bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of eddy currents in nuclear magnetic resonance imaging
Authors: Ahn C. B. , Cho Z. H.
Published: March 2007

The eddy currents in nuclear magnetic resonance (NMR) imaging are analyzed from the solutions of Maxwell's equations and their effects are examined over various experimental conditions from whole‐body diagnostic imaging to recently developed NMR microscopy. The analysis is focused mainly on the frequency characteristics and intensity variations of the eddy‐current‐induced field which depends on the overall system size, ratio of the gradient coil size to the magnet bore diameter, and the pulse‐sequence‐dependent parameters such as input current waveform and repetition time. From the analysis, the frequency response of the eddy‐current‐induced field is that of a high‐pass filter whose cutoff frequency is inversely proportional to the square of the overall system size. The intensity ratio of the generated field to the induced field is not affected by the overall system size, but is sensitively related to the ratio of the gradient coil size to the magnet bore diameter. © 1991 Academic Press, Inc.
Tissue oxygenation: A novel determination using 19F surface coil NMR spectroscopy of sequestered perfluorocarbon emulsion
Authors: Mason Ralph P. , Nunnally Ray L. , Antich Peter P.
Published: March 2007

This work examines the variation with oxygen tension (pO2) of the individual spin‐lattice relaxation times (TI) of the 19F resonances of the perfluorocarbon emulsion Oxy‐pherol‐ET (FC‐43). A linear relationship between 1/T1 and pO2 has been confirmed for all four resonances at any specific temperature. Using a saturation recovery sequence, T1 has been successfully measured using surface coil NMR spectroscopy. This has facilitated measurement of TI in vivo in a subcutaneous murine tumor. Mice were predosed with Oxypherol‐ET emulsion; following complete vascular clearance of the pertluorocarbon, 19F signal was observed specifically from material sequestered in tissue, thus avoiding flow artifacts. Comparison of the pO2 estimated from each of the 19F resonances provided an internal consistency check. A pO2 = 0.1 ± 2.2% was determined in a Meth‐A murine tumor. When the mouse breathed carbogen (95% O2, 5% CO2) no significant change in tumor pO2 was detected, whereas the pO2 in the liver showed a distinct increase. © 1991 Academic Press. Inc.
Effect of L‐thyroxine (LT4) and D‐thyroxine (DT4) on cardiac function and high‐energy phosphate metabolism: A 31P NMR study
Authors: Sandhu G. S. , Steele R. , Gonnella N. C.
Published: March 2007

31P NMR spectroscopy was used to monitor the cardiac energy metabolism in hypothyroid rat hearts. Differential alterations in phosphocreatine and inorganic phosphate levels were observed upon treatment of hypothyroid animals with DT4 and LT4, while both agents were equipotent in reducing cholesterol. These results show potential for NMR spectroscopy as a technique to determine therapeutic selectivity. © 1991 Academic Press. Inc.
Magnetic susceptibility measurement using a double‐DANTE tagging (DDT) sequence
Authors: Mosher Timothy J. , Smith Michael B.
Published: March 2007

Preliminary results are presented for the nuclear magnetic resonance (NMR) measurement of field gradients generated by differences in magnetic susceptibility. The DDT technique maps the resonant frequency throughout the sample in a single image. Regions of paramagnetic and diamagnetic susceptibility are differentiated with a single magnitude‐calculated image. © 1991 Academic Press. Inc.
Relative volume‐average murine tumor blood flow measurement via deuterium nuclear magnetic resonance spectroscopy
Authors: Mattiello James , Evelhoch Jeffrey L.
Published: March 2007

A deuterium NMR spectroscopic method to determine relative tumor blood flow (TBF) by measuring the increase in tumor HOD concentration after intravenous injection of 100 μl D2O (0.9% NaCl) is presented. An integration approach analogous to that validated for positron emission tomographic measurement of cerebral blood flow was implemented. Computer simulations indicated that integration from 30 to 120 s minimizes the sensitivity of the uptake integral to the shape of the arterial input function, which cannot be assessed in each mouse, while maintaining both a nearly linear relationship between TBF and the integral and high NMR signal‐to‐noise. A strong positive linear correlation was observed between the uptake integral and TBF measured by D2O clearance in both untreated tumors (n = 19; P < 0.001) and tumors after hyperthermia (n = 16; P < 0.001). This method can measure relative TBF in tumors with heterogeneous blood flow and is ideally suited to concurrent or interleaved measurement of TBF and metabolism via multinuclear NMR spectroscopy. © 1991 Academic Press. Inc.
Coronary angiography using fast selective inversion recovery
Authors: Wang Samuel J. , Hu Bob S. , Macovski Albert , Nishimura Dwight G.
Published: March 2007

Using a fast version of selective inversion recovery, we have obtained coronary angiograms of normal volunteers showing the proximal portions of the left coronary artery. Blood is tagged in the aortic root at end systole using a 2D inversion pulse. After a wash‐in time of 300–600 ms, the coronary vessels are imaged with a 2‐ to 3‐cm‐thick slab in either axial or oblique projection. The scan is completed within a breathhold in 24 heartbeats. © 1991 Academic Press. Inc.
Potential degradation in image quality due to selective averaging of phase‐encoding lines in Fourier transform MRI
Authors: Mugler John P.
Published: March 2007

The properties of the image noise for selective averaging of phase‐encoding lines have been investigated. For a given acquisition time, selective averaging results in a signal‐to‐noise ratio penalty compared to averaging all lines equally. In addition, selective averaging yields a non uniform distribution of noise characteristics in spatial frequency space, which can result in a change in the texture of the image noise. © 1991 Academic Press, Inc.
Anisotropy in diffusion‐weighted MRI
Authors: Moseley Michael E. , Kucharczyk John , Asgari Haleh S. , Norman David
Published: March 2007

