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C S Leung

Publications and source records attributed to C S Leung.

At least 19 recordsLinked to original sources
PubMed2003

A new method for improving metaphase chromosome spreading.

BACKGROUND: The success of complex molecular cytogenetic studies depends on having properly spread chromosomes. However, inconsistency of optimum chromosome spreading remains a major problem in cytogenetic studies. METHODS: The metaphase spreading process was carefully timed to identify the most critical phase of chromosome spreading. The effects of dropping height of cell suspension, slide condition, drying time, fixative ratio, and relative humidity on the quality of metaphase spreads were studied by quantitative examination of metaphase chromosome spreads. Normal and immortalized human epithelial ovarian cells, neuroblastoma cells, and normal lymphocytes were tested. RESULTS: Humidity over the slide was the most important variable affecting the quality of chromosome spreads. Consistent improvement in chromosome spreading (larger metaphase area, less chromosome overlaps, or lower frequencies of broken metaphases) was obtained for all cell types if dynamic cell rehydration, occurring as fixative absorbs moisture from air, was made to coincide with the prompt fixation of spread chromosomes to the slide. This was achieved by dropping cells on dry glass slides placed in a shallow metal tray and then quickly lowering the tray into a covered 50 degrees C water bath for slide drying. CONCLUSIONS: A new and simple method for improving metaphase chromosome spreading was developed based on our study on the characteristics of chromosome spreading.

Cell Line, Tumor↗
PubMed2003

Antithrombotic treatment of atrial fibrillation in a regional hospital in Hong Kong.

OBJECTIVE: To measure the use, appropriateness, and safety of antithrombotic therapy in Hong Kong Chinese patients with atrial fibrillation. DESIGN: Retrospective review. SETTING: Regional hospital, Hong Kong. SUBJECTS AND METHODS: Medical records of all patients with atrial fibrillation admitted to acute internal medicine wards in April 2000 and between July and October 2001 were reviewed for details of antithrombotics given, results of international normalised ratio monitoring for patients receiving warfarin, side-effects, and additional risk factors for complications of atrial fibrillation. Statistical analysis was undertaken to assess factors predictive of antithrombotic use. RESULTS: A total of 207 patients with chronic atrial fibrillation were included in the study. Of these, 44.0% of patients with non-valvular atrial fibrillation without contra-indications for warfarin use were receiving warfarin, 34.1% were receiving aspirin, and 22.0% were receiving no antithrombotic therapy. The majority of patients (69.1%) were treated appropriately according to the American College of Chest Physicians guidelines. The major side-effect rates for warfarin and aspirin were 2.14% and 1.72% per patient-year, respectively, which were comparable with western studies of usual clinical practice. The ischaemic stroke rate for patients taking warfarin or aspirin were 1.40% and 6.02% per patient-year, respectively. The median international normalised ratio was 1.96. The median frequency of international normalised ratio measurement was 45.58 days. CONCLUSIONS: This study found that antithrombotic use in a Hong Kong regional hospital for patients with atrial fibrillation was similar to that reported from western institutions. Complication and stroke rates were also comparable to the western data relating to usual clinical practice.

Adult↗
PubMed2002

A retrospective review of transcatheter hepatic arterial embolisation for ruptured hepatocellular carcinoma.

