[Effects of oxymatrine on the antitumor activity and toxicity of cyclophosphamide in mice].
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Alkaloids↗
Biomedical subjects
C Yuan
Publications and source records attributed to C Yuan.
[Radiological and physiological studies on overdistension of lung after pneumonectomy in patients with pulmonary tuberculosis].
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Adult↗
Synthesis of a material with high juvenile hormone activity.
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Alkenes↗
Three-dimensional fast spin-echo imaging: pulse sequence and in vivo image evaluation.
Three-dimensional (3D) magnetic resonance imaging allows thin-section acquisition and therefore more accurate multiplanar reconstruction than conventional two-dimensional spin-echo imaging. Unfortunately, addition of a third acquisition plane extends imaging time greatly. With gradient-echo techniques, 3D acquisitions have become clinically useful. These techniques are limited, however, by susceptibility and other field inhomogeneity artifacts and decreased signal-to-noise ratios compared with spin-echo techniques. The authors describe implementation of a true spin-echo 3D technique that, by using fast spin-echo parameters, reduces acquisition time to a clinically useful level. Potential applications of the technique are demonstrated.
Brain↗
Techniques for high-resolution MR imaging of atherosclerotic plaque.
Atherosclerotic cardiovascular disease is the most common cause of death in the United States. Investigation of atherosclerotic plaque morphology and composition is important because the findings may be useful in predicting prognosis or response to therapy. This study presents high-resolution magnetic resonance (MR) imaging techniques developed on a 1.5-T whole-body imager with a custom-built surface coil, for characterizing the composition and morphology of plaque removed at carotid endarterectomy. The initial comparison of MR imaging and histologic results showed good correlation. In conjunction with MR angiography, these techniques could be used in in vivo imaging to define the size, location, and contents of atherosclerotic plaque at the carotid bifurcation.
Artifacts↗
Multislab three-dimensional T2-weighted fast spin-echo imaging of the hippocampus: sequence optimization.
Three-dimensional (3D) fast spin-echo (FSE) imaging can produce contiguous thin sections for high-quality multiplanar reconstructions. Such reformatted images may be useful in the evaluation of three-dimensionally complex, curvilinear anatomic structures such as the hippocampus. The authors describe a 3D FSE protocol for T2-weighted imaging of the hippocampus. The protocol uses an overlapping-multiple-slab imaging strategy to decrease imaging times and a modified refocusing radio-frequency pulse train to improve the reformatted images. The authors describe their parameter optimization, discuss the benefits and limitations of the new sequence, and present representative images of healthy volunteers.
Artifacts↗
Phased-array magnetic resonance imaging of the carotid artery bifurcation: preliminary results in healthy volunteers and a patient with atherosclerotic disease.
A high resolution MR imaging technique using a custom designed flexible phased-array surface coil was developed to examine the wall of the carotid artery bifurcation in vivo. The phased-array consisted of two overlapping coils which increased the image signal-to-noise ratio at the depth of the carotid artery by approximately 70%, relative to a similarly sized single loop coil. The imaging protocol included a 2D T1-weighted (T1W) spin-echo scan and cardiac gated T2-weighted and proton density-weighted (PDW) fast spin-echo (FSE) scans. Images were obtained of six healthy volunteers and of one patient with known atherosclerotic disease several days before carotid endarterectomy. On T1W and PDW images of the healthy volunteers, the carotid arterial wall appeared to be comprised of two concentric rings; a high signal inner ring and a lower signal outer ring. The MR images of the patient revealed a calcified carotid bifurcation plaque which was confirmed during surgery. The endarterectomy specimen was imaged in vitro with MR and then sectioned histologically for correlation with the patients in vivo images. Our preliminary findings indicate that a high resolution technique may provide a noninvasive technique to study atherosclerosis of the carotid bifurcation.
Arteriosclerosis↗
Surface coil phased arrays for high-resolution imaging of the carotid arteries.
An MR phased-array coil assembly was developed to obtain high-resolution images of atherosclerotic plaques in the carotid artery. Images of volunteers and patients obtained by using alternative coil designs provided a subjective assessment of the coils' performance, field of view, ease of use, and susceptibility to motion artifacts. A quantitative measurement performed on a phantom indicated that a two-coil phased-array design should produce a 37% better signal-to-noise ratio at the carotids than would a conventional single 3-inch surface coil.
Arteriosclerosis↗
Atherosclerosis of the carotid artery: evaluation by magnetic resonance angiography.
Carotid artery atherosclerotic plaques (APs) can lead to brain ischemia, an event shown to correlate with both the degree of stenosis and the composition of the AP. Currently, accurate estimates of stenosis can be obtained by either x-ray angiography or three-dimensional time-of-flight (TOF) magnetic resonance angiography (MRA). Our purpose was to determine whether three-dimensional TOF MRA images could also provide information on plaque location, morphology, and composition. Seven pre-endarterectomy patients underwent three-dimensional TOF MRA. After endarterectomy, plaque histology was evaluated. Three-dimensional TOF MRA images contained sufficient soft tissue contrast to differentiate the plaques from the surrounding tissues in all cases. Estimation of plaque morphology had 80% correlation with histology. Finally, intraplaque hemorrhage and calcification were deplicted as regions of moderately high and very low intensity, respectively. These preliminary results suggest that three-dimensional TOF MRA may be useful in studying the development and progression of carotid atherosclerosis.
Aged↗
Black blood magnetic resonance angiography with Dy-DTPA polymer: effect on arterial intraluminal signal intensity, lumen diameter, and wall thickness.
