wise fashion into R2 and R2′ maps. As predicted, R2′ relaxation showed anisotropic behavior and changed according to sin2 (ϕ), confirming that columnar structures parallel with B0 will cause no MR susceptibility effects. Scans of the distal radius showed that R2′ relaxation was twice as great with the forearm perpendicular to B0 as when it was parallel to it, demonstrating different contributions from struts and columns. For both phantom and radial bone scans, R2 relaxation was isotropic and did not change with object orientation.
1H chemical shift imaging reveals loss of brain tumor choline signal after administration of Gd‐contrast
Authors: Sijens Paul E. , Van Den Bent Martin J. , Nowak Peter J. C. M. , van Dijk Pieter , Oudkerk Matthijs 
Published: March 2007

Abstract1H MR spectra obtained by chemical shift imaging (CSI) of contrast‐enhancing brain tumors before and after the administration of Gd‐contrast agent were quantitated and compared with the results in normal brain tissue included in the volume of interest. Twenty‐seven combined magnetic resonance imaging and spectroscopy (MRI, MRS) examinations of brain tumor lesions included T1‐weighted MRI and CSI (TR/TE 1500/135 ms double‐spin echo) repeated 5–10 min after the administration of Gd‐contrast agent (0.1–0.2 mM). In 1H MR spectra of contrast‐enhancing tumor Gd‐contrast induced a mean loss of 15% of the peak area of choline‐containing compounds (Cho, P < 0.001) that was correlated with precontrast Cho linewidth (r = −0.72, P < 0.00001). This phenomenon limits the diagnostic use of brain tumor MRS examinations performed immediately after contrast‐enhanced MRI.
Correction for vascular artifacts in cerebral blood flow values measured by using arterial spin tagging techniques
Authors: Ye Frank Q. , Mattay Venkata S. , Jezzard Peter , Frank Joseph A. , Weinberger Daniel R. , McLaughlin Alan C. 
Published: March 2007

Abstract„Vascular”︁ artifacts can have substantial effects on human cerebral blood flow values calculated by using arterial spin tagging approaches. One vascular artifact arises from the contribution of „tagged”︁ arterial water spins to the observed change in brain water MR signal. This artifact can be reduced if large bipolar gradients are used to „crush”︁ the MR signal from moving arterial water spins. A second vascular artifact arises from relaxation of „tagged”︁ arterial blood during transit from the tagging plane to the capillary exchange site in the imaging slice. This artifact can be corrected if the arterial transit times are measured by using „dynamic”︁ spin tagging approaches. The mean transit time from the tagging plane to capillary exchange sites in a gray matter region of interest was calculated to be ∼0.94 s. Cerebral blood flow values calculated for seven normal volunteers agree reasonably well with values calculated by using radioactive tracer approaches.
A MRI spatial mapping technique for microvascular permeability and tissue blood volume based on macromolecular contrast agent distribution
Authors: Demsar Franci , Roberts Timothy P. L. , Schwickert Heidi C. , Shames David M. , Van Dijke Cornelis F. , Mann Jeffry S. , Saeed Maythem , Brasch Robert C. 
Published: March 2007

AbstractA rapid and automated method for two‐dimensional spatial depiction (mapping) of quantitative physiological tissue characteristics derived from contrast enhanced MR imaging was developed and tested in disease models of cancer, inflammation, and myocardial reperfusion injury. Specifically, an established two‐compartment kinetic model of unidirectional mass transport was implemented on a pixel‐by‐pixel basis to generate maps of tissue permeability surface area product (PS) and fractional blood volume (BV) based on dynamic MRI intensity data after administration of albumin‐(Gd‐DTPA)30, a prototype macromolecular contrast medium (MMCM) designed for blood pool enhancement. Maps of PS and BV in disease models of adenocarcinoma, intramuscular abscess inflammation, and myocardial reperfusion injury clearly depicted zones of increased permeability (up to approximately 500.μl/cc/h‐compared to <25 μl/cc/h in normal tissues). As revealed on PS maps, the rank ordering of studied permeability abnormalities was reperfusion injury > inflammation > tumors. A rapid, automated mapping technique derived from dynamic contrast‐enhanced MRI data can be used to facilitate the identification and characterization of pathophysiologic abnormalities, specifically relative increases in blood volume and/or microvascular permeability.