摘要:

AbstractWater molecules associated with collagen have short transverse (T2) relaxation times. Projection‐reconstruction techniques are able to achieve an echo time (TE) much shorter than conventional techniques, allowing imaging of tissues withT2<5 ms. Using these techniques, a conventional 1.5‐T MRI human imaging system can directly image collagen‐associated water from knee menisci and tendons in normal volunteers and patients. Long‐T2suppression improves the contrast between these structures and the surrounding tissue with long‐T2relaxation times. Spectroscopic imaging provides improved lipid/water registration and information about chemical composition and relaxation times. Direct imaging of tendons and menisci may provide more information about these structures and provide a new way to assess both injury a

ISSN:0740-3194    

DOI:10.1002/mrm.1910340502

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe stability and reproducibility of the dynamic susceptibility contrast (DSC) MRI method for sequential relative cerebral blood volume (relCBV) measurements was evaluated to validate the method for use in quantitative studies of cerebral hemodynamics in humans. A spin echo echo planar imaging protocol was used in conjunction with multiple bolus injections of the susceptibility contrast agent gadoteridol (GD). The effects of variation in interbolus interval (10 min to 4 h), the number of injections (two to four), and the effect of the cerebral vasodilating agent acetazolamide (ACZ) were evaluated in 44 experiments performed with 22 normal subjects. Two fundamental observations were made. First, with multiple injections of GD, the change in MR signal over time was not consistent from first to subsequent boluses. A second bolus administered 10 min to 2 h after an initial bolus resulted in signal change of greater amplitude and duration, resulting in artifactually elevated estimates of relCBV, consistent with a residual effect of GD. Second, a relative steady state could be reached with serial injections of GD, such that the profile of subsequent boluses closely paralleled those of previous ones. This facilitates the reliable measurement of relCBV during activation, as demonstrated by use of ACZ.

ISSN:0740-3194    

DOI:10.1002/mrm.1910340503

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

年代:1995

数据来源: WILEY

摘要:

AbstractDermatomyositis is an autoimmune disease characterized by an erythematous rash and severe muscle weakness.31P Magnetic resonance spectroscopy (MRS) provides quantitative data for longitudinal monitoring of disease status and responses to immunosuppressive therapy. A disease variant, amyopathic dermatomyositis, presents with a typical rash but no clinical muscle weakness. However, metabolic abnormalities in the oxidative capacity of muscles of amyopathic patients during exercise were detected with31P MRS. Because MRS provided the best quantitative data for evaluating dermatomyositis, the31P metabolic parameters derived from the MR spectra were further processed using an artificial neural network (XERION). The neural network analyses provided additional clinical information from the weighted correlations of multiple31P parameters, namely, inorganic phosphate, phos‐phocreatine, ATP, phosphodiesters, and selected ratios. This investigation analyzes the relative importance of the various metabolic parameters for accurate patient characterization and provides insights into the pathogenesis of the diseas

ISSN:0740-3194    

DOI:10.1002/mrm.1910340504

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

年代:1995

数据来源: WILEY

摘要:

AbstractAn increase in intracellular Na+during ischaemia has been associated with myocardial injury. In this study, we determined whether inhibition of Na+/K+ATPase activity contributes to this increase and whether Na+/K+ATPase activity can be maintained by provision of glucose to perfused rat hearts during low flow, 0.5 ml/min, ischemia. We used31P NMR spectroscopy to determine changes in myocardial energetics and intracellular and extracellular volumes.23Na NMR spectroscopy, with DyTTHA3‐present as a shift reagent, was used to measure changes in intracellular Na+and87Rb NMR spectroscopy was used to estimate Na+/K+ATPase activity from Rb+influx rates, Rb+being an NMR‐sensitive congener of K+. In hearts provided with 11 mMglucose throughout ischemia, glycolysis continued and ATP was twofold higher than in hearts without glucose. In the glucose‐hearts, Rb+influx rate was threefold higher, intracellular Na+was fivefold lower at the end of ischemia and functional recovery during reperfusion was twofold higher. We propose that continuation of glycolysis throughout low flow ischemia allowed maintenance of sufficient Na+/K+ATPase activity to prevent the increase in intracellular Na+that would otherwise have led to myocardial i

ISSN:0740-3194    

DOI:10.1002/mrm.1910340505

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

年代:1995

数据来源: WILEY

摘要:

AbstractA comprehensive strategy for the acquisition, reconstruction, and postprocessing of MR spectroscopic images is presented. The reconstruction algorithm is the most critical component of this strategy. It is assumes that the desired image is spatially bounded, meaning that the desired image contains an object that is surrounded by a background of zeros. The reconstruction algorithm relies on prior knowledge of the background zeros fork‐space extrapolation. This algorithm is a good candidate for proton MR spectroscopic image reconstruction because these images are often spatially bounded and prior knowledge of the zeros is easily obtained from a rapidly acquired high resolution conventional MRI. Although the reconstruction algorithm can be used with the standard 3DFTk‐space distribution, a distribution that relies on anatomical features that are likely to occur in the spectroscopic image can produce better results. Prior knowledge of these anatomical features is also obtained from a conventional MRI. Finally, the postprocessing component of this strategy is valuable for reducing subcutaneous lipid contamination. Overall, the comprehensive approach presented here produces images that are better resolved than standard approaches without increasing acquisition time or reducing SNR. Examples using NAA data are provi

