bluuebunny/crossref_metadata_2025 huggingface dataset:
T1 snapshot flash measurement of rat brain glioma: kinetics of the tumor‐enhancing contrast agent manganese (iii) tetraphenylporphine sulfonate
Authors: Hoehn‐Berlage Mathias , Norris David , Bockhorst Kurt , Ernestus Ralf‐Ingo , Kloiber Otmar , Bonnekoh Petra , Leibfritz Dieter , Hossmann Konstantin‐Alexander
Published: March 2007

The ultrafast inversion recovery snapshot FLASH technique was used to determine the kinetics of the contrast agent manganese (III) tetraphenylporphine sulfonate (MnTPPS) in experimental brain tumors in rats. In the first part of the investigation this technique was validated with the conventional inversion recovery spin‐echo method by comparing in vivo T1 data of a normal rat brain. Agreement between T1 values obtained from both techniques was complete, as tested for a large number of pixels in identical coronal slices. In the second part the fast IR snapshot FLASH method was applied to study the effect of the NMR contrast agent MnTPPS on the T1 relaxation time of experimental gliomas in rat brains. T1 of normal brain tissue (1024–1035 ms), tumor (1217 ms), and edema (1199 ms) was determined with the inversion recovery version of the snapshot FLASH imaging technique. After intraperitoneal injection of MnTPPS (0.25 mmol/kg body wt) T1 decreased exponentially to 56% of control in tumor and to 62% in muscle. In normal and edematous brain tissue no significant changes in T1 were observed up to 5 h after injection of the contrast agent. Once the T1 contrast between tumor and peritumoral brain tissue had reached a saturation, the enhancement persisted for several hours to days. Therefore application of this contrast agent resulted in a sharp demarcation between glioma and peritumoral edema.
Spin‐echo m‐mode nmr imaging
Authors: Matsuda Tetsuya , Shimizu Koji , Sakurai Tsunetaro , Yamasaki Kazunari , Nagano Yutaka , Okada Ikutaro , Miki Shinji , Kawai Chuichi
Published: March 2007

A nuclear magnetic resonance (NMR) imaging and display method for the observation of the continuous motion of objects is presented. By modifying a line scan technique, the spin‐density distribution along a line is displayed in succession. Although spatial information is limited to only one dimension, the motion of the object is recorded at intervals of 55 ms by using a commercially available NMR imaging system. In a phantom study, this method yielded accurate velocity measurements along a single axis. When the method was applied to the human chest, an image analogous to that of M‐mode echocardiography was obtained. This method, which can be called spin‐echo M‐mode NMR imaging, approaches the functional analysis of cardiac wall motion in regions where echocardiography is not possible. The effects of respiratory motion on the left ventricular wall were recorded in addition to its intrinsic contractile motion in an image obtained along a line parallel to the cranio‐caudal axis of the body. The advantages of this method to assess cardiac wall motion in a patient with an arrhythmia were also demonstrated.
31p nme spectroscopic study of the effects of γ‐irradiation on rif‐1 tumor cells perfused in vitro
Authors: Ng Cheng E. , Mcgovern Kathy A. , Wehrle Janna P. , Glickson Jerry D.
Published: March 2007

In order to examine the mechanisms underlying radiation‐induced changes in phosphorus metabolite levels observed in RIF‐1 tumors in vivo, RIF‐1 cells in culture were perfused for up to 70 h following γ‐irradiation with 0‐25 Gy and monitored continuously by, 31P NMR spectroscopy at 8.5 T. Cells immobilized in the sample volume by incorporation into calcium alginate beads were bioenergetically stable, but did not replicate at the cell density used. Following an initial increase in PCr and NTP, which occurred in both control and irradiated cells, a dramatic decline in high‐energy phosphates was detected beginning 24‐30 h after irradiation with 15 or 25 Gy. In contrast, unirradiated cells or cells treated with 10 Gy remained metabolically stable for up to 72 h. The metabolic changes induced by irradiation of the cultured cells, which reflected cell death and lysis, were distinctly different from those observed in RIF‐1 tumors in vivo during the same postirradiation time interval‐an increase in high–energy relative to low‐energy phosphates. This suggests that the spectral changes in vivo do not result from direct modification of cellular energy metabolism by radiation injury.
A noninvasive assessment of myocardial oxygen tension: 19f nmr spectroscopy of sequestered perfluorocarbon emulsion
Authors: Mason Ralph P. , Jeffrey F. Mark H. , Malloy Craig R. , Babcock Evelyn E. , Antich Peter P.
Published: March 2007

Fluorine NMR spectroscopy of sequestered perfluorocarbon emulsion has been used to measure myocardial oxygen tension. This novel application provides a rapid noninvasive assessment of changes in oxygen tension in response to ischemia and reperfusion. Rats were predosed with Oxypherol‐ET (emulsion of perfluorotributylamine). Following vascular clearance of the emulsion the heart was excised and perfused using the Langendorff retrogradetechnique. 19F spin‐lattice relaxation time measurements provided an accurate estimate of myocardial pO2. Using a two‐point determination with a time resolution of 1 s, the loss of oxygen was found to be complete within 40 s of the onset of global ischemia. The fall in oxygen tension correlated closely with an observed loss of ventricular pressure. Magnetic resonance imaging showed that perfluorocarbon was distributed throughout the heart; thus, this reporter molecule provides a global measurement of oxygen tension.
Mr imaging of cerebral perfusion by phase‐angle reconstruction of bolus paramagnetic‐induced frequency shifts
Authors: Conturo Thomas E. , Barker Peter B. , Mathews Vincent P. , Monsein Lee H. , Bryan R. Nick
Published: March 2007

