bluuebunny/crossref_metadata_2025 huggingface dataset:
A new acquisition mode for 2D inflow refreshment angiography
Authors: Doyle Mark , Matsuda Tetsuya , Pohost Gerald M.
Published: March 2007

Time‐of‐flight angiography methods rely on blood/tissue contrast generated when fresh blood spins enter a partially saturated region. A series of projective angiographic views is generated by application of a maximum intensity projection algorithm to data acquired from a 3D volume. When the data are acquired as a set of 2D slices, the angiograms exhibit sensitivity to body motion, resulting in the generation of artifacts. We present a new 2D time‐of‐flight angiographic technique, STREAM, Suppressed Tissue with Refreshment Angiography Method. It exhibits low sensitivity to internal body motion, thus allowing acquisition of good quality, single average angiograms. To suppress the static tissue signal a unique “active” suppression strategy is employed. Additionally, to further suppress the lipid signal, the chemical‐shift phenomenon is exploited in the STREAM sequence. © 1991 Academic Press. Inc.
New spatial localization method using pulsed high‐order field gradients (SHOT: Selection with high‐order gradient)
Authors: Oh C. H. , Hilal S. K. , Cho Z. H. , Mun I. K.
Published: March 2007

A new spatial localization method using an additional set of high‐order magnetic field gradients is described. The method uses a nonlinear part of high‐order magnetic field gradient patterns which allows us to select a volume in conjunction with the selective radiofrequency (RF) pulse. Unlike the other existing volume selection methods such as ISIS or SPARS, the proposed selection method requires only one RF‐gradient pulse pair to select a volume in two directions. The center of the selected volume can be moved to any arbitrary location within the body by the addition of precalculated lower order gradients which are simultaneously pulsed with the high‐order gradient. The method also has the potential for localized spectroscopy from the FID signal which can be realized by using oscillating second‐ and first‐order gradients for 3D selection with a single RF pulse. By using the proposed localization method, it is possible to design more flexible pulse sequences, e.g., the shorter echo‐time spectroscopic pulse sequence. We have designed and constructed a six‐loop r2 (or x2 + y2) gradient coil for initial application. By simultaneously applying this second‐order gradient and proper x, y, and/or z gradients, 2D selections were achieved in arbitrarily selected positions in conjunction with a single selective RF pulse. Phantom and animal experiments have been performed and the results appear promising, especially in areas of NMR spectroscopic imaging applications where spatial localization is essential. © 1991 Academic Press. Inc.
Target‐point combination of MR images
Authors: Buxton Richard B. , Greensite Fred
Published: March 2007

A method is described for combining multiple magnetic resonance images of the same anatomic slice to produce a single image which incorporates the favorable contrast features of each of the original images. The target‐point method is a general method that includes linear combination as a subset and is designed to deal with the clinical need to maximize the contrast‐to‐noise ratio between several pairs of tissues simultaneously. Although it is intrinsically a nonlinear method, noise propagates approximately uniformly into the combined image. In examples of brain images the target‐point method produced images with higher mutual contrast than the first principal component weighted sum image. © 1991 Academic Press. Inc.
A modified pulse sequence for in vivo diffusion imaging with reduced motion artifacts
Authors: Prasad P. V. , Nalcioglu O.
Published: March 2007

A modified spin‐echo diffusion imaging pulse sequence incorporating bipolar gradients that is less sensitive to macroscopic motion‐induced artifacts is presented. Expressions for apparent diffusion coefficient in the presence of microcirculation and macroscopic motions and contrast‐to‐noise ratio in the diffusion map are derived. Diffusion coefficients of liquid phantoms have been measured using a 1.5‐T GE Signa system. Experiments performed to demonstrate the immunity to motion‐induced errors are reported. Brain images from human volunteer have also been included to show the potential clinical application of the proposed pulse sequence. © 1991 Academic Press. Inc.
Adaptive motion compensation in MRI: Accuracy of motion measurement
Authors: Felmlee Joel P. , Ehman Richard L. , Riederer Stephen J. , Korin Hope W.
Published: March 2007

It has been shown that magnetic resonance image data can be corrected for the effects of motion by using retrospective adaptive techniques which employ navigator (NAV) echoes. We demonstrate the accuracy with which NAV echoes can measure motion, as well as the independent nature of the respective view‐to‐view and intraview corrections. © 1991 Academic Press. Inc.
The effect of chlorpromazine and methylprednisolone on NMR relaxation times in the normal cat brain
Authors: Barnes D. , Harvey I. , McDonald W. I. , Ron M. A. , Moore S.
Published: March 2007

This small experimental study describes the effects on the NMR relaxation times in normal cat brain of a 5‐day course of high dose methylprednisolone and, separately, a 1‐month course of standard dose daily chlorpromazine. Methylprednisolone had no influence on T1 or T2 in these tissues, but chlorpromazine produced a transient fall of T1 of thalamus, and rise in T2 of white matter: both normalize after 4 weeks. The mechanism of these changes is unknown. It is concluded that these drugs should not interfere with the quantitative MRI monitoring of brain abnormalities in patients receiving them, although the unlikely occurrence of longer term effects of chlorpromazine has not been excluded. © 1991 Academic Press. Inc.
Evidence for a contribution of paramagnetic ions to water proton spin‐lattice relaxation in normal and malignant mouse tissues
Authors: Negendank William , Corbett Thomas , Crowley Michael , Kellogg Christopher
Published: March 2007

