bluuebunny/crossref_metadata_2025 huggingface dataset:
Use of Fluid‐Attenuated Inversion‐Recovery Pulse Sequences for Imaging the Spinal Cord
Authors: White Susan J. , Hajnal Joseph V. , Young Ian R. , Bydder Graeme M.
Published: March 2007

Fourteen patients with disease of the spinal cord were imaged with fluid‐attenuated inversion‐recovery (FLAIR) sequences in which the inversion time was chosen to substantially reduce or null the signal from CSF. Lesions were seen with greater conspicuity than with conventional contrast‐enhanced and ‐unenhanced T1‐ and T2‐‐weighted sequences in 11 cases.© 1992 Academic Press,Inc.
Distortions from curved flow in magnetic resonance imaging
Authors: Frank Lawrence R. , Buxton Richard B.
Published: March 2007

We present an analysis of how vessel curvature can create distortions in magnetic resonance images of flowing blood. Steady flow in curved vessels produces distortions of the vessel shape and intensity variations in the image due to motion during the interval between phase encoding or slice selection and the echo center. Even with steady flow, vessel curvature produces motion moments higher than velocity (acceleration, etc.), but use of a first order oblique flow compensated phase encoding gradient waveform reduced the distortion in the image. Numerical calculations of image distortions based on simple flow models are in good agreement with experimental results in a phantom.
An assessment of spin‐echo rotating‐frame imaging for spatially localized determination of short T2 relaxation times in vivo
Authors: Dixon Ruth M. , Styles Peter
Published: March 2007

The rotating frame method of localized spectroscopy can be augmented by the inclusion of a refocusing pulse to enable the measurement of T2 relaxation times. This technique is particularly appropriate for determining short relaxation parameters due to the absence of time consuming switched B0 field gradients. We have evaluated the accuracy of this protocol by measuring localized T2s in the range of 1 to 20 ms. Preliminary data obtained from muscle and liver of normal and iron overloaded human subjects are also presented.
Analysis of water‐macromolecule proton magnetization transfer in articular cartilage
Authors: Kim David K. , Ceckler Toni L. , Hascall Vincent C. , Calabro Anthony , Balaban Robert S.
Published: March 2007

These studies were designed to establish which structural elements of cartilage are responsible for proton magnetization transfer between water (Hf) and macromolecules (Hr) observed in MRI studies on articular cartilage. Saturation transfer techniques were used to monitor magnetization transfer in vitro on samples of the two major constituents of cartilage: collagen and proteoglycan. Articular cartilage samples were also evaluated in vitro before and after the removal of the proteoglycan fraction. Isolated hydrated collagen exhibited a significant proton magnetization transfer rate with water. In contrast, proteoglycans exhibited no proton magnetization transfer. Articular cartilage, in vitro, exhibited a high degree of magnetization transfer with water protons consistent with previous MRI studies in vivo. Enzymatic removal of proteoglycan from the cartilage did not alter the magnetization transfer rate between Hr and Hf. These data demonstrate that the structure and concentration of the collagen matrix are the predominant determinants of the magnetization transfer process in articular cartilage with little or no contribution from proteoglycans. This specificity of the magnetization transfer effect may prove useful in the noninvasive evaluation of cartilage composition and structure in vivo.
Magnetization transfer in cross‐linked bovine serum albumin solutions at 200 MHz: A model for tissue
Authors: Koenig Seymour H. , Brown Rodney D. , Ugolini Raphael
Published: March 2007

We report results for proton 1/T1, 1/T2, and K, the rate of magnetization transfer from solvent to solute, for 5 and 10 wt. % solutions of bovine serum albumin, both native and chemically cross‐linked, in undeuterated and ∼50% deuterated water, at 4.7 T (200.1 MHz) and 19°C. At this field, although K > 1/T1 for the cross‐linked samples, magnetization transfer contributes little to 1/T1 directly. Therefore K was measured using off‐resonance irradiation of the protein protons. The data for all the samples can be fit using a theoretical model for magnetization transfer, with three parameters: the intrinsic longitudinal relaxation rates of solute and solvent protons, and K. The magnitude of Kis so large that the newly‐identified, long‐lived (∼1 μs) hydration sites (S. H. Koenig, R. D. Brown III, and R. Ugolini, Magn. Reson. Med., 29, 77 (1993)) must be invoked to account for K, as is necessary to explain the differential effects of cross linking on the magnetic field dependence of 1/T1 of protons and deuterons and the large 1/T1 and 1/T2 values below ∼20 MHz in immobilized systems. Although these sites are few in number, their long resident lifetime becomes the correlation time for magnetization transfer when protein is immobilized, accounting for the large value of K. Recent data from several laboratories have shown that cross‐linked protein, as used here, is a good model for 1/T1 and 1/T2 of tissue, as a function of temperature and magnetic field.
In vitro characterization of lung cancers by the use of 1H nuclear magnetic resonance spectroscopy of tissue extracts and discriminant factor analysis
Authors: Hanaoka Hideto , Yoshioka Yoshichika , Ito Iichiro , Niitu Katuhiro , Yasuda Naoki
Published: March 2007

