bluuebunny/crossref_metadata_2025 huggingface dataset:
13 C NMR visibility of rabbit muscle glycogen in vivo
Authors: Gruetter Rolf , Prolla Tomas A. , Shulman Robert G.
Published: March 2007

The integrated 13C NMR intensity of the glycogen Cl resonance was measured in skeletal muscle (biceps femoris region) of nine rabbits under in vivo conditions. Concurrent chemical determinations of glycogen content showed that the in vivo signal was 1.02 ± 0.06 the intensity of analytical samples, where glycogen is known to be ∼ 100% visible. © 1991 Academic Press, Inc.
Coil optimization for MRI by conjugate gradient descent
Authors: Wong Eric C. , Jesmanowicz A. , Hyde James S.
Published: March 2007

A flexible iterative algorithm is presented for optimizing gradient and radio frequency coils for MRI. It is based on a model using discrete current elements and direct Biot‐Savart calculation of the fields. An error function is defined over a region of interest (ROI) and is minimized by conjugate gradient descent. The choice of error function allows optimization of the field uniformity, the inductance, and the efficiency of the coil in any combination. Neither the coil nor the ROI is restricted to any particular geometry. A 40‐ turn cylindrical z‐gradient coil of radius a and length 4a, designed for a ROI of radius 0.7a and length 2a has an average error in the gradient fields generated of 0.85%, an inductance of 0.014a mH/cm, and an efficiency of 6.65a−2 Gem/A. A 16‐turn birdcage‐like RF coil of radius 5 cm, designed for a ROI of radius 4 cm has an average error of 0.79%. © 1991 Academic Press, Inc.
Coupling effects in volume selective 1H spectroscopy of major brain metabolites
Authors: Ernst Th. , Hennig J.
Published: March 2007

The effect of PRESS and STEAM sequences on the spectra of coupled substances are discussed using the examples of weakly coupled AX and A2X systems. Maximum differences compared to uncoupled spins occur if the RF pulses are applied to antiphase magnetization. In this case, the spin echo of the PRESS experiment shows a modified dependence on the refocusing flip angle, which may lead to an attenuation of the acquired signal. In STEAM spectroscopy the evolution within the middle interval tm is dominated by zero quantum coherences and longitudinal polarization, whose maximum efficiencies are 25 and 12.5%, respectively. Zero quantum coherences may lead to strong modulations when the tm value is varied. The effects on the spectra of important coupled metabolites of the human brain such as glutamate, GABA, inositol, and particularly lactate, are demonstrated. The observed modulations seem to make the quantification of the spectra rather difficult at echo times above 50 ms. © 1991 Academic Press, Inc.
A simple method for obtaining cross‐term‐free images for diffusion anisotropy studies in NMR microimaging
Authors: Neeman Michal , Freyer James P. , Sillerud Laurel O.
Published: March 2007

The geometric average of two spin‐echo images obtained with opposite polarity diffusion gradients yields cross‐term‐free images that can be directly compared for diffusion anisotropy. This approach is demonstrated here for free water isotropic diffusion and anisotropic diffusion of water in the phloem system of celery (Apium graveolens). © 1991 Academic Press, Inc.
Human auditory system response to pulsed radiofrequency energy in RF coils for magnetic resonance at 2.4 to 170 MHz
Authors: Röschmann Peter
Published: March 2007

The threshold conditions for an auditory perception of pulsed radiofrequency (RF) energy absorption in the human head have been studied on six volunteers with RF coils for magnetic resonance (MR) imaging. For homogeneous RF exposure with MR head coils in the 2.4‐to 170‐MHz range and pulse widths 3 μs, ⩽Tp< 100 μs, the auditory thresholds were observed at 16 ± 4 mJ pulse energy. Localized RF exposure with optimized surface coils positioned flush with the ear lowers the auditory threshold to only 3 ± 0.6 mJ. The hearing threshold of RF pulses with Tp> 200 μs occurs at more or less constant peak power levels of typically 150 ± 50 W for head coils and as low as 20 W for surface coils. The results from this study confirm theoretical predictions from a thermoeleastic expansion model and compare well with reported thresholds from near field antenna measurements at 425 to 3000 MHz. Details of the threshold dependence on RF pulse length reveal primary sites of RF to acoustic energy conversion at the mastoid and temporal bone region and the outer layer of the brain from where thermoelastically generated pressure transients excite audible pressure waves at the resonance modes of the skull around 1.7 kHz and of the brain around 11 kHz. If not masked by usually dominating noise from switched gradients, the conditions for hearing RF pulses, as applied to head coils in MR studies with flip angle α at main field Bo, is given byTp/ms ⩽ 0.4 (α/π)Bo/[T]. At peak power levels up to 15 kW presently available in clinical MR systems, there is no evidence known for detrimental health effects arising from the RF auditory phenomenon which is a secondary cause associated with primary RF to thermal energy conversion in body tissues. To avoid the RF‐evoked sound pressure levels in the head rising above the discomfort threshold at 110 dB SPL, an upper limit of 30 kW applied peak pulse power is suggested for head coils and 6 kW for surface coils. © 1991 Academic Press, Inc.
Toward fully automatic estimation of in Vivo31P spectra
Authors: Burger Cyrill , McKinnon Graeme , Buchli Reto , Boesiger Peter
Published: March 2007

Fitting a model to an experimental spectrum is a difficult nonlinear estimation problem. The solution presented here is to start an iterative search procedure sufficiently close to the optimal model parameter set. This is achieved by providing tissue‐dependent a priori peak information and by a novel correlation method to get good primary estimates of the resonance and phase offset parameters. The resulting estimation procedure is fully automatic and has proven to be robust for 31P data. © 1991 Academic Press, Inc.
Pulsed NMR relaxometry of striated muscle fibers
Authors: English A. E. , Joy M. L. G. , Henkelman R. M.
Published: March 2007

