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Biomedical subjects

J Chong

Publications and source records attributed to J Chong.

At least 19 recordsLinked to original sources
PubMed2006

Magnetic resonance imaging of Asians with multiple sclerosis was similar to that of the West.

Magnetic resonance imaging (MRI) of the brain is the most important paraclinical diagnostic test in multiple sclerosis (MS). The appearance of MRI in Asians with MS is not well defined. We retrospectively surveyed the first brain and spinal cord MRI in patients diagnosed to have MS, according to Poser's criteria in seven regions throughout Asia to define the MRI changes among Asians with MS. There were 101 patients with first brain, and 86 with first spinal cord MRI, 66 of whom had both. The brain MRI showed a mean of 17 lesions per patient in T2 weighted images, mostly asymptomatic. Almost all the lesions were in the white matter, particularly in the juxtacortical, deep and periventricular white matter. A third of the lesions were greater than 5 mm, 14% enhanced with gadolinium. There were more supratentorial than infratentorial lesions at a ratio of 7.5: 1. Ninety five percent of the spinal cord lesions were in cervical and thoracic regions, 34% enhanced with gadolinium. The lesions extended over a mean of 3.6 +/- 3.3 vertebral bodies in length. Fifty (50%) of the brain and 54 (63%) of the spinal MRI patients had the optic-spinal form of MS. The MRI of the optic-spinal and classical groups of patients were similar in appearance and distribution, except that the optic-spinal MS patients have fewer brain but longer and more severe spinal cord lesions. In conclusion, the brain and spinal cord MRI of Asian patients with MS was similar to that of the West, although, in this study, Asian MS patients had larger spinal cord lesions.

Adult↗
PubMed2001

Acute muscle damage as a stimulus for training-induced gains in strength.

PURPOSE: The purpose of this study was to investigate the effect of a single acute bout of maximal eccentric work upon the strength gains during 9 subsequent weeks of strength training. Eccentric work causes acute muscle damage that may initiate compensatory hypertrophy and enhance training-induced gains in strength. METHODS: Twenty-six healthy adults (21 +/- 1 yr, 7 women) trained the elbow flexors 3 d per week for 9 wk. One arm (C) performed purely conventional isotonic training, i.e., lifting and lowering. The other arm (E) began with a single bout of maximal eccentric work but thereafter undertook identical isotonic training. Every week dynamic lifting strength (1 RM) and isometric strength were measured. RESULTS: The results indicated that an acute bout of eccentric muscle damage does not accentuate training-induced gains in strength. Isometric strength of arm E fell by 15 +/- 2% (mean +/- SEM) 2 d after the bout of eccentric work, and, 4 d afterward, plasma creatine kinase levels were 1502 +/- 397 IU.L-1. Although arm E displayed rapid gains in strength from 2 d after the bout of eccentric work, these were not sustained, and for several weeks arm E showed significantly smaller gains in strength than arm C (isometric strength, 2 wk; dynamic lifting strength, 5 wk). CONCLUSIONS: After 9 wk of training, the gains in both isometric and dynamic lifting strength were similar for the two arms. A single bout of damaging eccentric work did not enhance the response to conventional strength training and significantly compromised strength gains for several weeks.

Adaptation, Physiological↗
PubMed2001

Free and conjugated benzoic acid in tobacco plants and cell cultures. Induced accumulation upon elicitation of defense responses and role as salicylic acid precursors.

