摘要:

AbstractTo determine whether direct cellular effects of chemotherapy are responsible for31P NMR spectral changes observed in treated tumorsin vivo, RIF‐1 fibrosarcoma cells were examinedin vitrobefore, during, and after treatment with 4‐hy‐droperoxycyclophosphamide (4‐HC), an activated form of cyclophosphamide. When RIF‐1 cells were treated with 4‐HC in a metabolically stable but nonproliferating state, the31P NMR spectra were identical with those of untreated cells for up to 70 h. When actively proliferating RIF‐1 cells were treated with 4‐W, the intensities of the nucleotide triphosphate resonances, which increased linearly during control cell growth, remained constant for 50 h or longer. These studies demonstrate that the bioenergetic improvement observed following treatment of RIF‐1 tumorsin vivo[S.‐J. Li, J.P. Wehrle, S.S. Rajan, R.G. Steen, J.D. Glickson, and J. Hilton,Cancer Res.48, 4736 (1988)] does not result from direct effects of cyclophosphamide metabolites on RIF‐1 cell metabolism, but rather from indirect effects of treatment on tumor or host physiology. Key words:31P NMR spectroscopy; RIF‐1 tumor cells; c

ISSN:0740-3194    

DOI:10.1002/mrm.1910310302

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

年代:1994

数据来源: WILEY

摘要:

AbstractTo investigate human muscle bioenergetics quantitativelyin vivo, we used31P magnetic resonance spectroscopy to study the flexor digitorum superficialis of four adult males during dynamic ischemic and aerobic exercise at 0.50–1.00 W and during recovery from aerobic exercise. During exercise, changes in pH and [PCr] were larger at higher power, but in aerobic exercise neither end‐exercise [ADP]nor the initial postexercise PCr resynthesis rate altered with power. In ischemic exercise we estimated total ATP synthesis from the rates of PCr depletion and glycogenolysis (inferred using an analysis of proton buffering); this was linear with power output. In aerobic exercise, again we estimated ATP synthesis rates due to phosphocreatine hydrolysis and glycogenolysis (incorporating a correction for proton efflux) and also estimated oxidative ATP synthesis by difference, using the total ATP turnover rate established during ischemic exercise. We conclude that in early exercise oxidative ATP synthesis was small, increasing by the end of exercise to a value close (as predicted) to the initial postexercise rate of PCr resynthesis. Furthermore, a plausible estimate of proton efflux during aerobic exercise can be inferred from the pH‐dependence of proton efflux in rec

ISSN:0740-3194    

DOI:10.1002/mrm.1910310303

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

年代:1994

数据来源: WILEY

摘要:

AbstractTumoral pancreatic islet cells of the RIN5mF line were incubated for 120 min in media prepared in2H2O and containingD‐[1‐13C]glucose, andD‐[2‐13C]glucose, andD‐[6‐13C]glucose. The generation of C2‐ and C3‐ deuterated lactic acid was assessed by13C NMR. The interpretation of experimental results suggests that a) the efficiency of deuteration on the C1of D‐fructose 6‐phosphate does not exceed about 47% and 4% in the phosphoglucoisomerase and phosphomannoisomerase reactions, respectively; b) approximately 38% of the molecules ofD‐glyceraldehyde 3‐phosphate generated fromD‐glucose escape deuteration in the sequence of reactions catalyzed by triose phosphate isomerase and aldolase; and c) about 41% of the molecules of pyruvate generated by glycolysis are immediately converted to lactate, the remaining 59% of pyruvate molecules undergoing first a single or double back‐and‐forth interconversion withL‐alanine. It is proposed that this methodological approach, based on high resolution13C NMR spectroscopy, may provide novel information on the regulation of back‐and‐forth interconversion of glycolytic intermediates in intact cells as modulated, for inst

ISSN:0740-3194    

DOI:10.1002/mrm.1910310304

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe OMP particle and four additional iron oxide samples were investigated in terms of zero field cooled magnetization (ZFCM) curves and hysteresis loops. The observation of superparamagnetic blocking and the absence of magnetic remanence demonstrated that the samples are superparamagnetic at room temperature. The magnitude of the ZFCM peak temperatures are in qualitative agreement with the iron oxide crystal size. One sample deviated from the remaining four in that it had a significantly lower magnetic moment and an irregular ZFCM curve showing the presence of various less magnetic phases. The similar results obtained with the OMP particles and the individual OMP crystallites without the polymer support show that the superparamagnetic properties of the individual OMP crystallites are retained on the OMP particle. Depending on the application, the ZFCM experiment may be viewed as an alternative or a supplement to Mössbauer spectroscopy in studies of the superaparamagnetic blocking of iron oxides

ISSN:0740-3194    

DOI:10.1002/mrm.1910310305

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

年代:1994

数据来源: WILEY

摘要:

AbstractSpatially resolved maps of proton self‐diffusion coefficients (D) and relaxation times (T1andT2) were obtained on cartilage‐bone plug samples and on excised disks of canine cartilage at a transverse resolution of 30 μm, using microscopic magnetic resonance imaging (micro‐MRI). Results are compared for excised disks of cartilage and intact cartilage‐bone plugs. Correlations between the absolute water concentration, the self‐diffusion coefficient and theT1relaxation are reported. The diffusion coefficient is not a linear function of water concentration. The thickness of the disks is 600 μm, compared with the ca. 900 μm observed for the cartilage‐bone plugs, presumably due to the absence of the interfacial or tidemark layer of interdigitated cartilage and bone in the former samples. Our results suggest that excised disks of cartilage are excellent models for the articular surface and the first 500 or so microns of tissue. The molecular parameters of spin‐spin and spin‐lattice relaxation times, as well as the water self‐diffusion coefficient, are virtually identical in the two types of samples. However, the cartilage‐bone plugs have the additional feature of permitting the study of the tidemark region, a region that likely plays a major role in the transmissi