The longitudinal (T1,) and transverse (T2,) proton (1H) nuclear magnetic resonance (NMR) relaxation of fast‐and slow‐twitch muscle fibers are examined using rat muscle tissues in which one fiber type predominates. Both continuum and discrete exponential component fits are made to Carr‐Purcell‐Meiboom‐Gill (CPMG) and inversion recovery pulse sequence measurements. In addition, experiments which illustrate the large sources of variability that have led to apparent conflicts in the literature are presented. Based on the results of this study, unique NMR features that distinguish fast‐ and slow‐twitch muscle fibers are presented. The feasibility of differentiating fast‐and slow‐twitch muscle fibers using magnetic resonance (MR) imaging is briefly discussed. © 1991 Academic Press, Inc.
Localized in vivo proton spectroscopy in the brain of patients with multiple sclerosis
Authors: Larsson H. B. W. , Christiansen P. , Jensen M. , Frederiksen J. , Heltberg A. , Olesen J. , Henriksen O.
Published: March 2007

Localized proton spectroscopy was performed in 15 patients with acute or chronic multiple sclerosis (MS). Some of the patients were investigated serially, being given a total of 22 spectroscopic investigations. Resonances corresponding to free lipids were observed in six plaques. This was distinctly seen in two plaques at Days 70 and 85 after the occurrence of the plaques. A lesser content of lipids in plaques was observed as early as Day 10 and as late as nearly 1 year after occurrence. The relative concentration of N‐acetyl asparate (NAA) was significantly lower in patients than in controls, and the relative concentration of choline (Cho) was significantly higher in patients than in controls. These differences were most pronounced in older plaques. MR spectroscopic demonstration of lipids in a MS plaque probably reflects disintegration of myelin, and a decreased NAA/Cho ratio may be related either to gliosis or to axonal degeneration, which sometimes occurs in longstanding MS. © 1991 Academic Press, Inc.
Noninvasive determination of regional cerebral blood flow in rats using dynamic imaging with Gd(DTPA)
Authors: Rudin Markus , Sauter Andre
Published: March 2007

A method for the noninvasive, quantitative determination of regional cerebral blood flow (rCBF) in small laboratory animals, such as the rat, is described. The change in magnetic susceptibility in the vicinity of brain capillaries evoked by iv infusion of Gd(DTPA), a paramagnetic agent not crossing the blood‐brain barrier, is detected as an attenuation of the 1H signal in T2‐weighted MRI sequences. The reduction of the MR signal intensity after 1 or 2 min of Gd(DTPA) infusion correlates well (r > 0.95) with the rCBF values obtained using the well‐established [14C] iodoantipyrine method. At a slice thickness of 3 mm, the pixel size typically is 0.15 × 0.5 mm2. The clearance rate of Gd(DTPA) from blood allows repeated measurements of CBF to be made using this technique approximately every 30 min. The experimental results obtained in normal and ischemic rat brain have been rationalized within the frame of a two‐compartment model, allowing the definition of optimal experimental conditions for a given CBF: for normal and reduced CBF values (<150 ml/100 g/min) the reduction in MR signal intensity, measured after 1 or 2 min of Gd(DTPA) infusion, correlates closely with the CBF. However, for CBF values<150 ml/100g/min, a more reliable parameter would be the time constant of the MR signal attenuation during the infusion. © 1991 Academic Press, Inc.
Quantitation of the susceptibility difference between trabecular bone and bone marrow: Experimental studies
Authors: Majumdar S. , Thomasson D. , Shimakawa A. , Genant H. K.
Published: March 2007

In this study we quantify the effects of different relaxation mechanisms on the signal intensity in gradient‐echo images of tissue such as bone marrow in the presence of trabecular bone. The susceptibility difference between trabecular bone and soft tissue produces distortions in the magnetic lines of force which induce strong inhomogeneities in the static magnetic field. Diffusion of tissue protons in such magnetic field gradients produce a shortening of the transverse relaxation time T2, while the dephasing of the transverse magnetization due to susceptibility differences produces a shortening of the apparent relaxation time T as demonstrated in gradient‐echo images. We have used specimens of dried human vertebrae with different bone densities immersed in either saline to simulate tissue water or an emulsion of oil and water to simulate bone marrow to quantify these relaxation mechanisms in vitro. We have measured the MR relaxation times T1, T2, and T of protons within the trabecular spaces and correlated their variations with trabecular bone density. We have found that in vitro, at 1.5 T, the relaxation times T1 and T2 do not show significant variations with bone density and there are no significant contributions to the transverse relaxation rate due to the diffusion of tissue water in the magnetic field gradients. However, the relaxation rate, 1/T, of saline in the presence of trabecular bone increases at a rate of 0.2 s−1 mg/cc due to the dephasing of the transverse magnetization in the magnetic field inhomogeneities. Similar bone density‐related T variations were observed for fat protons within the trabeculae where the chemical‐shift‐induced modulations of signal intensity in an oil‐water emulsion have been separated from the susceptibility‐induced relaxation effects. In addition, we have verified these effects in vivo and quantified in vivo variations in fat and water relaxation rates of bone marrow in the epiphysis and diaphysis in the appendicular skeleton of normal volunteers and found that both fat and water T are shorter in the epiphysis compared to the diaphysis, which correlates well with previous observations. © 1991 Academic Press, Inc.
Pitfalls of contrast‐enhanced imaging in the nervous system
Authors: Brant‐Zawadzki Michael
Published: March 2007