BACKGROUND: Hepatocellular carcinoma (HCC) is a disease with a high prevalence in South East Asia. It is not uncommon to encounter rupture of the tumour in an emergency situation. Operative measures in this situation are often associated with high mortality rates. Transcatheter arterial embolisation (TAE) appears to be an effective alternative to surgery and is increasingly used by many centres. In this study, we have reviewed the outcome of our patients after receiving TAE and tried to identify prognostic indicator(s). PATIENTS AND METHODS: From 1996 to 2000, we had retrospectively reviewed the outcome of 31 patients who had undergone TAE for rupture of HCC and compared their survival with respect to different prognostic indicators. RESULTS: The were 31 patients with a mean age of 53 years. At the time of rupture, 19 patients had Child's A, 5 Child's B and 7 of Child's C disease. The most common presentation was abdominal pain (14 patients). Bleeding was successfully arrested in all 31 patients. The most common complication was fever (13 patients). The overall mean survival was 126 days. Eight patients died within 30 days of admission, the major cause of death was liver failure, which occurred in 6 patients. In addition, we had also postulated several prognostic indicators for patients' survival. The results showed that only those with a bilirubin level below 50 umol/L and who presented with shock had a poor outcome. CONCLUSION: TAE should be considered in the initial management of patients with ruptured HCC. It is effective in arresting tumour bleeding and allows the patient to have subsequent definitive management.

Carcinoma, Hepatocellular↗
PubMed2001

A pruning method for the recursive least squared algorithm.

The recursive least squared (RLS) algorithm is an effective online training method for neural networks. However, its conjunctions with weight decay and pruning have not been well studied. This paper elucidates how generalization ability can be improved by selecting an appropriate initial value of the error covariance matrix in the RLS algorithm. Moreover, how the pruning of neural networks can be benefited by using the final value of the error covariance matrix will also be investigated. Our study found that the RLS algorithm is implicitly a weight decay method, where the weight decay effect is controlled by the initial value of the error covariance matrix; and that the inverse of the error covariance matrix is approximately equal to the Hessian matrix of the network being trained. We propose that neural networks are first trained by the RLS algorithm and then some unimportant weights are removed based on the approximate Hessian matrix. Simulation results show that our approach is an effective training and pruning method for neural networks.

Algorithms↗
PubMed2000

Difference in susceptibilities of different cell lines to bilirubin damage.

OBJECTIVE: To investigate if there are differences in susceptibilities to bilirubin toxicity of different cell lines. METHODOLOGY: A modified 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) method was adopted to study the cytotoxic effect of bilirubin on several commercially available cell lines including human glioblastoma (ATCC CRL 1690, T98G), human neuroblastoma (ATCC HTB-10, SK-N-MC), human liver (ATCC CCL 13, Chang Liver, HeLa markers) and a mouse fibroblast (ATCC CCL-1, NCTC Colon 929). RESULTS: Cytotoxicity was observed when certain bilirubin:albumin molar ratios were exceeded in the medium of a cell line in culture. Different cells exhibited different susceptibilities to the cytotoxic effects of bilirubin; neuroblastoma and glioblastoma were most susceptible, fibroblasts were the least vulnerable. CONCLUSIONS: Our findings have confirmed the clinical impression that different cells sustain different degrees of cytotoxicities caused by bilirubin.

Albumins↗
PubMed2000

A local training and pruning approach for neural networks.

The training of neural networks using the extended Kalman filter (EKF) algorithm is plagued by the drawback of high computational complexity and storage requirement that may become prohibitive even for networks of moderate size. In this paper, we present a local EKF training and pruning approach that can solve this problem. In particular, the by-products obtained along with the local EKF training can be utilized to measure the importance of the network weights. Comparing with the original global approach, the proposed local EKF training and pruning approach results in a much lower computational complexity and storage requirement. Hence, it is more practical in solving real world problems. The performance of the proposed algorithm is demonstrated on one medium- and one large-scale problems, namely, sunspot data prediction and handwritten digit recognition.

Algorithms↗
PubMed1999

An adaptive Bayesian pruning for neural networks in a non-stationary environment.

Pruning a neural network to a reasonable smaller size, and if possible to give a better generalization, has long been investigated. Conventionally the common technique of pruning is based on considering error sensitivity measure, and the nature of the problem being solved is usually stationary. In this article, we present an adaptive pruning algorithm for use in a nonstationary environment. The idea relies on the use of the extended Kalman filter (EKF) training method. Since EKF is a recursive Bayesian algorithm, we define a weight-importance measure in term of the sensitivity of a posteriori probability. Making use of this new measure and the adaptive nature of EKF, we devise an adaptive pruning algorithm called adaptive Bayesian pruning. Simulation results indicate that in a noisy nonstationary environment, the proposed pruning algorithm is able to remove network redundancy adaptively and yet preserve the same generalization ability.

Bayes Theorem↗
PubMed1998

Porokeratotic eccrine ostial and dermal duct naevus with dermatomal trunk involvement: literature review and report on the efficacy of laser treatment.

Porokeratotic eccrine ostial and dermal duct naevus (PEODDN) is a rare, benign hamartomatous malformation involving the eccrine sweat duct. The existence of filiform keratinous plugs that represent cornoid lamellae overlying dilated infundibula of eccrine ducts is a distinctive feature and the presence of associated abnormal dermal ducts is frequent. We report a patient with PEODDN who exhibited lesions on the left side of her chest. Cases of PEODDN reported in the literature are reviewed. Our experience in treating this patient with ultrapulsed carbon dioxide laser is also presented.

Eccrine Glands↗
PubMed1998

Clinical evaluation of ceftibuten in gonorrhea. A pilot study in Hong Kong.

BACKGROUND: The escalating rates of gonococcal resistance to quinolone in Hong Kong have prompted a search for an alternative first-line antimicrobial agent for use in treating uncomplicated gonococcal urethritis. Ceftibuten is an orally active third-generation cephalosporin with potent in vitro activity against Neisseria gonorrhoeae. Its pharmacokinetic properties allow single-dose administration. OBJECTIVE: To evaluate the efficacy, safety, and tolerability of ceftibuten in the treatment of uncomplicated gonorrhea in men. STUDY DESIGN: Ceftibuten was evaluated in an open-label, noncomparative, multicenter study. Eligible men with uncomplicated gonococcal urethritis were treated with a single 400-mg oral dose of ceftibuten and reassessed 1 week and 3 weeks after treatment. The main outcome measures were the isolation of N. gonorrhoeae, patient-reported side effects, and other safety parameters (e.g., blood counts and renal and hepatic function tests). RESULTS: One hundred twenty-five men were enrolled in the study. The overall cure rate was 98.2% (110 of 112 evaluable patients). Adverse events, which occurred in 4.5% of patients, were all mild, well tolerated, and of short duration. No significant changes in laboratory test results were noted. Of the 125 isolates, 4.8% were -lactamase positive. Susceptibility to ofloxacin was found to be low in 59.2% of isolates (MIC 0.1 to < 1g/mL) and 25.6% of isolates were resistant (MIC1g/mL) to ofloxacin. CONCLUSIONS: A single 400-mg oral dose of ceftibuten is highly effective and well tolerated in the treatment of uncomplicated gonococcal urethritis in men.

Adolescent↗
PubMed1998

Scleredema in Chinese patients: a local retrospective study and general review.

The records from 12 Chinese adult patients with scleredema, who had attended the Social Hygiene Service of the Hong Kong Department of Health between 22 January 1990 and 19 March 1996, were retrieved and analysed. The neck was the commonest site of involvement (75%), followed by the back (42%), and the shoulder (17%). The vast majority (83%) of scleredema cases were associated with diabetes mellitus; half of these were insulin-dependent. Most of the patients (92%) had hypertension for which medical treatment was needed. No cases of skin disease were preceded by acute infection, and none had any associated paraproteinaemia. The degree of skin involvement did not affect the daily activities of most of the patients. This study revealed differences between the disease in our locality and those described in the western literature.

Journal Article↗
PubMed1997

Comparison of ThinPrep and conventional preparations: nongynecologic cytology evaluation.

