bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of proton magnetization transfer rate constants in heterogeneous biological systems
Authors: Brooks Douglas , Kuwata Kazuo , Schleich Thomas
Published: March 2007

Two procedures are currently in use for the determination of proton magnetization transfer rate constants between macro‐molecular tissue components and water. The first method assumes that there are only two spin baths (macromolecular plus solvent) and that during off‐resonance irradiation complete saturation of the “immobile” proton spin bath occurs (S. H. Koenig, R. D. Brown, 111, R. Ugolini, Magn. Reson. Med. 29, 311 (1993)). This approach neglects the possibility of incomplete saturation and polydispersity, and yields an apparent magnetization transfer rate constant, Kapp. The second approach utilizes a formalism which can account for polydispersity and incomplete saturation of the immobile spin bath (K. Kuwata, D. Brooks, H. Yang, T. Schleich, J. Magn. Reson., in press). In this work magnetization transfer rate constants derived by the use of both methods for two systems, ocular lens tissue and cross‐linked bovine serum albumin (BSA) were compared. For both samples Kapp was dependent on B2, off‐resonance irradiation frequency and power when the first method was used. The second method provided values of the magnetization transfer rate constant that were similar to the values obtained by the first method, as the limit of complete saturation was approached.
Further observations on the measurement of tissue T1 to monitor temperature in vivo by MRI
Authors: Young I. R. , Hand J. W. , Oatridge A. , Prior M. V. , Forse G. R.
Published: March 2007

Previous results for the measurement of T1 as a means of monitoring temperature have demonstrated a linear calibration with a coefficient of the order of 1.5%C. We have studied the changes in T1, further, and observe that changes in tissue perfusion are substantial contributors to the effects observed, and that the model of what is happening is complex and may not permit a simple temperature calibration.
Water and fat MR imaging with chemical shift selective 3D steady state methods
Authors: Sun L. , Aletras A. H. , Schmalbrock P. , Skinner T. E. , Chakeres D. , Irsik R. , Robitaille Pierre‐Marie
Published: March 2007

A new 3D acquisition regimen that enables the collection of conventional, water‐suppressed, and fat‐suppressed images with no increase in scan times compared with currently implemented 3D sequences is presented. The method is based on conventional 3D steady state with interleaved selective excitation of the fat resonance resulting in acquisition of a fat‐based image during the TR period experienced by the water spins. This new sequence is relatively tolerant to susceptibility artifacts and results in excellent water‐based images. Because the idea, which we propose, is independent of the type of steady‐state imaging protocol utilized, it can be easily applied with regimens that are specifically tailored to enhance contrast.
Automated single‐voxel proton MRS: Technical development and multisite verification
Authors: Webb Peter G. , Sailasuta Napapon , Kohler Susan J. , Raidy Tom , Moats Rex A. , Hurd Ralph
Published: March 2007

To improve clinical utility, an integrated method has been developed to automatically acquire and process single‐voxel in vivo proton spectra on a 1.5 T clinical scanner. This method includes automated adjustment of linear shims using a very rapid modified simplex method, automated water suppression, and applies a water referencing scheme to correct for phase and residual eddy current effects. No operator intervention is required for the acquisition and processing of these pure‐absorption spectra. This method was tested in a preliminary multisite trial to determine intersite and intrasite variability of metabolite ratio measurements. In a sample of over 100 examinations, the standard deviation of the ratios NAA:Cr, Cho:Cr, and ml:Cr were found to be under 15% when using this method, a substantially narrower range than has been found In studies relying on manual adjustment of the instrument and/or manual processing. This result indicates that automated setting of acquisition and processing parameters is of critical importance in the clinical application of in vivo spectroscopy.
Stability assessment of gadolinium complexes by P‐31 and H‐1 relaxometry
Authors: Elst Luce Vander , van Haverbeke Yves , Goudemant Jean‐François , Muller Robert N.
Published: March 2007

Longitudinal P‐31 relaxation rate enhancements of phosphate groups have been measured at pH 7–7.2 and 310°K on aqueous solutions containing adenosine triphosphate (ATP), phosphocreatine (PCr), inorganic phosphate (Pl) and some lanthanide complexes (Gd‐DOTA, Gd‐HPDO3A, Gd‐DO3A, Gd‐DTPA, Gd‐DTPA‐BMA). The macrocyclic complexes induce linear enhancements of the relaxation rates of all phosphorus nuclei. For Gd‐DOTA and Gd‐HPDO3A, the mechanism of the interaction with the P‐31 nuclei seems to be of the outer sphere type and a better efficiency is noted for the “neutral” Gd‐HPDO3A. A short‐lived ternary complex between Gd‐DO3A and the phosphorylated metabolites appears to be formed enabling an inner sphere interaction. In solutions containing the open chain complexes, Gd‐DTPA and Gd‐DTPA‐BMA, P‐31 relaxation rates of ATP exhibit significant and nonlinear enhancements that are much larger than those observed for PCr and Pi. A ternary complex involving the lanthanide Ion, its original chelator, and the ATP molecule is precluded by various experiments which confirm that the lanthanide ion shifts from the original complexes to the ATP phosphate groups.
Torque free asymmetric gradient coils for echo planar imaging
Authors: Abduljalil A. M. , Aletras A. H. , Robitaille Pierre‐Marie
Published: March 2007