Salicylic acid (SA) is a key endogenous component of local and systemic disease resistance in plants. In this study, we investigated the role of benzoic acid (BA) as precursor of SA biosynthesis in tobacco (Nicotiana tabacum cv Samsun NN) plants undergoing a hypersensitive response following infection with tobacco mosaic virus or in tobacco cell suspensions elicited with beta-megaspermin, an elicitor from Phytophthora megasperma. We found a small pool of conjugated BA in healthy leaves and untreated cell suspensions of tobacco, whereas free BA levels were barely detectable. Infection of plants with tobacco mosaic virus or elicitation of cells led to a rapid de novo synthesis and accumulation of conjugated BA, whereas free BA was weakly induced. In presence of diphenylene iodonium, an inhibitor of superoxide anion formation, SA accumulation was abolished in elicited cells and much higher BA levels were concomitantly induced, mainly as a conjugated form. Furthermore, piperonylic acid, an inhibitor of cinnamate-4-hydroxylase was used as a powerful tool to redirect the metabolic flow from the main phenylpropanoid pathway into the SA biosynthetic branch. Under these conditions, in vivo labeling and radioisotope dilution experiments with [(14)C]trans-cinnamic acid as precursor clearly indicated that the free form of BA produced in elicited tobacco cells is not the major precursor of SA biosynthesis. The main conjugated form of BA accumulating after elicitation of tobacco cells was identified for the first time as benzoyl-glucose. Our data point to the likely role of conjugated forms of BA in SA biosynthesis.

Benzoates↗
PubMed2001

MR imaging of the muscular component of myocutaneous flaps in the head and neck.

BACKGROUND AND PURPOSE: Myocutaneous flaps are commonly used for reconstruction in head and neck surgery. The purpose of this study was to characterize the MR imaging findings of the muscular component of these flaps, with an emphasis on enhancement patterns. Recognition of these imaging findings is important in differentiating postoperative changes from recurrent tumor. METHODS: MR studies were evaluated in 25 patients who had undergone 27 flap reconstructions after resection of a head and neck tumor. Twenty were free flaps and seven were pedicled rotation flaps, and a dominant component of all flaps was muscle. MR images were reviewed for signal intensity, enhancement characteristics, and morphology over a period of 7 to 79 months. RESULTS: On baseline postoperative images, 21 flaps showed moderate or intense enhancement of the muscular graft component relative to nonenhancing native muscle, three flaps showed mild enhancement, and three showed no enhancement. On follow-up images, 18 flaps that initially had intense enhancement showed persistent intense enhancement, and three showed decreasing enhancement. Two flaps with initial mild enhancement were unchanged on follow-up, and one became nonenhancing. None of the initially nonenhancing flaps subsequently enhanced. T1 signal intensity of muscular graft components was always isointense with normal muscle, whereas T2 signal intensity was variable and tended to be stable. Ninety-three percent of our muscular flap components showed striations typical of normal muscle and were best identified on T1-weighted images. No significant imaging differences were found between pedicled and free flaps. CONCLUSION: Most muscular flap components show moderate or intense enhancement on fat-suppressed contrast-enhanced MR images that may persist for many months and be quite striking. Radiologists should be familiar with the typical postoperative appearance of predominantly muscular flaps to avoid misdiagnosis as tumor extension or recurrence.

Adolescent↗
PubMed2000

Aspiration and imprint cytopathology of thyroid carcinoma associated with familial adenomatous polyposis.

Thyroid carcinomas occur in association with familial adenomatous polyposis (FAP), and some are the first symptom of FAP. Although several histological features have been reported, the cytopathology of FAP-associated thyroid carcinoma has not yet been described. We report on two cases of FAP-associated thyroid carcinomas diagnosed by fine-needle aspiration biopsy and one case imprinted after resection. All 3 patients belonged to the same family, and thyroid carcinoma was the first symptom of the proband. Cytological features include fascicular or whorl formation of spindle cells with papillary, follicular, and/or solid architectures, in addition to the typical features of papillary carcinoma. The cytological features of FAP-associated thyroid carcinomas are characteristic and may suggest FAP.

Adenomatous Polyposis Coli↗
PubMed2000

Smoking behavior in a smoking workplace.