Phase‐angle images are acquired dynamically during bouls paramagnetic contrast injection and demonstrate a phase‐enhancement effect in perfused cerebral tissues. Signal‐to‐noise is comparable to that of susceptibility‐based signal loss (ΔR) images. Assuming that phase shift is proportional to the tissue paramagnetic agent concentration, as supported by experimental data, the integrated area of the phase time response curves estimated the relative gray to white matter blood volume as 1.8:1 and was sensitive to acute ischemia. The relation between tissue phase shift and concentration is considered.
Simultaneous MR Acquisition of Arterial and Brain Signal‐Time Curves
Authors: Perman William H. , Gado Mokhtar H. , Larson Kenneth B. , Perlmutter Joel S.
Published: March 2007

Regional cerebral blood flow (rCBF) provides important information about local neuronal functional and cerebrovascular status. Determination of rCBF requires sequential measurements of tracer concentration in arterial blood and brain tissue unless the tracer is trapped in the brain in proportion to rCBF. Since gadopentate dimeglumine is not trapped within brain tissue, we have developed the simultaneous dual FLASH pulse sequence (SDFLASH) which sequentially measures the MR signal change in both the internal carotid artery and brain parenchyma simultaneously during the passage of a bolus of paramagnetic contrast material.© 1992 Academic Press,Inc.
Quantitative MRI of the Prostate and Uterus in Monkeys
Authors: Waterton John C. , Larcombe‐Mcdouall Jacqueline B. , Miller Diane
Published: March 2007

Quantitative MRI has been carried out in the prostate, seminal vesicles, uterus, and ovaries in the pig‐tailed monkey, Macaca nemestrina. T2‐weighted, fat‐suppressed, multislice experiments were performed at 2.35 T. Eight males, 14 ovariectomized females, and 20 intact females were studied. In the prostate, the caudal and cranial lobe were readily distinguished since the latter had a longer T2 value. For all tissues and organs, interanimal variations were large (up to 12‐fold variation in volume), but reproducibility was excellent in the prostate and in the ovariectomized monkey uterus with coefficients of variation (CV) of 3 and 5%, respectively. In the intact monkey uterus, cycle‐cycle reproducibility was good with CVs of 6–10% in the myometrium and 14–18% in the endometrium. In the follicular phase, endometrial growth (+3.8% day‐1, P < 0.001) was accompanied by myometrial shrinkage (‐1.6% day‐1, P < 0.001), while in the luteal phase, growth was seen in both tissues (+4.3% day‐1, P < 0.001 and +1.4% day−1, P < 0.001, respectively). The great value of these MRI techniques in obtaining data in pharmacological efficacy studies of endocrine drugs, and in limiting the number of animals used, is discussed.© 1992 Academic Press,Inc.
Fast Spiral Coronary Artery Imaging
Authors: Meyer Craig H. , Hu Bob S. , Nishimura Dwight G. , Macovski Albert
Published: March 2007

A flow‐independent method for imaging the coronary arteries within a breath‐hold on a standard whole‐body MR imager was developed. The technique is based on interleaved spiral k‐space scanning and forms a cardiac‐gated image in 20 heartbeats. The spiral readouts have good flow properties and generate minimal flow artifacts. The oblique slices are positioned so that the arteries are in the plane and so that the chamber blood does not obscure the arteries. Fat suppression by a spectral‐spatial pulse improves the visualization of the arteries.© 1992 Academic Press,Inc.
31P Transverse Relaxation Times of the ATP NMR Signals of Human Skeletal Muscle in Vivo
Authors: Jung Wulf‐Ingo , Straubinger Klaus , Bunse Michael , Schick Fritz , Küper Klaus , Dietze Günther , Lutz Otto
Published: March 2007

31P MRS examinations of the calf muscles of 12 healthy volunteers were performed to determine T2 of the coupled ATP signals by using the 90°–TE/2–2662‐TE/2‐acq selective spin‐echo sequence for elimination of phase and intensity distortions. The T2 relaxation times obtained are much longer than those usually assumed: γ‐ATP, 93 ms; α‐ATP, 74 ms; β‐ATP, 75 ms.© 1992 Academic Press,Inc.
Phosphoarginine‐Adenosine Triphosphate Exchange Detected in Vivo in a Microscopic Nematode Parasite by Flow 31P FT‐NMR Spectroscopy
Authors: Thompson S. N. , Platzer E. G. , Lee R.W.‐K.
Published: March 2007

In vivo flow 31P NMR spectroscopy of a microscopic nematode, Steinernema carpocapsae, is described. Long‐term viability was maintained during analysis by continuous circulation of an oxygenated suspension of the parasite through an NMR spectrometer. Saturation transfer and inversion recovery were employed under flowing conditions to investigate the kinetics of phosphoarginine ⇌ adenosine triphosphate exchange. The kinetic constants for the forward and reverse reactions were 0.37/s and 1.45/s, respectively. This report is the first to demonstrate a functional phosphagen kinase in the metabolism of a parasitic helminth.© 1992 Academic Press,Inc.
A high‐field superferric NMR magnet
Authors: Huson F. Russell , Bryan R. Nick , Mackay William W. , Herrick Richard C. , Colvin John , Ford Joseph J. , Pissanetzky Sergio , Plishker Gordon A. , Rocha Richard , Schmidt William , Teodorescu Michael , Shotzman Gary , Zeigler John
Published: March 2007