Using proton magnetic resonance spectroscopy (1H MRS) spectra were obtained in vitro from extracts of four types of lung cancer (squamous cell, adenocarcinoma, large cell, small cell) and normal lung. The hydrophilic phase of the chloroform/methanol‐water extracts yielded several distinct peaks. Among them the peak areas for cholines, creatines, glycine, and alanine, and their ratios were calculated and used as parameters to characterize different lung tissues. The ratios, cholines/alanine and glycine/alanine, were significantly (P < 0.001 to P < 0.05) higher for the normal lung than lung cancers. Creatines/glycine and creatines/cholines generally provided good discrimination (P < 0.001 to P < 0.05) between any two types of lung cancer. When data were further analyzed by discriminant factor analysis, there was 81.5 to 90.7% accuracy in predicting between normal lung and each cancer type, or among the four types of lung cancer. These results suggested that 1H MRS might be useful as an adjunct modality in the differential diagnosis of lung cancers.
Imaging oxygen tension in liver and spleen by 19F NMR
Authors: Holland Scott K. , Kennan Richard P. , Schaub Maria M. , D'Angelo Michael J. , Gore John C.
Published: March 2007

19F NMR imaging of the perfluorocarbon emulsion FluosolTM has been used to study regional variations in oxygen tension in rat liver and spleen. We have used the linear dependence of spin lattice relaxation rate (1/T1) on the partial oxygen pressure (pO2) of FluosolTM to determine the oxygen tension in the reticuloendothelial system (RES) of the liver and spleen of male Sprague‐Dawley rats which have serial infusions of FluosolTM. Oxygen tension maps have been computed from 19F NMR images using a calibration obtained for FluosolTM in vitro at 37.5°C. The spatial resolution of the pO2 maps computed using this technique is 1.2 × 1.2 mm in 3‐mm thick slices. Calculations from in vivo pO2 maps indicate an average change in the median pO2 of the RES from 118 to 80 mmHg for (n = 7) rats breathing 95% O2 and 5% CO2 (carbogen) and air, respectively.
MRI gradient waveform design by numerical optimization
Authors: Simonetti Orlando P. , Duerk Jeffrey L. , Chankong Vira
Published: March 2007

This manuscript describes a method of gradient waveform design by nonlinear constrained optimization. Methods of formulation and solution of the waveform optimization problem are briefly described for minimization of root mean squared current and minimization of waveform moments. Waveforms generated using these objectives are presented and compared with those obtained with other objectives. The method uses waveforms which are defined as a set of discrete amplitudes in order to remove artificial constraints on waveform shape imposed by “multilobe” designs. These point‐to‐point amplitudes are the parameters determined in the optimization procedure which includes knowledge of the specific imaging conditions and the specific gradient hardware system. Some beneficial results of this design approach are: a) physically realizable waveforms which optimally achieve specific imaging and motion artifact reduction goals, b) waveforms which are guaranteed to be optimal with respect to one of several possible objective, c) less reliance on the experience of the designer, and d) a potential reduction in waveform design time.
A wireless axial pair resonator
Authors: Maeda Hisatoshi , Toyooka Nobuo , Okawara Hiroshi
Published: March 2007

A wireless axial pair resonator consists of two coils coupling inductively with a body coil, which is used as a signal transmitter and receiver. Computer simulations gave signal enhancements of 1.41 and 1.47 for the resonators of 15‐ and 20‐cm diameter, whereas those of phantom studies gave 1.37 and 1.49.
Monocrystalline iron oxide nanocompounds (MION): Physicochemical properties
Authors: Shen Tueng , Weissleder Ralph , Papisov Mikhail , Bogdanov Alexei , Brady Thomas J.
Published: March 2007

We have previously described a novel monocrystalline iron oxide nanocompound (MION), a stable colloid that enables target specific MR imaging. In this study, the physicochemical properties of MION are reported using a variety of analytical techniques. High resolution electron microscopy indicates that a MION consists of hexagonal shaped electron‐dense cores of 4.6 ± 1.2 nm in diameter. This iron oxide core has an inverse spinel crystal structure which was confirmed by x‐ray powder diffraction. Chemical analysis showed that each core has 25 ± 6 dextran molecules (10 kD) attached, resulting in a unimodal hydrodynamic radius of 20 nm by laser light scattering. Because of the flexibillity of the dextran layer, the radius is only 8 nm in nonaqueous reverse micelles. At room temperature, MION exhibit superparamagnetic behavior with an induced magnetization of 68 emu/g Fe at 1.5 T. Mössbauer studies show that the saturation internal magnetic field is 505 KOe, and blocking temperature is at 100 K. The R1 relaxivity of MION is 16.5 (mM‐sec)‐1 and the R2 relaxivity is 34.8 (mM‐sec)‐1 in aqueous solution at 37°C and 0.47 T. In vitro phantom studies show that the detectability of MION in liver tissue is less than 50 nmol Fe/g tissue using gradient echo imaging techniques.
Measurement of capillary permeability to macromolecules by dynamic magnetic resonance imaging: A quantitative noninvasive technique
Authors: Shames David M. , Kuwatsuru Ryohei , Vexler Vladimir , Mühler Andreas , Brasch Robert C.
Published: March 2007