PURPOSE: This report addresses whether smoking increases as a function of working in a smoking environment. METHODS: Casino employees were targeted to complete a survey designed to assess smoking behavior. The survey contained standardized questions consistent with other major surveys on tobacco use to ensure comparability with state and national trends. Data collection occurred between September and November 1997. RESULTS: Out of 755 surveys distributed, 587 completed surveys were returned, resulting in a response rate of 77 percent. A test of proportions showed that the proportion of smokers had not changed significantly as a result of working in a smoking environment although the amount of smoking decreased significantly (one-sample t-test). The change in the amount of smoking was assessed using difference scores. Males and females did not differ in the rate in which their smoking changed. A significant correlation between age and the change score suggested that younger smokers were more likely to increase their intake whereas the older smoking employees were more likely to decrease their consumption by the time of the survey. IMPLICATIONS: The finding that individuals who work in a smoking environment decreased their smoking behavior merits further investigation in the area of smoking aversion.

Adolescent↗
PubMed2000

Nuclear localization of immunoreactive beta-catenin is specific to familial adenomatous polyposis in papillary thyroid carcinoma.

Thyroid carcinoma is the first symptom in some patients with familial adenomatous polyposis (FAP). We evaluated the cellular localization of beta-catenin in thyroid carcinomas associated (n = 4) or not associated (n = 173) with FAP, since loss of functional protein of the adenomatous polyposis coli (APC) gene leads to nuclear accumulation of beta-catenin in adenomas and carcinomas of the FAP colon. Immunoreactive beta-catenin was demonstrated at the cell membrane of glandular cells of the non-neoplastic thyroid and non-FAP carcinomas. On the other hand, cytoplasmic and nuclear accumulation of beta-catenin is specific to FAP-associated papillary carcinomas. The abnormality in the APC / beta-catenin pathway is thus also important in FAP-associated thyroid carcinoma, and beta-catenin immunohistochemistry is a feasible screening method to identify occult FAP in young patients with thyroid tumors.

Adenomatous Polyposis Coli↗
PubMed2000

The environmental effects of dental amalgam.

Dental amalgam is one of the most commonly used materials in restorative dentistry. However, one of its major components, mercury, is of particular concern due to its potential adverse effects on humans and the environment. In this review, the environmental impact of dental amalgam will be discussed, with particular reference to the effects attributed to its mercury component. Mercury commonly occurs in nature as sulfides and in a number of minerals. Globally, between 20,000-30,000 tons of mercury are discharged into the environment each year as a result of human activities. According to a recent German report, approximately 46 per cent of the freshly triturated amalgam is inserted as new amalgam restorations and the rest is waste. Depending on the presence of an amalgam separating unit, some of the generated amalgam-contaminated sludge is discharged into the sewage system. Lost or extracted teeth with amalgam fillings and amalgam-contaminated waste, such as trituration capsules and cotton rolls are discharged with the solid waste and, in most instances, are incinerated. Use of disinfectants containing oxidizing substances in dental aspirator kits may contribute to remobilization of mercury and its subsequent release into the environment. Nevertheless, dental mercury contamination is only a small proportion of terrestrial mercury (3-4 per cent), which is quite insignificant compared with industrial pollution and combustion of fossil fuels by vehicles. The environmental impact of dental mercury is mainly due to the poor management of dental amalgam waste. Proper collection of mercury-contaminated solid waste prevents the release of mercury vapour during combustion. In addition, the use of amalgam separating devices reduces the amount of amalgam-contaminated water released from dental clinics.

Dental Amalgam↗
PubMed2000

Masticator space abnormalities associated with mandibular osteoradionecrosis: MR and CT findings in five patients.

BACKGROUND AND PURPOSE: Imaging of patients with a clinical diagnosis of mandibular osteoradionecrosis (ORN) is often performed to support that clinical suspicion, evaluate the extent of the disease, or exclude coexistent tumor recurrence. The purpose of our study was to describe the clinical, MR imaging, and CT features of five patients with mandibular ORN associated with prominent soft-tissue abnormality in the adjacent masticator muscles. METHODS: The MR and CT examinations of five patients with mandibular ORN associated with soft-tissue abnormalities in the adjacent masticator muscles were reviewed. All patients had received external beam radiotherapy for primary head and neck malignancies, with a total radiation dose range of 60 Gy to 69 Gy in 30 to 38 fractions. RESULTS: CT revealed the typical osseous findings of cortical disruption, trabecular disorganization, and fragmentation in all five patients. Abnormal diffuse enhancement of the adjacent masseter and pterygoid muscles was noted in all patients. Four patients had prominent mass-like thickening of these muscles adjacent to the osseous abnormality. Of the three patients who underwent MR imaging, all showed homogeneous abnormal T1 hypointensity, T2 hyperintensity, and intense enhancement of the bone marrow in the involved mandible. The masticator muscles adjacent to the osseous abnormality also showed abnormal T2 hyperintensity and intense diffuse enhancement on MR images. CONCLUSION: Mandibular ORN can be associated with prominent soft-tissue thickening and enhancement in the adjacent musculature. These changes can appear mass-like and are not related to tumor recurrence or metastatic disease.

