bluuebunny/crossref_metadata_2025_split huggingface dataset:
Factors influencing the accuracy and precision of velocity‐encoded phase imaging
Authors: Buonocore Michael H. , Bogren Hugo 
Published: March 2007

AbstractVelocity‐encoded phase contrast imaging is being used increasingly in clinical imaging for quantization of blood flow. In this study, the accuracy and precision of ascending aorta flow measurements were found to depend on several subtle aspects of the scan prescription and image analysis. While the usual scan parameters such as TR, TE, and flip angle gave incremental changes in the flow measurements, four additional factors that had a much greater effect on the measurements were identified. These factors were (1) the zero velocity (background) pixel value, (2) the size and shape of the vessel region of interest, (3) the maximum velocity encoded in diastole, and (4) the temporal resolution. Statistical analysis was done on a total of 48 scans on nine normal subjects to confirm the significance of the measured differences using the various choices for each of these factors. These factors must be considered if accurate and precise measurements of blood flow are desired. Estimates of accuracy and precision suggest that quantitative flow measurements from velocity‐encoded MR imaging can be clinically useful.
Measurement of blood‐brain barrier permeability in a tumor model using magnetic resonance imaging with gadolinium‐dtpa
Authors: Kenney James , Schmiedl Udo , Maravilla Kenneth , Starr Frank , Graham Michael , Spence Alexander , Nelson James 
Published: March 2007

AbstractSequential MR imaging with gadolinium‐diethylenetriaminepentaacetic acid (Gd‐DTPA) and sequential measurements of plasma Gd‐DTPA concentration by inductively coupled plasma atomic emission spectroscopy (ICP‐AES) were used to estimate the blood‐to‐tissue transport coefficient (Ki) in the 36B‐10 rat glioma model. For these measurements, tissue Gd‐DTPA concentration was estimated from tumor enhancement by correlation with calibration measurements obtained by ICP‐AES analysis of tumor tissue. The 14 animals for which Ki, was calculated can be grouped into those imaged at 11 days following tumor implantation, at 13‐18 days, and at 20 days. The mean (+SEM) Ki values for these groups were 1.1 + 0.24, 9.2 + 0.8, and 13.4 + 1.7 ml/kg‐min, respectively. These results correspond well with published data obtained by quantitative autoradiography. It is concluded that frequent sequential imaging and a graphical approach to Ki, calculation are promising methods for determining the blood‐to‐tissue transport coefficient noninvasively by contrastenhanced MRI.
Charge dependence of the distribution of contrast agents in rat cerebral ventricles
Authors: Wan Xiaoming , Fu Tsu‐Ching , London Robert E. 
Published: March 2007

AbstractPrevious studies of MRI contrast resulting from the intracerebral administration of several contrast agents have suggested that the distribution of these agents may be dependent on the net charge. In order to further evaluate the significance of this parameter, the distribution of both aquo and CDTA‐chelated lanthanide and transition metal ions in the cerebral ventricles of rats has been evaluated based on their enhancement of MRI contrast. The agents were injected directly into the lateral ventricles of Sprague‐Dawley rats. Each of five different positively charged paramagnetic metal ions tested selectively enhanced the inner cellular layers of ventricular luminal wall of the rat brain, while such enhancement was absent using the corresponding negatively charged metal‐CDTA complexes. The abundance of negatively charged residues on the cell surface of the inner luminal layers is suggested to be the source of the observed charge affinity. Differences in the distribution of Mn2+ ions administered intracerebrally compared with intraperitoneal (ip) injection suggest that while the first treatment may result primarily in uncomplexed aquo ions which then interact with the luminal surface, manganese ions administered ip behave more like chelated ions and are most probably complexed to transferrin.
On the application of ultra‐fast rare experiments
Authors: Norris David G. , Börnert Peter , Reese Torsten , Leibfritz Dieter 
Published: March 2007

