PubMed Health⌕ Search

Biomedical subjects

R Yeung

Publications and source records attributed to R Yeung.

At least 19 recordsLinked to original sources
PubMed2006

Sources of variation in multi-centre brain MTR histogram studies: body-coil transmission eliminates inter-centre differences.

OBJECT: 1. Identify sources of variation affecting Magnetisation Transfer Ratio (MTR) histogram reproducibility between-centres. 2. Demonstrate complete elimination of inter-centre difference. MATERIALS AND METHODS: Six principle sources of variation were summarised and analysed. These are: the imager coil used for radiofrequency (RF) transmission, imager stability, the shape and other parameters describing the Magnetisation Transfer (MT) pulse, the MT sequence used (including its parameters), the image segmentation methodology, and the histogram generation technique. Transmit field nonuniformity and B1 errors are often the largest factors. PLUMB (Peak Location Uniformity in MTR histograms of the Brain) plots are a convenient way of visualising differences. Five multi-centres studies were undertaken to investigate and minimise differences. RESULTS: Transmission using a body coil, with a close-fitting array of surface coils for reception, gave the best uniformity. Differences between two centres, having MR imagers from different manufacturers, were completely eliminated by using body coil excitation, making a small adjustment to the MT pulse flip angle, and carrying out segmentation at a single centre. Histograms and their peak location and height values were indistinguishable. CONCLUSIONS: Body coil excitation is preferred for multi-centre studies. Analysis (segmentation and histogram generation) should ideally be carried out at a single site.

Artifacts↗
PubMed2004

Ameloblastoma in the Hong Kong Chinese. Part 1: systematic review and clinical presentation.

OBJECTIVES: The aim of Part 1 of this study was to determine the clinical presentation of central ameloblastomas in the Hong Kong Chinese and to compare them with other reported series by a systematic review (SR). METHODS: The study had two elements, that of a complete series of all ameloblastomas presenting at a major Chinese maxillofacial surgical unit as well as a SR. The files of the Department of Oral and Maxillofacial Surgery of the University of Hong Kong between 1989 and 2000 were reviewed for ameloblastoma cases. The relevant literature was identified by electronic databases, review of citation lists and hand searching of key journals. The principal selection criterion was that the study should represent a complete collection of cases. RESULTS: Fifty-three published series of cases were included in the SR. They generally reported little more than sex, mean age and range, and affected jaw. Only 16 studies considered recurrence. Sixty-one cases of ameloblastoma were identified in the present study. There were 30 males and 31 females, contrary to the predilection for males in other reports. Eighty-four percent of cases were found in the mandible, agreeing with the SR. The mean age at first presentation was 30.5 years, lower than that of the SR; only a Korean report and a small Bangladeshi report showed younger presentation. The present report had the shortest period between first becoming aware of the lesion and seeking treatment; this period was significantly shorter for younger patients. Although the present study was in agreement with the SR with regard to swelling, this study reported a significantly higher proportion of patients presenting with pain. CONCLUSION: Although the presentation of ameloblastoma within this Chinese community was broadly similar to that observed in other populations, it differed in a number of important respects. It had a younger age at first presentation than many other communities, including other Orientals; it was associated with a shorter period between first becoming aware of the lesion and seeking treatment, particularly in the young; and it was more frequently associated with pain than in the SR.

Adolescent↗
PubMed2004

Ameloblastoma in the Hong Kong Chinese. Part 2: systematic review and radiological presentation.

