bluuebunny/crossref_metadata_2025 huggingface dataset:
MR microimaging of articular cartilage and contrast enhancement by manganese ions
Authors: Kusaka Y. , Gründer W. , Rumpel H. , Dannhauer K.‐H. , Gersonde K.
Published: March 2007

Saline solutions of manganese ions (Mn2+) were used as articular contrast agents in magnetic resonance microscopy (9.4 T) of cartilage of chicken femoral condyles and pig temporomandibular joints. The diffusion of Mn2+ from the articular surface into the cartilage matrix led to a strong contrast enhancement in the cartilage. The combination of the high spatial resolution and the contrast enhancement allowed the visualization of fine structures (tissue types) in the cartilage, which correlate with the tissue zones in histological sections stained with cationic dyes. We assume that the electrostatic interactions between the negatively charged groups of the proteoglycans and Mn2+ are most important for the mechanism of contrast enhancement. Hence, the different signal intensities of the various zones of cartilage indicate differences in density of proteoglycans. The intraarticular injection of the cationic contrast agent could improve the possibility of an early diagnosis of cartilage dysfunction and degeneration. © 1992 Academic Press, Inc.
Magnetization transfer effects in multislice RARE sequences
Authors: Melki P. S. , Mulkern R. V.
Published: March 2007

Magnetization transfer effects are demonstrated to be significant in determining the signal intensity from brain tissues on images acquired with multislice rapid acquisition relaxation enhanced (RARE) sequences. We report studies designed to determine how the signal intensities vary with slice number or, equivalently, off‐resonance power deposition. The results obtained in fat, gray matter, and white matter are similar in form to those reported in kidney tissues during classic magnetization transfer experiments (J. Eng, T. L. Ceckler, and R. S. Balaban, Magn. Reson. Med. 17,304 (1991)). Of clinical significance to RARE practitioners is the increase of contrast‐to‐noise ratios between gray and white matter on proton density‐weighted images with increasing slice number. © 1992 Academic Press, Inc.
Magnetically coupled paramagnetic relaxation agents
Authors: Lester Cathy Coolbaugh , Bryant Robert G.
Published: March 2007

Measurements of the spin‐lattice relaxation rates of water protons made over a wide frequency range have demonstrated that the effects of paramagnetic relaxation agents may be considerably enhanced when the paramagnetic center is incorporated into a compact structure macromolecule such as a protein that is rotationally constrained. The immobilization of the macromolecule profoundly changes the nature of the magnetic field dependence of the relaxation rate for both the diamagnetic and the paramagnetic samples. The immobilization also amplifies the effect of the paramagnetic center as a water‐proton relaxation agent. The direct exchange of labile water molecules or protons is not a requirement for the high efficiency of this class of magnetic relaxation agents. © 1992 Academic Press, Inc.
Intravascular (catheter) NMR receiver probe: Preliminary design analysis and application to canine iliofemoral imaging
Authors: Hurst Gregory C. , Hua Jianmin , Duerk Jeffrey L. , Cohen Alan M.
Published: March 2007

This investigation explores the feasibility of a catheter‐based receiver probe for NMR study of arterial walls. Simulations and phantom experiments demonstrate the spatial response of several “inside‐out” probe coil designs, including loop, “birdcage,” “multipole,” “center return,” and opposed solenoids. For a target defined by an annulus in a plane perpendicular to B0, the opposed solenoid design provides substantially superior homogeneity to other designs considered. Canine iliofemoral artery images were acquired using a catheter probe in a whole‐body, 1.5‐T clinical imaging system. In situ (cadaver) images acquired with TE 70, TR 2400,2‐mm slice thickness, and 78 × 78‐μm in‐plane voxel size in 10‐min acquisition times show vessel wall structures identified as intima, internal elastic lamina, media, and adventitia. In vivo images from similar acquisition conditions are much more poorly resolved, presumably due to motion, despite the use of cardiac gating and gradient moment nulling, so the feasibility of obtaining high‐resolution in vivo MR images of the arterial wall remains in doubt. © 1992 Academic Press, Inc.
In vivo17O NMR study of rat brain during 17O2 inhalation
Authors: Fiat D. , Ligeti L. , Lyon R. C. , Ruttner Z. , Pekar J. , Moonen C. T. W. , McLaughlin A. C.
Published: March 2007

In vivo 17O NMR has been used to monitor the H2 17O concentration in rat brain during inhalation of 17O2. The results are discussed in terms of oxygen consumption in the brain and recirculation into the brain of H2 17O produced in other organs. © 1992 Academic Press, Inc.
Direct imaging of magnetic field gradients by group spin‐echoselection
Authors: Posse Stefan
Published: March 2007

