摘要:

AbstractA method is presented for obtaining high‐sensitivity arterial input functions following bolus intravenous contrast agent administration. Arterial contrast agent is monitored by phase reconstruction of single‐shot echo‐planar images. During bolus injections of a gadolinium (Gd) agent in a baboon, data were acquired at the mid‐abdominal aorta, and magnitude and phase‐shift images were reconstructed. Pair‐wise image subtraction was used to minimize phase aliasing. The phase‐based method is shown to have a significant potential improvement in sensitivity compared to the magnitude approach. The phase method also has a general linear response to concentration. This method may have potential utility in quantitative imaging of blood flow and contrast a

ISSN:0740-3194    

DOI:10.1002/mrm.1910360602

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

年代:1996

数据来源: WILEY

摘要:

AbstractThis paper reports the development of dedicated catheters and real‐time MR scan techniques for guiding vascular interventional procedures. By way of phantom experiments, it is shown that proper modification of the magnetic properties of catheters allows their conspicuous and consistent visualization in subsecond 2D gradient echo images and phase contrast angiograms. Dynamic scan times as low as 0.5 s could be achieved by exploiting the keyhole technique and purposeful postprocessing. The temporal resolution and spatial resolution of the resultant scan protocol shows promise for adequate tracking of catheter manipulatio

ISSN:0740-3194    

DOI:10.1002/mrm.1910360603

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

年代:1996

数据来源: WILEY

摘要:

AbstractPrevious studies have shown that reduction ofN‐acetyl‐aspartate (NAA) is correlated with the degree of neuronal loss at 3 days after kainate‐induced status epilepticus in the rat. In this study, magnetic resonance spectroscopic imaging (MRSI), measurement of NAA and lactate,T2‐weighted MRI, and diffusion‐weighted MRI were used to study early alterations in rat piriform cortex at 12 and 26 h after kainate administration. The major findings are that decreased NAA signal, increased lactate signal, and decreased apparent diffusion coefficient (ADC) were observed at 12 h, with little evidence of histological andT2‐weighted MRI changes. These results support the hypothesis that NAA, lactate signals, and ADC provide sensitive methods for detection of early and minimal brain da

ISSN:0740-3194    

DOI:10.1002/mrm.1910360604

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

年代:1996

数据来源: WILEY

摘要:

AbstractIn vivo, ex vivo, andin vitroproton magnetic resonance spectroscopy was performed in 12 patients with intracranial tuberculomas with an aim of detecting the biochemical constituents ofMycobacterium tuberculosisin a granuloma. One dimensional (1D) single pulse and spin‐echo sequences and 2D correlative spectroscopy were used for theex vivostudy to confirm the resonances seen onin vivostudy. Spectroscopic studies of the perchloric acid and lipid extract of granuloma andM. tuberculosiswere performed to look for similarity of resonance.In vivostudy showed the presence of lipids at 0.9, 1.3, 2.0, 2.8 ppm, and phosphoserine at 3.7 ppm. All these resonances were confirmed onex vivostudy. In addition, distinct resonances of serine and phenolic lipids were seen onex vivoandin vitrostudy of tuberculous granuloma, which have not been observed in other intracranial tumors. Lipid extract of granuloma andM. tuberculosisshowed phenolic lipids at 7.1 and 7.4 ppm, a constituent of the cell wall of the bacteria in a tuberculoma. It appears that it may be possible to finger print the biochemicals of the cell wall ofM. tuberculosisin a tuberculous granuloma and thus may help in detection and diagnosis of such lesion

ISSN:0740-3194    

DOI:10.1002/mrm.1910360605

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

年代:1996

数据来源: WILEY

摘要:

AbstractConventional magnetic resonance images have uniform spatial resolution across the entire field of view. A method of creating MR images with user‐specified spatial resolution along one dimension of the field of view was described recently by the authors. This paper presents the 2D generalization of this technique, which allows the user to specify arbitrary spatial resolution in arbitrary 2D regions. These images are reconstructed from signals that sparsely sample the k‐space representation of the image. Therefore, locally focused images can be acquired in less time than that required by Fourier imaging with uniformly high resolution. In this paper the authors show how to increase the temporal resolution of dynamic imaging (e.g., interventional imaging) by using high resolution in areas of expected change and lower resolution elsewhere. Alternatively, by matching the local spatial resolution to the expected edge content of the image, it is possible to avoid the localized truncation artifacts that mark Fourier images reconstructed from the same number of signals. For example, the authors show how proton spectroscopic images of the head may be improved by using high resolution in the neighborhood of scalp lipids that might otherwise cause truncation artifa

ISSN:0740-3194    

DOI:10.1002/mrm.1910360606

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

年代:1996

数据来源: WILEY

摘要:

AbstractDiffusion‐weighted single voxel experiments conducted atb‐values up to 1 × 104smm−2yielded biexponential signal attenuation curves for both normal and ischemic brain. The relative fractions of the rapidly and slowly decaying components (f1, f2)are f1= 0.80 ± 0.02, f2= 0.17 ± 0.02 in healthy adult rat brain and f1= 0.90 ± 0.02, f2= 0.11 ± 0.01 in normal neonatal rat brain, whereas the corresponding values for the postmortem situation are f1= 0.69 ± 0.02, f2= 0.33 ± 0.02. It is demonstrated that the changes in f1and f2occur simultaneously to those in the extracellular and intracellular space fractions (fex, fin) during: (i) cell swelling after total circulatory arrest, and (ii) the recovery fromN‐methyl‐D‐aspartate induced excitotoxic brain edema evoked by MK‐801, as measured by changes in the electrical impedance. Possible reasons for the discrepancy between the estimated magnitude components and the physiological values are presented and evaluated. Implications of the biexponential signal attenuation curves for diffusion‐weighted imaging exp