Paramagnetic ions complexed to proteins may lose, retain, or enhance solvent paramagnetic relaxation (SPR) relative to free solution. We measured T1 and T2 of three mouse cancers, their normal counterparts, and six additional tissues. Long T1 of cancers was not caused by necrosis or by different contents of water, fat, or blood. Dissociable (TCA‐extractable) and nondissociable (ashed) Mn, Cu, and Fe were measured by AA. Cancers had less Mn, Cu, and Fe than did normal counterparts. All 12 tissues had inverse correlations between T1 and dissociable Mn and Cu. For Mn alone to account for reduced T1, the extent to which SPR of the Mn‐protein complexes would be enhanced is by factors of 0.6 to 13, below the maximum observed in Mn‐enzymes. Different amounts of paramagnetic ion‐protein complexes may account for part of the differences in T1 of water protons in different tissues, and the longer T1 of cancer cell water may be caused in part by reduced amounts Of such complexes. © 1991 Academic Press. Inc.
Volume imaging with MR phased arrays
Authors: Hayes Cecil E. , Hattes Neil , Roemer Peter B.
Published: March 2007

A volume MR phased array was constructed with two coils placed anteriorly and two coils posteriorly. Data acquired simultaneously from the four coils on a phantom were combined into a single image having a signal‐to‐noise ratio 80% better than that from the body coil. Additional comparisons of the four‐coil phased array with a two‐coil phased array and a Helmholtz pair having the same overall dimensions show how variations of signal amplitude and phase in the individual coils affect the composite SNR. Images of the male and female pelvis demonstrate how the improved SNR can be used to reduce the number of excitations, decrease the field of view, increase the echo time, or reduce the slice thickness. © 1991 Academic Press. Inc.
Rapid in vivo proton shimming
Authors: Schneider Erika , Glover Gary
Published: March 2007

A rapid and completely automated method of adjusting the magnetic field (B0) homogeneity for in vivo proton spectroscopy and imaging is described. Bo inhomogeneity maps are generated by a gradient‐recalled echo pulse sequence in which the frequency dispersion is chosen to eliminate the effects of the fat/water chemical shift. Low‐order shim values are derived by magnitude‐weighted least‐squares fits to the B0 maps and automatically applied as DC offsets to the X, Y, and Z gradient amplifiers. Imaging with chemical shift selective saturation is used as a measure of the efficacy of the technique. Results indicate that AUTOSHIM improves the overall homogeneity; however, local high‐order field distortions which cannot be corrected by linear gradients are generated by certain air/tissue and bone/tissue morphology. In such cases a “ZOOM SHIM” may be applied over a limited region of interest for local homogeneity improvement at the expense of other regions. It is suggested that such scans are a necessity for recording the homogeneity during clinical MR spectroscopy. © 1991 Academic Press. Inc.
In vivo NMR spectral parameter estimation: A comparison between time and frequency domain methods
Authors: Joliot M. , Mazoyer B. M. , Huesman R. H.
Published: March 2007

We have compared various methods of in vivo NMR spectral parameter estimation, namely a nonlinear fit of the free induction decay signal in the time domain (NLTD), a nonlinear fit of the fast Fourier transform of the FID data in the frequency domain using either a continuous Lorentzian model (NLLM) or a Fourier‐sampled model (NLFM), and a time‐domain linear prediction method using singular value decomposition (LPSVD). Monte Carlo simulations of 31P and 13C in vivo experiments were used to assess the bias and statistical uncertainties of spectral parameters obtained with each method. In the 31P case, all methods appear to be equivalent except the LPSVD method that led to significantly biased peak amplitudes (up to 28%). In the 13C case, the only methods able to recover the glycogen peak were the NLTD method and its equivalent in the frequency domain (NLFM). In both the 31P and the 13C cases simulations demonstrated that 256 data points were sufficient. These results demonstrate the feasibility and the robustness of a nonlinear fit of the FID data in the time domain, and we illustrate this on 31P and 13C data sets obtained in humans. © 1991 Academic Press. Inc.
A quantitative comparison of the TERA modeling and DFT magnetic resonance image reconstruction techniques
Authors: Smith M. R. , Nichols S. T. , Constable R. T. , Henkelman R. M.
Published: March 2007

The resolution of magnetic resonance images reconstructed using the discrete Fourier transform (DFT) algorithm is limited by the effective window generated by the finite data length. The transient error reconstruction approach (TERA) is an alternative reconstruction method based on autoregressive moving average (ARMA) modeling techniques. Quantitative measurements comparing the truncation artifacts present during DIT and TERA image reconstruction show that the modeling method substantially reduces these artifacts on “full” (256 × 256), “truncated” (256 × 192), and “severely truncated” (256 × 128) data sets without introducing the global amplitude distortion found in other modeling techniques. Two global measures for determining the success of modeling are suggested. Problem areas for one‐dimensional modeling are examined and reasons for considering two‐dimensional modeling discussed. Analysis of both medical and phantom data reconstructions are presented. © 1991 Academic Press, Inc.
A coupled resonator model of the detection of nuclear magnetic resonance: Radiation damping, frequency pushing, spin noise, and the signal‐to‐noise ratio
Authors: Guéron M.
Published: March 2007

Magnetic resonance involves two coupled resonating systems: the spins and the tuned receiver coil. We simulate the spin system by an equivalent electrical resonator. An analysis of coupled resonators leads to a straightforward derivation of properties such as radiation damping, frequency pushing, and spin noise. The theory is applied to recent experiments (M. Guéron and J. L. Leroy, J. Magn. Reson. 85, 209–215 (1989)). The sensitivity of the spin noise experiment is shown to be T2/τ0, where 1/τ0 is the rate of radiation damping. This result leads directly to a fundamental formulation of the usual signal‐to‐noise ratio,

where m0 is the equilibrium magnetic moment, θ is the temperature, and F is the noise figure of the receiver. An equivalent electrical resonator can also be used to describe the active medium of masers. © 1991 Academic Press, Inc.
Echo‐planar imaging of diffusion and perfusion
Authors: Turner Robert , Le Bihan Denis , Scott Chesnicks A.
Published: March 2007