A new image processing method for single‐echo gradient echo imaging is presented which extracts local phase gradient information by k‐space filtering instead of by phased reconstruction and spatial differentiation. It is shown that localphase gradient directions and semiquantitative local phase gradient magnitudes can be directly measured, even in regions where phased image reconstruction suffers from multiple phase foldovers due to strong phase modulations. The directional information thus obtained can be used as a reference to identify and correct phase modulation foldovers i phase maps which may be computed from the same raw data. The method is applied here to measure static magnetic field gradients and illustrates fundamental k‐space signal properties of gradient echo imaging. Based on this concept, image artifacts caused by conventional strong k‐space filtering in gradient echo imaging are discussed.
Concurrent quantification of tissue metabolism and blood flow via 2h/31P NMR in vivo. i. assessment of absolute metabolite quantification
Authors: Song Sheng‐kwei , Hotchkiss Richard S. , Ackerman Joseph J. H.
Published: March 2007

In a series of three papers, we demonstrate and validate an approach for concurrent absolute quantification in situ of blood flow and energy metabolism with a modification of the NMR methodfor absolute concentration determination put forth by Thulborn and Ackerman [J. Magn. Reson. 55, 357 (1983)] and later expanded upon by Tofts and Wray. In this first paper of the series, we briefly review the theoretical basis for the concentration measurement and present, for the first time, a successful paired validation of metabolite quantification via 31P surface‐coil NMR through corroborative in vitro enzymatic assays. The paired radiolabeled microsphere validation of blood flow measurement via 2H surface‐coil NMR employing D2O as a freely diffusible tracer and the concurrent determination of blood flow and energy metabolism in a septic rat model are presented in the accompanying second and third paper to completethe series. In this article aclassical RF tank circuit is employed to describe the effect of conductive sample loading on the NMR receiver by considering its apparent series resistance. It is shown in aneasily visualized generalizable manner that the effect of sample loading on the observed NMR signal intensity can be accounted for quantitatively by monitoring changes in 90° pulse width at constant power at a fixed reference point, i.e., SSample= Sphantom(PW90pphantom/PW90sample). In a series of paired experiments the absolute concentrations of high energy phosphates obtained from resting rat leg muscle (n = 4) in situ (NMR) and in vitro (enzymatic) were determined as follows: [PCr]NMR = 17.2 ± 0.8 SD, [PCT]enzymatic, = 17.3 ± 2 SD, [ATP]NMR = 5.1 ± 0.8 SD, [ATP]enzymatic, = 5.0 ± 0.2 SD mmol/kg tissue wet wt. Results of these two independent methods of concentration determination were not statistically different (P = 0.94 and P = 0.74 respectively) and serve to rigorously validate the Thulborn approach for absolute quantification of phosphorous metabolites in situ via NMR. Furthermore, these results strongly suggest that ATP and PCr in resting rat leg muscle under normal physiologic conditions are 100% NMR visible. The free cytosolic [ADP]NMR was estimated from the creatine kinase reaction equilibrium expression to be 0.022 ± 0.003 SD mmol/kg tissue wet wt.
Proton NMR studies on ischemic rat brain tissue
Authors: Iwama T. , Yamada H. , Andoh T. , Sakai N. , Era S. , Sogami M. , Kuwata K. , Wataris H.
Published: March 2007

The spin‐lattice relaxation time (T1) of water protons and the cross‐relaxation time (Tis) between irradiated protein protons and observed water protons were measured in order to study water‐macromolecular interactions in ischemic rat brain tissues. Tissueswere obtained by bilateral common carotid artery occlusion from stroke‐prone spontaneously hypertensive rats. Water, Na, and K contents were measured in ischemic brain tissue at the same time. Water and Na content increased while the T1value and K content decreased following ischemic insults. The T1value did not change until 180 min after ischemia had been induced. Changes in the Tlsvalue occurred earlier than changes observed for the T1value, water, and electrolyte contents. Results indicate that the value of Tis, may be useful for detecting cerebral ischemia and that the physical structure of water‐macromolecular interaction may be altered soon after ischemic onset in brain tissue.
1H spectroscopic imaging of rat brain at 7 tesla
Authors: Fernandez E. J. , Maudsley A. A. , Higuchi T. , Weiner M. W.
Published: March 2007