Strong, extensive magnetic fringe fields are a significant problem with magnetic resonance imaging magnets. This is particularly acute with 4‐T, whole‐body research magnets. To date this problem has been addressed by restricting an extensive zone around the unshielded magnet or by placing external unsaturated iron shielding around the magnet. This paper describes a solution to this problem which uses superconducting coils closely integrated with fully saturated iron elements. A 4‐T, 30‐cm‐bore prototype, based on this design principle, was built and tested. The 5 G fringe field is contained within 1 meter of the magnet bore along the z axis. Homogeneity of the raw magnetic field is 10 ppm over 30% of the magnet's diameter after passive shimming. Compared with an unshielded magnet, 20% less superconductor is required to generate the magnetic field. Images and spectra are presented to demonstrate the magnet's viability for magnetic resonance imaging and spectroscopy.
Quantitative measurement of velocity at multiple positions using comb excitation and fourier velocity encoding
Authors: Dumoulin C. L. , Doorly D. J. , Caro C. G.
Published: March 2007

An MR imaging technique that simultaneously acquires Fourier velocity encoded data from multiple stations is described. The technique employs a comb excitation rf pulse that excites an arbitrary number of slices. As the Fourier velocity phase encoding gradient pulse is advanced, the phase of each slice is the comb is advanced by a unique amount. This causes the signals from the spins in a particular slice to appear at a position in the phase encoding direction, which is the sum of the spin velocity and an offset arising from the phase increment given to that excitation slice. Acquisition of spin velocity information occurs simultaneously for all slices, permitting the calculation of wave velocities arising from pulsatile flow. These wave velocities can then be used to determine vessel distensibility.
A 1H‐NMR method for determining temperature in cell culture perfusion systems
Authors: Lutz N. W. , Kuesel A. C. , Hull W. E.
Published: March 2007

This report describes a noninvasive 1H‐NMR method for measuring absolute temperatures (±0.2°C) in biological samples and, in particular, in cell culture perfusion systems, utilizing the linear temperature dependence of the water chemical shift relative to the temperature‐independent shift of one of the components of the biological medium, e.g., pyruvate, acetate, or lactate. The effects of flow on temperature can be monitored and appropriate adjustments of the temperature controller can be made.
Molecular self‐diffusion of intracellular metabolites in rat brain in vivo Investigated by Localized Proton NMR Diffusion Spectroscopy
Authors: Merboldt Klaus‐Dietmar , Hörstermann Dirk , Hänicke Wolfgang , Bruhn Harald , Frahm Jens
Published: March 2007

Molecular self‐diffusion coefficients of water (0.75 ± 0.05), Nacetylaspartate (0.27 ± 0.04), creatines (0.27 ± 0.04), and cholines (0.28 ± 0.08) × 10−5 cm2 s−1 were obtained from localized proton NMR spectra of rat brain in vivo using diffusion‐weighted stimulated‐echo (STEAM) sequences with a diffusion time of (Δ − δ/3) = 17 ms.
Phase velocity mapping with a real time line scan technique
Authors: Butts Kim , Hangiandreou Nicholas J. , Riederer Stephen J.
Published: March 2007

A real‐time, 20‐Hz, one‐dimensional MR velocity imaging technique is described. A two‐dimensional RF pulse excites a 3‐cm diameter column. Velocity maps are formed from the phase difference between successive flow encoded and compensated acquisitions. A three‐point subtraction variation provides reduced sensitivity to static spins.
Gel‐entrapment of perfluorocarbons: A fluorine‐19 NMR spectroscopic method for monitoring oxygen concentration in cell perfusion systems
Authors: McGovern K. A. , Schoeniger J. S. , Wehrle J. P. , Ng C. E. , Glickson J. D.
Published: March 2007

Oxygenation is a major determinant of the physiological state of cultured cells. 19F NMR can be used to determine the oxygen concentration available to cells immobilized in a gel matrix by measuring the relaxation rate (1/T1) of perfluorocarbons (PFC) incorporated into the gel matrix. In calcium alginate gel beads without cells the relaxation rate (1/T1) of the trifluoromethyl group of perfluorotripropylamine (FTPA) varies linearly with oxygen concentration, with a slope of 1.26 ± 0.15 × 10−3 s−1μM−1 and an intercept of 0.50 ± 0.04 s−1. During perfusion with medium equilibrated with 95%/5% O2/CO2, changes in PFC T1s indicate that the average oxygen concentration was reduced from 894 ± 102 μM in the absence of cells to 476 ± 65 μM and 475 ± 50 μM in the presence of 0.7 × 108 EMT6/Ro and RIF‐1 murine tumor cells per milliliter of gel, respectively. The presence of 0.2 μl of FTPA/ml of gel had no effect on the energy status of the cells as indicated by 31P NMR spectra.

To calculate oxygen gradients within the beads from the average PFC T1 of the sample, a mathematical model was used assuming that oxygen is the limiting nutrient for cell metabolism and that the cellular oxygen consumption rate is independent of oxygen concentration. Data for EMT6/RO cells were fit using experimentally determined perfusion parameters together with literature values for cell volume and oxygen consumption rate. The average PFC 1/T1s predicted using different literature values for volume and oxygen consumption− 1.10 ± 0.10 and 1.28 ± 0.36 s−1−agreed well with the experimentally measured value‐1.104 ± 0.004 s−1. Thus, the model is a suitable tool for calculation of oxygen consumption rates from PFC T1s in well‐oxygenated cell perfusion systems.
On self‐refocusing pulses for rapid gradient‐echo imaging
Authors: McKinnon G. C.
Published: March 2007

Self‐refocusing slice selective radio frequency pulses could potentially be used to reduce imaging times in rapid gradient‐echo sequences. However, in practice, the improvement is likely to be no greater than about 20%, and at the expense of much increased radio frequency power requirements.
QUEST ‐ a quick echo split nmr imaging technique
Authors: Heid O. , Deimling M. , Huk W.
Published: March 2007

