摘要:

AbstractA comparison study was performed of 3D and 2D spiralk‐space fMRI techniques using BOLD contrast with a 4.25‐min finger‐tapping task paradigm. The 3D sequence uses the conventional 2D spiral technique in conjunction with Fourier phase encoding in the slice select direction. Characteristics that were compared included image appearances, signal‐to‐noise ratio (SNR), fluctuation noise, functional contrast‐to‐noise ratio (fCNR), detected activation areas, inflow effect, and large vessel involvement. The results showed that, with constant total scan time, the 3D spiral acquisition has higher SNR and fCNR despite its slightly higher fluctuation noise. The capability for thin‐slice incoherent averaging is a further advantage of 3D over 2D. With these advantages as well as its intrinsic ability for contiguous slices and image reformatting, the 3D spiral fMRI technique may be superior to its

ISSN:0740-3194    

DOI:10.1002/mrm.1910390112

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

年代:1998

数据来源: WILEY

摘要:

AbstractA technique using hyperpolarized (HP)3He to image the small airways of the lung by using moderate flip angles and a short scanning period during early inspiration is demonstrated. Flip angles(α)ranging from 10–90° were used in guinea pig experiments with scanning during the entire inspiration period. A second series acquired data throughout a short window of the ventilatory cycle with α= 45°. The success of the animal studies has motivated implementation of similar imaging techniques in the clinical arena. Human studies involved imaging over the total inspiration period withα ≈︁10°. The first series of guinea pig experiments demonstrated that larger flip angles (50‐90°) destroy the magnetization before it reaches the smaller airways. At moderate flip angles (20‐40°), airway branching down to the fourth generation was apparent. Fifth‐order branchings were seen in the images of the second series. The trachea down to fourth generation pulmonary airway branching, along with some distal air spaces, was seen in th

ISSN:0740-3194    

DOI:10.1002/mrm.1910390113

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

年代:1998

数据来源: WILEY

摘要:

AbstractRat lungs were imaged by19F projection MRI of hexafluoroethane, mixed with 20% oxygen to form the inhaled gas. The 3D image had 700μmresolution, and the data took 4.3 h to acquire. Free induction decays were collected in the presence of steady magnetic field gradients in 686 different directions. To take advantage of fast relaxation (T1= 5.9 ± 0.2 ms), the repetition time was 5 ms. To eliminate signal loss from magnetic field inhomogeneities, data were collected within 2 ms of spin excitation (from 80μsto 2 ms after the 42‐μs π/2 pulses). The singular value decomposition of the transform from frequency to time domain was used to obtain projections despite the absence of data during and immediately after the RF pulses. Inert fluorinated gas imaging may be less expensive than polarized noble gas imaging and is appropriate for imaging steadystate rather than transient gas concentr

ISSN:0740-3194    

DOI:10.1002/mrm.1910390114

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

年代:1998

数据来源: WILEY

摘要:

AbstractFunctional magnetic resonance imaging has been successfully used to map the activation in the lateral geniculate nucleus (LGN) in both hemispheres as well as the primary visual cortex (V1) during a checkerboard visual stimulation. The average blood oxygenation level dependent (BOLD) change in LGN was less than that in V1. However, the BOLD temporal responses were similar between LGN and V1. The activation in the pulvinar nucleus during visual perception was also detected, and its activated location could be separated from LGN in 3D images. The LGN activation between intersubject and intrasubject multiple trials was compared. The results demonstrate that fMRI can reliably and robustly detect small subcortical nucleus activation in the human brain.

ISSN:0740-3194    

DOI:10.1002/mrm.1910390115

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

年代:1998

数据来源: WILEY

摘要:

AbstractHigh‐resolution functional imaging experiments at 0.95 Tesla have been performed to determine the changes in oxygen saturation in pial veins during motor activation by measuring both flow and susceptibility changes in the blood. Averaging across subjects, mean values for the change of the oxygenation level, δY = 0.16 ± 0.08 (n = 7) and δY = 0.13 ± 0.09 (n = 4), were obtained from the susceptibility sensitive and the flow sensitive acquisitions, respectively. The results suggest that the increase in blood flow is largely uncoupled from the oxygen consumption. The quoted errors reflect mainly the inter‐subject variability. In addition, low‐resolution echo planar imaging (EPI) measurements were performed on the same volunteers to quantify signal intensity changes. Using the measured change in oxygenation, the observed signal changes in the EPI experiments can be attributed to a 5% venous blo

