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Biomedical subjects

E C Wong

Publications and source records attributed to E C Wong.

At least 19 recordsLinked to original sources
PubMed1995

High-resolution magnetic resonance imaging evaluation of blood-retinal barrier integrity following transscleral diode laser treatment.

OBJECTIVE: To compare the effects of contact transscleral diode laser treatment and retinal cryotherapy on blood-retinal barrier integrity with the use of high-resolution magnetic resonance imaging techniques with constant infusion of gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA). METHODS: Transscleral diode laser photocoagulation and retinal cryotherapy were used to treat equivalent areas of the inferior retinal periphery of pigmented rabbits. Magnetic resonance imaging time-course studies with measurement of signal enhancements due to Gd-DTPA leakage were conducted 2 and 15 days following treatment. RESULTS: Two days following treatment, cryotherapy-treated eyes exhibited a mean (+/- SD) effective Gd-DTPA permeability coefficient of 4.6 +/- 0.8 x 10(-6) cm/s; in comparison, diode laser-treated eyes exhibited 1.6 x 1.4 x 10(-6) cm/s effective permeability. Significant decreases in the effective permeability were also noted 15 days after treatment in both groups. CONCLUSIONS: Transscleral contact probe diode laser photocoagulation induces less disruption of the blood-retinal barrier than does conventional cryotherapy. In addition, the continuous infusion method of Gd-DTPA delivery is a reliable and easily interpretable alternative to the commonly used bolus injection approach.

Animals↗
PubMed1995

Optimized isotropic diffusion weighting.

The authors introduce several sets of time-efficient gradient waveforms for applying isotropic diffusion weighting in NMR experiments. This creates signal attenuation that depends on the trace of the diffusion tensor and is therefore rotationally invariant. Numerical methods for the calculation of such gradient sets are outlined, and results are shown for isotropic and anisotropic gradient hardware and first order flow moment nulled diffusion weighting gradients. Preliminary experimental results from the human brain validate this new technique.

Algorithms↗
PubMed1994

Echo-volume imaging.

Two single-shot volume imaging techniques are described. The first, single-echo echo-volume imaging, is essentially the echo-volume imaging (EVI) sequence suggested by Mansfield (J. Phys. C. 10, L55 (1977)). The second is a multi-spin-echo approach in which one plane of k-space is collected during each spin echo. In both techniques, phase encoding gradients are applied in the z direction, and three-dimensional k-space is filled by a raster pattern in Cartesian coordinates. Spatial saturation is used to avoid aliasing in the y direction, and a selctive pulse is applied to excite the desired slab of tissue and eliminate aliasing in z. The average echo-times, measured from the center of the 90 degrees pulse to the center of the acquisition k-space (kx = ky = kz = 0), were 45 and 104 ms for single echo and multi-echo methods, respectively. Images of the human brain using both sequences are shown.

Artifacts↗
PubMed1992

Time course EPI of human brain function during task activation.

Using gradient-echo echo-planar MRI, a local signal increase of 4.3 +/- 0.3% is observed in the human brain during task activation, suggesting a local decrease in blood deoxyhemoglobin concentration and an increase in blood oxygenation. Images highlighting areas of signal enhancement temporally correlated to the task are created.

Brain↗
PubMed1992

A double-blind comparison of nasal budesonide and oral astemizole for the treatment of perennial rhinitis.

Sixty-nine outpatients with symptomatic perennial rhinitis were recruited to this double-blind, parallel-group study to compare budesonide nasal spray with oral astemizole. Following a 1-week run-in on placebo, 67 patients achieved a mean daily total symptom score of at least 4 (scoring for each symptom was 0 = none, 1 = mild, 2 = moderate, 3 = severe), and were randomized to study treatments - 33 to budesonide, 100 micrograms in each nostril morning and evening, and 34 to astemizole, one 10-mg tablet each morning, for a period of 4 weeks. No antihistamine preparations other than eye drops and no corticosteroids were permitted during the active treatment period. Patients recorded symptoms of blocked nose, runny nose, sneezing, itchy nose, sore eyes or runny eyes in diary cards each evening before retiring. Diary card data showed that there was significantly greater improvement in blocked nose, runny nose and runny eyes during the first 2 weeks of budesonide treatment than during the same period on astemizole. A similar, although non-significant, trend was observed for sneezing and itchy nose, but there was no apparent difference in the reporting of sore eyes. After 4 weeks, blocked nose and runny nose remained significantly less troublesome in the budesonide group. Both treatments were well-tolerated and no major adverse effects were reported. Patient ratings for treatment efficacy were significantly higher for budesonide than astemizole at both 2 weeks and 4 weeks.

Administration, Topical↗
PubMed1991

Association of calmodulin with isolated nuclei from rat hepatocytes.

