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Biomedical subjects

M C Choi

Publications and source records attributed to M C Choi.

16 recordsLinked to original sources
PubMed2006

Feasibility of transradial coronary angiography and angioplasty in Chinese patients.

OBJECTIVE: To assess the clinical applicability, efficacy, and safety of coronary angiography and angioplasty via a transradial approach in local Chinese patients. DESIGN: Prospective case series. SETTING: Regional hospital, Hong Kong. PATIENTS: All patients undergoing coronary angiography and coronary angioplasty between 1 January and 30 June 2004. INTERVENTIONS: Transradial coronary angiography and coronary angioplasty. MAIN OUTCOME MEASURES: Feasibility, success rate, and complications. RESULTS: A total of 268 coronary angiographies (62% of all coronary angiographies) and 118 coronary angioplasties (48% of all coronary angioplasties) were performed via a transradial approach. The procedural success rate for coronary angiography was 93.7% with a mean duration of 21.8 (standard deviation, 13.5) minutes compared with 17.9 (10.0) minutes for angiography via a femoral approach. Most (99%) patients were free from any complications. Of those patients who underwent elective transradial coronary angiography in the morning, 64% were discharged on the same day. Comparison of data in the first half of the study period with those in the second half revealed a significant increase in the percentage of coronary angiographies performed via a transradial approach (from 52% to 73%, P<0.0001), and an improved procedural success rate (from 91.5% to 95.3%, P=0.1). For transradial coronary angioplasty, the procedural success rate was 98%. A total of 246 lesions (2.08 lesions per patient) were treated with no procedure-related complications. CONCLUSIONS: Transradial coronary angiography and angioplasty are feasible in a significant proportion of local Chinese patients and achieve a high success rate and low complication rate. It tends to prolong procedural duration, but improves patients' comfort and permits earlier ambulation and discharge. The procedural success rate improves with accumulating experience.

Aged↗
PubMed2005

Okadaic acid, a causative toxin of diarrhetic shellfish poisoning, in green-lipped mussels Perna viridis from Hong Kong fish culture zones: method development and monitoring.

Green-lipped mussels (Perna viridis) were collected from seven fish culture zones (FCZs) in Hong Kong and analyzed for okadaic acid (OA). A conventional HPLC method was modified by incorporating a proteinase K digestion step. Results suggest that a higher recovery (2.5 times higher) of OA was obtained from spiked samples after the addition of 1.08 mg proteinase K in comparison with samples incubated without the proteolytic enzyme. For the hepatopancreas (HP) of individual field-collected mussels, the additional digestion step can enhance OA extraction by 3.1 times. Spatial and temporal variations in OA concentrations in the mussels from various FCZs were investigated. The highest concentration of OA in mussel HP samples was 1164.9 ng/g HP wet wt. With respect to OA concentrations in whole mussel tissues from seven sites and four seasonal samplings, the concentrations were between 70.0 and 131.0 ng/g wet wt., which did not exceed the generally recognized international regulatory criteria (>200 ng/g) for OA.

Animals↗
PubMed2004

Radiographic contrast study of the upper gastrointestinal tract of eight dogs using carboxymethylcellulose mixed with a low concentration of barium sulphate.

To evaluate the efficacy of a mixture of barium and carboxymethylcellulose (CMC) suspension in upper gastrointestinal contrast studies, and to determine its optimal concentration and method for use, eight healthy beagle dogs underwent conventional upper gastrointestinal contrast imaging and a modified procedure using a mixture of barium sulphate and CMC. Four different procedures were carried out on the dogs at weekly intervals. In the first, the dogs were administered 10 ml/kg of 60 per cent barium suspension for conventional study of the upper gastrointestinal tract. The second, third and fourth procedures involved modified methods in which the dogs were given 10 ml/kg of a mixture of 25 per cent barium and 0.5 per cent CMC prepared to a low, moderate or high viscosity, respectively. All four procedures were evaluated by four criteria: the quality of the images obtained, the translucency and distensibility of the bowel, and the transit time. The method of imaging which used a moderately viscious CMC formulation provided excellent image quality, high translucency, a rapid transit time and suitable bowel distension to enable more precise diagnosis of disorders of the gastrointestinal tract.

Administration, Oral↗
PubMed2000

Scleral melanocytosis and oculodermal melanocytosis (nevus of Ota) in Chinese children.