Use of the Stejskal‐Tanner sequence for performing diffusion images in the human brain tends to be complicated by the presence of artifacts caused by voluntary or involuntary, sometimes pulsatile, motion. We describe the implementation of the technique of echo‐planar diffusion imaging, which avoids these artifacts and allows reproducible quantitative values of the diffusion coefficient to be measured in vivo. The effects of perfusion are easily visible in a phantom containing a gel. The results for human brain show a significant “perfusion fraction” in grey matter, consistent with an extracellular, possibly microvascular, volume of about 10%. © 1991 Academic Press, Inc.
Effect of bulk tissue motion on quantitative perfusion and diffusion magnetic resonance imaging
Authors: Chenevert Thomas L. , Pipe James G.
Published: March 2007

The effect of irreproducible bulk tissue motions upon quantification of tissue perfusion and diffusion was studied via computer simulation of random phase error in conventional phase‐encoded perfusion/diffusion MRI. Simulations using acquisition parameters typical for human brain studies demonstrate that bulk motion irreproducibility of ≈60 pm/s can produce phase instability on the order of 20° which overwhelms estimates of perfusion fraction and produces significant errors in diffusion values. Bulk tissue motion control of the human brain via cardiac gating and substantial head restraint was studied by direct measurement of voxel phase stability. Phase instability of 10° to 20° was observed from right‐to‐left and anterior‐to‐posterior motions and significantly greater phase variability from superior‐to‐inferior motion. The spatial pattern of phase variability indicates the source is likely a mixture of cardiac pulsation and respiration. © 1991 Academic Press, Inc.
Very slow flow imaging
Authors: Décorps M. , Bourgeois D.
Published: March 2007

Two methods allowing imaging of very slow coherent flows are presented. The first method is based on the use of a radiofrequency field gradient. The second method is based on the use of gradients of the main field. Both methods include suppression of signal from stationary spins. A flow contour map is obtained which allows quantitative determination of velocity. The methods were proved to be efficient to image velocities as low as 10 μm ·−1. © 1991 Academic Press, Inc.
Diffusion‐weighted MR imaging of extraaxial tumors
Authors: Tsuruda Jay S. , Chew Wil M. , Moseley Michael E. , Norman David
Published: March 2007

The clinical usefulness of the application of spin‐echo diffusion‐weighted imaging in the evaluation of extraaxial cysts and epidermoid tumors is demonstrated in a series of 15 patients. Apparent diffusion coefficient (ADC) images based on intravoxel incoherent motion (IVIM) were obtained with a maximum gradient b value = 100 s/mm2. Lesion ADC was qualitatively compared to external phantoms. In all cases, epidermoid tumors revealed reduced ADC values similar to that of normal brain tissue. On the other hand, all cysts had ADC similar to the stationary water phantom. Lesion delineation was improved due to the replacement of normal pulsatile (very high ADC) cisternal CSF. Direct quantitative measurements of ADC using this technique may not be possible due to unavoidable motion artifact. © 1991 Academic Press, Inc.
Reduction of flow artifacts in NMR diffusion imaging using view‐angle tilted line‐integral projection reconstruction
Authors: Jung K. J. , Cho Z. H.
Published: March 2007

Most of the diffusion imaging techniques employ strong diffusion gradient pulses of long duration in order to achieve appreciable signal attenuation through the diffusion effect. However, these strong and long gradient pulses make the resultant images extremely sensitive to the motion or flow of the object. Fourier imaging, with which most of the current NMR imaging is performed, is especially sensitive to the fluctuating flow and the images are usually obscured by severe flow artifacts smeared in the phase‐encoding direction. In this paper, we have proposed a diffusion imaging technique which reduces the flow artifacts by use of the line‐integral projection reconstruction (LPR) imaging method. Furthermore, the inhomogeneity artifacts expected to occur in LPR imaging have been corrected by application of the view‐angle tilting technique. The pulse sequence of the view‐angle tilted LPR diffusion imaging is designed in such a way that it works for both isotropic and anisotropic diffusion. Experimental results are presented along with the experimental procedures. © 1991 Academic Press, Inc.
Hepatic intracellular pH in Vivo using F‐quene 1 and 19F NMR spectroscopy
Authors: Beech John S. , Iles Richard A.
Published: March 2007

Intracellular pH (pHi) has been determined in vivo in livers from anaesthetized rats using both 31P NMR and 19F NMR spectroscopy. In the 31P NMR study pH, determined from the chemical shift of endogenous Pi, was found to be 7.26 ± 0.02. In the 19F NMR study on a separate group of animals pHi was determined from the chemical shift of F‐Quene 1 infused via the portal vein and found to be 7.18 ± 0.01. In approximately half of the 19F NMR studies no 19F signal could be detected in the liver probably because of loss of F‐Quene 1 in the circulation. The small discrepancy between pHi determined by the two probes could be caused by different intra‐ or intercellular distributions or by unknown effects of F‐Quene 1 on metabolism. © 1991 Academic Press, Inc.
Spectroscopic imaging using variable angle excitation from adiabatic plane‐rotation pulses
Authors: Hendrich Kristy , Garwood Michael , Merkle Hellmut , Uǧurbil Kâmil
Published: March 2007