A novel millisecond NMR imaging method is introduced, which generalizes the principle of stopped‐pulse experiments. It has been dubbed QUEST for QUick Echo Split imaging Technique. Repeated dephasing and excitation is used to divide a primary free induction decay into an exponentially growing number of echoes. Very few gradient lobes and RF pulses already generate large numbers of echoes, so neither gradient switching speed nor RF absorption represents any real limitation. True spin echoes are easily produced.
Multi‐turn, printed surface coil inductance, and Q optimization
Authors: Raad Ahmad , Kan Siew
Published: March 2007

Wheeler's empirical inductance formula for a multi‐turn, close‐wound flat coil shows that the maximum inductance for a given length of wire occurs when the outer to inner radius ratio is equal to 15/7. A similar expression is proposed for a flat, printed spiral for surface coil antenna design by modifying one of the coefficients in Wheeler's formula. Measured inductance is in good agreement with this new formula and the optimum radius ratio for maximum inductance or Q is now of the order of 9/5.
Nuclear magnetic resonance hahn spin‐echo decay (T2) in live rats with endotoxin lung injury
Authors: Shioya Sumie , Christman Rebecca , Ailion David C. , Cutillo Antonio G. , Goodrich K. Craig
Published: March 2007

To determine the possibility of using nuclear magnetic resonance imaging to study experimentally induced lung injury, we measured in the lungs of spontaneously breathing living rats the time course of both the Hahn spin‐echo decay (T2) and the proton density after endotoxin injury. In order to minimize artifacts arising from motions of the nearby chest wall and heart, we used a motion‐insensitive technique (the interleaved line scan). A typical Hahn T2 measurement was obtained over a region of interest from a series of images each with a different echo time, which ranged from 16 to 110 ms. Lung water content was determined by integrating the proton density over the region of interest. The Hahn T2 and proton density were measured before and at 1, 3, 6, and 9 h after intravenous injection of endotoxin. The effects of the treatment administered before and after endotoxin injection were also evaluated. Endotoxin treatment caused lengthening of both fast (T2f) and slow (T2s) Hahn T2 components but had no significant effect on the proton density, consistent with the notion that endotoxin causes lung injury without significant lung water accumulation in rats. However, the methylprednisolone treatment prevented the lengthening of T2s but did not seem to have a significant effect on T2f. Our results suggest that NMR imaging can be used to detect and monitor experimental lung injury in intact living animals, even in the absence of variations of lung water content.
The appearance of neutral lipid signals in the 1H NMR spectra of a myeloma cell line correlates with the induced formation of cytoplasmic lipid droplets
Authors: Callies R. , Sri‐Pathmanathan R. M. , Ferguson D. Y. P. , Brindle K. M.
Published: March 2007

The appearance of high resolution neutral lipid signals in the 1H NMR spectra of myeloma cells grown in the presence of oleate was shown to correlate with the appearance of cytoplasmic lipid droplets observable by electron microscopy. The spin‐spin relaxation times of these lipid signals were similar to those measured previously for lipid resonances in other cell types. These data suggest that cytoplasmic lipid droplets could make a significant contribution to the neutral lipid signals observed in the 1H NMR spectra of some cells.
On the use of bayesian probability theory for analysis of exponential decay date: An example taken from intravoxel incoherent motion experiments
Authors: Neil Jeffrey J. , Bretthorst G. Larry
Published: March 2007

Traditionally, the method of nonlinear least squares (NLLS) analysis has been used to estimate the parameters obtained from exponential decay data. In this study, we evaluated the use of Bayesian probability theory to analyze such data; specifically, that resulting from intravoxel incoherent motion NMR experiments. Analysis was done both on simulated data to which different amounts of Gaussian noise had been added and on actual data derived from rat brain. On simulated data, Bayesian analysis performed substantially better than NLLS under conditions of relatively low signal‐to‐noise ratio. Bayesian probability theory also offers the advantages of: a) not requiring initial parameter estimates and hence not being susceptible to errors due to incorrect starting values and b) providing a much better representation of the uncertainty in the parameter estimates in the form of the probability density function. Bayesian analysis of rat brain data was used to demonstrate the shape of the probability density function from data sets of different quality.
Quantification of regional blood volumes by rapid T1 mapping
Authors: Schwarzbauer C. , Syha J. , Haase A.
Published: March 2007

A new method is presentd for the quantitative determination of regional blood volumes in vivo. It is based on rapid quantitative T1 mapping by Snapshot FLASH MRI combined with the injection of an intravascular MR contrast agent. Regional blood volumes in four different tissues of the rat (skeletal muscle, heart, liver, kidney) were determined in an In vivo experiment.
Radiative losses of a birdcage resonator
Authors: Harpen Michael D.
Published: March 2007

We present a derivation of the losses in a birdcage resonator due to radiation. We also present an expression for the radiation limited Q. It is shown that in head coil imaging at 63 MHz radiative losses may account for 20% of the total loss with a radiation limited Q on the order of 150. The results are shown to be consistent with those reported in the recent literature.
Allergen‐induced histamine secretion associated with lactate production in mast cells detected by 1H NMR
Authors: Yoshizaki Kazuo , Arizono Naoki , Hayano Takashi , Watari Hiroshi
Published: March 2007