AbstractThe ultra‐fast application of the RARE experiment is described in detail, with special emphasis on its multifarious applications with preparation experiments that produce transverse magnetization. The factors affecting the temporal evolution of the magnetization during the experiment are described, and the implications for the slice profile when using a Gaussian refocusing pulse are experimentally examined. The choice of phase‐encoding scheme for use with preparation experiments is discussed, as is the use of various phase‐encoding schemes to reduce line broadening in the phase‐encoding direction if a number of averages are acquired. An explanation for the decomposition of the echo are into two components if the read gradient is imbalanced is given, and the experimental conditions necessary for the coherent addition of these two echo groups are described. An alternative sequence that removes one of these groups from the acquisition window is proposed. The sensitivity of the sequence to flow and motion is investigated, and the drastic loss of signal in this situation explained. The in vivo and in vitro application of preparation experiments leading to the accurate measurement of T1, T2, diffusion constant, and magnetization transfer characteristics is presented. The implementation of zoom‐imaging using spin‐ and stimulated‐echo preparation is described, and 3D in vivo spin‐echo zoom images are presented. Simple phantom experiments demonstrating the feasibility of chemical‐shift selective and spectroscopic imaging are also given.
Evaluation of experimental early acute cerebral ischemia before the development of edema: use of dynamic, contrast‐enhanced and diffusion‐weighted mr scanning
Authors: Finelli D. A. , Hopkins A. L. , Selman W. R. , Crumrine R. C. , Bhatti S. U. , Lust W. D. 
Published: March 2007

AbstractThe ability of dynamic, contrast‐enhanced, magnetic susceptibility‐weighted scanning to delineate early experimental acute cerebral infarction was compared with that of heavily T2‐weighted and diffusion‐weighted spin echo scanning. Spontaneously hypertensive rats, which had undergone right middle cerebral artery occlusion, were studied from 15 min to 3 h post ligation on a 1.5‐T clinical whole‐body imager. In contrast to the diffusion‐ and T2‐weighted spin echo scans, the dynamic, contrast‐enhanced technique clearly and consistently delineated the nonperfused regions as early as I5 min post ligation.
Glycogen Detection by in Vivo 13C NMR: A Comparison of Proton Decoupling and Polarization Transfer
Authors: Saner M. , Mckinnon G. , Boesiger P. 
Published: March 2007

AbstractThe performance of gated proton decoupling and polarization transfer with respect to glycogen detection by 13C NMR was investigated. Experiments were performed on a 1.5 T whole‐body scanner using a 13C surface coil in combination with a proton head coil. Spectra were acquired from a glycogen phantom and from the lower leg of a healthy volunteer using proton decoupling and the polarization transfer method SINEPT. The signal strength of the C1 resonance of glycogen was determined and compared to a reference spectrum acquired without any form of sensitivity enhancement. In the phantom experiment both decoupling and SINEPT produced a signal gain of 3.5. Under in vivo conditions, the signal gain was approximately 2.5 for both techniques. We conclude that decoupling and polarization transfer are equivalently useful techniques for glycogen detection.© 1992 Academic Press,Inc.
Shaping the Signal Response during the Approach to Steady State in Three‐Dimensional Magnetization‐Prepared Rapid Gradient‐Echo Imaging Using Variable Flip Angles
Authors: Mugler John P. , Epstein Frederick H. , Brookeman James R. 
Published: March 2007

AbstractA theoretical algorithm for shaping the signal response during the approach to steady state in three‐dimensional magnetization‐prepared rapid gradient‐echo (3D MP‐RAGE) pulse sequences has been developed and implemented. This algorithm derives the flip angle series required to produce specifically chosen time evolutions of the signal intensities during the data acquisition segment of 3D MP‐RAGE sequences. Theoretical predictions for the cases of unshaped, uniform, and mono‐exponential decay signal responses were quantitatively validated with a doped‐water phantom on a 1.5‐T whole‐body imager and in all cases there was excellent agreement between the theoretical and experimental values. The effects of RF inhomogeneities and eddy currents on the signal response shaping were also investigated. To demonstrate the potential utility of the technique, the signal response shaping algorithm was applied to a Tl‐weighted 3D MP‐RAGE sequence to derive the acquisition flip angle series which theoretically yields the maximum white matter/gray matter signal difference (WGSD) consistent with the chosen response shape. Images obtained from a healthy volunteer using this variable flip angle sequence were compared with 3D RF‐spoiled steady‐state gradient‐echo images obtained in the same total imaging time. The 3D MP‐RAGE images demonstrated a 41% increase in the WGSD‐to‐noise ratio. These initial very promising results indicate that with further refinement to eliminate some intensity artifacts, the variable flip angle 3D MP‐RAGE technique may, with respect to certain image properties, provide considerable improvements over currently available 3D gradient‐echo imaging techniques.© 1992 Academic Press,Inc.
RF Current Density Imaging in Homogeneous Media
Authors: Scott G. C. , Joy M. L. G. , Armstrong R. L. , Henkelman R. M. 
Published: March 2007

