摘要:

AbstractBased on the principles of echo imaging, we presnet a method to acquire sufficient data for a 256 × 256 image in from 2 to 40s. The image contrast is dominated by the transverse relaxation timeT2Sampling all projections for 2D FT image reconstruction in one (or a few) echo trains leads to image artifacts due to the differentT2weighting of the echo. These artifacts cannot be described by a simple smearing out of the image in the phase direction. Proper distribution of the phase‐encoding steps on the echoes can be used to minimize artifacts and even lead to resolution enhancement. In spite of the short data acquisition times, the signal amplitudes of structures with longT2are nearly the same as those in a conventional 2D FT experiment. Our method, therefore, is an ideal screening technique for lesions with longT2. © 1986 Academic Press,

ISSN:0740-3194    

DOI:10.1002/mrm.1910030602

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

年代:1986

数据来源: WILEY

摘要:

AbstractPrevious studies have suggested that one of the mechanisms of adriamycin (ADR) cardiomyopathy is depletion of high‐energy phosphate stores (HEP). To examine this hypothesis, we used31P nuclear magnetic resonance to asses the adenosine triphosphate‐to phosphocreatine ratio (ATP‐to‐PCR ratio) in Langendorff‐Perfused rabbit hearts. Using either and acute (5 days of therapy at 5mg/kg /day) or chronic model (7 to 10 weeks of therapy at 1.2 or 1.5mg/kg twice a week) we compared isovolumetric LV systolic pressure, heart rate, ATP‐to‐PCR rations, and histologic lesions between the treated and control animals in each model. In the acute model, there was a significant incraease in the ATP‐to‐PCr ratio (P<0.02), without significant change in myocardial function. Despite significant hemodynamic and histologic alterations in the chronic model, compared to controle, we were unable to identify significant differences in ATP‐to PCr ratios. We conclude that (a) there appear to be differences in energy metablism between the acute cardiotoxicity and the chronic cardiomyopathy of ADR in the rabbit model and (b) the mechanism of the chronic cardiomyopathy from ADR therpy does not appear to be related to progressive impariment of cellular high‐energy phosphate metabolims as measured by the ATP‐to‐PCr ratio.

ISSN:0740-3194    

DOI:10.1002/mrm.1910030603

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

年代:1986

数据来源: WILEY

摘要:

AbstractBased on the principle of selective inversion of the fat or water signal we have developed a method which allows the simultaneous acquisition of separated fat and water images. In combination with multiecho techniques, this allows the determination of shift selective relaxation times. A detailed analysis of the relaxation behavior of a human leg at 0.23 T shows thatT2of fat and water can differ by a factor of two or more. We think, that the potential of MRI for differential diagnosis can be greatly enhanced using our method. © 1986 Academic Press, Inc

ISSN:0740-3194    

DOI:10.1002/mrm.1910030604

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

年代:1986

数据来源: WILEY

摘要:

AbstractHigh‐resolution1H NMR spectroscopy has been applied to a study of urine from five normal human subjects during a 48‐h period of fasting and for 22 h thereafter. The excretion rates of all three ketone bodies (acetoacetate, 3‐D‐hydroxybutyrate, and acetone), acetylcaritine, and sarcosine during this period were measured. Parallel increases in the excretion of the ketone bodies and acetylcarnitine were observed during fasting with little change in the output of creatinine and sarcosine. © 1986 Academic Pr

ISSN:0740-3194    

DOI:10.1002/mrm.1910030605

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

年代:1986

数据来源: WILEY

摘要:

AbstractA simple and new flow velocity measurement technique using conventional spin‐echo sequence is proposed and its applications to a preclinical result are presented. This technique utilizes the phase velocity encoding effect due to 180° rf and its corresponding selection gradient. This phase encoding and its phase velocity relations have been obtained by numerical solution of the Bloch equation. A flow velocity measurement obtained with a volunteer using this proposed technique indicates close agreement with other previously measured valu

ISSN:0740-3194    

DOI:10.1002/mrm.1910030606

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

年代:1986

数据来源: WILEY

摘要:

AbstractAt 37°C and 20 MHz, theT1andT2proton relaxation processes in intact rat liver tissue are multiexponential functions which in the majority of cases were decomposed into a major (α* ≈ 90%,T 1*= 374 ms,T 2*= 58 ms) and a minor (α** ≈ 10%,T 1**= 130 ms,T 2**= 181 ms) component. Both,T1andT2, are temperature‐dependent with a temperature shift of ΔT1= 1.5 ms/°C and ΔT2= 0.5 ms/°C, respectively. Storage of liver tissue at 4°C and 37°C led to remarkable changes of theT1andT2values. ForT2these changes occurred after a shorter storage time than forT1, but they are more pronounced forT1, To avoid such influences the relaxation measurements were performed within one hour after excision of the tissue. Even at 4°C, long‐term storage (>3h) must be avoided. A method for the quantitative determination of the fat content in liver based on multiexponential analysis of theT1relaxation process was evaluated employing mixtures of triolein with liver homogenate. Triolein is a two‐component system withT 1*= 144 ms (α* = 62%) andT 1**= 355 ms (α** = 38%). Finally, liver‐specific protocol conditions were defined forin vitrorelaxation

