bluuebunny/crossref_metadata_2025 huggingface dataset:
A new semiautomated, three‐dimensional technique allowing precise quantification of total and regional cerebellar volume using MRI
Authors: Luft Andreas R. , Skalej Martin , Welte Dorothea , Kolb Rupert , Biirk Katrin , Schulz Jorg B. , Klockgether Thomas , Voigt Karsten
Published: March 2007

A new method was developed to measure total and regional cerebellar volumes using MRI. Previously, the volumes of the cerebellum and its substructure had been studied planimetri‐cally. The new method uses three‐dimensional semiautomated volumetry with focus on reliability and performance. The method consists of a manual presegmentation using landmark‐adjusted planes followed by region‐growing segmentation and calculation of volume. The cerebellum is partitioned into 11 regions defined by planes, which are adjusted for internal cerebellar landmarks (three radial regions inside the vermis that extend into the medial hemisphere (one‐fourth of the transverse diameter of the hemisphere); one region in the lateral hemisphere (remaining three‐fourths)). Forty‐six healthy volunteers were examined and the effects of age, gender, and symmetry were estimated. Shrinkage in the vermis (especially anterior superior compartment) was marked. Age effects diminished laterally and were not observed in the lateral hemisphere. Age effects on the total cerebellar volume were marginal. Effects of gender and symmetry were nonsignificant. Technique and results are discussed and related to methods and findings of others.
The effect of sample freezing on proton magic‐angle spinning NMR spectra of biological tissue
Authors: Middleton David A. , Bradley Daniel P. , Connor Susan C. , Mullins Paul G. , Reid David G.
Published: March 2007

Magic‐angle spinning (MAS) has recently been shown to enhance spectral resolution in NMR examinations of intact biological tissue ex vivo. This work demonstrates that freezing certain tissue samples before examination by 1H MAS NMR can have a marked effect on their spectra. Spectra of rat kidney after freezing in liquid nitrogen, compared with spectra before freezing, showed a significant increase in signal intensities from alanine (>100%), glutamine (>40%), and glycine (>100%), and a decrease in signals assigned to lipids and other macromolecules. Some resonances‐such as from leucine, valine, isoleucine, and aspartate‐only became visible after freezing the tissue. These observations suggest that low temperature storage of tissue necropsies or biopsies might affect the results of a MAS NMR analysis, possibly resulting in the misinterpretation of metabolite changes to pathogen or disease effects.
Three‐dimensional 87Rb imaging of isolated pig hearts: Effects of regional ischemia
Authors: Kupriyanov Valery V. , Shen Jie , Kuzio Bozena , Sun Jiankang , Deslauriers Roxanne
Published: March 2007

The aim of this work was to investigate whether 1) Rb uptake is reduced in ischemic myocardium, and 2) 87Rb three‐dimensional (3D) imaging can detect the ischemic area. Hearts of domestic pigs (n = 8, 20–30 kg) were perfused retrogradely with Krebs‐Henseleit buffer in a 7‐T, 40‐cm horizontal bore magnet interfaced with Bruker MSLX spectrometer. Control (C) and ischemic (I) (45 min ligation of the left anterior descending coronary artery (LAD)) hearts were loaded with Rb+ by perfusion with a Rb+‐containing solution (2–4.7 mM, 30–100% of K+ substitution) for 35 min and 87Rb (C) or 31P (ischemic area in I) spectra were acquired. After mechanical arrest with 0.6–0.9 mM lidocaine, 87Rb images (7 min each, 1 cm3 resolution) were acquired (30–40 min) in the presence of Rb+‐containing perfusate. Subsequently, the hearts were stained with Evans blue (EB) and samples taken for measurements of Rb+ content. In the Group C, distribution of Rb+ in the left ventricle and the intensities of the 3D 87Rb images were uniform. In the ischemic area (Group I), verified by the lack of EB staining and changes in 31P spectra, the images showed a reduced intensity, which corresponded to decreased Rb+ content (33 ± 11% of the normal). Thus, 87Rb imaging reveals damaged cells detecting reduced Rb+ content in the ischemic area.
Detecting natural abundance carbon signal of NAA metabolite within 12‐cm3 localized volume of human brain using 1H‐{13C} NMR spectroscopy
Authors: Chen Wei , Adriany Gregor , Zhu Xiao‐Hong , Gruetter Rolf , Ugurbil Kamil
Published: March 2007

NMR spectroscopy has been applied extensively to study metabolism noninvasively in the human brain and other tissues. However, it usually suffers from poor signal‐to‐noise ratio due to low NMR sensitivity and low metabolite concentrations. In this study, the technique of proton‐observe‐carbon‐edited (POCE) NMR spectroscopy combined with a single‐shot localization sequence was used to detect the natural abundance carbon signal of the amino acid N‐acetyl aspartate from a 12‐cm3 localized volume in the occipital lobe of humans at 4 T. The results suggest that NMR spectroscopy is sensitive enough to detect signals from low concentration metabolites (<60 nmol/g) from small volumes in the human brain within several minutes of data acquisition. This reveals that in vivo NMR spectroscopy is a promising technique for detecting small metabolite changes and low traces of 13C isotopic labeling for dynamic metabolism studies aimed at investigating physiological and pathological questions.
Targeting of ultrasmall superparamagnetic iron oxide (USPIO) particles to tumor cells in Vivo by using transferrin receptor pathways
Authors: Kresse Mayk , Wagner Susanne , Pfefferer Detlev , Lawaczeck Rüdiger , Elste Volker , Semmler Wolfhard
Published: March 2007