In this work, we present a new torque‐free asymmetric gradient coil that is capable of generating high quality axial, sagittal, and coronal echo planar images of the human head. This gradient set was calculated using the Biot‐Savart law and least square approaches to optimize the field in the region of interest and to minimize net torques. The resulting structure has excellent shoulder‐to‐coil clearance and, as such, has the advantage of providing good patient access to the linear portion of the gradient while minimizing patient discomfort from claustrophobia.
In vivo and in vitro31P magnetic resonance spectroscopic studies of the hepatic response of healthy rats and rats with acute hepatic damage to fructose loading
Authors: Lu Wuhua , Locke Steven J. , Brauer Manfred
Published: March 2007

The hepatic response to a fructose challenge for control rats, and rats subjected to an acute sublethal dose of carbon tetrachloride (CCI4) or bromobenzene (BB), was compared using dynamic in vivo 31P MRS. Fructose loading conditions were used in which control rats showed only a modest increase in hepatic phosphomonoester (PME), and a small decrease in ATP, Pi, and intracellular pH after fructose administration. Both CCI4, and BB‐treated rats showed a much greater fructose‐induced accumulation of PME than did controls. Trolox C, a free radical scavenger, prevented most of this PME increase. BB‐treated rats, given sufficient time to recover from the hepa‐totoxic insult, responded to the fructose load similarly to controls. Liver aldolase activities of control, toxicant‐treated rats, and toxicant plus Trolox C‐treated rats correlated inversely with PME accumulation after fructose loading (correlation coefficient: −0.834, P < 0.05). Perchloric acid extracts of rat livers studied by in vitro 31P MRS confirmed that the PME accumulation after fructose loading is mainly due to an increase in fructose 1‐phosphate. These studies are consistent with the aldolase‐catalyzed cleavage of fructose 1‐phosphate being rate‐limiting in hepatic fructose metabolism, and that the CCI, and BB treatment modify and inactivate the aldolase enzyme.
The application of breath hold phase velocity mapping techniques to the measurement of coronary artery blood flow velocity: Phantom data and initial in vivo results
Authors: Keegan Jennifer , Firmin David , Gatehouse Peter , Longmore Donald
Published: March 2007

A segmented k‐space breath hold phase velocity mapping technique has been developed for the study of coronary artery blood flow velocity. In vitro validation has been performed using a number of pulsatile flow phantoms and the accuracy of the technique for determining the velocity increase at the site of a stenosis demonstrated in several phantom models. Examples of both in‐plane and through‐plane velocity maps of the left anterior descending and right coronary arteries of normal subjects in early diastole are presented. In one subject, through‐plane velocity maps were obtained in the right and left anterior descending arteries throughout the cardiac cycle in order to generate flow velocity time curves. The problems associated with coronary artery velocity mapping are discussed.
Automated processing for proton spectroscopic imaging using water reference deconvolution
Authors: Maudsley Andrew A. , Wu Zhe , Meyerhoff Dieter J. , Weiner Michael W.
Published: March 2007

Automated formation of MR spectroscopic images (MRSI) is necessary before routine application of these methods is possible for in vivo studies; however, this task is complicated by the presence of spatially dependent instrumental distortions and the complex nature of the MR spectrum. A data processing method is presented for completely automated formation of in vivo proton spectroscopic images, and applied for analysis of human brain metabolites. This procedure uses the water reference deconvolution method (G. A. Morris, J. Magn. Reson. 80,547(1988)) to correct for line shape distortions caused by instrumental and sample characteristics, followed by parametric spectral analysis. Results for automated image formation were found to compare favorably with operator dependent spectral integration methods. While the water reference deconvolution processing was found to provide good correction of spatially dependent resonance frequency shifts, it was found to be susceptible to errors for correction of line shape distortions. These occur due to differences between the water reference and the metabolite distributions.
Experimental confirmation of phase encoding of instantaneous derivatives of position
Authors: Duerk Jeffrey L. , Simonetti Orlando P. , Hurst Gregory C. , Finelli Daniel A.
Published: March 2007

Previous theoretical reports described the dependence of interpretation of the observed phase of the NMR signal on the time origin(s) of moment calculations and position's Taylor series expansion. This work provides experimental confirmation of predictions derived from that theory. For accelerative motion, experimental phase‐encoded velocity measurements give instantaneous values at a time corresponding to the origin used for waveform momemt calculations. For laminar flow, experimental intensity profiles agree well with theoretical simulations; new findings extend amplitude and spatial distributions of oblique flow profiles beyond previous descriptions. Experiments using sequences with controlled position of the time origins for phase and read axes show that displacement and motion artifacts are reduced when they're coincident (pulsed flow, nongated acquisitions), and virtually eliminated when combined with gating. Potentially significant clinical consequences of coincident and noncoincident time origins are demonstrated in human head MIP MRA images. These results have fundamental implications in waveform design.
Rapid tissue oxygen tension mapping using 19F inversion‐recovery echo‐planar imaging of P erfluoro‐15 ‐crown‐5‐ether
Authors: Dardzinski Bernard J. , Sotak Christopher H.
Published: March 2007