Adolescent↗
PubMed2000

The pterygopalatine fossa: postoperative MR imaging appearance.

BACKGROUND AND PURPOSE: The pterygopalatine fossa (PPF) is an important anatomic location of the deep portion of the face. It is essential to review this area on both pre- and posttreatment studies of head and neck malignancies to assess local extent of disease or recurrence and perineural tumor spread. The purpose of this study was to review the postoperative appearance of the PPF on MR images. METHODS: Imaging and clinical data of 10 patients who underwent surgical resection of tumor in which the PPF was violated at surgery were reviewed. Patients were included in the study if there was no imaging or clinical evidence of tumor in the PPF pre- or postoperatively. Postoperative MR studies were examined to assess the appearance of the PPF. RESULTS: The PPF is consistently and persistently abnormal after surgical violation. There is loss of the normal T1 signal hyperintensity and abnormal, increased contrast enhancement, as seen on fat-suppressed T1-weighted images. These postoperative changes are strikingly similar to those of tumor involvement. CONCLUSION: After surgical violation, the PPF will always appear abnormal on MR images, and the expected imaging findings must be recognized to avoid the misdiagnosis of tumor recurrence.

Aged↗
PubMed1999

An early salicylic acid-, pathogen- and elicitor-inducible tobacco glucosyltransferase: role in compartmentalization of phenolics and H2O2 metabolism.

Treatment of tobacco cell suspension cultures with a fungal elicitor of defense responses resulted in an early accumulation of the phenylpropanoid glucosyltransferase TOGT, along with the rapid synthesis and secretion of scopolin, the glucoside of scopoletin. Elicitor-triggered extracellular accumulation of the aglycone scopoletin and of free caffeic and ferulic acids could only be revealed in the presence of diphenylene iodonium, an inhibitor of extracellular H2O2 production. Our results strongly support a role for TOGT in the elicitor-stimulated production of transportable phenylpropanoid glucosides, followed by the release of free antioxidant phenolics into the extracellular medium and subsequent H2O2 scavenging.

Caffeic Acids↗
PubMed1999

A 3-year study on the effect of RGP contact lenses on myopic children.

AIM AND BACKGROUND: Recent studies in the West have shown that rigid gas-permeable (RGP) contact lenses can control the progress of myopia in children. These studies were done on Caucasian children, whose myopias are less rapidly progressive than those which we see in Singaporean children. This three-year study was started in 1993, with the following objectives: 1. To verify whether RGP contact lenses can control the progress of myopia in Singaporean children. 2. If so, to investigate the mechanism by which the lenses control myopia; whether by corneal flattening or by reducing the growth of the axial length. 3. If so, to assess if the effects are permanent, by discontinuing lens wear. MATERIALS AND METHODS: The study was carried out at the Eye Clinic of the School Health Service. Enough school children were referred to the clinic from the various schools to achieve about 100 children wearing contact lenses. Past studies showed that the drop-out rate would be 50%, as there is no cosmetic motivation in 10 year-old children to wear contact lenses. The successful wearers were those who had parental encouragement and support. RESULTS: The results show that there was a suppression of the progress of myopia in children wearing the lenses as compared to their counterparts wearing spectacles. However, only in ten eyes was there arrest of the myopia. For the lenses to be effective, they needed to be worn regularly for about eight hours a day. Reasons for the drop-outs included lack of motivation, lens intolerance and simply being too busy with the school curriculum. Discontinuance of lens wear for more than 2 months had minimal effect on the refraction, indicating that the controlling effect was not due purely to corneal change. CONCLUSION: It is recommended that more studies be done to confirm the findings of this study. Children with rapidly progressive myopia can wear rigid gas-permeable contact lenses to reduce the progression.

