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Biomedical subjects

T W Chow

Publications and source records attributed to T W Chow.

At least 19 recordsLinked to original sources
PubMed2006

Variations in regional SPECT hypoperfusion and clinical features in frontotemporal dementia.

OBJECTIVE: To characterize the presenting clinical features for frontotemporal dementia (FTD) and contrast them with the degree of frontal and temporal hypoperfusion on SPECT imaging. METHODS: The authors evaluated 74 patients who eventually met Consensus Criteria for the FTD form of frontotemporal lobar degeneration (excluding primary progressive aphasia and semantic dementia) on 2-year follow-up. On first presentation, these patients had undergone both an FTD Inventory for 12 features based on core and supportive Consensus Criteria and SPECT imaging. The initial clinical diagnostic features were contrasted with variations in regional SPECT hypoperfusion. RESULTS: The patients with FTD had more hypoperfusion in the right frontal lobe than in other regions; the subgroup of 25 patients who met Consensus Criteria from the first presentation had the most right frontal hypoperfusion. Frontal lobe involvement was associated with significant apathy, whereas temporal lobe involvement was associated with hypomania-like behavior. Right frontal lobe hypoperfusion further predicted loss of insight, environmental dependency, and stereotyped behaviors. Other associations included left frontal hypoperfusion with a decline in personal hygiene and left temporal hypoperfusion with compulsions and mental rigidity. CONCLUSIONS: On first presentation, frontotemporal dementia (FTD) is disproportionately a right frontal disease evident on behavioral measures and on SPECT. Nonetheless, patients with FTD can initially present with further regional differences in clinical diagnostic features, such as apathy with bifrontal hypoperfusion and hypomania-like behaviors with anterior temporal involvement.

Brain↗
PubMed2005

A 5-year prospective study on small diameter screw-shaped oral implants.

Alveloar ridges of limited dimensions could preclude the placement of dental implants of the regular dimension. Smaller diameter implants - narrow platform (NP) implants were commercially available to address this issue. The aim of the study was to determine the 5-year clinical performance of 3.3 mm diameter NP implants. Twenty-three machined screw-shaped NP implants were placed in nine patients (six males; three females) between 18 and 70 years of age. Clinical and radiographic examinations were performed annually for 5 years. Recognized implant success criteria was used. The criteria were based on the mean marginal alveolar bone loss, the placement of prosthesis of satisfactory appearance, and the absence of implant mobility, peri-implant radiolucency, pain, discomfort or infection. One implant failed at abutment connection. The remaining 22 implants were restored and functioned successfully according to the criteria. The mean marginal alveolar bone loss during the first year was 0.41 +/- 0.17 mm. The mean marginal alveolar bone loss between the second and fifth year was 0.03 +/- 0.06 mm. The success rate of NP implants according to a well-established set of criteria was 96%.

Adult↗
PubMed2005

Retrospective survival analysis of 3-unit fixed-fixed and 2-unit cantilevered fixed partial dentures.

To evaluate the cumulative survival (CS) rates of fixed partial dentures (FPDs) retained by full-veneer retainers, and those of resin-bonded FPDs provided by graduating dental students for the replacement of a single missing tooth. In 168 patients, 61 3-unit fixed-fixed FPDs and 25 2-unit cantilevered FPDs retained by full-veneer retainers, and 77 3-unit fixed-fixed resin-bonded FPDs and 47 2-unit cantilevered resin-bonded FPDs, were examined for their retention and integrity. The periodontal health, endodontic status and coronal tissues of all abutment teeth were also evaluated. The survival rates of these various designs were analysed with the Kaplan-Meier method. The mean age of all FPDs was 31 months. At 48 months after their insertion, 3-unit FPDs retained by full-veneer retainers had a CS rate of 82%, followed by 2-unit resin-bonded FPDs at 81%, 2-unit FPDs retained by full-veneer retainers at 77%, and 3-unit resin-bonded FPDs at 63%. No significant difference was found between the four designs (P>0.05). Up to both 48 and 60 months, the most common causes of failure were endodontic for FPDs retained by full-veneer retainers, and dislodgement for resin-bonded FPDs. The 3-unit fixed-fixed FPDs retained by full-veneer retainers had the most favourable prognosis after 48 months for replacing a single missing tooth, but the difference between designs was not statistically significant.

Bicuspid↗
PubMed2005

Prevalence of malnutrition and risk factors in geriatric patients of a convalescent and rehabilitation hospital.