Allergen‐induced histamine secretion in mast cells, obtained from rats infected with Nippostrongylus brasiliensis, was detected by a 1H NMR semi‐selective excitation technique. Lactate production was also detected in association with histamine secretion as observed in mast cells stimulated with other nonimmunological agents, such as compound 48/80, poly‐myxin B, and melittin. The assignment of the lactate resonance was confirmed using lactate oxidase. Thus, 1H NMR spectroscopy is a useful method to study the activation of mast cells in allergic reaction.
The proton NMR spectrum in acute EAE: The significance of the change in the Cho:Cr ratio
Authors: Brenner R. E. , Munro P. M. G. , Williams S. C. R. , Bell J. D. , Barker G. J. , Hawkins C. P. , Landon D. N. , McDonald W. I.
Published: March 2007

We have studied by nuclear magnetic resonance spectroscopy the evolution of the proton spectral changes in acute experimental allergic encephalomyelitis. We found an in vivo elevation in the ratio between the peaks assigned to “choline containing compounds” (Cho) and creatine plus phosphocreatine (Cr). This was associated with an increase in choline, betaine, and phosphorylcholine (PC) as well as a reduction in N‐acetylaspartate (NAA), aspartate, N‐acetylaspartatyl‐glutamate and inositol in vitro. Histological examination revealed inflammation with no evidence of demyelination or neuronal loss. We conclude that the increase in the ratio of Cho:Cr was due to an increase in the concentrations of PC, betaine, and choline in association with inflammation, and not as others have suggested, with demyelination. The reported reduction in NAA may be due to dysfunction of neurones rather than their loss.
Spin‐spin relaxation in experimental allergic Encephalomyelitis. Analysis of CPMG data using a non‐linear least squares method and linear inverse theory
Authors: Stewart Wendy A. , Mackay Alex L. , Whittall Kenneth P. , Moore G. R. Wayne , Paty Donald W.
Published: March 2007

We have used the CPMG pulse sequence to measure proton T2 values and water content in spinal cord and brain samples from Hartley guinea pigs inoculated to produce experimental allergic encephalomyelitis (EAE). Relaxation data were fitted using minuit, a non‐linear curve fitting routine. Three exponentials provided the best fit to spinal cord data (10 ms (13%), 76 ms (57%), 215 ms (30%)) and two exponentials for brain tissue (10 ms (4%), 92 ms (96%)). Least squares algorithms were also used to analyse the spinal cord data in terms of discrete and smooth distributions of relaxation times. The discrete least squares solutions consisted of three to five isolated spikes between 0.010 and 0.300 s. This type of solution was difficult to interpret in terms of water reservoirs. Smooth solutions consisted of two broad peaks, a small peak with a T2 near 0.010 s and a larger peak near 0.100 s. The integral ratio of the larger to the smaller peak was 7.092 ± 1.782 for normal tissue, and increased to a maximum of 16 with increasing parenchymal cellular infiltration and demyelination. The short T2 peak has been assigned to water in the hydration layers of the myelin sheath. The width of the longer T2 peak was sensitive to tissue heterogeneity. The least squares and smooth distribution analysis models could be used to distinguish samples with extensive parenchymal infiltration from normal tissue, even though only a maximum of 60% of the tissue was affected. The short T2 component could provide a direct method of measuring intact myelin, which would have a profound effect on the understanding of the evolution of pathology in multiple sclerosis.
Quantitative evaluation of several partial fourier reconstruction algorithms used in mri
Authors: McGibney G. , Smith M. R. , Nichols S. T. , Crawley A.
Published: March 2007

Partial Fourier reconstruction algorithms exploit the redundancy in magnetic resonance data sets so that half of the data is calculated during image reconstruction rather than acquired. The conjugate synthesis, Margosian, homodyne detection, Cuppen and POCS algorithms are evaluated using spatial frequency domain analysis to show their characteristics and where limitations may occur. The phase correction used in partial Fourier reconstruction is equivalent to a convolution in the frequency domain and the importance of accurately implementing this convolution is demonstrated. New reconstruction approaches, based on passing the partial data through a phase correcting, finite impulse response (FIR), digital filter are suggested. These FIR and MoFIR algorithms have a speed near that of the Margosian and homodyne detection reconstructions, but with a lower error; close to that of the Cuppen/POCS iterative approaches. Quantitative analysis of the partial Fourier algorithms, tested with three phase estimation techniques, are provided by comparing artificial and clinical data reconstructed using full and partial Fourier techniques.
1H editing of 2‐deuterated exogenous and natural endogenous D‐glucose in biological samples
Authors: Biesemans Monique , Kayser François , Van Cauteren Marc , Rehrer Nancy J. , Neirinck Peter , De Meirleir Kenny , Malaise Willy J. , Willem Rudolph
Published: March 2007

A spin‐echo based 1H homonuclear pulse sequence, enabling the selective editing of homonuclear first‐order J‐multiplet types, is presented and analyzed. Its effectiveness in quantification applications is assessed. Its potential usefulness in the quantitative distinction between 2‐deuterated and natural D‐,glucose in biological samples is briefly discussed, with emphasis on studies of hexose metabolism conducted in vitro.
Incorporating lactate/lipid discrimination into a spectroscopic imaging sequence
Authors: Adalsteinsson Elfar , Spielman Daniel M. , Wright Graham A. , Pauly John M. , Meyer Craig H. , Macovski Albert
Published: March 2007

A spectroscopic imaging sequence incorporating a two‐shot lactate editing method was used in two human brain studies to image lactate and NAA. The subtractive editing method allows separate images of lactate, NAA, and lipids to be collected during a single study with no SNR penalty. The sequence uses a spectral‐spatial excitation for slice selection and water suppression, and employs inversion recovery and an echo time of 136 ms for additional lipid suppression.
Effect of sample numbers on the kinetic data analysis of MR contrast agents
Authors: Lu Dongfeng , Gordon Monahan W.
Published: March 2007