Calmodulin plays an important role in regulating cell proliferation and intranuclear processes (J. Biol. Chem. 265: 18595, 1990). Therefore we studied the association of 125I-calmodulin with highly purified rat hepatocyte nuclear preparations which were characterized by marker enzymes and electron microscopy. Steady-state association of 125I-calmodulin was reached within 5 minutes. Half-maximal binding was achieved at approximately 7.1 microM. This association was partially Ca(2+)-dependent, but was not influenced by ATP, GTP or wheat germ agglutinin. Ultrastructural autoradiography showed specific association of 125I-calmodulin with peripheral and non-peripheral heterochromatin, nuclear membranes, and nucleoli. Specific binding (ratio of the grain density of 125I-calmodulin to Na125I) was greatest in the regions of the nucleoli and non-peripheral heterochromatin. The data indicate that exogenous calmodulin can associate with specific nuclear components in an energy-independent and Ca(2+)-dependent manner.

Adenosine Triphosphate↗
PubMed1991

Coil optimization for MRI by conjugate gradient descent.

A flexible iterative algorithm is presented for optimizing gradient and radio frequency coils for MRI. It is based on a model using discrete current elements and direct Biot-Savart calculation of the fields. An error function is defined over a region of interest (ROI) and is minimized by conjugate gradient descent. The choice of error function allows optimization of the field uniformity, the inductance, and the efficiency of the coil in any combination. Neither the coil nor the ROI is restricted to any particular geometry. A 40-turn cylindrical z-gradient coil of radius a and length 4a, designed for ROI of radius 0.7a and length 2a has an average error in the gradient fields generated of 0.85%, an inductance of 0.014a mH/cm, and an efficiency of 6.65a-2 Gcm/A. A 16-turn birdcage-like RF coil of radius 5 cm, designed for a ROI of radius 4 cm has an average error of 0.79%.

Algorithms↗
PubMed1991

High-resolution, short echo time MR imaging of the fingers and wrist with a local gradient coil.

The many fibrous tissues of the wrist and hand have short T2s, and, because of the small size of the tissues, their magnetic resonance (MR) imaging necessitates use of the high spatial resolution obtainable with fields of view as small as 2 cm x 2 cm x 1 mm. The authors demonstrate that the use of a local xyz gradient coil, positioned off-center in a clinical MR imager to facilitate patient positioning, permits acquisition of high-resolution images in spin-echo (SE) and gradient-recalled-echo (GRE) sequences with echo time (TE) as short as 6 msec (SE) or 3 msec (GRE). The authors compare this method for obtaining high-resolution images with the alternative method of using normal gradient strengths and increased pulse duration. The effects on image quality of TE, bandwidth, gradient strength, and chemical shift artifacts are presented. Images obtained with the local gradient coil of the carpal tunnel, carpal bones, and proximal interphalangeal joint in healthy volunteers are shown.

Finger Joint↗
PubMed1990

The efficacy of high dose inhaled budesonide in replacing oral corticosteroid in Asian patients with chronic asthma.

We studied 22 Asian patients with steroid dependent asthma. Using a clinical approach to the addition of high dose inhaled budesonide and tapering of systematic steroid, we were able to substitute 5 to 20 mg prednisolone with 800 micrograms per day of inhaled budesonide in all patients. There was also a greater reduction in nocturnal symptoms and awakenings and a smaller overnight fall in PEFR during treatment with budesonide than with prednisolone. Inhaled budesonide was an effective long term substitute for prednisolone in chronic asthma.

Administration, Inhalation↗
PubMed1989

Pharmacokinetic and pharmacodynamic comparison of conventional and controlled release formulations of metoprolol [correction of motoprolol] in healthy Chinese subjects.

A double-blind, crossover comparison of the pharmacokinetics and pharmacodynamics of controlled-release metoprolol (CR) 100 mg and 200 mg, metoprolol plain tablet 100 mg, metoprolol Durules 200 mg, and placebo was carried out in 10 healthy Chinese subjects. Standardized treadmill exercise tests according to the Bruce protocol were performed at a steady state of medication, before and 2, 6, 12, and 24 hours after the dose, and multiple blood samples were collected for determination of the metoprolol concentration. The plasma metoprolol levels over 24 hours were more uniform after metoprolol CR than Durules and the plain tablet. The mean peak concentrations for CR 100 mg, 200 mg, Durules, and the plain tablets were 231, 426, 790, and 1105 nmol/l, respectively. The corresponding fluctuation incides were 1.1, 1.5, 2.2, and 5.0. The effects on exercise heart rate (EHR) were investigated at steady state. Metoprolol CR produced more even reduction in EHR over 24 hours than Durules and plain tablets. All four treatments gave similar maximal reduction in EHR of about 20% at 2 hours after the dose. In conclusion, once daily metoprolol CR showed almost even blood levels and provided relatively constant levels of beta1 blockade over 24 hours in healthy Chinese subjects.