AbstractMRI has proven capable of imaging quasistatic volume current densities in electrolytic and biological media. In this paper, the feasibility of extending the method to image RF current density at the Larmor frequency is studied. RF current imaging could be relevant to MR power absorption and safety and to hyperthermia analysis, as well as creating dielectric and conductivity‐dependent tissue contrast. The approach is to deliberately induce or inject RF currents in a sample synchronous with an MR pulse sequence and measure the resulting transverse RF magnetic field components. Current density is extracted by computing the curl of the magnetic fields. The preliminary theory has been developed for uniform media where both displacement and conduction currents exist while skin effects or eddy currents are absent. If the derivative in the BO direction of the RF magnetic field component parallel to BO is negligible, then sufficient information exists to reconstruct the RF current density component that is parallel to BO without rotating the sample. The relative phase of the current can also be estimated. The method has been proven feasible by successfully imaging a uniform 85.6‐MHz current density in a salt water phantom. The experiment conforms closely to capacitively coupled hyperthermia heating.© 1992 Academic Press,Inc.
Localized proton MR spectroscopy of citrate in vitro and of the human prostate in vivo at 1.5 T
Authors: Schick Fritz , Bogers Hilmar , Kurz Siegfried , Jung Wulf‐Ingo , Pfeffer Markus , Lutz Otto 
Published: March 2007

AbstractCitrate is a secretory product of the normal prostate, a lack of citrate in prostate tissue is expected to be pathognomonic for adenocarcinoma. In the present study proton AB‐signal characteristics of citrate at low field strength of 1.5 T were investigated by volume selective spectroscopic and theoretical methods. The nonappearance of fast phase modulation of the J‐coupled system at low field strength in vivo is verified by measurements of sodium citrate solution. In vivo localized spectroscopy of small volume elements of (2 cm)3 with the double spin‐echo method within the prostatic gland provides citrate signal reception even using a Helmholtz coil with 170‐mm diameter. Volume selective proton spectra with different echo times are presented which are comparable to spectra acquired by former authors with endorectal coils.
Hypoxia and metabolic acidosis in the isolated heart: Evidence for synergistic injury
Authors: Zhou H. Z. , Malhotra D. , Doers J. , Shapiro J. I. 
Published: March 2007

AbstractAlthough hypoxia and metabolic acidosis have both been shown to impair cardic function, some workers have suggested that acidosis during a period of hypoxia will actually accelerate physiologic recovery from this insult. To address the interactions of metabolic acidosis and hypoxia further, isolated isovolumic rat hearts were exposed to normal perfusion conditions for 30 min to establish baseline conditions, then either continued normal conditions, metabolic acidosis, hypoxia, or combined acidosis and hypoxia for 30 min and subsequently reperfused under normal perfusion conditions for an additional 30 min. We observed that acidosis + hypoxia impaired recovery of cardic contraction more than acidosis or hypoxia alone following experimental perfusion. The combination of acidosis and and hypoxia also impaired cardiac energy metabolism more than acidosis or hypoxia alone as assessed by increases in tissue inorganic phosphate during experimental perfusion as well as during reperfusion. These data suggest that during hypoxia, acidosis appears to primarily impair cardic energy production as we have previously observed in the normoxic isolated rat heart. Therefore, in the intact beating heart, acidosis may not protect from hypoxic injury as has been suggested in simpler systems but may not protect from hypoxic injury as has been suggested in simpler systems but rather may exacerbate at.
MR microscopy of the rat lung using projection reconstruction
Authors: Gewalt S. L. , Glover G. H. , Hedlund L. W. , Cofer G. P. , Macfall J. R. , Johnson G. A. 
Published: March 2007