1H magnetic resonance spectroscopic imaging has been used to obtain metabolite maps of the rat brain. The spin‐echo‐based technique has been evaluated with respect to water and lipid suppression and sensitivity. Metabolite maps were constructed for choline. creatine + phosphocreatine, amino acids, Nacetyl aspartate, and lactate. A spatial resolution of 3 × 3 mm (in plane) with 7‐mm‐thick slices was achieved routinely in 60‐min (16 × 16 phase encoding) acquisitions. For higher intensity resonances, metabolite maps could be constructed in as little as 10 min. Results from phantoms and from rats under normal and focal ischemia conditions are presented.
Comparison of in Vivo and in vitro Hahn T2 measurements in rat lung
Authors: Shioya Sumie , Kolem Heinrich , Ailion David C. , Goodrich K. Craig , Cutillo Antonio G. , Morris Alan H. , Durney Carl H.
Published: March 2007

We compared in vivo and in vitro Hahn echo T2 measurements in rat lungs in both imaging and nonimaging modes. All measurements could be characterized by multiexponential functions consisting of either two or three exponentials. Essentially the same values of the time constants were observed for spontaneously breathing rats and for excised lungs. © 1991 Academic Press, Inc.
Quantitative MR in the diagnosis of multiple sclerosis
Authors: Haughton Victor M. , Yetkin F. Zerrin , Rao Stephen M. , Rimm Alfred A. , Fischer Mary E. , Papke R. Anne , Breger Robert K. , Khatri Bhupendra O.
Published: March 2007

In patients with multiple sclerosis (MS), the apparently uninvolved cerebral white matter between demyelinated plaques may have biochemical abnormalities. To what degree the changes in the white matter contribute to symptomatology in MS is unknown. In 39 patients with multiple sclerosis, and in 39 age‐matched nondiseased volunteers, T1 and T2 were calculated from spin‐echo images in four regions of apparently uninvolved white matter. In three of four white matter areas, the average T1 and T2 were significantly longer in the patients than in the controls. The T1 correlated with the disability, measured by the Kurtzke Extended Disability Status Scale, although the correlation was marginally significant. The results suggest that in patients with MS, white matter disease that is not visualized in MR as distinct foci of abnormal signal intensity may contribute to disease burden and disability.
Factors influencing the accuracy and precision of velocity‐encoded phase imaging
Authors: Buonocore Michael H. , Bogren Hugo
Published: March 2007

Velocity‐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

Sequential 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

Previous 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

The 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

The 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

The 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

A 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

MRI 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

Citrate 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

Although 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

Projection 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

We 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

We 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

31‐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

The 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

The 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

The 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

Steady‐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

In 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

We 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

Gradient 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.
In vitro proton NMR study of collagen in human aortic wall
Authors: Vinée Philippe , Meurer Bernard , Constantinesco André , Kohlberger Bernd , Hauenstein Karl Heinz , Laubenberger Jörg
Published: March 2007

The authors relate the findings in the 1H solid state line shape (at 60 MHz) of human aortic walls (n = 12) in native state and after histologically controlled selective lysis of collagen and elastin. An analysis of the line shape shows a composite free induction decay (FID) consisting of a low amplitude (3‐7%) fast decaying component (T2 = 20 us) and a slow decaying one (T2 > 1 ms). The fast component is identified as the protons of the collagen macromolecules. The second moment computed from the experimental fast component of the FID is in agreement with published studies examining the motional characteristics of collagen by multinuclear NMR employing spin labeling. A theoretical second moment is computed for the collagen macromolecular backbone from the atomic positions in the superhelix. Comparison with the observed experimental values allows determination of the step angle (29°) of the fast rotational motion of the collagen strands along their long axis.
In vivo oxygen tension and temperature: Simultaneous determination using 19F NMR spectroscopy of perfluorocarbon
Authors: Mason Ralph P. , Shukla Himu , Antich Peter P.
Published: March 2007

A novel technique is presented to measure in vivo simulataneously oxygen tension and temperature using 19F NMR spectroscopy of perfluorocarbon. This work examines the variation with oxygen tension (pO2) and temperature of the individual spin lattice relaxation rates (R1) of the 19F resonances of the perfluorocarbon emulsion Oxypherol‐ET. A linear relationship between R1 and pO2 is confirmed for all the resonances at any specific temperature in the range 27–50°C. Similarly, a linear relationship is determined between R1 and temperature at any specific pO2 in this temperature range. Each resonance behaves uniquely with respect to temperature and pO2 and consideration of 2 or more resonances uniquely defines pO2 and temperature simultaneously, and unambiguously. This concept is demonstrated in vivo in a murine tumor and perfused rat heart, where pO2 and temperature were both determined without prior knowledge.
Metabolic changes in activated T cells: An NMR study of human peripheral blood lymphocytes
Authors: Bental Michal , Deutsch Carol
Published: March 2007

