摘要:

AbstractIn 27 patients with low and high grade gliomas (n= 17), meningiomas (n= 4), and other supratentorial tumors and lesions (n= 6), the results of sodium‐23 MR imaging with high spatial resolution were compared to CT and proton MRI. The Na MR studies were performed with a 4.0‐T whole‐body MR system and an isotropic 3D‐Flash sequence (TR 70 ms, TE 11 ms), which depicts the longT2component of sodium. All patients tolerated the sodium study at 4.0 T well. The sodium images revealed almost all lesions, but the resolution was inferior to that of the reference methods. Two small meningiomas did not show up at all in the sodium study. Furthermore in one case small hemorrhages and calcifications within one of the tumors could not be found. Sodium imaging of the longT2component did not provide any additional information regarding the histology, grading, size, and differentiation of the tumor from the surrounding edema which had not already been provided by CT or H MRI. © 1991 Academic Pr

ISSN:0740-3194    

DOI:10.1002/mrm.1910220102

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

年代:1991

数据来源: WILEY

摘要:

AbstractIn vivo13C spectroscopy experiments were performed using a whole‐body MR system at a static field of 4 T. The main goal of the investigations was to evaluate the sensitivity increase achievable by means of13C/1H double‐resonance techniques at 4 T. Spectra from subcutaneous fat as well as muscle glycogen from the lower leg were acquired using frequency selective proton decoupling and the polarization transfer method SINEPT. With respect to measurements on subcutaneous fat, polarization transfer turned out to be more efficient than selective decoupling. About a fourfold enhancement in spectral peak intensity for the CC line doublet of the unsaturated fatty acid chain was obtained. Combining polarization transfer with decoupling yielded a factor of 6 in signal amplitude. In contrast to that, the signal enhancement observed in measurements on the glycogen C‐1 resonance was only around twofold. The lower efficiency is explained by fastT2relaxation of the proton transition. AT2value of about 3 ms was derived from the experimental data. Acquisition times as low as 3 min were realized for normal level glycogen in human calf muscle, enabling a time resolution adequate for dynamic studies on muscle glycogen depletion. Aspects of RF power absorption in tissue and the generally higher efficiency make polarization transfer methods preferable to selective decoupling in whole‐body13C spectroscopy at 4 T. © 1991 Academic

ISSN:0740-3194    

DOI:10.1002/mrm.1910220103

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

年代:1991

数据来源: WILEY

摘要:

AbstractLocalized proton spectroscopy was performed in 15 patients with acute or chronic multiple sclerosis (MS). Some of the patients were investigated serially, being given a total of 22 spectroscopic investigations. Resonances corresponding to free lipids were observed in six plaques. This was distinctly seen in two plaques at Days 70 and 85 after the occurrence of the plaques. A lesser content of lipids in plaques was observed as early as Day 10 and as late as nearly 1 year after occurrence. The relative concentration ofN‐acetyl asparate (NAA) was significantly lower in patients than in controls, and the relative concentration of choline (Cho) was significantly higher in patients than in controls. These differences were most pronounced in older plaques. MR spectroscopic demonstration of lipids in a MS plaque probably reflects disintegration of myelin, and a decreased NAA/Cho ratio may be related either to gliosis or to axonal degeneration, which sometimes occurs in longstanding MS. © 1991 Academic Press, I

ISSN:0740-3194    

DOI:10.1002/mrm.1910220104

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

年代:1991

数据来源: WILEY

摘要:

AbstractA method for the noninvasive, quantitative determination of regional cerebral blood flow (rCBF) in small laboratory animals, such as the rat, is described. The change in magnetic susceptibility in the vicinity of brain capillaries evoked by iv infusion of Gd(DTPA), a paramagnetic agent not crossing the blood‐brain barrier, is detected as an attenuation of the1H signal inT2‐weighted MRI sequences. The reduction of the MR signal intensity after 1 or 2 min of Gd(DTPA) infusion correlates well (r>0.95) with the rCBF values obtained using the well‐established [14C] iodoantipyrine method. At a slice thickness of 3 mm, the pixel size typically is 0.15 × 0.5 mm2. The clearance rate of Gd(DTPA) from blood allows repeated measurements of CBF to be made using this technique approximately every 30 min. The experimental results obtained in normal and ischemic rat brain have been rationalized within the frame of a two‐compartment model, allowing the definition of optimal experimental conditions for a given CBF: for normal and reduced CBF values (<150 ml/100 g/min) the reduction in MR signal intensity, measured after 1 or 2 min of Gd(DTPA) infusion, correlates closely with the CBF. However, for CBF values<150 ml/100g/min, a more reliable parameter would be the time constant of the MR signal attenuation during the infusion. © 1991 Academic P

