bluuebunny/crossref_metadata_2025_split huggingface dataset:
Echo‐planar imaging of diffusion and perfusion
Authors: Turner Robert , Le Bihan Denis , Scott Chesnicks A. 
Published: March 2007

AbstractUse 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

AbstractThe 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

AbstractTwo 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

AbstractThe 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

AbstractMost 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

AbstractIntracellular 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

AbstractThe 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

AbstractLiposomes 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

AbstractWe 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

AbstractThe 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

AbstractA 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

AbstractTwenty‐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

AbstractIn 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

AbstractA 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.
Cardiac tagging in the rat using a DANTE sequence
Authors: de Crespigny Alexander J. S. , Carpenter T. Adrian , Hall Laurance D. 
Published: March 2007

AbstractWe 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

AbstractA 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

AbstractWe 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

AbstractA 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

AbstractIn 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

AbstractIn 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

AbstractResponses 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

AbstractThis 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

AbstractSusceptibility 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

AbstractA 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

AbstractThe 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.