OBJECTIVES: The aim of this part of the study was to determine the radiological presentation on conventional radiographs of central ameloblastomas in the Hong Kong Chinese and compare them with other reported series by a systematic review (SR). METHODS: The study had two elements, that of a complete series of all ameloblastomas presenting at a major Chinese maxillofacial surgical unit and a SR. The files of the Department of Oral and Maxillofacial Surgery of the University of Hong Kong between 1989 and 2000 were reviewed for ameloblastoma cases. The relevant literature was identified by electronic databases, review of citation lists and handsearching of key journals. The principal selection criterion was that the study should represent a complete collection of cases. RESULTS: Only 13 reports gave any radiological details. The present study of the Hong Kong Chinese contained 61 cases. With the exception of radiodensity and shape of radiolucency, the majority of the 13 other reports did not record the other radiological features that could be important in the diagnosis. The present study agreed with the synthesis of the 13 reports with regards to complete radiolucency and cortication of ameloblastomas, but disagreed with regards to other important features. The present study had a significantly higher proportion of unilocular lesions, better marginal definition, and more frequent perforation of the cortex and buccolingual expansion. Nine of the ten maxillary lesions straddled both anterior and posterior sextants with four crossing the midline, whereas only 13 of the 51 mandibular cases affected both sextants, of which eight crossed the midline. The unicystic form, which was most prevalent, appeared significantly more frequently as unilocular radiolucencies in comparison with the non-unicystic forms. The frequencies of unicystic forms and unilocular presentations were significantly greater in the young. The lesions in the young were significantly sited solely in the posterior sextant. The lower border of the mandible was reached and affected by ameloblastoma in 36 cases in the present report. It was displaced and thinned in 15 cases whereas in just five it was at least partially undisplaced with the lesion expanding down past it either buccally or lingually to it. The unicystic form was significantly more associated with root resorption, tooth displacement and crowns of unerupted teeth. CONCLUSIONS: Radiologically, ameloblastomas in the Hong Kong Chinese differ significantly with regards to many features. This can be in part explained by the higher proportion of the unicystic form.

Age Factors↗
PubMed2004

Computed tomography of fibrous dysplasia.

OBJECTIVE: Fibrous dysplasia (FD) is an uncommon, but important lesion affecting the jaws. The aim of this study was to reveal its presentation on computed tomography (CT) in a consecutive series of cases. METHODS: The files of the Department of Oral and Maxillofacial Surgery of Hong Kong University between 1989 and 2000 were reviewed for cases of FD. RESULTS: Of the ten cases investigated by CT, two were rejected because of extensive biopsy or surgery before the CT investigation. Seven of the remaining eight cases were Chinese and one was Indian. The mandible and maxilla were equally affected. The cortex was generally intact, except when adjacent to the teeth in the maxilla. The margins were generally poorly-defined, but well-defined on at least some sections of each maxillary case. Five cases were extensive, affecting or nearly affecting the whole hemi-mandible or hemi-maxilla to the midline. All cases displayed expansion, which was fusiform in the mandible and an enlargement of the normal contour in the maxilla. The maxillary antrum was completely obturated in three maxillary cases; one displayed a rounded dome-shaped lesion more suggestive of a benign neoplasm. The orbital floor was displaced in three cases; one of those cases presented with proptosis. All maxillary cases extended back to the pterygoid process, but did not displace it. The "bone windows" of eight cases generally displayed a "ground-glass" pattern; one also displayed cyst-like radiolucencies. The soft tissue window, which depicts mineralized tissue as "white", showed that five cases were completely mineralized. CONCLUSION: CT can be used to determine the extent, specific dimensions and radiodensity of FD.

Adolescent↗
PubMed2002

Odontogenic myxomas in the Hong Kong Chinese: clinico-radiological presentation and systematic review.