AbstractProjection reconstruction has been implemented with self‐refocused selection pulses on a small bore, 2.0 T MR microscope, to allow imaging of lung parenchyma. Scan synchronous ventilation and cardiac gating have been integrated with the sequence to minimize motion artifacts. A systematic survey of the pulse sequence parameters has been undertaken in conjunction with the biological gating parameters to optimize resolution and signal‐to‐noise (SNR). The resulting projection images with effective echo time of <300 usec allow definition of lung parenchyma with an SNR improvement of ∼15 x over a more conventional 2DFT short echo gradient sequence.
Comparison of pig cornea preservation solutions using quantitative 31P NMR spectroscopy
Authors: Igarashi Hiromasa , Yoshida Akitoshi , Tanaka Kunio 
Published: March 2007

AbstractWe compared the abilities of three solutions (bicarbonate‐free glucose‐phosphate Ringer's solution (EP II), lactated Ringer's solution, and physiologic saline solution) to preserve pig cornea by measuring phosphate metabolites with 31P NMR spectroscopy. EP II preserves corneal viability better than others, and preserving extracted cornea also is better than preserving the whole eye.
A simple method of measuring gradient induced eddy currents to set compensation networks
Authors: Wysong R. E. , Lowe I. J. 
Published: March 2007

AbstractWe describe a technique for measuring the time dependence and field distortions of magnetic fields due to eddy currents (EC) produced by time‐dependent magnetic field gradients. The EC measuring technique uses a sample with short T1,T2 and many rf excitation pulses and free induction decays (FIDs) to measure the out‐of‐phase component of the FIDs, which are proportional to γΔB, the amount by which the signal is off resonance. The measuring technique is sensitive, easy to implement and interpret, and useful for setting preemphasis compensation networks.
31P localized spectroscopy of fetal brain in utero
Authors: Nakada Tsutomu , Kwee Ingrid L. 
Published: March 2007

Abstract31‐Phosphorus (31P) nuclear magnetic resonance (NMR) spectroscopy of fetal brain in utero was obtained entirely noninvasively in rat utilizing image selected in vivo spectroscopy (ISIS). The results were in excellent agreement with the data obtained using the surface coil method in the late stage fetus, namely, high phosphomonoester (PME), low phosphocreatine (PCr), and high intracellular pH. Localized spectroscopy provides unprecedented opportunities for the investigation of fetal brain metabolism in utero.
Citrate alterations in primary and metastatic human prostatic adenocarcinomas: 1H magnetic resonance spectroscopy and biochemical study
Authors: Kurhanewicz John , Dahiya Rajvir , Macdonald Jeffrey M. , Chang Lee‐Hong , James Thomas L. , Narayan Perinchery 
Published: March 2007

AbstractThe objectives of this study were to quantitatively verify the low levels of citrate previously observed in primary human prostatic adenocarcinomas and to determine whether citrate was further reduced in metastatic prostatic cancer. This was accomplished by comparison of citrate concentrations of DU 145 xenografts (a poorly differentiated human prostatic adenocarcinoma cell line grown in nude mice) with concentrations in primary human adenocarcinomas. Following in vivo 1H NMR studies of DU 145 xenografts, citrate concentrations of DU 145 xenografts and surgically removed primary prostatic adenocarcinoma tissue were determined by quantitative high resolution 1H NMR and enzymatic assay. The most significant findings of this study were that citrate concentrations in primary human adenocarcinomas (3.74 ± 0.19 μmolJg wet weight) were significantly lower than those observed for normal and benign hyperplastic (BPH) prostatic tissues. Furthermore there was a further ten‐fold reduction of citrate associated with DU 145 xenografts (0.31 ± 0.028 μmoleJg wet weight) compared with primary prostatic cancer. DU 145 xenografts also exhibited higher levels of uridine diphosphosugars and choline containing metabolites relative to primary prostatic adenocarcinomas. These findings support the hypothesis that citrate is low in primary prostatic cancer and further reduced in metastatic disease.
The sensitivity of magnetic resonance image signals of a rat brain to changes in the cerebral venous blood oxygenation
Authors: Ogawa Seiji , Lee T. M. , Barrere Bertrand 
Published: March 2007

AbstractThe sensitivity of magnetic resonance image signals of the brain to the change in the cerebral blood oxygenation was measured in gradient echo images of rat brains at a field strength of 7 T. The sensitivity depended on the blood vessel volume relative to the tissue volume within the image voxel, and signal intensities in the cortical area were well correlated with the change in the venous blood de‐oxygenation level at the sagittal sinus. Tissue signals in the image (15 ms echo time) showed a sensitivity of 10‐20% change for the full range of deoxygenation level from 0‐100%. From these observations and image simulations, the extent of the signal response to some neuro‐stimulation which induces an increase in regional cerebral blood flow has been estimated for 4 T field strength.
Fast perfluorocarbon imaging using 19F U‐FLARE
Authors: Börnert P. , Norris D. G. , Koch H. , Dreher W. , Reichelt H. , Leibfritz D. 
Published: March 2007

