摘要:

AbstractA comparison between a time domain analysis algorithm (VARPRO) and a frequency domain analysis algorithm (FITPLAc) for parameter estimation of magnetic resonance spectroscopy (MRS) data series is presented. VARPRO analyses the measured MRS signal (free induction decay; FID); FITPLAcanalyses the discrete Fourier transform of the FID, the frequency domain magnetic resonance spectrum. A rapid time domain method, used to subtract the dominating water resonance from a1H MRS FID, without affecting the metabolites of interest, is outlined and applied. Also a new “pseudo‐frequency selective” approach to time domain fitting is introduced. The possibilities of combining the most favorable features of time and frequency domain processing into one single MRS signal processing method are assessed. The1H MRS signals of ultracentrifuged very low (VLDL), intermediate (IDL), and high (HDL) density lipoprotein fractions from human blood plasma were used for the comparisons. The results from both algorithms were in good agre

ISSN:0740-3194    

DOI:10.1002/mrm.1910310402

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

年代:1994

数据来源: WILEY

摘要:

AbstractA new 3D acquisition regimen that enables the collection of conventional, water‐suppressed, and fat‐suppressed images with no increase in scan times compared with currently implemented 3D sequences is presented. The method is based on conventional 3D steady state with interleaved selective excitation of the fat resonance resulting in acquisition of a fat‐based image during theTRperiod experienced by the water spins. This new sequence is relatively tolerant to susceptibility artifacts and results in excellent water‐based images. Because the idea, which we propose, is independent of the type of steady‐state imaging protocol utilized, it can be easily applied with regimens that are specifically tailored to enhance

ISSN:0740-3194    

DOI:10.1002/mrm.1910310403

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

年代:1994

数据来源: WILEY

摘要:

AbstractTo improve clinical utility, an integrated method has been developed to automatically acquire and process single‐voxelin vivoproton spectra on a 1.5 T clinical scanner. This method includes automated adjustment of linear shims using a very rapid modified simplex method, automated water suppression, and applies a water referencing scheme to correct for phase and residual eddy current effects. No operator intervention is required for the acquisition and processing of these pure‐absorption spectra. This method was tested in a preliminary multisite trial to determine intersite and intrasite variability of metabolite ratio measurements. In a sample of over 100 examinations, the standard deviation of the ratios NAA:Cr, Cho:Cr, and ml:Cr were found to be under 15% when using this method, a substantially narrower range than has been found In studies relying on manual adjustment of the instrument and/or manual processing. This result indicates that automated setting of acquisition and processing parameters is of critical importance in the clinical application ofin vivospectrosc

ISSN:0740-3194    

DOI:10.1002/mrm.1910310404

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

年代:1994

数据来源: WILEY

摘要:

AbstractEntry of13C‐enriched acetyl‐CoA into the citric acid cycle results in scrambling of13C into the various carbon positions of all intermediate pools. The eventual result is that the13C resonances of all detectable intermediates or molecules exchanging with those intermediates appear as multiplets due to nearest neighbor spin‐spin couplings. We have previously shown that an isotopomer analysis of the glutamate13C multiplets provides a history of13C flow through the cycle pools and that relative substrate utilization and relative anaplerotic flux can be quantitated (C.R. Malloy, A.D. Sherry, and F.M.H. Jeffrey,Am. J. Physiol. 259, H987–H995 (1990)). A major limitation of the method forin vivoapplications is spectral resolution of multiline resonances required for a complete isotopomer analysis. We now show that (13C)homonuclear decoupling of the glutamate C3 resonance collapses nine‐line C4 and C2 resonances into three‐line multiplets. We demonstrate that these three line13C multiplets are well resolved in isolated, perfused rat hearts and present steady‐state equations that allow an isotopomer analysis from data obtained in intact tissue. This advancement offers for the first time the possibility of extending13C isotopomer methods to complex metabolic cond

ISSN:0740-3194    

DOI:10.1002/mrm.1910310405

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

年代:1994

数据来源: WILEY

摘要:

AbstractPhantom studies were conducted to investigate the impact of trabecular structure on theT2′ signal measured by MRI. For a separation of density from structural effects, several phantoms were built. They consisted of parallel polyethylene strings arranged in a variety of different patterns to simulate (a) a constant uniform trabecular distribution with increasing trabecular thickness and (b) different structures with identical overall trabecular density. An asymmetric spin echo sequence was used to determine the apparent relaxation timeT2′. Changes inT2′ are induced by susceptibility differences between the polyethylene strings simulating trabeculae and Gd‐TPA doped saline simulating bone marrow. The results showed an increasingT2′ decay rate with (a) decreasing spacing while the string density was constant and (b) with increasing string density while the string arrangement was constant. The results demonstrate that theT2′ signal is affected not only by density but also by spatial distribution. However, the results also indicate that a separation of the two effects is not possible from aT2′ measurement alone, but that e.g., a matching CT slice that would provide purely density information is additionally needed. Theoretical simulations confirmed