Human transferrin was covalently coupled to ultrasmall superparamagnetic iron oxide (USPIO) particles, and the trans‐ferrin‐USPIO obtained was investigated in vivo in experimental SMT/2A tumor‐bearing rats (rat mammary carcinoma). Physicochemical characterization showed an overall size of 36 nm (DLS) with a core size of 5 nm (TEM). Relaxivities were R,1 = 23.6 and R2 = 52.1 liter/mmol · s (0.47 T). Bound transferrin was 280 μg/mg of iron. Pharmacokinetic investigations revealed a half‐life of 17 min in normal rats. The MR evaluation of tumor signal intensity over time showed a 40% (range 25–55%) signal reduction 150 min after injection with the reduction persisting for at least 8 h. Control experiments using the parent USPIO compound or USPIO labeled with a nonspecific human serum albumin (HSA‐USPIO) showed a change of only 10% (range 5–15%) in tumor signal intensity over time. The results demonstrate that a combination of the USPIO relaxivity properties with the specificity of transferrin‐medi‐ated endocytosis allows in vivo detection of tumors by MR imaging.
A 16‐element phased‐array head coil
Authors: Porter Jay R. , Wright Steven M. , Reykowski Arne
Published: March 2007

Volume‐array coils offer increased signal‐to‐noise ratio (SNR) over standard volume coils near the array elements while preserving the SNR at the center of the volume. As the number of array elements is increased, the SNR advantage as well as the complexity of actually constructing the array increases also. In this study, a 16‐channel receive‐only array for imaging of the brain is demonstrated and compared to a circularly polarized (CP) head coil of similar shape and diameter. The array was formed from a 2 × 8 grid of square elements placed on a cylindrical form. Mutual coupling was minimized by a combination of overlapping element placement and current‐reducing matching networks. Simultaneous data acquisition from the 16 individual elements was performed using a four‐channel receiver system with each channel time domain multiplexed by a factor of 4. Theoretical and experimental comparisons between the array and a standard CP head coil show that the array offers an increase in SNR of nearly a factor of 3 near its surface while maintaining a comparable SNR to that of the CP head coil in the center of the region of interest.
Quantification of myocardial perhsion by MRI after coronary occlusion
Authors: Vallée Jean‐Paul M. , Sostman H. Dirk , Macfall James R. , Degrado Timothy R. , Zhang Jian , Sebbag Laurent , Cobb Fred R. , Wheeler Ted , Hedlund Larry W. , Turkington Timothy G. , Spritzer Charles E. , Coleman R. Edward
Published: March 2007

The objectives of this study were to define the relationship between the first order constant of Gd‐DTPA transfer (K1) and the myocardial blood flow (MBF) at rest and to compare it with an equivalent relationship obtained for positron emission tomography (PET). In a canine model of permanent coronary occlusion (n = 4), myocardial and blood time concentration curves obtained by 13N‐ammonia PET and Gd‐DTPA‐enhanced MRI were fitted by a one‐compartment model to determine K1. A linear relationship was observed between MRIderived K1 and MBF measured by microspheres (K1 = 0.88 × flow −0.015, R = 0.95), which compares favorably with the equivalent relationship derived from PET (K1 = 0.74 × flow +0.16, R = 0.88). The results of this preliminary study suggest that, at rest and distal to a permanently occluded coronary artery, myocardial perfusion quantification by MRI is possible and can challenge PET.
Integrated MRI assessment of regional function and perfusion in canine myocardial infarction
Authors: Kraitchman Dara L. , Young Alistair A. , Bloomgarden Daniel C. , Fayad Zahi A. , Dougherty Lawrence , Ferrari Victor A. , Boston Raymond C. , Axel Leon
Published: March 2007

A single integrated examination using regional measurements of perfusion from contrast‐enhanced MRI and three‐dimensional (3D) strain from tissue‐tagged MRI was developed to differentiate infarcted myocardium from adjacent tissue with functional abnormalities. Ten dogs were studied at baseline and 10 days after a 2‐hour occlusion of the left anterior descending coronary artery (LAD). Strain was determined using a 3D finite element model. Two‐dimensional measurements of hypoenhancing regions were highly correlated with myocardial viability (r = 0.96). Signal intensity versus time curves obtained from contrast‐enhanced MRI were used for quantitative perfusion analysis. The remote and adjacent noninfarcted tissue of the dogs with LAD occlusion, as well as the infarcted tissue, exhibited abnormal deformation patterns as compared to normal dogs positive predictive value (PPV) of strain determination of infarction = (66%). Integration of contrast‐enhanced MRI results with 3D strain analysis enabled the delineation of the myocardial infarction (PPV = 100%) from functionally compromised myocardium. This integrated cardiac examination shows promise for noninvasive serial assessment of potentially jeopardized noninfarcted myocardium to study the process of infarct remodeling and expansion.
Comparing individual signal‐averaged spectra
Authors: Spencer Richard G. S.
Published: March 2007

It is demonstrated here that individual signal‐averaged NMR spectra can be compared statistically in a rigorous fashion. This is accomplished by considering the ensemble of single acquisitions, which are summed to produce spectra. Applications of this concept include assessment of the statistical significance of apparent metabolite variations in control preparations and quantitative comparison of signals obtained during the fast response period in functional MRI.
Enhancement of nitroxide‐reducing activity in rats after chronic administration of vitamin E, vitamin C, and idebenone examined by an in Vivo electron spin resonance technique
Authors: Matsumoto Seiji , Mori Norio , Tsuchihashi Nobuaki , Ogata Tateaki , Lin Yijing , Yokoyama Hidekatsu , Ishida Shin‐Ichi
Published: March 2007