Using NMR spectroscopy, we studied purified, human T lymphocytes in a serum‐free medium. Purified cells were entrapped inside agarose beads and induced to proliferate by the mitogens phorbol‐12‐myristate‐13‐acetate and ionomycin. T lymphocytes in standard culture and inside agarose beads exhibit comparable viability, and similar extent and kinetics of DNA synthesis and Interleukin‐2 secretion. 31P‐NMR revealed decreased phosphomonoester and increased phosphodiester content in cells stimulated for two days or longer. 13C‐glucose utilization and 13C‐lactate production rates showed that 85% of the utilized glucose was converted to lactate. 1H‐NMR spectra of the perfusing media indicated that lactate was also produced from substrates other than glucose or glycogen. Glucose accounted for 25% of the lactate produced by quiescent cells, and for 67% of lactate production by stimulated cells. Glycolysis was enhanced 6‐fold within the first 2 hours following stimulation, and 15‐fold by 48 or 96 h. Aerobic lactate production was increased 3‐fold by 48 h, with only a minor enhancement during the first 12 h of stimulation. Our results indicate a shift from mostly aerobic to mostly anaerobic lactate production in T lymphocytes within the first 90 min of the G0 to G1 transition during cell cycle progression.
In vivo NMR imaging and spectroscopic investigation of renal pathology in lean and obese rat kidneys
Authors: Bosch Coleen S. , Ackerman Joseph J. H. , Tilton Ronald G. , Shalwitz Robert A.
Published: March 2007

Diabetic nephropathy is a major cause of end‐stage renal failure. While our understanding of the pathogenesis of nephropathy is incomplete, progressive glomerular injury appears to play a significant role in the decline of renal function. Proton NMR spectroscopy and imaging techniques were used to address changes in renal pathology associated with glomerular mesangial expansion in vivo in kidneys from spontaneously obese and lean (control) littermate Zucker rats. Fully functioning rat kidneys were surgically exposed and externalized for direct NMR signal detection via a coil placed around the organ. High‐resolution (78 μm in plane) proton images were obtained at 4.7 T magnetic field strength revealing fine structure within the well‐defined cortical and medullary regions. The obese rat kidney images were distinct in appearance from the lean kidney images and exhibited marked cortical expansion as well as increased overall kidney size. Enlargement of mean glomerular diameter was verified histologically in the obese kidneys as compared with the lean kidneys. Proton T1 and T2 relaxation times were determined from the entire kidney using standard spectroscopic techniques, and from specific regions within the kidney from multiple T1 and T2‐weighted images. Additionally, image contrast enhancement resulting from saturation transfer between protons in restricted‐mobility environments and mobile water protons within the kidney was investigated in the lean and obese rat kidneys using magnetization‐transfer imaging techniques. At the early stage of renal injury examined in this study, diseased and healthy kidneys could not be differentiated on the basis of relaxation times alone. The magnitude of saturation transfer obtained in cortical tissue in the lean and obese kidneys was also not statistically significantly different. However, the magnitude of saturation transfer achieved in the medullary tissue of obese kidneys was statistically significantly less than that achieved in lean kidneys.
Magnetization transfer characterization of hypertensive cardiomyopathy: Significance of tissue water content
Authors: Scholz Thomas D. , Ceckler Toni L. , Balaban Robert S.
Published: March 2007

Magnetization transfer measurements offer the potential for specific noninvasive tissue characterization. The goal of the present study was to determine if changes in magnetization transfer would accompany the myocardial remodeling that occurs with hypertrophic cardiomyopathy. Using 40‐week spontaneously hypertensive rat (SHR) myocardium, T1, T2, and T1 in the presence of off‐resonance irradiation (T1sat) were found to be greater compared to Wistar‐Kyoto (WKY) controls. The pseudo‐first order rate constant of magnetization transfer (kfor) was less in 40‐week SHR compared with WKY while the ratio of equilibrium magnetization in the presence and absence of off‐resonance irradiation (Ms/M0) was not different. The extent to which observed interspecies differences in tissue water content affected these parameters was investigated by dehydrating normal and hypertrophic myocardium. Significant correlations found between tissue water content and T1, T2, T1sat and kfor, but not Ms/M0, suggested changes in tissue water dominated the observed interspecies differences in relaxation parameters. Thus, ventricular remodeling in hypertrophic cardiomyopathy does not alter magnetization transfer though the accompanying change in tissue water content influences water proton relaxation.
Field dependent transverse relaxation rate increase may be a specific measure of tissue iron stores
Authors: Bartzokis George , Aravagiri Manickam , Oldendorf William H. , Mintz Jim , Marder Stephen R.
Published: March 2007