OBJECTIVES: To investigate the prevalence and risk factors of malnutrition in geriatric patients admitted to a convalescent and rehabilitation hospital. DESIGN: Cross-sectional study. SETTING: Regional hospital, Hong Kong. PATIENTS: A total of 120 patients (aged 60 years or older) referred to Tung Wah Eastern Hospital. MAIN OUTCOME MEASURES: Anthropometric, biochemical, and haematological parameters were measured for nutritional assessment. Malnutrition was defined as a body mass index of lower than 18.5 kg/m(2) and serum albumin level of lower than 35 g/L. The clinical outcomes of patients were also recorded. The predictive value of the Chinese Mini Nutritional Assessment as a nutritional screening tool was assessed. Potential risk factors associated with malnutrition were evaluated according to established protocols. RESULTS: The mean age of patients was 80.3 years (standard deviation, 7.4 years), and the mean body mass index was 21.9 kg/m(2) (standard deviation, 4.4 kg/m(2)). The prevalence of malnutrition was 16.7%. The age distribution of malnourished patients (mean, 86.2 years; standard deviation, 7.0 years; n=20) was significantly different to those nourished (mean, 79.1 years; standard deviation, 6.9 years; n=100) [P=0.0001]. Mortality was also higher in malnourished patients (25%) than nourished patients (4%) [P=0.001]. Based on the Chinese Mini Nutritional Assessment, 16.9% of patients were classified as malnourished (cut-off value, 18.5). The Chinese Mini Nutritional Assessment was useful as a screening tool to exclude patients who were not malnourished, ie it had a high negative predictive value (95%). Being totally dependent for the performance of activities of daily living, living in a home for the elderly, and being chair- or bed-bound posed a significantly increased risk of malnutrition. The presence of mental depression (geriatric depression scale score of 8 or higher), moderately or severely impaired cognitive function (abbreviated mental test score of lower than 7), or polypharmacy (five medications or more) did not significantly affect risk of malnutrition. CONCLUSIONS: Malnutrition was common in the geriatric patients studied and was associated with an increased mortality. The Chinese Mini Nutritional Assessment was a useful screening tool to exclude malnutrition. Significant risk factors of malnutrition were total dependence, living in a home for the elderly, and being chair- or bed-bound.

Age Factors↗
PubMed2004

Corrosion resistance of iron-platinum magnets.

OBJECTIVES: The objective of this study was to investigate the corrosion resistance of the prototype iron-platinum (FePt) magnets and non-encapsulated neodymium-iron-boron (NdFeB) magnets in three different pH environments. METHODS: The corrosion resistance of the magnets was studied using a corrosion indicator, the breakaway force. The breakaway forces of the magnets after immersion in three media, namely 1% lactic acid solution (pH=2.7), 0.1% sodium sulphide solution (pH=12) and adjusted artificial saliva (pH=6.8) were compared after 28 and 60-day periods. RESULTS: By day 7, all NdFeB magnets dissolved completely in the acid medium, and they showed significantly lower breakaway forces at day 28 and day 60 in artificial saliva (90%, 69%) and in alkaline medium (67%, 42%). In contrast, the FePt magnets did not show a drop in the breakaway forces after immersion in acid or artificial saliva, although approximately half of the original breakaway forces were recorded at day 28 and day 60 after immersion in strong alkali. CONCLUSIONS: The new iron-platinum magnets, which require no yoke assembly or protective casing, has good corrosion resistance for the oral environment. If its retentive force can be improved without increasing its thickness (0.3 mm), then it will have distinct advantages for clinical use.

Boron↗
PubMed2003

The use of lipiodol in spiral tomography for dental implant imaging.

Preoperative radiographic assessment is mandatory for the meticulous treatment planning and successful placement of implants. The precise topographical evaluation of selected implant sites, apart from the most straightforward cases, requires tomographic examination with the use of diagnostic radiographic templates. The incorporation of various radiopaque materials such as barium sulphate and lead foil as radiographic markers had not been entirely satisfactory. A new contrast medium, Lipiodol ethiodized oil (Laboratoire Guerbet, Paris, France), can easily be mixed with the monomer of autopolymerizing acrylic resin. The resultant acrylic template has several advantages. The tomographic images (Scanora; Soredex Orion Corporation, Helsinki, Finland) are radiographically homogenous and show the contour of the future prosthesis, the angulation of the planned implant, and the thickness of the soft tissue. In addition, the radiopaque template is optically transparent (with a slight yellow tint), which facilitates good visibility of surgical sites when the template is modified to become the surgical guide for implant placement. This transparent template can be further modified for implant position registration at the time of surgery. Because this multipurpose template is simple to construct and inexpensive, it can be recommended for routine use in implant dentistry.

