摘要:

AbstractSpin‐lattice relaxation in the rotating frame (T1ρ) dispersion spectroscopy and imaging were used to study normal and enzymatically degraded bovine articular cartilage. Normal specimens demonstrate significantT1ρ“dispersion” (∼60 to ∼130 ms) in the 100 Hz to 9 kHz frequency range. Proteoglycan‐degraded specimens have 33% greaterT1ρvalues than collagen‐degraded or normal samples.T1ρ‐weighted images reveal structure not found in conventionalT1‐orT2‐weighted images. Our results suggest thatT1ρmeasurements are selectively sensitive to proteoglycan content. The potential of this method in distinguishing the early degenerative changes in cartilage associated with ost

ISSN:0740-3194    

DOI:10.1002/mrm.1910380602

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

年代:1997

数据来源: WILEY

摘要:

AbstractA new imaging sequence for rapid determination of the apparent self‐diffusion tensor of water was developed and tested on fixed excised rat spinal cords. To reduce the time required to determine the tensor, the sequence utilized a new single‐shot approach with multiple spin echoes. An assumption of cylindrical symmetry in the sample was made, thus requiring the measurement of only four of the six unique elements of the tensor. This assumption was found experimentally to be valid, and the results obtained using the new sequence were found to be quantitatively the same as results obtained using a standard spin‐echo seq

ISSN:0740-3194    

DOI:10.1002/mrm.1910380603

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

年代:1997

数据来源: WILEY

摘要:

AbstractFunctional MRI (fMRI) provides a noninvasive method for mapping brain functional activity based on blood oxygenation level dependent (BOLD) image contrast that is primarily due to localized increases in perfusion. Recently, Malonek and Grinvald (Science272:551–554, 1996) suggested that during sustained functional activation, the increases in perfusion were spread over a much larger area than the localized electrical activity. In this study, it is demonstrated that the spatial distribution of the BOLD fMRI signal during sustained stimulation of rat whiskers has the same spatial pattern and dimension as that of neuronal electrical activity in the rat whisker barrel

ISSN:0740-3194    

DOI:10.1002/mrm.1910380604

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

年代:1997

数据来源: WILEY

摘要:

AbstractNo direct information on brain energetics and energy‐related compounds in the first seconds of physiological activation has been reported to date. In this study visual cortex high energy phosphate changes were monitored in 11 normal subjects during 3.5 s activation and the following 23.5 s by a simple31P magnetic resonance spectroscopic method. An intraactivation decrease of phosphocreatine (PCr) was observed in all subjects, with changes in pH in three, one of them also presenting a change in adenosine triphosphate (ATP). In the subgroup of eight subjects without changes in pH, the mean rate of mean PCr decrease (DPCr) was 7.24 ± 0.78 %/s, and the postactivation mean rate of mean PCr recovery was<1/2 DPCr. Short phasic neural activity requires a large amount of energy, i.e., at least three times basal consumption, in agreement with theoretical calculations. Additional energy demands in the visual cortex are several times those measured by positron emission tomography during prolonged stimulation studies, implying that mean energy requirements decrease with increases in duration of stimulation. During short activation, the vascular responses as detected by brainmapping techniques (BMT) are preceded by an important reduction of the intracellular high‐energy phosphate content, which returns to resting values during an interval that corresponds to the poststimulation return of BMT signals to base

ISSN:0740-3194    

DOI:10.1002/mrm.1910380605

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

年代:1997

数据来源: WILEY

摘要:

AbstractTo separate water and lipid resonance signals by phase‐sensitive MRI, a two‐point Dixon (2PD) reconstruction is presented in which phase‐unwrapping is used to obtain an inhomogeneity map based on only in‐phase and out‐of‐phase image data. Two relaxation‐weighted images, a “water image” and a “fat image,” representing a two‐resonance peak model of proton density, are output. The method is designed forT1‐ or density‐weighted spin‐echo imaging; a double‐echo scheme is more appropriate forT2‐weighted spin‐echo imaging. The technique is more time‐efficient for clinical fat‐water imaging than 3PD schemes, while s

ISSN:0740-3194    

DOI:10.1002/mrm.1910380606

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

年代:1997

数据来源: WILEY

摘要:

AbstractIt has recently been demonstrated that magnetic resonance (MR) imaging of human lungs and airways is possible with hyperpolarized gases such as3He. Because the influence of the apparent transversal relaxation (T2* decay) and diffusion in3He imaging have not been quantified, an imaging pulse sequence was developed to measure these two parameters simultaneously. The imaging pulse sequence generates two series of multiply recalled gradient echo images with both different echo‐spacings and diffusion‐sensitizing gradients. From differences in exponential signal decay between the two series,T2* and diffusion coefficients,D, of both hyperpolarized and unpolarized3He samples could be measured on a standard clinical imager using a home‐built Helmholtz coil. In a hyperpolarized sample of pure3He values ofD= (1.8 ± 0.2) ± 10−4m2/s andT2* = 36 ± 13 ms were measured, whileD= (0.3 ± 0.1) · 10−4m2/s andT2* = 136 ± 66 ms were found in a Boltzmann‐polar

ISSN:0740-3194    

DOI:10.1002/mrm.1910380607

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

年代:1997

数据来源: WILEY

摘要:

AbstractIn this work, substrate selection was monitored in the left ventricle of the canine myocardium by following pyruvate and lactate oxidation underin vivoconditions at basal and elevated workloads. These studies were conducted in the open chest model using dynamic13C NMR techniques in the presence and absence of dichloroacetic acid (DCA), a well‐known activator of pyruvate dehydrogenase (PDH). Following the infusion of (3‐13C) pyruvate or (3‐13C) lactate into the left anterior descending artery, highly variable13C enrichments of glutamate, alanine, aspartate, and citrate were noted under low (RPP25,500 mmHg/min) rate pressure products (RPP). At low workloads, the myocardium typically oxidized the infused (3‐13C) pyruvate or (3‐13C) lactate and incorporated the labeled carbon into the glutamate pool as expected. However, in a few notable instances (n= 3),13C‐enriched pyruvate and lactate were unable to label the glutamate pool underin vivoconditions even at the lowest RPPs, indicating a lack of selection for these substrates by the tricarboxylic acid (TCA) cycle. Nonetheless, the levels of glutamate C4 enrichment observed at low workloads could usually be enhanced by infusion of DCA. Importantly,13C NMR extract analysis revealed that (3‐13C) pyruvate or (3‐13C) lactate labeling of the glutamate pool was reduced (<20%) at high workloads in spite of increased D

ISSN:0740-3194    

DOI:10.1002/mrm.1910380608

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

年代:1997

数据来源: WILEY

摘要:

AbstractA uridine phosphorylase inhibitor, 5‐benzylacyclouridine (BAU), has been utilized as biochemical modulator of 5‐fluorouracil (5‐FU) anti‐tumor activity in a murine tumor model. The effect of BAU on 5‐FU metabolism has been evaluated usingin vitroandin vivo19F NMR spectroscopy. The analysis of the NMR data revealed an increased formation and retention of fluorouracil nucleotides and fluorouridine in colon 38 tumors treated with the regimen containing BAU and a reduction in 5‐FU catabolites (α‐fluoro‐β‐ureidopropionic acid and α‐fluoro‐β‐alanine). In the normal tissues evaluated, the presence of BAU did not significantly alter the metabolism and presence of fluoropyrimidine species, indicating a more selective effect on tumor tissues. Therapy experiments on C57/BL6 mice bearing colon 38 tumor showed that the administration of 120 mg/kg BAU 30 min before 5‐FU at 85 mg/kg, on a weekly basis, resulted in an increased antineoplastic effect compared to the same dose of 5‐FU alone. A smaller dose of 5‐FU (60 mg/kg) also administered 30 min after 120 mg/kg BAU caused a reduction in tumor growth similar to 5‐FU alone. The addition of BAU to 5‐FU (85 mg/kg) resulted in a slight increase, although statistically nonsignificant, in host toxicity without causing any toxic death during the chemotherapeutic treatment.19F NMR spectroscopy is here shown to be a powerful technique to evaluate changes in the metabolism of fluoropyrimidines after the use of biochemical modulator and to allow a correlation between improved therapeutic response with the bio

ISSN:0740-3194    

DOI:10.1002/mrm.1910380609

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

年代:1997

数据来源: WILEY

摘要:

AbstractMany NMR measurements of cardiac microcirculation (perfusion, intramyocardial blood volume) depend on some kind of assumption of intracapillary‐extravascular water exchange rate, e.g., fast exchange. The magnitude of this water exchange rate, however, is still unknown. The intention of this study was to determine a lower limit for this exchange rate by investigating the effect of perfusion on relaxation time. Studies were performed in the isolated perfused cardioplegic rat heart. After slice‐selective inversion, the spin lattice relaxation rate of myocardium within the slice was studied as a function of perfusion and compared with a mathematical model which predicts relaxation rate as a function of perfusion and intracapillary‐extravascular exchange rate. A linear relationship was found between relaxation rateT−1and perfusionPnormalized by perfusate/tissue partition coefficient of water, λ: ΔT−1=m· ΔP/λ with 0.82 ≤m≤ 1.06. Insertion of experimental data in the model revealed that a lower bound of the exchange rate from intra‐to extravascular space is 6.6 s−1(4.5 s−1,P<0.05), i.e., the intracapillary lifetime of a water molecule is less than 150 ms (222 ms,P<0.05). Based on this finding, theT1mapping after slice‐selective inversion could become a valuable noncontrast NMR method to measu

ISSN:0740-3194    

DOI:10.1002/mrm.1910380610

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

年代:1997

数据来源: WILEY

摘要:

AbstractHomocarnosine is a dipeptide of gamma‐aminobutyric acid (GABA) and histidine found uniquely in the brain, most likely in a subclass of GABAergic neurons. By comparison of spectra from the occipital lobe of patients receiving a homocarnosine elevation drug to normal subjects we have assigned two elevated resonances in the shortTE1H MRS spectrum to homocarnosine. These resonances are partially resolved at 7.05 and 8.02 ppm in a shortTEspectrum at 2.1 T when macromolecule resonances are removed by subtraction of a spectrum in which the metabolite resonances are nulled by inversion recovery. The chemical shift of both of these resonances is sensitive to pHi. By comparison with a titration curve the pHiwas calculated from the downfield resonance to be 7.06 in the patient group which is similar to values reported using the Piresonance. Based on thein vivoresults and theoretical considerations the potential sensitivity for using nonelevated homocarnosine to measure pH is similar to that ofPiunder physiological condition

ISSN:0740-3194    

DOI:10.1002/mrm.1910380611

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

年代:1997

数据来源: WILEY