ISSN:0740-3194    

DOI:10.1002/mrm.1910310306

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

年代:1994

数据来源: WILEY

摘要:

AbstractTo assess the effect of stimulus correlated motion on the appearance of functional magnetic resonance images, conventional visual and motor protocols were each performed by four normal volunteers and an image co‐registration technique was used to retrospectively monitor subject motion. In three studies synthetic data sets were constructed from single baseline images using the positional information obtained from the co‐registration procedure. Cumulative difference images were then created from both the synthetic and functional image sets. Stimulus correlated motion was detected in all eight studies and the synthetic cumulative difference images showed striking similarities to the equivalent functional images in each c

ISSN:0740-3194    

DOI:10.1002/mrm.1910310307

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

年代:1994

数据来源: WILEY

摘要:

AbstractA partial saturation method is described for obtaining rapid images of tissue 'H spin‐lattice relaxation rates following administration of the paramagnetic contrast agent gadolinium‐diethylenetriaminepentaacetate. The paramagnetic contribution to the relaxation rates is proportional to the concentration of contrast agent, making possible quantitative studies of paramagnetic contrast agent uptake or vessel leakage. Snapshot imaging capabilities are not required. Maps of contrast agent uptake rates are made in rat borne tumors before and following photodynamic therapy, which is known to cause vascular damage. Uptake efficiency is spatially heterogenous before and after therapy. Decreases in uptake rate are observed after two photo‐irradiation protocols, which differ by a factor of four in fluence rate but deliver the same total fluence. There is no apparent fluence rate dependence for changes in the uptake rates within 5 h after therapy. Whole tumor measurements of nucleotide triphosphates, inorganic phosphate, pH, and lactate made with NMR spectroscopy indicate that, while net ATP production is inhibited, lactate concentrations are not strongly affected by photodynamic therapy. The ratio of nucleotide triphosphates to inorganic phosphate falls to 0.21 ± 0.02 of initial values 5 h after tumors are treated with the lower fluence rate protocol, and falls to 0.40 ± 0.06 in tumors treated with the higher fluen

ISSN:0740-3194    

DOI:10.1002/mrm.1910310308

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

年代:1994

数据来源: WILEY

摘要:

AbstractNMR microscopy is currently being used as an investigational tool for the evaluation of micromorphometric parameters of trabecular bone as a possible means to assess its strength. Since, typically, the image voxel size is not significantly smaller than individual trabecular elements, partial volume blurring can be a major complication for accurate tissue classification. In this paper, a Bayesian segmentation technique is reported that achieves improved subvoxel tissue classification. Each voxel is subdivided either into eight subvoxels twice the original resolution, or up to four subvoxels along the transaxial direction and the subvoxels optimally classified as either bone or marrow. Based on a statistical model for partial volume blurring, the likelihood for the number of marrow subvoxels in each voxel can be computed on the basis of its measured signal. To resolve the ambiguity of the location of the marrow subvoxels, a Gibbs distribution is introduced to model the interaction between the subvoxels. Neighboring subvoxel pairs with the same tissue label are encouraged, and pairs with distinct labels are penalized. The segmentation is achieved by maximizing thea posterioriprobability of the label image using the block ICM (iterative conditional mode) algorithm. The potential of the proposed technique is demonstrated in real and synthetic NMR microscopic images.

ISSN:0740-3194    

DOI:10.1002/mrm.1910310309

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe ability of MRI to acquire not only anatomical but also functional information makes MRI guided vascular interventions an interesting goal. Recent developments in ultrafast MR imaging sequences such as fast gradient echo or echo planar (EPI) mean that not only real time MRI but also MRI guided vascular interventions are real possibilities for the not too distant future. However, currently available guide wires and catheters are potentially unusable in MRI because they are either ferromagnetic or MRI invisible. In order to find different materials suitable for real time MRI, various devices were examined with fast gradient echo and interleaved EPI pulse sequences. The measurements were performed using a continuously running, pseudo real time MRI system to investigate the dynamic imaging behavior under guide wire insertion. Suggestions are made as how to construct guide wires and catheters, which can be visualized with ultrafast imaging sequences, while not causing prohibitive artifacts or image distortions.

ISSN:0740-3194    

DOI:10.1002/mrm.1910310310

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

年代:1994

数据来源: WILEY

摘要:

AbstractAccurate values were obtained for the lactate zero‐quantum coherence frequency, ωZQ= ωi‐ωs= CH3–CH chemical shift difference, and scalar coupling constant, J, by using the methyl signal's amplitude modulation during the TM period of a STEAM sequence, 90°–TE/2–90°–TM–90°–TE/2‐ Acquire. Although most previous work has usedJ= 7.35 Hz, or 1/J= 136 ms, the actual value isJ= 6.93 ± 0.05 Hz or 1/J= 144.3 ± 1 ms. In addition, the CH3–CH chemical shift difference = 2.7956 ± 0.0005 ppm, and the relaxation time for zero‐quantum coherence, TZQ, was much shorter than either T2or T1for the methyl resonance. A small component of the signal withTE= 144 ms, which was not modulated at the zero‐quantum coherence frequency or by scalar coupling, was assigned to longitudinal two‐spin order magnetization (IzSz) created by imperfect radio frequency pulse profiles. This information will allow improved editing of the lactate signal and more accurate quan

ISSN:0740-3194    

DOI:10.1002/mrm.1910310311

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

年代:1994

数据来源: WILEY