Fluorine‐19 inversion‐recovery, echo‐planar imaging (IR‐EPI) wais used in conjunction with a new PFC emulsion, perfluoro‐15‐crown‐5‐ether, to map the spatial distribution of oxygen tension in murine liver, spleen and radiation induced fibrosarcoma (RIF‐1) tumors. Intravenously administered PFC emulsions were allowed to sequester in the liver, spleen, and tumor 3 to 7 days prior to imaging experiments. Seven, 64 × 64 IR‐EPls were acquired with successively increasing inversion times (TI). A nonlinear least‐squares regression algorithm was used to fit the seven two‐dimensional matrices, on a pixel‐by‐pixel basis, to solve for the relaxation rate, R1, of the sequestered PFC. From in vitro calibration curves, the oxygen tension (pO2,) was calculated from the measured R1. Oxygen tension maps were then murine liver and spleen were produced (in 2.5 min) to demonstrate the technique and changes in tissue oxygenation as a function of breathing gas (air and carbogen (95% O2 ‐ 5% CO2)) are presented. Tissue pO2 maps from RIF‐1 tumors (n = 5) were obtained in less than 10 min and changes in tumor pO2 were studied when the breathing gals was switched from air to carbogen. The results from tumor pO2 maps were compared with 19F MR spectroscopy measurements to check for consistency. Histogram analysis yielded an average liver and spleen pO2 of 43 torr and 26 torr for RIF‐1 tumors when the animals were breathing air. Statistically significant changes in tumor oxygenation as a function of breathing gas were obtained from both pO2 maps (6 ± 2 torr, P < 0.05) and 19F MR spectroscopy (13 ± 3 torr, P < 0.01) as evaluated using the Student's paired t test.
Detection of brain glutamate and glutamine in spectroscopic images at 4.1 T
Authors: Mason Graeme F. , Pan Jullie W. , Ponder Steven L. , Twieg Donald B. , Pohost Gerald M. , Hetherington Hoby P.
Published: March 2007

Brain glutamate and glutamine were detected in healthy human volunteers in spectroscopic images with a nominal voxel size of 2.25 cm3 at an echo time of 15 ms. Due to the increased frequency separation and simplification of J‐coupling patterns, the separate detection of brain glutamate and glutamine at short echo times was possible. Creatine, choline, and N‐acetylaspartate with other N‐acetylated compounds were also detected. The ratios of the metabolite resonance intensities were in agreement with previously published values.
Analysis of macromolecule resonances in 1H NMR spectra of human brain
Authors: Behar Kevin L. , Rothman Douglas L. , Spencer Dennis D. , Petroff Ognen A. C.
Published: March 2007

Macromolecule resonances underlying metabolites in 1H NMR spectra were investigated in temporal lobe biopsy tissue from epilepsy patients and from localized 1H spectra of the brains of healthy volunteers. The 1H NMR spectrum of brain tissue was cornpared with that of cytosol and dialyzed cytosol after removal of low molecular weight molecules (4500 daltons) at 8.4 and 2.1 Tesla. The assignment of specific resonances to macromolecules in 2.1 Tesla, short‐ TE, localized human brain 1H NMR spectra in vivo was made on the basis of a J‐editing method using the spectral parameters (δ, J) and connectivities determined from 2D experiments in vitro. Two prominent corinectivities associated with macromolecules in vitro (0.93–2.05 δ and 1.6–3.00 δ) were also detected in vivo by the J‐editing method. Advantage was taken of the large difference in measured T1 relaxation times between macromolecule and metabolite resonances in the brain spectrum to acquire ‘metabolite‐nulled’ macromolecule spectra. These spectra appear identical to the spectra of macromolecules isolated in vitro.
In vivo measurement of water diffusion in the human heart
Authors: Edelman Robert R. , Gaa Jochen , Wedeen Van J. , Loh Evan , Hare Joshua M. , Prasad Pottumarthi , Li Wei
Published: March 2007

Existing magnetic resonance methods for diffusion imaging, including echo planar, are ineffective in the beating heart due to motion‐induced signal attenuation. To overcome this problem, we used a diffusion‐weighted stimulated echo‐echo planar magnetic resonance imaging sequence. The two lobes of the diffusion‐sensitizing gradient were synchronized to the same point in successive cardiac cycles in order to fix the cardiac position and avoid bulk motion effects. The apparent diffusion coefficients (ADCs) of the interventricular septum in 12 healthy subjects for diffusion gradients along the x‐, y‐, and z‐directions were 1.40 ± 0.27, 1.48 ± 0.35, and 1.78 ± 0.27 × 10−3 mm2/s. The ADCs of the interventricular septum in a second group of 15 healthy subjects for diffusion gradients along the short axis, horizontal and vertical long axes were 0.92 ± 0.15. 1.50 ± 0.15, and 1.10 ± 0.24 × mm2/s. Because the ADCs were less than the measured values for skeletal muscle and their standard deviations were low, it seems unlikely that bulk motion effects made the dominant contribution to the measured myocardial ADC for the interventricular septum, although motion and/or susceptibility artifacts frequently degraded measurements in the free wall of the left ventricle. Additional evidence that ADC was not predominantly determined by wall motion was obtained in a third group of patients with various cardiac abnormalities, in whom there was only a weak correlation between ADC and ejection fraction. Although further study is needed to better understand the factors contributing to the myocardial ADC, we hypothesize that the measured diffusional anisotropy in the septum might be explained largely on the basis of myofiber orientation.
Localized MR 1H spectroscopy reveals alterations of susceptibility in bone marrow with hemosiderosis
Authors: Schick Fritz , Einsele Hermann , Kost Renate , Duda Stephan H. , Horny Hans‐Peter , Lutz Otto , Claussen Claus D.
Published: March 2007

A noninvasive investigation of the structure of hemopoietic bone marrow is based on the determination of the magnetic field distribution within small volume elements in vertebral bodies by localized 1H MR spectroscopy. In patients with he‐matological diseases the status of the bone marrow was found to considerably influence the homogeneity of the magnetic field in trabecular bone in vivo. The line widths of the 1H signals were evaluated in follow‐up studies during initial chemotherapy of eight patients with leukemia. lntraindividual comparison revealed significant broadening of the field distribution after a few weeks of cytotoxic treatment in five of the patients. Additionally, 19 patients after bone marrow transplantation showed significantly broader field distributions in the lipid signals than 13 matched healthy volunteers. These alterations of the microscopic field homogeneity were not caused by trabecular density effects. Iliac crest biopsies revealed high amounts of hemosiderin in the cases with broadened line widths. Ten of the 19 patients after bone marrow transplantation showed high amounts of hemosiderin and broad lines in the spectra. The content of hemosiderin of the other patients was not significantly increased.
Correlation between choline level and Gd‐DTPA enhancement in patients with brain metastases of mammary carcinoma
Authors: Sijens Paul E. , van Dijk Pieter , Oudkerk Matthijs
Published: March 2007