AIM: The aim of this study was to determine the clinical and radiological presentation on plain films of central odontogenic myxomas (OM) in the Hong Kong Chinese and compare them to other reported series by a systematic review (SR). METHODS: The study had two elements, that of a complete series of all OMs presenting at a major Chinese maxillofacial surgical unit and a SR. The files of the Department of Oral and Maxillofacial Surgery of the University of Hong Kong between 1989 and 2000 were reviewed for OM cases. The relevant literature was identified by electronic databases, review of citation lists and handsearching of key journals. The principal selection criterion was that the study should represent a complete collection of cases. RESULTS: The SR revealed that only a quarter of the reports provided any quantitative radiological details. Just under half of the included reports provided the relative period prevalence of OMs compared to other odontogenic tumours, but these reports almost completely excluded consideration not only of the radiology but also specific clinical details. Furthermore, they did not report of recurrence data, an important feature of the OM. Most of the most recent reports were concerned with relative period prevalence. The relative period prevalence and 'number of OMs per hospital per year' of studies separated by two or more decades in Hong Kong and Nigeria indicate an increase in the number of lesions diagnosed as OMs. The 10 Hong Kong cases were broadly consistent with the predilections for females and the mandible of other reports. The mean age at first presentation in the present report is 36.9, older than the other reports. Most lesions are large, affecting both posterior and anterior quadrants. They appear to be larger than those in many other reports. Two of the OMs are accompanied by histories of recent rapid growth. Tooth displacement and root resorption are more frequently observed in OMs in the present study. Although all OMs in the present study are still being followed up after surgery, none have recurred. CONCLUSION: Although the presentation of larger lesions in the older Chinese could in part be explained by attitudes rooted in traditional medicine in spite of the widespread availability of modern medical care in Hong Kong, there is a history of recent rapid growth in at least two cases. An emphasis by recent reports on the OMs' relative period prevalence of concurrent odontogenic lesions, has omitted recording the radiology and the specific clinical details usually required for diagnosis.,

Adolescent↗
PubMed2001

The generation and characterization of a cell line derived from a sporadic renal angiomyolipoma: use of telomerase to obtain stable populations of cells from benign neoplasms.

Angiomyolipomas are benign tumors of the kidney derived from putative perivascular epithelioid cells, that may undergo differentiation into cells with features of melanocytes, smooth muscle, and fat. To gain further insight into angiomyolipomas, we have generated the first human angiomyolipoma cell line by sequential introduction of SV40 large T antigen and human telomerase into human angiomyolipoma cells. These cells show phenotypic characteristics of angiomyolipomas, namely differentiation markers of smooth muscle (smooth muscle actin), adipose tissue (peroxisome proliferator-activator receptor gamma, PPARgamma), and melanocytes (microophthalmia, MITF), thus demonstrating that a single cell type can exhibit all of these phenotypes. These cells should serve as a valuable tool to elucidate signal transduction pathways underlying renal angiomyolipomas.

Actins↗
PubMed1998

Intraoperative ultrasound does not improve detection of liver metastases in resectable pancreatic cancer.

BACKGROUND: In colorectal cancer, intraoperative ultrasound (IOUS) is superior to other imaging studies in characterizing hepatic metastases. The value of IOUS in detecting liver metastases from pancreatic cancer has not been evaluated previously. METHODS: Between 1990 and 1995, IOUS was prospectively employed to evaluate the liver for metastases in 32 patients with resectable pancreatic adenocarcinoma. Preoperatively, all patients had computed tomography (CT) and 22 patients had CT portography. RESULTS: At exploration, 5 of the 32 patients (15%) had extrapancreatic disease, 3 (9%) with liver implants. IOUS did not identify any additional hepatic metastases. Four preoperative studies were suspicious for metastatic disease in the liver. In these 4 patients, no hepatic metastases were identified by exploration or intraoperative ultrasound. CONCLUSIONS: We no longer routinely perform hepatic IOUS when evaluating patients with pancreatic adenocarcinoma for pancreaticoduodenectomy. When a preoperative study indicates possible hepatic involvement, IOUS can confirm the presence or absence of liver metastases.

Adenocarcinoma↗
PubMed1995

Acute mass burns caused by o-chlorobenzylidene malononitrile (CS) tear gas.