Rats were given vitamin E (vit‐E), idebenone (ID), or vitamin (C wit‐C) in their food for 2 or 4 weeks. After feeding, the ability of rats to reduce 4‐hydroxy‐2,2,6,6‐tetramethylpiperidine‐l‐oxyl (Tempol) in terms of the half‐life of Ternpol was examined as a specific marker. Ternpol was repeatedly injected intravenously, and its half‐life was serially evaluated by an in vivo electron spin resonance (ESR) technique. The radical‐reducing ability in rats was enhanced differently by Vit‐E, ID, and Vit‐C, i.e., slow onset of the ability after Vit‐E and ID (lipid‐soluble antioxidants) and fast onset after Vit‐C (a water‐soluble antioxidant).
A rapid 2D time‐resolved variable‐rate k‐space sampling MR technique for passive catheter tracking during endovascular procedures
Authors: Unal Orhan , Korosec Frank R. , Frayne Richard , Strother Charles M. , Mistretta Charles A.
Published: March 2007

A new, fast, 2D MR imaging technique allowing passive catheter visualization adequate for use as a tool for guiding the movement of a catheter during endovascular procedures is described. This imaging technique samples low spatial frequencies more often than high spatial frequencies; it also uses both k‐space view sharing and temporal interpolation. Unlike other techniques for passive visualization that exploit magnetic‐susceptibility–induced artifacts, we have adopted a strategy that takes advantage of the T1‐shortening effect of paramagnetic contrast agents, such as Gd‐DTPA and a projection dephaser. This not only permits visualization of the entire catheter length but also minimizes the risk of intravascular heating. Using this method, a temporal frame rate of up to eight images per second and a tip localization accuracy of ± 1mm (root mean square difference) can be achieved.
Measurement of tumor vascular volume and mean microvascular random flow velocity magnitude by dynamic GD‐DTPA‐Albumin enhanced and diffusion‐weighted MRI
Authors: Wang Zhiheng , Su Min‐Ying , Nalcioglu Orhan
Published: March 2007

Tumor vascular volume fraction and the magnitude of the mean microvascular random flow velocity were measured in an animal tumor model by combining dynamic Gd‐DTPA‐albumin enhanced MRI and diffusion‐weighted MRI in conjunction with a compartmental modeling analysis. The vascular volume fraction maps were obtained from the dynamic Gd‐DTPA‐albumin enhanced MRI measurement. It was found that the vascular volume fraction for Walker 256 tumor was higher within the outgrowing rim and decreased towards the central region. The average value obtained from five animals was 0.062 ± 0.009 ml/g. By using the vascular volume fraction from the Gd‐DTPA‐albumin enhanced MRI measurement, maps of the magnitude of the mean microvascular random flow velocity were obtained from the diffusion‐weighted MRI measurements with the compartmental modeling analysis. The relative extravascular and intravascular contributions to the diffusion‐weighted MRI signal were determined for three tissue groups with different Gd‐DTPA‐albumin enhancement characteristics, and the flow and molecular diffusion‐induced attenuation factors for the intravascular compartment were also compared. The mean microvascular random flow velocity magnitude maps were obtained with an average value of 0.67 ± 0.06 mm/s.
Diffusional anisotropy of T2 components in bovine optic nerve
Authors: Stanisz Greg J. , Henkelman R. Mark
Published: March 2007

A diffusion‐CPMG hybrid experiment was used to analyze the diffusion characteristics of different T2 relaxation components in bovine optic nerve. Data were collected using a pulsed field gradient (PFG) multi spin echo (MSE) CPMG sequence for parallel and perpendicular axon orientation and four diffusion times. The apparent diffusion coefficient (ADC) was evaluated for two observed T2 components as a function of axonal orientation and diffusion time Δ. The short T2 component exhibited minor diffusional anisotropy and larger ADC, whereas the long T2 component showed significant anisotropy effects. This is consistent with the hypothesis that the short T2 component is associated with water within the myelin sheath, which is less restricted than axonal water that is limited by cell membrane permeability.
Functional MRI of the rat somatosensory cortex: Effects of hyperventilation
Authors: Hsu Edward W. , Hedlund Laurence W. , MacFall James R.
Published: March 2007

Functional mapping of the rat somatosensory cortex was performed with T2*‐sensitized MRI using a forepaw electrical stimulation model in α‐chloralose‐anesthetized rats at 7 T under both normocapnia and mild hyperventilation‐induced hypocapnia. A highly localized activation area, consistent with the known somatosensory cortical region, was detected in all seven animals studied during hypocapnia and in five of the same animals during normocapnia. Quantitatively, hypocapnia was found to significantly increase both the size of the fMRl activation area (3.4 ± 0.6 mm2 versus 1.5 ± 0.6 mm2 in normocapnia, mean ± standard error, n = 7, P < 0.03) and the average fMRl signal intensity increase (3.4 ± 0.6% versus 2.7 ± 0.4%, n = 5, P < 0.05). The increased sensitivity of fMRl to functional activation may reflect a widened arterial‐venous oxygenation difference resulting from an increased effective oxygen extraction during hyperventilation. The dependence of the fMRl response on the ventilation state underscores the need to control for physiological parameters in animal fMRl studies.
Feature space analysis of MRI
Authors: Soltanian‐Zadeh Hamid , Windham Joe P. , Peck Donald J. , Mikkelsen Tom
Published: March 2007