Single voxel 1HH double spin‐echo MR spectroscopy was used to examine 15 cases of brain metastasis of mammary carcinoma (18 lesions) in relation to Gd‐DTPA enhanced MR imaging. For lesions larger than 50% of MRS voxel size, there was significant correlation between Gd‐DTPA‐enhanced MRI signal and MRS‐detected signal of choline (Cho) containing compounds (r = 0.86, P < 0.01; n = 8). The observed loss of correlation when including the smaller lesions was overcome by correcting for partial volume effects (r = 0.69, P < 0.002; n = 18). Metastasis spectra showed increased Cho compared with control spectra, except for those lesions showing detectable lactate (Lact) signal. The detection of Lact in four of the larger lesions coincided with comparatively low levels of creatine (Cr) and Cho and heterogeneous Gd‐DTPA enhancement (ring‐enhancement). It was concluded that in brain metastases of mammary carcinoma Lact represents a product of ischemia preceding/during tissue decay resulting in central necrosis, rather than tumor specific metabolism resulting in increased glycolysis.
Radial turbo spin echo imaging
Authors: Rasche Volker , Holz Dietrich , Schepper Willi
Published: March 2007

Fast MR imaging methods should provide a familiar contrast behavior at a reduced scan time. The multi‐spin echo approach (TSE) is one of the most promising techniques satisfying this condition. Although the data acquisition time is significantly reduced, image quality may still suffer from artifacts due to patient motion and flow. The radial turbo spin echo (rTSE) approach combines TSE methods and projection reconstruction (PR) techniques. In PR images, artifacts induced by patient motion or flow are known to have a different appearance with lower level of intensity. The contrast and artifact behavior of the rTSE approach has been investigated. The new technique has been applied to abdominal imaging with acquisition times shorter than 30 s and to heart imaging in combination with cardiac triggering.
High speed bolus tagging: time resolved velocity quantification of pulsatile flow in a single breath hold
Authors: Chien Daisy , Saloner David , Laub Gerhard , Simonetti Orlando , Anderson Charles M.
Published: March 2007

We have implemented a high speed method for cardiac‐trig gered blood velocity quantification within a single breath hold on a conventional MR system. The method, based on bolus tagging, was tested using a pulsatile flow phantom and evaluated in vivo. The image acquisition time was reduced by a factor of N by acquiring N phase encode lines per bolus tag application. The clarity of the flow tag was found to vary with how k‐space was covered during data collection. The technique was optimized and multiple bolus tag images were obtained throughout the cardiac cycle within a single breath‐hold.
Echo‐volume imaging
Authors: Song Allen W. , Wong Eric C. , Hyde James S.
Published: March 2007

Two single‐shot volume imaging techniques are described. The first, single‐echo echo‐volume imaging, is essentially the echo‐volume imaging (EVI) sequence suggested by Mansfield (J. Phys. C. 10, L55 (1977)). The second is a multi‐spin‐echo approach in which one plane of k‐space is collected during each spin echo. In both techniques, phase encoding gradients are applied in the z direction, and three‐dimensional k‐space is filled by a raster pattern in Cartesian coordinates. Spatial saturation is used to avoid aliasing in the y direction, and a selective pulse is applied to excite the desired slab of tissue and eliminate aliasing in z. The average echo‐times, measured from the center of the 90° pulse to the center of the acquisition k‐space(kx= ky kz = 0), were 45 and 104 ms for single echo and multi‐echo methods, respectively. Images of the human brain using both sequences are shown.
Gradient moment nulling in fast spin echo
Authors: Hinks R. Scott , Constable R. Todd
Published: March 2007

The fast spin echo sequence combines data from many echo signals in a Carr‐Purcell‐Meiboom‐Gill echo train to form a single image. Much of the signal in the second and later echoes results from the coherent addition of stimulated echo signal components back to the spin echo signal. Because stimulated echoes experience no dephasing effects during the time that they are stored as M, magnetization, they experience a different gradient first moment than does the spin echo. This leads to flow‐related phase differences between different echo components and results in flow voids and ghosting, even when the first moment is nulled for the spin echo signal. A method of gradient moment nulling that correctly compensates both spin echo and stimulated echo components has been developed. The simplest solution involves nulling the first gradient moment at least at the RF pulses and preferably at both the RF pulses and the echoes. Phantom and volunteer studies demonstrate good suppression of flowrelated artifacts.
Echo‐Planar Diffusion Spectroscopic Imaging
Authors: Bito Yoshitaka , Hirata Satoshi , Nabeshima Takayuki , Yamamoto Etsuji
Published: March 2007

High‐speed diffusion spectroscopic imaging based on an echo‐planar technique is presented. A pair of diffusion gradients is applied prior to a rapidly oscillating magnetic field gradient which encodes both chemical shift and spatial information. By applying this technique to a phantom consisting of acetone and water, a diffusion spectroscopic image is obtained in about 15 min, about 64 times faster than the time required in the conventional method. The measured diffusion coefficients show good agreement with previously reported values. This kind of diffusion spectroscopic imaging is expected to provide a way to observe more specific metabolism.
Coronary MRI with a Respiratory Feedback Monitor: The 2D Imaging Case
Authors: Wang Yi , Christy Paul S. , Korosec Frank R. , Alley Marcus T. , Grist Thomas M. , Polzin Jason A. , Mistretta Charles A.
Published: March 2007