The technique of chemical‐shift (spectroscopic) imaging has been implemented using a variable angle adiabatic plane‐rotation pulse for small angle excitation over the entire sensitive volume of a surface coil. Optimum signal‐to‐noise ratio per unit time is obtained in applications where the pulse repetition rate is fast relative to 1/5 T1. © 1991 Academic Press, Inc.
In vivo oximetry using a nitroxide‐liposome system
Authors: Glockner James F. , Chan Hsiao‐Chang , Swartz Harold M.
Published: March 2007

Liposomes containing the deuterated, charged, aqueous soluble nitroxide 4‐trimethylammonium‐2,2,6,6‐tetramethylpiperidine‐d16‐1‐oxyl (d‐Cat1) were used as probes to measure oxygen concentrations in vivo. Following intramuscular or intraperitoneal injection of the liposome suspension, ICR mice were placed over the surface probe of a low frequency (1.1 GHz) electron paramagnetic resonance (EPR) spectrometer. The linewidth of the deuterated nitroxide is sensitive to changes in the dissolved oxygen concentration: this parameter was calibrated separately so that linewidths measured in the injected mice could be converted into oxygen tensions. This technique detected substantial changes in pO2 as the oxygen content of the breathing gas was changed from 21 to 85 to 0%. Intravenous injection of the liposomes also is possible, and the liposomes accumulate in the liver and spleen, where detectable, oxygen‐sensitive EPR signals can be measured. © 1991 Academic Press, Inc.
Diffusion‐weighted imaging of kainic acid lesions in the rat brain
Authors: King M. D. , Bruggen N. Van , Ahier R. G. , Cremer J. E. , Hajnal J. V. , Williams S. R. , Doran M.
Published: March 2007

We present T2‐weighted and diffusion‐weighted images of kainic acid lesions in the rat brain. Our observations show improved image contrast between edematous lesions and unaffected tissue using diffusion‐weighted imaging. Furthermore, we show that the anisotropic intensity changes associated with this sequence can be used to highlight white matter tracts and to provide information concerning their orientation in the rat brain. © 1991 Academic Press, Inc.
A 7Li NMR study of visibility, spin relaxation, and transport in normal human erythrocytes
Authors: Gullapalli Rao P. , Hawk Roger M. , Komoroski Richard A.
Published: March 2007

The behavior of the lithium (Li) ion in normal human erythrocytes has been studied by 7Li NMR. The uptake of Li into the cells was followed as a function of solution conditions, temperature, hematocrit, and blood age using dysprosium tripolyphosphate shift reagent. Under our conditions the uptake of Li increases with increasing hematocrit and blood age. For packed cells the extracellular 7Li spin‐lattice relaxation time was only slightly longer than the intracellular relaxation time. Thus, T1 may not be useful for separate observation of intra‐and extracellular Li in vivo. The intra‐ and extracellular T2s were substantially shorter than the corresponding T1s. Also, the intracellular T2 was considerably shorter than that for the extracellular compartment, suggesting that T2 may provide a noninvasive handle for observation of intracellular Li. Nuclear Overhauser enhancements could be observed for both extra‐and intracellular 7Li, confirming that dipolar coupling to 1H is a contributing relaxation mechanism. The 7Li NMR visibility was esentially 100% at high Li concentrations, decreasing to about 84% at 1 mM Li. Based on time course studies of the invisibility, and a comparison of NMR and inductively coupled plasma results, it appears that the invisibility of the intra‐ and extracellular compartments for packed cells in the same. Although a 23Na double‐quantum signal could be observed for red blood cells, no double‐quantum signal was observed for 7Li. © 1991 Academic Press, Inc.
Use of high temperature superconductor in a receiver coil for magnetic resonance imaging
Authors: Hall A. S. , Alford N. Mcn. , Button T. W. , Gilderdale D. J. , Gehring K. A. , Young I. R.
Published: March 2007

A planar YBa2Cu3Ox (YBCO) coil has been used as a pick‐up coil in a nuclear magnetic resonance imager. It was found that the quality factor Q of the YBCO coil was greater than its copper counterpart by approaching 50% even in a field of 0.15 T. The Q of the copper coil at 77 K and in a field of 0.15 T was 1200 while that of the YBCO coil under identical conditions was 1700. © 1991 Academic Press, Inc.
MRI of the pancreas transplant: Lack of correlation between imaging and clinical status
Authors: Kelcz Frederick , Sollinger Hans W. , Pirsch John D.
Published: March 2007

Twenty‐five MRI scans were performed on 14 patients with cadaveric pancreatic transplants to determine the role of this modality in the evaluation of transplant dysfunction. Our population included 12 normal transplants and 13 recipients with pancreatic graft dysfunction (either rejection or pancreatitis). Six of the latter patients had two or more scans permitting reassessment of the same transplant in various states of health. T1‐and T2‐weighted MR images were evaluated qualitatively and quantitatively to see if certain patterns were associated with clinical status. We found that although MRI was capable of producing excellent images of the in situ pancreatic transplant, this modality was unable to reliably distinguish the normal from the abnormal transplant. This conclusion differs from prior assessments; possible reasons for this are discussed. © 1991 Academic Press, Inc.
SLIP, a lipid suppression technique to improve image contrast in inflow angiography
Authors: Doyle Mark , Matsuda Tetsuya , Pohost Gerald M.
Published: March 2007