ISSN:0740-3194    

DOI:10.1002/mrm.1910360607

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

年代:1996

数据来源: WILEY

摘要:

AbstractThe goal of this work was to develop a comprehensive understanding of the relationship between vascular proton exchange rates and the accuracy and precision of tissue blood volume estimates using intravascularT1contrast agents. Using computer simulations, the effects of vascular proton exchange and experimental pulse sequence parameters on measurement accuracy were quantified.T1and signal measurements made in a rat model implanted with R3230 mammary adenocarcinoma tumors demonstrated that the theoretical findings are biologically relevant; data demonstrated that over‐simplified exchange models may result in measures of tumor, muscle, and liver blood volume fractions that depend on experimental parameters such as the vascular contrast concentration. As a solution to the measurement of blood volume in tissues with exchange that is unknown, methods that minimize exchange rate dependence were examined. Simulations that estimated both the accuracy and precision of such methods indicated that both the inversion recovery and the transverse‐spoiled gradient echo methods using a “noexchange” model provide the best trade‐off between accuracy and

ISSN:0740-3194    

DOI:10.1002/mrm.1910360608

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

年代:1996

数据来源: WILEY

摘要:

AbstractThe effects of three physiologically different vasomodulators, angiotensin II (a vasoconstrictor), hydralazine (a vasodilator), and histamine (a permeability modulator), on the pharmaco‐kinetics of entry of small molecules (measured by Gd‐DTPA concentration) into normal and abnormal tissue were studied in rats implanted with R3230 AC tumors. Sequential dynamic Gd‐DTPA‐enhanced MRI studies, one before and one after vasomodulator administration, were performed, and the signal intensities of various tissues analyzed. Angiotensin II (6 μg/kg) reduced blood flow in tumors, but increased it in muscles. Hydralazine (5 mg/kg) reduced blood flow in tumors, kidneys, and livers, and slowed Gd‐DTPA clearance from tumors, livers, and muscles. Histamine (25 μg/kg) increased renal blood flow, hastening Gd‐DTPA clearance causing reduced measurable blood flow in tumors and muscles. By simultaneously monitoring the effects in various tissues, the pharmacokinetic effect of each drug in the entire body coul

ISSN:0740-3194    

DOI:10.1002/mrm.1910360609

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

年代:1996

数据来源: WILEY

摘要:

AbstractPrevious studies of the brains of normal infants demonstrated lower lactate (Lac)/choline (Cho), Lac/creatine (Cr), and Lac/N‐acetylaspartate (Naa) peak‐area ratios in the thalamic region (predominantly gray matter) compared with occipitoparietal (mainly unmyelinated white matter) values. In the present study, thalamic Cho, Cr, and Naa concentrations between 32–42 weeks' gestational plus postnatal age were greater than occipito‐parietal: 4.6 ± 0.8 (mean ± SE), 10.5 ± 2.0, and 9.0 ± 0.7 versus 1.8 ± 0.6, 5.8 ± 1.5, and 3.4 ± 1.1 mmol/kg wet weight, respectively: Lac concentrations were similar, 2.7 ± 0.6 and 3.3 ± 1.3 mmol/kg wet weight, respectively. In the thalamic region, Cho and NaaT2s increased, and Cho and Lac concentrations decreased, during development. Lower thalamic Lac peak‐area ratios are principally due to higher thalamic concentrations of Cho, Cr, and Naa rather than less Lac. The high thalamic Cho concentration may relate to active myelination; the high thalamic Naa concentration may be due to advanced gray‐matter development including active myelination. Lac concentration is higher in neonatal

ISSN:0740-3194    

DOI:10.1002/mrm.1910360610

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

年代:1996

数据来源: WILEY

摘要:

Abstract6‐aminonicotinamide (6AN) has been shown to enhance radio‐sensitivityin vitro, although previousin vivostudies failed to show an effect.31P NMR spectra were obtained by using a one‐dimensional chemical shift imaging technique on a first generation transplant of the CD8FI spontaneous mammary carcinoma tumor model. Spectra were obtained both before and 10 h after treatment with 6AN (20 mg/kg). Changes in pH, nucleoside triphosphate/inorganic phosphate, and phosphocreatine/inorganic phosphate measured at 10 h post‐6AN were not significant. A new peak was detected 10 h post‐6AN, which was assigned to 6‐phosphogluconate (6PG), indicating inhibition of the pentose phosphate pathway (PPP). Based on the spectral data demonstrating inhibition of the PPP at 10 h post‐6AN, tumor‐bearing mice were irradiated (15 Gy × 3 fractions) on Days 1, 10 or 11, and 21 10 h after administration of 6‐aminonicotinamide (20 mg/kg). Tumor‐bearing mice receiving 6AN alone (20 mg/kg × 3), radiation alone (15 Gy × 3), or saline were also studied. Tumor growth delay studies indicated that 6AN alone induced a small but significant tumor growth delay (4.3 ± 0.8 days). Radiation alone induced a tumor growth delay of 34.5 ± 2.7 days. Treatment with 6AN followed by radiation induced a tumor growth delay of 57.0 ± 3.8 days. This was significantly greater than the TGD values for treatment with 6AN alone or radiation (P<0.01). No complete regressions were noted after treatment with 6AN or radiation alone. Concomitant therapy with 6AN plus radiation yielded 6/28 complete regressions (21%), which was significantly greater than radiation (P<0.05) or 6AN alone (P<0.01)

ISSN:0740-3194    

DOI:10.1002/mrm.1910360611

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

年代:1996

数据来源: WILEY