摘要:

AbstractMethods are lacking for accurate, noninvasive circumferential edge detection and wall shear stress calculation. Using stan dard MR phase contrast sequences, parts of the velocity pro files were fitted to a multiple sectored three‐dimensional pa raboloid model enabling exact calculation of vessel wall position and wall shear stress in 24 locations evenly distrib uted around the luminal vessel wall. The model was evaluated byin vitroscans and computer simulations and applied to the common carotid artery of humans.In vitro, the luminal area of a glass tube was assessed with an error of 0.9%. Computer simulations of peak systolic data revealed errors of ±0.9% (vessel area) and ±3.25% (wall shear stress). Thein vivoresults showed substantial difference between anterior and posterior wall shear stress values due to skewed velocity profiles. A new noninvasive method for highly accurate mea surement of circumferential subpixel vessel wall position and wall shear stress has been develo

ISSN:0740-3194    

DOI:10.1002/mrm.1910400502

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

年代:1998

数据来源: WILEY

摘要:

AbstractCoronary artery disease continues to be the leading cause of death for adults in the United States. Magnetic resonance imaging (MR) has the potential to dramatically impact the diagnosis of heart disease by noninvasively providing a wide range of anatomic and physiologic information. Previous re search has shown that coronary flow, one component of a complete examination, can be accurately measured in the left anterior descending arteryin vivaThe current work validates MR flow measurements in canine circumflex arteries using transit time ultrasound as a standard. The circumflex artery experiences greater in‐plane motion and is a more stringent test for flow measurement accuracy. This work also com pares two methods of processing MR velocity data, phase difference and complex difference techniques, and examines the sources of error present in the animal validation model. Phase difference processing with a 30% magnitude threshold best matched the mean ultrasound flow values (30% PD = 1.04 × US + 1.49,r= 0.94), but it was very sensitive to vessel boundary identification. The complex difference process was less sensitive to vessel boundary identification and correlated well with the transit time ultrasound despite systematic un‐derestimations. The reasons for the discrepancies are shown to stem from a number of possible sources including variabil ity of the ultrasound standard, low signal‐to‐noise ratios in the MR images, sensitivity of the MR technique to vessel bound ary identification, and motion artifacts in th

ISSN:0740-3194    

DOI:10.1002/mrm.1910400503

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

年代:1998

数据来源: WILEY

摘要:

AbstractA new technique, CAPTIVE, that is a synthesis of arterial spin labeling (ASL) blood flow and steady‐state susceptibility con trast relative blood volume imaging is described. Using a single injection of a novel, long half‐life intravascular magnetopharma‐ceutical with a high tissue:blood susceptibility difference (Δ χ) to ΔR1 ratio, changes in tissue transverse relaxivity (ΔR2 or ΔR2*) that arise from changes in blood volume were measured, while preserving the ability to measure blood flow using traditionalT1‐based ASL techniques. This modification permits the contin uous measurement of both blood flow and blood volume. Also, because the contrast agent can be used to remove the signal from intravascular spins, it is possible to measure the first‐pass water extraction fraction. Contrast‐to‐noise is easily traded off with repetition rate, allowing the use of non‐EPI scanners and more flexible imaging paradigms. The basic theory of these measurements, several experimental scenarios, and validating results are presented. Specifically, the PaCO2‐reactivity of mi‐crovascular and total relative cerebral blood volume (rCBV), ce rebral blood flow (CBF), and the water extraction‐flow product (EF) in rats with the new contrast agent MPEG‐PL‐DyDTPA is measured, and the values are concordant with those of previous literature. As an example of one possible application, continuous flow and volume measurements during transient focal ischemia are presented. It is believed that CAPTIVE imaging will yield a more complete picture of the hemodynamic state of an organ, and has further application for understanding

ISSN:0740-3194    

DOI:10.1002/mrm.1910400504

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

年代:1998

数据来源: WILEY

摘要:

AbstractThe effect of ischemia and reperfusion on transverse relax ation (T2) of intracellular Na+(Na+i) was measured with 5‐min time resolution in isolated rat hearts. NaiT2relaxation was biexponential with 28 ± 7% fast (T2f)and 72 ± 7% slow (T2s) decay. This ratio was constant throughout the protocol. Dur ing 20 min of ischemia, NaiT2sincreased from 18.9 ± 2.7 ms to 26.4 ± 1.1 ms (P<0.001), whereasT2fdid not change significantly (3.1 ± 1.8 versus 2.3 ± 1.6 ms during control), and Na+iincreased from 9.0 ± 1.0 to 19.5 ± 1.0 mmol/liter (P<0.001). T2sand Na+ideclined again during reperfusion. Changes in T2srelaxation correlated significantly (r = 0.73,P<0.001) with the time cours