In rapidly acquired gradient echo images, lipid regions usually appear as areas of high signal intensity. In 2D inflow angiograms processed by the maximum intensity projection algorithm, this high lipid signal may prevent angiographic visualization of some blood vessels. We present a new approach to suppress the lipid signal, SLIP, spatially separated lipid presaturation. The SLIP technique suppresses lipid signal over a narrow region by exploiting the chemical‐shift effect. SLIP requires an arrangement of a thin slice and a wide presaturation slab already available in 2D inflow refreshment angiography. Thus SLIP was incorporated to an inflow angiography sequence without increasing the acquisition time. The use of SLIP resulted in considerable improvement in angiographic contrast and increased the number of vessels detected in projection angiograms. The SLIP technique does not require high homogeneity of the main magnet field. © 1991 Academic Press, Inc.
Analysis of phospholipids in human amniotic fluid by 31P NMR
Authors: Pearce J. M. , Shifman M. A. , Pappas A. A. , Komoroski R. A.
Published: March 2007

A recently described solvent‐reagent system for obtaining narrow linewidths in 31P NMR spectra of phospholipid extracts was applied to human amniotic fluid. Resolution of the major components was achieved by manipulating the solvent composition, and assignments were made by spiking samples with standard compounds. Spin‐lattice relaxation times were determined and used to optimize data acquisition. NMR estimates of the phosphatidylcholine to sphingomyelin ratio for 33 patients were compared to those obtained by TLC densitometry, a common clinical assay for fetal pulmonary maturity. Estimates of the levels of phosphatidylglycerol and phosphatidylinositol could also be obtained from 31P NMR. High‐resolution 31P NMR in this solvent‐reagent system provides a relatively straightforward and reliable alternative method for assessing fetal pulmonary status by phospholipid quantitation in human amniotic fluid. The 31P NMR method has the advantage that it is sensitive to total, and not just unsaturated, phosphatidylcholine. © 1991 Academic Press, Inc.
A means of microsphere reference sampling that is compatible with nuclear magnetic resonance instruments
Authors: Wendt Richard E. , Rokey Roxann , Marks Allison
Published: March 2007

A new device has been developed and tested that simplifies the collection of reference blood samples from an experimental animal located in the strong magnetic field of a nuclear magnetic resonance instrument during the injection of microspheres. © 1991 Academic Press, Inc.
Cardiac tagging in the rat using a DANTE sequence
Authors: de Crespigny Alexander J. S. , Carpenter T. Adrian , Hall Laurance D.
Published: March 2007

We demonstrate the application of a DANTE tagging sequence to in vivo imaging of the rat heart. This sequence generates narrow parallel tag lines in a short space of time and is combined with cardiac gating to image the heart wall at eight points throughout the cycle. © 1991 Academic Press, Inc.
CSF‐suppressed quantitative single‐shot diffusion imaging
Authors: Kwong K. K. , McKinstry R. C. , Chien D. , Crawley A. P. , Pearlman J. D. , Rosen B. R.
Published: March 2007

A CSF‐suppressed, inversion‐recovery (IR) single‐shot diffusion sequence was used to demonstrate that CSF makes a dominant contribution to the nonmonoexponential diffusion decay behavior observed in cortical gray matter brain tissue. © 1991 Academic Press, Inc.
Snapshot imaging using a FLARE sequence
Authors: Jones Richard A. , Rinck Peter A.
Published: March 2007

We have implemented a snapshot FLARE sequence using a scan time of 320 ms for a 64 × 128 image. As in the conventional FLARE sequence the T2 weighting of the image can be altered by manipulating the phase encoding scheme with the position of the zeroth phase encoding effectively determining the amount of T2 weighting. Reducing the flip angle of the refocusing pulse reduces both the RF power deposition and the blurring in images of short T2 samples, at the expense of reduced signal and contrast. © 1991 Academic Press, Inc.
Filtering noise from images with wavelet transforms
Authors: Weaver J. B. , Xu Yansun , Healy D. M. , Cromwell L. D.
Published: March 2007

A new method of filtering MR images is presented that uses wavelet transforms instead of Fourier transforms. The new filtering method does not reduce the sharpness of edges. However, the new method does eliminate any small structures that are similar in size to the noise eliminated. There are many possible extensions of the filter. © 1991 Academic Press, Inc.
Sodium‐23 imaging of supratentorial lesions at 4.0 T
Authors: Schuierer G. , Ladebeck R. , Barfuß H. , Hentschel D. , Huk W. J.
Published: March 2007

In 27 patients with low and high grade gliomas (n = 17), meningiomas (n = 4), and other supratentorial tumors and lesions (n = 6), the results of sodium‐23 MR imaging with high spatial resolution were compared to CT and proton MRI. The Na MR studies were performed with a 4.0‐T whole‐body MR system and an isotropic 3D‐Flash sequence (TR 70 ms, TE 11 ms), which depicts the long T2 component of sodium. All patients tolerated the sodium study at 4.0 T well. The sodium images revealed almost all lesions, but the resolution was inferior to that of the reference methods. Two small meningiomas did not show up at all in the sodium study. Furthermore in one case small hemorrhages and calcifications within one of the tumors could not be found. Sodium imaging of the long T2 component did not provide any additional information regarding the histology, grading, size, and differentiation of the tumor from the surrounding edema which had not already been provided by CT or H MRI. © 1991 Academic Press, Inc.
Sensitivity enhancement in whole‐body natural abundance 13C spectroscopy using 13C/1H double‐resonance techniques at 4 tesla
Authors: Bomsdorf H. , Röschmann P. , Wieland J.
Published: March 2007