The inability to return the heart to the same position for all breath‐holds during 2D coronary MR imaging can result in imaging different locations than desired. This can lead to problems such as (i) missing a whole vessel, or a part of it, (ii) misaligning segments of vessels imaged in different breath‐holds, and (iii) degrading image quality when a single slice is acquired in multiple breath‐holds. To reduce inconsistencies in the breath‐hold level, we designed a respiratory feedback monitor (RFM) that uses a bellows to monitor the circumference of the subject's chest. When the circumference of the subject's chest is within preset limits, an audio signal alerts subjects to hold their breath at that position. Use of the RFM significantly reduces the problems caused by inconsistent breath‐holds and the number of breath‐holds for an examination in 2D coronary MR imaging.
The Voxel Sensitivity Function in Fourier Transform Imaging: Applications to Magnetic Resonance Angiography
Authors: Parker Dennis L. , Du Yiping P. , Davis Wayne L.
Published: March 2007

In this paper the problem of small structure visualization in magnetic resonance imaging (MRI) is considered. The relationship between the structure and the image intensities is defined in terms of the voxel sensitivity function (VSF). Using the VSF, the spatial dependence of the voxel signal for small spheres and cylinders is computed. Although the spatial fluctuation is smaller in the MRI VSF than that which would be obtained from a uniformly sensitive cubical voxel, the deviation still results in significant signal loss near the edges and corners of the voxels. Finally, the VSF formalism is used to demonstrate the improvement in signal uniformity that can be obtained by using zero‐filled (band‐limited or sinc) interpolation.
In Vivo Dynamic MRI Tracking of Rat T‐Cells Labeled with Superparamagnetic Iron‐Oxide Particles
Authors: Yeh Tzu‐Chen , Zhang Weiguo , Ildstad Suzanne T. , Ho Chien
Published: March 2007

Dynamic MRI tracking of rat T‐cells in vivo is performed in rat testicles after labeling isolated rat T‐cells in vitro with superparamagnetic dextran‐coated iron‐oxide particles, BMS180549. Tissue inflammation induced by the local injection of the calcium ionophore, A23187, is used to attract labeled T‐cells. Gradient‐echo MR images of rat testicles show a statistically significant decrease (4%) of the signal intensity in areas of injection of A23187 as early as 30 min after intravenous infusion of 2 x 108 labeled T‐cells. The signal change reaches its maximum (6–7% decrease) at about 60–120 min after cell infusion. T2‐mapping also shows a decrease of T2 in the areas with A23187. Image quantitation, which includes a chemical‐shift effect, significantly enhances the sensitivity for detection of superparamagnetically labeled T‐cells. Localization of labeled T‐cells in rat testicles has been verified by fluorescence microscopy studies of T‐cells co‐labeled with a lipophilic fluorescent carbocyanine dye, 1,1‐dioctadecyl‐3,3,3',3'‐tetramethyl‐lindocarbocyanine perchlorate. These results represent the first successful demonstration of dynamic tracking of specific cells in vivo using MRI.
Computerized Consensus Diagnosis: A Classification Strategy for the Robust Analysis of MR Spectra. I. Application to 1H Spectra of Thyroid Neoplasms
Authors: Somorjai Ray L. , Nikulin Alexander E. , Pizzi Nic , Jackson Dick , Scarth Gordon , Dolenko Brion , Gordon Heather , Russell Peter , Lean Cynthia L. , Delbridge Leigh , Mountford Carolyn E. , Smith Ian C. P.
Published: March 2007

We introduce and apply a new classification strategy we call computerized consensus diagnosis (CCD). Its purpose is to provide robust, reliable classification of biomedical data. The strategy involves the cross‐validated training of several classifiers of diverse conceptual and methodological origin on the same data, and appropriately combining their outcomes. The strategy is tested on proton magnetic resonance spectra of human thyroid biopsies, which are successfully allocated to normal or carcinoma classes. We used Linear Discriminant Analysis, a Neural Net‐based method, and Genetic Programming as independent classifiers on two spectral regions, and chose the median of the six classification outcomes as the consensus. This procedure yielded 100% specificity and 100% sensitivity on the training sets, and 100% specificity and 98% sensitivity on samples of known malignancy in the test sets. We discuss the necessary steps any classification approach must take to guarantee reliability, and stress the importance of fuzziness and undecidability in robust classification.
MR Imaging with Hyperpolarized 3He Gas
Authors: Middleton Hunter , Black Robert D. , Saam Brian , Cates Gordon D. , Cofer Gary P. , Guenther Robert , Happer William , Hedlund Lawrence W. , Alan Johnson G. , Juvan Kim , Swartz John
Published: March 2007

Magnetic resonance images of the lungs of a guinea pig have been produced using hyperpolarized helium as the source of the MR signal. The resulting images are not yet sufficiently optimized to reveal fine structural detail within the lung, but the spectacular signal from this normally signal‐deficient organ system offers great promise for eventual in vivo imaging experiments. Fast 2D and 3D GRASS sequences with very small flip angles were employed to conserve the nonrenewable longitudinal magnetization. We discuss various unique features associated with performing MRI with hyperpolarized gases, such as the selection of the noble gas species, polarization technique, and constraints on the MR pulse sequence.
Changes in T2*‐Weighted Images During Hyperoxia Differentiate Tumors from Normal Tissue
Authors: Kuperman Vadim Y U. , River Jonathan N. , Lewis Martha Z. , Lubich Leslie M. , Karczmar Gregory S.
Published: March 2007