ISSN:0740-3194    

DOI:10.1002/mrm.1910220105

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

年代:1991

数据来源: WILEY

摘要:

AbstractTreatment of RIF‐1 solid tumors with 5‐fluorouracil (5‐FU, 100 or 200 mg/kg, ip) caused substantial regression of the tumors, with regrowth initiated on Day 6 (100 mg/kg) or Day 9 (200 mg/kg). Blood perfusion in the tumor, estimated by uptake of86Rb+, was significantly increased after treatment with 5‐FU, while Rb+uptake in normal tissues (skin, muscle) was unaffected. The increase in tumor perfusion during the first few days following treatment was significantly greater in animals treated with the higher dose of 5‐FU. Perfusion‐dependent86Rb+uptake returned to control levels by the 9th day after treatment with 100 mg/kg of 5‐FU, but remained elevated on Days 9–12 after the higher dose. By the lst day following treatment with 5‐FU,in vivo31P NMR spectra of treated tumors indicated significantly higher ratios of phosphocreatine toPi, higher pH, and lower ratios ofPito nucleoside triphophates compared to untreated age‐matched controls. These changes persisted for 9 days following the lower 5‐FU dose and for at least 12 days following the higher dose. Treatment with 5‐FU induces profound, dose‐dependent changes in tumor bioenergetics, which may result, at least in part, from changes in tumor perfusion after cytoreduction.

ISSN:0740-3194    

DOI:10.1002/mrm.1910220106

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

年代:1991

数据来源: WILEY

摘要:

AbstractNew fatty‐acyl contrast agents,N3−2′‐myristoyloxyethyl‐N6−2′‐hydroxyethyl‐1, 8‐dioxotriethylenetetraamine‐N, N, N′, N′‐tetraacetic acid (MHE‐DTTA) andN3,N6‐bis (2′‐myristoyloxyethyl)‐1, 8‐dioxo‐triethylenetetraamine‐N, N, N′, N′‐tetraacetic acid (BME‐DTTA) were prepared by sequential alkylation, acylation, and catalytic hydrogenation from bis(hydroxyethyl)‐ethylenediamine with satisfactory yields (overall 36–46%). The 1:1 gadolinium complexes of the ligands MHE‐DTTA and BME‐DTTA were incorporated into liposomes and their relaxivitiesin vitrowere determined. The relaxivities of both agents were similar and were greater than those of Gd3+aquoion, Gd(EDTA), and Gd(DTPA) at both 0.23 T and 0.47 T. The relaxivities of these two agents increased from the lower to the higher magnetic field, indicating a positive field dependence. This is advantageous because of the widespread use of high‐field (B0>0.5 T) NMR imaging instruments. Stability constants (logK) of Gd(MHE‐DTTA) and Gd(BME‐DTTA) were found to be 15.27 ± 2.21 and 16.78 ± 0.36, respectively. LD50of both compounds was>0.2 mmol/kg. These stabilities and lower limits of LD50indicate the pos

ISSN:0740-3194    

DOI:10.1002/mrm.1910220107

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

年代:1991

数据来源: WILEY

摘要:

AbstractResponses specific to the spin‐spin relaxation time (T2) have been observed in two time‐dependent studies of the intracellular water in normal and transformed Syrian hamster fetal fibroblasts. At 300‐MHz (7.0 T), the spin‐lattice relaxation time (T1) was insensitive to several aspects of cellular physiology that produced changes in theT2and the apparent self‐diffusion coefficient (Dapp) of intracellular water. In normal cells stimulated with epidermal growth factor (EGF),T1was insensitive to time‐dependent changes detected byT2andDapp. In synchronized tumor cells,T1was insensitive to cell‐cycle‐dependent changes detected byT2. The strongly coupled behavior ofT2andDappthat was observed as a function of time in EGF‐stimulated cells indicates that the diffusion of intracellular water through inhomogeneous local magnetic field gradients produced effects observable inT2. Conformational changes in large intracellular macromolecular assemblies such as chromatin or the cytoskeleton may alter the magnitude and inhomogeneity of local field gradients, producing responses inT2andDapponly. © 1991 A