The use of tear gas in controlling riots has been an accepted practice in many countries for the past four decades. In a recent event, a large quantity of tear-gas canisters were used during a situation of unrest in a Hong Kong Refugees' Detention Centre. We report 96 cases of acute burn injury as an unpredicted side effect of o-chlorobenzylidene malononitrile (CS) tear gas. There were 47 females and 49 males with an age ranging between < 1 to 51 years. These burns were categorized as minor burns, with the total body surface area (TBSA) ranging from 1 to 8 per cent with mean percentage of 3. Most of the patients sustained superficial or partial-skin thickness injuries. Only two patients were admitted to the Prince of Wales Hospital Burns Centre because of deeper burns; debridement and skin grafting was required in one of them. The mechanism of burn injury was due to the flame generated from the grenade explosion, direct contact between the hot canister and the victim's skin, and the effect of the chemical powder inside the canisters when it splashed onto the victim's body. We suggest that the noxious transient effects of tear gas are underestimated, furthermore varying cutaneous effects and deep burns may result from its uncontrolled use during riots. There is a continuing need to reassess the potential toxic effects of CS tear gas as a riot control agent and to debate whether its future use can be condoned under any circumstances.

Acute Disease↗
PubMed1993

Universal mapping probes and the origin of human chromosome 3.

Universal mapping probes (UMPs) are defined as short segments of human DNA that are useful for physical and genetic mapping in a wide variety of mammals. The most useful UMPs contain a conserved DNA sequence immediately adjoined to a highly polymorphic CA repeat. The conserved region determines physical gene location, whereas the CA repeat facilitates genetic mapping. Both the CA repeat and its neighboring sequence are highly conserved in evolution. This permits molecular, cytogenetic, and genetic mapping of UMPs throughout mammalia. UMPs are significant because they make genetic information cumulative among well-studied species and because they transfer such information from "map rich" organisms to those that are "map poor." As a demonstration of the utility of UMPs, comparative maps between human chromosome 3 (HSA3) and the rat genome have been constructed. HSA3 is defined by at least 12 syntenic clusters located on seven different rat chromosomes. These data, together with previous comparative mapping information between human, mouse, and bovine genomes, allow us to propose a distinct evolutionary pathway that connects HSA3 with the chromosomes of rodents, artiodactyls, and primates. The model predicts a parsimonious phylogenetic tree, is readily testable, and will be of considerable use for determining the pathways of mammalian evolution.

Animals↗
PubMed1990

Human antral damage induced by alcohol is potentiated by enprostil.

Enprostil, a synthetic analogue of prostaglandin E2, has been shown to protect the human gastroduodenal mucosa from aspirin injury. This study was designed to determine if enprostil protected against alcohol damage. A double-blind, randomized, cross-over study was performed on eight healthy adult men. After an overnight fast, a gastroscope was inserted and the antral mucosa was sprayed with a 10-mL test solution containing either enprostil (70 micrograms) or its vehicle (control). After 15 minutes, mucosal injury was scored (0-5), and the mucosa was sprayed with 100 mL 80% ethanol. Mucosal injury was scored after a further 15, 20, 25, and 30 minutes. The entire experiment was recorded on video film, which a second endoscopist used to score the damage independently. The two experiments were separated by an interval of 1 week. There was close agreement between the two endoscopists (r = 0.9385), and their scores were averaged. Using Friedman's two-way analysis of variance, a highly significant (P less than 0.00004) increase in injury was demonstrated following enprostil pretreatment. The Wilcoxin signed rank test showed the differences to be significant (P less than 0.05) at every time point. We conclude that enprostil, rather than protecting the human antral mucosa from alcohol injury, appears to potentiate this injury and may itself be damaging in therapeutic concentrations. This unexpected result cannot yet be explained but demands caution in the clinical use of enprostil.

Adult↗
PubMed1988

Aspirin-induced human antral injury is reduced by vodka pretreatment.