Acrylic Resins↗
PubMed2003

Events in the mould during heat processing of poly(methyl methacrylate).

Recordings of temperature and pressure in the mould have raised questions concerning the flow of poly(methylmethacrylate) during heat processing. Three simple experiments investigated flow of polymerised and partly polymerised poly(methylmethacrylate). Flow was not observed at normal processing temperatures. These results, combined with the results of previous work, suggest that as the mould heats up, thermal expansion of the dough exceeds polymerisation contraction, causing increase in pressure rather than flow. Maximum pressure occurs at maximum temperature. Thereafter, thermal expansion is reduced, polymerisation contraction increases and pressure in the mould drops. When the lowest pressure is reached the poly(methylmethacrylate) is polymerised.

Denture Bases↗
PubMed2002

Neuropsychiatric symptoms of Alzheimer's disease differ in Chinese and American patients.

BACKGROUND: The prevalence of Alzheimer's disease is similar across ethnic groups. To our knowledge, no comparison of behavioral symptoms has been addressed. OBJECTIVE: This cross-sectional, retrospective, descriptive study compares neuropsychiatric symptoms of Chinese subjects with Alzheimer's disease (AD) at tertiary care centers in Taiwan and Hong Kong against Caucasian subjects in Los Angeles, California. We compared the frequency and severity of symptoms and caregiver responses to neuropsychiatric symptoms of AD using the Neuropsychiatric Inventory (NPI). We hypothesized that Chinese patients do not seek care unless they have high severity of neuropsychiatric symptoms and that Caucasian Americans do not wait for behavioral disturbances to develop before coming to medical attention. RESULTS: The Caucasian sample had the highest mean educational level and mildest Clinical Dementia Rating (CDR) scale distributions of all four groups. Older age and lower educational levels contributed to higher CDR scale scores, which in turn correlated with higher total NPI scores. Only one of the Chinese samples had a higher frequency of severe neuropsychiatric symptoms than the Caucasian sample. Chinese caregivers reported anxiety and delusions more frequently (58.1%) than Caucasians (37.3% and 39.6%; chi(2), p < 0.01 and p < 0.05, respectively). Caucasians reported appetite changes (47.3%) and apathy (59.2%) more frequently than the Chinese samples (chi(2), p < 0.05 and p < 0.01, respectively). Caregivers at all four centers were distressed by behaviors qualified as severe. CONCLUSION: We found support for our hypothesis, in that Chinese subjects presented during a more severe stage of dementia than American subjects, but the delay in seeking care could not be correlated with significant differences in neuropsychiatric profiles of the demented subjects. Other barriers to dementia care warrant investigation.

Aged↗
PubMed2002

Effect of neuropsychiatric symptoms of Alzheimer's disease on Chinese and American caregivers.

BACKGROUND: In Chinese culture, extended family support, acceptance of age-related cognitive changes and filial tradition of caring for elders may decrease caregiver burden and distress in the context of dementia. OBJECTIVE: To study cross-regional and cross-cultural differences in symptom-related caregiver distress due to the behavioral problems of Chinese and American patients with Alzheimer's disease. METHOD: Caregivers of patients with Alzheimer's disease at Taipei Veterans General Hospital, Taiwan (n = 89), Chinese University of Hong Kong (n = 31) and the UCLA Alzheimer's Disease Research Center, Los Angeles, California (n = 169) reported the neuropsychiatric symptoms of patients and their corresponding distress on the Neuropsychiatric Inventory. RESULT: Presence or absence of distress due to the neuropsychiatric symptoms of the patients with Alzheimer's disease was assessed. The three centers differed significantly in the proportions of caregivers with distress caused by depression (p < 0.05) and apathy (p < 0.001). UCLA had higher proportions of caregivers with depression-related distress than Taipei. UCLA caregivers were also more stressed by apathy than caregivers in Taipei and Hong Kong. Logistic regression further supported the findings that depression-related and apathy-related caregiver distress differed between Chinese and American caregivers (p < 0.05). CONCLUSIONS: The results were surprising, in that American and Chinese (Taipei and Hong Kong) caregivers exhibited similar distress or lack of distress in response to delusions, hallucinations, agitation, anxiety, euphoria, disinhibition, irritability, aberrant motor behavior, sleep and appetite symptoms of Alzheimer's disease patients. Chinese caregivers were less affected by depression and apathy in patients with Alzheimer's disease than Caucasian caregivers.