Diffusional anisotropy of water protons, induced by nonrandom, directional barriers which hinder or retard water motion, is measurable by MRI. Faster water diffusion was observed when the diffusion‐sensitizing gradient direction paralleled the long axes of white matter tracts, indicative of fewer bamers to water motion. Diffusion perpendicular to this 3xis was as much as four times slower. Anisotropy was seen pre‐ and postmortem in all axial, sagittal, and coronal planes, with and without cardiac gating. Ordering has also been observed in feline optic nerve and in human peripheral nerves. Utilization of this technique can greatly improve understanding and assessment of demyelinating disorders, of white matter infarcts and neoplasms, and of neonatal brain and spinal cord development. © 1991 Academic Press, Inc.
Oblique NMR imaging of the uterus in macaques: Uterine resdonse to estrogen stimulation
Authors: Waterton John C. , Miller Diane , Dukes Michael , Morrell John S. W.
Published: March 2007

We report methods for quantitative NMR imaging of the primate uterus and the application of these methods of measuring the response of the monkey (Macaca nemestrina) uterus (endometrial volume. myometrial volume, T2 values, myometrial junction zone) to estrogen stimulation. High‐gield (2.35 T), fat‐suppressed, T2‐weighted (TE50) oblique methods were used, Slice thickeness, location, and angle were varied on each examination to obtain six contiguous slices between the cervix and fundus, regardles of size or orientation of the uterus. Basal endometrial and myometrial volumes were 0.05± 0.01 cm3 and 1.31 ± 0.23 cm3 in chronically ovariectomized animals. These increased by 15.7 ± 3.6‐fold and 3.1 ± 0.4 fold, respectively, during 7 days of estrogen stimulation (estradiol benzoate, 5 ųg/kg sc daily) while myometrial T2 increased from 52 ± 1 to 67 ± 4 ms. These changes reversed following menstrual bleeding. © 1991 Academic Press, Inc.
Safety of gadolinium‐DTPA: Extended clinical experience
Authors: Niendorf H. P. , Haustein J. , Cornelius I. , Alhassan A. , Clauß W.
Published: March 2007

This review reports data on the general and renal tolerance of the paramagnetic contrast agent Gd‐DTPA after intravenous administration. Gd‐DTPA was administered usually at a dose level of 0.1‐0.2 mmol/kg body wt (range: 0.005‐0.25 mmol/kg body wt) in cranial, spinal and body MR indications. In phase I‐IIIa studies a total of 2154 healthy volunteers and patients were investigated, usually at a dose of 0.1 mmol/kg body wt. From the obtained results it was concluded that adverse events (AEs) may be expected in the order of magnitude of 1%. In phase IIIb‐IV studies 13,439 patients were investigated at 0.1 or 0.2 mmol/kg body wt. Tolerance data were collected according to a standardized protocol and metaanalysis of obtained data was performed. AEs, irrespective of their drug relationship, were observed in 1.15% of the patients. The observed AEs were comparable to those after intravenous administration of iodinated nonionic X‐ray contrast media. There was no correlation between patient age and the incidence of AEs. In patients with a known history of allergy the incidence of AEs increased to 2.6%. In pediatric use no added risk was observed in a total of 826 neonates, children, and adolescents up to 18 years of age. Gd‐DTPA showed good renal tolerance in patients with and without preexisting impairment of renal function. A prospective open safety and pharmacokinetic study was conducted in patients with hemodialysis. Gd‐DTPA was shown to be eliminated completely by hemodialysis. Fast bolus injections were tolerated without added risk. Presented data from postmarketing surveillance (up to March 31, 1991) cover an estimated total of more than 2,000,000 applications. In conclusion, Gd‐DTPA showed an excellent safety profile after intravenous administration of diagnostic doses to patients of all age groups, irrespective of the injection speed and preexisting renal impairment. The overall incidence of AEs after intravenous injection of 0.1 or 0.2 mmol Gd‐DTPA/kg body wt was found to be 1–2%. © 1991 Academic Press, Inc.
Correction of chemical‐shift artifacts in multislice F‐19 imaging with perfluorooctyl bromide
Authors: Özdemirel B. , Nalcioglu O.
Published: March 2007

Chemical‐shift artifact correction methods for multislice F‐19 imaging with perfluorooctyl bromide are described and results obtained with physical phantoms presented. Utilization of the two long‐T2 spectral peaks of PFOB in multislice imaging enhances the imaging efficiency considerably. Simultaneous imaging of the adjacent slices is achieved by appropriately adjusting the slice selection gradient amplitude, the bandwidth, and the slice position offset frequency of the selective RF pulses in relation to the frequency separation between the two peaks. © 1992 Academic Press, Inc.
Q optimization of RF inductors for use in NMR probes
Authors: Kan Siew , Gonord Patrick
Published: March 2007

Radiofrequency inductors are important components of many NMR probe circuits, and a high quality factor Q of these inductors is necessary to achieve good signal‐to‐noise ratios. We have designed high Q inductors using an optimum coil diameter to coil length ratio of the order of 2.54. The latter was calculated from Lorenz's inductance formula for a solenoid and checked experimentally using a series of inductors of various diameters and lengths. The results show good agreement between theory and practice. © 1992 Academic Press, Inc.
Rapid localization of concave volumes by conformal NMR spectroscopy
Authors: Sharp Jonathan C. , Leach Martin O.
Published: March 2007