A simple, linear kinetic model has been developed for the noninvasive assessment of capillary permeability to macromolecules in the rat by dynamic magnetic resonance imaging using albumin‐Gd‐DTPA. Data required by the model are signal intensity responses from a target tissue and a venous structure such as inferior vena cava before and after bolus intravenous injection of albumin‐Gd‐DTPA. Additional requirements include an early temporal resolution of approximately one image/min and a blood sample for hematocrit. The model does not require measurement of albumin‐Gd‐DTPA concentration in either arterial or venous blood. Pilot experiments suggest that this technique is adequate for estimation of the fractional leak rate of macromolecules from plasma to interstitial water as well as tissue plasma volume, the product of which yields a measure of the permeability surface area product of the tissue if the extraction fraction is modest (<0.2). The technique may be generally applicable to the study of abnormal capillary permeability in humans as well as animals.
Real‐time acquisition, display, and interactive graphic control of NMR cardiac profiles and images
Authors: Hardy Christopher J. , Darrow Robert D. , Nieters Edward J. , Roemer Peter B. , Watkins Ronald D. , Adams William J. , Hattes Neil R. , Maier Josepth K.
Published: March 2007

A highly interactive MRI scanner interface has been developed that allows, for the first time, real‐time graphic control of one‐dimensional (1D) and two‐dimensional (2D) cardiac MRI exams. The system comprises a Mercury array processor (AP) in a Sun SPARCserver with two connections to the MRI scanner, a data link that passes the NMR data directly to the AP as they are collected, and a control link that passes commands from the Sun to the scanner to redirect the imaging pulse sequence in real time. In the 1D techniques, a cylinder or “pencil” of magnetization is repeatedly excited using gradient‐echo or spin‐echo line‐scan sequences, with the magnetization read out each time along the length of the cylinder, and a scrolling display generated on the Sun monitor. Rubber‐band lines drawn on the scout image redirect the pencil or imaging slice to different locations, with the changes immediately visible in the display. M‐mode imaging, 1D flow imaging, and 2D fast cardiac imaging have been demonstrated on normal volunteers using this system. This platform represents an operator‐“friendly” way of directing real‐time imaging of the heart.
Measurement of T1 relaxation times of cardiac phosphate metabolites using BIR‐4 adiabatic RF pulses and a variable nutation method
Authors: Sakuma Hajime , Nelson Sarah J. , Vigneron Daniel B. , Hartiala Jaakko , Higgins Charles B.
Published: March 2007

T1relaxation times of PCr and β‐ATP in human cardiac and skeletal muscle were evaluated using a variable nutation method. This allows T1measurements with a constant TR and a significant reduction in acquisition time compared with the partial saturation method. Four 1D CSI datasets were obtained using 30°, 45°, 60°, and 90° BIR‐4 adiabatic RF pulses within 40 min. The T1of the phosphate phantom obtained with this method agreed with values obtained with the partial saturation method. The T1s of PCr and β‐ATP in heart are 3.98 = 0.18 s and 1.86 ± 0.16 s (mean = SE). Our results demonstrated that T1 values in heart and skeletal muscle are not significantly different.
Resolution of phospholipid molecular species by 31P NMR
Authors: Pearce J. M. , Komoroski R. A.
Published: March 2007

Phosphorus‐31 NMR chemical shifts of phospholipids (PLs) solubilized in bile salts were studied with respect to variations in the structure of the acyl substituents. The presence of double bonds in the acyl chains of phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), and phosphatidic acid (PA) induced small but consistent upfield shifts relative to the corresponding disaturated acyl PL signals. The magnitudes of the unsaturation‐related upfield shifts were approximately twice as large in sodium cholate as in sodium deoxycholate. Chemical shift separations of PC, PE, and PG dipalmitoyl‐dioleoyl species pairs increased slightly at lower temperatures. Resolution of the PC species pair was maximized and nearly independent of cholate‐to‐PL ratio at values greater than about 100 in 2% cholate. Only the PA species resolution varied significantly over the pH range 6.5 to 9.5, in the vicinity of its pK2. Shift differences for a homologous series of disaturated acyl PCs showed a logarithmic dependence on chain length. Spectra for a variety of PC standards were used to interpret the composite PC signals from egg yolk extract, soybean extract and whole human amniotic fluid. The 31P NMR analyses were consistent with published chromatographic studies. Interpretation of composite PL signals in the cholate system is simplified for mixtures having restricted acyl chain length and degree of unsaturation.
Echo‐planar spin‐echo and inversion pulses
Authors: Pauly John , Spielman Dan , Macovski Albert
Published: March 2007

The echo‐planar k‐space trajectory can be used as the basis for any two‐dimensional selective pulse. The main application is spectral‐spatial pulses, which must be based on the echoplanar trajectory. In this paper we show how echo‐planar spinecho (EPSE) pulses may be designed.
Analysis of systematic and random error in MR volumetric flow measurements
Authors: Wolf Ronald L. , Ehman Richard L. , Riederer Stephen J. , Rossman Phillip J.
Published: March 2007

The spatial aspects of error in 2D MR cine phase‐velocity mapping are considered in order to define acquisition strategies which will minimize error in measuring volumetric flow. Error was separated into two categories: systematic and random. Potential sources of systematic error examined were intravoxel phase dispersion (IVPD), partial volume effects, misalignment of flow axis and flow‐encoding gradients, and improper choice of vessel voxels for flux calculations. Random error was addressed using analysis of propagation of variance. Analytical expressions for sources of error were derived; and computer models were used to test the analytical models. Flow phantom studies examining error in MR volumetric flow measurements were performed and compared with error predicted by the analytical models. Expected error in several clinical situations of interest was then derived to find appropriate acquisition strategies. Spatial resolution, signal to noise ratio, velocity sensitivity and the ratio of the modulus of moving isochromats to that of static isochromats were found to be the most important parameters in controlling error and were found to cause competing effects with respect to systematic and random error.
Three‐Dimensional NMR microscopy of rat spleen and liver
Authors: Zhou Xiaohong , Magin Richard L. , Alameda Jay C. , Reynolds Harry A. , Lauterbur Paul C.
Published: March 2007