Aged↗
PubMed2002

Pressure and temperature changes in heat-cured acrylic resin during processing.

OBJECTIVES: The aims of this study were to measure the pressure and temperature changes of acrylic resin during processing, to record the highest temperature reached when fast cured in boiling water and to determine the elevated boiling point of monomer under high pressure. METHODS: A subminiature pressure transducer (temperature compensated to 94 degrees C) and a thermocouple were placed on the palate of a standardized maxillary complete denture base. A heat-cured resin (Trevalon C) was polymerized by a long heating cycle (72 degrees C for 6.5 h and 92 degrees C for 1.5 h). Recordings of pressure and temperature (n=6) were made at initial clamping of denture flasks and throughout the processing cycles of resin. The temperature of the resin was also monitored during a fast cycle, which was accomplished by placing the flask directly into boiling water for 40 min. RESULTS: The pressure of acrylic dough inside the clamped flask was initially 11.5 atm (SD=3.2) and reached a peak of 22.0 atm (SD=3.5) during the long heating cycle. The elevated boiling point of monomer at increased pressure was calculated to be about 193 degrees C (at 11.5 atm) and 228 degrees C (at 22.0 atm). These elevated boiling points are higher than the maximum temperature 131 degrees C (SD=6.6) reached during the fast curing cycle. No porosity was observed even in the denture bases heat-cured by the fast cycle. SIGNIFICANCE: The highest temperature reached by heating of resin during processing is well below the elevated boiling point of monomer. Monomer therefore does not boil in clamped denture flasks under sufficient pressure. Thus adequate clamp pressure prevents gaseous porosity irrespective of curing cycle used.

Acrylic Resins↗
PubMed2002

Usage and status of cobalt-chromium removable partial dentures 5-6 years after placement.

The aim of this study was to describe the usage of cobalt-chromium (Co-Cr) removable partial dentures (RPDs) by patients 5-6 years after denture insertion and to find out the factors that affected their denture usage. A random sample of patients provided with Co-Cr RPDs from a dental teaching hospital in Hong Kong was selected. Patients were interviewed using a structured questionnaire concerning their assessment and use of the dentures. Those who had been constantly wearing their original RPDs were examined by one calibrated examiner under optimal clinical conditions. The response rate of the patients who could be contacted was 98%. The results from 189 patient interviews showed that usage of the RPDs declined with time and that half of the dentures had been discarded or replaced 5-6 years after insertion. These discarded RPDs had been in use for an average of 19.5 months. The main reason given by the patients for not using the RPDs was general dissatisfaction with the dentures in various combinations of comfort, fit and chewing ability and, less importantly, with food trapping and appearance. No statistically significant association between denture usage and their respective Kennedy classification was found. The status of the Co-Cr RPDs that had been constantly used for 5-6 years was generally good. The majority of these RPDs demonstrated fair to good cleanliness, stability and retention and had no defect of any sort.

Adult↗
PubMed2002

In vitro comparison of blood pump induced platelet microaggregates between a centrifugal and roller pump during cardiopulmonary bypass.

UNLABELLED: Platelets are consumed during cardiopulmonary bypass (CPB) and mechanical ventricular assistance, at least partly as a result of the formation of platelet microaggregates in the blood pump. There is no commonly accepted method currently available to detect platelet microaggregates during the use of CPB or left ventricular assist devices (LVAD). The purpose of this study was to develop a flow cytometric method for the quantification of platelet microaggregates generated in blood pumps, and to evaluate the effect of cellular fragments from hemolyzed erythrocytes on the perioperative assessment of platelet counts during CPB. METHOD: Fresh human anticoagulated blood (1IU heparin/mL, activated clotting time 250+/-24 sec.) was circulated for 120 minutes in an artificial circulatory system, containing either a centrifugal pump (CP) or roller pump (RP). Whole blood was used to quantify platelet consumption and to detect circulating platelet microaggregates in a flow cytometer. Platelet consumption was additionally analyzed using an automated "Coulter" blood cell counter. Hemolysis was analyzed by measurement of plasma free hemoglobin (fHb), as well a by flow cytometric detection of red blood cell (RBC) fragments. RESULTS: Flow cytometric analysis demonstrated significantly more circulating platelet aggregates and platelet consumption in the RP than in the CP (p<0.01). Quantification of RBC fragments and plasma free hemoglobin (fHb) levels also indicated significantly increased hemolysis in the RP than in the CP (p<0.01). In contrast, the Coulter count data indicated less platelet consumption in the PP compared to the CP. CONCLUSION: Fragments from hemolyzed erythrocytes have the same size distribution as intact platelets and the number of RBC fragments correlates with the extent of pump-induced hemolysis during CPB. Our data suggest that assessment of platelets by "Coulter counting" cannot distinguish platelets from RBC fragments and may underestimate platelet consumption in the presence of hemolysis during CPB. We conclude that flow cytometry is more accurate in the perioperative assessment of platelet count and platelet aggregation during CPB and LVAD support.