Experiments were performed to determine whether changes in T2*‐weighted MR images during and after hyperoxia differentiate tumors from normal tissue. Mammary adenocarcinomas implanted in the right hind limbs of rats were studied. Gradient echo images were obtained at 2 Tesla with an evolution time of 20 ms and a recycle time of 1 s. Breathing gas was either air or 100% O2. Significant increases in image intensity were observed in tumor centers and rims during hyperoxia while much smaller changes were detected in the surrounding muscle. The relaxation rate (1/T2*) in tumors decreased during hyperoxia by an average of 2.5 ± 1.0 s−1, while in muscle the average change was an increase of 0.6 ± 2.1 s−1. The largest decreases in relaxation rate were detected in non‐necrotic tumor regions with relatively low density of blood vessels. Immediately following hyperoxia significant decreases in intensity were detected in tumors while much smaller decreases were detected in the surrounding muscle.
Effect of Radio Frequency Inhomogeneity Correction on the Reproducibility of Intra‐Cranial Volumes Using MR Image Data
Authors: Narayana Ponnada A. , Borthakur Arijitt
Published: March 2007

The volumes of total brain, white matter, gray matter, and cerebrospinal fluid in normal volunteers were determined using a supervised nonparametric feature map segmentation of dual‐contrast MR images after correcting for the radio frequency (RF) inhomogeneity. Reproducibility of the segmentation was evaluated in terms of inter‐observer and scan‐to‐scan variations. A comparison with the published results indicates that the scan‐to‐scan and inter‐observer variabilities in the determination of tissue volumes are substantially reduced following the RF inhomogeneity correction.
Dynamic Monitoring of Total‐Body Absorption by 19F NMR Spectroscopy: One Hour Ventilation of HFA‐134a in Male and Female Rats
Authors: Finch John R. , Dadey Eric J. , Smith Stanford L. , Harrison Lester I. , Digenis George A.
Published: March 2007

Six male and six female Sprague‐Dawley rats were ventilated head‐only for 1 h on a 15% atmosphere of 1, 1, 1, 2‐tetrafluoroethane (HFA‐134a) in air in a magnetic resonance imaging spectrometer. Results from these dynamic 19F NMR studies suggest that a steady‐state in vivo concentration of HFA‐134a was approached at approximately 25 min into the exposure. Quantitative integration analysis using an external standard estimated this plateau to be 58.3 ± 11.9 mg of absorbed HFA‐134a per rat. The HFA‐134a 19F NMR signal disappeared rapidly following removal of the test atmosphere, with an elimination half‐life of 4.6 ± 0.6 min in the male rats and 4.9 ± 1.5 min in the female rats. The data suggest that there was no statistical difference between the sexes in amount absorbed or in elimination half‐lives.
EPI Imaging of Global Increase of Brain MR Signal with Breath‐hold Preceded by Breathing O2
Authors: Kwong Kenneth K. , Wanke Isabel , Donahue Kathleen M. , Davis Timothy L. , Rosen Bruce R.
Published: March 2007

Brain MR signal has been observed to decrease during cessation of breathing due to the increase of deoxyhemoglobin in the blood. However, for both animal and human studies, we have demonstrated that if the subjects breathed 100% oxygen in advance of apnea for a short time, T2*‐weighted MR brain signal increased when breathing was stopped for a period of 30–60 s. This demonstrates the possibility of measuring responses to hemodynamic change throughout the entire brain with a single respiratory perturbation in a rapid, reliable, and robust manner.
Motion Artifacts in fMRI: Comparison of 2DFT with PR and Spiral Scan Methods
Authors: Glover Gary H. , Lee Adrian T.
Published: March 2007

Activation signals based on BOLD contrast changes consequent to neuronal stimulation typically produce cortical intensity differences of < 10% at 1.5T. Hemodynamically driven pulsation of the brain can cause highly pulsatile phase shifts, which in turn result in motion artifacts whose intensity is larger than the activation signals in 2DFT scan methods. This paper presents a theoretical and experimental comparison of the magnitude of such artifacts for 2DFT and two other methods using non‐Cartesian k‐space trajectories. It is shown that artifacts increase with TR for 2DFT methods, and that projection reconstruction (PR) and spiral methods have significantly reduced artifact intensities, because these trajectories collect low spatial frequencies with every view. The spiral technique is found to be superior in terms of efficiency and motion insensitivity.
Magnetic Resonance Imaging of Microwave Induced Tissue Heating
Authors: Schwarzmaier Hans‐Joachim , Kahn Thomas
Published: March 2007

MR‐guided interstitial thermotherapy offers a minimally invasive treatment for localized tumors and tissue structures exhibiting functional abnormalities. In this study, microwaves (2.45 GHz) were used for tissue irradiation to overcome some limitations of the heating sources used so far. To this end, a microwave antenna was positioned in a specimen of porcine myocardium and irradiated for 10 min under MRI control using a T1‐weighted FLASH sequence. The heating procedure resulted in a spherical tissue lesion of 26 mm in diameter. Thus, we could demonstrate the feasibility to monitor the microwave‐induced coagulation process by MR‐imaging in vitro.
MR Microscopy of the Rat Carotid Artery after Balloon Injury by Using an Implanted Imaging Coil
Authors: Summers Ronald M. , Hedlund Laurence W. , Cofer Gary P. , Gottsman Michael B. , Manibo Jose F. , Allan Johnson G.
Published: March 2007

