摘要:

AbstractThe superparamagnetic particle dextran magnetite was studied as a liver tumor contrast agent for magnetic resonance imaging (MRI). The effects of dextran magnetite on the longitudinal (T1) and transverse (T2) relaxation times in liver, spleen, and an implanted rat liver tumor were measured at 0.47 T (IBM/Bruker PC‐20 relaxometer) over the dose range of 23 to 69 μmol Fe/kg. Dextran magnetite substantially reduced theT2of the liver and spleen, but not of the tumor, thereby providing a basis for improved tumor imaging. TheT1of the tumor was not affected following injection of dextran magnetite in the dose range studied, while the spleenT1was reduced substantially more than theT1of the liver. Histological studies using the iron reaction for Prussian blue clearly showed dextran magnetite in the liver and spleen, but not in the tumor. While dextran magnetite was sequestered in macrophages in both liver and spleen, the distribution in the liver was more diffuse (70 μm average particle separation) than that in the spleen (25 μm separation). The lack of aT1effect in the liver is consistent with the fact that a majority of the water in the tissue cannot diffuse to the relaxational centers on the time scale of the liver's intrinsicT1(280 ms). In the spleen, however, the dextran magnetite is more densely packed in the red pulp allowing a significant fraction of the water to be relaxed by aT1mechanism. Spin‐echo images of the implanted tumor (mammary adenocarcinoma, R3230AC) in the livers of Fischer 344 rats were obtained at 0.50 T (Siemens Magnetom). The tumor‐to‐liver contrast was improved for bothT1andT2‐weighted spin‐echo images after intravenous injection of the dextran magnetite contrast agent. The contrast determined from these images agreed with that predicted by the measuredT1and theT2(Hahn spin‐echo) values. In addition, gradient‐echoT2‐weighted images with good contrast were obtained in a much shorter imaging time than was needed forT2‐weighted spin‐echo images. These results demonstrate that the MRI contrast enhancement observed with dextran magnetite is based on its selective uptake and distribution in the macrophages in the liver and spleen and that this agent has substantial potential as a superparamagnetic MR contrast agent. ©

ISSN:0740-3194    

DOI:10.1002/mrm.1910200102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractAn efficient method for measuringin vivo13C NMR spectra of tumors has been developed and employed to monitor glucose metabolism in radiation‐induced fibrosarcomas (RIF‐1) subcutaneously implanted in C3H/HeN mice. [1‐13C]Glucose was injected directly into the tumors at a dose of 1 g/kg body wt. Spectra were obtained with a Bruker AM 360‐WB spectrometer (8.4 T/8.9 cm bore) employing a homebuilt probe equipped with a four‐turn solenoidal coil (1.5 cm outer diameter) for detection of13C signals and a Helmholtz coil (two 3‐cm turns separated by a 3‐cm gap, oriented orthogonally to the13C coil) for1H decoupling. In addition to the natural abundance13C resonances of the tumors, signals were detected from the α‐and β‐anomers of labeled glucose. Within 15 min following injection of labeled glucose [3‐13C]lactate and [3‐13C]alanine were detected. Lactate labeling approached steady state levels within about 50 min after glucose injection; in contrast, alanine labeling increased continuously over the duration of the experiment (70 min). Sixty minutes after glucose injection, the ratio of the intensity of [3‐13C]lactate to the principal lipid methylene resonance (30 ppm from external tetramethylsilane), which served as an internal intensity reference, was correlated with tumor size, whereas the corresponding ratio of the [3‐13C] alanine resonance was not. Labeling of glutamate was below the level of detection in thein vivospectra; however, labeling of C4‐glutamate at a level approximately 50‐fold lower than the level of [3‐13C]lactate was detected in perchloric acid extracts. Incorporation of13C label into C2‐and C3‐glutamate and C2‐lactate was al

ISSN:0740-3194    

DOI:10.1002/mrm.1910200103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractA method is presented by which volume selectivein vivo1H spectra of two different voxels can be acquired in an interlaced mode using PRESS or STEAM spectroscopy. Spatially tilted gradients are employed for voxel definition so as to avoid mutual saturation. Independent volume selective shimming of the voxels is possible. Two spectra of volumes as small as (1.5 cm)3can be acquired from human brain within 14 min even from very disadvantageous locatins close to air‐bone interfaces. © 1991 Academic Press, I