Mild irritants have been shown to protect the rat gastric mucosa against noxious agents. This study was designed to test the protective potential of low-dose ethanol against acetylsalicylic acid (ASA) -induced gastric injury. Ten healthy volunteers who were nondrinkers and had normal baseline upper gastrointestinal endoscopy participated in a randomized double-blind crossover study. Thirty minutes after either vodka (37.5 ml) in tomato juice or tomato juice alone, each subject took 975 mg ASA and then underwent endoscopy 1 hr later. The degree of mucosal injury was scored, and blood was taken for ethanol and salicylate levels. There was a washout interval of seven days between the two treatments. Endoscopic scores were analyzed using the sign test. After a single dose of ASA, mucosal injury was confined to the fundus and antrum, while the duodenum was minimally affected. A significant reduction in antral damage was seen with ethanol pretreatment (P less than 0.05). The same trend was evident in the fundus but did not achieve statistical significance. Serum salicylate levels averaged 13.2 +/- 0.8 mg/100 ml and were not different between the two treatments. Ethanol concentration ranged from 1.1 to 6.2 mmol/liter following the vodka drink and was 0 after the placebo.

Adult↗
PubMed1986

Light-dependent activity of the antitumor antibiotics ravidomycin and desacetylravidomycin.

The antitumor antibiotics ravidomycin and desacetylravidomycin were studied by the biochemical lambda prophage induction assay. In this assay, induction of the enzyme beta-galactosidase is measured as a specific indication of the ability of an agent to directly or indirectly damage DNA. Induction was observed only when these two antibiotics were irradiated with light in the presence of the indicator organism. Drug treated with light followed by incubation with the indicator organism in the dark did not cause induction. Light in both the near UV and visible wave length ranges activated these antibiotics; near UV and visible blue wavelengths were most effective, while 597-nm light was totally ineffective. The amount of induction caused by these drugs varied directly with the dosage of light provided. Bacterial growth inhibition, as well as cytotoxicity for a human colon carcinoma cell line, was also dramatically enhanced by light. These data suggest that ravidomycin and desacetylravidomycin are potent photosensitizing, DNA-damaging agents.

Aminoglycosides↗
PubMed1980

A comparison of serum phenytoin determination by the substrate-labeled fluorescent immunoassay with gas chromatography, liquid chromatography, radioimmunoassay and "EMIT".

Patients' sera were analyzed for phenytoin by the Substrate-Labeled Fluorescent Immunoassay (SLFIA), gas chromatography (GC), liquid chromatography (LC), Radioimmunoassay (RIA) and EMIT and the results were compared. The EMIT assay was performed using a "PACER Analyzer". All assay results compared favorably. The correlation coefficients were: SLFIA vs GC, 0.995 (n = 45); SLFIA vs. LC, 0.993 (n = 37); SLFIA vs. EMIT, 0.965 (n = 67); SLFIA vs. RIA, 0.977 (n = 34). These results show that phenytoin levels determined by the SLFIA compare well with those obtained by the other four assay techniques.

Chromatography, Gas↗
PubMed1980

Comparison of the effects of inhaled SCH 1000 and fenoterol on exercise-induced bronchospasm in children.

The effect of 40 microgram of SCH 1000 (ipratropium bromide, an anticholinergic agent) on bronchodilation and suppression of exercise-induced bronchospasm (EIB) was compared with 400 microgram of fenoterol and a placebo in a single-blind controlled study. Twenty-seven randomly selected asthmatic children performed a standardized treadmill exercise challenge and the 17 children who were shown to have EIB continued in the study. Pulmonary function was evaluated before and after drug administration and exercise. When individual results were analyzed and grouped according to the responsiveness of EIB to the drugs, two patterns emerged: (1) the EIB was more severe in those (6/17) children who did not respond to either drug than in the rest of children; (2) the resting pulmonary function was significantly better in the children (4/17) who responded to both drugs than in those (7/17) who responded to fenoterol alone. In conclusion SCH 1000 was shown to be an effective bronchodilator comparable to, but no better than, fenoterol. It had minimal side effects. As an EIB inhibitor it depended on relatively normal base line pulmonary function and only a moderate deterioration following exercise, whereas fenoterol depended on the exercise response alone. Although anticholinergic drugs are not very extensively used, SCH 1000 may be useful in some patients where the beta 2 adrenergic drugs cause signficant side effects or are contraindicated.

Adolescent↗