This brief review covers the evolving clinical role of paramagnetic contrast agents in magnetic resonance imaging of the central nervous system, with particular emphasis on potential pitfalls. The safety and efficacy of Gd‐DTPA is now well‐established. Approximately 35–40% of all scans performed in this country now utilize the agent. The major pitfalls center on overinterpretation of the characterization of disease by either enhancement or lack thereof in any particular process. © 1991 Academic Press, Inc.
Alkalosis monitored by 31P NMR in a human glioma cell line exposed to the anti‐tumor drug 1, 3‐bis (2‐chloroethyl)‐1‐nitrosourea
Authors: Commodari Fernando , Sanctuary Bryan C. , Feindel William , Shoubridge Eric A.
Published: March 2007

A transient alkalosis of similar magnitude to that observed in vivo has been observed using 31P NMR and 2‐deoxy‐D‐glucose‐6‐phosphate as a pH marker in a human glioma cell line, SKI‐1, with demonstrated sensitivity to 1, 3‐bis (2‐chloroethyl)‐1‐nitrosourea. At an effective dose of 5 ± 1 × 10 μg/ml, an increase of 0.13 ± 0.05 pH units was observed within 4 ± 1 × 10 min of introducing the drug into the perfusion chamber. Although the in vitro response is of a time course much faster than that in vivo, these results suggest that this immediate pH change could be an indicator of the cytotoxic action of the drug. © 1991 Academic Press, Inc.
31P spectroscopy of the human prostate gland in vivo using a transrectal probe
Authors: Kurhanewicz John , Thomas Albert , Jajodia Prahalad , Weiner Michael W. , James Thomas L. , Vigneron Daniel B. , Narayan Perinchery
Published: March 2007

Using a transrectal probe, good quality 31P magnetic resonance spectroscopy of the human prostate was performed safely, consistently, and in a reasonable amount of time (average of 60 min). Initial results indicate that transrectal 31P MRS has the ability to characterize the phosphorylated metabolites of normal, hyperplastic, and malignant prostates. This study demonstrated that malignant prostates are characterized by significantly decreased levels of phosphocreatine (PCr) and increased levels of phosphomonesters (PME) as compared to healthy prostates. © 1991 Academic Press, Inc.
Practical Implementation and Optimization of One‐shot T1 imaging
Authors: Kay I. , Henkelman R. M.
Published: March 2007

Longitudinal relaxation times (T1) can be measured rapidly in an imaging context using a “one‐shot” method based on the pulse sequence originally proposed by D. C. Look and D. R. Locker (Rev. Sci. Instrum. 41, 250 1970). This sequence is significantly faster than either repeated inversion recovery or repeated saturation recovery methods. The method uses a 180° inversion pulse followed by multiple small‐angle α pulses that sample the longitudinal magnetization during its recovery. Choices of inversion pulse, tip angle, and time intervals are discussed for optimal clinical use. We can produce 29 images sampling the full T1 recovery curve with a 256 × 256 resolution in about 10 min. From this data, T1 images can be calculated with a precision of 10%. © 1991 Academic Press, Inc.
Measurement of water movement in the rabbit eye in vivo using H217O
Authors: Kwong Kenneth K. , Xiong Jing , Kuan Wei‐Peng , Cheng Hong‐Ming
Published: March 2007

Topically applied (eyedrop) H2 17O (10% enrichment) was used in magnetic resonance studies to quantify intraocular water dispersion in vivo. The rate of H2 17O removed from the aqueous chamber is in the order of 0.1 ml/min/ml of tissue. Similar results are obtained with either proton imaging or 17O spectroscopy. Parallel experiments of direct injection of H217O into the aqueous chamber supported the topical data. Proton MR imaging of H217O dissipation from the aqueous chamber with clinical imagers, coupled with eyedrop application. suggerts clinical possibilites. © 1991 Academic Press, Inc.
Inhomogeneity correction for in vivo spectroscopy by high‐resolution water referencing
Authors: Webb Peter , Spielman Daniel , Macovski Albert
Published: March 2007

One of the most common sources of distortion in in vivo spectroscopy is the inhomogeneity of the main magnetic field. This effect is particularly problematic when performing spectroscopic imaging, as the shim cannot be simultaneously optimized for all voxels. In this paper we present a technique to measure inhomogeneity rapidly, then show how to use the measurement to improve the analysis of the spectrum. This technique can be applied in conjunction with any spectroscopic localization method and any spectral quantitation algorithm. We present results from spectroscopic imaging of phantoms, then show application to a single‐voxel water‐suppressed proton brain study. We find that the quantitation of the in vivo spectrum is made immune to inhomogeneous line broadening. © 1992 Academic Press, Inc.
13CNMR studies of glucose metabolism in human leukemic CEM‐C7 and CEM‐C1 cells
Authors: Post Jan F. M. , Baum Erna , Ezell Edward L.
Published: March 2007

Glucose metabolism of human leukemic cell lines CEM‐C7 and CEM‐C1 was investigated in vivo by 13C NMR using 13C‐labeled glucose. Exact knowledge of glucose concentration, cell count, and cell viability of the cell suspensions made it possible to analyze glucose metabolism in detail. In both cell lines aerobic glycolysis accounts for virtually all glucose consumption. The use of D‐[13C2] glucose provided a simple method to measure the glucose flux through the pentose phosphate pathway as 9% (CEM‐C1) and 11% (CEM‐C7) of glucose channeled into glycolysis. The dexamethasone‐sensitive CEM‐C7 cells consume glucose at a rate about 50% higher than the dexamethasone‐resistant CEM‐CI cells. It is shown that this higher consumption correlates with a larger size of the CEM‐C7 cells. Therefore in CEM cells the development of drug resistance does not seem to involve related changes in cell energetics. © 1992 Academic Press, Inc.
Iron–dextran as a magnetic susceptibility contrast agent: Flow‐related contrast effects in the T2‐weighted spin‐echo MRI of normal rat and cat brain
Authors: White David L. , Aicher Klaus P. , Tzika A. Aria , Kucharczyk John , Engelstad Barry L. , Moseley Michael E.
Published: March 2007

