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Biomedical subjects

G Z Yang

Publications and source records attributed to G Z Yang.

At least 55 records · Page 3Linked to original sources
PubMed1997

Automatic tracking of the aorta in cardiovascular MR images using deformable models.

We present a new algorithm for the robust and accurate tracking of the aorta in cardiovascular magnetic resonance (MR) images. First, a rough estimate of the location and diameter of the aorta is obtained by applying a multiscale medial-response function using the available a priori knowledge. Then, this estimate is refined using an energy-minimizing deformable model which we define in a Markov-random-field (MRF) framework. In this context, we propose a global minimization technique based on stochastic relaxation, Simulated annealing (SA), which is shown to be superior to other minimization techniques, for minimizing the energy of the deformable model. We have evaluated the performance and robustness of the algorithm on clinical compliance studies in cardiovascular MR images. The segmentation and tracking has been successfully tested in spin-echo MR images of the aorta. The results show the ability of the algorithm to produce not only accurate, but also very reliable results in clinical routine applications.

Algorithms↗
PubMed1997

CT image enhancement with wavelet analysis for the detection of small airways disease.

Bronchiolar obstruction is commonly manifested in computed tomography (CT) images as areas of decreased attenuation relative to adjacent normal lung parenchyma. The certain identification of such areas is difficult in practice, particularly if they are poorly marginated. This paper presents a novel approach to the enhancement of feature differences between normal and diseased lung parenchyma so that reliable visual assessment can be made. The method relies on a hybrid structural filtering technique which removes pulmonary vessels appearing in the CT cross-sectional images without affecting intrinsic subtle intensity details of the lung parenchyma. In order to restore possible structural distortions introduced by the hybrid filter, a feature localization process based on wavelet reconstruction of feature extrema is used. After contrast enhancement the resultant images are used to delineate region borders of the diseased areas and quantification is made with regard to the extent of the disease.

Bronchiolitis Obliterans↗
PubMed1997

[Study on the structure-activity relationships of retinoids. II. 3D-QSAR of retinoids and receptor interaction].

Precise prediction of the binding constant of ligand to receptor is an important aspect of structure-based drug design. Almost all methods including de novo design and 3D database search are over concentrated on structure generation rather than quantitative evaluation of the binding properties of the newly produced molecule. Using epididymal retinoic acid binding protein (ERABP) as a model, we simulated the interaction between retinoids and their receptor with DOCK program and obtained an equation for predicting the binding constants. According to the docking conformers of the ligands, CoMFA was also used to deduce a pharmacophoric model of this series of compound.

Receptors, Retinoic Acid↗
PubMed1997

[Studies on retinoids. IV. Design, synthesis and structure-activity relationships of di-t-butylphenyl compounds].

Retinoic acid and its analogues play important roles in modulating cell growth, differentiation, immunity and apoptosis. Clinically they are used for cancer chemoprevention and chemotherapy. Based upon the moiety of 3,5-di-t-butyl-4-hydroxy phenyl ring, a series of substituted aromatic amide, ester and chalcones were designed and synthesized, which mimic the molecular shape, size, and spacial disposition of functional groups of retinoic acid. The general structure is as follows: [formula: see text] where R stands for hydrogen atom or methyl group, Y is the linkage -CONH-, -NHCO-, -COO-, -COCH = CH-, or a member of a heterocycle, X represents various substituents at different positions. The SAR indicates that the presence of hydrophobic group(s) at one end of the molecule, and a carboxyl group at the other end, and a conjugative system of molecule are necessary and full prerequisite for exhibiting activity. Loss of any one factor of them will abolish the activity. Being obligatory for anti-oxidative effect, the phenolic hydroxy group does not convey biological activity, because after methylation of the hydroxy group the compound increases the differentiation-inducing activity and loses the anti-oxidative effect, indicating that there is no correlation between the two activities. With a stable conformation of two phenyl rings with cis-conformation N-methylated acyl amide (No. 30) features in bent shape of the molecule, instead of an extended conformer, which is taken by the non-N-methylated partner and all-trans retinoic acid. A bent conformer of No. 30 accounts for the inactivity. In this paper compounds No. 4f, 4g, 5a, 7, 13, 32, 37, and 38 exhibited significant activity among them 4-[3-(3, 5-di-t-4-methoxyphenyl)-3-oxo-1-propenyl] benzoic acid (No. 38) showed high activity comparable to that of retinoic acid. The pharmacological action of No. 38 is under investigation.