ISSN:0740-3194    

DOI:10.1002/mrm.1910200104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractCalculations and experiments that provide support for our previously stated theorem are presented: If two coils simultaneously receiving magnetic resonance signals from the same anatomic region exhibit zero mutual inductance, there can be no correlation of the noise. It is shown that correlation does not exist even in the presence of mutual inductance unless the two signal paths have amplifiers prior to signal combination. It is further found that in the presence of mutual inductance with ideal amplifiers (0 dB noise figure) in the two signal paths, there is no correlation of noise. In order to satisfy the condition of zero mutual inductance, it may be necessary to employ a decoupling circuit external to the body. A novel coil assembly, which was used in the experiments, places a single‐turn surface coil in the median plane between the two loops of a counter rotating current coil. The signal‐to‐noise ratio can be improved by combining signals. This is in analogy to quadrature receiving coils, where the mutual inductance is zero because vector reception fields are perpendicular. In the present geometry, vector reception fields are collinear, but are parallel and antiparallel on the two sides of the coil assembly, resulting in zero mutual inductance. © 1991 Academic Pres

ISSN:0740-3194    

DOI:10.1002/mrm.1910200105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractIn this report we describe the three factors that need to be measured when quantitating an edited resonance relative to an internal standard using a surface coil. These factors are necessary by virtue of the water, fat suppressing, and localization schemes used in studying a1H metabolite. First, use of semi‐selective pulses requires amplitude correction of the edited and reference resonances. Second, use of a single surface coil results in different sensitive volumes for different resonances due to the inhomogeneous B1and therefore requires separate acquisition of the resonances. Third, editing pulses alter the sensitive volumes and this correction must be made internally by applying the same editing pulse to the reference resonance. A rationalization of this correction is given in terms of rotation operators. We apply these corrections to quantitate edited lactate relative to total creatine in a MnCl2‐doped phantom and find 91% rather than 145% of known concentration. In human skeletal musclein vivoafter exhaustive exercise, we measured the lactate after exercise and found it to be 27.2 mMin two experiments, in reasonable agreement with literature values for the given exercise protocol. © 1991 Academic Press,

ISSN:0740-3194    

DOI:10.1002/mrm.1910200106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractWe have madein vivo1H NMR measurements of the time course of pH and lactate in human skeletal muscle after exercise. Spectra were obtained in a 4.7‐T 30 cm bore Bruker Biospec spectrometer with a 2.5‐cm diameter single surface coil. pH was determined from the shift of the endogenous carnosine H‐C2peak while lactate concentrations were determined by comparison with endogenous total creatine, taken to be 28.5 mM/ kg wet wt. Fitting the data shows that the exponential decay of lactate (‐0.094 ± 0.014 min‐1,t1/2 = 10.6 min) is slower than that of pH (‐0.147 ± 0.015 min‐1,t1/2= 4.7 min),n= 7 with two different volunteers. These values are significantly different withP<0.0005. Relaxation times of lactate and creatine were also measured for lactate quantitation: creatine Tl. 1.23 ± 12 s. T2, 136.2 ± 26.4 ms (both in resting human muscle); lactate Tl (in postmortem rabbit muscle), 1.0 ± 11 s and T2, 80 ms (in postexercise human muscle). At the end of intense exercise, the lactate level reached was 25.3 ± 4.0 mMand the average pH drop was 1.0 pH unit. We discuss the implicaions of these measurements in conjunction with existing data on other sources of H+flux, phosphocreatine resynthesis, H+transport, and contribution of inorganic phosphate to buffering. © 1991

ISSN:0740-3194    

DOI:10.1002/mrm.1910200107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractMissing pulse steady state free precession (MP‐SSFP), an extension of steady state free precession (SSFP), was evaluated for its ability to measure slow fluid flows. In experiments using flow phantoms, the MP‐SSFP signal was sensitive to fluid velocities in the millimeters per second range. Isolated perfused rabbit kidneys were then used to determine if MP‐SSFP could measure perfusion in a biological tissue. The signal intensities in the different anatomical regions of the kidney were observed to be related to the total flow to the organ. Furthermore, increasing the flow sensitivity of the pulse sequence by increasing the gradient strength resulted in decreases in the image signal intensity. The MP‐SSFP signal was more sensitive to flow in the medulla than in the cortex. This can be related to slow flow sensitivity of MP‐SSFP and the known differences in velocity profiles between these two regions. These results suggest that MP‐SSFP may be a powerful tool for the noninvasive measurement of slow fluid flows in different regions of the kidney. © 1991 Academi