AbstractThe application of an ultra‐fast low angle RARE technique for the 19F imaging of perfluorocarbons (PFCs) used as temporary blood substitutes is described. This sequence is attractive for fast 19F imaging studies that measure the biodistribution of PFCs in vivo, due to its high signal‐to‐noise ratio. Extensions of this technique for the chemical shift selective measurement of fluorine T1 values are presented. Using the linear dependence between the oxygen partial pressure (pO2) and the T1 relaxation rate of PFC resonances this technique makes possible the fast in vivo measurement of oxygen tension. Using the sequence in a diffusion sensitized form 19F measurements of the diffusion constants of PFCs are also presented. Phantom experiments to test the methods, and in vivo images obtained in rat studies are given and discussed.
The diffusion sensitivity of fast steady‐state free precession imaging
Authors: Buxton Richard B. 
Published: March 2007

AbstractSteady‐state free precession (SSFP) imaging with an added field gradient pulse is strongly sensitive to self‐diffusion and other motions of water. In an earlier theoretical analysis of diffusion attenuation due to a single gradient pulse Wu and Buxton (J. Magn. Reson. 90, 243, 1990) concluded that the diffusion sensitivity would be increased with smaller flip angles. In this paper a partial partition analysis of the different echo pathways contributing to the signal is used to illustrate the contribution of stimulated echo pathways with long diffusion times as the source of the enhanced diffusion sensitivity with low flip angles. Experimental imaging studies in phantoms and the brain of a human subject demonstrate substantially greater signal attenuation with small flip angles (<30°). The theoretical equation of Wu and Buxton provides a reasonable fit to the experimental data, accounting for the flip angle and TR dependence, but the estimated diffusion coefficients are larger than expected from previous studies. The large attenuation observed in the human studies, particularly in cerebrospinal fluid, is most likely due to other tissue motions. Both the theoretical calculations and the experimental data show that for the same gradient strength the diffusion sensitivity of SSFP is much greater than the diffusion sensitivity of conventional spin‐echo methods.
Reinvestigation of the transmembrane difference in 7Li NMR T1 values in Li+‐loaded human erythrocyte suspensions
Authors: De Freitas Duarte Mota , Rong Qinfen , Mo Suilan 
Published: March 2007

AbstractIn contrast to the findings in a recent study (R. P. Gullapalli, R. M. Hawk, R. A. Komoroski, Magn. Reson. Med. 20, 240 (1991), we found that, even at high hematocrits, the T1 values for extracellular 7Li were at least three times longer than those for intracellular Li+. We conclude that a transmembrane difference in T1 values can be used for separate observation of intracellular and extracellular Li+ in human red blood cell suspensions.
Equivalent circuit for birdcage resonators
Authors: Harpen Michael D. 
Published: March 2007

AbstractWe present an equivalent circuit analysis for both low pass and high pass birdcage resonators loaded with lossy samples. In a generalization of the method of Hoult and Lauterbur (J. Magn. Reson. 34, 425 (1979)), we also derive circuit component values by application of the laws of electrodynamics. Measured resonance spectra, quality factors, and feed point impedances in a test resonator are shown to be in agreement with those predicted by the proposed model.
Endogenous susceptibility contrast in myocardium during apnea measured using gradient recalled echo planar imaging
Authors: Wendland Michael F. , Saeed Maythem , Lauerma Kirsi , De Crespigny Alexander , Moseley Michael E. , Higgins Charles B. 
Published: March 2007

AbstractGradient recalled echo planar imaging was used to monitor changes in myocardial and left ventricular chamber blood intensity during apnea in rats. Significant signal loss in both blood (to 62 ± 5% and 51 ± 6% of baseline) and myocardium (to 79 ± 2% and 76 ± 3% of baseline) was observed at 45 and 90 s apnea while O2 saturation decreased from 98 ± 1% to 62 ± 7% and 36 ± 9%, respectively. These results show that myocardial intensity is modulated by alterations in blood oxygenation.