Benzoates↗
PubMed1996

Computation of flow pressure fields from magnetic resonance velocity mapping.

Magnetic resonance phase velocity mapping has unrivalled capacities for acquiring in vivo multi-directional blood flow information. In this study, the authors set out to derive both spatial and temporal components of acceleration, and hence differences of pressure in a flow field using cine magnetic resonance velocity data. An efficient numerical algorithm based on the Navier-Stokes equations for incompressible Newtonian fluid was used. The computational approach was validated with in vitro flow phantoms. This work aims to contribute to a better understanding of cardiovascular dynamics and to serve as a basis for investigating pulsatile pressure/flow relationships associated with normal and impaired cardiovascular function.

Algorithms↗
PubMed1996

A comparison of left ventricular myocardial velocity in diastole measured by magnetic resonance and left ventricular filling measured by Doppler echocardiography.

Abnormal diastolic left ventricular function is an early marker for myocardial disease and may be impaired even when global systolic function is normal. Subendocardial function is affected early in ischaemic heart disease and by altering left ventricular long axis motion, may contribute to abnormal transmitral pressure gradients. Regional myocardial long axis velocity in diastole measured by magnetic resonance was compared with left ventricular filling measured by Doppler echocardiography in 25 patients with coronary artery disease. Fifteen patients also underwent magnetic resonance assessment at the time of onset of early diastolic blood flow. The onset of diastolic long axis velocity preceded flow across the mitral valve by a mean of 46 ms. Mean long axis myocardial velocity correlated with peak early filling velocity (E) (r = 0.73, P < 0.001), early deceleration (r = -0.73, P < 0.001), and the early to late filling ratio (E/A) ratio (r = 0.6, P < 0.01). Maximum myocardial long axis velocity also correlated with peak early filling velocity (r = 0.56, P < 0.01), early deceleration rate (r = 0.63, P < 0.001), and the E/A ratio (r = 0.53, P < 0.01). The variability of long axis velocity around the ventricle correlated inversely with peak early filling, (r = -0.7, P < 0.001), early deceleration (r = -0.56, P < 0.01), and the E/A ratio (r = -0.48, P < 0.02). Peak atrial filling velocity did not correlate with any measure of long axis myocardial velocity. We conclude that early diastolic long axis myocardial velocity has a significant effect on left ventricular filling.

Adult↗
PubMed1995

Magnetic resonance velocity vector mapping of blood flow in thoracic aortic aneurysms and grafts.

Magnetic resonance imaging with multidirectional cine velocity mapping was used to study relationships between aortic blood flow patterns and the geometry of thoracic aortic aneurysms and grafts. Ten patients with 13 thoracic aortic aneurysms, single or multiple, or grafts (4) participated in the study. The causes of disease were atherosclerosis (4), Marfan's syndrome (2), trauma (1), and unknown (1), and there were two dissections. Spin-echo imaging and cine velocity mapping in 10 mm thick slices with vertical and horizontal velocity encoding were done. Maps of the two velocity components were processed into multiple computer-generated streaks whose orientation and length corresponded to velocity vectors in the chosen plane. The dynamic arrow maps were compared with previously reported aortic arrow maps from normal subjects. The forward flow occupied the entire lumen in the normal aorta in systole and small vortices were only present in the sinuses of Valsalva. Atherosclerotic aneurysms in the ascending aorta were located at the anterior right and had oblique, eccentric jet flows that created a large secondary vortex in the aneurysm. Patients with Marfan's syndrome had a central jet and two large vortices, one on each side. All other aneurysms, dissections, and grafts had irregular flows and vortices not seen in normal subjects. Magnetic resonance imaging with multidirectional velocity mapping is a powerful noninvasive tool to assess morphologic features and disturbed blood flow in aortic aneurysms and grafts. Recognizably altered flow patterns were found to be associated with altered vessel geometry. The significance of this requires further investigation.