“Conformal” spectroscopy is a method for the acquisition of accurately localized NMR spectra from noncuboidal regions with optimum signal‐to‐noise ratio, and is based upon the localization of volumes defined by a number of oblique intersecting selected slices. We have previously demonstrated conformal localization of volumes with convex surfaces. In this paper we extend the technique to the localization of concave volumes.
A new approach to split resonator design
Authors: Harpen Michael D.
Published: March 2007

Using a novel application of the method of images we show how a plane array of resonant elements can be substituted for the conducting plane in a semicylindrical or split resonator. In an experimental low‐pass split resonator‐plane array system used as a magnetic resonance imaging receive coil at 0.5 T sensitivity values are shown to be uniform (∼ ±3%) across the field of view. © 1992 Academic Press, Inc.
Localized 1H NMR spectra of glutamate in the human brain
Authors: Rothman D. L. , Hanstock C. C. , Petroff O. A. C. , Novotny E. J. , Prichard J. W. , Shulman R. G.
Published: March 2007

Localized 1H NMR spectra at TE = 12 ms were obtained from cerebralcortex of human subjects using ISIS with surface suppression. The 2.29‐ppm resonance was assigned to C4 glutamate with contributions from C4 glutamine and GABA using in vivo spectral editing and comparison of chemical shift with pure compounds. The measured intensity ratio between the 2.29 resonance and the creatine resonance at 3.03 ppm was in good agreement with the ratio predicted from previously reported measurements of glutamate. glutamine, and GABA concentrations in biopsied human brain tissue.
Selective suppression of lipid resonances by lipid‐soluble nitroxides in NMR spectroscopy
Authors: Chen Kai , Lutz Norbert W. , Wehrle Janna P. , Glickson Jerry D. , Swartz Harold M.
Published: March 2007

The ability of lipid‐soluble nitroxides to suppress selectively the peaks of lipid resonances in 31P, 1H, and 13C NMR spectra was investigated in serum as part ofstudies aimed at using these contrast agents for magnetic resonance imaging and magnetic resonance spectroscopy in vivo. Nitroxides are especially interesting potential contrast agents because they can reversibly be converted in cells to diamagnetic hydroxylamines, with conversion rates that are dependent on the redox potential and the intracellular concentration of oxygen; the characterization of nitroxide‐dependent changes in NMR spectra may therefore be a useful means to measureoxygen‐dependent redox metabolism in vivo. The fatty acid analogs, doxyl stearates, suppressed the methyl resonance of choline and the methyl and methylene peaks of lipids in the 1H NMR spectra of serum samples. As a consequence, lactate peaks, which were not readily detected became clearly resolved and could be evaluated quantitatively. The 31P resonance of phosphatidylcholine in the 31P NMR spectrum was suppressed by 5doxyl stearate and 4‐(N,Ndimethyl‐Nhexadecyl)ammonium‐2,2,6,6‐tetramethylpiperidine‐I‐oxyl, iodide (Cat16). In the 13C NMR spectrum, the resonances of the methyl groups of choline and the lipids also were broadened significantly by addition of 5‐doxyl stearate. Differential suppression of lipid resonances can be employed to facilitate quantitation of lactate.
Deblurring for non‐2D fourier transform magnetic resonance imaging
Authors: Noll Douglas C. , Pauly John M. , Meyer Craig H. , Nishimura Dwight G. , Macovskj Albert
Published: March 2007

For several non‐2D Fourier transform imaging methods, off‐resonant reconstruction does not just cause geometric distortion, but changes the shape of the point spread function and causes blurring. This effect is well known for projection reconstruction and spiral k‐space scanning sequences. We introduce here a method that automatically removes blur introduced by magnetic field inhomogeneity and susceptibility without using a resonant frequency map, making these imaging methods more useful. In this method, the raw data are modulated to several different frequencies and reconstructed to create a series of base images. Determination of degree of blur is done by calculating a focusing measure for each point in each base image and a composite image is then constructed using only the unblurred regions from each base image. This method has been successfully applied to phantom and in vivo images using projection‐reconstruction and spiral‐scan sequences. © 1992 Academic Press, Inc.
Improving resolution in MRI by interleaving data acquisition for increased digitization rates
Authors: Barker G. J. , Williams S. C. R.
Published: March 2007

In certain situations in magnetic resonance imaging the digital resolution in the frequency encode direction may be compromised by hardware limits on data digitization rates. We demonstrate a method of overcoming this restriction, without hardware modifications, by interleaving data from several acquisitions to produce a higher resolution composite data set. © 1992 Academic Press, Inc.
MR imaging of brain surface using steady‐state free precession
Authors: Takane Atsushi , Koizumi Hideaki
Published: March 2007

We present an imaging technique that affords direct and noninvasive visualization of brain surface structure. This technique utilizes the signal before the rf pulse in steady‐state free precession. This signal highly reflects the spin‐spin relaxation time T2, as was studied in our laboratory (Matsui et al. J. Magn. Reson. 62 12, 1985). Therefore the cerebrospinal fluid (CSf), having a long T2, is depicted as high intensity. The CSF permeates cerebral sulci and fissures. The imaging time with this technique is less than 1 min. © 1992 Academic Press, Inc.
Magnetization transfer contrast in fat‐suppressed steady‐state three‐dimensional MR images
Authors: Flame Duane P. , Pierce W. Brad , Harms Steven E. , Griffey Richard H.
Published: March 2007