Neointimal hyperplasia after angioplasty was followed in vivo in rats by using MR microscopy and surgically implanted RF imaging coils. By using an inductively coupled pick‐up coil, the arteries were imaged 4 days before and 3, 7, and 14 days after angioplasty with a 3DFT spin echo sequence. Eight of 10 angioplastied rats showed moderate to severe stensois based MR measures of lumen diameter reduction from baseline images. There was a good correlation between total wall thickness between MR and hematoxylin and eosin (H&E)‐stained sections obtained on the last day. Arteries in the intact and sham groups remained unchanged from baseline measurements. Because this imaging technique examines the artery under in vivo conditions of arterial pressure and flow, it promises to be a useful tool for evaluating pharmacological and mechanical methods of reducing the incidence of vascular stenosis.
Role of Increased Cerebral myo‐Inositol in the Dementia of Down Syndrome
Authors: Shonk Truda , Ross Brian D.
Published: March 2007

The purpose of this study was to determine cerebral myo‐inositol (ml) in adults with Down syndrome (DS), and to trace the chronobiology of DS to Alzheimer disease (AD). AD has characteristic neuropathology of neurofibrillary plaques and tangles; indirect evidence links this to earlier deposition of β‐amyloid. Elevated ml, which distinguishes AD from other common dementias, is also elevated in 23 young patients who have DS without dementia. In one patient who has DS with dementia, ml is elevated and N‐acetylaspartate (NAA) decreased. The similarity to AD is striking and may suggest a progressive neurochemical disorder in which elevation of ml precede loss of NAA in both AD and DS.
3D coronary MR angiography in multiple breath‐holds using a respiratory feedback monitor
Authors: Wang Yi , Grimm Roger C. , Rossman Phillip J. , Debbins Josef P. , Riederer Stephen J. , Ehman Richard L.
Published: March 2007

To reduce respiratory blur and ghosts in 3D coronary imaging, a data acquisition scheme using consistent multiple breath‐holds was implemented. A navigator echo was acquired and processed in real time to dynamically measure diaphragm position. This information was provided as a visual prompt to the patient to maintain consistency in breath‐hold levels such that the variation range of diastolic heart position was less than 2 mm. Preliminary results indicate that this multiple breath‐hold acquisition scheme, compared with acquisition under respiration, can significantly reduce blur and ghost artifacts in 3D coronary imaging.
3D Echo Planar Imaging: Application to the Human Head
Authors: Abduljalil Amir M. , Aletras Anthony H. , Robitaille Pierre‐Marie
Published: March 2007

In this work, the authors present 3D images acquired from the human head using echo planar encoding for two of the three dimensions of k‐space. The third dimension of k‐space is filled by selecting and phase encoding a slab of spins as in conventional 3D steady state (GRASS based) acquisition regimens. Using this approach, a 128 x 64 x 64 3D data matrix could be obtained in 3.4–4.7 sec using effective TE values of 24 and 34 ms, respectively. High quality 3D images could be acquired once phase ghosts present on 2D images were minimized through proper adjustments of scanner hardware.
Optimized gradient waveforms for spiral scanning
Authors: King Kevin F. , K. F. Foo Thomas , Crawford Carl R.
Published: March 2007

Spiral scanning gradient waveforms can be optimized with respect to blurring from off‐resonance effects by minimizing the readout time. This is achieved by maximizing the gradient amplitude during the scan so that the edge of k‐space is reached as quickly as possible. Gradient hardware constraints are incorporated by considering a circuit model for the gradient coil and amplifier. The optimized gradient waveforms are determined by a set of coupled differential equations. The resulting solutions have shorter readout time than solutions that do not consider the circuit model.
Analytical resolution and noise characteristics of linearly reconstructed magnetic resonance data with arbitraryk‐space sampling
Authors: Pipe Mr James , , Duerk Jeffrey L.
Published: March 2007

The effects of time‐varying readout gradients and data sampling with variable dwell times in magnetic resonance imaging are examined. General reconstruction formulas are given for linear reconstruction with even k‐space weighting. Closed analytic expressions for estimator variance are given for data sampling during arbitrary gradient waveforms with both uniform kx step size and nonuniform kx step size. It is shown that estimator variance increases (the signal‐to‐noise ratio decreases) for nonconstant gradient waveforms. It is also shown that estimator variance is greater for constant k‐space sampling strategies than for constant time sampling at the Nyquist rate. Data collected during a triangular readout gradient waveform, with either constant time or constant k‐space sampling, versus conventional (constant gradient) collection confirms theoretical predictions for estimator variance. The benefits of collecting data while the readout gradient is ramping up from and down to zero are discussed.
Oximetry by dynamic nuclear polarization
Authors: Grucker Daniel , Guiberteau Thierry , Eclancher Bernard
Published: March 2007

This study describes quantitatively the effect of O2 on the dynamic nuclear polarization (DNP) of water protons. It is shown theoretically how DNP enhancement is altered by the paramagnetism of O2. The nonlinear effect of oxygen on the enhancement factor has been approximated by a first order expression that provides accurate predictions of the experimental results obtained with phosphate‐buffered solutions of 2,2,6,6 tetramethyl‐4‐oxo‐piperidine‐N‐oxyl. The proton relaxation rates and DNP line width were measured for nitroxide concentrations ranging from 0.5 to 10 mM and for oxygen partial pressures ranging from 0 to 760 mmHg. A method is suggested for the calculation of the nitroxide and oxygen concentrations of a sample, based on two measurements, one with on‐resonance EPR irradiation, the other with slightly off‐resonance irradiation. Although the correlation between the values for the actual and calculated oxygen concentrations is good, the accuracy of the calculated oxygen concentration values remains poor, because of the large number of parameters involved in this calculation.
Mapping the biodistribution and catabolism of 5‐fluorouracil in tumor‐bearing rats by chemical‐shift selective 19F MR imaging
Authors: Brix Gunnar , Bellemann Matthias E. , Haberkorn Uwe , Gerlach Ludwig , Bachert Peter , Lorenz Walter J.
Published: March 2007