In vivo 13C spectroscopy experiments were performed using a whole‐body MR system at a static field of 4 T. The main goal of the investigations was to evaluate the sensitivity increase achievable by means of 13C/1H double‐resonance techniques at 4 T. Spectra from subcutaneous fat as well as muscle glycogen from the lower leg were acquired using frequency selective proton decoupling and the polarization transfer method SINEPT. With respect to measurements on subcutaneous fat, polarization transfer turned out to be more efficient than selective decoupling. About a fourfold enhancement in spectral peak intensity for the CC line doublet of the unsaturated fatty acid chain was obtained. Combining polarization transfer with decoupling yielded a factor of 6 in signal amplitude. In contrast to that, the signal enhancement observed in measurements on the glycogen C‐1 resonance was only around twofold. The lower efficiency is explained by fast T2 relaxation of the proton transition. A T2 value of about 3 ms was derived from the experimental data. Acquisition times as low as 3 min were realized for normal level glycogen in human calf muscle, enabling a time resolution adequate for dynamic studies on muscle glycogen depletion. Aspects of RF power absorption in tissue and the generally higher efficiency make polarization transfer methods preferable to selective decoupling in whole‐body 13C spectroscopy at 4 T. © 1991 Academic Press, Inc.
NMR studies of intracellular water at 300 MHz: T2‐specific relaxation mechanisms in synchronized or EGF‐stimulated cells
Authors: Callahan D. E. , Deamond S. F. , Creasey D. C. , Trapane T. L. , Bruce S. A. , Ts'O P. O. P. , Kan L.‐S.
Published: March 2007

Responses specific to the spin‐spin relaxation time (T2) have been observed in two time‐dependent studies of the intracellular water in normal and transformed Syrian hamster fetal fibroblasts. At 300‐MHz (7.0 T), the spin‐lattice relaxation time (T1) was insensitive to several aspects of cellular physiology that produced changes in the T2 and the apparent self‐diffusion coefficient (Dapp) of intracellular water. In normal cells stimulated with epidermal growth factor (EGF), T1 was insensitive to time‐dependent changes detected by T2 and Dapp. In synchronized tumor cells, T1 was insensitive to cell‐cycle‐dependent changes detected by T2. The strongly coupled behavior of T2 and Dapp that was observed as a function of time in EGF‐stimulated cells indicates that the diffusion of intracellular water through inhomogeneous local magnetic field gradients produced effects observable in T2. Conformational changes in large intracellular macromolecular assemblies such as chromatin or the cytoskeleton may alter the magnitude and inhomogeneity of local field gradients, producing responses in T2 and Dapp only. © 1991 Academic Press, Inc.
An evaluation of the integrity of the blood‐testis barrier by magnetic resonance imaging
Authors: Farghali Hassan , Williams Donald S. , Simplaceanu Elena , Ho Chien , Van Thiel David H.
Published: March 2007

This present investigation was initiated to noninvasively evaluate the usefulness of intravenous gadopentetate dimeglumine (Gd‐PTDM) ‐enhanced magnetic resonance imaging (MRI) in assessing the integrity of the blood‐testis barrier (BTB). The intensity of different image slices was measured in pre‐and post‐Gd‐PTDM images in rats receiving cytochalasin D or alcohol treatment. It was found that MRI can be used to assess the integrity of the BTB and may be a useful tool in the evaluation of potentially toxic agents that affect the testis, particularly those that affect the BTB. © 1991 Academic Press, Inc.
On the relative importance of paramagnetic relaxation and diffusion‐mediated susceptibility losses in tissues
Authors: Kennan R. P. , Zhong J. , Gore J. C.
Published: March 2007

Susceptibility agents such as dysprosium may reduce the apparent T2 of a tissue by inducing magnetic field gradients so that diffusion of water molecules causes dephasing of the transverse magnetization. Gadolinium has a susceptibility that is about 30% lower than dysprosium, so that diffusion losses are expected to be only half as big, but it also may produce paramagnetic relaxation by dipolar interactions. The relative importance of these two processes is dependent on several parameters, including the metal concentration, pulse sequence timing, field strength, and the permeability of tissue interfaces to water exchange. The conditions under which exchange‐mediated dipolar interactions are less important than diffusion losses have been derived for capillary borne contrast agents in realistic situations. © 1991 Academic Press, Inc.
Functional MR of the kidney
Authors: Frank Joseph A. , Choyke Peter L. , Austin Howard A. , Girton Mary E.
Published: March 2007

A bolus injection of Gadopentetate Dimeglumine with dynamic gradient echo MR imaging has allowed for the visualization of normal and abnormal renal function. Following an injection of gadopentetate dimeglumine, NMR T1 relaxation times obtained on serial collections of serum and urine at timed intervals were used to derive the glomerular filtration rate. The merger of dynamic contrast‐enhanced MRI with an in vitro NMR‐derived GFR provides for assessment of renal function without the use of radioactive agents. © 1991 Academic Press, Inc.
Contrast enhancement for the myocardium
Authors: Higgins Charles B. , Saeed Maythem , Wendland Michael
Published: March 2007

The potential of MR imaging and spectroscopy in ischemic heart disease is substantial. MR contrast media have the potential to improve the differential tissue characterization among normal, ischemic, and infarcted myocardium. Several reports in animals and patients have revealed that MR contrast media can improve the delineation of acute myocardial infarctions (1–7). Studies from several centers in Europe and Asia have demonstrated that the contrast between the normal and acutely infarcted myocardium substantially increased with the use of gadolinium‐DTPA administered intravenously (1, 2, 4, 5). In these studies, the acutely infarcted myocardium on delayed MR scans demonstrated greater enhancement with the paramagnetic contrast media than normal myocardium, producing a greater percentage contrast between the two regions. These studies are consistent with previous reports using gadolinium‐DTPA contrast media to enhance the differential in signal intensity between the normal and infarcted myocardium in animal models (3, 6, 7).