The degree to which MRI magnet field strength affects measured transverse relaxation rates (R2) defines a measure termed the field dependent R2 increase (FDRI). We report here the results of in vivo and in vitro experiments that were conducted to evaluate whether FDRI is a potentially useful measure of tissue iron stores. T2 relaxation times were obtained using two clinical MRI instruments operating at 0.5 and 1.5 Tesla, and relaxation rates (R2) were calculated as the reciprocal of T2. The in vivo experiment measured R2 in human brain frontal white matter, caudate nucleus, putamen, and globus pallidus. The FDRI was very highly correlated with published brain iron levels for the four regions examined. The in vitro experiment measured R2 in agarose gel‐based phantoms containing physiologic forms and amounts proteins involved in iron storage and transport (ferritin, apoferritin, transferrin, and apotransferrin). Significant field dependence was observed only for the ferritin phantoms. The differences in the R2 values obtained at the two field strengths were striking, and were proportional to the ferritin levels of the phantoms. These studies suggest that FDRI may be a specific measure of tissue ferritin. The quantitative significance of the results to imaging and possible applications to the clinical investigation of pathologic states are discussed.
A perifusion loop‐gap resonator NMR probe for aerobic cell suspensions
Authors: Anderson Mark E. , Markley John L. , Arùs Carles , Chobanian Michael C.
Published: March 2007

NMR studies of aerobic cell metabolism require that spectral data of high sensitivity and resolution be acquired from samples maintained under suitable conditions. The loop‐gap resonator 31P NMR probe described here was designed for investigations of highly aerobic‐dependent renal proximal tubules in an environment similar to those of conventional incubation flasks. The inherently higher sensitivity of the loop‐gap resonator design and associated circuitry made it possible to obtain adequate spectra in short periods of time with small amounts of sample. Cellular physiological properties of perifused aerobic renal proximal tubule cell suspensions in the loop‐gap resonator probe were found to be similar to equivalent tissue samples incubated in conventional flasks. Furthermore, the loop‐gap perifusion probe was found to provide useful 31P NMR spectra of the kidney tubule system after acquisition times as short as 3 min.
Diffusion in red blood cell suspensions: Separation of the intracellular and extracellular NMR sodium signal
Authors: van der Veen J. W. C. , van Gelderen P. , Creyghton J. H. N. , Bovée W. M. M. J.
Published: March 2007

It is shown that the signal of intracellular and extracellular sodium of red blood cells can be separated by a difference in diffusion. Comparison with proton diffusion experiments conducted in parallel showed that this difference was caused by restriction to the cell volume. The measured proton and sodium root mean square displacements agreed well with the cell dimensions. However, this experiment is limited to use in vitro by the required gradient strength.
A novel flow‐suppression technique using tailored RF pulses
Authors: Ro Y. M. , Cho Z. H.
Published: March 2007

The pulsatile nature of blood flow makes zipper‐like artifacts along the coding direction in the two‐dimensional Fourier transform NMR image. So far, spatial presaturation, one of the correction methods, is known to be effective in eliminating flow artifacts when the Fourier spin echo acquisition is employed. However, this method requires an additional RF pulse and a spoiling gradient for presaturation. Described in this paper is a new flow suppression technique, based on spin dephasing, using a set of tailored RF pulses. The proposed method does not require additional saturation RF pulses or spoiling gradient pulses, making it advantageous over other methods. In addition, the method is relatively robust to flow velocity. The proposed technique is equivalent to the existing flow saturation technique except that the elimination of the flow component is achieved by a pair of tailored 90–180° RF pulses in the spin echo sequence. The principle of the proposed method is the creation of a linear phase gradient within the slice along the slice selection direction for the moving material by use of two opposing quadratic phase RF pulses, i.e., 90° and 180° RF pulses with opposing quadratic phase distributions. That is to say, all the spins of the moving materials along the slice selection direction become dephased. Therefore, no observable signal is generated. Computer simulations and experimental results obtained using a 2.0‐T whole‐body imaging system on both a phantom and a human volunteer are also presented.