Iron–dextran (1 mmol Fe/kg) was used as an intravascular, paramagnetic contrast agent in rat and cat brain in conventional spin‐echo T2‐weighted (TR 2800/TE 100)1H magnetic resonance imaging. The resulting images displayed differential decreases (30–50%) in intensity whose pattern was similar to that obtained with the superparamagnetic particulate iron oxide AMI‐25 (0.18 mmol Fe/kg). Postcontrast images displayed improved anatomic detail, and contrast effects were observed to be greater in cortical and subcortical gray matter than in adjacent white matter. Intravenous injection of acetazolamide after administration of iron‐dextran caused a small additional decrease in image intensity. Measurement of whole blood and plasma at 5 min postinjection of either contrast agent revealed significant increases in their volume magnetic susceptibilities. The contrast effect appears to be related to magnetic susceptibility changes brought about by the iron–dextran it has both blood volume and blood flow components. The static model of magnetic susceptibility effects in brain capillaries is modified to include bolus flow of erythrocytes, providing a mechanism for the observed flow effects. © 1992 Academic Press, Inc.
Separation of diffusion and slow flow effects by use of flow rephasing and dephasing
Authors: Fujita N. , Harada K. , Sakurai K. , Akai Y. , Kozuka T.
Published: March 2007

Spin‐echo signal intensity alterations due to diffusion and slow flow are investigated in connection with modified Stejskal‐Tanner pulse sequences for 2D Fourier MR imaging, one for flow rephasing and the other for flow dephasing gradient waveforms. The theoretical considerations and experimental results concerning the diffusion coefficient measurements of slowly flowing material by these sequences are summarized as follows: (a) By using the flow dephasing sequence with different diffusion and flow‐sensitive gradients, slow flow effects can be distinguished from diffusion effects based on the quantitative difference between the diffusion‐and flow‐sensitive gradient amplitude dependences of these processes. (b) By using the combination of the flow rephasing and dephasing sequences with the same diffusion sensitivity, slow flow effects can be distinguished from diffusion effects directly based on their qualitative difference. By use of the latter approach, several in vivo images are also presented, which mainly represent macroscopic motions of spins, including slow flow such as tissue perfusion. © 1992 Academic Press, Inc.
Wavelet‐encoded MR imaging
Authors: Weaver John B. , Xu Yansun , Healy Dennis M. , Driscoll James R.
Published: March 2007

Wavelet encoding is presented and compared to phase encoding. In wavelet encoding a distribution of spins is excited by a slice selective RF pulse; for each repetition time the distribution excited has the profile of a wavelet at different scale and translation. The spin density can be reconstructed with an inverse wavelet transform. Wavelet encoding has three advantages over phase encoding: (1) there is no Gibblquot's ringing from partial volume effects, (2) the effective repetition time can be 36 times the repetition time for a 256 × 256 image, and (3) motion artifacts are local and dramatically reduced. Using wavelet encoding, a 256 × 256 T2‐weighted projection image can be acquired in 33s. © 1992 Academic Press, Inc.
Perfusion and diffusion MR imaging
Authors: King M. D. , Van Bruggen N. , Busza A. L. , Houseman J. , Williams S. R. , Gadian D. G.
Published: March 2007

Diffusion‐weighted images of the rat brain were obtained using the pulsed‐gradient spinecho method. An attempt was made to extract perfusion‐related parameters from signal intensity data taken from the caudate‐putamen region of the images, by using a nonlinear least‐squares calculation to fit the Le Bihan biexponential expression (Le Bihan et al., Radiology, 168, 497 (1988)) to the data. The perfusion‐related parameters could not be obtained with sufficient accuracy to be useful, although the perfusion‐weighted images appear to contain meaningful qualitative information. An analysis of the perfusion model is presented and shows why the Le Bihan pseudo‐diffusion coefficient is particularly difficult to measure with reasonable accuracy. © 1992 Academic Press, Inc.
Two‐dimensional selective adiabatic pulses
Authors: Conolly Steven , Pauly John , Nishimura Dwight , Macovsiu Albert
Published: March 2007

Using the technique of separable k‐space excitation, we have designed a two‐dimensional selective adiabatic pulse that inverts magnetization from a square region in the xy plane with insensitivity to RF variations. We also have designed a two‐dimensional adiabatic pulse that inverts selectively in frequency and in one spatial dimension. The pulses should be useful for both MR imaging and spectroscopy. We present experimental results to demonstrate that the two‐dimensional adiabatic pulses are feasible on commercial MR imaging systems. © 1992 Academic Press, Inc.
The analytic theory, optimization, and performance of transparent pulses
Authors: Buonocore Michael H.
Published: March 2007

Transparent pulses are defined by the property of having no net effect on stationary spins, while selectively nutating and dephasing flowing spins. They are derived from the inverse scattering transform, a nonlinear extension of the inverse Fourier transform. They can be used as presaturation pulses to suppress selectively the signal from flowing spins. Their intended imaging application is suppression of blood flow artifacts arising from the heart and major vessels. Diastolic images of these areas have significant artifacts that hinder accurate delineation of vessel and chamber boundaries. Transparent pulses significantly improve delineation of these boundaries and therefore could be used to improve the accuracy and precision of cross‐sectional area measurements. In this paper, the analytic theory, numerical optimization, and performance characteristics are described. Experimental evidence of flow signal suppression is provided in diastolic imaging of the heart in normal subjects. The long duration and power requirements of the present generation of transparent pulses currently limits their general Clinical use. © 1992 Academic Press, Inc.
Concurrent quantification of tissue metabolism and blood flow via 2h/31P NMR in Viva iii. alterations of muscle blood flow and metabolism during sepsis
Authors: Song Sheng‐Kwei , Hotchkiss Richard S. , Karl Irene E. , Ackerman Joseph J. H.
Published: March 2007