Child↗
PubMed1999

MR findings in AIDS-associated myelopathy.

BACKGROUND AND PURPOSE: The most common cause of spinal cord disease among patients with AIDS or those infected with HIV-1 is AIDS-associated myelopathy. The purpose of this study was to determine the MR characteristics of the spinal cord in this patient population and to correlate these findings with the clinical severity of myelopathy. METHODS: MR images of the spinal cord in 21 patients with documented HIV-1 infection or AIDS and a clinical diagnosis of AIDS-associated myelopathy were assessed retrospectively for atrophy, intrinsic signal abnormality, and abnormal enhancement. The clinical severity of myelopathy was graded by a neurologist on the basis of physical examination, and a qualitative correlation was made with the MR findings. RESULTS: MR findings were abnormal in 18 of the 21 patients. The most common feature was spinal cord atrophy (n = 15), typically involving the thoracic cord with or without cervical cord involvement, followed by intrinsic cord signal abnormality (n = 6), and normal-appearing cord (n = 3). Three patients had both cord atrophy and intrinsic cord signal abnormality. The cord signal abnormality was diffuse, without predilection for any specific distribution pattern. Enhancement was not seen in any of the 10 patients who received intravenous contrast material. Only one of 16 patients with moderate to severe myelopathy had normal MR findings, as compared with two of five patients with mild myelopathy. CONCLUSION: MR findings in the spinal cord are abnormal in the majority of patients with AIDS-associated myelopathy, typically showing spinal cord atrophy, with or without intrinsic cord signal abnormality. Patients with moderate to severe myelopathy have an increased frequency of spinal cord abnormalities, but a definite correlation between clinical severity of myelopathy and extent of MR abnormalities remains to be established.

Acquired Immunodeficiency Syndrome↗
PubMed1998

Two tobacco genes induced by infection, elicitor and salicylic acid encode glucosyltransferases acting on phenylpropanoids and benzoic acid derivatives, including salicylic acid.

Two tobacco genes (TOGT) with homology to glucosyltransferase genes known to be induced by salicylic acid (SA) also responded rapidly to a fungal elicitor or to an avirulent pathogen. SA, although an efficient inducer, was shown not to be essential in the signal transduction pathway regulating TOGT gene expression during the resistance response. Recombinant TOGT proteins produced in Escherichia coli exhibited low, but significant, glucosyltransferase activity towards SA, but very high activity towards hydroxycoumarins and hydroxycinnamic acids, with glucose esters being the predominant products. These results point to a possible important function in defense of these glucosyltransferases in conjugating aromatic metabolites prior to their transport and cross-linking to the cell wall.

Benzoates↗
PubMed1998

Diffusion-weighted MRI in acute subcortical infarction.

BACKGROUND AND PURPOSE: Conventional imaging lacks sensitivity and specificity for the detection of early subcortical cerebral infarction. The purposes of our study were (1) to determine the accuracy of diffusion-weighted (DW) MRI for early subcortical infarction and (2) to determine the efficacy of DW MRI for differentiating acute from nonacute subcortical infarctions when conventional MR demonstrates multiple infarctions. METHODS: Thirty-nine patients with clinically diagnosed acute subcortical infarction and 17 control subjects were imaged with both conventional and DW MRI from 7 hours to 4 days (mean, 2.0 days) after onset of symptoms. All images were read blinded to specific clinical findings. In all cases, the precise neuroanatomic locations of lesions were noted. These lesions were subsequently correlated by an experienced stroke neurologist to determine whether their locations correlated to the patients' symptoms. RESULTS: The accuracy of DW MRI for acute subcortical infarction was 94.6%. In 4 of 39 cases, the acute infarction was not detected on conventional MRI. In 24 of 39 cases, conventional MRI showed the acute lesion as well as multiple other subcortical lesions. In each of these 24 cases, the DW MRI showed a single lesion to be acute, and in all 24 cases, that lesion corresponded to the patients' acute symptoms. CONCLUSIONS: DW MRI has very high accuracy for acute subcortical infarction and can differentiate acute from nonacute lesions. These data have significant implications in guiding patient management and patient selection for clinical trials.