Three‐dimensional microscopic NMR images of spleen and liver specimens from rats injected wlth dextran magnetite particles and from controls were obtained at 4.7 T, using a specially designed probe in conjunction with a 3D filtered back projection reconstruction algorithm. All of the images were reconstructed as 643 arrays with (25 μm)3 isotropic voxels. With the aid of the MR contrast agent, the red pulp and marginal zone of the spleen and the portal triad of the liver could be distinguished from the surrounding tissue in T2‐weighted images. For mature rat spleen, natural contrast in T2‐weighted images was found to distinguish the same features. Histolog‐ical examinations of the tissues with and without contrast agent were also performed using an optical microscope. Microscoplc NMR images, despite their lower resolution, clearly revealed many features seen in the optical images.
A pitfall associated with determination of transverse relaxation times of the 31P NMR signals of ATP using the Hahn spin‐echo
Authors: Jung Wulf‐Ingo , Straubinger Klaus , Bunse Michael , Widmaier Stefan , Schick Fritz , Küper Klaus , Dietze Günther , Lutz Otto
Published: March 2007

T2 measurements of 31P NMR signals of ATP using the Hahn 90°–180° spin‐echo sequence imply difficulties whenever the 180° pulse angle is not completely perfect. The reason for this finding is the crucial influence of the J ‐couplings of the ATP signals which result in intensity modulations and consequently in false T2 values even when the echo times are chosen to TE = n/J. Examinations on the calf muscles of healthy volunteers were performed to demonstrate this effect and its influence on in vivo T2 determinations. The T2 relaxation times evaluated with the Hahn spin‐echo in combination with a Helmholtz coil are far shorter than the true T2 values.
Improved myocardial tagging contrast
Authors: Fischer S. E. , McKinnon G. C. , Maier S. E. , Boesiger P.
Published: March 2007

Myocardial tagging is a new noninvasive MRI method that allows the study of myocardial motion with high accuracy. However, with conventional tagging techniques tagging contrast is impaired at later heart phases due to longitudinal relaxation. An improved method, called Complementary SPAtial Modulation of Magnetization (CSPAMM), which separates the component of the magnetization with the tagging information from the relaxed component by subtraction of two measurements with first a positive and then a negative tagging grid, is presented. This technique improves the grid contrast and greatly facilitates the automatic evaluation of the myocardial motion. Thus the motion assessment of the entire heart cycle becomes possible. The improvements are documented by numerical simulations and by experiments on phantoms and on human volunteers.
Fast MRI by creating multiple spin echoes in a CPMG sequence
Authors: Oshio Koichi , Jolesz Ferenc A.
Published: March 2007

A fast multislice imaging technique has been developed. RASTER (Rapid Acquisition with Stimulated Echo Refocusing) is based on RARE (Rapid Acquisition with Relaxation Enhancement), and creates multiple spin echoes/each 180° pulse utilizing stimulated echoes, and phase encode each differently. The sequence can be much faster than RARE while keeping the same spin echo image contrast. The main limitation of the technique is reduced signal‐to‐noise ratio.
MRI evaluation of myocardial perfusion without a contrast agent using magnetization transfer
Authors: Prasad P. V. , Burstein D. , Edelman R. R.
Published: March 2007

We propose a new magnetic resonance imaging (MRI) technique that is sensitive to myocardial tissue perfusion that obviates the use of an extrinsic contrast agent. Significant advantages of such a technique are that it avoids accumulation of contrast agent when repeated studies are performed on the same subject and that it is completely noninvasive. The method makes use of a combination of magnetization transfer (MT) and T1sut (measured spin‐lattice reiaxation time in the presence of MT) weighting. in this Communication, we present observations from experiments with an isolated rat heart model that demonstrate increase of MT‐weighted signal Intensity and T1sut with flow. Also included are data showing that these effects can be made synergistic for enhancing the sensitivity to perfusion. We have observed about a 3% change in MT‐weighted intensity end up to 10% change in MTT1sut‐weighted intensity for a change of 1 ml/min in global flow rate.
Feature‐recognizing MRI
Authors: Cao Yue , Levin David N.
Published: March 2007

We describe a new theory of MR imaging that utilizes prior information in the form of a set of “training” images thought to be similar to the “unknown” objects to be scanned. First, the training images are processed to find an orthonormal series representation of these images that is more convergent than the usual Fourier series. The coefficients in this new series can be calculated from a subset of the phase‐encoded signals needed to construct the Fourier image representation. The characteristics of the training images also determine exactly which phase‐encoded signals should be measured in order to minimize error in the image reconstruction. The optimal phase‐encodings are usually scattered nonuniformly in k‐space. Good results were obtained when this theory was applied to imaging data from simulated objects and to experimental data from phantom scans. This theory provides the basis for developing efficient scanning and image reconstruction techniques that are “tailored” to each body part or to particular disease states.
Accurate measurement of T1in vivo in less than 3 seconds using echo‐planar imaging
Authors: Gowland P. , Mansfield P.
Published: March 2007

This paper describes a rapid and accurate method for meassuring T1 in vivo using an echo‐planar imaging version of the Look‐Locher sequence. T1 values from 76 to 1330 ms have been measured in 3 s with a mean accuracy of 4.6%.
Motion suppression improves quantification of rat liver volume in vivo by magnetic resonance imaging
Authors: Cockman M. D. , Hayes D. A. , Kuzmak B. R.
Published: March 2007

