摘要:

AbstractIntradermal injection (1 × 106cells) of rat mammary adenocarcinoma (13762A) was made in the back skin in 12 rats. Tumor growth and characterization was followed with nuclear magnetic resonance imaging (NMRI) in 9 rats (3 rats died before completion of the study) at 3, 4, and 5 weeks after injection, using spin echo, inversion‐recovery, and calculatedT1techniques. Three rats were sacrificed after each of the three imaging periods for histological studies designed to distinguish solid tumor mass from necrosis. Qualitative NMR imagingT1values increased as the tumors increased in size as evidenced by a progressive decrease in image intensity compared to the surrounding tissues on theT1weighted images. CalculatedT1values also increased as the tumors aged (Week 3 = 0.3 ± 0.11; Week 4 = 0.45 ± 0.07; Week 5 = 0.42 ± 0.03). Planimetry of tumor areas on histological sections showed that as tumors increased in size, the ratio of necrotic area to solid tumor area increased (Week 3 = 0.3 ± 0.11; Week 4 = 0.45 ± 0.07; Week 5 = 0.51 ± 0.05). These findings indicate that the progressive increase inT1observed on NMR images may be secondary to the increasing degree of necrosis, with a resultant change in water content and state. Thus, the range ofT1values observed in tumors of similar type may be due to change in tumor physiology and anatomy as tumor growth progresses. In conclusion, careful correlation of histological data with NMR image data is necessary before NMR imaging can be used to provide reliable noninvasive histological information concerning tumor pathology. © 1986 Academic P

ISSN:0740-3194    

DOI:10.1002/mrm.1910030102

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

年代:1986

数据来源: WILEY

摘要:

AbstractWe have measured the percent change in 2, 3‐diphosphoglycerate (DPG) concentration in cord blood erythrocytes and adult erythrocytes during incubation at 37°C using31P nuclear magnetic resonance spectroscopy. DPG concentrations remained unchanged during the first 4.0 ± 0.9 h (mean + SD) for cord blood erythrocytes and 6.0 ± 1.0 h for adult blood erythrocytes. After this plateau phase, cord blood and adult erythrocyte DPG concentrations decreased at a rate of 11.6 ± 0.4 and 11.4 ± 0.5% of the baseline DPG concentration per hour, respectively. There was no statistically significant difference in the percent rate of DPG degradation when comparing cord blood erythrocytes to adult erythrocytes during either the plateau phase or the decay phase. Starting at the onset of the decay phase, the neonate 3‐P DPG resonance shifted downfield at a rate of 0.03 ± 0.006 ppm per hour; the adult 3‐P DPG resonance shifted downfield at a rate of 0.02 ± 0.003 ppm per hour. © 1986 Academ

ISSN:0740-3194    

DOI:10.1002/mrm.1910030103

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

年代:1986

数据来源: WILEY

摘要:

AbstractA new technique of real‐value representation in inversion‐recovery (IR) imaging by use of a phase‐correction method is proposed. In this scheme, negative magnetizations at the beginning of the inversion point (T1⋍ 0) are correctly represented as negative values rather than positive. By use of this new scheme, a consistent IR image set as a function of several inversion times (T1) can be obtained. The latter, i. e., consistent image set which represents the real value ofT1weighted images at several inversion times is important in the search for tumors and abnormalities since the inversion time (T1) in the pulse sequence strongly affectsT1contrast. © 1986 Academic Pr

ISSN:0740-3194    

DOI:10.1002/mrm.1910030104

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

年代:1986

数据来源: WILEY

摘要:

AbstractThis paper describes an experimental protocol designed to optimize13C NMR spectra from the liver of the living anesthetized rat at 1.9 T. The protocol involves the use of a Helmholtz NMR coil which is positioned around the liver after surgical exposure.1H decoupling is facilitated by double tuning this coil to both the1H and the13C frequencies. The protocol was shown to be suitable for studying the hepatic metabolism of13C‐labeled substratesin vivoby investigating the metabolism of [3‐13C] alanine. Labeled glucose, glutamate, glutamine, and aspartate were formed and detected by13C NMRin vivoin this experiment. The labeling patterns in these metabolites provided evidence that the major flow of alanine carbon into the Krebs cycle is via the pyruvate carboxylase reaction rather than through pyruvate dehydrogenase. © 1986 Academic Press,

ISSN:0740-3194    

DOI:10.1002/mrm.1910030105

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

年代:1986

数据来源: WILEY

摘要:

AbstractMR image synthesis has previously been developed as a means of retrospectively optimizing contrast of arbitrary materials in MR images. The first step of this process is to form computedN(H),T1, andT2images from source images acquired at a variety of echo delay and repetion times. The second step is to take these computed images, along with operatorselected timing parameters, and mathematically generate a synthesized image. Computation is carried out pixel by pixel according to the equation describing the chosen pulse sequence. This paper presents a study of design considerations for a digital image processor capable of rapidly performing the second step, the actual synthesis. In this work the computations inherent to image synthesis are identified, and the feasibility of performing them in highspeed hardware examined. An analysis of the imprecision due to bit‐limited calculations shows that an error bound of 0.4% is possible with a 16‐bit processor design. A method is described which uses a commercially available image processor by which images can be synthesized according to any of the standard pulse sequences in less than 600 ms. © 1986 Academic Press,