ISSN:0740-3194    

DOI:10.1002/mrm.1910220108

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

年代:1991

数据来源: WILEY

摘要:

AbstractThis present investigation was initiated to noninvasively evaluate the usefulness of intravenous gadopentetate dimeglumine (Gd‐PTDM) ‐enhanced magnetic resonance imaging (MRI) in assessing the integrity of the blood‐testis barrier (BTB). The intensity of different image slices was measured in pre‐and post‐Gd‐PTDM images in rats receiving cytochalasin D or alcohol treatment. It was found that MRI can be used to assess the integrity of the BTB and may be a useful tool in the evaluation of potentially toxic agents that affect the testis, particularly those that affect the BTB. © 1991 Academi

ISSN:0740-3194    

DOI:10.1002/mrm.1910220109

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

年代:1991

数据来源: WILEY

摘要:

AbstractSuccinyl (SDF), phenylsuccinyl (PSDF), glutaryl (GDF), and phenylglutaryl (PGDF) derivatives of desferrioxamine B (DF) have been synthesized. In rats given the59Fe(III) chelates of each these ligands at tracer levels, 82–94% of the59Fe was eliminated within 1–2 days.59Fe given as DF, SDF, and GDF chelates was excreted primarily in the urine, while nearly 50% of that given as PSDF and PGDF was excreted in the feces. Correspondingly, Fe‐DF, Fe‐SDF, and Fe‐GDF (0.2 mmol/kg) produced early, marked renal, but no gastrointestinal magnetic resonance imaging (MRI) enhancement. Fe‐PSDF and Fe‐PGDF (0.2 mmol/kg) produced marked and rapid MRI enhancement of the upper small intestine. In animals with cannulated bile ducts,59Fe for59Fe‐PGDF (carrier added, 0.1 mmol/kg) appeared rapidly in the collected bile, but not in the intestinal contents, proving that the contrast agent reaches the bowel via the bile. These changes in the excretion and MRI enhancement patterns brought about by the presence of a phenyl substituent apparently were not related to changes in lipophilicity or protein binding. © 1991 Aca

ISSN:0740-3194    

DOI:10.1002/mrm.1910220110

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

年代:1991

数据来源: WILEY

摘要:

AbstractInherent differences in tissue magnetic susceptibility produce inhomogeneities in the static magnetic field which give rise to an additional dephasing of the transverse magnetization in gradient‐echo images. The enhanced dephasing of the signal results in an increase of the apparent relaxation rate 1/T 2*and a corresponding decrease in signal intensity. These effects have been used to explain the regional loss of marrow signal intensity in the appendicular skeleton, where in the presence of trabecular bone in the proximal tibia there is an enhanced loss of signal compared to the tibial shaft where there is no trabeculation. It has been postulated that differences in tissue magnetic susceptibility arising due to the marrow‐trabeculae interface give rise to magnetic field inhomogeneities and a reducedT 2*. In this study computer simulations are used to determine whether susceptibility differences comparable to that between trabecular bone and tissue relate to the reduction of tissueT 2*and whether the reduction inT 2*is also related to the concentration and magnitude of susceptibility differences. In addition the effects of the spatial distribution of these particulate discontinuities in susceptibility on the measured relaxation timeT 2*are also estimated. This model demonstrates that 1/T 2*increases as the number density and magnitude of such susceptibility differences increase. In a pixel of linear dimensionLconsisting of material simulating tissue water, the presence of circular point susceptibility differences of dimension 0.001Lwith magnetic susceptibility equivalent to trabecular bone, 1/T 2*, increases at a rate of 1.60 × 10−2s−1/NforNranging from 25–2500. Differences in magnetic susceptibility that are less than that between soft tissue and trabecular bone are also modeled and the simulations demonstrate that differences in magnetic susceptibility, much lower than that between trabecular bone and tissue equivalent interfaces, also produce a relaxation rate enhancement in gradient‐echo images.

ISSN:0740-3194    

DOI:10.1002/mrm.1910220111

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

年代:1991

数据来源: WILEY