In response to the presence of certain compounds, rat liver weight can increase. Under the assumption that the liver density does not change, the liver volume will increase as well. To develop the capability to monitor this process noninvasively over time, we used liver volumes determined from MR images to estimate the in vivo liver volumes and weights of normal rats. We acquired multislice, spin‐echo images from 18 rats using several protocols for suppression of motion artifacts. We found that volumes determined from data obtained using a combination of gradient moment mulling and respiratory gating, or a combination of signal averaging and “retarded” (after the π pulse) phase‐encoding, produced the most accurate estimates of in vivo liver volume and weight.
Localized real‐time velocity spectra determination
Authors: Hu Bob S. , Pauly John M. , Nishimura Dwight G.
Published: March 2007

The accurate measurement of flow velocity has long been a subject of NMR research. In the field of medical imaging, a variety of techniques primarily based on the principle of Fourier encoding have been described. Due to time constraints, necessary trade‐offs exist between spatial versus velocity spectral resolution. In general, either the average velocity of individual pixels is displayed or velocity spectral determinations are made at the cost of spatial localization. The recent development of multidimensional excitation pulses makes spatial localization possible during the excitation phase of the pulse sequences. This approach, coupled with time varying gradient readout, can be used to obtain single‐shot localized velocity spectra. Using these concepts, we have obtained in vivo real‐time measurements of localized velocity spectra on our clinical imager.
Generalized K‐space analysis and correction of motion effects in MR imaging
Authors: Louis Lauzon M. , Rutt Brian K.
Published: March 2007

A new approach to understanding and reducing motion artifacts in magnetic resonance imaging (MRI) is introduced. This paper presents a novel technique for correcting generalized motion artifacts arising from translation, rotation, dilation, and compression, or any combination thereof. We also describe a new pulse sequence and a specialized postprocessing technique required to suppress these motion artifacts. The correction algorithm corrects for generalized motion. The theoreticial basis of the correction scheme is founded upon the (k,t)‐space formalism and the concept of pulse sequence contrast mapping functions. The proposed (k,t) formalism is based on the Fourier projection slice theorem and allows us to determine how motion artifacts arise. The correction technique currently suffers from some spatial resolution and signal‐to‐noise ratio limitations, and works better for small object than large objects. These problems will be investigated in subsequent studies.
31P NMR spectra of intact red blood cells: Quantitation of UDPGlucose and UDPGalactose
Authors: Wehrli Suzanne L. , Palmieri Michael J. , Reynolds Robert A. , Segal Stanton
Published: March 2007

The combined levels of uridine diphosphogalactose (UDPGal) and uridine diphosphoglucose (UDPGlu) were measured directly by 31P NMR spectroscopy in intact fully oxygenated erythrocytes. Quantitative analysis was obtained using a sealed capillary of methylene diphosphonate (MDP) calibrated with standard solutions of UDPGlu and UDPGal of known concentration prepared in KRB/BSA. The combined peaks of UDPGlu and UDPGal were integrated after subtraction of the underlying broad component originating from membrane phospholipids. The average concentration of 27.16 ± 5.18 nmole/ml or 8.08 ± 1.36 μmole/100 g hemoglobin obtained for these metabolites correlated well with their total determined by HPLC of trichloracetic acid (TCA) extracts of the same samples.
31P relaxation rates to evaluate physiological events in the heart
Authors: Osbakken Mary D. , Wroblewski Krzysztof , Zhang Danning , Ivanics Tamas , Wehrli Suzanne
Published: March 2007

The present study was performed to determine whether 31P NMR relaxation times (T1) of adenosine triphosphate (ATP) might be used to monitor the resultant altered myocardial physiology produced by ischemia and possibly to explain mechanisms of altered physiology. To this end, pre‐and post‐ischemic T1s were determined in hearts perfused in the Lan‐gendorff mode, using 31P NMR inversion recovery methods. In hearts without any pretreatment (CON), post‐ischemic ATP Ti values were significantly decreased compared with pre‐isch‐emic values (P <0.05): Pre‐isch: γ = 0.58 ± 0.08; α = 62 ± 0.06; β = 0.38 ± 0.08; Post‐isch: γ = 0.33 plusmn; 0.05; α = 0.43 ± 0. 03; β = 0. 23 plusmn; 0.05. In groups pretreated with creatine (CR), cyclocreatine (CY), or superoxide dismutase plus catalase (SOD‐CAT) before ischemia, the post‐ischemic ATP T1 values were simlilar and were not significantly changed from pre‐ischemic values. These combined data suggest that T1s of ATP might be used to monitor altered myocardial physiology and could provide insight into mechanisms of alteration.
Assessment of human colorectal biopsies by 1H MRS: Correlation with histopathology
Authors: Lean Cynthia L. , Newland R. C. , Ende D. A. , Bokey E. L. , Smith Ian C. P. , Mountford Carolyn E.
Published: March 2007