Two thousand nine hundred fourteen Chinese children (1510 males and 1404 females) were examined for the presence of scleral melanocytosis (SM) and oculodermal melanocytosis in a cross-sectional prevalence survey. SM was found in 4.9% of boys and 4.1% of girls under the age of 1 year. The peak prevalence was at 6 years of age, when 44.6% of boys and 46.6% of girls were affected. At 18 years of age, only 11.1% of boys and 13.2% of girls had SM. The overall prevalence, regardless of age, was 27.6% in boys and 27. 1% in girls. The condition was bilateral in 78% of cases. The medial superior quadrant was the most frequently affected site, and the lateral inferior quadrant was the least frequently affected site. Oculodermal melanocytosis occurred only in one patient; the pigmentation affected the left side of the face and the ipsilateral sclera.

Adolescent↗
PubMed1999

Hyperhidrosis.

Explore the source record for details and available documents.

Female↗
PubMed1999

Hypohidrosis in children.

Hypohidrosis has many causes. The condition may be generalised or segmental, acute or progressive and central or peripheral in origin. Most of the causes can be diagnosed from the history and physical examination. Laboratory investigations are usually not necessary. Treatment should be directed at the underlying cause whenever possible.

Child↗
PubMed1992

Control of steroidogenesis in Leydig cells.

Luteinizing hormone (LH) interacts with its plasma membrane receptor to stimulate steroidogenesis not only via cyclic AMP but also other pathways which include arachidonic acid and leukotrienes and regulation of chloride and calcium channels. The same stimulatory pathways may lead to desensitization and down-regulation of the LH receptor and steroidogenesis. The LH receptor exists in a dynamic state, being truncated, or internalized, degraded or recycled. Desensitization is controlled by protein kinase C (PKC) in the rat and by cyclic AMP dependent protein kinase and PKC in the mouse Leydig cells. Using an adapted anti-sense oligonucleotide strategy we have shown that the cytoplasmic C-terminal sequence of the LH receptor is essential for desensitization to occur. In contrast, these sequences of the LH receptor are not required for the stimulation of cyclic AMP and steroid production. We have also shown that the extracellular domain of the LH receptor is secreted from the Leydig cell and may act as a LH-binding protein.

Animals↗
PubMedDate not supplied

Magnetic field modification of electron-beam dose distributions in inhomogeneous media.

Modern curative radiotherapy requires higher doses to the tumor volume and, necessarily, minimal doses to the surrounding normal tissues. Attempts to use heavy charged particles to achieve such optimization are currently under investigation in many centers. Our data indicate that a static, superimposed magnetic field on a clinical electron-therapy beam also offers the capability of some "tailoring" of isodose distributions. Furthermore, a variable, superimposed magnetic field minimizes those tissue-generated dose heterogeneities which are inherent with all charged-particle beams. We suggest that magnetically modified, clinically available electron beams also offer a practical and less expensive means of achieving tailored, heterogeneity-corrected isodose distributions.

Electrons↗
PubMedDate not supplied

Variation in output factor caused by secondary blocking for 7-16 MeV electron beams.

The effect of secondary blocking on the output for 7-16 MeV electron beams is investigated for the two most widely used methods of field shaping, i.e.,(a) shield on surface, and (b) shield at end of cone with subsequent air gap. For those two methods differences in output on the order of 10% are observed. These effects are explained in terms of the blocking geometry and its influence on scattered radiation.

Radiotherapy, High-Energy↗
PubMedDate not supplied

Characterization of Clinac-18 electron-beam energy using a magnetic analysis method.

Clinac-18 electron-beam energies and spectral energy distributions were measured by a magnetic analysis method to verify results obtained by the standard range method. A comparison of these measurements with nominal energies quoted by the manufacturer indicates that electron-beam measured by both methods are in agreement with the manufacturer's specifications to +/- 0.6 MeV. Spectral energy distribution of the electron beam was measured to be approximately 1 MeV (FWHM) at all energies.

Electrons↗
PubMedDate not supplied

Lipowitz metal shielding thickness for dose reduction of 6-20 MeV electrons.

The relative dose reduction by Lipowitz metal of 6 to 20 MeV electrons from a Varian Associates Clinac-20 linear accelerator has been measured using a parallel plate thin wall ionization chamber. Metal thickness required for a 5% attenuation level for a 10 X 10 cm2 field are as follows: 6 MeV-2.3 mm, 9 MeV-4.4 mm, 12 MeV-8.5 mm, 16 MeV--18.0 mm, 20 MeV-25.0 mm.

Humans↗