ISSN:0740-3194    

DOI:10.1002/mrm.1910340506

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe authors describe the feasibility of dynamic MRI using a novel superparamagnetic iron oxide contrast agent. Resovist® was injected as a bolus at doses of 4, 8, and 16 μmol Fe/kg bodyweight in three consented patients participating in a Phase 2 clinical multicenter trial for hepatic MRI. Dynamic images of the brain were obtained with a conventional FLASH sequence. Results were analyzed by evaluation of dynamic images, cerebral blood volume maps, and normalized signal intensity time curves. Resovist® enabled rapid injections and a dose‐dependent strong reduction in gray and white matter signal intensity. The small injection volume and good tolerability may enable Resovist® to serve as a perfusion agent. Dedicated clinical trials are warranted to assess the potentials of Resovist® for perfusion MRI an

ISSN:0740-3194    

DOI:10.1002/mrm.1910340507

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

年代:1995

数据来源: WILEY

摘要:

AbstractPhase contrast flow velocity measurements were performed in six healthy volunteers and 30 patients with arteriosclerotic disease. The iliac arteries were investigated in 8 cases and the femoral arteries in 28 cases. In the first 24 patients, 16 evenly distributed data sets were acquired during one cardiac cycle. In the last 12 patients, a trigger pulse followed by the acquisition of 30 evenly distributed data sets was applied every second heart beat. This procedure allowed data to be acquired over a full heart cycle without any acquisition gap. The measured flow velocities were displayed as function of time. Systolic acceleration, postsystolic deceleration and pulsatility of flow velocity were calculated and compared with stenosis grades determined from DSA angiograms. Flattening of the flow velocity patterns was found to correlate with the local severity of arteriosclerotic disease.

ISSN:0740-3194    

DOI:10.1002/mrm.1910340508

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

年代:1995

数据来源: WILEY

摘要:

AbstractThree dimensional (3D) phase contrast angiograms contain velocity data, which is discarded after the reconstruction of the projections. In extension to earlier work on velocity quantification with ungated 2D phase data, this paper shows that a useful estimate of the average velocity and flow rate can be extracted from ungated 3D phase contrast angiograms. Simulations and experiments in a phantom andin vivowere performed. For pulsatile flow and strong spin saturation, an over‐estimation of the flow rate at the net in‐flow end of the imaging volume and underestimation at the net out‐flow end was observed. Imaging at lower RF tip angles yielded flow rates close to the correct value within the entire imaging volume. In contrast to ungated 2D experiments, the flow rates determined by repeated 3D experiments showed no vari

ISSN:0740-3194    

DOI:10.1002/mrm.1910340509

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe enhancement of the water proton transverse relaxation, ΔR2, brought about by a difference between intra and extracellular paramagnetic susceptibilities in a suspension of red blood cells (RBC) has been evaluated both experimentally and theoretically in terms of (i) the refocusing interval, Δ180, of a CPMG pulse sequence, (ii) the difference in paramagnetic susceptibility, and (iii) the shape of the cell surface. At a hematocrit of 45, the increase in the relaxation enhancement, ΔR2, with increasing Δ180, was a factor of two greater for the naturally biconcave RBC, than for the quasi‐spherical RBC in hypotonic suspensions. This difference could be modeled in terms of a transmembrane correlation time, τ = 5.5 ms, across an RBC surface characterized by a demagnetizing factor which differs by 0.13 from that of a sphere. The increase in ΔR2with increasing magentization difference between the RBC and its surroundings was found to be marginally less than quadratic, both experimentally and from th

ISSN:0740-3194    

DOI:10.1002/mrm.1910340510

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

年代:1995

数据来源: WILEY

摘要:

AbstractN‐Acetylaspartate (NAA), which constitutes the major proportion of the dominant resonance in proton MR spectra of brain, is localized in mature brain exclusively in neurons and neuronal processes. A decrease in NAA has been observed in many cerebral pathologies and has usually been interpreted as an index of irreversible neuronal loss. The authors report a follow‐up study of six patients with acute brain damage (four from demyelinating lesion and two from mitochondrial encephalopathy with lactic acidosis and stroke‐like episodes [MELAS]). All patients underwent serial MR spectroscopy examinations. The four patients with acute demyelinating lesions initially showed decreases in NAA in the centers of the lesions that ranged between 34‐72% of values from homologous brain volumes in the other hemisphere. All four patients subsequently showed substantial recovery of NAA as their clinical status improved. The two patients with MELAS syndrome had large decreases of NAA signal (50% and 20% of normal values, respectively) from their occipital lobe lesions during the acute stroke‐like episodes. After the acute phase of the illness a progressive increase of NAA in the same volumes was seen in both patients (to 76% and 60% of normal values, respectively). These results demonstrate that significant recovery of NAA can occur after acute brain damage. The potential contribution of reversible neuronal dysfunction (as well as neuronal loss) must be considered in the interpretation of decreases in the NAA resonance associated with acute brain

ISSN:0740-3194    

DOI:10.1002/mrm.1910340511

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

年代:1995

数据来源: WILEY