Adult↗
PubMed1989

Omeprazole in acute and long-term treatment of Asian patients with peptic ulcer refractory to H2-antagonists.

Twenty-seven patients with peptic ulcer (19 with duodenal ulcer (DU) and eight with gastric ulcer (GU] refractory to H2-antagonists were treated with 40 mg of omeprazole once daily for 4-8 weeks, depending on the rate of ulcer healing. Clinical assessment, endoscopy and laboratory tests were performed at entry, after 2 and after 4 weeks, and if unhealed, also after 8 weeks' treatment. Ten healed patients were given a maintenance therapy of omeprazole 20 mg daily for up to 12 months during which the patients returned for endoscopy, gastric biopsy and laboratory tests at 3-monthly intervals. The initial treatment healed 15 of 19 (79%) DU patients in 2 weeks and all DU patients by 4 weeks. Seven of eight (87%) GU patients healed in 4 weeks and only one required 8 weeks' treatment. Symptom relief was rapid, with most patients being symptom-free within the first day of treatment. Six patients received 12 months' continuous maintenance therapy, one patient 9 months and three patients 6 months' treatment. All patients remained in remission whilst on omeprazole therapy. No adverse events were reported throughout the study. There were no clinically significant changes in haematology or blood chemistry after healing or during the long-term treatment. Biopsy samples revealed no histological changes in the gastric mucosa at any stage. Omeprazole 40 mg therefore was found to produce rapid healing and symptom relief in Asian patients with H2-antagonist-resistant peptic ulcers. Maintenance therapy with omeprazole 20 mg daily was shown to be safe and effective in preventing recurrence of peptic ulceration.

Adult↗
PubMed1989

Budesonide aerosols in Thai asthmatic children.

Thirteen children with chronic bronchial asthma, 8 boys and 5 girls, aged between 5 and 15 (mean 10) years, with a duration of asthma ranging from 1 to 12 (mean 6) years, were studied by a control, oral prednisolone 5 mg twice a day and inhaled budesonide 100 micrograms twice daily, each for 3 weeks. The clinical efficacy assessed daily by day and night symptom scores, cough, limitation of activity and inhaled terbutaline used, showed improvement of the parameters measured during budesonide and prednisolone treatment period but did not reach statistical significance except for the night symptom scores (p less than 0.05) between the control and inhaled budesonide period and the cough between the control and oral prednisolone period. Slight improvement in pulmonary function was observed during budesonide and prednisolone. No changes of complete blood counts before and after inhaled budesonide were noted. No oral and pharyngeal thrush were observed in any studied period. Inhaled budesonide appears to be effective for treatment of chronic bronchial asthma but still requires long-term studies with higher dosages to be certain that its effect is better and maintained and without systemic side effects.

Administration, Topical↗
PubMed1988

Characteristics of calmodulin phosphorylation by the insulin receptor kinase.

Calmodulin is a substrate for the insulin receptor kinase. The time sequence of events resulting in insulin-stimulated phosphorylation of calmodulin was analyzed at a number of different insulin concentrations using partially purified solubilized insulin receptor preparations from rat adipocytes. The respective insulin concentrations needed to reach half-maximal binding, phosphorylation of the beta-subunit of the insulin receptor, and phosphorylation of calmodulin were 4.5 X 10(-10), 4.3 X 10(-10), and 3.9 X 10(-10) M, respectively. At all insulin concentrations, the time to reach 50% of the maximum (defined as the value obtained at 60 min) occurred in the sequence: insulin binding less than beta-subunit phosphorylation less than calmodulin phosphorylation. Insulin binding and beta-subunit phosphorylation occurred almost immediately, whereas there was a lag phase preceding calmodulin phosphorylation. Although stoichiometry was generally low under routine assay conditions (0.01-0.10 mol phosphate/mol calmodulin), it could be increased 4.3 +/- 0.5-fold (n = 5) by pretreating the calmodulin with 0.1 N NaOH. Insulin-stimulated phosphorylation of calmodulin was exclusively on tyrosine residues. The calmodulin molecule in animals contains only two tyrosine residues, located at positions 99 and 138. The amount of phosphate incorporation into a semisynthetic calmodulin (VU1) which contains only one of these tyrosine residues (tyrosine-138) was half that obtained with porcine or chicken calmodulin. Therefore, insulin, via its receptor kinase, stimulates the phosphorylation of calmodulin; calmodulin can be phosphorylated on both tyrosine residues 99 and 138.

Adipose Tissue↗