ISSN:0740-3194    

DOI:10.1002/mrm.1910200108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractA Carr‐Purcell‐Meiboom‐Gill imaging sequence consisting of 128 echoes is used to extract transverse magnetization decay curves (TDCs) at 1.9 T from 1.7 × 1.7 × 5‐mm3voxels within the cortex, outer medulla, and inner medulla of perfused rabbit kidneys. The spatially localized TDCs within each tissue type are found to be better approximated by biexponential, as opposed to monoexponential, functions. The biexponential parameters characterizing the TDCs demonstrate an improved degree of tissue specificity over that available from monoexponential analyses. The fraction of the quickly relaxing TDC component and the relaxation rate of this component are observed to decrease from cortex to inner medulla. A two‐site exchange analysis is used to convert biexponential TDC parameters into water volume fractions and exchange rates. The exchange rates between the fast and slowly relaxing pools increased from cortex to inner medulla. All exchange rates were less than 1.5 Hz, indicating a relatively slow water exchange process. The imaging methods and subsequent analyses offer the potential to generate unconventional MR images with tissue contrast dependent upon water compartmentation and exchange. © 1991 Academi

ISSN:0740-3194    

DOI:10.1002/mrm.1910200109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractPulsed gradient diffusion‐weighted spin‐echo images (7 to 11 gradient strengths) were obtained in a coronal slice through the midbrain for five normal adult white rats before and after sacrifice in a 2‐T CSI system with air temperature control. The pulse sequence was cardiac gated and respiratory synchronized in order to minimize motion artifacts (Tr>2 s, Te ‐ 30 ms). Diffusion coefficients reflecting several tissue compartments (D*) in brain and muscle were calculated and referenced to simultaneously imaged tubes of water. In the living animals, brain cortical matter had a value ofD*= (0.82 ± 0.02) × 103mm2/s, deeper brain regions had a value ofD*= (0.73 ± 0.02) × 10‐3mm2/s, and the muscle had a value ofD*= (1.4 ± 0.1) × 103mm2/s. Postmortem the values in brain dropped by approximately 30%, while remaining constant in muscle. Signal intensity in the spin‐echo images for muscle tissue rose by 50% over a 1‐ to 2‐h interval after sacrifice while that of brain tissue remained relatively stable. © 19

ISSN:0740-3194    

DOI:10.1002/mrm.1910200110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractIn vivo31P nuclear magnetic resonance (NMR) spectroscopy provides unique opportunities to study the biochemistry of an organ within the intact animal in a totally noninvasive way. We have usedin vivoandin vitro31P NMR spectroscopy to study steady state changes in the major phosphorus‐containing metabolites of the rat liver in control and chronically ethanol‐treated rats. Chronic (4 month) ethanol treatment caused a statistically significant increase in the inorganic phosphate and phosphodiester resonances of rat liver inin vivo31P NMR spectra relative to pair‐fed control rats. Phosphomonoester and adenosine 5'‐triphosphate resonances, as well as intracellular pH, were not appreciably altered. The effects of chronic ethanol treatment were particularly apparent in the response of the liver to a metabolic challenge of glycerol. Glycerol is phosphorylated almost exclusively in the liver and metabolized predominately via glycolysis and gluconeogenesis. Ourin vivo31P NMR results after administration of glycerol showed a significant increase in the phosphomonoester resonance in the liver of chromic ethanol‐treated rats but not for their pair fed controls.In vitro31P NMR studies of perchloric acid extracts of liver showed that the increase was due to an accumulation of sn‐glycerol 3‐phosphate. This effect is due to the NAD+‐dependent glycerol 3‐phosphate dehydrogenase step being inhibited in the chronic ethanol‐treated rats. This glycerol test may be useful in assessing the ability of the liver to rapidly regenerate NAD+in situand may be a more sensitive indicator of redox imbalance than steady state ratios of redox pairs (e. g., lactate /pyruvate). © 1991

ISSN:0740-3194    

DOI:10.1002/mrm.1910200111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY