摘要:

AbstractSpin‐echo images of 10 myocardial infarcts in nine mini‐pigs were obtained at 30 h, 3 days, and approximately 10 days postinfarction. Infarcts were not detected at all at 30 h in five out of five cases examined. At 3 days postembolization (six cases) one infarct was certainly detected, whilst at 10 days (nine cases) all infarcts were seen as high‐signal areas in long TE spin‐echo sequences. After 2 weeks no further infarct signal change was detected (three cases), but myocardial thinning became more evident. Using techniques similar to those reported here, early postinfarct changes in the dog have been detected by other authors. Possible reasons for this difference between pig and dog are discussed. © 1987 Academic Pr

ISSN:0740-3194    

DOI:10.1002/mrm.1910050302

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

年代:1987

数据来源: WILEY

摘要:

AbstractThe design of an NMR excitation scheme, whether selective or nonselective, is essentially the simultaneous inversion of an array of Bloch equations driven by magnetic fields which differ according to well‐defined constraints. We find that if relaxation effects are negligible, nearly exact inversion of the Bloch equations is straightforward when performed in a special time‐varying frame of reference. Repeated inversions of the Bloch equations for small perturbations provide the basis for arbitrarily large, optimal adjustments of the magnetization response to an applied time‐varying magnetic field. Choice of the target response to be sought at each iteration is not trivial if overall adjustments of more than one‐half rotation are required. We present the analysis both formally and in geometric terms and show how it leads to a general algorithm for the optimization of NMR excitation schemes. The unprecedented efficiency of the algorithm and its ability to generate novel pulses from distant starting approximations are demonstrated in the optimization of slice‐selective π/2 pulses for inversion and refocusing, and a prefocused slice‐selective π/2 pulse. Other applications are discussed, including use of the algorithm to compensate for instrumental imperfections such as radiofrequency inhomogeneity. © 1987 Acade

ISSN:0740-3194    

DOI:10.1002/mrm.1910050303

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

年代:1987

数据来源: WILEY

摘要:

AbstractThe change in phase of transverse spin magnetization induced by macroscopic spin motion in the direction of an applied magnetic field gradient is used to generate projection angiograms. The method can provide a quantitative measure of laminar and pulsatile flow. Cardiac synchronization is not required provided that data are acquired at many points in the cardiac cycle. The use of short TR and a large number of excitations provides better suppression of stationary tissue and patient motion artifacts than is possible with cardiac gated studies. In addition to improvements in image quality, a substantial shortening of Scan time is obtained. © 1987 Academic Press, Inc

ISSN:0740-3194    

DOI:10.1002/mrm.1910050304

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

年代:1987

数据来源: WILEY

摘要:

AbstractUsing a 1‐m‐bore super conductive magnet at 0.1 T, whole‐body transverse images through adult humans have been obtained at repetition times of 57 ms. The techniques used were minor variations of echo‐planar imaging (EPI) employing large pulsed gradients to provide complete coverage of the plane in phase space, and low‐angle RF excitation sequences allowing rapid repetition of the experiment. In addition active magnetic screening of the gradient coils was implemented to protect the surrounding magnet from the eddy currents induced by the necessarily fast switching of the large gradient fields. © 1987 Academic

ISSN:0740-3194    

DOI:10.1002/mrm.1910050305

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

年代:1987

数据来源: WILEY

摘要:

AbstractThe hybrid technique of projection‐reconstruction echo‐planar (PREP) imaging for obtaining chemical‐shift images is demonstrated experimentally using a fluorine sample. The technique which is a variation on echo‐planar imaging (EPI) relies on a multipass procedure. It is nevertheless quite efficient and consequently chemical‐shift images may be produced in a few minutes. The method produces images in 64 chemical‐shift regions, each region mapped spatially by 64 × 64 pixels. The imaging time was just over 4 min. These 64 chemical‐shifted images can be straightforwardly added together to form an undistorted image of the complete object. In addition the chemical‐shift spectrum can be extracted and the various chemical‐shift images can be unambiguously assigned to

