摘要:

AbstractA general mathematical description of depth pulse sequences in terms of rotation matrices permits a single matrix, known as a cycle matrix, to be written down for each phase‐cycled pulse in the overall sequence, such that the result for the total phase‐cycled sequence is the product of the individual cycle matrices. It is straightforward to include the effect of the tilted rf axis off resonance and obtain exact solutions. The two types of phase‐cycled pulse used in a depth pulse scheme are 2θ[±x] and 2θ[±x, ± y]and for the general off‐resonance case, four of the off‐diagonal elements in the 2θ[±x] cycle matrix, and all of the off‐diagonal elements in the 2θ[±x, ± y]cycle matrix, are zero. These simplifications enable important improvements of depth pulse schemes for the elimination of high‐flux signals, the reduction of signals from sample regions experiencing pulse angles differing from 90°, and the avoidance of deletrious off‐resonance effects such as the production of dispersion signals. In all cases, the dependence of signal intensity off resonance can be easily and exactly calculated. There are important applicati

ISSN:0740-3194    

DOI:10.1002/mrm.1910020202

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

年代:1985

数据来源: WILEY

摘要:

AbstractWe have developed a noninvasive method with general applicability for measuring intracellular oxygen using the spin label TEMPOL (2, 2, 6, 6‐tetramethypiperidine‐N‐oxyl‐4‐ol) which has superhyperfine structure in its electron spin resonance spectra that is broadened in the presence of oxygen. This broadening is linear over a range of 1 to 6 ppm oxygen which covers the important physiological range of oxygen concentration. Viscosity, TEMPOL concentration, and instrument modulation intensity also can affect superhyperfine structure but the contributions from these effects can be determined. The TEMPOL distributes equally into the intra‐and extracellular compartments but its intracellular signal can be studied selectively by addition of transition metal ions such as potassium ferricyanide and potassium tris (oxalato)chromiate, which broaden away the signal from extracellular TEMPOL and do not cross the cell membrane to affect the intracellular TEMPOL Results with a cell culture line (mouse thymus‐bone marrow) indicate that under our experimental conditions these cells may maintain an average intracellular oxygen concentration lower than the extracellular oxygen concentration, and that there is not a constant relationship between extracellular and intracellular oxygen c

ISSN:0740-3194    

DOI:10.1002/mrm.1910020203

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

年代:1985

数据来源: WILEY

摘要:

AbstractCharacterization of tissue by pulsed nuclear magnetic resonance spectrometry opened a new area of research. The differences in the NMR parametersT1andT2of normal and malignant tissues constitute the basis for their distinction by pulsed NMR spectrometry and also by NMR imagingin vivo. The present studies were undertaken to correlate the role of constituent histological elements encountered in various maligancy‐associated changes andT1variations and are based on evaluation of samples taken from surgically resected specimens of carcinoma of the esophagus, comprising the uninvolved portions of the esophagus and the gastric end on gross examination. The uninvolved and involved regions showed low and highT1values, respectively. HighT1values were also encountered in the zones of samples of uninvolved esophagus which histologically revealed areas with dysplasia. This feature, viz., dysplasia representing maligancyassociated changes, has been found to recur in many samples. Detailed histological studies provided further evidence confirming that areas with dysplasia contribute to an increase inT1values whereas in zones at the gastric end metaplasia and hyperplasia are more common. The results are of value for demarcation of tumor area byin vivoNMR imagin

ISSN:0740-3194    

DOI:10.1002/mrm.1910020204

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

年代:1985

数据来源: WILEY

摘要:

AbstractThe effect of NMR image noise on erros in calculated values of relaxation times is quantitatively assessed by use of relaxation time noise figures, which are derived on the basis of statistical principles as functions of pulse delay, repetition, and recovery intrvals for several types of pulse sequences. Two strategies for determining relaxation times are considered: two point (ratio of intensities for two experiments) and multipoint (least‐squares fit of intensities to pulse‐sequence functions fornexperiments). For given total measurement times, values of pulse interval times are found which give minimum relaxation time noise figures. A comparison of ratio methods shows that the best is a combination saturation ‐recovery inversion‐recovery (SR/IR) technique. For short measurement times (less than about 10T1) this optimized SR/IR ratio determination is also superior to the best multipoint method, a series of inversion—recovery experiments with equally incremented inversion‐recovery times. An examination of the effect of signal averaging on the relaxation time noise shows that up to a measurement time characteristic of the particular method used (e. g., for times up to about5T1for the SR/IR ratio determination, 100T1for the multipoint inversion‐recovery method), increased measurement time is more effectively allotted to longer pulse intervals than to signal averaging. Numerical examples are tabulated which can help one to set optimum values for pulse intervals, given a rough estimate of the relaxation time to

ISSN:0740-3194    

DOI:10.1002/mrm.1910020205

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

年代:1985

数据来源: WILEY

摘要:

AbstractSince contrast in magnetic resonance imaging (MRI) is so sensitive to the magnetic relaxation rates of tissue protons, the use of paramagnetic ions to alter contrast in a tissue‐specific fashion is an alluring prospect. The influence of these ions on the proton relaxation rates in homogeneous solutions is known to vary dramatically according to whether the ions are present as hydrated aquoions, in solute chelate, or immobilized in macromolecules. In tissue, there is the additional complication of access of water to the ions. In the present study, Mn2+ions were introduced into rabbits both orally and intravenously in various chemical complexes. Accumulation of these ions in rabbit liver is demonstrated here, qualitatively, by MRI. The quantitation of the change in relaxation rates is investigated in excised samples of liver and kidney by study of the magnetic field dependence (dispersion) of the relaxation rates of the protons (NMRD profiles) of tissue water. Results are presented for several sets of experiments, including doseresponse data for weakly chelated Mn2+and time‐response data for free and complexed Mn2+. The general findings are that, for liver, the response (the increment in the NMRD profile) is relatively rapid (<2 m); that it is relatively independent of how, or in what form, the Mn2+is introduced; that it persists for several hours (at least); and that it saturates with increasing body load of Mn2+. Moreover, from the form of the NMRD profiles of liver, it is clear that the Mn2+ions are bound irrotationally, perhaps to cell membrane, and, when introduced in chelated form, can become separated even from strongly associated chelate complexes. For kidney, the results are qualitatively similar, though different in det

ISSN:0740-3194    

DOI:10.1002/mrm.1910020206

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

年代:1985

数据来源: WILEY

摘要:

AbstractA shielded solenoidal probe, suitable forin vivoNMR studies of subcutancous solid tumors, is described. The31P NMR spectra obtained from phantom samples andin vivosubeutaneous solid tumors in mice show that spurious signals from the body are totally eliminated if the proper shield is used.

ISSN:0740-3194    

DOI:10.1002/mrm.1910020207

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

年代:1985

数据来源: WILEY

摘要:

AbstractThe relaxation properties of agar gels render it a potentially useful basic reference material for calibrating the NMR equipment. TheT1andT2values are close to the values observed for most biological tissues; they are stable and can be varied by controlling the concentration of MnCl2. The temperature, concentration, and volume dependence ofT1andT2were studied.

ISSN:0740-3194    

DOI:10.1002/mrm.1910020208

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

年代:1985

数据来源: WILEY

摘要:

AbstractCoil development is fundamental to the optimization of imaging systems at any field; however, it is especially critical for low‐field systems where signal strength is limited. Here we demonstrate a type of surface coil design which makes possible the acquisition of high‐quality images of the neck and extremit

ISSN:0740-3194    

DOI:10.1002/mrm.1910020209

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

年代:1985

数据来源: WILEY

ISSN:0740-3194    

DOI:10.1002/mrm.1910020201

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

年代:1985

数据来源: WILEY