In the conclusion of this series of reports, the application of 31P/2H NMR to investigate the pathophysiology of sepsis in rat hindlimb muscle is demonstrated. Sepsis decreased muscle [PCr] by 18%, 18 ± 4 SD vs 22 ± 4 SD mmol/kg tissue wet wt (P = 0.01) in control rats but [ATP] was unchanged, 6 mmol/kg tissue wet wt (P = 0.2). The derived free cytosolic [ADP] in the two groups was similar, [ADP]septic = 0.023 ± 0.004 SD and [ADP]control, = 0.021 ± 0.003 SD mmol/kg tissue wet wt, and not statistically different (P =0.14). Likewise [Pi] in the septic and control groups was not statistically different, [Pi]septic = 1.1 ± 0.5 SD and [Pi]control, = 1.2 ± 0.4 SD mmol/kg tissue wet wt (P = 0.2). Septic rats presented the symptom of respiratory alkalosis evidenced by elevated blood pH. Sepsis decreased muscle blood flow by 33%, P = 0.003, but examination of individual subjects did not demonstrate a correlation with the reduction in [PCr]. Thus, a metabolic energy deficit caused by cellular ischemia/hypoxia is not a likely cause of cellular abnormality in rat hindlimb muscle during sepsis.
Twisting radial lines with application to robust magnetic resonance imaging of irregular flow
Authors: Jackson John I. , Nishimura Dwight G. , Macovski Albert
Published: March 2007

A problem with magnetic resonance angiograms of vessels containing irregular flow isthat flow‐induced dephasing can result in voids in the image. These void regionsare susceptible to misinterpretation as regions of stenosis or other vessel pathology. Flow‐induced dephasing can be minimized by using radial lines to cover k space. However, radial lines provide a very nonuniform, and hence, inefficient, coverage of k space. By twisting the outer portions of the radial trajectories, undistorted images of very rapid and turbulent flow can be obtained with a reasonable number of RF excitations. o 1992 Academic Press, Inc.
Specific MR imaging of human lymphocytes by monoclonal antibody‐guided dextran‐magnetite particles
Authors: Bulte Jeff W. M. , Hoekstra Yke , Kamman Richard L. , Magin Richard L. , Webb Andrew G. , Briggs Richard W. , Gwan Go K. , Hulstaert Caesar E. , Miltenyi Stefan , Hauw The T. , De Leij Lou
Published: March 2007

Human lymphocytes were labeled with biotinylated anti‐lymphocyte‐directed monoclonal antibodies, to which streptavidin and subsequently biotinylated dextran‐magnetite particles were coupled. This labeling resulted in a strong and selective negative contrast enhancement of lymphocyte suspensions at 2.0 T, caused predominantly by the specific increase of R2 with a small but significant specific increase of R2. The R1 was found to decrease with increasing field strength. The immunolabeling procedure described here may be used for the selective signal depletion of target cells in MR imaging.
Improved efficiency in 2DFT magnetization‐prepared rapid gradient echo imaging: Application to abdominal imaging
Authors: Bampton Anna E. H. , Riederer Stephen J.
Published: March 2007

The incorporation of the phase offset multiplanar (Pomp) technique into breathheld magnetization‐prepared gradient echo imaging is discussed as a means for improving imaging efficiency without sacrificing resolution. contrast, or SNR improvement. The phase encoding order necessary to preserve the centric approach is described. When combined with interleaving, the Pomp technique enables four 256 × 256 imagesto be acquired in a 12‐s breathhold, doubling the efficiency of the original technique. This scan efficiency is compared with that of other TI‐weighted 2DFT methods.
Localized 13C NMR spectroscopy of myo‐inositol in the human brain in vivo
Authors: Gruetter Rolf , Rothman Douglas L. , Novotny Edward J. , Hulman Robert G.
Published: March 2007

Natural abundance 13C NMR spectra obtained from 144‐cm3volumes in the human brain contained well‐resolved resonances of myo‐inositol after 60 min of data accumulation. A mean concentration of 7.2 ± 0.5 pmol/g (±SE, n = 7) was calculated from the comparison with phantoms. 13C NMR spectroscopy thus provides a complementaryrole in the quantitation of metabolites also observed in the crowded 1H spectrum.
NMR studies of erythrocytes immobilized in agarose and alginate gels
Authors: Lundberg Peter , Berners‐Price Susan J. , Roy Sushmita , Kuchel Philip W.
Published: March 2007

31P and 13C NMR were used to study the energy metabolism in perfused, human erythrocytes. The erythrocytes were immobilized in agarose threads, Ca‐ or Ba‐alginate beads, and Ba‐alginate‐coated agarose threads. Erythrocytes were easily washed out from the agarose threads, but not from alginate‐containing gels. Various small molecules, such as hypophosphite, dimethyl methylphosphonate, and methylphosphonate, were taken up from the perfusion medium in a normal manner. In addition, the 2,3‐bisphosphoglycerate (2,3‐DPG) chemical shifts were sensitive to the oxygen partial pressure suggesting that O2 molecules were diffusing through the gel and modifying the binding of 2,3‐DPG to hemoglobin. A combination of inosine and pyruvate stimulated the synthesis of 2,3‐DPG. but only if inorganic phosphate was present in the perfusion medium. Inosine only resulted in a dramatic rise in the intracellular sugarphosphate concentrations. Furthermore, [2‐13C]glucose was converted to [2‐13C]lactate by immobilized cells at a rate which was comparable to that in a control suspension. In summary, immobilization in Ba‐alginate‐coated agarose threads was an efficient way of trapping human erythrocytes for whole cell NMR investigations. © 1992 Academic Press, Inc.
Measurement of brain perfusion by volume‐localized NMR spectroscopy using inversion of arterial water spins: Accounting for transit time and cross‐relaxation
Authors: Zhang Weiguo , Williams Donald S. , Detre John A. , Koretsky Alan P.
Published: March 2007