This paper presents an MRI feature‐space image‐analysis method and its application to brain tumor studies. The proposed method generates a transformed feature space in which the normal tissues (white matter, gray matter, and CSF) become orthonormal. As such, the method is expected to have site‐to‐site and patient‐to‐patient consistency, and is useful for identification of tissue types, segmentation of tissues, and quantitative measurements on tissues. The steps of the work accomplished are as follows: (1) Four T2‐weighted and two T1‐weighted images (before and after injection of gadolinium) were acquired for 10 tumor patients. (2) Images were analyzed by an image analyst according to the proposed algorithm. (3) Biopsy samples were extracted from each patient and were subsequently analyzed by the pathology laboratory. (4) Image‐analysis results were compared with the biopsy results. Pre‐ and postsurgery feature spaces were also compared. The proposed method made it possible to visualize the MRI feature space and to segment the image. In all cases, the operators were able to find clusters for normal and abnorma tissues. Also, clusters for different zones of the tumor were found. The method successfully segmented the image into normal tissues (white matter, gray matter, and CSF) and different zones of the lesion (tumor, cyst, edema, radiation necrosis, necrotic core, and infiltrated tumor). The results agreed with those obtained from the biopsy samples. Comparison of pre‐ with postsurgery and radiation feature spaces illustrated that the original solid tumor was not present in the second study, but a new tissue component appeared in a different location of the feature space. This tissue could be radiation necrosis generated as a result of radiation.
Sampling errors in projection reconstruction MRI
Authors: Joseph Peter M.
Published: March 2007

Certain kinds of artifacts have been reported when projection reconstruction (PR) techniques are used in magnetic resonance imaging (MRI). These will occur if the spacing between samples in k‐space is too large. It has been suggested that PR requires finer k‐space sampling than does two‐dimensional Fourier reconstruction, and that the usual Nyquist criterion is inadequate. This paper examines this problem, with the conclusion that the Nyquist sampling criterion is adequate to avoid aliasing effects, provided that a band‐limited interpolation is used in k‐space. This procedure is motivated by analysis of the PR technique as it is commonly implemented in x‐ray computed tomography. A related problem is shown to be the construction of a filter function in k‐space that gives proper weight to the low spatial frequencies. It is shown that a simple k filter does not satisfy this requirement, and a procedure for deriving a suitable filter is described. The methods are tested in simulated PR profiles of circular disks of two different sizes. It is shown that the combination of the two new methods gives virtually perfect reconstruction for disks up to the size implied by the Nyquist limit.
Partial fourier reconstruction for three‐dimensional gradient echo functional MRI: Comparison of phase correction methods
Authors: Stenger V. Andrew , Noll Douglas C. , Boada Fernando E.
Published: March 2007

Partial Fourier (PF) methods take advantage of data symmetry to allow for either faster image acquisition or increased image resolution, Faster acquisition and increased spatial resolution are advantageous for fMRl because of increased temporal resolution and/or reduced partial volume effects, respectively. Standard PF methods, which use a phase reference obtained from a low resolution image, are adequate for the reconstruction of time‐stationary images acquired using either spin echoes or short TE gradient echoes. In fMRI, however, multiple images are acquired using long TE gradient echoes, which introduces possible phase drifts in the fMRl data and high spatial frequencies in the phase reference. This work investigates several techniques developed to reconstruct fMRl data obtained with PF acquisitions. PF methods that account for both high‐frequency spatial variations and time‐dependent drifts in the phase reference are discussed and are quantitatively evaluated using receiver operator characteristic curve analysis.
Optimization of chemical shift selective suppression of fat
Authors: Kuroda Kagayaki , Oshio Koichi , Mulkern Robert V. , Jolesz Ferenc A.
Published: March 2007

Strategies to optimize flip angles for chemical shift selective fat suppression are discussed. Mathematical models for fat suppression in spoiled gradient recalled acquisition, spin echo, and RARE, which incorporate steady state conditions and multiple spectral components of fat, are developed. The optimal suppression flip angle is found to be larger than that determined with a single fat component model by more than 10° due to contributions from unflipped components such as olefinic and glycerol protons that lie outside the suppression band.
A motion correction scheme by twin‐echo navigation for diffusion‐weighted magnetic resonance imaging with multiple RF echo acquisition
Authors: Mori Susumu , van Zijl Peter C. M.
Published: March 2007

In this paper, a series of diffusion‐weighted fast spin‐echo (FSE) sequences with a new motion correction scheme are introduced. This correction scheme is based on the navigator echo technique. Unlike conventional spin‐echo imaging, motion correction for FSE is complicated by the phase oscillation between odd‐numbered and even‐numbered echoes and the complex phase relationship between spin echo and stimulated echo components. In our approach, incoherent phase shifting due to motion is monitored by consecutive acquisition of two navigator echoes, which provide information on both inter‐echo and intra‐echo train phase shifts. Applications to both phantom and in vivo studies are presented.
Quantification of intravascular and extravascular contributions to BOLD effects induced by alteration in oxygenation or intravascular contrast agents
Authors: Zhong Jianhui , Kennan Richard P. , Fulbright Robert K. , Gore John C.
Published: March 2007