A chemical‐shift selective (CHESS) 19F MR imaging technique was used to map selectively the antineoplastic drug 5‐fluorouracil (5‐FU) and its major catabolite α‐fluoro‐β‐alanine (FBAL) in tumor‐bearing rats. The pulse sequence employed a CHESS RF saturation pulse to suppress either the 5‐FU or the FBAL resonance before the other component in the two‐line 19F MR spectra was measured. Selective 5‐FU and FBAL images with a spatial resolution of 10 x 10 x 15 mm3 (1.5 ml) were obtained in 40 min from six ACI rats with implanted Morris hepatoma. Because the transmitter frequency could always be set to the Larmor frequency of the 19F resonance employed for imaging, the images were free of chemical‐shift artifacts in readout and slice‐selection direction. Whereas FBAL appeared only in the liver, the kidneys, and the bladder, 5‐FU could also be detected in all major organs and in the muscular system. In the Morris hepatomas, a small 5‐FU uptake and no FBAL accumulation were measured. The CHESS 19F MRI technique provides useful physiological and biochemical data on the biodistribution of the antineoplastic drug 5‐FU and on the different catabolic activities of the tissues.
Dynamic Gd‐DTPA enhanced MRI measurement of tissue cell volume fraction
Authors: Donahue Kathleen M. , Weisskoff Robert M. , Parmelee David J. , Callahan Ronald J. , Wilkinson Robert A. , Mandeville Joseph B. , Rosen Bruce R.
Published: March 2007

A new technique for measuring tissue cellular volume fraction, based on an improved modeling of the dynamic distribution of Gd‐DTPA and the effect of proton exchange, is described. This technique uses peak T1 enhancement and blood Gd‐DTPA concentration to compute tissue cellular volume fraction. The feasibility of this technique is demonstrated with computer simulations that explore the limits of the simplifying assumptions (small vascular space, slow vascular‐extravascular proton exchange), and by direct comparison of MR and radionuclide cell fraction measurements made in muscle, liver, and tumor tissue in a rat model. The computer simulations demonstrate that with slow to intermediate vascular proton exchange and vascular fractions less than 10% the error in our cell fraction measurements typically remains less than 10%. Consistent with this prediction, a direct comparison between MR and radionuclide measurements of cell fraction demonstrates mean percent differences of less than 10%: 1.9% in muscle (n = 4); 9% in liver (n = 1) and 9.5% in tumor (n = 4). Similarly, for all rats studied, the MR‐measured cell fractions (muscle (0.92 ± 0.04, n = 20); liver (0.76 ± 0.11, n = 9); whole tumor (0.69 ± 0.15, n = 22)) agree with the cell fraction values reported in the literature. In general, the authors' results demonstrate the feasibility of a simple method for measuring tissue cell fraction that is robust across a broad range of vascular volume, flow, and exchange conditions. Consequently, this method may prove to be an important means for evaluating the response of tumors to therapy.
Correction of motional artifacts in diffusion‐weighted images using a reference phase map
Authors: Uluǧ Aziz MÜFit , Barker Peter B. , Zijl Peter C. M. Van
Published: March 2007

A method of correcting motional artifacts in diffusion‐weighted images is described. Motion causes changes in the phase of the k‐space NMR signal and thereby introduces positional shifts (or ghosts) in the spatial domain. By correcting the phase of the NMR signal before Fourier transformation, the image sharpness is greatly enhanced. The new method measures the phases of the NMR signal once and stores this phase information in a phase map. Subsequent images with motional artifacts are corrected during postprocessing using this reference phase map.
Calculation of signal intensities in hybrid sequences for fast NMR imaging
Authors: Deichmann Ralf , Adolf Holger , Nöth Ulrike , Kuchenbrod Erwin , Schwarzbauer Christian , Haase Axel
Published: March 2007

A number of techniques that recently have been used for fast NMR‐imaging are based on a hybrid sequence of echo planar imaging (EPI) and FLASH imaging: after each NMR excitation several k‐space lines are measured. The complete k‐space is covered by performance of several excitations. It has been observed that there is usually an optimal hybrid sequence that maximizes the signal‐to‐noise ratio. In this work, a method is presented that allows a determination of the optimal sequence as a function of the relaxation times T1 and T2*.
The apparent diffusion constant measured by mri correlates with po2 in a rif‐1 tumor
Authors: Dunn Jeff F. , Ding Shujun , O'Hara Julia A. , Liu Ke J. , Rhodes Erik , Weaver John B. , Swartz Harold M.
Published: March 2007

As tissue oxygen tension (pO2 is an important variable in cancer therapy, it would be of major clinical benefit to be able to measure pO2 noninvasively. Current methods for determining pO2 in clinical settings are limited to superficial tumors. The authors measured the apparent diffusion constant (ADC) in an implanted murine fibrosarcoma (RIF‐1) using magnetic resonance imaging and correlated the ADC with tissue pO2 measured by electron paramagnetic resonance oximetry. The ADC correlates significantly with tissue pO2 in this tumor (r = 0.89; n = 14) and so may provide a noninvasive index of pO2 in tumors.