ISSN:0740-3194    

DOI:10.1002/mrm.1910030607

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

年代:1986

数据来源: WILEY

摘要:

AbstractThe use of paramagnetic ions, bound to macromolecules and trapped in liposomes, as MRI contrast agents is suggested. As an example, the system of Mn2+bound to serum proteins was tested. The binding of the metal ions to the macromolecules enhances their relaxation and at the same time decreases their rate of diffusion out of the liposomes. The use of liposomes is expected to reduce the potential toxicity of the paramagnetic ions and allows their targeting toward specific tissues. © 1986 Academic Press, Inc

ISSN:0740-3194    

DOI:10.1002/mrm.1910030608

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

年代:1986

数据来源: WILEY

摘要:

AbstractRecently W. T. Dixon (Radiology153, 189 (1984)) introduced a simple method of proton chemical‐shift imaging which requires only two images, a conventional (in‐phase) image and an image in which fat and water protons are 180° out of phase during signal acquisition, to separate the signals from fat and water protons. We have tested the application of this method to the quantitative determination of fat content and fat and water longitudinal relaxation times, and analyzed the effects of random and systematic errors. Ten phantoms were constructed with a range of fat contents (0–50% by weight) and waterT1's (300–800 ms). Fat and waterT1's were measured with a 0.6‐T clinical imaging system in two ways: (1) using the system as a spectrometer with all gradients off, and (2) from least‐squares fits to in‐phase and out‐of‐phase image data made with six values ofTR. The image‐derived values of waterT1agreed well with spectrometer‐derived values (r= 0.97) and the image derived fat fraction correlated strongly with the fat fraction by weight (r= 0.995). The effects of random and systematic errors were analyzed for a minimum data set of four images: in‐phase and out‐of‐phase images at two values ofTR. The pair ofTRvalues which minimize the variance in waterT1were calculated, and for these pulse sequences the effects of two potential systematic errors were calculated: (1) inhomogeneities in the main field, which will reduce the intensity in out‐of‐phase images compared to in‐phase images even for pure water samples, and (2) an incorrect shift of the 180° pulse in the out‐of‐phase pulse sequence, corresponding to an inaccurate assumed chemical shift. With careful attention to such systematic effects the Dixon method is capable of producing reliable quantitative m

ISSN:0740-3194    

DOI:10.1002/mrm.1910030609

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

年代:1986

数据来源: WILEY

摘要:

AbstractAn MRI installation (Magnetom, Siemens, software version B1 of NUMARIS) working at 0.35 T was used to estimateT1,T2, and relative proton density in the spleen, liver, adipose tissue, and vertebral body in 14 healthy volunteers. Two double‐echo sequences were applied for all subjects:TR= 500 ms,TE1= 35 andTE2= 70 ms; andTR= 1600 ms,TE1= 35 andTE2= 70 ms. The images were sampled in regions of interest and appropriate relaxation expressions fitted to the ROI data yielding relaxation parameters and relative proton densities. Relaxation expressions, included in standard software (Siemens), were compared to more elaborate functions, developed in parallel to this study. The latter were found more appropriate, especially for highT1values, and gave the following mean values for the four tissues (estimated uncertainty of mean in parentheses)T1(ms) 915(36), 428(5), 261(7), and 501(11);T2(ms) 79.7(8.8), 51.0(0.2), 59.8(1.0), and 64.7(0.8); and corresponding relative proton density (ρ, arbitrary units) 2088(136), 2182(10), 2915(49), and 2136(21). The uncertainty in the values was estimated in the fitting procedure and does not include systematic errors. The relative noise in the ROIs was about 9% and the reproducibility of the ROI mean values about 8%. © 1986 Academic Press,

ISSN:0740-3194    

DOI:10.1002/mrm.1910030610

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

年代:1986

数据来源: WILEY

摘要:

Abstract1H‐decoupled13C NMR spectra (20.2 MHz) of the living rabbit brain were collected with a surface coil following the intravenous infusion of [1‐13C]glucose. Within 15 min of infusion, the α and β anomers of glucose were detected and, shortly thereafter, the carbon atoms at positions C4, C3, and C2 of glutamate and(or) glutamine. After reductions of inspired oxygen from 30 to 5%, lactate C3 was detected. The intensity of the lactate resonance rose progressively during hypoxia and later fell during recovery with oxygen. The13C fractional isotopic enrichment of arterial blood glucose was measured by1H NMR providing information on the rate and extent of blood glucose labeling. © 1986 Academic Pres

ISSN:0740-3194    

DOI:10.1002/mrm.1910030611

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

年代:1986

数据来源: WILEY