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Biomedical subjects

Tim K Lee

Publications and source records attributed to Tim K Lee.

11 recordsLinked to original sources
PubMed2007

Influence of geometry on polychromatic speckle contrast.

Understanding speckle behavior is very important in speckle metrology application. The contrast of a polychromatic speckle depends not only on surface roughness and the coherence length of a light source, as shown in previous works, but also on optical geometry. We applied the Fresnel approach of diffraction theory for the free-space geometry and derived a simple analytical relationship between contrast, coherence length, size of illuminated spot, and distances between source, object, and observation plane. The effect of contrast reduction is found to be significant for low-coherence light sources.

Journal Article↗
PubMed2006

Adverse effects of ultraviolet radiation: a brief review.

Solar ultraviolet radiation (UVR) has always been part of the environment of man. UVB is required for the conversion of 7-deoxycholesterol to vitamin D, which is critically important in the maintenance of healthy bones and research is making clear that it has other potential roles in maintenance of human health. Exposure to UVR, whether of solar or artificial origin, also carries potential risks to human health. UVR is a known carcinogen and excessive exposure-at least to solar radiation in sunlight-increases risk of cancer of the lip, basal cell, and squamous cell carcinoma of the skin and cutaneous melanoma, particularly in fair skin populations. There is also evidence that solar UVR increases risk of several diseases of the eye, including cortical cataract, some conjunctival neoplasms, and perhaps ocular melanoma. Solar UVR may also be involved in autoimmune and viral diseases although more research is needed in these areas. Artificial UVR from tanning beds, welding torches, and other sources, may contribute to the burden of disease from UVR. This brief review will assess the human evidence for adverse health effects from solar and artificial UVR and will attempt to assign a degree of certainty to the major disease-exposure relationships based on the weight of available scientific evidence.

Comorbidity↗
PubMed2005

Determining the asymmetry of skin lesion with fuzzy borders.

It is highly desirable to identify malignant melanoma, a common cancer, at an early stage. One important clinical feature of this cancer is asymmetrical skin lesions. In this paper, we propose an adaptive fuzzy approach that uses symmetric distance (SD) to measure lesions with fuzzy borders. The use of a number of SD variations and the adoption of a backpropagation neural network enhances the discriminative power of the approach. Digitized images from the Lesion Clinic in Vancouver, Canada, demonstrate the accurate classification of asymmetric lesions at around 80%.

Algorithms↗
PubMed2005

Site-specific protective effect of broad-spectrum sunscreen on nevus development among white schoolchildren in a randomized trial.

BACKGROUND: Melanocytic nevus density is a strong risk factor for cutaneous malignant melanoma. Reducing the number of nevi in children may reduce the risk of their developing melanoma as adults. OBJECTIVE: We sought to assess the effect of sunscreen use on nevus development by anatomic sites and by nevi of different sizes for white schoolchildren in a randomized trial. METHODS: We compared the new nevus count between the sunscreen intervention group (n = 145) and the control group (n = 164) by anatomic site. RESULTS: Children randomized to the sunscreen group had significantly fewer new nevi on the trunk than children in the control group. The differences were more pronounced among the freckled children than children with no freckles. LIMITATIONS: Potential limitations to this study include relatively small numbers of enrolled children, and a follow-up period of only 3 years. CONCLUSION: Sunscreen use attenuated new nevus development on intermittently sun-exposed body sites for white schoolchildren, particularly among the freckled children.

Age Factors↗
PubMed2005

Counting moles automatically from back images.

Density of moles is a strong predictor of malignant melanoma, therefore, enumeration of moles is often an integral part of many studies that look at malignant melanoma. An automatic method of segmenting and counting moles would help standardize studies, compared with manual counting. We have developed an unsupervised algorithm for segmenting and counting moles from two-dimensional color images of the back torso region, as part of a study to evaluate the effectiveness of sunscreen. The method consists of a new variant of mean shift filtering that forms clusters in the image and removes noise, a region growing procedure to select candidates, and a rule-based classifier to identify moles. When this algorithm was compared to an assessment by an expert dermatologist, the algorithm showed a sensitivity rate of 91% and diagnostic accuracy of 90% on the test set, for moles larger than 1.5 mm in diameter.

Algorithms↗
PubMed2005

Predictive power of irregular border shapes for malignant melanomas.

BACKGROUND/PURPOSE: The Irregularity Index is a measure of border irregularity from pigmented skin lesion images. The measure attempts to quantify the degree of irregularity of the structural indentations and protrusions along a lesion border. A carefully designed study has shown that the parameters derived from the Irregularity Index were highly correlated with expert dermatologists' notion of border shape. This paper investigates the predictive power of these parameters on a set of data with known histological diagnosis. METHODS: A set of 188 pigmented skin lesions (30 malignant melanomas and 158 benign lesions) was selected for the study. Their images were segmented and their border shapes were analysed by the Irregularity Index, producing four border irregularity parameters. The predictive power of these four parameters was estimated by a series of statistical tests. RESULTS: The mean values of the four border irregularity parameters were significantly different between the melanoma group and the benign lesion group. When using the four parameters to predict its disease status, the leave-one-out classification rate was 82.4%, and the area under the receiver operating characteristic curve was 0.77. A malignant melanoma was 8.9 times more likely to have an irregular border than a benign lesion. CONCLUSION: This study confirmed that border irregularity is an important clinical feature for the diagnosis of malignant melanoma. It also indicates that the computer-derived measures based on the Irregularity Index capture to certain extent the kind of irregularity which is exhibited by melanomas.