ISSN:0740-3194    

DOI:10.1002/mrm.1910050306

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

年代:1987

数据来源: WILEY

摘要:

AbstractA field‐mapping procedure based on volume‐selective spectroscopy is described. For proton NMR the method may be used to optimize magnet shimming, on the sample under investigation, prior to spectroscopy or imaging experiments. Examples of field maps obtained on our 4.7‐T system, using phantoms and biological samples of up to 6 cm in diameter, are presented. © 1987 Academic Pres

ISSN:0740-3194    

DOI:10.1002/mrm.1910050307

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

年代:1987

数据来源: WILEY

摘要:

AbstractEnhancements of1H nuclear magnetic transverse relaxation rates by Mn(II)‐ and Gd(III)‐ethylenediaminetetraacetic acid (EDTA)‐human serum albumin (HSA) complexes are compared with MnCl2in human plasma and isotonic saline. HSA–EDTA–Mn and HSA–EDTA–Gd in saline, at physiological concentrations of HSA, afforded T2's comparable to2mMMnCl2in 4% HSA saline. The above reagents are new and potentially useful relaxation agents for the measurement of H2O exchange rates in erythrocyte suspensions. The exchange rate of water across the red cell membrane was determined using these new reagents over the temperature range from 20 to 37°C. © 1987 Acad

ISSN:0740-3194    

DOI:10.1002/mrm.1910050308

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

年代:1987

数据来源: WILEY

摘要:

AbstractEffects of the sampling rate on spatial resolution and the signal‐to‐noise ratio in spin‐echo MR imaging were calculated. The theoretical results suggest that asT 2★decreases, due to either static magnetic field inhomogeneitics or shortened T2relaxation times, the calculated optimum sampling rate increases accordingly. Since biological tissues exhibit wide variations in their magnetic susceptibilities andT2relaxation times for various isotopes but modern magnets are characterized by good magnetic field homogeneity, the optimum sampling rate should exhibit an observable dependence on the tissue type. Proton and sodium imaging experiments confirm this conclusion. © 1987 Academic

ISSN:0740-3194    

DOI:10.1002/mrm.1910050309

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

年代:1987

数据来源: WILEY

摘要:

AbstractThe deuterium nuclear spin relaxation times have been measured in tissues taken from rats given 20% deuterium oxide in their drinking water. The spin–lattice and spin–spin relaxation times were measured at 13.7 MHz by the inversion–recovery and Carr–Purcell–Meiboom–Gill FT methods, respectively. The reciprocals of the spin–lattice (T1) relaxation times were found to correlate well with those of protons in similar nondeuteriated tissues at a similar frequency (13.6 MHz) measured in a separate study. A least‐squares analysis of the data yields (I/Tl)II = (0.991)(I/T1)D – 3.48 for five tissues (standard deviations of 0.097 for the slope and 0.383 for the intercept with a correlation coefficient of 0.986). Implications with respect to relaxation mechanisms are discussed. 0_1987 Ac

ISSN:0740-3194    

DOI:10.1002/mrm.1910050310

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

年代:1987

数据来源: WILEY

摘要:

AbstractThe possibility of using19MRI for detection of tumors using a 2‐T NMR system was examined in animals. Anticarcino‐embryonic antigen (CEA) antibody conjugated with perfluorochemical (perfluorotributylamine, FTBA) was administered to nude mouse inoculated with LOVO, a CEA‐producing human cancer cell line. Tumor imaging based on the19F NMR was examined after excision of the tumors from nude mice (ex vivo). The imaging pattern of the tumor coincided with the antibody distribution determined immunohistologically. © 1987 Academic Pres

ISSN:0740-3194    

DOI:10.1002/mrm.1910050311

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

年代:1987

数据来源: WILEY