摘要:

AbstractAccurate phasing of MRS spectra is often difficult unless time varying phase effects produced by gradient‐induced eddy currents that persist during data acquisition are eliminated. This effect is particularly problematic in1H‐CSI spectra where frequency shifts produced by static field inhomogeneity and phase shifts produced by eddy currents combine. In this paper we present a method that corrects both shifts and eliminates manual phasing of individual CSI spectra typically required to recover a pure absorption line shape. The method uses a time domain phase correction derived from the ambient water signal acquired under identical conditions (i.e., acquisition parameters, gradient sequence) as the solvent‐sup pressed CSI data. Results from CSI experiments on phantoms andin vivosolvent suppressed1H‐CSI spectra from normal human brain are presented demonstrating the capabilities of the te

ISSN:0740-3194    

DOI:10.1002/mrm.1910300302

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe decay of nitroxide spin label electron paramagnetic resonance (EPR) absorption intensity was used to investigate the doxorubicin‐mediated intracellular generation of free radicals. The effects of 50–500 μg/ml doxorubicin on human tumor cells (MCF‐7, breast cancer cells, and HL‐60, promyelocytic leukemia, cells) were studied by measuring 2,2,6,64etramethylpip‐eridine‐1‐oxyl (TEMPO) absorption intensity decay (TAID) at a TEMPO concentration of 10 μM. Doxorubicin accelerated the TAID in both cell lines with a detection limit of 50 μg/ml for MCF‐7 cells and 500 μg/ml doxorubicin for HL‐60 cells. Preincubation of cells with the iron chelating agent, deferoxamine (5 mM), partially prevented the effects of doxorubicin on the TAID. Catalase and copper, zinc‐superoxide dismutase (Cu, Zn‐SOD) had no influence on the effects of doxorubicin on the TAID in intact cells. However, Cu, Zn‐SOD completely abolished the effects of doxorubicin on the TAID in a MCF‐7 cell‐free system. Our findings suggest that doxorubicin mediates the intracellular generation of O2and that i

ISSN:0740-3194    

DOI:10.1002/mrm.1910300303

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

年代:1993

数据来源: WILEY

摘要:

AbstractRapid measurements ofin vivoproton spin‐lattice relaxation times (T1) in human tissues were performed by magnetic resonance imaging in a 1.5 T whole‐body super‐conducting MR scanner. The measurements employ serial TurboFLASH imaging (Snapshot‐FLASH) with scan times for a single experiment below 4 s. Using centric phase encoding order, an appropriate fitling of theT1‐parameter from images with minimum motion artifacts is possible. ComparativeT1‐determination with a multipoint inversion recovery and spin‐echo technique was performed on phantoms containing Gd‐DTPA solutions with differentT1‐values. We found a maximum deviation of 3.3% forT1<1100 ms and of 12.1% for 1100 ms

ISSN:0740-3194    

DOI:10.1002/mrm.1910300304

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

年代:1993

数据来源: WILEY

摘要:

AbstractSome of the important features of how pulsatile flow generates artifacts in three‐dimensional magnetic resonance imaging are analyzed and demonstrated. Time variations in the magnetic resonance signal during the heart cycle lead to more complex patterns of artifacts in 3D imaging than in 2D imaging. The appearance and location of these artifacts within the image volume are shown to be describable as displacements along a line in a plane parallel to that defined by the phase and volume encode directions. The angle of the line in the plane depends solely upon the imaging parameters while the ghost displacement along the line is proportional to the signal modulation frequency. Aliasing of these ghosts leads to a variety of artifact patterns which are sensitive to the pulsation period and repetition time of the pulse sequence. Numerical simulations of these effects were found to be in good agreement with experimental images of an elastic model of a human carotid artery under simulated physiological conditions and with images of two human subject

ISSN:0740-3194    

DOI:10.1002/mrm.1910300305

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

年代:1993

数据来源: WILEY

摘要:

AbstractWe describe a new theory of MR imaging that utilizes prior information in the form of a set of “training” images thought to be similar to the “unknown” objects to be scanned. First, the training images are processed to find an orthonormal series representation of these images that is more convergent than the usual Fourier series. The coefficients in this new series can be calculated from a subset of the phase‐encoded signals needed to construct the Fourier image representation. The characteristics of the training images also determine exactly which phase‐encoded signals should be measured in order to minimize error in the image reconstruction. The optimal phase‐encodings are usually scattered nonuniformly ink‐space. Good results were obtained when this theory was applied to imaging data from simulated objects and to experimental data from phantom scans. This theory provides the basis for developing efficient scanning and image reconstruction techniques that are “tailored” to each body part or to partic

ISSN:0740-3194    

DOI:10.1002/mrm.1910300306

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

年代:1993

数据来源: WILEY

摘要:

AbstractDiffusion‐weighted, echo‐planar imaging (EPI) was used to map regional changes In the apparent diffusion coefficient (ADC) during experimental focal ischemia in the rat brain following permanent middle cerebral arterial occlusion (MCAO). Sixteen 64 × 64 diffusion‐weighted EPIs were acquired in 32 s with successively increasing amplitudes of the diffusion‐sensitive gradient pulses. A linear least‐squares regression algorithm was used to fit 15 of the 16 two‐dimensional matrices, on a pixel‐by‐pixel basis, to solve for the slope from which the ADC value was calculated. The correlation coefficient of the fit, R2was used to filter the final ADC maps, and the ADCs were then scaled appropriately to be displayed in a 256 gray level format. Ranges (bins) of 0.05 × 10−3mm2/s were then grouped and color coded to qualify and quantify the evolution of ischemia in the MCA territory. The percentage of area in the ischemic and contralateral hemispheres in seven ADC bins were calculated at 30, 60, and 120 min after MCAO for 10 animals and demonstrated a significant increase in ADC bins below 0.45 × 10−3mm2/s and a decrease in bins above 0.50 × 10−3mm2/s over the. The postmortem infarct area, as measured by TTC staining, was highly correlated with the portion of the ischemic hemisphere falling below ADC values of 0.55 × 10−3mm2/s at 2 h after stroke onset. These studies suggest that focally ischemic brain tissue can be quantitatively subdivided according to ADC values and that ADC values below 0.55 × 10−3mm2/s 2 h following ischemia highly predict infarction in a rat p

ISSN:0740-3194    

DOI:10.1002/mrm.1910300307

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

年代:1993

数据来源: WILEY

摘要:

AbstractMagnetic resonance imaging detects blood‐brain barrier disruption after gadolinium‐DTPA enhancement of central nervous system lesions of multiple sclerosis. Experimental allergic encephalomyelitis has many clinical and pathological features in common with multiple sclerosis including alterations in the integrity of the blood‐brain barrier. We have comparedT2‐weighted cranial MR images with Gd‐DTPA dimeglumine‐enhancedT1‐weighted images of myelin bask protein‐induced acute (Days 8–42 postimmunlzation) and central nervous system‐induced chronic‐progressive (Days 70–95 post immunization) forms of experimental allergic encephalomyelitis in the guinea pig. Although animals from both groups had abnormalT2‐weighted images, only the myelin bask protein‐acute‐EAE animals (Days 14–24 postimmunlzation) showed enhancement on postcontrast MR studies. The different responses of the acute and chronic diseases may result from different immunogens, severity of disease, or different permeability of the blood‐brain barrier. Therefore, gadolinium‐DTPA‐enhanced,T1‐weighted MR images distinguish acutely active and chronic inflammatory lesions in

ISSN:0740-3194    

DOI:10.1002/mrm.1910300308

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

年代:1993

数据来源: WILEY

摘要:

AbstractWe have previously shown that the concentration of Gd‐DTPA as, a function of time ([Gd‐DTPA]t(t)) in the myocardium following an intravenous bolus injection of Gd‐DTPA can be moldered using the Modified Kety Equation. Fitting this model to measurements of [Gd‐DTPA]t(t) in a region of myocardium would allow the determination of myocardial distribution volume (λ) and the product of flow (F) and extraction efficiency (E), i.e.,FE.Thus, to measureF,E must be known. We describe here techniques developed to measure local values ofEin normal and diseased myocardium. These techniques are valid for any inert diffusible MR contra

ISSN:0740-3194    

DOI:10.1002/mrm.1910300309

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

年代:1993

数据来源: WILEY

摘要:

AbstractWe have previously shown that the myocardial Gd‐DTPA concentration ([Gd‐DTPA]t(t)) after a bolus injection of Gd‐DTPA can be predicted by the Modified Kety Equation (MKE). If [Gd‐DTPA]t(t) can be determined by MRI and the data fit to the MICE, then the distribution volume (λ) of Gd‐DTPA and the myocardial flow (F) times the extraction efficiency (E), i.e., theFEproduct, can be determined. ThereforeFcan only be quantified ifEis known. We measured the globalEin vivoin normal canine myocardium, and measuredEand λ,in vitro, locally in normal, acute ischemic (n = 5; coronary artery occlusion<4 h), infarcted (n = 4; coronary artery occlusion, 6 days) and reperfused (n = 4; coronary artery occlusion 2 h, and reperfusion 2 h and 6 days) myocardium. Results indicate thatEdiffers withFand with individuals and consequently,Fcannot be quantified using the MKE unless the localEis also determ

ISSN:0740-3194    

DOI:10.1002/mrm.1910300310

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

年代:1993

数据来源: WILEY

摘要:

AbstractComparison of31P NMR spectra of the rat gastrocnemius, obtainedin vivoand from PCA extracts, after electrically induced contractions, demonstrates that glucose‐6‐phosphate (G6P) is the major metabolite in the low‐field part of the PME spectral region.In vivo31P NMR can thus be used to measure the muscle G6P concentration after exe

ISSN:0740-3194    

DOI:10.1002/mrm.1910300311

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

年代:1993

数据来源: WILEY