A simple model is presented that allows quantitative separation of the contributions of signals from water in blood and extravascular parenchyma due to changes in blood oxygenation, induced either by brain activation or by alteration of inspired oxygen. The separation is based on the progressive attenuation of the signals in the vasculature of different levels when bipolar field gradient pulses are applied. Diffusion‐weighted spin‐echo echo‐planar imaging sequences were used to measure signal changes under various conditions in both animals and human volunteers. Normoxic‐hyperoxic episodes were induced in rats before and after injection of a superparamagnetic iron oxide contrast agent. Signal changes produced by visual stimulation were measured in human volunteers, and in volunteers subject to alternating normoxic‐hyperoxic episodes, and with administration of Gd‐DTPA. Analysis of the results with our simple model suggests that the apparent diffusion coefficient increases and R2 ( = 1/T2) decreases upon brain activation, with a large component from extravascular water related to the decrease in the blood de‐oxyhemoglobin concentration. Furthermore, this study suggests that apparent diffusion coefficient of the extravascular component alone may provide localization of neuronal activation.
Evidence of muscle BOLD effect revealed by simultaneous interleaved gradient‐echo NMRI and myoglobin NMRS during leg ischemia
Authors: Lebon Vincent , Brillault‐Salvat Cécile , Bloch Gilles , Leroy‐Willig Anne , Carlier Pierre G.
Published: March 2007

The purpose of this work was to investigate the temporal relationship between intensity changes in T2*‐weighted NMR images and tissue oxygen content, measured by myoglobin proton NMR spectroscopy, in the skeletal muscle. During an ischemic stress test, the calf muscles of five healthy volunteers were studied at 3 Tesla. An interleaved NMRI‐NMRS sequence was used, which made it possible to record T2*‐weighted images and myoglobin spectra simultaneously. During ischemia, rapid changes in muscle signal intensity were observed on T2*‐weighted images, which immediately preceded myoglobin desaturation. Bearing in mind the respective P50 of hemoglobin and myoglobin, this observation clearly favored the hypothesis that hemoglobin desaturation was responsible for the changes in T2*. This interpretation was further supported by the temporal coincidence between the experimental NMR data and a model of hemoglobin desaturation solely derived from physiological considerations.
Accurate determination of spin‐density and T1 in the presence of RF‐field inhomogeneities and flip‐angle miscalibration
Authors: Venkatesan Ramesh , Lin Weili , Haacke E. Mark
Published: March 2007

A method is presented for the accurate extraction of relative spin‐density (ρo) and spin‐lattice relaxation time (T1) in the presence of RF‐field inhomogeneities and flip‐angle miscalibration. The method requires collecting images at several flip‐angles with a three‐dimensional, spoiled steady‐state, gradient‐echo imaging sequence. Results show that the predominant effect of an overestimated flip‐angle is to shift the T1 estimate to a higher value, whereas reductions in the normalized RF‐field from unity cause ρo and T1 distributions to be skewed toward lower values. Phantom and in vivo results demonstrate that the proposed method overcomes both of these systematic errors. The method was shown to be valid for up to a 50% reduction in RF sensitivity. A self‐consistency argument was used to validate the absence of systematic errors in the extracted ρo and T1 values over a large number of voxels. This made it possible to obtain a very precise estimate of muscle T1 at 1.5 T, yielding a 95% confidence interval of (1077.7 ± 3.5) ms.
One‐shot spatially resolved velocity imaging
Authors: Luk Pat Gerard T. , Pauly John M. , Hu Bob S. , Nishimura Dwight G.
Published: March 2007

For quantitative velocity measurement, we have developed a technique that acquires full velocity spectra without cardiac gating. After a cylindrical excitation restricts imaging to one spatial dimension, data are acquired while an oscillating gradient is played out. After each excitation, an image of velocity versus spatial location is obtained. For a given spatial location, a series of these images can be used to form an image of velocity versus time. Acquisition times are much shorter than for phase‐contrast imaging or Fourier‐encoded velocity imaging, obviating the need for cardiac gating. Although a two‐shot version of this technique has been presented previously, we have developed a one‐shot version that offers higher temporal resolution for a given velocity resolution and superior off‐resonance properties.
Evaluation of respiratory artifact correction techniques in multishot spiral functional mri using receiver operator characteristic analyses
Authors: Noll Douglas C. , Genovese Christopher R. , Vazquez Alberto L. , O'Brien Jennifer L. , Eddy William F.
Published: March 2007

Navigator corrections and low‐spatial frequency (LSF) over‐sampling are investigated as methods for reducing respiration‐related effects in multishot functional MRI. Both techniques take advantage of the smoothly varying or nearly constant phase variations linked to the respiration cycle. These techniques were tested in functional MRI studies with spiralk‐space acquisitions. Receiver operator characteristic (ROC) analyses and the temporal variance averaged across the brain were used to evaluate their effectiveness. Both methods were found to increase the area under the ROC curve and to reduce the standard deviation, with the LSF oversampling method being more effective.
Quantitation of circumferential subpixel vessel wall position and wall shear stress by multiple sectored three‐dimensional paraboloid modeling of velocity encoded cine MR
Authors: Oyre Sten , Ringgaard Steffen , Kozerke Sebastian , Paaske William P. , Scheidegger Markus B. , Boesiger Peter , Pedersen Erik M.
Published: March 2007

Methods are lacking for accurate, noninvasive circumferential edge detection and wall shear stress calculation. Using stan dard MR phase contrast sequences, parts of the velocity pro files were fitted to a multiple sectored three‐dimensional pa raboloid model enabling exact calculation of vessel wall position and wall shear stress in 24 locations evenly distrib uted around the luminal vessel wall. The model was evaluated by in vitro scans and computer simulations and applied to the common carotid artery of humans. In vitro, the luminal area of a glass tube was assessed with an error of 0.9%. Computer simulations of peak systolic data revealed errors of ±0.9% (vessel area) and ±3.25% (wall shear stress). The in vivo results showed substantial difference between anterior and posterior wall shear stress values due to skewed velocity profiles. A new noninvasive method for highly accurate mea surement of circumferential subpixel vessel wall position and wall shear stress has been developed.
Simultaneous oxygenation and perfbsion imaging study of functional activity in primary visual cortex at different visual stimulation frequency: Quantitative correlation between BOLD and CBF changes
Authors: Zhu Xiao‐Hong , Kim Seong‐Gi , Andersen Peter , Ogawa Seiji , Uğgurbil Kamil , Chen Wei
Published: March 2007

