摘要:

AbstractThe effects of various calcium antagonists on the ATP, PCr, andPilevels as well as intracellular pH in normal and ischemic rat brain were examined by 31P NMR spectroscopy using a surface coil. None of the calcium antagonists tested showed any effect in the nonischemic rat brain. However, when global ischemia was induced by cardiac arrest, the ensuring rapid decrease of ATP and PCr and concomitant increase ofpiwere significantly retarded by dihydropyridine calcium antagonists, but not by verapamil. The fall in pH caused by ischemia was not affected by either drug. Barbiturates showed effects similar to calcium antagonists, whereas calcium agonists showed the opposite. These results suggest that dihydropyridine calcium antagonists, similar to barbiturates, decrease the high‐energy phosphate consumption of the brain, which might be beneficial in instances where their production is severely hampered, e.g., during ischemia. © 1987 Academic Press, I

ISSN:0740-3194    

DOI:10.1002/mrm.1910040102

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

年代:1987

数据来源: WILEY

摘要:

AbstractReversal of the read gradient in a SSFP imaging experiment allows a full spin echo to be collected in the interval τ between successive rf pulses. Orthogonal gradient pulses are used to dephase and subsequently rephase the transverse magnetization each τ enabling 2D or 3D Fourier techniques. The minimum data collection time per slice in the 3D technique is 3.1 s (128 × 256). For a 2D data collection, an oscillating bipolar sawtooth gradient is used to select the slice. Each phase‐encode value must be averaged over an equivalent portion of the oscillating slice‐selection gradient and this condition gives a minimum of 25 s for 2D data collection. Excellent slice selection is achieved with less than 5% of the signal lying outside the slice profile central lobe. Images at 0.14 T show tissue contrast may be manipulated by changing the rf pulse angle, an example of which is the presence or absence of gray/white matter contrast at rf pulse angles of 30 and 90°, respectively. The pulse angle θ dependence of five samples with different values ofT2/T1was measured and numerically calculated with good agreement between theory and experiment for θ ⩽ 90°. © 1987 Academ

ISSN:0740-3194    

DOI:10.1002/mrm.1910040103

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

年代:1987

数据来源: WILEY

摘要:

AbstractMn(III), Fe(III), and Gd(III) complexes of tetrakis(4‐sulfonatophenyl)porphyrin (TPPS) and several other porphyrins were evaluated as potential MRI contrast agents. Based on consideration of relaxivity and stability properties in solution, Mn TPPS was found to be the compound of choice. At pH 7 the Gd and Mn complexes significantly enhanced the water proton relaxation rate, while the relaxivity of Fe TPPS exhibited a significant loss of relaxivity above pH 6 due to oxy‐dimer formation. Although GdTPPS exhibited the highest relaxivity in solution, this property was rapidly lost due to dissociation of the metal ion. By contrast MnTPPS remained stable in human plasma after incubation for 9 days. Upon intravenous injection into athymic mice bearing subcutaneous human colon carcinoma xenografts, MnTPPS provided enhanced relaxation of the tissue water in several excised mouse tissues, notably kidney, liver, and tumor. The results at a fixed field (0.25 T) and relaxation dispersion studies showed decreases in water relaxation rates with time for kidney and liver, but an increase for the tumor, with a maximum near 4 days at the highest dose u

ISSN:0740-3194    

DOI:10.1002/mrm.1910040104

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

年代:1987

数据来源: WILEY

摘要:

AbstractAccurateT2images calculated from multiple‐echo sequences are difficult to obtain over a number of contiguous slices due to the presence of unwanted echoes that are generated at the slice edges. This problem is similar to problems encountered in single‐slice imaging in the presence of rf pulse imperfections. In this paper, we use computer simulations to show that all unwanted echoes can be eliminated by defocusing them using additions to the slice‐selection gradients. AccurateT2images may then be calculated from the remaining echoes. We also present a method of experimentally displaying the slice shapes of unwanted echoes generated by a multislice imaging sequence. © 1987 Academic Pres

ISSN:0740-3194    

DOI:10.1002/mrm.1910040105

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

年代:1987

数据来源: WILEY

摘要:

AbstractHinshaw's sensitive‐point method and Macovski's post‐filtering localization techniques are analyzed under very general imaging conditions. It is shown that one can obtain an expression for the FID signal induced by all resonating particles at any particular point in the imaged object. Contributors to the signal may have different relaxation behaviors, spin rates, and velocity components. In fact, in the case of flows, different nuclei contribute to the signal at different times during the observation. Localization enables us to impose local assumptions on our model rather than global ones, as is usually done in MRI. Applications to imaging slow and fast flows andin vivospectroscopy are discussed. © 1987 Academic Press,

ISSN:0740-3194    

DOI:10.1002/mrm.1910040106

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

年代:1987

数据来源: WILEY

摘要:

AbstractAny clinical whole‐body MR imager can be adapted for experimental small animal imaging. The design of an if receiver coil and an efficient magnified imaging technique are presented. Application of this small animal imaging technique is illustrated using a study of paramagnetic contrast enhancement of a tumor in the mouse. © 1987 Academic Press, I

ISSN:0740-3194    

DOI:10.1002/mrm.1910040107

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

年代:1987

数据来源: WILEY

摘要:

AbstractA method is presented for the detection of quadrupole splitting in tissue, where the spectral line splittings are typically unobservable. The method used is a study of the rate of rotation of the flip angle as a function of radiofrequency (rf) amplitude. Our results with samples of skeletal muscle and cat brain indicate the absence of quadrupole splitting. © 1987 Academic Press, Inc

ISSN:0740-3194    

DOI:10.1002/mrm.1910040108

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

年代:1987

数据来源: WILEY

摘要:

AbstractResults are reported which demonstrate that the maximum entropy method can be applied to phase‐encoding NMR imaging. © 1987 Academic Press, I

ISSN:0740-3194    

DOI:10.1002/mrm.1910040109

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

年代:1987

数据来源: WILEY

摘要:

Abstract31P magnetic resonance spectroscopy (MRS) was performedin vivoon normal and ischemic rat intestine. Within 3 min after induction of ischemia, there is a dramatic fall in adenosine triphosphate (ATP) and rise in inorganic phosphate (Pi). Our results suggest that MRS may prove useful in the early detection of mesenteric ischemia. © 1987 Academic Press Inc

ISSN:0740-3194    

DOI:10.1002/mrm.1910040110

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

年代:1987

数据来源: WILEY

摘要:

AbstractInduction of iron overload in mice using 1% (w/w) dietary carbonyl iron resulted in marked decreases in2H and31P NMR relaxation times. Natural‐abundance deuterium (2H) NMR spectroscopy has been used to measure2HT1valuesin vivoin the presence of body paramagnetic iron. This procedure offers a method for noninvasive determination of body iron stores. © 1987 Academic Press, I

ISSN:0740-3194    

DOI:10.1002/mrm.1910040111

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

年代:1987

数据来源: WILEY