The theoretical model for perfusion measurement by NMR using arterial labeling of endogenous water is extended to include the effects of transit time and cross‐relaxation of tissue water with macromolecules. Water magnetization in rat brain is monitored using the STEAM method to simultaneously determine the transit time, magnetization transfer rate constant, and perfusion. The results show that the transit time in rat brain is quite short, and thus its effect on perfusion measurement is small. It is also demonstrated both theoretically and experimentally that the steady‐state effects of cross‐relaxation with macromolecules on perfusion measurement are accounted for by a proper control experiment. © 1992 Academic Press, Inc.
Effects of the interaction between ferric iron and L‐dopa melanin on T1 and T2 relaxation times determined by magnetic resonance imaging
Authors: Tosk Jeffrey M. , Holshouser Barbara A. , Aloia Roland C. , Hinshaw David B. , Hasso Anton N. , Macmurray James P. , Will A. Douglas , Bozzetti Louis P.
Published: March 2007

T1 and T2 relaxation times of agar phantoms containing L‐dopa melanin and Fe3+ were measured under MRI conditions. Fe3+ shortened T1 and T2 relaxation times. Melanin influenced relaxation times only in the presence of Fe3+; thus, contrast in MR images of the basal ganglia may depend upon levels of both paramagnetic iron and neuromelanin.
Design and evaluation of shielded gradient coils
Authors: Carlson J. W. , Derby K. A. , Hawryszko K. C. , Weideman M.
Published: March 2007

Techniques are described for the design of shielded gradient coils for superconducting MRI systems. These design methods are suited for constructing the most efficient gradient coil that meets a specified homogeneity requirement. Tradeoffs in coil design of efficiency with coil size and gap size are discussed. Residual eddy currents from coils constructed with a finite number of wires are calculated and give guidelines for the construction of efficient, whole‐body gradient coils.
Volume‐selective proton MRS in vertebral bodies
Authors: Schick Fritz , Bongers Hilmar , Jung Wulf‐Ingo , Skalej Martin , Lutz Otto , Claussen Claus D.
Published: March 2007

Volume‐selective 1H magnetic resonance spectra of small volume elements of (13 mm)3 positioned in lumbar vertebral bodies have been investigated in 15 healthy persons of different ages and sexes and in 11 patients with leukemia using double spin‐echo sequences. Signal intensities and positions of the spectral lines have been evaluated. Interindividual spectra of VOI located in the center of vertebral bodies, intraindividual spectra of central VOI in different vertebral bodies, and spectra of different localizations within the same vertebral body have been compared as well as spectra before and partly after cytostatic treatment in leukemia patients. Unexpected phenomena of the signal shapes have been found. The water signal distributions in healthy persons compared to patients after bone marrow transplantation show significant differences. The success of the cytostatic treatment in cases of leukemia is accompanied by an increase in the intensity of the lipid signals and a decrease in the water signals.
Pulsed saturation transfer contrast
Authors: Hu Bob S. , Conolly Steven M. , Wright Graham A. , Nishimura Dwight G. , Macovski Albert
Published: March 2007

In vivo 1H conventional NMR image contrast generation usually relies on the macroscopic T1 and T2 relaxation parameters of the tissues of interest. Recently cross‐relaxation related image contrast has been reported by Wolff and Balaban in animal models. Due primarily to the broad lineshape of the intended saturation spin pool and the use of off‐resonance irradiation, high specific absorption rate and an auxiliary RF amplifier have been necessary to produce these images. The relatively long spin‐lattice relaxation property of this spin pool, however, suggests the use of pulse methods to achieve saturation. In this paper, we show that short‐T2 spin pools can be selectively saturated with short intense RF pulses. Cross‐relaxation time constants can be measured using the technique of saturation recovery. In vivo magnetization‐transfer‐weighted images can be produced using pulses on commercial whole‐body imagers without additional hardware.
Partial RF echo‐planar imaging with the FAISE method. II. Contrast equivalence with spin‐echo sequences
Authors: Melki Philippe S. , Jolesz Ferenc A. , Mulkern Robert V.
Published: March 2007

The fast acquisition interleaved spin‐echo (FAISE) sequence and its dual‐echo version (DEFAISE) are partial RF echo‐planar methods which utilize a specific phase‐encode reordering algorithm to manipulate T2 contrast via an operator‐controlled pseudo‐echo time, pTE. The repetition time, TR, between successive applications of the Carr‐Purcell‐ Meiboom‐Gill (CPMG) echo trains used in FAISE may be reduced to introduce T1 weighting. To quantitatively determine the extent to which FAISE T1 and T2 contrast characteristics agree with spin‐echo methods, signal intensities from FAISE acquisitions were compared with signal intensities from equivalent CPMG acquisitions. In phantoms and in human heads, the contrast Characteristics of FAISE are found to be highly correlated with that obtained with equivalent CPMG sequences. However, conventional SE sequences generally utilize longer echo spacings than employed with FAISE/CPMG. Thus, echo spacing‐dependent mechanisms such as spin‐spin coupling and magnetic susceptibility lead to some differences in contrast between conventional SE and FAISE. Finally, FAISE appears to be more sensitive to magnetization transfer effects than conventional SE sequences since more off‐resonance irradiation is applied to individual slices during multislice acquisitions.
Detection and assignment of the glucose signal in 1h nmr difference spectra of the human brain
Authors: Gruetter Rolf , Rothman Douglas L. , Novotny Edward J. , Shulman Gerald I. , Prichard James W. , Shulman Robert G.
Published: March 2007