Acute Disease↗
PubMed1998

Diffusion-weighted MR of acute cerebral infarction: comparison of data processing methods.

BACKGROUND AND PURPOSE: Some investigators have proposed that either calculated diffusion trace images or apparent diffusion coefficient (ADC) maps, which require imaging with multiple diffusion sensitivities and/or postacquisition image processing, are essential for the accurate interpretation of diffusion-weighted images in acute stroke because of the possible pitfalls of regional diffusion anisotropy, magnetic susceptibility artifacts, and confounding T2 effects, all of which alter signal on diffusion-weighted MR images. The purpose of our study was to compare the sensitivity, specificity, and accuracy of simple, orthogonal-axis diffusion-weighted imaging for the diagnosis of early cerebral infarction with three other sets of postacquisition-processed images: isotropic diffusion-weighted, diffusion trace-weighted, and diffusion trace images. METHODS: Twenty-six consecutive adult patients with signs and symptoms consistent with a clinical diagnosis of early cortical and/or subcortical cerebral infarction and 17 control subjects were studied with multisection, single-shot, spin-echo echo-planar diffusion-weighted imaging at 1.5 T to generate a set of three orthogonal-axis diffusion-weighted images. Isotropic diffusion-weighted, diffusion trace-weighted, and diffusion trace (mean ADC) images were then generated off-line and all four sets of images were interpreted blindly by two neuroradiologists. RESULTS: The average sensitivity, specificity, and accuracy for the orthogonal-axis diffusion-weighted images were 98.1%, 97.1%, and 97.7%, respectively. The average sensitivity, specificity, and accuracy for isotropic diffusion-weighted images were 88.5%, 100%, and 93% respectively. The average sensitivity, specificity, and accuracy for diffusion trace-weighted images were 82.7%, 73.6%, and 79.1%, respectively. The average sensitivity, specificity, and accuracy for diffusion trace images were 50.0%, 85.3%, and 64.0%, respectively. CONCLUSION: Orthogonal-axis diffusion-weighted images have the highest sensitivity and accuracy and very high specificity for early cerebral infarction. Our data contradict the contention that quantitative diffusion maps, requiring imaging with multiple diffusion sensitivities and/or subsequent image processing, are necessary for clinical stroke imaging.

Acute Disease↗
PubMed1994

Occupational exposure to Helicobacter pylori for the endoscopy professional: a sera epidemiological study.

OBJECTIVES: The purpose of this prospective study was to determine if medical and nursing staff in the United States who are regularly involved in endoscopic procedures are at an increased risk of acquiring Helicobacter pylori infection. METHODS: One hundred and twenty-two gastroendoscopists and endoscopy nurses attending an advanced gastroendoscopy course (17 women, 105 men) completed a questionnaire consisting of past medical and professional history. Serum from each subject was collected and tested using a validated ELISA assay (sensitivity 99%, specificity 96%). H. pylori prevalence in the experimental group was compared to that of 510 blood donors. RESULTS: In all age groups, H. pylori positivity was significantly higher among the study subjects compared with controls. Caucasian subjects, when matched to controls for age, race, and level of education, had significantly higher rates of H. pylori positivity. Foreign-born subjects, when compared to US-born subjects, also had higher rates of H. pylori positivity. There was no statistical difference of H. pylori positivity with respect to gender, years involved in endoscopy, or number of endoscopies performed monthly. CONCLUSION: H. pylori infection is more common in gastroendoscopists and endoscopy nurses than the general population and should be viewed as an occupational hazard.

Adult↗