Samples (3 mm3 of histopathologically normal (n = 15) and carclnomatous tissue (n = 15) were obtained from colectomy specimens and examined by 1H MRS. A combination of one‐and two‐dimensional spectra, obtained with appropriate acquisition and processing parameters, provide multiple diagnostic parameters allowing the distinction between normal and carcinomatous tissue. The diagnostic parameters include rosonances from choline, choline‐based, and other metabolites, cell surface fucosylation, and altered lipid profiles. Tissues histopathologically classified as normal, while remaining distinct from the malignant spectral profile, were found to fit into two categories, one of which had some of the spectral characteristics of malignancy. These results indicate that 1H MRS identifies abnormal colorectal mucosa, which is not morphologically manifest.Such abnormalities have been reported previously to exist in premalignant colorectal tissue by monoclonal antibody studies. Collectively, these results suggest that a clinical study of colorectal biopsies by 1H MRS could provide support for the use of MRS as an adjunct to current pathological procedures.
Oxygen tension in a murine tumor: A combined EPR and MRI study
Authors: Bačić G. , Liu K. J. , O'Hara J. A. , Harris R. D. , Szybinski K. , Goda F. , Swartz H. M.
Published: March 2007

The effects of fusinite, a new agent for the measurement of the concentration of oxygen in vivo by EPR, on MRI images have been studied. There was little effect on spin‐echo T1‐weighted images, but the fusinite resulted in large effects on T2‐weighted images. Especially large effects could be observed when using spoiled gradient echo sequences (SPGR). The observed measurements of oxygen by EPR corresponded to the relative vascularity at the site of the fusinite both histologically and by MRI studies of vascularity using Gd‐DTPA as a contrast agent. We conclude that by using the effects of fusinite on magnetic susceptibility, it can be located accurately and noninvasively with MRI and thereby the value of the use of fusinite to measure concentration of oxygen in vivo is enhanced.
Relaxometry, animal biodistribution, and magnetic resonance imaging studies of some new gadolinium (III) macrocyclic phosphinate and phosphonate monoester complexes
Authors: Geraldes C. F. G. C. , Sherry A. D. , Lázár I. , Miseta A. , Bogner P. , Berenyi E. , Sumegi B. , Kiefer G. E. , McMillan K. , Maton F. , Muller R. N.
Published: March 2007

The Gd3+ complexes of three new phosphorus containing tetraaza macrocycles (1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetrakis (methylene ethylphosphonic acid), H4DOTEP; 1,4,7,10‐tetraazacyclododecane‐l,4,7,10‐tetrakis (methylene phosphonic acid monoethylester), H4DOTPME; and the corresponding n‐butyl ester, H4DOTPMB) were prepared and examined for possible use as MRI contrast agents. Although thermodynamically and kinetically less stable than Gd(DOTA)− in saline and HSA solution, the stability of these new macrocyclic complexes appears to be sufficiently high for in vivo applications. NMRD relaxivity profiles of the three complexes indicate that the number of inner sphere water molecules for these chelates is ≤1 and that the more hydrophobic chelate, Gd(DOT‐PMB), binds to human serum albumin (HSA). Biodistribution studies of the radioactive 153Sm or 159Gd chelates in rats, gamma imaging of the 153Sm chelates in rats, and proton MRI studies of the nonradioactive Gd3+ chelates in rabbits all indicate that the DOTPMB complexes accumulate preferentially in the liver, spleen, and small intestines while the more hydrophilic DOTEP and DOTPME complexes appear to display renal clearances similar to other low molecular weight contrast agents.
Measurement of regional blood oxygenation and cerebral hemodynamics
Authors: Hoppel Bernice E. , Weisskoff Robert M. , Thulborn Keith R. , Moore John B. , Kwong Kenneth K. , Rosen Bruce R.
Published: March 2007

An echo planar linewidth mapping technique, Shufflebutt, has allowed temporal measurements of changes in linewidth caused by static inhomogeneities (ΔLWSI) and transverse relaxation rate (ΔR2) in models of hypoxia and hypercapnia. We demonstrate these changes are due to intravascular susceptibility differences(ΔX) between the blood and tissue. Contrast agent injections at a /ΔX equivalent to that of deoxygenatetd blood showed a twofold difference between the contrast agent and physiological anoxia values. Hypercapnia decreased both ΔLWSI and ΔR2 consistent with an increase in blood oxygenation. We attribute these findings to constant oxygen extraction during an increase in blood flow, resulting in less deoxygenated venous blood and thus reduced ΔX. For in vivoperturbations we found that ΔR/ΔR2′ ≈ 0.33, a ratio much different from that measured in whole blood phantoms (ΔR/ΔR2′ ≈ 2). This demonstrates that signal changes in these studies are produced predominantly by dephasing of extravascular protons due to field inhomogeneities produced by intravascular deoxygenated hemoglobin (deoxyHb).
A rapid interleaved method for measuring signal intensity curves in both blood and tissue during contrast agent administration
Authors: Taylor N. J. , Rowland I. J. , Tanner S. F. , Leach M. O.
Published: March 2007

A method has been developed that uses dynamic MR imaging to measure simultaneously the changes in signal intensity due to paramagnetic contrast agent in blood and tissue, using interleaved single‐angle projection and imaging sequences. The basic projection/image sequence has a projection time resolution of 50 ms and can measure rapid changes in the blood signal intensity. Variants with a tissue suppression slab have time resolutions of 57 or 75 ms. Orientation of the projection and image planes can be defined independently. This technique will facilitate functional measurements using MR contrast agents, allowing the blood input function to be determined with excellent time resolution.
Intravascular susceptibility contrast mechanisms in tissues
Authors: Kennan Richard P. , Zhong Jianhui , Gore John C.
Published: March 2007