Cardiopulmonary Bypass↗
PubMed2001

Competency-based education in a clinical course in conservative dentistry.

The conceptual difference between a competency-based education and an education based upon a conventional dental curriculum is, perhaps, the starting point for the development of new curricula. The two systems are not, in themselves, exclusive. There is common ground to be found, and the concept of combining instruction with competency-based learning experiences is emerging in recent publications. This paper describes a competency-based approach applied to a clinical course in conservative dentistry. The learning outcomes of the fourth-year dental students in the new course were assessed using methods that included continuous clinical assessments, student presentations and peer-group reflective evaluations, patient management reviews, a clinical progress examination, the range and amount of work completed, and a written examination and viva voce. Different weightings were given to various elements of the assessment. A formal student assessment of the course rated it as being satisfactory.

Clinical Competence↗
PubMed2001

Enhanced 3D shape recovery using the neural-based hybrid reflectance model.

It is known that most real surfaces usually are neither perfectly Lambertian model nor ideally specular model; rather, they are formed by the hybrid structure of these two models. This hybrid reflectance model still suffers from the noise, strong specular, and unknown reflectivity conditions. In this article, these limitations are addressed, and a new neural-based hybrid reflectance model is proposed. The goal of this method is to optimize a proper reflectance model by learning the weight and parameters of the hybrid structure of feedforward neural networks and radial basis function networks and to recover the 3D object shape by the shape from shading technique with this resulting model. Experimental results, including synthetic and real images, were performed to demonstrate the performance of the proposed reflectance model in the case of different specular effects and noise environments.

Journal Article↗
PubMed2001

An investigation into the feasibility of fetal lung maturity prediction using statistical textural features.

Fetal lung and liver tissues were examined by ultrasound in 240 subjects during 24 to 38 weeks of gestational age in order to investigate the feasibility of predicting the maturity of the lung from the textural features of sonograms. A region of interest of 64 x 64 pixels is used for extracting textural features. Since the histological properties of the liver are claimed to remain constant with respect to gestational age, features obtained from the lung region are compared with those from liver. Though the mean values of some of the features show a specific trend with respect to gestation age, the variance is too high to guarantee definite prediction of the gestational age. Thus, we restricted our purview to an investigation into the feasibility of fetal lung maturity prediction using statistical textural features. Out of 64 features extracted, those features that are correlated with gestation age and less computationally intensive are selected. The results of our study show that the sonographic features hold some promise in determining whether the fetal lung is mature or immature.

Feasibility Studies↗
PubMed2001

Computer-assisted learning (CAL) in undergraduate clinical dentistry: a review.

OBJECTIVE: To review the effectiveness of computer-assisted learning (CAL) in undergraduate clinical dentistry. METHODS: A review of dental and related medical literature was conducted using a selective MEDLINE search and by manual search. RESULTS: An attempt was made to evaluate the results of computer-based teaching methods in clinical dentistry, and the future. Analysis of several controlled studies showed equivocal learning improvements for CAL when compared with other teaching methods in clinical dentistry. However, CAL technology and appreciation of the standards required for effective learning programmes have changed considerably since these early studies were published. CONCLUSIONS: There is considerable potential for effective computer-based education in undergraduate clinical dental programmes, and the Internet can provide better access to such material. However, using newer technologies, further controlled studies of the learning effectiveness and cost-effectiveness of CAL in clinical dentistry are required.

Computer-Assisted Instruction↗
PubMed2001

A review on thromboprophylaxis in pregnancy.

Thromboembolic disease remains an important cause of maternal mortality worldwide. The risk assessments for prevention of thromboembolism in pregnancy are controversial due to lack of large-scale randomised controlled trials. Unfractionated heparin is at present, the anticoagulant of choice during pregnancy. However, it may be superseded by low-molecular-weight heparin in the near future because of its safety and efficacy.

Anticoagulants↗