The Monte Carlo simulation method is used to determine the uncertainties of the estimated area and mean transit time (MTT) of a regional cerebral concentration‐time curve of a bolus injected paramagnetic contrast agent. Many factors contribute to these uncertainties. This study concentrates on the error propagation from the sample noise at different sample time points along the concentration‐time curve. The uncertainties of area and MTT were determined as a function of the sample noise and the number of sample time points. For example, the percentage standard deviations (uncertainties) of both area and MTT are less than 12% with five samples whose signal‐to‐noise ratios are greater than 50.
Improved sensitivity to magnetic susceptibility contrast
Authors: De Crespigny A. J. , Roberts T. P. L. , Kucharcyzk J. , Moseley M. E.
Published: March 2007

Changes in the local magnetic susceptibility of brain tissue due to injected paramagnetic contrast agent are manifest as both a linebroadening and frequency shift of the water resonance. By combining these two effects, the sensitivity of gradient recalled echo images to such changes can be increased.
Fast imaging using subencoding data sets from multiple detectors
Authors: Ra J. B. , Rim C. Y.
Published: March 2007

A new fast imaging method using a subencoding data acquisition scheme and a multiple coil receiver system is proposed and demonstrated. In this method, a set of aliased images are produced from receiver coils by using the subencoded data without sacrificing the desired resolution, and resolved to an aliasing‐free image by using the distance‐dependent sensitivity information of each coil. The reduction rate of data acquisition time is proportional to the number of receiver coils. This method can be easily adapted to conventional imaging methods including fast imaging to further reduce the scan time.
Diffusion‐weighted MR microscopy with fast spin‐echo
Authors: Beaulieu Chris F. , Zhou Xiaohong , Cofer Gary P. , Johnson G. Allan
Published: March 2007

A diffusion‐weighted fast spin‐echo (FSE) imaging sequence for high‐field MR microscopy was developed and experimentally validated in a phantom and in a live rat. Pulsed diffusion gradients were executed before and after the initial 180° pulse in the FSE pulse train. This produced diffusion‐related reductions in image signal intensity corresponding to gradient (“b”) factors between 1.80 and 1352 s/mm2. The degree of diffusion weighting was demonstrated to be independent of echo train length for experiments using trains up to 16 echoes long. Quantitative measurements on a phantom and on a live rat produced diffusion coefficients consistent with literature values. Importantly, the eight‐ to 16‐fold increase in imaging efficiency with FSE was not accompanied by a significant loss of spatial resolution or contrast. This permits acquisition of in vivo three‐dimensional data in time periods that are appropriate for evolving biological processes. The combination of accurate diffusion weighting and high spatial resolution provided by FSE makes the technique particularly useful for MR microscopy.
Lactate imaging of the human brain at 1.5 T using a double‐quantum filter
Authors: De Graaf A. A. , Luyten P. R. , Den Hollander J. A. , Heindel W. , Bovée W. M. M. J.
Published: March 2007

The use of a double‐quantum filtered 1H NMR spectroscopic imaging technique is described to detect the spatial distribution of lactate in the human brain. In two patients the feasibility of this technique is shown and compared with existing single‐quantum spectroscopic imaging and single voxel techniques. Singles lice double‐quantum fitered lactate images were obtained showing the lactate distribution over the entire slice in the brain. The lipid signal suppression was sufficient for the unambiguous detection of lactate. The signal loss of the lactate signal due to the incorporation of the double‐quantum filter was 50–70% relative to the single‐quantum signal.
13C NMR investigation of synovial fluids
Authors: Albert Klaus , Michele Sabine , Günther Ulrich , Fial Manfred , Gall Hugo , Saal Johannes
Published: March 2007

13C NMR spectra of synovial fluids from 20 patients suffering from rheumatic diseases have been recorded. Structural changes in hyaluronic acid, the main carrier of the viscoelastic properties of synovial fluid, could be observed in the NMR spectra of the native biological fluid. By comparing these spectra with those of purified hyaluronic acid, a rough estimation of the degree of depolymerization of synovial hyaluronlic acid was possible. The patients with rheumatoid arthritis appeared to have a lower degree of polymerization compared to patients with osteoarthrosis. Thus, 13C NMR spectroscopy prolvides useful information about biophysical properties of sartorial fluid.
Self‐correction of proton spectroscopic images for gradient eddy current distortions and static field inhomogeneities
Authors: Johnson G. , Jung K. J. , Wu E. X. , Hilal S. K.
Published: March 2007

A postprocessing method of correcting for gradient eddy current distortions and inter‐voxel static field inhomogeneities in spectroscopic imaging is presented. Data is acquired normally and all spatial processing is performed. The FID k each voxel is then digitally filtered to extract the signal from a signal reference line. Phase multiplying the original FID by the phase of this reference signal corrects for gradient eddy currents and static field offsets. Computer simulations show that the method is robust with respect to noise, filter bandwidth and the presence of small lines close to the reference line. The method is demonstrated on proton spectroscopic images of phantoms.
Magnetization‐prepared cardiac imaging using gradient echo acquisition
Authors: Liu Yu , Riederer Stephen J. , Ehman Richard L.
Published: March 2007

Magnetization‐prepared 2DFT and 3DFT gradlent echo techniques are presented for acquisition of black blood cardiac images. Both methods incorporate RF pulses for blood saturation, centric or centric‐like view ordering, data acquisition during late dlastole, and breath‐holding. In a series of 13 volunteer studies, these methods have consistently provided good visuallzation of intraventricular structures.
Gadolinium enhancement in acute and chronic‐progressive experimental allergic encephalomyelitis in the guinea pig
Authors: Karlik S. J. , Grant E. A. , Lee D. , Noseworthy J. H.
Published: March 2007

