摘要:

AbstractWe have developed a new class of magnetic resonance imaging contrast agents with large proton relaxation enhancements and high molecular relaxivities. The reagents are built from the polyamidoamine form of Starburs™ dendrimers in which free amines have been conjugated to the chelator 2‐(4‐isothiocyanatobnenzyl)‐6‐methyl‐diethylenetriaminepenta‐acetic acid. The dendrimer gadolinium poly‐chelates have enhancement factors, i.e., the ratlo of the relaxivity per Gd(III) ion to that of Gd(III)‐diethylenetriaminepentaacetic acid, of up to 6. These factors are more than twice those observed for analogous metal‐chelate conjugates formed with serum albumins, polylysine, or dextran. One of the dendrimer‐metal chelate conjugates has 170 gadolinium ions bound, which greatly exceeds the number bound to other macromolecular agents reported In the literature, and has a molecular relaxivity of 5,800 (mM· s)−1, at 25 MHz, 20°C, and pH of 7.4. We observed that these dendrimer‐based agents enhance conventional MR images and 3D time of flight MR angiograms, and that those with molecular weights of 8,508 and 139,000 g/mole have enhancement half lives of 40 ± 10 and 200 ± 100 min, much longer than the 24 ± 4 min measured for Gd(III)‐diethylenetriaminepentaacetic acid. Our results suggest that this new and powerful class of contrast agents have the potential for diverse and ext

ISSN:0740-3194    

DOI:10.1002/mrm.1910310102

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe factors affecting the rate of loss of transverse magnetization in gradient echo and spin‐echo pulse sequences have been quantified using computer modeling for media containing arrays of susceptibility variations. The results are particularly relevant for describing the signal losses that occur in tissues containing capillaries of altered intrinsic susceptibility from the administration of exogenous contrast agents or arising from changes in blood oxygenation. The precise magnitudes and relationship of gradient echo and spin‐echo decay rates depend on geometrical factors such as the sizes and spacings of the inhomogeneities, the rate of water diffusion, field strength, and echo times. The conventional separation of contributions to transverse decay rates arising from so‐called static field effects and diffusion is shown to be inappropriate for many situations of practical interest because diffusion introduces a motional averaging of the static field even in gradient echo sequences. The result of diffusion in some regimes is to reduce the decay rate from field inhomogeneities in gradient echo sequences, so that T2* is longer in media such as tissue where water diffuses reasonably rapidly, than would be the case for stationary nuclei. The effects of different types of contrast agent and the implications for functional imaging based on the effects of deoxyhemoglobin in brain tissue are consi

ISSN:0740-3194    

DOI:10.1002/mrm.1910310103

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

年代:1994

数据来源: WILEY

摘要:

AbstractStreamline display is a unique alternative to cross‐sectional slice or projection display, because streamlines more clearly show the patterns of blood flow within the vessel. Flow patterns associated with atherosclerosis, such as streamline separation and recirculation, can be quickly identified with this display. Streamlines can be calculated using velocity data obtained from 3‐D phase contrast angiographic pulse sequences. However, these streamlines often pass through the wall of vessel or show intraluminal sources and sinks of blood. The author has developed iterative least squares algorithms to improve the realism of streamlines. The velocity data is modified so that the resulting streamlines do not pass through the vessel wall and there are no intraluminal sources or sinks. He has applied the algorithms to velocity data obtained from a flow phantom and the carotid arteries of normal volunteers. Streamlines derived from the processed velocity fields are more realistic and provide more precise flow quantitat

ISSN:0740-3194    

DOI:10.1002/mrm.1910310104

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe purpose of this study was to characterize the contrast caused by a susceptibility MRI contrast agents, on spin echoT2‐weighted imaging of reperfused myocardial infarction. Our interest in this model focused on the expected requirement that such agents be compartmentalized in the tissue to cause signal loss on spin echo images, a condition which may not be present in reperfused infarcted myocardium. Accordingly, nine rats were subjected to 2 h of left coronary artery occlusion followed by 3 ± 0.5 h of reperfusion prior to administration of contrast media. Three sets of MR images were acquired: (a) baseline axial images at the midventricle, bothT1‐weighted (TR/TE= 300/20) andT2‐weighted (TR/TE= 1500/60); (b)T1‐weighted images after administering aT1‐enhancing agent, Gd‐DTPA‐BMA (0.2 mmol/kg), to document that contrast media is delivered to the reperfused infarction; and (c)T2‐weighted images after administering the susceptibility agent, Dy‐DTPA‐BMA (1.0 mmol/kg). Gadolinium‐enhancedT1images depicted reperfused infarction as regions with greatly enhanced signal intensity compared with unin‐farcted myocardium, indicating that contrast agent was delivered to the infarcted zone. Dysprosium‐enhancedT1images depicted the injury as a region of persistent signal intensity relative to depletion of signal in normal myocardium, consistent with failure of the contrast agent to cause signal loss. Similar infarction sizes were observed for unenhancedT2‐weighted images (33 ± 5%), gadolinium‐enhancedT1weighted images (36 ± 5%) and postmortem staining (30 ± 6%); strong correlations (r>0.9) were noted in comparisons of these data. Dysprosium‐enhanced images exhibited a smaller region of differential signal presumed to be infarction (20 ± 5%, P<0.05) and weak correlations (r<0.75) with the other measurements. We conclude that the smaller infarction depicted on dysprosium‐enhanced images is a subregion of the true infarction in which myocardial necrosis is sufficiently advanced that the agent is homogeneously distributed throughout all tissue compartments, preventingT2*‐