A relationship between regional cerebral blood flow (CBF) and blood oxygenation level dependent (BOLD) changes in the primary visual cortex (V1) at varied visual stimulation fre quency has been examined quantitatively using the multislice FAIR technique. A linear correlation in the common activation areas between functional BOLD and CBF maps was observed. This supports the hypothesis that the task‐stimulated BOLD changes in microvasculature are correlated with the CBF changes that presumably reflect the degree of neuronal ac tivity. The linear correlation coefficients for intrasubject com parisons are more significant than those for intersubject com parisons. This suggests that using intrasubject comparisons for quantitative studies of neuronal activity related to different task stimuli and task performances should be more reliable than using intersubject comparisons.
Proton double‐quantum filtered MRI—A new method for imaging ordered tissues
Authors: Tsoref Liat , Shinar Hadassah , Seo Yoshiteru , Eliav Uzi , Navon Gil
Published: March 2007

The imaging of connective tissues such as cartilage and ten dons using standard MRI techniques is hampered by their low signal relative to the surrounding tissues. 1H double‐quantum filtered (DQF) MRI is an imaging method that detects mole cules associated with ordered structures, while the signal from isotropic fluids is filtered out, thus creating a new type of contrast. The technique is demonstrated on an intact rat tail, where the image of the tendons is highlighted. Although the signal‐to‐noise ratio is inferior to that in gradient‐echo MRI, the contrast between the tendons and the surrounding tissues is significantly better in the DQF MRI. It is demonstrated how, by adjusting the parameters of the DQF imaging pulse se quence, one can modify the contrast and enhance the images of specific compartments within an organ. A comparison with 2H DQF imaging of the same tissue is also given.
Synthesis and preliminary evaluation of MP‐2269: A novel, nonaromatic small‐molecule blood‐pool MR contrast agent
Authors: Wallace Rebecca A. , Haar Joe P. , Miller Donald B. , Woulfe Steven R. , Polta John A. , Galen Karen P. , Hynes Michael R. , Adzamli Kofi
Published: March 2007

A nonaromatic, small‐molecule, gadolinium(3+)‐chelate code named MP‐2269 was synthesized and evaluated in animals as a potential MR contrast agent for blood pool. The ligand of MP‐2269 was prepared by conjugating a lipophilic, albumin‐binding moiety, 4‐pentylbicyclo[2.2.2]octane‐1‐carboxylic acid, to an amino‐functionalized DTPA derivative by means of a diaspartic acid linker. Proton relaxometry studies in vitro yielded spin‐lattice relaxivities (R1) for MP‐2269 of 6.2, 20.0 and 26.1 mM−1 sec−1 in water, rabbit blood, and human blood, respectively. The enhanced relaxivities in blood indicate sig nificant binding of the agent to blood proteins. At a dose of 45 μmol/kg, MP‐2269 showed a biphasic rabbit blood clearance profile with half‐lives of 4.7 and 142 minutes, respectively, for the fast and slow components. In rats, the agent is cleared predominantly through the hepatobiliary pathway (∼70% in 24 h by this mode). The LD50 value of MP‐2269 is ∼3.0 mmol/kg in mice. Preliminary MR angiograms obtained in the rabbit showed excellent enhancement of blood vessels. Hence, MP‐2269 has potential for future exploitation as a contrast agent for MR angiography.
A comparison between magnetization transfer ratios and myelin water percentages in normals and multiple sclerosis patients
Authors: Vavasour Irene M. , Whittall Kenneth P. , Mackay Alex L. , Li David K. B. , Vorobeychik Galina , Paty Donald W.
Published: March 2007

Magnetization transfer and T2 relaxation data were obtained for five white and six gray matter brain structures from 10 normal volunteers and 9 multiple sclerosis patients. Thirty MS lesions were also anatyzed. Magnetization transfer ratios and myelin water percentages were compared. Both techniques showed a significant difference between the average of white and gray matter of the normal volunteers as well as the average of nor mal‐appearing white matter and gray matter of the multiple sclerosis patients. The average magnetization transfer ratio and myelin water percentage for lesions were significantly lower than those of normal‐appearing white matter. Myelin water per centages and magnetization transfer ratios were uncorrelated in white and gray matter but showed a small (R = 0.5, P = 0.005) but significant correlation in multiple sclerosis lesions. In sum mary, the myelin water percentage and the magnetization trans fer ratio provide quantifiable but largely independent measures of multiple sclerosis lesion pathology.
Polar sampling in k‐space: Reconstruction effects
Authors: Lauzon M. Louis , Rutt Brian K.
Published: March 2007