ISSN:0740-3194    

DOI:10.1002/mrm.1910030106

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

年代:1986

数据来源: WILEY

摘要:

AbstractThe energetics of human muscle have been investigatedin vivoduring and after fatiguing aerobic, dynamic exercise. Changes in cytoplasmic pH and concentrations of phosphocreatine, ATP andPiwere followed using31P nuclear magnetic resonance spectroscopy. ATP was significantly depleted in 6 out of 12 experiments and in these 6 experiments decreased to 55 ± 5% of the pre‐exercise concentration. Depleted muscle had a lower phosphocreatine concentration (17 ± 5% of resting value) and lower pH (6.12 ± 0.04) than fatigued muscle in which ATP loss was not observed (26 ± 5% for phosphocreatine and 6.37 ± 0.09 for pH). The free energy of hydrolysis of ATP was not significantly different in the two groups and was also similar in exhausted and nonexhausted muscle. Loss of ATP was associated with altered recovery of the muscle: [phosphocreatine], [Pi], and pH returned more slowly to their pre‐exercise values and the initial rate of oxidative phosphorylation was diminished. The restitution of [ATP]to its pre‐exercise value was much slower than that of the other metabolites. © 1986 Academic

ISSN:0740-3194    

DOI:10.1002/mrm.1910030107

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

年代:1986

数据来源: WILEY

摘要:

AbstractHigh‐order radiofrequency transmitter coils are described that permit, in the context of NMR imaging, a knowledgeable trade‐off between coil complexity and the degree of inhomogeneity over a specified volume of space. A mathematical formulation of high‐order coils is developed for an axially symmetric polarizing de field and transverse rf field. The field is created by a number of longitudinal current filaments with equal angular separations on the wall of a cylinder. In its most general form, each current can be independently specified. Circularly or linearly polarized fields can be created. Quadrature and saddleshaped coils emerge as special cases of the general formulation. The development has been tested experimentally and good agreement found. High‐order coils can also be used as receivers, permitting more equal weighting of the sensitivities of each pixel. © 1986 Academic Pr

ISSN:0740-3194    

DOI:10.1002/mrm.1910030108

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

年代:1986

数据来源: WILEY

摘要:

AbstractA simplified model relating signal intensity in an MR image to spin‐lattice relaxation time (T1), repetition time (TR), number of signal averages and the average tip angle (α) of the protons within the slice has been developed. This model has been used to select the optimal repetition times of two spin‐echo images for a fixed total imaging time to maximize signal to noise in calculatedT1images. Theoretical predictions ofT1are virtually identical to spectroscopically measured values, and the relative noise (δT1) inT1images calculated from two measured spin‐echo images is in good agreement with the theoretically predicted values of δT1/T1. This model predicts that: (a) for aT1of approximately 500 ms, the leastT1image noise is obtained with one of the spin‐echo images collected with aTRof 400–500 ms. The longer theTRof the other spin‐echo image, the lower theT1image noise, but past aTRof approximately 1400 ms,T1image signal/noise is optimized for the same total imaging time by increasing the number of averages in the shorterTRspin‐echo image rather than increasing theTRof the second spin‐echo image. (b) The error is reduced and the optimumTR1is reduced asαis increased from 63 to 90°. (c) For a range ofT1, optimal selection ofTR1andTR2based on an intermediate value ofT1, results in relatively little increase over optimal values in δT1/T1for the entireT1range. © 19

ISSN:0740-3194    

DOI:10.1002/mrm.1910030109

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

年代:1986

数据来源: WILEY

摘要:

AbstractA new type of loop‐gap resonator, which because of its topology is called a “sectorial resonator,” is described in considerable analytical detail. It was used for31P NMR of the livers of two human adult normal volunteers. An effective strategy for suppression of signals from surface tissue was developed. Depth selection was achieved using a separate excitation coil, permitting a reasonable degree of control of the shape of the sensitive region by adjustment of the dimensions of the excitation coil and of the type of pulse delivered. In addition a new principle for cancellation is described: the topology of the sectorial resonator leads to cancellation signals from tissue masses at the two openings of the structure. Using a phase‐altenated repeated 90° FID pulse sequence, good spectra were achieved in 2.5 min that are free from contamination by the phosphocreatine peak. © 1986 Academic P

ISSN:0740-3194    

DOI:10.1002/mrm.1910030110

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

年代:1986

数据来源: WILEY

摘要:

AbstractThe water component of an NMR image is suppressed by selectively detecting only those protons which are coupled to other protons. Selectivity is obtained by polarization transfer between the coupled spins. Since spin‐spin coupling is independent of magnetic field strength, the suppression obtainable by polarization transfer is independent of chemical shift. Consequently, this technique does not require extremely homogeneous magnetic field for the separation of water and lipid signals. In addition, water suppression by this technique is independent ofT1andT2. Suppression of the water signal intensity has been observed experimentally to be as high as a factor of 100. Suppression is limited only by instrumental imperfections. © 1986 Academic Press, I

ISSN:0740-3194    

DOI:10.1002/mrm.1910030111

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

年代:1986

数据来源: WILEY