ISSN:0740-3194    

DOI:10.1002/mrm.1910310105

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

年代:1994

数据来源: WILEY

摘要:

AbstractWe present a method to quantify the MR field inhomogeneity geometric distortion to subplxel accuracy without using objects of known dimensions and without using an external standard such as CT. Our method may be used to quantify the geometric accuracy of MR images of anatomical structures of unknown geometry and also to test any geometry correction scheme. We have quantified the distortion in a tissue phantom and found the largest error to be approximately 2.8 pixels (1.8 mm) for B0= 1.5 T, G = 3.13 mT/m and FOV = 160 × 160 × 70.7 mm3. We also found that our previously published correction technique reduced the largest error to 0.3 pixels (μ = 0.02 and σ = 0.07 pixe

ISSN:0740-3194    

DOI:10.1002/mrm.1910310106

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

年代:1994

数据来源: WILEY

摘要:

Abstract1H and31P NMR techniques were applied to study the changes in metabolite profiles in human urine resulting from radiation exposure following the Chemobyl reactor accident. In cases of acute leukemia and different accumulated doses of external radiation (from 0.20 to 4.00 Sv), the proton spectra were classified on the basis of the peaks due toN‐trimethyl groups, creatinine, citrate, glycine, and hippurate. Unidentified resonances were observed between 15.9 and 21.4 ppm in six phosphorus spectra of patients with preleukemia and acute leukemia. Characteristic spectral changes were similar for external radiation and Incorporation‐induced internal irradiation. The spectral patterns described may serve as a criterion of radiation inj

ISSN:0740-3194    

DOI:10.1002/mrm.1910310107

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

年代:1994

数据来源: WILEY

摘要:

AbstractLocalized proton magnetic resonance spectroscopy with short echo time (TE= 20 ms) was used to investigate biochemical changes in the cerebral white matter of 20 young adult patients (median 19 years) with phenylketonuria (PKU). Results were compared with those of a group of 12 age‐matched healthy volunteers (median 25 years). Concentrations of Nacetyl‐aspartate (NAA) and choline (Cho) relative to creatine (Cr) were unchanged. However, concentrations of inositol (Ins) relative to creatine were found to be significantly lower (P<0.001) in the PKU patients (0.30 ± 0.09 versus 0.57 ± 0.17). Individual inositol concentrations did not correlate with age, diet, serum phenylalanine (Phe) levels or extent of pathological regions in the T,‐weighted images. The lack of correlation with individual data suggests that the decreased inositol concentration could be related to a metabolic deficiency during fetal development. No signal from the phenyl ring protons of phenylalanine was detected in the PKU patients (phenylalanine serum concentration ⩽ 1.27 mM), which suggests that concentration of phenylalanine may be lower in brain than

ISSN:0740-3194    

DOI:10.1002/mrm.1910310108

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe commercial synthetic homopolypeptide polyaspartate (average MW = 30,000, approximately 220 monomers) in solution quantitatively binds up to 40 mol Gd2+ions per mole of polyaspartate. The water proton relaxivity of the solutions is far higher than that of clinically used or commonly investigated gadolinium(III) complexes. It is shown that polymetallic macromolecular complexes combine the high relaxing efficiency of monometallic macromolecular complexes with the favorable metal/ligand mass ratio of small monometallic complexes.

ISSN:0740-3194    

DOI:10.1002/mrm.1910310109

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

年代:1994

数据来源: WILEY

摘要:

AbstractBreakdown of the blood‐retinal barrier (BRB), frequently an early clinical sign in retinopathy, can be accurately determined using contrast‐enhanced MRI. However, increased vitreous fluidity with age and disease may affect the accuracy of the MRI method. We compared the permeability surface area product per area of leaky retina in eyes with normal vitreous (5.42 ± 0.48 × 10−4cm/min, mean ± SEM,n= 5) to the contralateral gas‐compressed vitrectomized eyes (5.41 ± 0.54 × 10−4cm/min,n= 5). The effect of vitrectomy was not significant (P= 0.325) using a Wilcoxon matched pairs signed rank test on the signed differences of

ISSN:0740-3194    

DOI:10.1002/mrm.1910310110

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

年代:1994

数据来源: WILEY

摘要:

AbstractThis work describes an interleaved echo planar imaging (EPI) method for use on a standard whole body scanner. The data acquisition is divided into two to eight repetitions rather than one to two, as implemented by dedicated EPI systems. Interleaving allows the use of a lower sampling bandwidth with a significant increase in signal‐to‐noise. The method also has the advantages of relative ease of implementation, no need for postprocessing to remove image distortion, and no need for shimming on a case‐by‐case basis. The interleaved EPI method was applied to two applications ideally suited to EPI: breathhold T2‐weighted abdominal imaging and functional imaging.In vivoliver‐lesion contrast as measured in a 35‐patient study showed increased contrast for the Interleaved EPI by an average factor of 1.21 (± 0.34) over conventional spin‐echo imaging. CNR measurements showed the EPI to be comparable with conventional spin echo with a relative factor of 1.00 (± 0.36). Functional imaging with an eight‐shot interleaved EPI sequence provided 128 × 128 images of cerebral activation during bila

ISSN:0740-3194    

DOI:10.1002/mrm.1910310111

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

年代:1994

数据来源: WILEY