We demonstrate that magnetization transfer contrast can be used to improve the diagnostic utility of fat‐suppressed steady‐state three‐dimensional gradient‐recalled images. Fat suppression is achieved using a “jump‐return” pair of contiguous shaped pulses. No time interval exists between the pulses, and no RF echo is generated. The sequence normally produces images with “density” weighting. Preparation of the spin magnetization with off‐resonance frequency‐selective excitation creates magnetization transfer contrast which attenuates signal intensity in proportion to the exchange rate of magnetization from free water with magnetization from water bound to macromolecules or protons that have restricted mobility. The resulting images have excellent fat suppression with low sensitivity to motion since no subtraction is used. In addition, the mechanism of signal attenuation is independent of paramagnetic effects, and addition of Gd‐DTPA produces signal enhancement from vascularized regions of tissue. Examples are presented for the knee and breast, where the observation of pathology with signal enhancement from Gd‐DTPA is improved over conventional 3D fat‐suppressed images.
Analysis of the evolution of focal cerebral ischemia in the rat using the eigenimage filter
Authors: Peck Donald J. , Spickler Eric M. , Knight Robert A. , Hearshen David O. , Windham Joe P.
Published: March 2007

The eigenimage filter was used to evaluate the results of a MRI study of cerebral ischemia in a rat model. This linear filter segments a desired feature in an image sequence from other features which may interfere with its observation. The animals were imaged temporally, after occlusion of the middle cerebral artery, to investigate the evolution of the ischemic process. The temporal evolution of ischemia was evaluated by analysis of the “eigenimages” calculated T2 and T1 map images, and images for the angles between signature vectors defined in the eigenimage technique. The eigenimages and angle map images demonstrated an improved visibility of the lesion at all time points, as compared to the original images and T2 and T1 map images. The eigenimages also demonstrated signal intensity changes within the area of ischemia. These changes are speculated to be related to variations in local cerebral blood flow resulting in varying degrees of tissue damage. The eigenimage intensities and the angles between signature vectors demonstrated time‐related changes similar to the T2 and T1 values. Since the eigenimage filter and angle calculations are not dependent upon physical models (like T2 and T1), and the errors associated with these models, they may be preferable as methods for tissue characterization.
Validation of 13c nmr measurement of human skeletal muscle glycogen by direct biochemical assay of needle biopsy samples
Authors: Taylor Roy , Price Thomas B. , Rothman Douglas L. , Shulman Robert G. , Shulman Gerald I.
Published: March 2007

Recent developments in 13C nuclear magnetic resonance (NMR) spectroscopy have permitted noninvasive assessment of glycogen concentration in human skeletal muscle. Before these indirect measurements could be accepted as accurate, it was essential that validation should be carried out by comparing the widely used method of muscle biopsy and direct biochemical assay for glycogen concentration with measurement by NMR. Eight normal subjects underwent six NMR scans of gastrocnemius and three biopsies of the same muscle on the same day. The overall mean for muscle glycogen concentration was 87.4 mM by NMR and 88.3 mM by biopsy. There was a close correlation between the pairs of observations on each subject (R = 0.95; P 0.0001). The mean coefficient f variation for NMR measurement was 4.3 ± 2.1% and that for biopsy was 9.3 ± 5.9%. The performance of the muscle biopsies was accompanied by a small but significant rise in plasma‐free fatty acids (529 ± 157 to 667 ± 250; P < 0.01), epinephrine (17 ± 6 to 25 ± 8 pg/ml; P < 0.02), and norepinephrine (318 ± 119 to 400 ± 140 pg/ml; P < 0.02) but no change in plasma glucose, plasma insulin, nor muscle glycogen concentration assessed by NMR. The study demonstrates that in vivo 13C NMR measurement of human muscle glycogen can be regarded as accurate, and the technique is associated with a higher precision than biopsy with direct biochemical assessment.
Relationship between the degree of unsaturation of dietary fatty acids and adipose tissue fatty acids assessed by natural‐ abundance 13c magnetic resonance spectroscopy in man
Authors: Beckmann N. , Brocard J.‐J. , Keller U. , Seelig J.
Published: March 2007

Natural‐abundance 13C magnetic resonance spectroscopy was used for determining noninvasively the relative concentration of mono‐ and polyunsaturated fatty acids of adipose tissue in two groups of volunteers. The first consisted of subjects who had followed a fat‐reduced diet for at least half a year before the 13C measurements. The second were control subjects who were on a usual high‐fat diet. The ratio of unsaturated to total fatty acids in adipose tissue determined by 13C MRS correlated significantly with the same ratio in fat of the diet composition estimated by a dietician according to food records. The results indicate that 13C MRS is capable of assessing the degree of unsaturation of dietary fatty acids consumed during the preceding months.
Improved cardiac gating and ventilation timing in animal experiments
Authors: Pruski Jan C. , Abduljalil Amir , Robitaille Pierre‐Marie
Published: March 2007

In this work we present an improved solution for cardiac gating and ventilation timing in in vivo spectroscopic and imaging experiments. This approach makes use of a pulse conditioner to extract primary timing signals from noisy and fluctuating input signals. A timing controller is then used to set all additional timing outputs. Full feedback control is utilized in this timing controller to optimize both magnetic resonance and respiratory timing. Feedback control also helps ensure that timing errors will not occur during acquisition.
13C and 1H NMR Study of the Metabolic Degradation of 4‐Pentenoate in Different Dog Nephron Segments
Authors: Boulanger Yvan , Wong Hong , Fleser Angelica , Commodari Fernando , Vinay Patrick
Published: March 2007

The metabolism of 4‐pentenoate in isolated kidney tubules has been investigated by 1H and 13C NMR. The 4‐pentenoate metabolite, 3‐keto‐4‐pentenoyl‐CoA, accumulated in proximal tubules only and its formation could be competitively inhibited by octanoate. 4‐Pentenoate was metabolized in thick ascending limbs but not in papillary collecting ducts.© 1992 Academic Press,Inc.
Phase‐Scrambled RF Excitation for 3D Volume‐Selective Multislice NMR Imaging
Authors: Oh C. H. , Hilal S. K. , Wu E. X. , Cho Z. H.
Published: March 2007