The difference between 1H NMR spectra obtained during eu‐ and hyperglycemia exhibited well‐resolved glucose peaks between 3 and 4 ppm as demonstrated by comparison with solution spectra. Estimated increases were consistent with recent 13C NMR quantitations of intracerebral glucose. Difference spectra were measured in 36‐ml volumes from the human brain every 3 min.
Sensitivity ofin vivomrs of the n‐δ proton in proximal histidine of deoxymyoglobin
Authors: Wang Zhiyue , Wang Dah‐Jyuu , Noyszewski Elizabeth A. , Bogdan Andrew R. , Haselgrove John C. , Reddy Ravinder , Zimmerman Robert A. , Leigh John S.
Published: March 2007

The sensitivity ofin vivoMRS of the N‐δ proton of the proximal histidine of deoxymyoglobin in human skeletal muscles is discussed. Longitudinal relaxation time T1of this deoxymyoglobin signal was measured in cuffed human forearms at 1.5 T and found to be 9.9 ms. Deoxymyoglobin spectra can be obtained from a forearm in seconds. The detection sensitivity of deoxymyoglobin in fully ischemic skeletal muscles and that of31P MRS of PCr in normal resting muscles are compared.
The Loss of Small Objects in Variable TE Imaging: Implications for FSE, RARE, and EPI
Authors: Constable R.Todd , Gore John C.
Published: March 2007

The importance to MR image quality of the order of acquisition of different phaseencoded views with sequences that have variable TR and TE has been recently reported. It has been shown that the effective point spread function (PSF) may be manipulated by varying TE or TR, or both, with each phase‐encoding step. This paper explores the behavior of the PSF in a variable TE sequence and its dependence on both imaging and tissue parameters. It is shown that the PSF is different for each tissue type and that its effect on tissue contrast is a function of both the shape and size of the structure. The important problem of signal loss from small objects that arises when the effective PSF is broad and the difficulty in detecting this phenomenon in practical MR images is illustrated. It is shown that the PSF can produce significant blurring and loss of object contrast in fast spin‐echo images but that this blurring may be not be obvious in practice because the noise is unaffected by the PSF. It is also shown that the signal from small lesions with short T2 can easily be lost through this blurring mechanism. The importance of signal loss from small objects and its implication for the clinical use of such sequences as fast spinecho or rapid acquisition relaxation‐enhanced and echo planar imaging is stressed.© 1992 Academic Press,Inc.
Atraumatic quantitation of cerebral perfusion in cats by 19f magnetic resonance imaging
Authors: Branch Craig A. , Ewing James R. , Helpern J. A. , Ordidge R. J. , Butt Shazad , Welch K. M. A.
Published: March 2007

We have noninvasively produced low‐resolution, quantitative nuclear magnetic resonance images of cerebral blood flow in 2‐ml voxels in eight cats. Typical signal‐to‐noise of 4 to 1 was obtained in cerebral voxels in 16.5‐s epochs. Mean flow during normocapnia (paCO2 = 39 ± 4 mm Hg) and hypercapnia (paCO2 = 62 ± 4 mm Hg) was 53 ± 20 ml/100 gmin and 140 ± 36 ml/100 g‐min, respectively. Fast flows in normocapnia were 94 ± 13 and 182 ± 39 ml/100 g‐min in hypercapnia. These results suggest that an atraumatic quantitative imaging assessment of cerebral perfusion may be possible in humans using these techniques.© 1992 Academic Press,Inc.
1 /T1p and Low‐Field 1 / T1 of Tissue Water Protons Arise from Magnetization Transfer to Macromolecular Solid‐State Broadened Lines
Authors: Brown Rodney D. , Koenig Seymour H.
Published: March 2007

We argue that, for solutions of immobilized protein and for tissue, the dependence of 1 / T1 of solvent protons on B0 at low fields and 1 / T1p on B1 for all B0 are both manifestations of the same underlying phenomena: magnetization transfer between mobile water protons and solid‐state broadened protein proton levels. Broadening causes rapid mixing of spin orientation within the transverse plane, at all B0, unless B1 is greater than the protein internal field; this affects 1 / T1p of solvent protons by magnetization transfer. Similarly, decreasing B0 below the internal field mixes all orientations of magnetization, which affects the solvent proton low‐field 1 / T1 and high‐field 1 / T2.© 1992 Academic Press,Inc.
Projection Reconstruction Techniques for Reduction of Motion Effects in MRI
Authors: Glover G. H. , Pauly J. M.
Published: March 2007

Projection reconstruction (PR) techniques are shown to have intrinsic advantages over spin‐warp (2DFT) methods with respect to diminished artifacts from respiratory motion. The benefits result from (1) portrayal of artifacts as radial streaks, with the amplitude smallest near the moving elements; (2) streak deployment perpendicular to the direction of motion of moving elements and often residing outside the anatomic boundaries of the subject; (3) inherent signal averaging of low spatial frequencies from oversampling of central k‐space data. In addition, respiratory‐ordered view angle (ROVA) acquisition is found to diminish residual streaking significantly by reducing interview inconsistencies. Comparisons of 2DFT and PR acquisitions are made with and without ROVA. Reconstructions from magnitude‐only projections are found to have increased streaks from motion‐induced phase shifts.© 1992 Academic Press,Inc.
Magnetic Resonance Neurography
Authors: Howe F. A. , Filler A. G. , Bell B. A. , Griffiths J. R.
Published: March 2007