Adult↗
PubMed1995

Assessment of magnetic resonance velocity mapping of global ventricular function during dobutamine infusion in coronary artery disease.

BACKGROUND: Magnetic resonance imaging (MRI) is a versatile technique for examination of the cardiovascular system but only recently has assessment of myocardial ischaemia in coronary artery disease (CAD) become possible, for example by demonstrating abnormalities of regional ventricular contraction during stress. Global ventricular function during stress was assessed by MRI of aortic flow, which has not been previously attempted. DESIGN: Variables measured by MRI reflecting the effect of ischaemia on global ventricular function during dobutamine stress were correlated with thallium-201 myocardial perfusion tomography. PATIENTS: 10 normal controls and 25 patients with CAD. SETTING: Tertiary cardiac referral centre. METHODS: Novel MRI sequences and analysis systems were used to measure the following variables during staged dobutamine infusion to 20 micrograms/kg/min: stroke volume, cardiac output, cardiac power output, peak flow, peak flow acceleration, aortic back flow, and flow wave velocity. Heart rate, blood pressure, double product, and maximum tolerated dobutamine dose were also measured. Multiple regression analysis was used to compare changes during stress with 201TI tomography. RESULTS: All parameters except for stroke volume and diastolic blood pressure increased in the controls. In the patients with CAD a significant relation was shown between the extent of reversible ischaemia and the change in peak flow acceleration (P < 0.00001), peak flow (P = 0.002), cardiac power output (P = 0.036), maximum dobutamine dose (P = 0.039), and systolic blood pressure (P = 0.04). Peak flow acceleration accounted for 58.4% of the variation in reversible ischaemia, and after allowing for this, only cardiac power output remained independently predictive adding a further 4.2% to the model (adjusted r2 = 0.626). A decrease in peak flow acceleration with an increase in dobutamine infusion indicated moderate or severe ischaemia (chi 2 = 10.2, P = 0.017). CONCLUSION: MRI may be used to assess variables of aortic flow during stress, which includes acceleration with high temporal resolution. Peak flow acceleration was the most sensitive indicator of the effect of ischaemia on global ventricular function.

Adult↗
PubMed1994

Regional myocardial velocity imaged by magnetic resonance in patients with ischaemic heart disease.

OBJECTIVE: To assess the pattern of global and regional left ventricular long axis motion during early diastole in patients with ischaemic heart disease with and without myocardial infarction using magnetic resonance velocity mapping. DESIGN: Prospective study of 26 patients with a history of myocardial infarction (age 29-78, mean 55 years) and 21 patients with coronary artery disease without infarction (age range 39-71, mean 58 years). Values were compared with a control group (19 controls, age 35-76, mean 52 years) with a low likelihood of cardiovascular disease. RESULTS: Regional long axis velocity varied with time and position around the ventricle. All measurements were taken at the time of maximum early diastolic long axis velocity. Patients with coronary artery disease without infarction had lower values for maximum (mean (SD)) (99 (30) v 125 (33) mm/s, P < 0.05) and mean peak early diastolic wall motion (63 (13) v 82 (22) mm/s, P < 0.05) than controls. The coefficient of variation showed greater inhomogeneity of relaxation in patients than in controls (38 (18)% v 27 (10)%). All values were lower in patients with previous infarction than in patients with coronary artery disease without infarction and normal subjects. In patients with previous myocardial infarction the maximum (mean (SD)) early diastolic velocity was 80 (22) mm/s (P < 0.01 compared with controls and P < 0.05 compared with patients without infarction) and the mean (SD) velocity was 47 (18) mm/s (P < 0.01 compared with controls). The coefficient of variation was greater (52 (33)%) than for controls (P < 0.05) and patients with coronary artery disease without infarction. 18 of 26 patients with previous myocardial infarction and 13 of 21 patients with coronary artery disease without infarction had regional abnormalities corresponding to areas of fixed or reversible ischaemia on exercise electrocardiography or thallium myocardial perfusion tomography. CONCLUSIONS: Magnetic resonance velocity mapping can be used to assess regional long axis myocardial velocity. Ischaemic heart disease causes alterations in the patterns of left ventricular long axis velocity during early diastole.