The expanded use of MR in ischemic heart disease will likely depend upon employing contrast media to enhance regional myocardial signal in proportion to regional blood flow. Such contrast media are needed for using MRI to demonstrate regions of myocardial ischemia and to depict reperfusion of a myocardial region after an ischemic event. © 1991 Academic Press, Inc.
Blood Clearance of Dextran Magnetite Particles Determined by a noninvasive in vivo ESR method
Authors: Iannone A. , Magin R. L. , Walczak T. , Federico M. , Swartz H. M. , Tomasi A. , Vannini V.
Published: March 2007

Dextran magnetite (DM) is a potential MR contrast agent with superparmagnetic properties. Its fast clearance from the blood and selective uptake by tissue macrophages provide advantages for imaging tumors in the liver and spleen. DM consists of a suspension of solid particles with a wide distribution of sizes, In this study we have used ESR spectroscopy to determine the blood clearance of DM injected iv mice. The spectra are obtained on living animals by inserting the tail of a mice into the waveguide cavity of the ESR spectrometer and recording the ESR spectrum continously. This procedure allows the direct measurement of the plasma clearance of DM from individual animals, without blood sampling. We applied this method to study the clearance of suspensions of DM particles with different averge sizes. © 1991 Academic Press, Inc.
Determination of cytosolic ADP and AMP concentrations and the free energy of ATP hydrolysis in human muscle and brain tissues with 31P NMR spectroscopy
Authors: Roth K. , Weiner M. W.
Published: March 2007

Based on experimentally determined concentrations of PCr, Pi, ATP, and H+, the ADP and AMP concentrations and the free energy for the ATP hydrolysis in normal human brain and muscle were calculated assuming that the creatine kinase‐ and the myokinase‐catalyzed reactions were in equilibrium, accounting for changes in pH and free Mg2+ ion concentration. © 1991 Academic Press, Inc.
In vivo1H and 31P NMR spectroscopy of the developing rat brain
Authors: Hida Kazutoshi , Kwee Ingrid L. , Nakada Tsutomu
Published: March 2007

The biochemical changes associated with brain maturation during the first 28 days postnatal were investigated utilizing proton and phosphorus‐31 nuclear magnetic resonance spectroscopy in rat pups in vivo. Phosphocreatine was found to increase linearly during this period of development. Phosphomonoester was high at birth, peaked around the 10th day postnatal, and declined thereafter. N‐Acetyl‐aspartate was low at birth, increased in an approximately linear fashion, and reached adult levels by about Day 28 postnatal. Choline was high at birth and declined thereafter. Taurine, a sulfur amino acid abundant in fetal brain, was also present in high levels on the first day postnatal. © 1992 Academic Press, Inc.
NMR relaxation times in acute myocardial infarction: Relative influence of changes in tissue water and fat content
Authors: Scholz Thomas D. , Martins James B. , Skorton David J.
Published: March 2007

Tissue changes known to occur with acute myocardial infarction include increases in tissue water and lipid content. We sought to evaluate the relative contribution of alterations in tissue water and fat content to the changes of Tl and T2 relaxation times with infarction. Nine mongrel dogs underwent coronary artery occlusion for 6–12 h. T1 and T2 at 20 MHz and tissue water and fat content of normal and infarcted tissue were measured. Tissue water content, T1, and T2 were significantly greater in infarcted myocardium compared to normal (P < 0.05). Tissue fat content, while not significantly different, increased linearly in infarcted samples as a function of duration of ischemia (r = 0.77). Despite this increase in fat content, only tissue water content was significantly linearly related to T1 (r = 0.97) and T2 (r = 0.91). Increases in T1 and T2 of infarcted tissue appeared to be most significantly influenced by changes in tissue water content. While total tissue fat content increased with duration of ischemia, it did not appear to significantly alter T1 or T2. © 1992 Academic Press, Inc.
Fast angiography using selective inversion recovery
Authors: Wang Samuel J. , Nishimura Dwight G. , Macovski Albert
Published: March 2007

We have developed an enhancement of selective inversion recovery that allows us to obtain high‐resolution angiograms in reduced Scan time. By applying several read pulses following each tagging inversion pulse, we can obtain several phase encodes in each cardiac cycle, thereby reducing the total scan time required for a complete image. Using this technique, high‐resolution angiograms can be obtained in as little as 15 s. Because the phase encodes are collected in short bursts separated by long pauses, care must be taken to maintain uniform signal weighting across phase‐encoding views and avoid ghosting. We use an increasing flip‐angle sequence to equalize signal level weighting across the readouts. The phase encodes are collected in a special order to minimize ghosting. A postprocessing technique is used to further reduce signal nonuniformity between phase encodes. This fast angiography technique can significantly reduce artifacts due to patient motion during scanning and is especially useful for imaging vasculature in regions of the body where respiratory motion is a problem. © 1992 Academic Press, Inc.
1H NMR study of cortex neurons and cerebellar granule cells on microcarriers and their PCA extracts: Lactate production under hypoxia
Authors: Sonnewald U. , Petersen S. B. , Krane J. , Westergaard N. , Schousboe A.
Published: March 2007