ThinPrep processing, an automated cytopreparatory method, has been reported to show good correlation with conventional preparations and to reduce the rate of false-negative diagnoses. In a retrospective review of 230 consecutive nongynecologic cytology cases, we compare the ThinPrep (TP) method with conventional preparations (CP). There were 129 fine-needle aspiration (FNA) specimens from various sites, including 51 breasts, 40 thyroids, 14 lungs, 8 livers, and 16 miscellaneous sites. The sources of 101 body cavity fluids included 68 pleural/peritoneal effusions, 25 peritoneal/pelvic washings, and 8 miscellaneous sites. Each case was evaluated for cellularity, morphologic, details, and obscuring background material. Diagnoses of the TP slides were classified as insufficient, normal, benign, suspicious, or malignant. Each case was then correlated with the tissue diagnosis when available. In TP slides, cellular arrangements, nuclear details, and nuclear cytoplasmic ratio were preserved, while blood and diathesis were eliminated. There was no statistically significant difference between TP and CP in the diagnostic categories. However, in six cases of "insufficient for diagnosis" on FNA by CP, TP yielded sufficient cells and tissue fragments for diagnosis. One case each of FNA and body fluid with a diagnosis of "suspicious for malignancy" by CP was considered "positive" on TP slides. The overall sensitivity of TP was 97.6%, and the specificity was 92.9%. The positive predictive value was 93.0%. We conclude that the ThinPrep method shows good correlation with conventional preparations in both FNA and body fluids.

Biopsy, Needle↗
PubMed1997

Solitary angiokeratoma of the oral cavity.

Angiokeratoma is a rare, cutaneous disorder that typically occurs at multiple sites and is often associated with a number of metabolic disorders. Although solitary cutaneous forms have been reported, to date localized lesions within the oral cavity have not been described. We report on an 82-year-old man with a history of squamous cell carcinoma of the ear and scalp who also had a solitary pigmented lesion of the oral cavity. Excisional biopsy of the buccal mucosal lesion showed features consistent with angiokeratoma. We report the first intra-oral solitary angiokeratoma and review the clinical and pathologic features of this unusual condition.

Aged↗
PubMed1997

p53 mutations detected in colorectal carcinoma patients in Hong Kong.

A mutational spectrum for exons 5-8 of the p53 tumor suppressor gene in colorectal carcinomas in Hong Kong Chinese was established. Ninety-nine colorectal carcinomas from Hong Kong patients were analyzed for mutations in p53 gene by PCR-single-strand conformation polymorphism analysis and direct DNA sequencing. Thirty-five of the 99 tumors (35.4%) contained mutations. Point mutations accounted for 80% of all genetic changes and were predominantly base transitions at CpG dinucleotide sites, mutations that were also predominant in Caucasian carcinomas. The major hot spots at codons 175 and 248 of p53 in Caucasians are also hot spots in the Chinese gene. Identical mutations in codons 152 and 306 were detected in two independent tumors in the Chinese, which were reported only rarely in Caucasians. Moreover, a significantly higher frequency (20%) of deletion and insertion mutations was observed in Hong Kong colorectal cancer patients. Distinct genetic and/or environmental factors may contribute to these findings.

Adult↗
PubMed1996

Attraction basin of bidirectional association memories.

In this paper, we investigate the attraction basin of the bidirectional associative memory (BAM) model. The BAM is a two-layer heteroassociator that stores a prescribed set of bipolar library pairs. It consists of two layers of neurons. One layer has n neurons and the other has p neurons. We will first point out why the conventional energy approach cannot tell us about the attraction basin of each library pair. We then rigorously derive the statistical dynamics of the BAM, which shows how the upper bound on the number of errors changes during recalling for an arbitrary error pattern in the initial state. From the dynamics, we can estimate the attraction basin for the worst case errors, as well as the memory capacity and the number of errors in the retrieved pairs. The memory capacity is alpha rn, where alpha r (0 < alpha r < 1) depends on the ratio [formula: see text]. The number of errors in the retrieved pairs is [formula: see text] when the number of library pairs is alpha n. When r = 1, the lower bound on the attraction basin for the worst case errors is about 0.0068n.

Algorithms↗