An RF excitation technique with which one can improve the effective dynamic range of the receiver and reduce the interference between slices for 3D volume‐selective multislice MRI is described. The basic idea of the technique is to use phase scrambling in conjunction with slice encoding through the use of RF pulses. The spins in each slice are encoded by RF pulses which have the scrambled as well as slice‐encoded phase components along the slice‐selection direction. The scrambled, or randomly distributed, phase reduces the peak signal intensity, thereby reducing the dynamic range of the signal. Since the proposed technique utilizes RF slice encoding together with phase scrambling, interslice image interference is greatly reduced and the dynamic range is improved. In addition, the method has several advantages such as a reduction in the power requirement for the RF pulses and the elimination of the necessity for hardware such as nonlinear gradient coils.© 1992 Academic Press,Inc.
NMR measurement of 39K detectability and relaxation constants in rat tissue
Authors: Wellard R. Mark , Shehan B. Philip , Adam William R. , Craik David J.
Published: March 2007

Differences in the NMR detectability of 39K in various excised rat tissues (liver, brain, kidney, muscle, and testes) have been observed. The lowest NMR detectability occurs for liver (61 ± 3% of potassium as measured by flame photometry) and highest for erythrocytes (100 ± 7%). These differences in detectability correlate with differences in the measured 39K NMR relaxation constants in the same tissues. 39K detectabilities were also found to correlate inversely with the mitochondrial content of the tissues. Mitochondria prepared from liver showed greatly reduced 39K NMR detectability when compared with the tissue from which it was derived, 31.6 ± 9% of potassium measured by flame photometry compared to 61 ± 3%. The detectability of potassium in mitochondria was too low to enable the measurement of relaxation constants. This study indicates that differences in tissue structure, particularly mitochondrial content are important in determining 39K detectability and measured relaxation rates.
A new perfluorocarbon for use in fluorine‐19 magnetic resonance imaging and spectroscopy
Authors: Sotak Christopher H. , Hees Paul S. , Huang Hsu‐Nan , Hung Ming‐H. , Krespan Carl G. , Raynolds Stuart
Published: March 2007

A new perfluorocarbon, PTBD (perfluoro‐2,2, 2′, 2′‐tetrameth‐yl‐4,4′‐bis(1, 3‐dioxolane)), is described for use in 19F MR imaging and spectroscopy. Two‐thirds of the molecular fluorine in PTBD resonates at a single frequency and can be imaged without the use of frequency‐selective spin‐echo (SE) MRI pulse sequences to suppress chemical shift artifacts. The absence of strong homonuclear spin‐spin coupling to the imagable ‐CF3 groups in PTBD minimizes signal attenuation in 19F SE MRI due to J‐modulation effects. For equimolar concentrations of perfluorocarbon, PTBD gives an approximately 17% increase in sensitivity, relative to literature results for perfluorinated amines, at short values of TE (∼10 ms) in 19F SE MRI. These attributes allow 19F MRI of PTBD to be performed on standard clinical imaging instrumentation (without special hardware andJor software modification) and an in vivo example in a mouse is shown. This investigation involved characterizing the MR T1 and T2 relaxation times of PTBD as well as the MR spin‐lattice relaxation rate, R1 (1JT1), of PTBD as a function of dissolved oxygen concentration. The T1 and T2 relaxation times and R1 relaxation rates of perfluorooctyl bromide (PFOB) were also obtained, under similar experimental conditions, to compare and contrast PTBD with a representative perfluorocarbon that has been widely employed for 19F MRIJMRS applications.
A cylindrically symmetric magnetic shield for a large‐bore 3.0 Tesla magnet
Authors: Ewing James R. , Warner Rory , Helpern Joseph A.
Published: March 2007

A 3.0 Tesla, 0.80‐m bore magnet replaced our previous 1.9 Tesla, 0.76‐m magnet. The 3.0 Tesla replacement magnet had a dipole moment of 1.7 with respect to that of the 1.9 Tesla magnet. The pre‐existing cylindrically symmetric passive steel shielding was modified to confine the fringe fields of the replacement magnet to match those of the previous magnet.

A cylindrically symmetric inner shield insert of about 20,000 kg was designed, fabricated, and installed. Upon energization of the magnet, the combined shielding met all design criteria. Alternative designs, optimization of cylindrically symmetric designs, and costs of fabrication, are presented herein.
Phased spectroscopic images: Application to the characterization of the 1H 1.3‐ppm resonance in intracerbral tumors in the rat
Authors: Le Fur Y. , Ziegler A. , Bourgeois D. , Decorps M. , Remy C.
Published: March 2007

Spectra obtained with phase‐encoding techniques show phase‐shifts varying from voxel to voxel. The procedure allowing voxel‐dependent phase‐shifts to be compensated is presented. The method has been applied to the characterization of the 1.3‐ppm resonance observed in intracerebral tumors in the rat.
Oxygen measurement inside an NMR magnet with a catheter electrode
Authors: Eijgelshoven M. H. J. , Lekkerkerk C. , van Beek J. H. G. M. , van Echteld C. J. A.
Published: March 2007

In this study we show the possibility of continuous oxygen tension measurement inside an NMR magnet without disturbance of simultaneous NMR data acquisition. Our modified Clark‐type oxygen electrode has a fast response (2 s) and can be inserted deep into small bore NMR systems thanks to its small diameter (2 mm).
Simultaneous multi‐site EPR spectroscopy in vivo
Authors: Smirnov Alex I. , Norby Shong‐Wan , Clarkson R. B. , Walczak Ted , Swartz Harold M.
Published: March 2007