ISSN:0740-3194    

DOI:10.1002/mrm.1910400505

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

年代:1998

数据来源: WILEY

摘要:

AbstractThe intra‐individual and inter‐individual variations of the globalN‐acetylaspartate (NAA) concentration were measured in a cohort of five 42 ± 5 year‐old normal females. The total NAA signal from the whole head was obtained with non‐localized non‐echo proton spectroscopy (1H‐MRS) and con verted into absolute mole amounts using phantom replace ment. Since NAA is assumed to be present only in neurons, its concentration was obtained by dividing these mole amounts with the brains' volume, calculated from high resolution MRI. The key feature of the procedure is its near‐complete sup pression of the intense subcutaneous and bone marrow lipids' signals, whose chemical shifts neighbor and underlay the NAA. This was achieved by exploiting the lipids' much shorterT1s, compared to that of NAA, for destructive interference of their signals in co‐addition following alternating, nonselective 180° inversions. The average global, inter‐individual NAA concentration in that group was found to be 10.63 mMwith a 95% confidence inter

ISSN:0740-3194    

DOI:10.1002/mrm.1910400506

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

年代:1998

数据来源: WILEY

ISSN:0740-3194    

DOI:10.1002/mrm.1910400507

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

年代:1998

数据来源: WILEY

摘要:

AbstractA new method for B1‐insensitive water suppression using adiabatic RF pulses is described. The transition zone of the inversion profile of adiabatic full passage (AFP) pulses is used for frequency‐selective excitation followed by dephasing of the excited water with magnetic field gradients. Several im provements of AFP pulses, which also have implications for other applications, are described. The technique was evalu ated by simulations based on the Bloch equations (including relaxation),in vitroexperiments and anin vivoverification on neonatal and adult rat br

ISSN:0740-3194    

DOI:10.1002/mrm.1910400508

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

年代:1998

数据来源: WILEY

摘要:

AbstractCoronary arteries are segmented from the blood pool using mathematical morphology operations from a 3D magnetic resonance spiral acquisition on a continuously breathing healthy volunteer. The segmented volume is maximal intensity projected at different views to yield coronary angiograms showing the left anterior descending artery (LAD), right coro nary artery (RCA), and left circumflex artery (LCX). Magnetic resonance coronary angiography provides a retrospective ro tating view of the coronary artery tree that complements oblique reformatted sections.

ISSN:0740-3194    

DOI:10.1002/mrm.1910400509

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

年代:1998

数据来源: WILEY

摘要:

AbstractA relationship between regional cerebral blood flow (CBF) and blood oxygenation level dependent (BOLD) changes in the primary visual cortex (V1) at varied visual stimulation fre quency has been examined quantitatively using the multislice FAIR technique. A linear correlation in the common activation areas between functional BOLD and CBF maps was observed. This supports the hypothesis that the task‐stimulated BOLD changes in microvasculature are correlated with the CBF changes that presumably reflect the degree of neuronal ac tivity. The linear correlation coefficients for intrasubject com parisons are more significant than those for intersubject com parisons. This suggests that using intrasubject comparisons for quantitative studies of neuronal activity related to different task stimuli and task performances should be more reliable than using intersubject comparison

ISSN:0740-3194    

DOI:10.1002/mrm.1910400510

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

年代:1998

数据来源: WILEY

摘要:

AbstractIt is shown that the flow‐sensitive alternating inversion recov ery (FAIR) technique is complicated by the effect of radiation damping, leading to problems in calibrating this method on phantoms and to inaccuracies in measured flows. A modified scheme called FAIRER (FAIR excluding radiation damping) is proposed, which suppresses the damping effects by employ ing very weak magnetic field gradients (0.06 G/cm) during the inversion recovery, spin‐echo, and predelay periods. Results on phantoms andin vivoon cat brain are presented that demonstrate that FAIRER effectively solves these probl

ISSN:0740-3194    

DOI:10.1002/mrm.1910400511

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

年代:1998

数据来源: WILEY