The factors affecting the rate of loss of transverse magnetization in gradient echo and spin‐echo pulse sequences have been quantified using computer modeling for media containing arrays of susceptibility variations. The results are particularly relevant for describing the signal losses that occur in tissues containing capillaries of altered intrinsic susceptibility from the administration of exogenous contrast agents or arising from changes in blood oxygenation. The precise magnitudes and relationship of gradient echo and spin‐echo decay rates depend on geometrical factors such as the sizes and spacings of the inhomogeneities, the rate of water diffusion, field strength, and echo times. The conventional separation of contributions to transverse decay rates arising from so‐called static field effects and diffusion is shown to be inappropriate for many situations of practical interest because diffusion introduces a motional averaging of the static field even in gradient echo sequences. The result of diffusion in some regimes is to reduce the decay rate from field inhomogeneities in gradient echo sequences, so that T2* is longer in media such as tissue where water diffuses reasonably rapidly, than would be the case for stationary nuclei. The effects of different types of contrast agent and the implications for functional imaging based on the effects of deoxyhemoglobin in brain tissue are considered.
Reperfused myocardial infarctions on T1‐ and susceptibility‐enhanced MRI: Evidence for loss of compartmentalization of contrast media
Authors: Saeed Maythem , Wendland Michael F. , Masui Takayuki , Higgins Charles B.
Published: March 2007

The purpose of this study was to characterize the contrast caused by a susceptibility MRI contrast agents, on spin echo T2‐weighted imaging of reperfused myocardial infarction. Our interest in this model focused on the expected requirement that such agents be compartmentalized in the tissue to cause signal loss on spin echo images, a condition which may not be present in reperfused infarcted myocardium. Accordingly, nine rats were subjected to 2 h of left coronary artery occlusion followed by 3 ± 0.5 h of reperfusion prior to administration of contrast media. Three sets of MR images were acquired: (a) baseline axial images at the midventricle, both T1‐weighted (TR/TE = 300/20) and T2‐weighted (TR/TE = 1500/60); (b) T1‐weighted images after administering a T1‐enhancing agent, Gd‐DTPA‐BMA (0.2 mmol/kg), to document that contrast media is delivered to the reperfused infarction; and (c) T2‐weighted images after administering the susceptibility agent, Dy‐DTPA‐BMA (1.0 mmol/kg). Gadolinium‐enhanced T1 images depicted reperfused infarction as regions with greatly enhanced signal intensity compared with unin‐farcted myocardium, indicating that contrast agent was delivered to the infarcted zone. Dysprosium‐enhanced T1 images depicted the injury as a region of persistent signal intensity relative to depletion of signal in normal myocardium, consistent with failure of the contrast agent to cause signal loss. Similar infarction sizes were observed for unenhanced T2‐weighted images (33 ± 5%), gadolinium‐enhanced T1 weighted images (36 ± 5%) and postmortem staining (30 ± 6%); strong correlations (r > 0.9) were noted in comparisons of these data. Dysprosium‐enhanced images exhibited a smaller region of differential signal presumed to be infarction (20 ± 5%, P < 0.05) and weak correlations (r < 0.75) with the other measurements. We conclude that the smaller infarction depicted on dysprosium‐enhanced images is a subregion of the true infarction in which myocardial necrosis is sufficiently advanced that the agent is homogeneously distributed throughout all tissue compartments, preventing T2*‐dependent phase loss on spin echo images.
Interleaved echo planar imaging on a standard MRI system
Authors: Butts Kim , Riederer Stephen J. , Ehman Richard L. , Thompson Richard M. , Jack Clifford R.
Published: March 2007

This work describes an interleaved echo planar imaging (EPI) method for use on a standard whole body scanner. The data acquisition is divided into two to eight repetitions rather than one to two, as implemented by dedicated EPI systems. Interleaving allows the use of a lower sampling bandwidth with a significant increase in signal‐to‐noise. The method also has the advantages of relative ease of implementation, no need for postprocessing to remove image distortion, and no need for shimming on a case‐by‐case basis. The interleaved EPI method was applied to two applications ideally suited to EPI: breathhold T2‐weighted abdominal imaging and functional imaging. In vivo liver‐lesion contrast as measured in a 35‐patient study showed increased contrast for the Interleaved EPI by an average factor of 1.21 (± 0.34) over conventional spin‐echo imaging. CNR measurements showed the EPI to be comparable with conventional spin echo with a relative factor of 1.00 (± 0.36). Functional imaging with an eight‐shot interleaved EPI sequence provided 128 × 128 images of cerebral activation during bilateral finger tapping.
Detection of brain activation using oxygenation sensitive functional spectroscopy
Authors: Hennig J. , Emst Th. , Speck O. , Deuschl G. , Feifel E.
Published: March 2007

A nonwater‐suppressed localized spectroscopy experiment using the PRESS‐sequence has been used to study the signal changes of the water resonance during cortical activation. Significant effects with an effect‐to‐noise ratio up to 50:1 for a single shot experiment have been observed upon photic stimulation. The exceedingly high signal‐to‐noise ratio of the experiment was used to demonstrate signal changes as low as 0.1% after electrical stimulation of the median nerve.
Fructose 3‐phosphate and 5‐phosphoribosyl‐1‐pyrophosphate formation in perhsed human erythrocytes: 31P NMR studies
Authors: Lundberg Peter , Roy Sushmita , Kuchel Philip W.
Published: March 2007