A gradient technique to measure electron paramagnetic resonance spectra simultaneously at several different locations is described. The technique is based on the use of point probes containing paramagnetic centers. The value of the magnetic field gradient is chosen to be sufficient to separate the EPR signals from the different paramagnetic probes yet at the same time small enough to change only minimally the shape of individual signals. The conditions to apply this technique are considered in detail. When experimental data have a high signal‐to‐noise ratio, the lineshape distortion induced by the gradient can be corrected with the aid of a known distribution function of paramagnetic centers within the probe. The maximum entropy deconvolution algorithm is successfully applied for the correction of significantly distorted lines. The technique is experimentally tested and applied to measure the concentration of oxygen in hypertrophied rat myocardium and normal rat kidney in vivo by low frequency EPR (L‐band, 1.2 GHz). No types of EPR oxygen‐sensitive probes‐lithium phthalocyanine crystals and synthetic carbohydrate chars‐were used.
A comparison of an inductively coupled implanted coil with optimized surface coils for in vivo NMR imaging of the spinal cord
Authors: Wirth III E. D. , Mareci T. H. , Beck B. L. , Fitzsimmons J. R. , Reier P. J.
Published: March 2007

A study was performed to determine whether an implanted, inductively coupled nuclear magnetic resonance (NMR) imaging spine coil could provide a significant gain in signal‐to‐noise ratio (SNR) on images of the spinal cord relative to the SNR of optimized surface coils. Implanted coils were surgically affixed to the upper lumbar spine (first lumbar through third lumbar vertebrae) in a total of four adult cats. The implanted coil was inductively coupled to an external 12 × 12 cm square surface coil that was mounted on a 14‐cm diameter Plexiglas® cradle (Townsend Industries, Des Moines, IA). Two similar cradles were prepared with transmit‐only 12 × 12 cm surface coils and either a receive‐only 6 × 6 cm square surface coil or a receive‐only quadrature coil pair (two 4 × 6 cm coils overlapped slightly to minimize their mutual inductance) with 'the same surface area (6 × 6 cm). A total of five single‐slice, T1‐weighted spin‐echo images (TR = 500 ms, TE = 30 ms, 4‐mm slice thickness) were acquired from a 1‐liter saline phantom and from the second lumbar spinal level in an adult cat with a normal, uninjured spinal cord. On the spinal cord images, the quadrature coil exhibited a factor of 1.65 increase in SNR relative to the single‐turn surface coil, whereas the implanted coil achieved a factor of 2.19 increase in SNR. The improved SNR for the quadrature and implanted coils was observed as a dramatic improvement in the clarity of the images. The high SNR available with the implanted coils allows the acquisition of higher resolution NMR images and opens up the possibility of measuring localized spectroscopy in vivo within the spinal cord.
Asymmetric single‐turn solenoid for MRI of the wrist
Authors: Szeglowski Scott D. , Hornak Joseph P.
Published: March 2007

A single‐turn solenoid, lacking the conventional cylindrical or rectangular symmetry, was constructed for magnetic imaging of the human wrist at 1.5 Tesla. As is characteristic of singleturn solenoids, this wedge‐shaped geometry solenoid was found to have a high filling factor and quality factor, as well as produce images with a favorable signal‐to‐noise ratio. The radio frequency (RF) transmitter power required to produce a 90° pulse in the solenoid was 130 mW. The asymmetric solenoid had a small variation in the intensity of the RF field across its volume, which is characteristic of symmetrical single‐turn solenoids. The combination of these four properties of the coil resulted in the production of excellent 1.5‐mm thick anatomical images of the wrist.
Continuous measurement of cell volume changes in perfused rat salivary glands by proton NMR
Authors: Larcombe‐McDouall Jacky B. , Seo Yoshiteru , Steward Martin C.
Published: March 2007

Changes in intracellular and extracellular water content have been measured in perfused rat salivary glands by repetitive application of an inversion recovery (IR) pulse sequence. The relaxation reagent Gd‐DTPA (10 mM) was included in the per‐fusate so that the intracellular and extracellular water proton signals could be distinguished by their different longitudinal relaxation times. Changes in water content in response to altered perfusion pressure and perfusate osmolarity were determined at 30‐s intervals and indicated a clear separation of the intracellular and extracellular components. Using a modification of the IR pulse sequence, changes in intracellular water content were also measured at 6‐s intervals. With this time resolution, differences in the rates of cell shrinkage in response to hyperosmotic perfusates and the secretomotor agonist acetylcholine were observed. The results suggest that this approach offers a relatively noninvasive method for studying cell volume regulation in intact, perfused tissues and organs.
In vivo19F spin relaxation and localized spectroscopy of fluoxetine in human brain
Authors: Komoroski Richard A. , Newton Joseph E. O. , Cardwell David , Sprigg Jay , Pearce John , Karson Craig N.
Published: March 2007