Magnetic resonance images are most commonly computed by taking the inverse Fourier transform of the k‐space data. This transformation can potentially create artifacts in the im age, depending on the reconstruction algorithm used. For equally spaced radial and azimuthal k‐space polar sampling, both gridding and convolution backprojection are applicable. However, these algorithms potentially can yield different res olution, signal‐to‐noise ratio, and aliasing characteristics in the reconstructed image. Here, these effects are analyzed and their tradeoffs are discussed. It is shown that, provided the modulation transfer function and the signal‐to‐noise ratio are considered together, these algorithms perform similarly. In contrast, their aliasing behavior is different, since their re spective point spread functions (PSF) differ. In gridding, the PSF is composed of the mainlobe and ringlobes that lead to aliasing. Conversely, there are no ringlobes in the convolution backprojection PSF, thus radial aliasing effects are mini mized. Also, a hybrid gridding and convolution backprojection reconstruction is presented for radially nonequidistant k‐space polar sampling.
In vivo lactate and β‐hydroxybutyrate editing using a pure‐phase refocusing pulse train
Authors: Shen Jun , Novotny Edward J. , Rothman Douglas L.
Published: March 2007

A refocusing pulse train consisting of a semiselective refo cusing pulse and a selective inversion pulse to obtain a pure‐phase refocusing at the frequency of maximal excitation of the semiselective refocusing pulse is proposed and applied to in vivo lactate and β‐hydroxybutyrate editing using difference spectroscopy. It is shown, using both rotation matrix theory and phantom experiments, that the soft inversion pulse has to be halved to flank the semiselective pulse to obtain perfect refocusing and cancellation of interfering resonances. The editing method is used to obtain lactate and β‐hydroxybu‐tyrate spectra from the occipital cortex of juvenile epilepsy patients before and after ketogenic diet treatment.
In vivo gradient echo microimaging of rodent spinal cord at 7 T
Authors: Meyerand Mary E. , Cremillieux Yannick , Wadghiri Youssef Zaim , Azzawi Ali , Hoopes Paul J. , Dunn Jeffrey F.
Published: March 2007

An optimization scheme was developed for gradient echo imaging using a half‐birdcage RF coil at 7 T to obtain maximal contrast between gray and white matter in the spinal cord of rodents. This optimization was combined with microimaging techniques to obtain in vivo pixel sizes of 78 × 78 × 700 μm. These techniques can be implemented in an in vivo study to investigate the myelin structure within the white matter of the rodent spinal cord.
NMR imaging of changes in vascular morphology due to tumor angiogenesis
Authors: Dennie Joelle , Mandeville Joseph B. , Boxerman Jerrold L. , Packard Scott D. , Rosen Bruce R. , Weisskoff Robert M.
Published: March 2007

Tumor‐sprouted vessels are greater in both number and diameter in comparison to their healthy counterparts. A novel technique based on magnetic susceptibility contrast mechanisms that are sensitive to varying sizes of blood vessels is presented to measure differences between the relaxation rates (1/T2 and 1/T) in a rat glioma model and normal cerebral cortex. ΔR2 and ΔR2*, the differences between relaxation rates precontrast and postcontrast agent injection, were measured for an intravascular equilibrium contrast agent (MION) at various echo times. Since ΔR2*/ΔR2 increases as vessel size increases, this ratio can be used as a measure of the average vessel size within an ROI or a voxel. The stability and longevity of the contrast agent within the vasculature were verified (n = 2 trials), and the ratio of ΔR2*/ΔR2 between the tumor and normal cortex was measured to be 1.9 ± 0.2 (n = 4, echo time = 20 ms, and susceptibility difference (Δχ) ≈︁ 10−6). This ratio compared favorably to a predicted ratio determined using histologically determined vessel sizes and theoretical Monte Carlo modeling results (1.9 ± 0.1). Maps of the ratio of ΔR2*/ΔR2 were also made on a pixel‐by‐pixel basis. These techniques support the hypothesis that susceptibility contrast MRI can provide useful quantitative metrics of in vivo tumor vascular morphology.
EPISTAR MRI: Multislice mapping of cerebral blood flow
Authors: Edelman Robert R. , Chen Qun
Published: March 2007

A method is described for multislice EPISTAR that perfectly compensates magnetization transfer effects. lnflowing arterial spins are labeled with a 360° adiabatic pulse. Two control tags are applied sequentially at the same location as the labeling pulse, each with a 180° adiabatic pulse so the total RF irradiation, frequency shift, and bandwidth of the labeling and control pulses are identical. Therefore, magnetization transfer effects are the same as for the labeling pulse and cancel with image subtraction for all slices. The method also eliminates tagging of venous spins and concern about asymmetric magnetization transfer effects.
In vivo topical EPR spectroscopy and imaging of nitroxide free radicals and polynitroxyl‐albumin
Authors: Kuppusamy Periannan , Wang Penghai , Shankar Ravi A. , Ma Li , Trimble Charles E. , Hsia Carleton J. C. , Zweier Jay L.
Published: March 2007

Piperidine nitroxides have considerable clinical potential, both as antioxidant therapeutic compounds and contrast agents in magnetic resonance imaging. However, their development has thus far been limited by their rapid bioreduction in vivo. Recently, it was reported that polynitroxyl albumin (PNA) can reverse the bioreduction of the reduced 4‐hydroxy‐2,2,6,6‐tetramethylpiperidine‐N‐oxyl (Tempol) in the rat heart, enabling the performance of high resolution EPR imaging for prolonged time (Kuppusamy et al., Biochemistry 35, 7051–7057 (1996)). In this report, the efficacy of PNA in maintaining Tempol concentrations in vivo in mice was demonstrated, using L‐band (1.25 GHz) EPR spectroscopy and imaging. The EPR signal of intravenous Tempol had a half‐life of 1.0 ± 0.2 min and became undetectable within 6 min. Subcutaneous Tempol, however, decayed at a slower rate (half‐life, 5.0 ± 0.5 min) suggesting that Tempol had been bioreduced to the corresponding hydroxylamine form, Tempol‐H. Subcutane‐ously injected PNA restored 20% of the Tempol signal in the vicinity of the PNA deposit. In vivo topical EPR imaging demonstrated that the Tempol signal was restored at the site of PNA injection, but not at locations remote from the PNA injection site. The ability of PNA to maintain Tempol in its paramagnetic state in vivo should enable a wide range of therapeutic and diagnostic applications of piperidinyl nitroxides.
Automated spectral analysis I: Formation of a priori information by spectral simulation
Authors: Young Karl , Govindaraju Varanavasi , Soher Brian J. , Maudsley Andrew A.
Published: March 2007