Algorithms↗
PubMed2005

Cross-sectional study of hepatitis B awareness among Chinese and Southeast Asian Canadians in the Vancouver-Richmond community.

BACKGROUND: Hepatitis B (HBV) is endemic and a leading cause of morbidity and mortality in Asia. British Columbia has the highest proportion of Chinese and Southeast Asians among all Canadian provinces. The present study was designed to evaluate the degree of concern for and knowledge of HBV in this high-risk community. METHODS: Unselected patrons of two large Asian commercial centres in Richmond, British Columbia were surveyed. The variables studied were population demographics, concern for HBV, level of HBV knowledge and awareness of HBV-related cirrhosis or hepatocellular carcinoma (HCC). Associations were assessed using c2 testing and multiple logistic regression analysis. RESULTS: A total of 1008 individuals participated in the survey. Fifteen incomplete surveys were excluded. Only 7.7% felt that HBV was not a concern for the community. Only 13% of respondents felt that HBV education was adequate in the community. The main sources of community health education were their doctor's office (56.3%) and media (49.1%). A high number stated they were "aware" of HBV (68%) but over 60% were unaware that HBV could cause HCC or cirrhosis and only 61.3% scored a 'reasonable' level of HBV knowledge. Higher HBV knowledge was significantly associated with increasing age (P<0.001), higher education (P<0.001) and the use of media for health education (P<0.001). Awareness that HBV may cause HCC and cirrhosis was significantly associated with age (P<0.001), education (P=0.006) and birthplace (P=0.001). INTERPRETATION: HBV education is necessary in this local Asian community. Programs should target younger, less educated adults and elaborate on the potential serious health consequences of HBV. Vehicles for public education should include the physicians' offices and local media.

Adult↗
PubMed2005

Tanning beds, sunlamps, and risk of cutaneous malignant melanoma.

BACKGROUND: A number of studies have been conducted evaluating the risk of cutaneous malignant melanoma after exposure to sunlamps and/or sunbeds. The proportion of subjects in the individual studies who have reported exposure has, in general, been modest, and the resulting risk estimates for melanoma have been unstable with wide 95% confidence intervals (95% CI). The inconclusive results seen in individual studies have resulted in confusion as to the carcinogenicity of these devices. METHODS: We conducted a systematic review and meta-analysis of these studies. A review of the literature from Jan 1, 1984 to April 2004 using MEDLINE identified 12 case-control studies and 1 cohort study which quantitatively evaluated the use of sunlamps and/or sunbeds and subsequent melanoma. After applying exclusion/inclusion criteria, 9 case-control and 1 cohort study provided data for the analysis. Summary odds ratios (OR) and 95% CIs for sunlamp/sunbed use and subsequent melanoma were calculated using a random-effect model. RESULTS: Ten studies provided data for assessment of melanoma risk among subjects who reported "ever" being exposed compared with those "never" exposed. A positive association was found between exposure and risk (summary OR, 1.25; 95% CI, 1.05-1.49). Significant heterogeneity between studies was present. Evaluation of the metrics "first exposure as a young adult" (5 studies) and "longest duration or highest frequency of exposure" (6 studies) also yielded significantly elevated risk estimates (summary OR, 1.69; 95% CI, 1.32-2.18, and 1.61; 95% CI, 1.21-2.12, respectively, with no heterogeneity in either analysis). CONCLUSIONS: Results indicate a significantly increased risk of cutaneous melanoma subsequent to sunbed/sunlamp exposure.

Epidemiologic Studies↗
PubMed2003

Irregularity index: a new border irregularity measure for cutaneous melanocytic lesions.

One of the important clinical features that differentiates benign melanocytic nevi from malignant melanomas is the irregularity of the lesion border. There are two types of border irregularities: texture irregularities, the small variations along the border, and structure irregularities, the global indentations and protrusions. Texture irregularities are subject to noise, whereas structure irregularities may suggest excessive cell growth or regression of a melanoma. We have designed a new algorithm for measuring the structure irregularities in the border. Our algorithm first locates all the local and global indentations and protrusions and organizes them in a hierarchical structure. Then an area-based index, called the irregularity index, is computed for each indentation and protrusion along the border. From the individual irregularity indices, two important new measures, the most significant irregularity index and the overall irregularity index are derived. These two new indices provide a measure of the degree of irregularity along the lesion border. A double-blinded test was performed to examine the effectiveness of these two new indices. Fourteen experienced dermatologists were asked to evaluate the borders of 40 pigmented lesions. The clinical evaluation result was then compared with the two new indices and other published shape measurements. The user study showed that both of the new indices vastly outperformed the other shape descriptors. Moreover, our algorithm captured the knowledge of expert dermatologists in analysing malignancy of a lesion based on its shape alone, indicating that the new measures may be useful for diagnosing melanomas.

Algorithms↗