We have made cross‐sectional image “neurograms” in which peripheral nerve has a greater signal intensity than that of other tissue. Neurographic images of the rabbit forelimb were obtained using a spin‐echo magnetic resonance imaging (MRI) technique that combines fat suppression and diffusion weighting. After fat suppression the nerve shows up in relative isolation and is brighter than the surrounding tissue due to its longer T2 relaxation time of ≈︁ 50 ms compared to ≈︁ 27 ms for muscle. The addition of pulsed gradients for diffusion weighting of the MR signal further enhances the intensity of the nerve signal relative to that of surrounding muscle tissue. The greater diffusional anisotropy of nerve tissue (D∥/D∥ = 3.1) compared to that of muscle (D∥/D∥ = 1.9) allows further enhancement of the nerve by a subtraction of two diffusion‐weighted images, one with the gradients oriented parallel and one with the gradients oriented perpendicular to the nerve orientation. We show that by manipulation of the MRI parameters, either echo time or pulsed gradient strength, the nerves can be made to show up as the most intense feature. This verifies the feasibility of generating three‐dimensional “neurographic” images, analogous to angiograms, but which demonstrate the peripheral nerve tracts in apparent isolation.© 1992 Academic Press,Inc.
A three‐dimensional spin‐echo or inversion pulse
Authors: Pauly John M. , Hu Bob S. , Wang Samuel J. , Nishimura Dwight G. , Macovski Albert
Published: March 2007

In theory, multidimensional pulses can be designed to be selective in any number of dimensions. In practice, available gradient power has enforced a limit to two dimensions. We show here that three‐dimensional π pulses are feasible on commercial imaging machines provided that the range of offresonance frequencies are limited.
Determination of saturation factors in 31P NMR spectra of the developing human brain
Authors: Gruetter Rolf , Fusch Christoph , Martin Ernst , Boesch Chris
Published: March 2007

In order to assess the influence of longitudinal relaxation on previously reported variations in 31P NMR signals during brain development, we used an accelerated two‐point technique to determine T1 at 2.35 Tesla in 8 min. Comparison between 10 normal neonates (age range 37–46 weeks postconception) and 10 healthy infants (age range 80–157 weeks postconception) indicated that T1 does not vary substantially during the first year of life, except in the phosphomonoester (PME) region of the spectra. T1 of total PME decreases with age which we could explain by its variable multicomponent nature: The signal from (unresolved) components at the downfield shoulder of PME (attributed mostly to phosphorylethanolamine at 6.72 ppm) with a T1 of at least 6.4 s decreases with age relative to contributions from other phosphomonoester compounds resonating predominantly at the upfield side of the peak (approximately 6.3 ppm), with T1 below 2.9 s. Because the T1 heterogeneity of PME may depend on its relative composition, quantitative 31P NMR spectroscopy may require an assessment of the influence of longitudinal relaxation on the signal amplitudes in each measurement.
The origin of biexponential T2 relaxation in muscle water
Authors: Cole William C. , Leblanc Adrian D. , Jhingran Satish G.
Published: March 2007

Two theories have been proposed to explain the multiexponential transverse relaxation of muscle water protons: “anatomical” and “chemical” compartmentation. In an attempt to obtain evidence to support one or the other of these two theories, interstitial and intracellular macromolecular preparations were studied and compared with rat muscle tissue by proton NMR transverse relaxation (T2) measurements. All macromolecule preparations displayed monoexponential T2 decay. Membrane alteration with DMSO/glycerin did not eliminate the biexponential T2 decay of muscle tissue. Maceration converted biexponential T2 decay of muscle tissue to single exponential decay. It is concluded that the observed two component exponential T2 decay of muscle represents anatomical compartmentation of tissue water, probably intracellular versus extracellular.
Functional mapping of the human visual cortex at 4 and 1.5 tesla using deoxygenation contrast EPI
Authors: Turner R. , Jezzard P. , Wen H. , Kwong K. K. , Le Bihan D. , Zeffiro T. , Balaban R. S.
Published: March 2007

The effects of photic stimulation on the visual cortex of human brain were studied by means of gradient‐echo echo‐planar imaging (EPI). Whole‐body 4 and 1.5 T MRI systems, equipped with a small z axis head gradient coil, were used. Variations of image intensity of up to 28% at 4 T, and up to 7% at 1.5 T, were observed in primary visual cortex, corresponding to an increase of blood oxygenation in regions of increased neural activity. The larger effects at 4 T are due to the increased importance of the susceptibility difference between deoxy‐genated and oxygenated blood at high fields.
Consistent projection reconstruction (CPR) techniques for MRI
Authors: Glover Gary H. , Noll Douglas C.
Published: March 2007

Motion of the subject causes inconsistencies In MR scan data which in turn produce streaks in projection reconstruction (PR) scans or ghosts in 2DFT imaging. It is shown that a data manifold consistent with a static object may be extracted from input scan data by applying consistency criteria based on moment or Fourier expansions of the object's projections. The criteria limit the spectrum of azimuthal variation relative to the radial moments or radial spectral components, and their application diminishes k‐space inconsistencies from motion or flow by discarding unallowed expansion terms. This consistent projection reconstruction (CPR) algorithm was applied to the reconstruction of projection data from a moving phantom and from human abdominal sections, and in each case provided reduced motion streaks relative to conventional reconstructions. In addition, CPR was found to be effective when used with 2DFT data by resampling the Cartesian data as radial projections, but to a lesser extent.