Lactate production of 6‐day‐old cerebral cortex neurons and 7‐day‐old cerebellar granule cells from mouse brain attached to cytodex 3 microcarriers was studied as a function of time, under hypoxic conditions using 1H NMR. Perchloric acid extracts of both cell types were prepared and 1H NMR spectra showed compounds characteristic for these neurons. In particular the granule cell extracts showed a large amount of glutamate as expected from biochemical experiments, whereas the cortex neurons showed a large amount of 4‐ aminobutyric acid. © 1992 Academic Press, Inc.
Respiratory kinematics of the upper abdominal organs: A quantitative study
Authors: Korin Hope W. , Ehman Richard L. , Riederer Stephen J. , Felmlee Joel P. , Grimm Roger C.
Published: March 2007

Despite the fact that respiratory motion is a major factor limiting the image quality of MR examinations in the upper abdomen, little quantitative information is available about the kinematics of visceral motion during respiration. The objective of this study was to obtain a measure of the relative longitudinal and transverse displacements of the upper abdominal organs during breathing using an MR line scan technique. © 1992 Academic Press, Inc.
Permeability of liposomal membranes to water: Results from the magnetic field dependence of T1 of solvent protons in suspensions of vesicles with entrapped paramagnetic ions
Authors: Koenig Seymour H. , Ahkong Quet F. , Brown Rodney D. , Lafleur Michael , Spiller Marga , Unger Evan , Tilcock Colin
Published: March 2007

The diffusive permeability to water molecules, Pd, of lipid vesicles with entrapped paramagnetic solute ions can be determined rapidly from analysis of the magnetic field dependence (nuclear magnetic relaxation dispersion, or NMRD profile) of T1 of exterior solvent water protons. Such data yield τ the mean lifetime of solvent molecules inside the vesicles, from τ = (fTlpara) – T1ves, where f is the volume fraction of entrapped water, T1Para is the observed T1 corrected for buffer background, and T1Ves is the relaxation time of water protons in the entrapped solution. For small spherical unilamellar vesicles of inner radius R, Pd = R/3τ. f can be obtained accurately from knowledge of both the concentration of Gd(DTPA)2− in the solution in which the vesicles were formed and the average concentration of ions in the final sample. At low temperatures, in the limit of slow exchange, T1Para becomes independent of field and τ = f T1Para; the observation of a field independent profile is a control that confirms that no paramagnetic material is external to the vesicles. We have measured T1Para, using a field‐cycling relaxometer, for suspensions of POPC (1‐palmitoyl‐2‐oleoyl‐lecithin) vesicles with 100–500 mM entrapped Gd(DTPA)2− and membrane concentrations of cholesterol ranging from 0 to 40 mol %. These profiles, which span the field range 0.01–50 MHz proton Larmor frequency, were taken at 5, 15, 25, and 35°C. Concentrations of Gd(DTPA)2− were determined independently by both ICP analyses and NMRD methods. Values for Pd for vesicles with 100 mM Gd(DTPA)2− and outer diameters 100 nm ± 20%, as determined by quasielastic light scattering, are 63, 47, 24, 16, and 8.7 × 10−4cm s−1, at 25°C, for cholesterol concentrations of 0, 10, 20, 30, and 40%, respectively. The corresponding activation enthalpies are 14, 14, 14, 17, and 17 kcal/M. Comparison with 2H NMR studies of deuterated POPC vesicles with no cholesterol at 20°C, and with 10% at 40°C, which yielded the same order parameter for the palmitoyl acyl chains, gives no indication of a correlation between order parameter and permeability.
A double‐tuned probe for metabolic NMR studies
Authors: Najim Elhadi , Grivet Jean‐Philippe
Published: March 2007

A double‐tuned single coil probe for high field metabolic NMR studies has been designed and tested. The resonant coil is a single‐turn of copper foil wound on a quartz cylinder. It is fed by a short length of parallel strip line made of the same material; the feeder is also used as a tuning capacitance. Electrical parameters (quality factors, efficiencies at proton and carbon frequencies) and magnetic resonance data (90° pulse lengths, minimum decoupler power) for lossy samples have been measured. The probe allows for the optimal use of the limited high homogeneity region of a vertical magnet. It shows good sensitivity and efficient decoupling. © 1992 Academic Press, Inc.
High‐Resolution 1H NMR spectroscopy studies of extracts of human cerebral neoplasms
Authors: Peeling James , Sutherland Garnette
Published: March 2007

High‐resolution 1H NMR spectroscopy has been used to measure the concentrations of metabolites (alanine, N‐acetylaspartate, γ‐aminobutyric acid, glutamate, glutamine, aspartate, taurine, glycine, succinate, creatine, cholines, inositol, and glucose) in perchloric acid extracts of human epileptic cortex and brain tumors. All tissue was obtained by surgical biopsy, excised before thermal coagulation, and immediately frozen in liquid nitrogen. Lower levels of N‐acetylaspartate and γ‐aminobutyric acid and a shift in the glutamate/glutamine ratio toward glutamine in the tumors reflect neuronal loss. Abnormal glucose metabolism (aerobic glycolysis) in the tumors gives decreased levels of succinate, glutamate, aspartate, glutamine, and creatine and generally increased concentrations of glycine and alanine. Differences in metabolite concentrations that may be of use in differential tumor diagnosis include lower creatine and inositol in meningiomas than in astrocytomas. Lower taurine differentiates benign from malignant astrocytomas. Malignant astrocytomas and metastatic tumors are more regionally heterogeneous than meningiomas or benign astrocytomas. Mannitol, administered perioperatively to all patients from whom tissue was obtained, was observed only in the spectra of extracts of tissue from tumors which enhanced on computerized tomographic imaging. © 1992 Academic Press, Inc.