Fluorine‐19 NMR spectroscopy was used to monitor the anti‐depressant drug fluoxetine (and its metabolite norfluoxetine) in vivo in human brain. A quadrature birdcage head coil, developed for operation at 60.1 MHz, yielded a signal from the head 2 to 4 times stronger than for surface coils. It was used to measure the in vivo 19F spin‐lattice relaxation time (T1) of fluoxetine for five patients by the inversion‐recovery technique. The individual T1s varied from 149 to 386 ms, which was attributed in part to interindividual differences based on the reproducibility of a phantom T1. The individual T1 correlated weakly with approximate brain concentration. A lower limit of 3 to 4 ms was found for the spin‐spin relaxation time from line width measurements. Low resolution 4‐dimensional spectroscopic imaging confirmed that the single in vivo 19F resonance for fluoxetine arose primarily from brain. The spectrum of a cerebral hemisphere (in formalin) obtained at autopsy from a patient on 40 mg/day of fluoxetine for 19 weeks was comparable with that seen for patients in vivo. The in vivo signal arose about equally from fluoxetine and the active me tabolite norfluoxetine, as demonstrated by the in vitro 19F NMR spectrum of the lipophilic extract of a small section of brain. In virto quantitation of frozen samples from three brain regions yielded combined fluoxetine/norfluoxetine concentrations of 12.3 to 18.6 μ/ml, which is higher than typically determined in vivo, and suggests that the fluorinated drugs may not be 100% visible in vivo.
Vascular interventions guided by ultrafast MR imaging: Evaluation of different materials
Authors: Köchli V. D. , McKinnon G. C. , Hofmann E. , von Schulthess Gustav K.
Published: March 2007

The ability of MRI to acquire not only anatomical but also functional information makes MRI guided vascular interventions an interesting goal. Recent developments in ultrafast MR imaging sequences such as fast gradient echo or echo planar (EPI) mean that not only real time MRI but also MRI guided vascular interventions are real possibilities for the not too distant future. However, currently available guide wires and catheters are potentially unusable in MRI because they are either ferromagnetic or MRI invisible. In order to find different materials suitable for real time MRI, various devices were examined with fast gradient echo and interleaved EPI pulse sequences. The measurements were performed using a continuously running, pseudo real time MRI system to investigate the dynamic imaging behavior under guide wire insertion. Suggestions are made as how to construct guide wires and catheters, which can be visualized with ultrafast imaging sequences, while not causing prohibitive artifacts or image distortions.
Scalar coupling and zero‐quantum coherence relaxation in STEAM: Implications for spectral editing of lactate
Authors: Kingsley Peter B.
Published: March 2007

Accurate values were obtained for the lactate zero‐quantum coherence frequency, ωZQ = ωi‐ωs = CH3–CH chemical shift difference, and scalar coupling constant, J, by using the methyl signal's amplitude modulation during the TM period of a STEAM sequence, 90°–TE/2–90°–TM–90°–TE/2‐ Acquire. Although most previous work has used J= 7.35 Hz, or 1/J= 136 ms, the actual value is J= 6.93 ± 0.05 Hz or 1/J = 144.3 ± 1 ms. In addition, the CH3–CH chemical shift difference = 2.7956 ± 0.0005 ppm, and the relaxation time for zero‐quantum coherence, TZQ, was much shorter than either T2 or T1 for the methyl resonance. A small component of the signal with TE= 144 ms, which was not modulated at the zero‐quantum coherence frequency or by scalar coupling, was assigned to longitudinal two‐spin order magnetization (IzSz) created by imperfect radio frequency pulse profiles. This information will allow improved editing of the lactate signal and more accurate quantitation of lactate concentrations.
Time and frequency domain analysis of NMR data compared: An application to 1D 1H spectra of lipoproteins
Authors: van den Boogaart A. , Ala‐Korpela M. , Jokisaari J. , Griffiths J. R.
Published: March 2007

A comparison between a time domain analysis algorithm (VARPRO) and a frequency domain analysis algorithm (FITPLAc) for parameter estimation of magnetic resonance spectroscopy (MRS) data series is presented. VARPRO analyses the measured MRS signal (free induction decay; FID); FITPLAc analyses the discrete Fourier transform of the FID, the frequency domain magnetic resonance spectrum. A rapid time domain method, used to subtract the dominating water resonance from a 1H MRS FID, without affecting the metabolites of interest, is outlined and applied. Also a new “pseudo‐frequency selective” approach to time domain fitting is introduced. The possibilities of combining the most favorable features of time and frequency domain processing into one single MRS signal processing method are assessed. The 1H MRS signals of ultracentrifuged very low (VLDL), intermediate (IDL), and high (HDL) density lipoprotein fractions from human blood plasma were used for the comparisons. The results from both algorithms were in good agreement.
Dual contrast GRASE (gradient‐spin echo) imaging using mixed bandwidth
Authors: Feinberg David A. , Kiefer Berthold , Litt Andrew W.
Published: March 2007

Equal time spacing of RF pulses in the CPMG sequence imposes a constraint of equal signal read periods in spin‐echo train imaging. GRASE imaging differs by using multiple read gradients in each π‐π time interval, which are not constrained to be equal in number or duration. This additional degree of freedom is developed in dual contrast imaging. Closely spaced read periods are used for the PDW image to reduce T2 decay effects, while fewer low‐bandwidth read periods in each of several π‐π intervals are used to raise the signal‐to‐noise ratio and avoid signal averaging in the T2‐weighted image. Key words: magnetic resonance imaging; gradient‐spin echo; fast imaging.
In vivo visualization of myelin water in brain by magnetic resonance
Authors: Mackay Alex , Whittall Kenneth , Adler Julian , Li David , Paty Donald , Graeb Douglas
Published: March 2007

We exploit the intrinsic difference in magnetic resonance spin‐spin relaxation time, T2, between water associated with myelin sheaths and water in other central nervous system tissue in order to measure myelin water content within any region of an image or to generate indirectly a myelin map of the brain. In normal volunteers, myelin water maps give the expected myelin distribution. In multiple sclerosis patients, lesions exhibit different myelin water contents providing insight into the de‐myelination process unavailable from conventional magnetic resonance images. In vivo myelin measurement has important applications in the clinical management of multiple sclerosis and other white matter diseases.
A novel saturation transfer contrast method for 3D time‐of‐flight magnetic resonance angiography: A slice‐selective off‐resonance sinc pulse (SORS) technique
Authors: Miyazaki Mitsue , Kojima Fumitoshi , Ichinose Nobuyasu , Onozato Yukio , Igarashi Hiromitsu
Published: March 2007