Adult↗
PubMed1993

Helical and retrograde secondary flow patterns in the aortic arch studied by three-directional magnetic resonance velocity mapping.

BACKGROUND: Helical and retrograde secondary flows have been recorded in the aorta, but their origins and movements in relation to the arch have not been clarified. We set out to do this using magnetic resonance velocity mapping. METHODS AND RESULTS: Three-directional phase contrast cine magnetic resonance velocity mapping was used to map multidirectional flow velocities in the aortas of 10 healthy volunteers. Computer processing was used to visualize flow vector patterns in selected planes. Right-handed helical flows predominated in the upper aortic arch in late systole, being clearly recognizable in 9 of the 10 subjects. Nonaxial components of velocity in this region reached 0.29 m/s (+/- 0.05 m/s) as axial velocities declined from a peak of 1.0 m/s (+/- 0.1 m/s). Helical flow patterns in the upper descending aorta varied between subjects, apparently depending on arch curvature. End-systolic retrograde flow originated from regions of blood with low momentum, usually along inner wall curvatures. Flow studies in a curved tubular phantom showed right-handed helical flow in the upper "arch" when the inflow section was positioned to simulate ascending aortic curvature, and retrograde flow occurred along the inner wall at end systole during pulsatile flow. CONCLUSIONS: Helical and retrograde streams are consistent features of intra-aortic flow in healthy subjects that result, at least in part, from the curvature of the arch and the pulsatility of flow in it. They may have significance in relation to circulatory dynamics and the pathogenesis of atheroma in the arch.

Adult↗
PubMed1993

Growth factor gene expression in lung fibroblasts.

A lung fibroblast cell line was isolated from lung biopsy of a patient with lung fibrosis. Gene expression of ten growth factors in the fibroblasts were investigated by a reverse transcription-DNA polymerase chain reaction. The results indicated that the fibroblasts expressed acidic fibroblast growth factor (aFGF) mRNA transcript. Further experiments revealed that recombinant aFGF could be internalized by the fibroblasts and stimulated the proliferation of the cells. These data suggest that aFGF may activate lung fibroblasts in a way of autocrine and, therefore, may be involved in the development of lung fibrosis.

Base Sequence↗
PubMed1993

TNF alpha mRNA expression in bronchoalveolar lavage cells from patients with lung fibrosis and TNF alpha activity in the lavage supernatants.

Tumor necrosis factor alpha (TNF alpha) mRNA expression in bronchoalveolar lavage (BAL) cells from patients with lung fibrosis was studied by a reverse transcription-DNA polymerase chain reaction (RT-PCR). The results indicated that two thirds of the tested samples were TNF alpha mRNA positive. On the other hand, TNF alpha activity was detected in a big part of the BAL supernatants from the patients. Furthermore, recombinant TNF alpha was found to be mitogenic to lung fibroblasts. These data suggest that TNF alpha expression in BAL cells may play a role in the development of lung fibrosis in human.

Base Sequence↗
PubMed1993

Validation of measurement of regional myocardial perfusion in humans by ultrafast x-ray computed tomography.