Magnetic resonance imaging detects blood‐brain barrier disruption after gadolinium‐DTPA enhancement of central nervous system lesions of multiple sclerosis. Experimental allergic encephalomyelitis has many clinical and pathological features in common with multiple sclerosis including alterations in the integrity of the blood‐brain barrier. We have compared T2‐weighted cranial MR images with Gd‐DTPA dimeglumine‐enhanced T1‐weighted images of myelin bask protein‐induced acute (Days 8–42 postimmunlzation) and central nervous system‐induced chronic‐progressive (Days 70–95 post immunization) forms of experimental allergic encephalomyelitis in the guinea pig. Although animals from both groups had abnormal T2‐weighted images, only the myelin bask protein‐acute‐EAE animals (Days 14–24 postimmunlzation) showed enhancement on postcontrast MR studies. The different responses of the acute and chronic diseases may result from different immunogens, severity of disease, or different permeability of the blood‐brain barrier. Therefore, gadolinium‐DTPA‐enhanced, T1‐weighted MR images distinguish acutely active and chronic inflammatory lesions in experimental allergic encephalomyelitis.
4 Tesla gradient recalled echo characteristics of photic stimulation‐induced signal changes in the human primary visual cortex
Authors: Menon Ravi S. , Ogawa Seiji , Tank David W. , Uǧurbil Kǎmil
Published: March 2007

Multi‐echo measurements of photic stimulation‐induced signal changes in human visual cortex were made at 4 Tesla in order to quantify the nature of the signal change and its vascular origin, and to determine the optimum echo time for detection of the changes. Utilizing high resolution images, two distinct regions (ascribed to be microvasculature and visible venous vessels) were identified as giving rise to the signal increase. The fractional signal changes in gray matter areas depended linearly on echo time (TE) in the range of 10 to 60 ms and extrapolated to virtually zero for TE = 0, indicating that in‐flow effects secondary to stimulation‐induced blood flow increases were negligible in our functional imaging studies; instead, signal change due to photic stimulation originated from the increase in the apparent transverse relaxation rate, 1/T2*. This decrease in (1/T2*, brought about by the alterations in hemodynamic parameters, was 1.3 ± 0.4 s−1 for gray matter and 3.0 ± 0.7 s−1 (averaged over 10 individuals) for venous vessels visible in the images. The optimum choice of echo time was found to be TE ≥ T2*.
Dynamic 13C−1H nuclear polarization of lipid methylene resonances applied to broadband proton‐decoupled in vivo13C MR spectroscopy of human breast and calf tissue
Authors: Ende Gabriele , Bachert Peter
Published: March 2007

Dynamic nuclear polarization of the coupled 13C−lH spin system was studied for optimizing the signal‐to‐noise ratio of in vivo 13C MR spectra. In particular, the truncated driven and transient nuclear Overhauser effect (NOE) of the proton‐decoupled 13C resonances from methylene carbons in vegetable oil and in human calf tissue was observed. Maximum in vivo NOE enhancements n = 1.5 and 0.9 were found, respectively. Theoretical fits to the data yield 13C−1 cross‐relaxation times in the order of 0.6 s. Significant signal enhancement over the whole in vivo 13C chemical shift range is obtained with minimum expense utilizing the NOE of the dipolar coupled 13C−1 spin system in addition to proton‐decoupling. NOE‐enhanced proton‐decoupled in vivo 13C MR spectra were acquired within 17 min in volunteer examinations from the human breast and the calf. These spectra show well‐resolved resonances of carbons in lipids and several other cellular compounds.
Cylindrical coils near self‐resonance
Authors: Harpen Michael D.
Published: March 2007

We present a model of birdcage resonator operation when the size of the resonator approaches a quarter wave length resulting in significant phase shifts along the current conducting elements. In the model resonators are treated as generalized trainsmission lines. Line termination determines whether the resonator is of the low pass or high pass type. The model correctly describes the dependence of resonant frequency on resonant mode number as well as the distribution of current along the length of the resonator.
A new T2*‐weighting technique for magnetic resonance imaging
Authors: Hu Xiaoping , Kim Seong‐Gi
Published: March 2007

This paper describes a method that prepares the longitudinal magnetization with T2* weighting for subsequent acquisition. The main advantage of our technique is its insensitivity to static: field inhomogeneity. We have combined this approach with, an ultrafast gradient‐echo (Turbo‐FLASH) sequence and conducted experiments on phantoms and volunteers to demonstrate its capability and utility. With such a technique a T2*‐weighted image can be generated in less than a second. In the paper, the detail of the technique and experimental results are presented.
Evaluation of a nitroxyl fatty acid as liver contrast agent for magnetic resonance imaging
Authors: Gallez Bernard , Debuyst René , Demeure Roger , Dejehet Fernand , Grandin Cécile , Van Beers Bernard , Taper Henryk , Pringot Jacques , Dumont Pierre
Published: March 2007

In this study, we report the synthesis and the evaluation as MRI contrast agent of a new compound (nitroxyl fatty acid, NFA), where a pyrrolidinoxyl radical (3‐carboxy‐proxyl, PCA) is linked to a fatty acid moiety. Fatty acids were selected as vector because they present a high affinity for the liver, their efficient cellular uptake being the result of a specific interaction with a transmembrane transporter (liver plasma membrane‐fatty acid binding protein). The uptake of 3H‐oleic acid is inhibited after the injection of 1 mmol/kg of NFA, suggesting that INFA recognizes the same transmembrane transporter as the natural fatty acids. The higher relaxivity R1 of NFA in albumin solutions, compared with PCA, was explained by the immobilization of the nitroxyl radical in the protein. MR imaging was performed using T1‐weighted images on mice in order to compare the contrast effect obtained after the injection of 1 mmol/kg of radical. The % signal enhancement in the liver 5 min after intravenous injection was 49 ± 4 and 14 ± 5 for NFA and PCA, respectively. NFA allowed a better delimitation of some necrotic tumors (Novikoff hepatocarcinoma) due to its preferential uptake by the nontumorous tissue.
Ultrafast interleaved gradient‐echo‐planar imaging on a standard scanner
Authors: McKinnon G. C.
Published: March 2007