ISSN:0740-3194    

DOI:10.1002/mrm.1910390116

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

年代:1998

数据来源: WILEY

摘要:

AbstractMultiple receive coil arrays are often designed for unilateral imaging of anatomy having bilateral symmetry. A technique is described for extending the utility of such arrays to simultaneously image both bilaterally symmetric anatomical features. A separate, complete multiple receive coil array is placed at each location. Two separate, noncontiguous 3D volumes are then acquired, one at each location, in an interleaved fashion. High‐impedance blocking networks are alternately activated and deactivated to minimize coupling between the arrays. It is demonstrated that there is no degradation in image quality when compared to a unilateral exam. A general method for analyzing the interactions between separate multiple coil arrays is presente

ISSN:0740-3194    

DOI:10.1002/mrm.1910390117

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

年代:1998

数据来源: WILEY

摘要:

AbstractRight ventricular (RV) regional function, in both normal and diseased states, is not well characterized. Using 1D MR myocardial tagging, RV and septal intramyocardial segmental shortening was noninvasively measured in ten healthy subjects and in seven patients with chronic pulmonary hypertension. The normal RV free wall regional shortening was not uniform. A pattern of increasing RV free wall short‐axis shortening was found from the RV outflow tract to the RV apex, and a more complex pattern of RV free wall long‐axis shortening was observed. Both regional short‐ and long‐axis shortening were globally reduced in pulmonary hypertension patients, with the greatest decreases in the RV outflow tract and in the basal septal wall region. Regional RV function can be quantitatively evaluated using MR tagging to determine the impact of chronic pulmonary hypertension on RV perf

ISSN:0740-3194    

DOI:10.1002/mrm.1910390118

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

年代:1998

数据来源: WILEY

摘要:

AbstractThe effect of off‐resonance irradiation on the water proton NMR signal intensity has been investigated as follows: (a) in the presence of a paramagnetic probe like manganese(II); (b) in the presence of bovine serum albumin (BSA) and two gadolinium(III) complexes, Gd‐DTPA and Gd‐BOPTA; (c) in the presence of cross‐linked BSA and the two above‐mentioned gadolinium(III) complexes. The experimental data have been rationalized on the basis of the available theoretical models. The effectiveness of the two complexes as contrast agents for MRI has been predicted. It is shown that contrast agents providing comparable longitudinal and transverse relaxation rate enhancements are those of general interest for off‐resonance magnetization t

ISSN:0740-3194    

DOI:10.1002/mrm.1910390119

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

年代:1998

数据来源: WILEY

摘要:

AbstractProbability theory is applied to the analysis of fMRI data. The posterior distribution of the parameters is shown to incorporate all the information available from the data, the hypotheses, and the prior information. Under appropriate simplifying conditions, the theory reduces to the standard statistical test, including the general linear model. The theory is particularly suited to handle the spatial variations in the noise present in fMRI, allowing the comparison of activated voxels that have different, and unknown, noise. The theory also explicitly includes prior information, which is shown to be critical in the attainment ofreliableactivation maps.

ISSN:0740-3194    

DOI:10.1002/mrm.1910390120

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

年代:1998

数据来源: WILEY

摘要:

AbstractFluorine (19F) magnetic resonance spectroscopy (MRS) was used to quantify the combined concentration of the anorectic drug dexfenfluramine (DF) and its active metabolite d‐norfenfluramine (dNF) in rhesus monkey brain. The accuracy of the MRS technique was assessed by comparison with gas chromatography. Brain19F MRS signals were converted to brain DF + dNF concentrations after correction for signal relaxation losses and drug distribution in nonbrain tissue. Gas chromatography (GC) was used to assay brain DF and dNF concentrations following MRS evaluation. DF + dNF concentrations measured by19F MRS averaged 104 ± 36μM(mean ± SD) and GC measurements averaged 71 ± 12μM.Correction for the distribution of DF and its metabolites in nonbrain tissue yielded a DF + metabolite brain concentration that was within one standard deviation of the GC‐derived value. The concentration of DF plus dNF measured by19F MRS was similar to or greater than the value obtained by GC, which indicates that DF and its active metabolite dNF are fully detected by19F MRS in primate brainin vivo.The application of these techniques to human subjects should enable the measurement of low micromolar‐range brain concentrations of DF and other fluorin

ISSN:0740-3194    

DOI:10.1002/mrm.1910390121

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

年代:1998

数据来源: WILEY