Four rabbits in which atherosclerotic disease was induced by diet and balloon angioplasty underwent conventional angiography and MR angiography (MRA) using a black blood pulse sequence before and 10 minutes after the i.v. injection of a macromolecular contrast agent, NC 100283 (1.0 mmol/kg), a dysprosium diethylenetriaminepentaacetic acid hexamethylenediamine copolymer (Dy-DTPA polymer). Intraluminal signal intensity, apparent wall thickness, and lumen size measurements of the aorta and proximal common iliac arteries on precontrast MRA images were compared with postcontrast images. Aortic lumen diameter measurements on the precontrast and postcontrast MRA studies were compared with lumen diameters from conventional angiograms. Intraluminal signal intensity decreased on postcontrast MRA images compared with precontrast images, with an average loss of signal equal to 29% (P < .05). Apparent wall thickness decreased by 24% (P < .05). Lumen diameter and area were generally larger (average of 15% and 33%, respectively) on postcontrast MRA images than on precontrast images. Aortic lumen diameter measurements from postcontrast MRA agreed closely (95% confidence interval of the mean difference was -.2 to .3 mm), and precontrast MRA images tended to underestimate aortic lumen diameter (95% confidence interval of the mean difference was .3 to .8 mm) compared with conventional angiography. Postcontrast MRA with NC 100283, a macromolecular Dy-DTPA contrast agent, provides more accurate assessment of aortic lumen diameter than precontrast MRA, using conventional angiography as the standard reference.
Animals↗
Three-dimensional fast spin echo T1-weighted imaging of the pediatric spine.
OBJECTIVE: We evaluated the feasibility of using a three-dimensional (3D) fast SE (FSE) pulse sequence to acquire T1-weighted (T1W) images of the pediatric spine. MATERIALS AND METHODS: The 3D FSE T1W images were acquired in nine pediatric patients undergoing spine MRI for different clinical indications. The 3D FSE images were compared with our standard 2D SE T1W images. RESULTS: Image contrast was comparable between the two sequences. The 3D FSE sequence produced contiguous thin sections that allowed multiplanar reformations not possible with the 2D SE sequence. CONCLUSION: 3D T1W spine imaging with conventional SE-like contrast is feasible with 3D FSE.
Cerebrospinal Fluid↗
Molecular electronics: strategies and progress in China.
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Adsorption↗
The solution of Bloch equations for flowing spins during a selective pulse using a finite difference method.
The movement of spins during periods of selective pulses result in a modulation of the signal intensity and phase of the received magnetic resonance imaging (MRI) signal, and is a major cause of signal loss from vessels imaged with slice-selective pulses. Methods are well developed for compensation of phase perturbations for spins flowing at constant velocity during the time of applied gradients. However, for spins flowing during selective pulses, the magnitude of the amplitude and phase perturbations has not been understood nor to this time has any method of flow compensation been proposed. This is due in part to the difficulty in using the Bloch equations to quantify the amplitude and phase modulation during radiofrequency (rf) excitation since solutions cannot be obtained analytically. In this paper a finite difference method is used to solve Bloch equations for flowing spins during a 90 degrees selective pulse. Compared with stationary spins, the magnetization distribution for flowing spins exhibits a shift of the slice profile in the direction of the flow, an expansion of the profile, phase shifts, and changes in profile shape. The profiles show residual phase errors which become more severe with higher flow velocities, with flow compensation schemes which apply in the case of spins flowing during applied gradients, and in the absence of an rf pulse. The measurement and understanding of the magnetization distribution is important to designing pulse sequences that compensate for flow. Flow compensated pulse sequences are necessary to reduce image flow artifacts and to increase signal of vessels in MR angiographic images.
Computers↗
Characterization of atherosclerotic plaques at the carotid bifurcation: correlation of high-resolution MR imaging with histologic analysis--preliminary study.
The clinical symptoms and morbidity that result from carotid artery disease, the primary cause of stroke, are mainly due to plaque ulceration, thrombosis, intraplaque hemorrhage, and thinned fibrous caps. The contents of atherosclerotic plaques of the carotid artery can be determined with in vivo high-resolution magnetic resonance imaging with flow suppression. Eight patients scheduled to undergo endarterectomy and four healthy volunteers were imaged with a 1.5-T imager and custom-made carotid phased-array coils. T1-weighted spin-echo images and cardiac-gated proton-density--weighted fast spin-echo images were acquired. In vivo imaging findings as determined by three radiologists were correlated with ex vivo imaging and histologic findings. Among the eight plaque specimens, regions of hemorrhage, calcium, lipid deposits, and fibrous plaques were identified on T1- and proton-density-weighted images. Calcium and lipid deposits were detectable on both T1- and proton-density--weighted images. Hemorrhage and fibrous plaques were better demonstrated on proton-density--weighted images.
Adult↗
Role of digitalis-like substance in the hypertension of streptozotocin-induced diabetes and simulated weightlessness in rats.
We have examined the role of plasma Na+-K+ pump inhibitor (SPI) in the hypertension of streptozotocin induced insulin dependent diabetes (IDDM) in reduced renal mass rats. The increase in blood pressure (BP) was associated with an increase in extracellular fluid volume (ECFV), and SPI and a decrease in myocardial Na+,K+ATPase (NKA) activity, suggesting that increased SPI, which inhibits cardiovascular muscle (CVM) cell NKA activity, may be involved in the mechanism of IDDM-hypertension. In a second study, using prolonged suspension resulted in a decrease in cardiac NKA activity, suggesting that cardiovascular deconditioning following space flight might in part result from insufficient SPI.
Animals↗