Ultra‐fast imaging traditionally implies either echo‐planar imaging on specially developed gradient systems, or very short repetition time gradient‐echo imaging on standard magnetic resonance imaging scanners. An alternative strategy for very fast imaging with conventional whole‐body scanners is discussed here. The technique is a hybrid, whereby the advantages of gradient‐echo imaging and echo‐planar imaging are combined. It is here denoted interleaved gradient‐echo‐planar imaging. It is not a single specific measurement sequence, but rather a continuum of sequences whereby multiple excitations with multiple gradient‐echos are employed. The power of this fast imaging approach is that one has much more flexibility toward the optimization of the measurement sequence with respect to imaging time, T2 relaxation, gradient power, resolution, image distortion, and signal‐to‐noise ratio. In vlvo human heart images, acquired in 110 ms, and with a resolution of 2.5 mm, have been obtained with a standard whole‐body scanner.
In vivo fluorine‐19 magnetic resonance spectroscopy of cerebral halothane in postoperative patients: Preliminary results
Authors: Menon D. K. , Lockwood G. G. , Peden C. J. , Cox I. J. , Sargentoni J. , Bell J. D. , Coutts G. A. , Whitwam J. G.
Published: March 2007

This study reports the use of 19F MRS to study halothane in the brain of eight patients recovering from halothane anesthesia of short duration. Resonances attributable to halothane were observed up to 90 min after withdrawal of the anesthetic agent. The signal‐to‐noise ratio for an unlocalized spectrum acquired using a 6 cm surface coil was typically 20 with data collection times of 2 min. In seven patients a single resonance was seen with a mean (±SD) chemical shift of +43.3 (±1.8) ppm, referenced to NaF at 0 ppm. This resonance exhibited a T1 value of between 0.5 and 1 s, and a T2* (estimated from the linewidth of the resonance) between 3.5 and 10 ms. In one patient two resonances were observed with chemical shifts of +38 and +41 ppm. Because we cannot exclude the possibility that this was due to field inhomogeneity, the significance of the last finding is uncertain. However, phantom studies show that the chemical shift of halothane in different environments (such as water, olive oil, methanol, and lecithin) can vary to an extent that accounts for the two resonances seen in our patient. These results demonstrate the feasibility of in vivo 19F MRS studies of fluorinated volatile agents in humans. The potential for clinical 19F MRS of fluorinated anesthetics is discussed.
Flow compensation in MRI using a phase‐corrected real reconstruction
Authors: Riek Jonathan K. , Totterman Saara M. , Tekalp A. Murat , Smith Warren E. , Kwok Edmund
Published: March 2007

Flow‐ and motion‐related artifacts are problematic in clinical MR imaging. In this paper we discuss the utility of a phase‐corrected real reconstruction to reduce flow artifacts. This techinique is particularly useful when flow‐compensation pulse sequences may not be possible, such as when a very short echo delay or small field‐of‐view is desired. We will demonstrate that the phase‐corrected real reconstruction provides superior results to the magnitude reconstruction either used alone or in conjunction with existing flow‐compensation techniques.
Spatially selective RF pulses and the effects of digitization on their performance
Authors: Slotboom J. , Creyghton J. H. N. , Korbee D. , Mehlkopf A. F. , Bovée W. M. M. J.
Published: March 2007

Spectrometers make use of D/A converters to generate RF and gradient shapes. This paper examines by exact simulations the time and amplitude digitization effects, inherent to the use of D/A converters, on the performance of amplitude modulated (AM) frequency selective RF pulses. By making use of Fourier theory and the small tip angle approximation, an approximate model of these effects on the magnetization slice profiles is derived and verified for several pulse types by computer simulations. This approximate model will be used to derive requirements for D/A converters with respect to spatial localization. The dynamics of the spin system allows pulse width modulation (PWM) as an alternative to AM for pulse envelope encoding. The effects of PWM on the slice profile are examined and compared with conventional AM pulses. It is shown by simulation and measurement that adiabatic PWM pulses can be found. In contrast to AM modulated adiabatic pulses, adiabatic PWM pulses have side bands with the same slice quality as the main slice and might therefore be useful as multislice selective pulses.
Algorithms for improving calculated streamlines in 3‐D phase contrast angiography
Authors: Buonocore Michael H.
Published: March 2007

Streamline display is a unique alternative to cross‐sectional slice or projection display, because streamlines more clearly show the patterns of blood flow within the vessel. Flow patterns associated with atherosclerosis, such as streamline separation and recirculation, can be quickly identified with this display. Streamlines can be calculated using velocity data obtained from 3‐D phase contrast angiographic pulse sequences. However, these streamlines often pass through the wall of vessel or show intraluminal sources and sinks of blood. The author has developed iterative least squares algorithms to improve the realism of streamlines. The velocity data is modified so that the resulting streamlines do not pass through the vessel wall and there are no intraluminal sources or sinks. He has applied the algorithms to velocity data obtained from a flow phantom and the carotid arteries of normal volunteers. Streamlines derived from the processed velocity fields are more realistic and provide more precise flow quantitation.