31P NMR was used to study the formation of fructose 3‐phos‐phate (F3P) and 5‐phosphoribosyl‐1‐pyrophosphate (PRPP) in perfused human erythrocytes, in the presence of 10 different combinations and concentrations of glucose, inosine, pyru‐vate, fructose, and inorganic phosphate (Pi). (1) The cells were immobilized in alginate‐coated agarose threads and perfused with a medium containing fructose, and the level of F3P increased continuously over more than 10 h. The net rate of F3P formation was independent of the concentration of 2,3‐bis‐phosphoglycerate (2,3‐DPG) present in the cells. (2) PRPP was formed in high concentrations, relative to normal, in immobilized cells when they were perfused with a medium containing Pi at a low pH (6.6). (3) The 2,3‐DPG level decreased simultaneously when the sample was perfused with a medium containing fructose, but without inosine or pyruvate. The measured intracellular pH and free Mg2+ concentration were constant in these experiments. (4) The experiments confirmed the presence of fructose‐3‐phosphokinase (E.C. 2.7.1.‐) and ribose‐phosphate pyrophosphokinase (E.C. 2.7.6.1) activity in the human erythrocytes and that the biosynthetic pathways are active in immobilized cells at 37°C. (5) The rates of accumulation of 2,3‐DPG and phosphomonoesters (PME) appeared to be strongly correlated.
Optimization of parameter values for complex pulse sequences by simulated annealing: Application to 3D MP‐RAGE imaging of the brain
Authors: Epstein Frederick H. , Mugler John P. , Brookeman James R.
Published: March 2007

A number of pulse sequence techniques, including magnetization‐prepared gradient echo (MP‐GRE), segmented GRE, and hybrid RARE, employ a relatively large number of variable pulse sequence parameters and acquire the image data during a transient signal evolution. These sequences have recently been proposed and/or used for clinical applications in the brain, spine, liver, and coronary arteries. Thus, the need for a method of deriving optimal pulse sequence parameter values for this class of sequences now exists. Due to the complexity of these sequences, conventional optimization approaches, such as applying differential calculus to signal difference equations, are inadequate. We have developed a general framework for adapting the simulated annealing algorithm to pulse sequence parameter value optimization, and applied this framework to the specific case of optimizing the white matter‐gray matter signal difference for a T1‐weighted variable flip angle 3D MP‐RAGE sequence. Using our algorithm, the values of 35 sequence parameters, including the magnetization‐preparation RF pulse flip angle and delay time, 32 flip angles in the variable flip angle gradient‐echo acquisition sequence, and the magnetization recovery time, were derived. Optimized 3D MP‐RAGE achieved up to a 130% increase in white matter‐gray matter signal difference compared with optimized 3D RF‐spoiled FLASH with the same total acquisition time. The simulated annealing approach was effective at deriving optimal parameter values for a specific 3D MP‐RAGE imaging objective, and may be useful for other imaging objectives and sequences in this general class.
A method for in vivo high resolution MRI of rat spinal cord injury
Authors: Ford John C. , Hackney David B. , Joseph Peter M. , Phelan Megan , Alsop David C. , Tabor Stacy L. , Hand Christopher M. , Markowitz Ronald S. , Black Perry
Published: March 2007

We have developed an implanted radiofrequency coil to obtain high resolution in vivo MR images at 1.9 Tesla of rat spinal cords that have been injured using a standardized weight drop technique. The signal‐to‐noise ratio and motion artifact suppression of these images is superior to that achieved in earlier attempts at this field strength using an external surface coil. The high quality and spatial resolution provided by this technique afford the possibility for longitudinal studies of experimental spinal cord injury before and after treatment, as well as detailed correlation of in vivo MRI contrast, histopathological findings, and functional deficit, in a controlled setting.
Discrimination of fluorinated uridine metabolites in N‐417 small cell lung cancer cell extracts via 19F‐ and 31P‐NMR
Authors: Pederson Nathanael V. , Zanghi James A. , Miller William M. , Knop Richard H.
Published: March 2007

31P‐NMR extract spectra of N‐417 Small Cell Lung Cancer (SCLC) cells cultured with fluorouridine (FUrd) reveal new peaks with chemical shifts in the diphosphodiester and nucleoside triphosphate regions. These peaks were identified as FUTP, FUDP, FUDP‐glucose, FUDP‐glucuronate, FUDP‐GlcNAc, and FUDP‐GalNAc via enzymatic conversion and 19F‐and 31P‐NYR analysis. Distinct 19F chemical shifts were assigned for FUTP, FUDP, and the FUDP‐sugars.
Signal targeting with alternating radiofrequency (STAR) sequences: Application to MR angiography
Authors: Edelman Robert R. , Siewert Bettina , Adamis Mary , Gaa Jochen , Laub Gerhard , Wielopolski Piotr
Published: March 2007

We describe a time of flight subtraction method for cine MR angiography that provides nearly perfect suppression of background signal intensity with excellent flow contrast. The method consists of a preparation phase, during which the longitudinal magnetization of the target tissue is inverted on alternate acquisitions and the background tissue is presaturated, followed by a readout phase using a cine segmented turboFLASH sequence with a shared echo modification to improve temporal resolution. With appropriate alternation of the phases of the radiofrequency excitation pulses, there is cancellation of the background signal intensity but flow signal is optimized. By using a thick section (up to 25 mm), substantial portions of the vascular territory are encompassed in a single plane. This permits rapid, dynamic assessment of flow patterns in areas such as the circle of Willis, carotid bifurcation, or renal arteries. Applications of the method for bright and dark blood cine MR angiography are demonstrated.