ISSN:0740-3194    

DOI:10.1002/mrm.1910310406

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

年代:1994

数据来源: WILEY

摘要:

AbstractCurrent MR meal markers may interfere with gastric motility and secretion restricting the use of MRI in the measurement of gastric physiology. We therefore evaluated Gd‐DOTA as a liquid phase marker,in vitroby determining dissociation, and adherence to the solids, andin vivoby simultaneous MRI (0.35 T scanner, multipleT1‐weighted sections of the upper abdomen) and double indicator (perfusion marker PEG 4000, meal marker99mTc‐DTPA) measurements of emptying and secretion, following ingestion of 500 ml 10% glucose.In vitroGd‐DOTA was stable at a pH>2 with<2% dissociation at 24 h during incubation with HCI. Dissociation during incubation with HCI was linearly dependent on H+concentration (0.77

ISSN:0740-3194    

DOI:10.1002/mrm.1910310407

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

年代:1994

数据来源: WILEY

摘要:

AbstractWe report NMR diffusion measurements of water in three central nervous system models, namely the nonmyelinated olfactory, and the myelinated trigeminal and optic nerves of the spotted and long‐nosed garfish. A similar degree of anisotropy of the average diffusion coefficients (DNMR) is observed for all three freshly excised nerve types (DNMRparallel)/DNMR‐(perpendicular) is 3.6 ± 1.2, 3.2 ± 0.9, and 2.6 ± 0.4 for the olfactory, trigeminal, and optic nerves, respectively). The anisotropy of DNHR for the nonmyelinated olfactory nerve argues strongly that myelin is not a necessary determinant of diffusional anisotropy in ordered axonal systems (even though it may contribute when present). Garfish nerves treated with vinblastine, in order to depolymerize microtubules and inhibit fast axonal transport, also exhibit diffusional anisotropy {DNMR(parallel)/DNMR(perpendicular) is 2.6 ± 0.4,2.8 ± 0.8, and 2.2 ± 0.7 for the olfactory, trigeminal, and optic nerves, respectively) thus excluding a significant role for microtubules and fast axonal transport in that observed a

ISSN:0740-3194    

DOI:10.1002/mrm.1910310408

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

年代:1994

数据来源: WILEY

摘要:

AbstractMyocardial tagging is a powerful tool for the assessment of in‐plane cardiac motion. However, for previous myocardial tagging techniques, the imaged slice is fixed with respect to the magnet coordinate system. Thus, images acquired at different heart phases do not always represent the same slice of the myocardium. A new myocardial tagging technique is presented, which takes the through‐plane motion into consideration. It involves tagging of the desired myocardial slice and applying a subtraction imaging technique to image just that part of the myocardium. The examination time can be reduced considerably by the acquisition of two one‐dimensionally tagged images. To increase the signal‐to‐noise ratio especially at later heart phases, variable imaging RF excitation flip angles are applied. To reduce motion artifacts a repetitive breathhold scheme was applied.in vivoresults demonstrate that the tags can be accurately tracked within the entire heart period with a temporal resolution of 35 ms, even at a top basal level of the heart and right

ISSN:0740-3194    

DOI:10.1002/mrm.1910310409

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

年代:1994

数据来源: WILEY

摘要:

AbstractA three‐dimensional (3D), ECG‐triggered, selective inversion recovery (SIR) rapid gradient‐echo (RAGE) technique is proposed to obtain MR angiograms of the main renal arteries. By using the selective inversion recovery and fat saturation, the background is significantly suppressed while blood maintains a high signal intensity as compared with conventional 3D time‐of‐flight (TOF) MR angiography. The sequence is ECG‐triggered so that blood in‐flow is maximized during systole, and intravoxel dephasing and pulsatile flow artifacts are minimized by collecting data during diastole. As a result, vessel boundary blurring and ghosting artifacts due to background motion are dramatically reduced, and the conspicuity and lumen definition of the arteries are significantly improved. High‐quality MR angiograms of the main renal arteries with excellent blood/tissue contrast and suppression of motion artifacts have been consistently obtained for normal volunteers, with the length of visualization being 51 ± 07 mm for the left, and 57 ± 06 mm for the right renal arteries, significantly greater than using conventional 3D TOF pulse sequences. Statistical analysis was performed by using a one‐sided Student's t test. Key words: renal artery; MR angiography; three‐d

ISSN:0740-3194    

DOI:10.1002/mrm.1910310410

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

年代:1994

数据来源: WILEY

摘要:

AbstractWe present details of a novel RF coil for use in NMR microscopy. This coil is an inductively coupled surface coil which is built into a standard microscope slide. The coil is highly sensitive and is also designed so that the sample to be imaged can be viewed under an optical microscope. This facility allows comparison of optical and NMR micrographs, as well as accurate sample positioning. Using the slide coil, images of onion epidermal cells with an in‐plane resolution of 4.5 μm have been produc

ISSN:0740-3194    

DOI:10.1002/mrm.1910310411

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

年代:1994

数据来源: WILEY