A spectral simulation method is described for generating a priori information for use in parametric spectral analysis. The method makes use of GAMMA (S. A. Smith, T. O. Levante, B. H. Meier, R. R. Ernst, J. Magn. Reson., 106A, 75–105, 1994), a programming environment that facilitates simulation of magnetic resonance phenomena. The input parameters consist of the chemical shifts and scalar spin‐coupling constants for the compounds to be analyzed, the acquisition pulse sequence, and the field strength used. The resultant spectral information consists of the relative amplitude, frequency, and phase of all resonances, which are stored in a spectral database. This procedure can be rapidly and conveniently modified to reflect different acquisition parameters and data analysis requirements.
Automated spectral analysis III: Application to in Vivo proton MR Spectroscopy and spectroscopic imaging
Authors: Soher Brian J. , Young Karl , Govindaraju Varanavasi , Maudsley Andrew A.
Published: March 2007

An automated method for analysis of in vivo proton magnetic resonance (MR) spectra and reconstruction of metabolite distributions from MR spectroscopic imaging (MRSI) data is described. A parametric spectral model using acquisition specific, a priori information is combined with a wavelet‐based, nonparametric characterization of baseline signals. For image reconstruction, the initial fit estimates were additionally modified according to a priori spatial constraints. The automated fitting procedure was applied to four different examples of MRS data obtained at 1.5 T and 4.1 T. For analysis of major metabolites at medium TE values, the method was shown to perform reliably even in the presence of large baseline signals and relatively poor signal‐to‐noise ratios typical of in vivo proton MRSI. identification of additional metabolites was also demonstrated for short TE data. Automated formation of metabolite images will greatly facilitate and expand the clinical applications of MR spectroscopic imaging.
In vivo1H MR spectroscopic imaging and difusion weighted mri in experimental hydrocephalus
Authors: Braun Kees P. J. , de Graaf Robin A. , Vandertop W. Peter , Gooskens Rob H. J. M. , Tulleken Kees A. F. , Nicolay Klaas
Published: March 2007

The severity and progression of ventricular enlargement, the occurrence of cerebral edema, and the localization of isch‐emic metabolic changes were investigated in a rat model of hydrocephalus, using in vivo 1H MR spectroscopic imaging (SI) and diffusion weighted MRI (DW MRI). Hydrocephalic rats were studied 1, 2, 4, and 8 weeks after injection of kaolin into the cisterna magna. Parametric images of the apparent diffusion coefficient (ADC) revealed a varying degree of ventricu‐lomegaly in all rats, with different time courses of ventricular explansion. Extracellular white matter edema was observed during the early stages of hydrocephalus, most extensively in cases of progressive ventriculomegaly. In gray matter regions, ADC values were not changed, compared with controls. In case of fatal hydrocephalus, high lactate levels were observed throughout the whole brain. In all other rats, at all time points after kaolin injection, lactate was detected only in voxels containing cerebrospinal fluid. This suggests accumulation of lactate in the ventricles, and/or an ongoing peri ventricular production of lactate as a consequence of cerebral ischemia in experimental hydrocephalus.
Physiological basis for BOLD MR signal changes due to neuronal stimulation: Separation of blood volume and magnetic susceptibility effects
Authors: Kennan Richard P. , Scanley B. Ellen , Innis Robert B. , Gore John C.
Published: March 2007

An NMR method is applied for separating blood volume and magnetic susceptibility effects in response to neuronal stimulation in a rat model. The method uses high susceptibility contrast agents to enhance blood volume induced signal changes. In the absence of exogenous agent, the dominant source of signal change on neuronal activation is associated with the signal increase from the blood oxygen level dependent (BOLD) effect. The relative negative contribution of blood volume changes to BOLD changes is maximally estimated to be 34%. The blood volume changes associated with median nerve stimulation (7 Hz) in the motor cortex are 26 ± 7% and the corresponding blood susceptibility changes are 0.021 ± 0.006 ppm. These methods can be applied to enhance the sensitivity of fMRl signal response and provide accurate quantitative measures of blood volume response to stimulation.
SAR and B1 field distributions in a heterogeneous human head model within a birdcage coil
Authors: Collins Christopher M. , Li Shizhe , Smith Michael B.
Published: March 2007

Calculations of radiofrequency magnetic (B1) field and specific energy absorption rate (SAR) distributions in a sphere of tissue and a multi‐tissue human head model in a 12‐element birdcage coil are presented. The coil model is driven in linear and quadrature modes at 63, 175, 200, and 300 MHz. Plots of B, field magnitude and SAR distributions, average SAR, maximum local SAR, and measures of B1 field homogeneity and signal‐to‐noise ratio are given. SAR levels for arbitrary pulse sequences can be estimated from the calculated data. Maximum local SAR levels are lower at lower frequencies, in quadrature rather than in linear coils, and in linear fields oriented posterior‐to‐anterior rather than left‐to‐right in the head. It should be possible to perform many experiments in the head at frequencies up to 300 MHz without exceeding standard limits for local or average SAR levels.