Saturation transfer contrast (STC) techniques have been employed to decrease the signal intensity of observed water by saturating a broad proton component. The STC pulse, generally spatially nonselective, reduces the signal of brain background tissues as well as inflowing blood in 3D time‐of‐flight (TOF) angiography. We present a novel technique, a slice‐selective off‐resonance sinc pulse (SORS), which is employed to enhance inflowing blood and to suppress the signal of stationary background tissues. The STC effects of the SORS and other spatially nonselective methods influencing inflowing blood is discussed in detail. Angiograms using the SORS method are also presented to demonstrate improved vessel conspicuity. In addition, the SORS method is applicable to imagers with a whole‐body RF transmitter system.
31P NMR assessment of orthotopic liver rejection in a rat model
Authors: Bowers John L. , Kawano Katsunori , Metz Kenneth R. , Teramoto Kenichi , McCullough Ann , Clouse Melvin E.
Published: March 2007

31P NMR spectroscopy was used serially to study rejecting (ACI→LEW) and nonrejecting (ACl→ACl) orthotopic liver transplants in rats. Recipients were evaluated on post‐transplant days 1,3, 5, 7, 9, and 11. The relative changes in phosphomonoester (PME), inorganic phosphate (Pi), high‐energy phosphates and pH were studied. The earliest significant difference between the rejecting and nonrejecting groups was a decrease in the α‐NTP peak area on Day 5. This was followed by significant decreases in β‐NTP and pH, and increases in PME and Pi on Day 7. High‐resolution 31P NMR spectra of perchloric acid extracts demonstrated the PME increase to be due mainly to elevated phosphoethanolamine. Using the parameter (Pi + PME)/(α + β + γ‐NTP), rejecting livers were distinguished from nonrejecting livers at a moderate stage of rejection.
A MRI bolus tagging method for observing helical flow in the descending aorta
Authors: Hoydu Alison K. , Bergey Philip D. , Haselgrove John C.
Published: March 2007

We present a MRI bolus tagging method for exploring the helical nature of blood flow in the aorta. Two image series are collected, the first to quantify longitudinal flow (coronal/sagittal imaging plane‐transverse saturation plane), the second to measure rotational flow (transverse imaging plane‐coronal/sagittal saturation plane). The experimental protocol has been established in healthy adult volunteers and children with normal vasculature. Our results permit immediate visualization of the unique nature of helical flow in each volunteer. We demonstrate evidence of rapid helical twist, no helical twist, and reversal of twist.
Real‐Time Functional Magnetic Resonance Imaging
Authors: Cox Robert W. , Jesmanowicz Andrzej , Hyde James S.
Published: March 2007

A recursive algorithm suitable for functional magnetic resonance imaging (FMRI) calculations is presented. The correlation coefficient of a time course of images with a reference time series, with the mean and any linear trend projected out, may be computed with 22 operations per voxel, per image; the storage overhead is four numbers per voxel. A statistical model for the FMRI signal is presented, and thresholds for the correlation coefficient are derived from it. Selected images from the first real‐time functional neuroimaging experiment (at 3 Tesla) are presented. Using a 50‐MHz workstation equipped with a 14‐bit analog‐to‐digital converter, each echo planar image was acquired, reconstructed, correlated, thresh‐olded, and displayed in pseudocolor (highlighting active regions in the brain) within 500 ms of the RF pulse.
ATP production and mechanical work in exercising skeletal muscle: A theoretical analysis applied to 31P magnetic resonance spectroscopic studies of dialyzed uremic patients
Authors: Kemp Graham J. , Thompson Campbell H. , Taylor Doris J. , Radda George K.
Published: March 2007

31P magnetic resonance spectroscopy (31P MRS) can yield much information about bioenergetics in skeletal muscle. During mixed aerobic/glycolytic exercise, changes in phos‐phocreatine (PCr) concentration and pH may be abnormal because of reduced muscle mass or reduced efficiency (which the authors combine here as “effective muscle mass”) or because of reduced oxidative capacity. The authors show how these can be distinguished by calculating the nonoxidative and oxidative costs of mechanical work, and also of work per unit of effective muscle mass (measured using the initial rate of ATP turnover). These quantities are substantially time‐independent during incremental exercise, and so can be used to compare exercise studies of differing duration. The authors illustrate this analysis by showing that in dialyzed patients with chronic renal failure, the substantial exercise abnormalities seen by 31P MRS are due mainly to a decrease in effective muscle mass, which outweighs the oxidative defect implied by the abnormal PCr recovery kinetics.
Chemical Shift Imaging from Simultaneous Acquisition of a Primary and a Stimulated Echo
Authors: Franconi Florence , Akoka Serge
Published: March 2007

An imaging method is presented for obtaining chemical shift images from only one acquisition. Images are acquired with the same spatial resolution as in regular spin‐echo imaging. The sequence is based on the simultaneous acquisition of a spin echo and a stimulated echo in a single pass. The use of 90° radiofrequency pulse flip angles results in the same proton density, T2 and T1 weighting for the two echoes. Application of this sequence to chemical shift imaging is discussed for three fat suppression techniques (chopper, CHESS, and hybrid). Imaging was performed on phantoms and volunteers. The image quality was the same as those obtained by the chopper and the hybrid methods and the acquisition time was reduced by a factor of two.