The objective was to validate the measurement of myocardial perfusion in humans by ultrafast computed tomography (CT), by comparing measurements with those from single photon emission computed tomography (SPECT). Measurement of myocardial perfusion with high spatial resolution (including the differentiation of subendocardial and subepicardial perfusion) may be possible by ultrafast CT in humans. Although there are encouraging data from experiments with dogs, the technique has not been validated in humans. In 11 patients, ultrafast CT measurement of regional perfusion in a single short-axis slice was compared with that obtained by SPECT, and in 14, reproducibility of ultrafast CT was evaluated. The ultrafast CT scanner was set to acquire 20 images, gated to end-diastole. The images were divided into 32 equal segments, and the time course and extent of opacification of the left ventricular cavity and myocardium were analyzed to calculate absolute perfusion. The thallium tomograms were also divided into 32 segments for comparison. The pattern of relative perfusion by segment was represented as a curve. In 18 of 22 paired scans, the mean difference of the position of the minimum and maximum points of the curves was less than 4, indicating close agreement between the two techniques. When scoring segmental perfusion as normal or abnormal, there was agreement between the methods in 129 of 176 segments ([symbol: see text] 0.41). Reproducibility (mean difference +/- 1 SD) of basal scans was 0.005 +/- 0.2 mL/min/mL, and during adenosine vasodilation was 0.05 +/- 0.32 mL/min/mL. Absolute perfusion (mean +/- 1 SD) at rest was 0.52 +/- 0.21 mL/min/mL. During adenosine infusion, perfusion increased to a mean of 0.84 +/- 0.42 mL/min/mL. Ultrafast CT and intravenous contrast can be used to assess relative myocardial perfusion in humans, at rest and during adenosine vasodilatation, although it may underestimate absolute perfusion, particularly at high flow.

Adenosine↗
PubMed1993

[Promoting effect of panaxatriol ginsenoside on gene expression of human interleukin-1].

Effect of panaxatriol ginsenoside (PG) on interleukin-1 (IL-1) gene expression was studied by using wheat germ extract (cell-free translation system) and IL-1 bioassay. The results showed that IL-1 production increased by 40% (487-682 U.ml-1) at maximum during cell culture (0-84 h) after PG (10 micrograms.ml-1) was added to phytohemagglutinin (PHA, 50 micrograms.ml-1) stimulated lymph node cells. Meanwhile, IL-1 mRNA from PHA combined with PG stimulated lymph node cells translated 39.5% more IL-1 than that of PHA-stimulated cells at maximum (2500-3489 U/mg RNA).

Cells, Cultured↗
PubMed1992

[The lead generation of protein tyrosine kinase inhibitors by quantitative structure-activity relationship analysis].

Analysis of the quantitative relationship between a series of substituted benzylidenemalononitriles and the inhibitory action on protein tyrosine kinases were carried out using the Hansch-Fujita method. The results indicate that the presence of two or three hydroxy groups attached to a phenyl ring, which connects an extended (trans form) conjugated chain, is essential to the inhibition. Compared with the structure of other kinds of inhibitors, a presumable basic structure for inhibiting the enzyme was generated.

Benzylidene Compounds↗
PubMed1991

Separation of electronic and hydrophobic effects for the papain hydrolysis of substituted N-benzoylglycine esters.

The role of hydrophobic and electronic effects on the kinetic constants kcat and Km for the papain hydrolysis of a series of 22 substituted N-benzoylglycine pyridyl esters was investigated. The series studied comprises a wide variety of substituents on the N-benzoyl ring, with about a 300,000-fold range in their hydrophobicities, and 2.1-fold range in their electronic Hammet constants (sigma). It was found that the variation in the log kcat and log 1/Km constants could be explained by the following quantitative-structure activity relationships (QSAR): log 1/Km = 0.40 pi 4 + 4.40 and log 1/kcat = 0.45 sigma + 0.18. The substituent constant, pi 4, is the hydrophobic parameter for the 4-N-benzoyl substituents. QSAR analysis of two smaller sets of glycine phenyl and methyl esters produced similar results. A clear separation of the substituent effects indicates that in the case of these particular esters, acylation appears to be the rate limiting catalytic step.

Catalysis↗
PubMed1989

[Studies on the anti-virus effect of Glycyrrhiza uralensis Fish. polysaccharide].

The anti-virus activity of GPS has been investigated in vitro using L-929 and FL cell line infected with 7 kinds of DNA or RNA virus, and the mechanism by which GPS exhibits the anti-virus activity has been studied. The results show that GPS may inhibit the growth of VSV, AdVIII, HSV-1 or VV and CPE is also suppressed by GPS for protecting culture cell from virus infection.

Animals↗